Shashank Priya*, Hyun-Cheol Song, Yuan Zhou, Ronnie Varghese, Anuj Chopra,
Sang-Gook Kim, Isaku Kanno, Liao Wu, Dong Sam Ha, Jungho Ryu and Ronald G. Polcawich
A Review on Piezoelectric Energy Harvesting:
Materials, Methods, and Circuits
DOI 10.1515/ehs-2016-0028
Abstract: Piezoelectric microelectromechanical systems
(PiezoMEMS) are attractive for developing next genera-
tion self-powered microsystems. PiezoMEMS promises to
eliminate the costly assembly for microsensors/microsys-
tems and provide various mechanisms for recharging the
batteries, thereby, moving us closer towards batteryless
wireless sensors systems and networks. In order to
achieve practical implementation of this technology, a
fully assembled energy harvester on the order of a quar-
ter size dollar coin (diameter = 24.26mm, thickness = 1.75
mm) should be able to generate about 100 μW continuous
power from low frequency ambient vibrations (below
100Hz). This paper reviews the state-of-the-art in micro-
scale piezoelectric energy harvesting, summarizing key
metrics such as power density and bandwidth of reported
structures at low frequency input. This paper also
describes the recent advancements in piezoelectric mate-
rials and resonator structures. Epitaxial growth and grain
texturing of piezoelectric materials is being developed to
achieve much higher energy conversion efficiency. For
embedded medical systems, lead-free piezoelectric thin
films are being developed and MEMS processes for these
new classes of materials are being investigated. Non-
linear resonating beams for wide bandwidth resonance
are also reviewed as they would enable wide bandwidth
and low frequency operation of energy harvesters.
Particle/granule spray deposition techniques such as
aerosol-deposition (AD) and granule spray in vacuum
(GSV) are being matured to realize the meso-scale struc-
tures in a rapid manner. Another important element of an
energy harvester is a power management circuit, which
should maximize the net energy harvested. Towards this
objective, it is essential for the power management circuit
of a small-scale energy harvester to dissipate minimal
power, and thus it requires special circuit design techni-
ques and a simple maximum power point tracking
scheme. Overall, the progress made by the research and
industrial community has brought the energy harvesting
technology closer to the practical applications in near
future.
Keywords: energy harvesting, piezoelectric, MEMS,
PiezoMEMS, electromechanical coupling, power density,
epitaxial PZT, grain texturing, lead-free, non-linear reso-
nance, aerosol deposition (AD)/granule spray in vacuum
(GSV), cantilever, maximum power point
1 Introduction
The vast reduction in the size and power consumption of
sensors and CMOS circuitry has led to a focused research
effort on on-board power sources which can replace or
recharge batteries. The concern with batteries has been
that they must be charged before use. Similarly, the sen-
sors and data acquisition components in distributed net-
works require centralized energy sources for their
operation. In some applications such as sensors for struc-
tural health monitoring in remote locations, geographi-
cally inaccessible temperature or humidity sensors,
battery charging or replacement operations can be costly
or even impractical. The need to replace batteries in a
large-scale sensor network can be problematic and costly.
The replacement is nearly impossible in hazardous, harsh
and large terrain deployment. An example would be
embedded sensor networks in urban battlefields.
Logically, the emphasis in such cases has been on devel-
oping the on-site generators that can transform any
*Corresponding author: Shashank Priya, Center for Energy
Harvesting Materials and Systems (CEHMS), Virginia Tech,
Blacksburg, VA 24061, USA, E-mail: spriya@vt.edu
Hyun-Cheol Song: E-mail: songhc@vt.edu, Yuan Zhou:
E-mail: yzhou6@vt.edu, Ronnie Varghese: E-mail: ronniev@vt.edu,
Anuj Chopra: E-mail: anujchopraiitm@gmail.com, Center for Energy
Harvesting Materials and Systems (CEHMS), Virginia Tech,
Blacksburg, VA 24061, USA
Sang-Gook Kim, Department of Mechanical Engineering,
Massachusetts Institute of Technology, Cambridge, MA 02139, USA,
E-mail: sangkim@mit.edu
Isaku Kanno, Department of Mechanical Engineering, Kobe University,
Kobe 657–8501, Japan, E-mail: kanno@mech.kobe-u.ac.jp
Liao Wu, Dong Sam Ha: E-mail: ha@vt.edu, Department of Electrical
and Computer Engineering, Virginia Tech, Blacksburg, VA 24061, USA
Jungho Ryu, Functional Ceramics Group, Korea Institute of Materials
Science (KIMS), Changwon, Gyeongnam 51508, Korea,
E-mail: jhryu@kims.re.kr
Ronald G. Polcawich, US Army Research Laboratory, Adelphi,
MD 20783, USA, E-mail: ronald.g.polcawich.civ@mail.mil
Energy Harvesting and Systems 2017; aop
Authenticated | jhryu@kims.re.kr author's copy
Download Date | 2/2/17 7:13 AM
available form of energy at that location into electrical
energy (Priya and Inman 2009). Recent advances in low-
power VLSI design have enabled ultra-small power inte-
grated circuits, which can run with only 10’s nW to 100’s
μW of power (Chandrakasan et al. 1998). This scaling trend
has opened the door for on-chip energy harvesting solu-
tions, eliminating the need for chemical batteries or com-
plex wiring for micro-sensors and thus forming the
foundation for battery-less autonomous sensors and net-
work systems.
An alternative to implementation of a conventional
battery as power supply is to make use of the parasitic
energy available locally in the environment. Unused
energy is produced by industrial machines, human activ-
ity, vehicles, structures and environment sources, all of
which could be an excellent source of capturing small
power without affecting the source itself. Furthermore,
the energy harvesting can provide solution for harsh envir-
onmental conditions unfit for battery use for example for
temperature exceeding 60°C. In recent years, several
energy harvesting approaches have been proposed using
solar, thermoelectric, electromagnetic, piezoelectric, and
capacitive schemes at meso, micro and nano scales
(Beeby, Tudor, and White 2006; Priya and Inman 2009;
Wang and Song 2006). These can be simply classified in
two categories: (i) energy harvesting for sensor and com-
munication networks using Microelectromechanical sys-
tems (MEMS)/thin film approach, and (ii) energy
harvesting for electronic devices using bulk devices.
MEMS devices combine the response of electrical and
mechanical components. The size of these devices varies
from sub-micron to millimeter range. MEMS integration
with modern electronics provides, capability to interact
with vast range of platform leading to new and enhanced
functionality for sensors and energy harvesters.
Mechanical vibration energy can be converted into
electrical energy using piezoelectric, electromagnetic and
electrostatic transducers. Out of them, piezoelectric trans-
ducers are considered more attractive option due to their
high energy density (Roundy and Wright 2004). In com-
parison to the electrostatic transducers, piezoelectric
MEMS devices offer following advantages: (1) scaling of
devices for miniaturization because the energy density of
piezoelectric materials remains high with reducing film
thickness, (2) low voltage operation of piezoelectric
actuators, (3) additional possibility to harvest energy
due to coupling between mechanical and electrical com-
ponent, and (4) easy implementation of high frequency,
and temperature-stable resonant devices. Since thin films
of piezoelectric materials provide the possibility to design
more economical and thinner size devices, a lot of
research on fabrication of piezoelectric thin films for
MEMS devices has been conducted.
This paper mainly focuses on small-scale power
energy harvesting techniques (~ 1–100μW) using a
MEMS/thin film/thick film approach for the self-supported
operation of portable or embedded micro devices and
systems. Further, we focus on mechanical vibration energy
as the prime source for generating electric power. The
question one might ask at this stage is: “What is the best
mechanism for converting mechanical energy into electri-
cal energy at the ~mm3 dimensions?” Priya et al. have
studied the scaling of output power as a function of effec-
tive material volume (V) for different mechanisms (Marin,
Bressers, and Priya 2011). By taking into account constitu-
tive equations for the respective conversion mechanism,
the output power of electromagnetic mechanism is propor-
tional to V2, while that of piezoelectric mechanism is
proportional to V
3
4. Thus, at smaller scales, the piezoelec-
tric mechanism becomes more attractive as compared to
electromagnetics. To obtain an approximation of the criti-
cal size where piezoelectricity becomes more useful, Figure
1 plots harvester volume vs. normalized output power
(normalized by acceleration and multiplied by frequency)
for various piezoelectric and electromagnetic prototypes
reported in the literature (Marin, Bressers, and Priya
2011). From Figure 1, it can be determined that ~0.5 cm3
is in the vicinity of the critical size. At a smaller device
volume than this critical size, the electromagnetic trans-
formation factor (similar to electromechanical coupling in
piezoelectrics) ΦT ffi
P
Bðyc, zcÞ ΔLcoilð Þ cos θ yc, zcð Þð ÞΦ ybð Þ
Figure 1: Output power as a function of effective material volume for
piezoelectric and electromagnetic vibration energy harvesting
mechanisms. Variation of output power normalized by acceleration
and multiplied by frequency as a function of device volume for
various energy harvesters found in literature and commercially
(Marin 2013).
2 S. Priya et al.: A Review on Piezoelectric Energy Harvesting
Authenticated | jhryu@kims.re.kr author's copy
Download Date | 2/2/17 7:13 AM
reduces sharply with decrease in magnitude of induction
and length of coil. Here B represents the magnetic field,
L is the length of coil, θ is the angle between~z ×~B and the
differential conductor length d~l, yc, zc are coordinates on
plane of the coil, and yb is the coordinate on the beam.
Another major problem with inductive harvesters at small
scales is their low output voltage, which makes it difficult
to use rectification and AC/DC conversion circuits (Bono
et al. 2009). In addition to the normalized power and out-
put voltage, assembly at this scale critically affects the cost
of the system. Below the critical volume, assembly of the
conductive induction coil and magnetic layer becomes
challenging. The mechanisms at this scale can be cost-
effective if they can be fabricated by monolithic MEMS
processes without substantial post assembly efforts. Thus
for MEMS-scale energy harvesters smaller than ~0.5 cm3,
piezoelectric transduction is the most appropriate scenario.
Electrostatic harvesters have the surface potential decay
problem because dielectrics are not perfect insulators.
Specially, the surface potential decay is severe in an extre-
mely moist environment since most surplus charges on or
just below the surface of electret materials are neutralized
by the ions in the water. (Sessler 2001; Sorimachi,
Takahashi, and Tokonami 2009). We should point out
that the use of synchronous circuits has been shown to
be a viable alternative for such systems (Lefeuvre et al.
2014). On the other hand, piezoelectric harvester can
directly convert mechanical energy into electric energy
and can be directly integrated into monolithic MEMS-
scale systems (Beeby, Tudor, and White 2006; Hajati and
Kim 2011; Jeon et al. 2005; Kang et al. 2016; Kim et al. 2009;
Morimoto et al. 2010; Muralt, Polcawich, and Trolier-
McKinstry 2009b; Roundy and Wright 2004).
There is commonly a concern whether one can one
achieve self-powering when the power required is much
larger than that can be achieved by MEMS-scale
piezoelectric harvester. Most reported piezoelectric
devices show orders of magnitude smaller normalized
power density than that required by the sensors and
systems at the present time. In scenarios where multiple
environmental resources are available besides mechan-
ical energy, self-powering may be achieved by develop-
ing a smart architecture, which utilizes all the
environmental resources such as, wind, magnetic fields,
light, sound, temperature gradients, and RF waves.
However, the best scenario for cost and size is to
improve the MEMS-scale piezoelectric harvester technol-
ogy to generate enough power. The physics behind the
piezoelectrically generated power is reviewed in this
paper along with approaches to enhance the power
density by addressing piezoelectric materials, magneto-
electrics and non-linear structural designs. Further dis-
cussion on common energy harvesting circuit topology
is provided that can boost the transfer of harvested
energy into storage devices.
The general principle for conversion of low frequency
mechanical stress into electrical energy using a piezo-
electric transducer is shown schematically in Figure 2
(Kim et al. 2007). This transformation from mechanical
to electrical energy is obtained through the direct piezo-
electric effect. The resulting energy can be stored after
using a rectifier and DC-DC converter circuit. There are
three primary steps in power generation as outlined in
this schematic: (a) trapping the mechanical AC stress
from available source, (b) converting the mechanical
energy into electrical energy by direct piezoelectric trans-
duction, and (c) processing and storing the generated
electrical energy. Depending upon the frequency and
amplitude of the mechanical stress, one can design the
required transducer, its dimensions, vibration mode and
the desired piezoelectric material. The power density of a
harvesting system is dependent upon the strategies that
Figure 2: Energy flow of a piezoelectric
generator (Kim et al. 2007).
S. Priya et al.: A Review on Piezoelectric Energy Harvesting 3
Authenticated | jhryu@kims.re.kr author's copy
Download Date | 2/2/17 7:13 AM
maximize the trapping of energy and reduce the losses
occurring at each step, namely, mechanical loss due to
mismatch in mechanical impedance, and electromecha-
nical loss depending upon the magnitude of the coupling
factor (Findeisen 2013; Ginsberg and Ginsberg 2001; Jiang
and Miles 1999; Uchino 2009).
Most reported piezoelectric harvesters utilize the
resonance of a cantilever beam structure, which amplifies
the small ambient vibration into an in-plane strain gov-
erned by the Euler – Bernoulli beam equation (Beeby,
Tudor, and White 2006; Muralt, Polcawich, and Trolier-
McKinstry 2009b; Priya and Inman 2009). In order to
harvest power robustly, the bandwidth of a linear canti-
lever beam harvester should be wide enough to accom-
modate the uncertain variance of ambient vibrations
(Hajati and Kim 2011). Therefore, the resonance band-
width is an important characteristic for trapping suffi-
cient amount of energy to the beam and should be
accounted for determining the performance of energy
harvesters. Piezoelectric MEMS technology is the most
cost-effective energy harvesting technology if it can pro-
vide high enough power density and wide enough band-
width. Three major attributes to make the piezoelectric
MEMS energy harvesting technology deployable for real
applications are: the cost of the system, the normalized
power density and the operational frequency range
(bandwidth and the center frequency). The current
state-of-the-art piezoelectric MEMS technologies are
reviewed in this paper with respect to these attributes.
2 Review of Piezoelectric Energy
Harvesting
The basic principle of piezoelectric cantilever based
energy harvester can be explained by accounting for
the flow of energy between different domains in Phase
I and Phase II as shown in Figure 2. Ambient vibration
injects energy into the system through the base
excitation at each cycle. This input energy is converted
to kinetic energy of the proof mass and then to potential
energy stored as the beam’s mechanical strain (Hajati
2011). Part of the elastic energy stored in the beam is
transformed into electrical energy in the form of
induced charge across the piezoelectric layer, which is
deposited on the beam. Piezoelectric energy harvesters
generally have bimorph or unimorph cantilever beam
structures (Figure 3) (Renaud et al. 2008; Roundy and
Wright 2004). However, at the MEMS-scale, bimorph
cantilever are less manufacturable with existing micro-
fabrication processes. As a result, MEMS cantilevers
mostly have a unimorph configuration. A seismic mass
is usually attached at the tip of the cantilever to adjust
the resonant frequency to the available environmental
frequency, normally below 100Hz (Reilly et al. 2009;
Roundy, Wright, and Rabaey 2003).
Recently, MEMS technologies have been applied
towards the development of integrated energy harvest-
ers, and many piezoelectric MEMS energy harvesters
have been developed (Aktakka 2012; Beeby, Tudor, and
White 2006; Bertacchini et al. 2011; Defosseux et al. 2012;
Durou et al. 2010; Elfrink et al. 2009a, 2009b, 2010;
Erturk and Inman 2008; Fang et al. 2006; Hajati and
Kim 2011; Hirasawa et al. 2010; Isarakorn et al. 2011;
Jeon et al. 2005; Lee et al. 2009; Lei et al. 2011;
Marzencki et al. 2007; Massaro et al. 2011; Miller et al.
2011; Muralt et al. 2009a; Park, Park, and Lee 2010;
Roundy, Wright, and Rabaey 2003a, 2003b; Shen et al.
2008; Van Schaijk et al. 2008; Xu et al. 2012b; Yen et al.
2011). Useful metrics in comparing these devices are
their active area, active volume, resonant frequency,
harvested power and power densities in volume or
area. Devices with relatively higher power densities (in
volume or area) or non-PZT materials such as AlN and
lead-free KNN are selectively shown in Table 1. In order
to understand the performance attributes defined earlier
and better compare the devices reported, basic models
of vibration kinematics and piezoelectrics are summar-
ized below.
Figure 3: Basic structure of piezoelectric
energy harvesters: (a) Bimorph structure,
(b) Unimorph structure.
4 S. Priya et al.: A Review on Piezoelectric Energy Harvesting
Authenticated | jhryu@kims.re.kr author's copy
Download Date | 2/2/17 7:13 AM
2.1 Fundamentals of Piezoelectricity
Piezoelectricity is the property of certain crystals to gen-
erate an electric potential in response to applied mechan-
ical stress. There are two different kinds of phenomena
commonly observed which are termed as direct and the
converse piezoelectric effects. When the mechanical
stress is applied to a piezoelectric material, an electric
charge proportional to the applied stress is produced.
This refers to the direct piezoelectric effect. Conversely,
when electric field is applied to the same material, strain
or displacement is produced proportional to the magni-
tude of electric field. This is called as converse piezo-
electric effect. The following two constitutive equations
are used to describe the piezoelectric effect:
Di =dijσj + εTii Ei or Di = eijSj + ε
S
iiEi [1]
Sj = sEijσj +dijEi or Tj = c
E
ijSj − eijEi [2]
Here in these two constitutive equations, Di is the elec-
trical displacement, Sj is mechanical strain, σj is mechan-
ical stress, Ei is the electric field, cij is the elastic stiffness
coefficient, sij is the elastic compliance coefficient, and εij
is the permittivity. The superscript used in the equation
shows the constant parameter used. dij and eij are piezo-
electric coefficients which are third rank tensors.
Piezoelectric ceramics are anisotropic in nature imply-
ing that the electromechanical properties exhibit maximum
along specific crystallographic direction. The properties are
commonly described using two subscripts (reduced order
tensor notation) which indicate the direction of the electrical
and mechanical parameters. Figure 4 shows the direction
indexes of constants in rectangular crystallographic system.
The principal properties along X, Y and Z axes are described
using 1, 2 and 3 notations, respectively. The shear constants
are represented by 4, 5 and 6 respectively. For example, in
case of piezoelectric charge constant d31, the first index “3”
indicates that electrodes are perpendicular to axis 3 and the
second index “1” indicates that the applied stress or induced
strain is along direction 1. A superscript index on the elec-
tromechanical constant is used to represent the constant
condition under which measurements were conducted. For
example – in case of compliance, sE36, “E” indicates that the
compliance was measured under constant electric field or
with electrodes connected together.
Non-centrosymmetricity is requirement for observing
the piezoelectric effect and most of the high performance
piezoelectric materials are ferroelectric perovskites as
shown in Figure 5. The leading representative of the
perovskite piezoelectric ceramics, Pb(Zr,Ti)O3 (PZT), has
many possible variations depending upon the doping and
solid solution. As shown in Figure 4(a), PZT unit cell has
Table 1: Comparison of recent small scale piezoelectric energy harvesters.
Reference Active
material
Active
area,
mm
Active
volume,
mm
Acceleration, g Frequency,
Hz
Power,
µW
Normalized areal
power density,
(µW/(mm.Hz.g))
Normalized
Volumetric power
density, (µW/
(mm.Hz.g))
Muralt et al. (a) PZT, d . . .  . . ×
−
. ×−
Morimotoet et al. () PZT, d . . .  . . ×
−
. ×−
Hajati and Kim () PZT, d  . .   . ×
−
. ×−
Durou et al. () PZT  .  . . ×−
Defosseux et al. () AIN, d .
(est.)
. .  . . × − . ×−
Marzencki et al. () AIN, d
(vac.)
.
(est.)
– .  . . × −
Hirasawa et al. () AIN . .  . . ×−
Elfrink et al. () AIN  .   . ×−
Xu et al. (a) PZT . .  . . ×−
Lei et al. () PZT . .   . ×−
Park, Park, and Lee () PZT, d . . .  . . ×
−
. ×−
Fang et al. () PZT, d . . .  . . ×
−
. ×−
Lee et al. () PZT, d . . . . . . ×
−
. ×−
Aktakka () PZT, d   .   . ×
−
. ×−
Kanno et al. () KNN, d . . .  . . ×
−
. ×−
Source: Initial data was taken from Park, Park, and Lee (2010) and Aktakka (2012) and updated to reflect the new developments. Devices with high
power density (in volume or area) or typical non-PZT devices are selected.
S. Priya et al.: A Review on Piezoelectric Energy Harvesting 5
Authenticated | jhryu@kims.re.kr author's copy
Download Date | 2/2/17 7:13 AM
a symmetric cubic structure above the Curie temperature
(paraelectric), however, below that it transforms into
asymmetric tetragonal structure (approximately Zr/Ti
ratio <1, where Zr + Ti = 1) as schematically depicted in
Figure 5(b). Thus, PZT unit cell shows spontaneous polar-
ization because of the shift in the position of B-site atom.
Neighboring dipoles formed in the distorted perovskite
unit cell align together to form domains. Typically, poly-
crystalline piezoelectric ceramics have randomly oriented
domain distribution as shown in Figure 6(a), thus, overall
net polarization of material is negligible. Because of the
ferroelectric nature of the material, domains can be per-
manently aligned by applying strong electric field. This
process is called poling (see Figure 6(b)) and is normally
performed at an elevated temperature slightly below Curie
point to facilitate the domain wall motion. During poling
process, most of the domains are aligned along applied
electric field direction and neighboring domains exhibit
new dimensions through nucleation and growth. After
poling process, most of the dipoles retain their alignment
imparting the piezoelectric material a remanent polariza-
tion (see Figure 6(c)).
Besides piezoelectric ceramics, there are piezoelectric
polymer materials which have semi-crystalline structure
for examples polyvinylidene fluoride (PVDF), polya-
mides, ParyleneC, liquid crystal polymers, PVDF-TrFE
block copolymer etc. The operation principle of these
piezoelectric polymers are similar to piezoelectric ceramic
Figure 4: Direction index of electromechanical constants in poled
piezoelectric ceramics.
Figure 5: Perovskite PZT unit cell. (a) PZT
unit cell in the symmetric cubic state
above the Curie temperature.
(b) Tetragonally distorted unit cell below
the Curie temperature.
Figure 6: Piezoelectric domains in
piezoelectric materials. (a) Randomly
oriented domains, (b) Domains during
and (c) after poling process.
6 S. Priya et al.: A Review on Piezoelectric Energy Harvesting
Authenticated | jhryu@kims.re.kr author's copy
Download Date | 2/2/17 7:13 AM
materials. The semi-crystalline polymers have micro-
scopic crystals inside matrix which are also polarized
and function as dipoles as described Figure 6. The micro-
crystals are distributed within an amorphous matrix. To
obtain effective piezoelectricity in such materials, these
small crystals should be reoriented and kept in one orien-
tation through electrical poling or mechanical stretch
process. There is another type of piezoelectric material
known as voided charged polymer (VCP, sometimes
called ferroelectret or piezoelectret) that contains internal
gas voids. When the polymer surfaces surrounding the
void are charged by electrical poling or X-ray, the space
charges are created inside matrix and the VCP behaves
like piezoelectric material. These polymers have very
high d33 values. However, these piezoelectric polymers
have serious life time and ageing problems. The VCP
is easily neutralized in extremely moist environment
and the surface charge can be rapidly decayed in high
temperature.
2.2 Transfer Function for Energy Harvester
The simple vibration energy harvester can be modeled as a
second-order, spring-mass system. The characteristics of
the energy harvester can be described by damping con-
stant and natural frequency of the system. A cantilever
beam structure with piezoelectric plate and proof mass is
equivalent to a lumped spring mass system of a vibrating
rigid body. Thus, the governing equation of motion of a
lumped spring mass system can be written as:
m  d
2z tð Þ
dt2
+ b  dz tð Þ
dt
+ k  z tð Þ= −m  d
2y tð Þ
dt2
[3]
which can be transformed using Laplace transform as
following:
m  s2z sð Þ + b  s  z sð Þ+ k  s  z sð Þ= −m  a sð Þ [4]
where a sð Þ is the Laplace transform of the acceleration,
a tð Þ, given as:
a tð Þ = d
2y tð Þ
dt2
[5]
Therefore, the transfer function of the energy harvester
can be expressed as:
z sð Þ
a sð Þ =
1
s2 + bm s+
k
m
  = 1
(s2 +ωr Qs+ωr2 )
[6]
where Q=
ffiffiffiffiffiffi
km
p
=b is quality factor of system and ωr is
resonance frequency of the energy harvester. The natural
frequency of the spring mass system and energy har-
vester can be given as:
ωn =
ffiffiffiffi
K
M
r
[7]
where K and M are the transverse stiffness and effective
mass, respectively. The stiffness K can be calculated from
loading condition. In case of simple cantilever beam
structure, the stiffness can be expressed as:
K = 3EI=L3 [8]
where E is modulus of elasticity, I is the moment of
inertia, and L is the length of beam. The moment of
inertia for a rectangular cross-section is I = 112
 
bh3,
where b and h are the width and thickness of the beam
in transverse direction, respectively.
2.3 Frequency Dependence of Output Power
The vibration displacement of energy harvester can be
maximized in resonance. The harvester will convert
mechanical to electric energy most effectively when
the applied vibration frequency is closer to the fixed
natural frequency of the device. As shown in Figure 7,
a few percent of mismatched frequency with resonance
results in a dramatic decrease of output power.
Therefore, tuning or adjusting frequency to an external
vibration source is essential in order to improve energy
conversion efficiency. From eq. [7], the natural
Figure 7: Frequency dependent output power of typical vibration
energy harvester. The maximum output power can be achieved at
resonance frequency.
S. Priya et al.: A Review on Piezoelectric Energy Harvesting 7
Authenticated | jhryu@kims.re.kr author's copy
Download Date | 2/2/17 7:13 AM
frequency of the energy harvester is closely related to
dimension and effective mass. The natural frequency of
the energy harvester is usually adjusted by changing the
weight of proof mass. However, the bandwidth at reso-
nance frequency is usually narrow and thus needs some
additional mechanism to effectively capture ambient
vibrations which usually represent a wide spectrum of
frequencies or time varying vibration spectra.
2.4 Vibration Kinematics
Vibration is common ambient energy source that can be
found in household appliances (refrigerators, microwave
ovens, washing machines etc.), large civil structures
(buildings, bridges etc.), industrial plant (refineries),
automobiles and many other common locations. Table 2
shows some of the common sources of mechanical energy
that can be harnessed through piezoelectrics. Table 3
quantifies the vibration energy available in some of
these environments (Marin and Priya 2012; Priya 2007).
The general model of a vibration energy harvester is
a typical mass-spring-damper system. Maximum power is
achieved when the excitation frequency ω is equal to the
natural frequency ωn. Maximum extractable electrical
power in terms of mechanical damping ratio ζm, electrical
damping ratio ζe, proof mass m and acceleration A
becomes,
P =
ζ e
4ωn ζ e + ζmð Þ2
mA2 [9]
Several conclusions can be drawn from the observation of
eq. [9] (Xu 2012). The extractable power from the beam is
inversely proportional to resonance frequency at a fixed
acceleration, A; therefore the energy harvester should be
designed at lowest possible frequency to achieve highest
power if we do not consider that frequencies of external
vibration sources are normally fixed in real applications.
The extractable power is also proportional to the square
of acceleration (Chandrakasan et al. 1998), which limits
the energy available for conversion with low-g vibrations
whatever the specific design is chosen. It can also be seen
that power is proportional to the proof mass, so a large
proof mass is always desirable for energy harvesting.
Finally, the term composed of the mechanical and elec-
trical damping ratio implies that the maximum power is
achieved when the electrical damping matches the
mechanical damping (Dutoit, Wardle, and Kim 2005).
When the electrical damping is equal to mechanical
damping (ζ e = ζmÞ, the maximum electrical power is
given as:
Pε, max ωnð Þ= mA
2
16ωnζm
=
mY2ω3n
16ζm
[10]
where the acceleration amplitude A and proof mass
deflection Y are related by the relationship given as:
Table 2: Sources of energy available in the surrounding which are/can be tapped for generating electricity.
Human body Vehicles Structures Industrial Environment
Breathing, blood pressure,
exhalation, body heat
Aircraft, uav, helicopter,
automobiles, trains
Bridges, roads, tunnels,
farm house structures
Motors, compressors,
chillers, pumps, fans
Wind, solar, temperature
gradient, daily
temperature
Walking, arm motion, finger
motion, jogging, swimming,
eating, talking
Tires, tracks, peddles,
brakes, shock absorbers,
turbines
Control-switch, hvac
systems, ducts,
cleaners, etc.
Conveyors, cutting g
and dicing, vibrating
mach.
Ocean currents, acoustic
waves, em waves, rf
signal
Table 3: Peak acceleration and frequency of common structures (Aktakka 2012; Lee et al. 2009).
Vibration source Peak acceleration (m/s) Frequency (Hz)
Base of a  HP -axis machine tool  
Notebook computer while CD is being read . 
Clothes dryer . 
Second story floor of a wood frame office building . 
Railway .–. –
Truck .–. –
Ship .–. –
8 S. Priya et al.: A Review on Piezoelectric Energy Harvesting
Authenticated | jhryu@kims.re.kr author's copy
Download Date | 2/2/17 7:13 AM
A=ω2nY [11]
Equation [10] represents the theoretical maximum of
extractable power, which can be dissipated in the elec-
trical load. This is actually a limiting factor for all linear
resonator based energy harvesters if the piezoelectric
layer’s transformation capacity is not a limiting factor. It
has been reported that a nonlinear resonator based
energy harvester can circumvent this limit and is able to
generate much higher power than the mechanical damp-
ing, which will be discussed in the later section. Another
parameter of interest in design of thin film harvesters is
given by the generalized electromechanical coupling
(GEMC) factor, kG
2 (Uchino 2009). The GEMC factor is
obtained from the equation:
k2G =
ω2short −ω
2
open
ω2short
[12]
where ωshort and ωopen are the angular resonance
frequencies of the associated short and open circuits,
respectively. The GEMC represents the power genera-
tion performance of the vibration harvesters, and this
value can be theoretically derived from the mechanical
properties, thickness ratio, and electromechanical
coupling factors of piezoelectric thin films (Wang
et al. 1999).
2.5 Energy Conversion and Figures of Merit
Piezoelectric energy harvesters can be categorized by the
targeted energy sources, such as ambient vibrations,
impact or shock stress, fluid flow and human motion.
Regardless of the various energy sources, the basic working
principle is the same – the environment applies a stress on
piezoelectric material and by the direct piezoelectric effect,
the input mechanical energy is converted in to electrical
energy. Piezoelectric generators produce high voltages and
low currents, and require no voltage source to operate.
Some believe they are more difficult to be integrated into
microsystems (Roundy, Wright, and Rabaey 2003a), but
there have been several successful implementations of
MEMS scale piezoelectric energy harvesters (see Table 1).
In case of the thin films, piezoelectric response is drasti-
cally reduced compared to bulk PZT due to clamping effect
of the substrate (Lefki and Dormans 1994; Li et al. 2004).
Since both longitudinal and transverse piezoelectric com-
ponents are coupled to each other, thus on application of
electric field normal to the films surface, an expansion in
longitudinal piezoelectric response and a contraction in
transverse piezoelectric response is observed due to clamp-
ing effect. The effective piezoelectric coefficient of a thin
film on a rigid substrate can be written as (Bono et al. 2009;
Krulevitch et al. 1996).
d33, f =d33 − 2d31
s13, f
s11, f + s12, f
[13]
e31, f = e31 −
cE13
cE33
eE33 [14]
Since the second term in the right hand side of eq. [13]
contributes negatively to the effective piezoelectric
response, thus effective piezoelectric response is reduced.
The electromechanical coupling coefficient (k) is another
parameter which is very important especially in resonat-
ing structures. The electromechanical coupling coeffi-
cient can be given as:
k33 =
ffiffiffiffiffiffiffiffiffiffiffi
d233
eT33s
E
33
s
[15]
The electromechanical coupling coefficient represents the
ratio of the mechanical (electrical) energy converted into
the input electrical (mechanical) energy for the piezoelec-
tric material.
Two piezoelectric modes, d31 or d33, are commonly
used in piezoelectric micro devices (Figure 8). The rela-
tive directions of the electric field and the strain distin-
guish them: d31 when the electric field is perpendicular to
the input strain, d33 when they are parallel (Bernstein
et al. 1999). Conventional MEMS piezoelectric devices/
actuators have d31 configuration in which a piezoelectric
layer is sandwiched between top and bottom electrodes.
For a d31 mode energy harvester, the generated voltage is
proportional to the thickness of the piezoelectric layer
(txx), the effective piezoelectric constant, g31, f (Vm/N),
and the applied stress, σxx
V31 = σxxg31, f txx [16]
For typical values of g31, f and accelerations, the gen-
erated voltage becomes too small for the rectifying cir-
cuits as the thickness of the piezoelectric layer drops
below 1 μm (mostly less than 0.5 μm) in MEMS–scale
harvesters. Therefore, d31 mode of a piezoelectric device
is often not favorable for energy harvesting applications
even though the generated power could be higher. For
high permittivity ferroelectric piezoelectrics, the d33 mode
can generate higher open circuit voltages by increasing
the spacing between the IDT electrodes where polariza-
tion wraps from one electrode to the next in alternating
directions as shown in Figure 8. Jeon et al. showed that
S. Priya et al.: A Review on Piezoelectric Energy Harvesting 9
Authenticated | jhryu@kims.re.kr author's copy
Download Date | 2/2/17 7:13 AM
operating piezoelectric elements in d33 mode is more
advantageous than in d31 mode for MEMS-scale PZT har-
vesters (Jeon et al. 2005).
The power trapped in each cycle from eq. [9] is dis-
sipated to structural and aerodynamic damping as well
as to electrical energy via piezoelectric effect. To max-
imize the harvested power, the electrical damping needs
to be increased while the structural and aerodynamic
damping needs to be minimized. The electrical power
generated via d33 mode piezoelectric effect of a unimorph
cantilever can be expressed as:
Ppiezo =Vpiezox  Epiezo  s2  ωexc  k333 [17]
k233 =
Stored energy
Input mechanical energy
=
d233Epiezo
εpiezo
=
e233
εpiezoEpiezo
[18]
where Vpiezo, Epiezo, s, ωexc, k33, εpiezo, and e33 are the
volume of the piezo material, Young’s modulus, strain,
excitation frequency, electromechanical coupling coeffi-
cient, dielectric permittivity and piezoelectric coefficient.
As long as the beam’s stored energy minus the mechan-
ical loss (dissipated via structural and aerodynamic
damping), which can be defined as “extractable energy,”
is bigger than the “conversion energy” from eq. [17], the
maximum harvested energy is determined by the piezo-
electric layer’s volume and coupling coefficient. Similar
statement can be made for the d31 mode piezoelectric
harvesters.
The coupling coefficient described in eq. [18] may
only be applied to conditions where the passive elastic
layer’s stiffness can be neglected. For most MEMS
energy harvesters with unimorph structure where the
piezoelectric layer is much thinner compared to the
passive elastic layer, eq. [18] may not be accurate. For
an MEMS energy harvester, which consists of a thin
layer of piezoelectric material and a much thicker pas-
sive elastic layer, the coupling factor can be written as
(Xu and Kim 2012):
k2 = stored electrical energy=total input
mechanical energy = stored electrical energy=
mechanical energy input to elastic layerð
+mechanical energy input to piezoelectric layerÞ
[19]
It can be readily seen that only a portion of the input
mechanical energy is injected into the piezoelectric layer
to be converted into electrical energy, while much of the
energy stays in the elastic layer as strain energy and will
not be converted. Therefore, the coupling coefficient will
be lower than the real intrinsic conversion rate of the
piezoelectric material itself.
Figure of merit (FOM) for the piezoelectric materials
can be derived by considering the power response of the
piezoelectric transducer. Recently, Oliver and Priya have
conducted detailed modeling of the piezoelectric cantile-
ver (Bedekar, Oliver, and Priya 2010) and proposed a
dimensionless figure of merit (DFOM) for piezoelectric
transducer material in energy harvesting application as
(Priya 2010):
DFOM=
k231Qm
sE11
 
on− resonance
d31g31
tanδ
 
off − resonance
[20]
where k31 is the transversal electromechanical coupling
factor, Qm is the mechanical quality factor, s11
E is the
elastic compliance at the constant field condition, d31 is
the transversal piezoelectric strain constant, g31 is the
transversal piezoelectric voltage constant, and tanδ
Figure 8: Two modes of piezoelectric
conversion of input mechanical strain
depending on the relative direction of
the stress σxx (or strain) and the electric
field, E. (Credit: Prof. Sang-Gook Kim).
10 S. Priya et al.: A Review on Piezoelectric Energy Harvesting
Authenticated | jhryu@kims.re.kr author's copy
Download Date | 2/2/17 7:13 AM
is the loss factor. The DFOM is a product of two FOM’s
representing off-resonance and on-resonance conditions.
By comparing DFOMs for the commercial piezoelec-
tric compositions, one could identify the better piezoelec-
tric composition for energy harvesting applications.
Defosseux et al. have compared the off-resonance FOM
for the PZT and AlN and noticed higher magnitude
response for AlN (7.8 × 10−11m2/C as compared to 4 × 10
−11m2/C) (Defosseux et al. 2012). For PZT, the values were
taken to be ε33/εo = 935, d31=–110 × 10−12m/V and
tanδ= 3.6% (measured on PZT 53/47 [100]-textured 2 µm
thin film (Ledermann et al. 2003)). For AlN, the values
were taken to be ε33/εo = 10, d31=–2.6 × 10−12m/V and
tanδ=0.1% (dielectric properties measured at 10 kHz for
film with thickness of 2 µm by Martin et al. (2004) and
piezoelectric property was reported by Tsubouchi and
Mikoshiba for 1 µm thick film (Tsubouchi and Mikoshiba
1985). Considering the fact that AlN processing can be
made compatible with CMOS, these results indicate the
promise of AlN films towards developing MEMS
harvesters.
2.6 Impedance Matching
Likewise the natural frequency matching with an external
vibration source, the impedance of the piezoelectric gen-
erator should be matched to that of an external circuit in
order to maximize the power extraction. Usually, an elec-
trical impedance matching circuit is placed between the
piezoelectric generator and external loads such as a
rechargeable battery and supercapacitor. Thus, the match-
ing network should be lossless and requires that the input
impedance should be matched to the output impedance.
Equation [21] shows the electrical input impedance of the
energy source generated by the piezoelectric harvester.
Z =
1
2πω  C0 [21]
where ω is vibration frequency of energy harvester, C0 is
capacitance of piezoelectric materials. The impedance
matching circuit consists of load resistors in accordance
with the impedance of the piezoelectric generator calcu-
lated by eq. [21].
2.7 Challenges of Piezoelectric MEMS
Energy Harvesters
Many piezoelectric MEMS energy harvesters have been
developed and some of them are shown in Table 1.
Their form factors are all different, and can only be
compared with the power density which can be defined
as the ratio of generated power over the active material
volume (volume power density, μW/mm3) or over the
active material area (area power density, μW/mm2). But,
harvesters with high resonant frequency or that requires
high acceleration ambient vibration need to be penalized
considering the low frequency – low g characteristics of
ambient vibrations. In order to generate a comparative
figure, normalization was done with respect to both area
and volume of harvesters, natural frequency and input
acceleration.
Based upon eq. [16], the maximum extractable output
power is proportional to (1/frequency) and (acceleration2)
(Chandrakasan et al. 1998). From eq. [17], the converted
electrical power is proportional to the excitation fre-
quency. Thus, some researchers have taken into account
both frequency and acceleration variation, by normalizing
the power with frequency or acceleration (Chandrakasan
et al. 1998). We propose a simple metric for the normal-
ization as Power / (frequency × acceleration2 × area or
volume) and refer to it as “areal or volumetric normalized
power density” in this paper. Accordingly, a device gen-
erating higher power at lower frequency, acceleration and
with area/volume will have higher normalized power den-
sity. For comparison, we utilized most common units used
in literature to describe the physical quantities – Hz for
frequency, mm2 for area, and g2 for acceleration. Table 1 is
based on best estimates and data available in literature.
Only the active piezoelectric area or volume is used to
compute normalized areal power density (NAPD) and nor-
malized volumetric power density (NVPD) depending
upon the data availability in literature for MEMS devices
developed using thin film deposition and lithography
techniques.
For NAPD, harvester area (cantilever, non-linear
beam, diaphragm, S-shape beam, corrugated beam, zig-
zag beam etc.) is calculated based on the data in the
literature. We understand that energy harvested and
transformed to electrical power is proportional to volume
of piezoelectric material and hence volume may also be
taken into account instead of area. For example, Hajati’s
non-linear beam energy harvester (Hajati and Kim 2011)
showed 1–3 orders higher NVPD than that of any
reported devices, but has a relatively low NAPD since it
has very thin PZT (0.25 μm) over large area (120mm). For
battery-less operation of various wireless sensor nodes in
real world applications, it will be ideal to harvest about
100 μW continuous power at the size of a quarter dollar
coin (diameter = 24.26mm, total thickness = 1.75mm) at
100Hz or lower ambient vibrations with less than 1 g
S. Priya et al.: A Review on Piezoelectric Energy Harvesting 11
Authenticated | jhryu@kims.re.kr author's copy
Download Date | 2/2/17 7:13 AM
acceleration. This requirement can be converted to a
NVPD (assuming one 0.5 μm thick piezoelectric layer in
the device) = 4.3 μW/(mm3·Hz·g2). Most reported devices
show orders of magnitude smaller normalized power
density than this (See Table 1), even if we can increase
the desired output power as increasing thickness of
piezoelectric layer. One of the direct solutions to address
this challenge is to improve the electro-mechanical cou-
pling coefficient of the piezoelectric thin films. Another
approach is to seek new resonating beam structure
designs from which more energy can be extracted at
lower frequency and acceleration.
Another metric commonly used in literature is nor-
malized figure of merit, which takes into account band-
width. Bandwidth is also an important characteristic and
should be accounted for determining the performance of
piezoelectric harvesters under unpredictable or
uncontrollable spectra of ambient vibrations. Most piezo-
electric energy harvesters have been designed based on a
linear resonator, e. g. a cantilever with a proof mass. The
extractable power of an energy harvester based on a
linear resonator is proportional to the gain (quality factor,
Q= fr/Δf where fr is resonance frequency, Δf is full width
at half maximum) of the resonator, which is inversely
proportional to the bandwidth. If the center frequency
of a beam is off about 2% from the input frequency, the
amplitude of the beam bending drops to about 50% of
the resonance peak. If it is off 5%, then there is no
resonance to amplify the strain on the piezoelectric mate-
rial. Accordingly, there is a trade-off between the output
power and the bandwidth. Since we cannot control the
frequency of ambient vibrations, an energy harvester
with a narrow bandwidth (of most linear resonators) is
impractical in most real applications. Several approaches
have been adopted to circumvent this gain-bandwidth
dilemma. For example, the natural frequency of resonat-
ing beams can be tuned by changing the axial tension of
a beam through non-contact mechanisms such as mag-
netic attractive and repulsive forces. Beam dimensions
and proof mass have also been tuned mechanically to
widen the bandwidth. (Al-Ashtari et al. 2012; Mansour,
Arafa, and Megahed 2010). However, frequency tuning
inevitably consumes power, the tuning efficiency is low
and the tuning range is limited. Multiple beams of differ-
ent lengths have also been utilized to address this chal-
lenge, which may not be practical in terms of size and
cost. Simpler and less costly methods have been sought
that can provide both the wide bandwidth and high
power density as required for practical MEMS-scale
devices.
3 Recent Advances in Piezoelectric
MEMS Energy Harvesting
In order to address the challenges described above,
advances have been made both in improving the perfor-
mance of piezoelectric materials and design of resonating
beam structures to achieve higher power density and
wider bandwidth.
3.1 Grain Textured and Epitaxial
Piezoelectric Films
Bulk PZT ceramics have plethora of dielectric and piezo-
electric properties which can be controlled using doping
(Funakubo et al. 2012). Lead based relaxor-lead titanate
compounds so called relaxor ferroelectrics include Pb
(Zn1/3Nb2/3)O3-PbTiO3(PZN–PT), Pb(Mg1/3Nb2/3)O3-PbTiO3
(PMN–PT) and Pb(Y1/2Nb1/2)O3-PbTiO3(PYN–PT), exhibit
large electromechanical coupling coefficients which
makes these materials more attractive option for micro-
actuator and micro-sensor applications. For device min-
iaturization it is important to grow films using these
materials. PZT thin films are deposited with variety of
methods such as sputtering, chemical solution deposition
(i. e. sol-gel), MOCVD and laser ablation processes. Since
piezoelectric properties of these materials are strongly
dependent on film quality and growth orientation, thus,
the control of growth orientation is highly desired with
(001) texturing (Trolier-McKinstry and Muralt 2004).
Additionally, the composition of the piezoelectric mate-
rial plays a crucial role in deciding the piezoelectric
properties of films. For example, in case of PZT thin
films, composition near the morphotropic phase bound-
ary (MPB) is commonly preferred due to its high piezo-
electric response (Jaffe 1971). From application point of
view, it is very important to integrate these oxides on Si
substrates which could pave the way for efficient fabrica-
tion of devices. However, the growth of oxide films on Si
substrate is still a complicated process due to technical
difficulties such as inter-diffusion, large lattice mismatch,
and thermal expansion mismatch (Chopra et al. 2013).
Tremendous efforts have been made to integrate the
oxide films on Si substrate with control of crystal
orientation.
The most simple and direct solution towards enhan-
cing the output power at the fixed size of a device is to
increase the piezoelectric and electromechanical cou-
pling coefficient. Grain texturing has been shown to be
12 S. Priya et al.: A Review on Piezoelectric Energy Harvesting
Authenticated | jhryu@kims.re.kr author's copy
Download Date | 2/2/17 7:13 AM
an effective method for improving the magnitude of phy-
sical constants in piezoelectrics by achieving a domain-
engineered state. In the vicinity of morphotropic phase
boundary, a rhombohedral composition oriented along
<100> direction is known to exhibit optimum magnitude
of electromechanical coefficients (Du et al. 1998). Park
and Shrout attributed this high electromechanical perfor-
mance to domain engineered state achieved through
polarization rotation from <111> to <100> (Park and
Shrout 1997). Thus, texturing is desired in PZT but
poses several challenges in synthesis.
An important characteristic in driving the texture of
complex oxides on Si substrates is proper texturing of the
electrode layers. Most commonly, Pt electrodes are
employed for many applications and achieving highly
(111) textured Pt films on Si requires proper control of
the adhesion layer, typically TiO2. Recent efforts have
identified the importance of surface roughness of the
underlying passive elastic layers (commonly SiO2), resi-
dual oxygen content during the Ti sputtering process,
sputter temperature, Ti thickness, and high temperature
oxidation of the Ti into textured TiO2 as critical para-
meters enabling a nearly pure (111) textured Pt layer
with a FWHM ranging from 1.5 to 2.5 degrees (Potrepka
et al. 2011). Combining a highly textured Pt electrode with
proper seed layer can be used to achieve (001) texture
(Sanchez et al. 2013).
In addressing the optimization of synthesis condi-
tions, Temperature-Time-Transformation (TTT) diagrams
have been proposed to document texture evolution during
thermal treatment of PZT thin films on platinized silicon
substrates (Varghese et al. 2011). By varying the anneal-
ing/pyrolysis temperature and time, extensive exploration
of the sol-gel thermal budget operating space yielded the
TTT diagram as shown in Figure 9(a)–(c). It can be seen
that films with pyrolysis at 300 °C for 3 min were textured
in (100) direction until >750 °C annealing temperature,
after which they start showing random orientation. On
the other hand, the films pyrolyzed at lower temperature
and for shorter times are textured in (100) direction for a
narrow threshold annealing temperature range. Ternary
diagram [Figure 9(d)] illustrates the frequency of each
textured orientation obtained for each pyrolysis binned
as per the ranges in annealing temperature and time.
Thus, one is able to quantify the operating regime for
achieving specific texture orientation. These diagrams
are also invoked to understand the texturing mechanism
(Chen and Chen 1994) and can be further expanded to
include other piezoelectric materials system (Zhou, Apo,
and Priya 2013a).
Several studies in literature have been conducted on
tuning the piezoelectric properties through interfacial
stress. Recent results by Han et al. have shown ~90%
enhancement of ferroelectric and piezoelectric properties
in MPB composition PZT thick films by tailoring the
magnitude of residual stress by choosing substrates
with different coefficient of thermal expansion. The
results from this study are summarized in Table 4
(Brennecka et al. 2004; Han et al. 2011a; Tuttle et al.
1992; Yokoyama et al. 2002). The direct piezoelectric con-
stant (d33, eff, pC/N) was measured by d33 meter and the
effective piezoelectric constant (d33, eff, pm/V) was
obtained by measuring variation in displacement with
applied electric field using laser interferometer. The dif-
ference between these two coefficients is attributed to the
substrate clamping effect. The electrical properties
showed that the films on Yttria stabilized Zirconia (YSZ)
substrates with highest in-plane compressive stress had
the best piezoelectric properties while that on Si wafer
with tensile in-plane compressive stress showed lower
properties. The enhanced piezoelectric properties were
attributed to the reason that c-domain parallel to the
thickness were easy to form under in-plane compressive
stress. This technique is quite appealing as it can be
easily implemented in the fabrication of MEMS
components.
Epitaxial PZT thin films with c-axis orientation are
excellent materials for MEMS energy harvesters (Kanno
et al. 1997; Morimoto et al. 2010). However, epitaxial sub-
strates, such as MgO and SrTiO3, are usually not suitable
for unimorph cantilevers because of their brittleness and
difficulty of microfabrication. One of the solutions is
transferring the epitaxial PZT films on flexible cantile-
vers. Qi et al. transferred epitaxial PZT thin films depos-
ited on MgO substrates to PDMS substrates and have
evaluated performance of stretchable piezoelectric energy
harvester (Qi et al. 2011). Morimoto et al. have developed
high efficiency piezoelectric energy harvesters using
c-axis oriented PZT thin films by radio-frequency (rf)-
sputtering, which were transferred onto stainless steel
(Morimoto et al. 2010). The fabrication process from this
study is shown in Figure 10. The c-axis oriented PZT thin
films were grown on (100) MgO single crystals with an
epitaxial (001) Pt bottom electrodes. Reciprocal lattice
space maps before and after transfer process clearly
showed spotty diffractions of the (204) PZT, indicating
that the transfer process did not degrade the crystal
structure of the epitaxial PZT film. After the PZT film
was bonded to 50-μm-thick stainless steel sheets with
epoxy resin, the MgO substrate was etched out in
S. Priya et al.: A Review on Piezoelectric Energy Harvesting 13
Authenticated | jhryu@kims.re.kr author's copy
Download Date | 2/2/17 7:13 AM
phosphoric acid. The photograph of the stainless steel
cantilever beam covered with the epitaxial PZT is shown
in Figure 10. The relative dielectric constant εr of the
transferred films on stainless steel was as low as 166,
while the piezoelectric coefficients e31,f of the transferred
PZT films was around −6 C/m2. The thickness and length
of stainless steel cantilever was 50 μm and 18.5mm
respectively. Because of the thin dimension of the metal
cantilever, the first resonance was found to occur at
126Hz. Averaged output voltage and calculated value
are plotted in Figure 11 (acceleration: 5m/s2). The max-
imum output electric power of 5.3 μW was obtained
across a load resistance of 50 kΩ. In this measurement,
GEMC, kG
2 was calculated to be 1.3 × 10−2 which is much
larger than polycrystalline PZT thin films on Si sub-
strates. This result is attributed to large electromechani-
cal coupling coefficient k31 of epitaxial PZT thin films.
The output power increases monotonically with the accel-
eration, reaching 244 μW at 50m/s2. The flexible metal
cantilever enables considerable reduction of the resonant
frequency and offers enhanced toughness compared with
brittle Si-based cantilevers.
Recently, direct deposition of PZT thin films on
Nickel foil for MEMS energy harvesters have been
Figure 9: Temperature-time-transformation diagrams of PZT-sol-gel thin films pyrolyzed at (a) no pyrolysis; (b) 250 °C, 1.5 min; (c) 300 °C,
3 min; and (d) the ternary plot of all the data. (Varghese et al. 2011).
Table 4: Relationship between in-plane stress and electric/piezoelectric properties in PZT thick films deposited on various substrates (Han
et al. 2011a).
Substrate In-plane Stress [MPa] d
eff [pC/N] d
eff [pm/V] εr [ khz] tan δ [ khz] ΔPr/2 [μC/cm2] ΔEc/ [kv/cm]
Silicon . ± .(tensile)  .  . . .
Sapphire −. ± .(compressive)  .  . . .
YSZ −. ± .(compressive)  .  . . .
14 S. Priya et al.: A Review on Piezoelectric Energy Harvesting
Authenticated | jhryu@kims.re.kr author's copy
Download Date | 2/2/17 7:13 AM
successfully demonstrated by Yeo and Trolier-McKinstry
(2014). (001) oriented PZT thin films were grown by sol-
gel process on Ni substrate. HfO2 and (001) oriented
LaNiO3 films were used as a passivation layer to suppress
the substrate oxidation and buffer layer to subsequently
grow (001) oriented film, respectively. Surface and cross-
sectional microstructure images of PZT films on Ni are
shown in Figure 12(a) and (b). The PZT film have colum-
nar structure and there was no evidence of cracks or
delamination among layers as shown in Figure 12(b).
The permittivity and loss tangents of (001) oriented PZT
films on Ni are near 780 and 0.04 at 1 kHz. The PZT film
on Ni foil displayed a well-saturated hysteresis loop with
a large remanent polarization of ~36 μC/cm2, while the
(100) oriented PZT on Si substrate showed much lower
remanent polarization as plotted in Figure 13. In addition,
this PZT film on Ni had a large transverse piezoelectric
constant e31,f of –10.6 C/m
2. This PZT film directly grown
on metal substrate is favorable for a low resonance
frequency and robust MEMS energy harvester.
Epitaxial growth of ferroelectric thin films on silicon
suffers minimal leakage and optical scattering which
results in a drastic improvement of electrical properties
when compared to polycrystalline films. Thus epitaxial
integration of ferroelectric films such as PZT, PST
(PbSc0.5Ta0.5O3) on Si substrate is highly desirable for
the development of next generation devices. However,
direct integration of PZT on Si using Pulsed laser deposi-
tion (PLD) still remains a challenging task due to inter-
diffusion, structural and chemical incompatibilities, and
thermal and lattice mismatch issues. These issues can be
addressed using buffer layers such as SrTiO3 and yttria-
stabilized zirconia (YSZ)/CeO2 (Chopra et al. 2013; Du
et al. 1998). These buffer layers act as diffusion barrier
as well as help in bridging the lattice mismatch between
film and substrate. PLD is one of the preferred methods
for fast deposition of high quality films. Zirconium (Zr) is
one of the few metals which has a higher affinity towards
O2 than Si. This makes YSZ inert to Si and prevents
oxidation of Si during deposition in O2 atmosphere.
CeO2 is another buffer layer which is employed in combi-
nation with YSZ to reduce the lattice mismatch further.
Successful integration of functional oxides on Si sub-
strate has been reported in literature (Chopra et al. 2013,
Chopra, Alexe, and Hesse 2015a; Gardeniers, Smith, and
Cobianu 1995). (001)-oriented growth of oxides is
achieved by fabricating Si (100)/YSZ/CeO2/LaNiO3 struc-
tures (Chopra et al. 2013). The orientation of the films can
be switched from (001) to (110) just by replacing the
heterostructure with Si (100)/YSZ/SrRuO3. LaNiO3 and
SrRuO3 both act as a bottom electrode in their respective
heterostructures, which are necessary for the electrical
measurements. The XRD measurements performed on
such heterostructures reveal a (001) and (110)-oriented
growth as shown in Figure 14.
The in-plane XRD scans confirm that both the dis-
cussed structures are epitaxial, however LNO and subse-
quent layers in the (001)-oriented heterostructure were
Figure 10: Fabrication process flow and photograph of transferred epi-
taxial PZT thin films on stainless steel cantilever (Morimoto et al. 2010).
0.0
2.0
4.0
6.0
0.0
1.0
2.0
3.0
1 10 100 1000
Experiment
Calculation
Peak-to-peak voltage
O
ut
pu
t p
ow
er
 [μ
W
] Output voltage [V
pp ]
Load resistance [kΩ]
Figure 11: Output voltage and generated power of transferred epi-
taxial PZT thin films as a function of load resistance (Morimoto et al.
2010).
S. Priya et al.: A Review on Piezoelectric Energy Harvesting 15
Authenticated | jhryu@kims.re.kr author's copy
Download Date | 2/2/17 7:13 AM
found to be rotated in plane by 45 degrees with respect to
the underlying YSZ and CeO2 layers as shown in Figure
15(a). This kind of in-plane rotation is facilitated due to
good arrangement in the lattice parameters of both CeO2
(a=0.541 nm) and LNO (apc = 0.386 nm) which resulted in
an in-plane rotation for the top ferroelectric layer too.
Recently successful integration of PZT films on glass
substrates using 2D nanosheets has been demonstrated
(Chopra et al. 2015b; Jumpertz et al. 2014). The biggest
advantage of using nanosheets is reduction in growth
temperature. Crystalline growth of YSZ, CeO2 and SrTiO3
buffer layers is achieved at very high temperature of
750 °C which is not suitable for substrates like glass.
Thus, low temperature growth of buffer layers was
achieved by replacing the oxide buffer layers with
nanosheets which grow at room temperature. The
nanosheets were transferred to the substrates using lang-
muir-blodgett deposition process. The orientation control
of PZT films was achieved using Ca2Nb3O10 (CNO) and
Ti0.87O2 (TO) nanosheets. A (001)-oriented growth of LNO
films was achieved using CNO nanosheets due to the
Figure 12: (a) Surface and (b) cross-sectional SEM images of PZT films deposited on LNO (100nm)/HfO2 (30nm)/Ni foil after PbO-precursor
cover coat (Yeo and Trolier-McKinstry 2014).
Figure 13 : P-E hysteresis curves of (001) oriented PZT (52/48) films
on Ni and silicon substrates respectively (Yeo and Trolier-McKinstry
2014).
Figure 14: Out of plane XRD patterns obtained from the PST films
deposited on (a) LNO/CeO2/YSZ/Si, (b) SRO/YSZ/Si (Chopra, Alexe,
and Hesse 2015a).
Figure 15: (a) In-plane φ-scan for PST on LNO/CeO2/YSZ/Si showing
LNO and PST has 45 o in-plane rotation with respect to CeO2/YSZ/Si.
(b) A schematic showing the 45 o rotation (Chopra et al. 2013,
Chopra, Alexe, and Hesse 2015a).
16 S. Priya et al.: A Review on Piezoelectric Energy Harvesting
Authenticated | jhryu@kims.re.kr author's copy
Download Date | 2/2/17 7:13 AM
exact lattice match between CNO nanosheets (lattice
parameter = a = 3.86Å) and LNO (lattice parameter = a =
3.86Å) which further promoted a (001)-oriented growth
of subsequent PZT thin films. On the other hand, TO-
nanosheets which are known to have a lepidocrocite-
type structure with a lattice parameter of a= 3.76Å and
b= 2.97 Å promotes (110)-oriented growth of both LNO
and subsequent layer of PZT as shown in Figure 16(a).
However, all the films deposited were polycrystalline due
to random in-plane distribution of nanosheets. Growth of
nanosheets with single orientation in in-plane direction is
the next challenge in the field which is being addressed
to achieve a complete epitaxial growth of subsequent
layers. Fatigue and piezoelectric measurements demon-
strated on nanosheet buffered PZT films showed stable
and good piezoelectric properties which are essential for
the stable operation of the next generation devices. A
comparison of the piezoelectric response of PZT films on
nanosheets and Pt is shown below in Figure 16(b).
It is well-known that relaxor ferroelectric single crys-
tals, such as PMN-PT and PZN-PT, show about 10 times
larger piezoelectric coefficient than that of conventional
PZT ceramics (Kuwata, Uchino, and Nomura 1982; Park
and Shrout 1997). Recently, Baek et al. successfully grew
epitaxial PMN-PT thin films on SrTiO3–buffered miscut Si
substrate by off-axis sputtering. The piezoelectric coeffi-
cient e31,f in their work was reported to be –27 C/m
2,
which is the highest value reported (Baek et al. 2011).
Using these films, they fabricated a unimorph micro-can-
tilever and confirmed the excellent inverse piezoelectric
performance. Because of the large electromechanical cou-
pling coefficient k31 (or figure of merit: e
2
31,f/εr) of PMN-PT
epitaxial thin films, this system is quite promising
towards improving the performance of current MEMS
energy harvesters.
3.2 Lead-Free Piezoelectric Films
For powering medical implants and human use of energy
harvesters, lead-free piezoelectric material is desirable.
Potassium sodium niobate (KxNa1–xNbO3) abbreviated as
KNN, is considered as a most promising lead-free piezo-
electric material owing to its higher Curie temperature
and higher ferroelectric orthorhombic – ferroelectric tet-
ragonal transition temperature (Ahn et al. 2008a). The
piezoelectric properties of KNN based compositions are
directly correlated to the fraction of orthorhombic (O) and
tetragonal (T) phase as shown in Figure 17(a). One of the
strategies for achieving higher piezoelectric response has
been to modulate the composition such that O/T transi-
tion lies close to room temperature (Ahn et al. 2008b).
Another strategy adopted for designing lead-free compo-
sitions is based upon the trend between atomic weight
ratio of A to B sites (Rw =Wa/Wb) and longitudinal piezo-
electric constant d33 as shown in Figure 17(b) (Ahn et al.
2009). It can be observed that 1/Rw for KNN ceramics (for
Na/K ratio of 0.5) is similar to Rw for PZT ceramics at MPB
composition and both of these materials exhibit high
piezoelectric response. Piezoelectric compositions show
large response when RW for A-site heavy perovskites and
1/RW for B-site heavy perovskites is higher than 2.0.
The fabrication process of these lead-free piezoelec-
tric materials in thin-film form is still under development,
and it is expected that these materials will be utilized in
the design of MEMS energy harvesters in the near future
(Zhou et al. (2013b)). Recently, Shibata et al. reported that
KNN thin films deposited by RF magnetron sputtering
showed large transverse piezoelectric properties compar-
able to those of PZT thin films (Shibata et al. 2011). Kanno
et al. have compared the energy harvesting performance
of KNN thin films with PZT thin films by using simple
Figure 16: (a) Out of plane (θ–2θ) scans
and (b) Longitudinal piezoelectric
response of the PZT films deposited on
Pt, Ti0.87O2 and Ca2Nb3O10 buffer layers
coated on glass substrate (Bayraktar
et al. 2014).
S. Priya et al.: A Review on Piezoelectric Energy Harvesting 17
Authenticated | jhryu@kims.re.kr author's copy
Download Date | 2/2/17 7:13 AM
unimorph Si-cantilevers (Kanno et al. 2012). The piezo-
electric coefficient of both KNN and PZT films showed
almost the same value of e31,f =−10 C/m
2 (Kanno et al.
2012). The relative dielectric constants of the KNN and
PZT films were 744 and 872, respectively. Figure 11 shows
the average output power P=V2/(2R) as a function of load
for energy harvesters made of KNN and PZT unimorph
cantilevers. Measurements were performed at the reso-
nance frequency of each cantilever (KNN: 1.0 kHz, PZT:
0.89 kHz; acceleration 10m/s2). Peak output power for
the KNN and PZT films was 1.1 µW at 1.7 kΩ and 1.0 µW
at 1.2 kΩ, respectively. Because KNN and PZT thin films
have almost same dielectric and piezoelectric properties,
the KNN film performs comparably to the PZT film with
respect to power generation. GEMC kG
2 of KNN and PZT
energy harvesters was around 0.6 ~ 1.7 × 10−3 as deter-
mined by fitting the calculated value of eq. [12] to experi-
mental results.
3.3 Aluminum Nitride (AlN) – A MEMS
Compatible Piezoelectric Film
AlN is a piezoelectric material with wurtzite structure.
The properties of AlN based films are highly process
dependent. Aluminum nitride has a band gap of 6.2 eV
with lattice parameter of a = 13.112Ǻ and c = 4.982Ǻ. It is
a potential candidate for UV light emission and SAW
devices due to large acoustic wave (SAW) velocity (Duffy
et al. 1973). AlN films have been deposited using chemi-
cal vapor deposition (CVD) (Chubachi, Sato, and Kojima
1984), plasma assisted CVD (Zhang et al. 1993), metalor-
ganic CVD (Saxler et al. 1994), reactive DC-magnetron
sputtering (Meng, Heremans, and Cheng 1991), plasma
assisted molecular beam epitaxy (MBE) (Stevens et al.
1994), laser-induced chemical vapor deposition (Li and
Tansley 1990), and pulsed laser deposition (Norton,
Kotula, and Carter 1991). Most of these techniques
required a high processing temperature (1,000 °C) to
obtain the best crystal quality and texture in the depos-
ited thin films. However, high quality growth at low
temperature is desired to ensure the compatibility with
IC technology. In this regards, different process techni-
ques have been developed (Aita 1982; Shiosaki et al.
1980; Takeda, Mori, and Takahashi 1981). In addition
to (0001)–orientation, it is also observed that tuning of
the ion energy and flux of the bombarding ions (Ar + ,
N2 + ) is equally important (Dubois, and Muralt 2001).
AlN films have a much higher phase velocity and che-
mical stability in comparison to the ZnO films. However,
AlN has lower piezoelectric coupling and it is difficult to
control the growth of AlN films.
Recently, significant progress has been made towards
incorporating the AlN films in energy harvesting applica-
tions. Schaijk et al. have demonstrated the performance of
micomachined AlN cantilevers and shown that device with
dimension of 3 × 1.3mm was able to provide 10µW at the
resonance frequency of 1,155Hz under 8 g acceleration
(Van Schaijk et al. 2008). Under practical acceleration
values of 1 g or lower, the power generated was smaller
than 1 µW. Heidrich et al. have investigated the energy
generation from [001] textured AlN cantilevers and corru-
gated membranes for bio-implants. The growth was con-
ducted on Si (001) substrates, which resulted in tensile
(< + 300MPa) and compressive strains (>–100MPa)
depending upon the deposition parameters. In the non-
resonant condition of 70Hz, for a 3 × 4 corrugated mem-
brane array (radius of individual membrane= 400µm) the
0 50 100 150 200
100
150
200
250
300
350
d
33
 (
p
C
/N
)
TO-T (°C)
: KNN
: KNN-LiNbO3
: KNN-LiSbO3
: KNN-Li(Nb,Ta,Sb)O3
: KNN-BaTiO3
: KNN-CaTiO3
: KNN-LiNbO3-BaTiO3
: KNN-LiNbO3-LiSbO3-BaTiO3
Figure 17: (a) Variation of longitudinal piezoelectric coefficient with O–T transition temperature in KNN system, and (b) Variation of
longitudinal piezoelectric coefficient as a function of weight ratio in bulk perovskites (Ahn et al. 2008b).
18 S. Priya et al.: A Review on Piezoelectric Energy Harvesting
Authenticated | jhryu@kims.re.kr author's copy
Download Date | 2/2/17 7:13 AM
peak power of 10µW was measured across 10kΩ with a
bias of 1V and acceleration of 0.01 g (Heidrich et al. 2011).
Yen et al. conducted detailed experimentation and model-
ing of the corrugated AIN cantilever structures. At a reso-
nance frequency of 853Hz, a cantilever with a width of
2,400µm, length of 500µm, and a 2 µm thick piezoelectric
layer was able to provide 0.17 µW under an acceleration of
1 g using a tip mass of dimension 2,400× 500× 680µm
(Ting-Ta et al. 2011). Andosca et al. also demonstrated a
AlN thin film based MEMS energy harvester with high
power density. The energy harvester with a width of
6.0 µm, length of 7.8 µm, a 2 µm thick AlN film and a
proof mass of 28.9mg was able to generate 119 µW power
under 1 g acceleration at a resonance frequency of 56.6Hz
(Andosca et al. 2012).
A simulation study in this area has been conducted by
Stoppel et al., who computed the effect of thickness on
power generation (Stoppel et al. 2011). It was pointed out
that since the Young’s modulus of AIN (345GPa) is about
4 × that of PZT, the thickness of AIN for maximum power
output is about 3 × smaller than that of PZT. For a canti-
lever with 2 µm thick AIN operating at resonance fre-
quency of 105.6Hz under acceleration of 1m/s2, output
power of 0.8 µW was measured across 21MΩ load. Based
upon the experimental data available in literature, the
normalized output power (power/frequency × acceleration)
for AIN micro devices ranges between 2.034 × 10−5–757 × 10
−5 µW/(Hz ×m/s2). Ignoring the data from Stoppel et al., the
spread is more reasonable 2.034× 10−5–11 × 10−5 µW/
(Hz ×m/s2). These values are quite good and considering
the compatibility of AlN with CMOS process and long
history in optimizing the deposition process, we expect
that this area will continue to grow.
3.4 Piezoelectric Thick Films by Powder/
Granule Spray in Vacuum Process
The powder spray in vacuum process so called aerosol
deposition (AD) is a unique ceramic film deposition tech-
nology that is able to fabricate highly dense thick films
(submicron to several hundred μm) at room temperature.
This process utilizes high kinetic energy of ejected aero-
sol consisting of a mixture of fine ceramic particles and
carrier gas from a nozzle. The process was firstly intro-
duced by Akedo and co-workers at AIST, Japan in late
1990s (Akedo and Lebedev 2000). The process has unique
advantages compared to other thin/thick film deposition
process such as high deposition rate (over several tens
μm/min depending on the deposition area), low proces-
sing temperature, composition control, high adhesion
strength between substrate and film as well as micro-
patterning of ceramic thick films during deposition
(Zhou et al. 2011). Due to its low temperature processing,
low sinterability ceramic thick films such as KNN based
lead-free piezoelectrics and PbTiO3 ceramics with full
density can be deposited on various types of substrates
(Han et al. 2011b; Ryu et al. 2007, 2014; Wang et al. 2008).
Figure 18 shows ferroelectric/piezoelectric property mod-
ulation of AD-PZT film according to the variation of resi-
dual stress level (Han et al. 2011a). By generating high
compressive residual stress in the PZT thick films, the
piezoelectric properties can be enhanced by ~2 × . All
these advantages are highly attractive for MEMS based
piezoelectric device applications as mentioned in pre-
vious section.
Lee and co-workers at National Taiwan University
reported the MEMS devices based upon the AD process
in 2008 (Lee et al. 2009; Wang et al. 2008). Figure 19
represents their device pictures. By using AD process,
they succeeded to fabricate over 10μm PZT thick film on
the silicon wafer and realized MEMS energy harvesters and
other piezoelectric devices. The output power from their
MEMS energy harvester with AD PZT was in the vicinity of
2μW at ~ 255kHz under 2 g acceleration. This is reasonably
good performance compared to the other MEMS based
piezoelectric energy harvesters (Lee et al. 2009).
Park and co-workers at KIMS, Korea, have been con-
ducting detailed study on optimization of deposition rate
and uniformity in large area films by the granule spray in
vacuum process. They have succeeded to overcome the
limitation of AD by using intentionally granulated raw
powder and feeding system, termed as ‘granule spray in
vacuum process (GSV)’. Figure 20 shows the typical
microstructure of patterned highly dense PZT thick films
for MEMS ultrasonic transducers by GSV. The deposition
rate of the PZT thick film by GSV was 1.4 μm/min in the
area of 1440 cm3. That is over two orders of faster rate
than that of the other thin film processes. The film was
very uniform as shown in Figure 20(a). Directly patterned
highly dense 11 μm thick PZT film was fabricated on 6
inch Si/SiO2/Ti/Pt wafer by GSV, and the films were not
damaged during post processes including back-DRIE
process.
3.5 Nonlinear Resonance Based Energy
Harvesting Structures
Most of the reported vibration energy harvesters use a
linear cantilever resonator structure to amplify small
ambient vibration. While such structures are easy to
S. Priya et al.: A Review on Piezoelectric Energy Harvesting 19
Authenticated | jhryu@kims.re.kr author's copy
Download Date | 2/2/17 7:13 AM
model, design and build, they typically have a narrow
bandwidth. In contrast, nonlinear resonators have differ-
ent dynamic response and greatly increase the bandwidth
by hardening or softening the resonance characteristic of
the beam structure. In addition, it has been found that
non-linear resonating beams can extract more electrical
energy than that of linear resonating beams (Hajati and
Kim 2011; Marinkovic and Koser 2009) when external
vibration source has variable frequency.
Nonlinearity may come from magnetic force or con-
strained mechanical structures. The magnetic forces
between the magnets and the iron create a nonlinear
spring, whose nonlinearity is determined by the strength
of the magnets and the size of the air gap between the
magnets and the iron stator. Due to the mutual attrac-
tions, the ferromagnetic beam has three equilibrium posi-
tions (statically bi-stable configuration), and the
vibration mode has the form of the bi-stable Duffing
resonance. Electromagnetic energy harvesters have been
reported showing hardening or softening resonance char-
acteristics (Ando et al. 2010; Barton, Burrow, and Clare
2010; Erturk and Inman 2011; Mann and Sims 2009).
However, magnet-based beams require assembly of hard
magnets, which is expected to be costly as the size of the
device shrinks.
Nonlinear resonance could be better achieved by a
monolithically fabricated MEMS structures. Efforts have
been made to achieve wide bandwidth piezoelectric
Figure 18: Conceptual diagram of high
piezoelectric performance in PZT thick
films grown on various substrates; the
stresses were controlled by the thermal
expansion mismatch between substrates
and PZT films (Han et al. 2011a).
Figure 19: Silicon based MEMS devices
with AD-PZT by Lee et al. (a),
(b) Suspended double-layer PZT struc-
ture released by XeF2 dry etching (Wang
et al. 2008), (c) piezoelectric MEMS
energy harvester with AD-PZT thick film
(Lee et al. 2009).
20 S. Priya et al.: A Review on Piezoelectric Energy Harvesting
Authenticated | jhryu@kims.re.kr author's copy
Download Date | 2/2/17 7:13 AM
energy harvester by exerting an axial compression and
forming a buckled configuration, to make a bi-stable
oscillator (Cottone et al. 2012; Marinkovic and Koser
2009). Recently, Hajati et al. demonstrated a monolithic
MEMS-based non-linear resonant piezoelectric micro
energy harvester, which achieved an ultra-wide band-
width of >>20% of the center frequency and generated
power more than 22 μW (see Figure 21) (Hajati and Kim
2011). More than one order of magnitude improvements
were demonstrated in comparison to the devices pre-
viously reported in both the power bandwidth and the
normalized power density (NPDV) (see Table 1). The basic
design is based on a doubly clamped beam resonator
with dimensions, 6mm×6mm× 5.5 μm (L ×W×H), PZT
thickness 0.25 μm. Four of these resonators are arranged
perpendicular to each other and form one energy har-
vester, which is about the size of a US quarter coin
(Figure 21(a)). At large deflection (exceeding 2–3 times
the thickness of the beam), a net stretching in addition to
bending results, which changes the dynamic response to
a non-linear one (Figure 21(b)).
Unlike a linear resonance system, where the electri-
cal damping cannot exceed the mechanical damping
(Dutoit, Wardle, and Kim 2005), it has been shown that
electrical damping in a nonlinear resonance system could
surpass the mechanical damping, extracting much higher
output power than that of the linear systems. The non-
linear impedance serves as a negative feedback and
stabilizes the deflection when the electrical damping
changes (Hajati, Xu, and Kim 2011). This is why the
power bandwidth of nonlinear systems can be much
wider than that of linear systems at equivalent beam
dimensions.
Bi-stable nonlinear resonant beams were recently
developed not only to widen the power bandwidth but
also to lower the working frequency range and input
vibration amplitude of energy harvesters (Xu and Kim
2015). Electromechanical lumped model predicts both
stiffening and softening frequency responses for the
inter-well and intra-well oscillations of bi-stable systems.
Preliminary meso-scale experiments match well with the
dynamic simulation and show that the softening fre-
quency response generates much higher power than
mono-stable configuration at lower frequencies, provid-
ing opportunity for MEMS harvesters to be operated at
low frequency and low g input vibrations. MEMS-scale
multi-layer buckled plate test results show that at least
50 μW power could be generated below 100Hz frequency
and 0.2 g acceleration (Figure 22).
Prior studies have shown that the presence of non-
linearity based on magnetic interaction or buckled beams
has a significant influence on the performance of energy
harvesters. The bandwidth of nonlinear energy harvester
was increased by bistable effect, however, it is obvious
that the frequency response to input vibration was more
complicated as compared to linear case. The instability of
Figure 20: (a) Large area PZT deposition
by GSV process. (b) 6 inch Si/SiO2/Ti/Pt
wafer with directly patterned PZT thick
film. (c) and (d) cross-sectional SEM
micrographs of piezoelectric MEMS
ultrasonic device by GSV.
S. Priya et al.: A Review on Piezoelectric Energy Harvesting 21
Authenticated | jhryu@kims.re.kr author's copy
Download Date | 2/2/17 7:13 AM
frequency response makes it difficult to precisely modu-
late the bandwidth and tune the resonance frequency of
the energy harvester in realistic environment. We expect
that nonlinearity can provide a solution for widening the
bandwidth but it will require additional control features
to exploit the enhancement in the output power.
3.6 Self-resonance Frequency Tuning
Technique
To maximize output power, energy harvesters should be
excited in resonance with external vibration sources. In
the other words, the natural frequency of the energy
harvester should be matched to those of external vibra-
tion sources. The typical linear energy harvester has only
one dominant natural frequency which should be care-
fully selected in accordance with the external vibration
frequency. However, when the excitation frequency is
unknown or varies with time, the energy harvester with
fixed natural frequency cannot achieve an optimal output
power. Therefore, in practice, the resonance frequency
tuning scheme is essential to increase its power output.
Most reported frequency tuning mechanisms are pas-
sively adjusted or require additional energy in order to
automatically tune the frequency. Hence, the self-fre-
quency tuning mechanisms which do not require extra
energy or very small amount energy for autonomous
tuning are necessary.
Jo et al. presented the cantilever structure that can
automatically switch its natural frequency and maintain
Figure 21: Non-linear beam MEMS energy harvester with ultra-wide bandwidth (a) Photo of fabricated device on a coin. (b) Simulated
dynamic response of a nonlinear resonator. (c) Open circuit voltage versus frequency (note that nonlinear stretching happens twice in each
excitation cycle). (d) Curve 1: estimated extractable power versus frequency, Curve 2: Generated power via the piezoelectrics (Hajati and
Kim 2011).
Figure 22: Schematic view of a bi-stable beam energy harvester (Xu
and Kim 2015).
22 S. Priya et al.: A Review on Piezoelectric Energy Harvesting
Authenticated | jhryu@kims.re.kr author's copy
Download Date | 2/2/17 7:13 AM
its switched frequency without an additional energy con-
sumption (Jo, Kim, and Kim 2011). The proposed har-
vester was composed of a cantilever couple with
different lengths, similar to seesaw structure. The
coupled cantilevers are able to move laterally and have
two different optimal vibration phases at each resonance
frequencies. As shown in Figure 23, the vibration phase of
the coupled energy harvesters can shift to the other phase
when the external frequency are closed to the resonance
frequency of the other phase. The difference between the
horizontal inertia forces by deflection difference of canti-
levers is the key to switch the harvester between the two
phases. This harvester is self-frequency tunable and no
additional power is required for tuning. As shown in
Figure 24, this harvester cannot cover whole frequency
range but still is much more efficient than typical
harvesters.
The close loop active frequency tuning system have been
proposed by Zhu et al. (2008). The schematic of tuning
mechanism is described in Figure 25. The natural fre-
quency of energy harvester can be adjusted by attraction
force between two magnets. The magnetic force also can
be controlled by changing distance of two magnets using
the linear actuator. Thus, the axial load on the cantilever
can be changed. Overall tuning process was controlled by
a microcontroller which detects the output voltage of the
generator periodically and gives an instruction to drive a
linear actuator to adjust the distance between two mag-
nets. When the output power reaches maximum, the
system changes to sleep mode to save power. The micro-
controller periodically wakes up to monitor the power
output and execute natural frequency tuning process.
They claimed that the microcontroller and linear actuator
can be operated using only power generated from micro-
generator itself. However, the power consumption for
frequency tuning procedure was still very high on the
order of 2.04mJ/mm. If one can dramatically reduce the
power consumption of the microcontroller and linear
actuator, the closed loop frequency tuning system could
be one of the promising candidate for self-resonance
tuning technique except in continuously varied frequency
or complex mode vibration environment.
3.7 Low Frequency Energy Harvesting
Structures
Micro scale low frequency energy harvester has been
mainly dominated by inductive or electromagnetic
devices. However, the miniaturization of such devices is
limited by the size of the magnet used as the inertial mass
and the size of the coil that can be fabricated on the
MEMS scale. Consequently, for MEMS scale energy har-
vester, piezoelectricity is the transduction of choice and
especially due to its compatibility with cleanroom based
silicon micromachining techniques. Recent study by
Mitcheson et al. (2007) has shown that at mm-scale,
piezoelectric mechanism provides the best output power
density at low frequencies as compared to other possible
mechanisms for vibration EH. However, piezoelectric
based energy harvester presents a fundamental challenge
at the small dimensions since the resonance frequency of
the structure increases (kHz range) as the dimension
decreases. This challenge should be overcome in order
to become compatible with the practical applications.
The most commonly used approach for reducing the
natural frequency involves the addition of a large inertial
tip mass to the free end of a simple single cantilever beam
structures (Choi et al. 2006; Liu et al. 2012; Tsujiura et al.
2013; Xu et al. 2012a). Other methods involve the use of
increased effective surface area cantilevers such as spirals
(Deterre et al. 2013). Recently, Song et al. demonstrated
the spiral MEMS energy harvesters using typical silicon
Figure 23: Schematic view of resonance frequency switchable
energy harvester (Jo, Kim, and Kim 2011).
Figure 24: Output power of frequency switching scheme: (1) when
the excited frequency increases from 10Hz, the first output peak
shows at 24Hz and the second peak shows at 35Hz, (2) when the
excited frequency decreases from 40Hz, the first output peak shows
at 33Hz and the second peak shows at 24Hz (Jo, Kim, and Kim
2011).
S. Priya et al.: A Review on Piezoelectric Energy Harvesting 23
Authenticated | jhryu@kims.re.kr author's copy
Download Date | 2/2/17 7:13 AM
MEMS process as shown in Figure 26. In order to under-
stand the natural frequency characteristics of the spiral
cantilever structure, different turns of spiral MEMS har-
vesters were fabricated as illustrated in Figure 26(b). The
natural frequency of the spiral MEMS harvester was inver-
sely proportional to number of turns and can be reduced
to less than 50Hz within 1.85mm diameter circle active
dimension. The generated output voltage was gradually
increased until 5 turns and then started to slightly
decrease with increasing number of turns. This might be
because the active dimension of spiral region was gradu-
ally increased and thus voltage cancelation mode due to
torsion are more likely to dominate with higher number of
turns. Five turn spiral energy harvester showed the max-
imum generated voltage. More precise MEMS fabrication
process and structural modification to reduce the complex
vibration modes are required in producing higher turn
spiral energy harvesters.
The use of tip masses severely affects the structural
integrity and durability of the harvesters while the
increased effective surface area designs exhibit torsion
(causing voltage cancellation effect) in the very important
first vibration mode. Therefore, it is of great importance
to create a more effective method by developing uniquely
Figure 25: Schematic diagram of the closed loop tuning system (Zhu et al. 2008).
Figure 26: (a) Spiral MEMS energy harvester with low natural frequency (a) photo of fabricated device on a coin, (b) spiral MEMS energy
harvesters with variation of number of turns, (c) open circuit output voltage versus frequency with number of turns of spiral MEMS energy
harvesters, and (d) natural frequency variation with number of turns.
24 S. Priya et al.: A Review on Piezoelectric Energy Harvesting
Authenticated | jhryu@kims.re.kr author's copy
Download Date | 2/2/17 7:13 AM
shaped cantilevers, such as arc-based cantilevers, which
exhibit low natural frequencies. To harvest energy at the
low frequency of ambient vibrations, extensive research
has led us to the development of circular Zigzag structure
that permits inertial mass free attainment of such low
frequencies. Recently, Varghese et al. reported a set of
new tip mass free vibration energy structures that are
capable of attaining resonant frequency of less than
100Hz with less torsion than spiral designs and with a
smaller foot print than zigzag or meandering structures,
as shown in Figure 27 (Apo 2014; Varghese 2013). This
design, termed as arc-based cantilever (ABC), has
achieved <100Hz resonant operation both on the Si
MEMS platform and with bulk piezo material as com-
pared to traditional cantilevers. The arc-based cantilever
is a continuous cantilever that can be divided into purely
circular arc segments, thereby making it a low frequency
structure with dominant bending characteristic in the
first (or fundamental) frequency mode (Apo,
Sanghadasa, and Priya 2013). Different configurations of
micro ABCs were investigated through analytical model-
ing and validation experiments. As shown in Figure 27(a),
two arc-based micro-cantilevers (S-shaped, C-shaped)
were designed based on the well-known linear configura-
tions (simple and zigzag.) In addition to the metal micro-
milling, [Figure 27(b)] such structures were also fabri-
cated and demonstrated using a silicon micromachining
process [Figure 27(c)]. All the arc-based cantilevers were
shown to resonate below 100Hz and they exhibited
dominant bending behavior in the fundamental mode
(Apo, Sanghadasa, and Priya 2013, 2014). These designs
therefore provide a foundation for the development of
standalone arc-based micro-cantilevers which can be
used for energy harvesting, actuation and sensing appli-
cations. The model for ABC structures is based on the
classical Timoshenko beam theory and includes the
effects of bending, torsion, transverse shear deformation
and rotary inertia. It was developed with a provision for
multilayered beam modeling (Apo 2014). The micro-can-
tilever can be modified and optimized to fit desired con-
figurations based on the numbers of arcs, longest side
length, spacing and width.
Recently, Sharpes et al. also demonstrated a strat-
egy of using highly compliant two-dimensional beam
shapes to harvest energy from low frequency excitations
(Sharpes, Abdelkefi, and Priya 2015). They fabricated 3
different 2D shapes of Zigzag, Flex and Elephant config-
urations as shown in insets of Figure 28(a), (b) and (c).
All of samples occupy a 25.4 × 25.4mm2 (1 inch2) area
and fabricated using mild steel and APC850 piezoelec-
tric ceramics. In order to maintain the low natural fre-
quency, the piezoelectric layers were placed at the most
stress concentrated single area of each shapes rather
than whole area through a finite element simulation.
Neodymium magnet tip masses of 1.88 g weight were
attached to the end of each beams to decrease reso-
nance frequency and increase out power. As shown in
Figure 28(a), the Zigzag harvester is capable of produ-
cing 2.93 μW across 0.75MΩ at 65.6 Hz. The Flex har-
vester produced 32.2 μW across 1MΩ at 62.0 Hz base
Figure 27: Arc-based microcantilvers:
(a) Design development of the cantile-
vers, (b) Micromilled S-shaped cantile-
vers (Apo 2014), (c) As fabricated silicon
MEMS cantilever structures (Varghese
2013).
S. Priya et al.: A Review on Piezoelectric Energy Harvesting 25
Authenticated | jhryu@kims.re.kr author's copy
Download Date | 2/2/17 7:13 AM
excitation frequency in Figure 28(b). In both designs,
the electromechanical coupling is quite small, as no
frequency shift was observable between the short-circuit
(RL = 10
3Ω) and open-circuit (RL = 107Ω) frequencies.
However, for the Elephant harvester, we note a substan-
tial shift between short-circuit and open-circuit frequen-
cies, as well as, a large power output of 81.3 μW across
1M Ω at 68.125 Hz, as shown in Figure 28(c). From these
findings, we can conclude the merits of Elephant
design, and how it is beneficial towards efficient low-
frequency piezoelectric energy harvesting compared to
the other shapes.
Two main issues in realizing MEMS energy harvesters
are the broadband and low operational resonance fre-
quency. Previously discussed low resonance frequency
structures with nonlinear behavior excited through the
magnetic coupling or the buckled structure could provide
breakthrough. In addition to design of nonlinear broad-
band vibration structure for low resonance frequency, the
MEMS fabrication process for incorporating complex
structures should be developed.
3.8 Development of New Fabrication and
Characterization Methodologies
Unlike inductive harvesting, piezoelectric and magneto-
electric devices lend easily to MEMS scaling. The proces-
sing of such Piezo-MEMS devices often requires special
fabrication, characterization and testing techniques.
Generally, MEMS devices are fabricated on silicon wafer
starting with growth of high quality piezoelectric films.
Ron et al. developed a novel fabrication methodology
to realize these structures with reduced number of
Figure 28: Experimental results for average power production as a function of frequency and electrical load resistance for (a) Zigzag, (b) Flex,
and (c) Elephant configurations, with (d) Average power as a function of electrical load resistance at each harvester’s respective resonance
frequency. All input vibrations were at 0.1 g base acceleration (Sharpes, Abdelkefi, and Priya 2015).
26 S. Priya et al.: A Review on Piezoelectric Energy Harvesting
Authenticated | jhryu@kims.re.kr author's copy
Download Date | 2/2/17 7:13 AM
processing steps (Varghese 2013). They also described the
extensive work on MEMS wafer test bench setup.
The MEMS fabrication process flow consisted of two
modules as shown in Figure 29: (a) the electrical module
for PZT capacitor formation and (b) the mechanical mod-
ule wherein the Si based micro-cantilever structures were
created (Varghese 2013). When the modules are com-
bined, this simplified process flow reduces the number
of fabrication steps by ~40%. Using this modular
approach, a self-aligned and self-isolated MEMS fabrica-
tion process with only two photolithography steps was
demonstrated, as shown in Figure 29(c). The key feature
of this process is the use of a patterned SiO2 hard mask to
define the beam thickness in the DRIE and then after
removal of that SiO2 hard mask, using a 2
nd patterned
photoresist mask to proceed with a 2nd DRIE to release
the cantilever. Unlike the process used for the unreleased
MEMS structure of a Piezo accelerometer (Durou et al.
2010), this process is developed to a) in-situ remove the
SiO2 hard mask before the 2
nd DRIE and b) then conduct
the 2nd DRIE on the front side for release. The removal of
the SiO2 hard mask after the 1
st DRIE can be skipped in
some cases and the DRIE SiO2:Si etch rate selectivity can
be utilized to define the cantilever beam thickness. That
is, after SiO2 hard mask definition, 1
st DRIE and 2nd DRIE
mask pattern is applied, but SiO2 need not be removed.
This inorganic hard mask will etch slower than Si and
thus when the Si DRIE reaches the front of the wafer, the
sections that were covered by SiO2 would have lagged
behind during etch and would be thicker. Using this
modular approach, different cantilever structural designs
were investigated and based on this learning, a low
frequency structure that resembles an arc-based cantile-
ver was developed [Figure 29(c)].
For electrical testing, MEMS harvesters are generally
tested individually after the wafer has been singulated by
dicing. This requires that the MEMS device be packaged or
temporarily glued to a special carrier wafer without
damage. Prior to packaging and simulation, Ron et al.
introduced a novel concept of wafer level testing
(Varghese 2013). As shown in Figure 30(a), wafer probe
card is fabricated from a custom printed circuit board
(PCB) with gold plated pogo pin probes, where all the
pogo pin locations and wiring were designed according
to the MEMS device layout on the wafer. All wiring is thus
confined to the outside of the test setup and does not
Figure 29: Fabrication process details of
the modules in a Piezo-MEMS process
flow (a) Electrical module,
(b) Mechanical module, and
(c) Schematic of the MEMS fabrication
process with two lithography steps
(Varghese 2013).
S. Priya et al.: A Review on Piezoelectric Energy Harvesting 27
Authenticated | jhryu@kims.re.kr author's copy
Download Date | 2/2/17 7:13 AM
interfere with the laser vibrometry measurement [Figure
30(b)]. For mechanical testing of MEMS wafers, a Polytec
MSA 500 was used with a special clamp that holds the
wafer along its edges, as shown in Figure 30(c). As the
shaker is moving, the whole wafer and all its MEMS
devices move simultaneously, thus, one can scan each
cantilever from tip to base and take the transfer function
between the tip and base to compute the resonance fre-
quency. Typical 3D animation plot of the actual vibration
characteristics is illustrated in Figure 30(d). This approach
is especially useful if one has numerous devices on a wafer.
4 Circuit for Impedance Matching
Maximum power transfer occurs when the load impe-
dance is the complex conjugate of the source impedance.
Since a piezoelectric generator exhibits a large capacitive
term as shown in Figure 31, a complex conjugate match-
ing requires a large inductance for the load to cancel the
capacitive term. For example, the required inductance is
137H at 44Hz for the piezoelectric generator in Figure 31
and 470H at 50Hz. Further, the inductance value
depends on the vibration frequency. Therefore, it is
impractical to use a passive inductor for the matching.
Saggini et al. investigated a complex conjugate matching
scheme, which emulates an inductor (Saggini et al. 2010).
They used a bidirectional DC/DC converter, in which the
input voltage is higher than the output voltage. So the
current flows from the piezoelectric generator to the bat-
tery under the buck mode and in the opposite direction
under the boost mode. Their approach results in a com-
plex circuit to dissipate large power. An alternative solu-
tion to the complex conjugate matching is to adopt
resistive matching. Suppose that the source impedance
of a piezoelectric generator Zs=RS + jXS is connected in
Figure 30: (a) As manufactured PCB board with pogo pins soldered on and (b) Clamped over a device wafer, (c) Vibration measurement setup
with 3D laser vibrometer, (d) Animation plots of the velocity FRF at fundamental resonance of a arc-based micro cantilever (Varghese. 2013).
28 S. Priya et al.: A Review on Piezoelectric Energy Harvesting
Authenticated | jhryu@kims.re.kr author's copy
Download Date | 2/2/17 7:13 AM
series with the load resistance RL. The optimal value of RL
for the maximum power transfer is expressed as:
RL =
ffiffiffiffiffiffiffiffiffiffiffiffiffiffi
R2S +X
2
S
q
(Kong et al. 2010). Note that the optimal
RL is a function of RS and XS, i. e., dependent on the
excitation frequency of the piezoelectric generator.
Hence, it requires a harvester circuit to change the load
resistance value dynamically according to the excitation
frequency, and the operation is called maximum power
point tracking (MPPT). The cost for a resistive matching
compared with a complex conjugate matching is that the
maximum power is delivered to the load only at the
resonant frequency. The power level drops sharply at
frequencies away from the resonant frequency (Kong
and Ha 2012).
4.1 Maximum Power Point Tracking for PZT
Resistive Matching
The source impedance of a transducer such as piezoelec-
tric generator and photovoltaic cell changes as the oper-
ating condition changes, which requires MPPT.
Deployment of an MPPT scheme is advantageous only
when the additional power harvested owing to the
MPPT is greater than the power dissipated by the MPPT
circuit itself. As the additional power, which can be
harvested through the MPPT, is limited by the transducer
and its operating condition, there exists a breakeven
point for adoption of an MPPT scheme. Another design
issue with MPPT is accuracy and speed of the tracking,
which are often traded. Also, a more accurate and hence
more sophisticated MPPT scheme dissipates more power
for the MPPT circuit. So adoption of an accurate scheme
does not necessarily increase the net energy harvested.
Two commonly adopted MPPT algorithms for energy
harvesting are hill climbing and fractional open circuit
voltage (FOCV). The hill climbing algorithm, also called
“perturb and observe”, for the dynamic resistive match-
ing is illustrated in Figure 32. It increments the load
resistance by a predetermined step and then measures
the power, often the average current, delivered to the
load. If the power increases, the search direction is cor-
rect, and it increments the resistance again in the next
cycle. If the power decreases, it reverses the direction.
The algorithm guarantees convergence to the optimal
point if there is no local maxima, and it is the case for
piezoelectric generators. The hill climbing algorithm can
be implemented with a microcontroller unit (MCU) or a
mixed-signal circuit (Kong, Deyerle, Ha, 2011; Sankman
and Ma 2014). Considering the voltage of a storage device
roughly remains the same for each cycle, the power can
be measured through measurement of the average cur-
rent into the storage device. The FOCV algorithm relies on
the fact that the voltage across the load is one half of the
open circuit voltage of the source (Lu, Tsui, and Ki 2011,
Shim et al. 2015). The FOCV algorithm is simpler to imple-
ment compared with the hill climbing algorithm.
However, the FOCV algorithm necessitates the load be
open once in a while to measure the open circuit voltage,
and the energy harvesting is interrupted during the time.
As noted earlier, the optimal load resistance for a resis-
tive matching for a piezoelectric generator is RL =ffiffiffiffiffiffiffiffiffiffiffiffiffiffi
R2s +X2s
p
The load resistance seen by the piezoelectric
generator is the input resistance of the converter con-
nected to the generator. The effective input resistance of
a buck-boost converter in the discontinuous conduction
mode (DCM) is obtained as Rin = 2LD2Ts, where L is the
inductance, D is the duty cycle, and TS is the switching
Figure 31: Magnitude and phase of a PZT cantilever.
Figure 32: Schematic description of the Hill climbing algorithm.
S. Priya et al.: A Review on Piezoelectric Energy Harvesting 29
Authenticated | jhryu@kims.re.kr author's copy
Download Date | 2/2/17 7:13 AM
period. So the duty cycle D can be controlled to change
the effective input resistance of the converter. It should
be noted that the duty cycle D is changed to control the
input resistance, and the output voltage of the converter
is also changed accordingly. To regulate the output vol-
tage, it needs another converter stage or some other
means such as use of a Zener diode.
Once MPPT achieves the optimal or near optimal
resistor value, the MPPT operation can be halted to save
power until the operation condition changes. A design
issue is to set the optimal wake up and sleep periods or
duty cycle, which depends on several factors such as the
speed and amount of the operating condition change and
the speed of MPPT.
4.2 Synchronized Switch Harvesting on
Inductor (SSHI) and Synchronous
Electric Charge Extraction (SECE)
Synchronized Switch Harvesting on Inductor (SSHI) aims
to eliminate the effect of the capacitive term of piezo-
electric generators (Guyomar et al. 2005; Ramadass and
Chandrakasan 2010, Wu et al. to appear). Figure 33 shows
an SSHI circuit composed of an inductor L and a switch S.
Note that the PZT model in the figure is a simplified
Norton equivalent circuit. The PZT capacitor Cp is nega-
tively charged at the crossing point of the PZT current Ip
from negative to positive. The SSHI scheme minimizes the
wasted energy to charge the capacitor positively using an
LC resonant circuit. The switch SW is closed momentarily
right after the zero crossing of the PZT current ip. The
capacitor Cp and the inductor L form a resonant circuit
with a resonant frequency much higher than the PZT
vibration frequency. The capacitor voltage VP rises
quickly due to the oscillation of the resonant circuit,
and then the switch is opened at the opposite peak
value of VP, reducing dispense of the PZT energy to
discharge the capacitor. When PZT current Ip changes
from positive to negative, the same operation is per-
formed to save the energy for charging the capacitor
negatively. An SSHI circuit increases the energy har-
vested when compared with a rectifier only circuit at
the cost of higher circuit complexity.
The SSHI scheme requires impedance matching for
maximum power transfer. Synchronous Electric Charge
Extraction (SECE), which is an extension of the SSHI
method, eliminates such a need. The SECE scheme uses
an LC resonant circuit to transfer the energy stored in the
PZT capacitor to the inductor first and then the inductor
energy is transferred to the load through a DC-DC con-
verter (Lefeuvre et al. 2005, Gasnier et al. 2014, and Dini
et al. 2016). The extracted power of the SECE method does
not depend on the load, and so the load can vary without
affecting the efficiency.
4.3 Rectifiers and Voltage Doublers
Piezoelectric generators require rectification in order to
convert output AC voltage in to DC. A full bride rectifier
with passive diodes can be easily incorporated but the
forward diode voltage drop can cause substantial power
loss. Active or synchronous rectifiers reduce losses asso-
ciated with passive diodes. An active rectifier turns on or
off a MOSFET in appropriate time periods to effectively
rectify the voltage (Hashemi, Sawan, and Savaria 2012;
Lam, Ki, and Tsui 2006; Le et al. 2006). Figure 34 shows
a comparator based active rectification, which senses
the polarity of the input voltage to turn on or off the
MOSFET. If the current through the MOSFET is small,
e. g. near crossing zero points, the difference in the
drain and source voltage is small to cause an operation
error. Various circuit configurations for rectifications
have been suggested (Rincón-Mora and Yang, 2016;
Hwang et al. 2015), and a major design issue is to
lower power dissipation of the gate control circuit,
such as the comparator shown in Figure 34. Another
issue with piezoelectric generator is that the rectified
voltage is very small, which leads to low efficiency of
the boost converter. A voltage doubler can be used
to mitigate this issue (Tabesh and Fréchette 2010).
CRECT
VRECT
SW
L
SSHI
RPCP
IP
Piezo Harvester
VP
+
–
Figure 33: Synchronized Switch Harvesting on Inductor (SSHI). Figure 34: Circuit diagram for active rectification.
30 S. Priya et al.: A Review on Piezoelectric Energy Harvesting
Authenticated | jhryu@kims.re.kr author's copy
Download Date | 2/2/17 7:13 AM
A voltage doubler increases the output voltage by 2X
while rectification. It is possible to combine the voltage
doubling technique and active diodes.
Recently, reconfigurable power management circuit
using a 0.25 μm complementary metal-oxide semicon-
ductor (CMOS) process has been developed by KAIST
and SNU team (Hwang et al. 2015) as shown in Figure
35. The multiple storage capacitors of the reconfigurable
charger array can adjust the magnitude of capacitance
by controlling serial and parallel alignments of capaci-
tors. At the charging stage, impedance is matched
between the reconfigurable capacitor array and the
energy harvester to extract maximum energy while mini-
mizing energy loss, whereas at the discharging stage, the
capacitors are rearranged to supply the demanded con-
stant low-voltage into the external load. The reconfigur-
able rectifying circuit can transfer four times higher
electric energy to the load resistor compared to the tradi-
tional rectifying circuit.
5 Summary
MEMS piezoelectric energy harvesters at the ~mm3 dimen-
sions will lead to battery-less autonomous sensors systems
and networks if 10’s to 100’s μW of power can be extracted
from the ambient vibration continuously, robustly and at
low cost. The key attributes to make a good piezoelectric
MEMS energy harvester can be summarized as its compact-
ness, output voltage, output power (density), bandwidth,
operating frequency, input vibration amplitude, lifetime
and cost. Among them, higher power density and wider
bandwidth of resonance are the two biggest challenges
currently facing the technology. Figure 36(a) and (b) and
Table 1 show the normalized power densities of some
recently developed MEMS energy harvesters, where orders
of magnitude improvement can be seen in the last 5 years.
Giant piezoelectric coefficient materials, epitaxially grown
films, grain textured piezoelectric materials and thin/thick
films, high performance lead-free piezoelectric materials are
the recent advancements made towards increasing the elec-
tromechanical energy conversion of piezoelectric harvesters.
Nonlinear resonators are extremely promising to extract
more electrical energy from the beam. Recent advances in
piezoelectric materials and harvester structural design, indi-
vidually or in combination, are bringing us closer to battery-
less autonomous sensors systems and networks. We expect
that in the near future, a coin size harvester will be able to
harvest about 100μWcontinuous power below 100Hz at less
than 0.5 g vibration and at reasonable cost. High efficiency
and low power dissipation of energy harvester circuits will
Figure 35: (a) A top-view optical microscopy image and (b) schematic
circuit diagram of the reconfigurable rectifying circuit system inte-
grated with energy harvester, bridge rectifier, reconfigurable capa-
citor charger array, and external load. (Hwang et al., 2015)
0.000
0.005
0.010
0.015
0.020
0.025
d31 mode
(vacuum)
d31 mode 
(air)
 PZT
N
o
rm
al
iz
ed
 A
re
al
 P
o
w
er
 D
en
si
ty
(µ
W
/(
m
m
2 .
H
z.
g
))
Year
d31 mode
KNN
 AlN
2004 2006 2008 2010 2012 2014 2006 2008 2010 2012 2014
1E–4
1E–3
0.01
0.1
1
KNN
PZT
N
o
rm
alized
 V
o
lu
m
etric P
o
w
er
D
en
sity (µ
W
/(m
m
3.H
z.g
))
AlN
N
o
rm
al
iz
ed
 V
o
lu
m
et
ri
c 
P
o
w
er
D
en
si
ty
 (
µ
W
/(
m
m
3 .
H
z.
g
))
Year
PZT
1E–5
1E–4
1E–3
0.01
0.1
1
AlN
Figure 36: Normalized (a) areal (µW/(mm2.Hz.g)) and (b) volumetric power density (µW/(mm3.Hz.g)), of piezoelectric MEMS energy
harvesters recently reported in Table 1.
S. Priya et al.: A Review on Piezoelectric Energy Harvesting 31
Authenticated | jhryu@kims.re.kr author's copy
Download Date | 2/2/17 7:13 AM
remain important and be critical to maximize the net energy
harvested for future micro-scale energy harvesters.
Funding: H.-C.S. and A.C. acknowledges the support from
Office of Basic Energy Sciences, Department of Energy
(DE-FG02-06ER46290), Y.Z. and R.V. acknowledge sup-
port from AFOSR (FA9550-14-1-0376), S.-G.K. acknowl-
edges the support from DARPA Grant (HR0011-06-1-
0045), MIT-Iberian Nanotechnology Laboratory Program.
Works at KIMS were supported by KIMS internal R&D
programs (PNK4661 and PNK4991). Dong Ha’s work was
supported in part by the Center for Integrated Smart
Sensors funded by the Korea Ministry of Science, ICT &
Future Planning as Global Frontier Project (CISS-2-3). S.P.
acknowledges the financial support from Norfolk State
University through NSF CREST program.
References
Ahn, C.-W., C.-H. Choi, H.-Y. Park, S. Nahm, and S. Priya. 2008a.
“Dielectric and Piezoelectric Properties of (1–x)(Na0. 5K0. 5)
NbO3–xBaTiO3 Ceramics.” Journal of Materials Science
43:6784–97.
Ahn, C.-W., D. Maurya, C.-S. Park, S. Nahm, and S. Priya. 2009. “A
Generalized Rule for Large Piezoelectric Response in Perovskite
Oxide Ceramics and Its Application for Design of Lead-Free
Compositions.” Journal of Applied Physics 105:114108.
Ahn, C.-W., C.-S. Park, D. Viehland, S. Nahm, D.-H. Kang, K.-S. Bae,
and S. Priya. 2008b. “Correlation Between Phase Transitions
and Piezoelectric Properties in Lead-Free (K, Na, Li)
NbO3–BaTiO3 Ceramics.” Japanese Journal of Applied Physics
47:8880.
Aita, C. 1982. “Basal Orientation Aluminum Nitride Grown at Low
Temperature by RF Diode Sputtering.” Journal of Applied
Physics 53:1807–8.
Akedo, J., and M. Lebedev. 2000. “Piezoelectric Properties and
Poling Effect of Pb (Zr, Ti) O3 Thick Films Prepared for
Microactuators by Aerosol Deposition.” Applied Physics Letters
77:1710.
Aktakka, E. E. 2012. “Integration of Bulk Piezoelectric Materials into
Microsystems.” Ph. D Dissertation in the University of
Michigan.
Al-Ashtari, W., M. Hunstig, T. Hemsel, and W. Sextro. 2012.
“Frequency Tuning of Piezoelectric Energy Harvesters by
Magnetic Force.” Smart Materials and Structures 21:035019.
Ando, B., S. Baglio, C. Trigona, N. Dumas, L. Latorre, and P. Nouet.
2010. “Nonlinear Mechanism in MEMS Devices for Energy
Harvesting Applications.” Journal of Micromechanics and
Microengineering 20:125020.
Andosca, R. A., T. G. McDonald, V. Genova, S. Rosenberg, J. Keating, C.
Benedixen, and J. Wu. 2012. “Experimental and Theoretical
Studies on MEMS Piezoelectric Vibrational Energy Harvesters with
Mass Loading.” Sensors and Actuators A: Physical 178:76–87.
Apo, D. J. 2014. “Low Frequency Microscale Energy Harvesting.”
Ph. D. Disseration in Virginia Tech.
Apo, D. J., M. Sanghadasa, and S. Priya. 2013. “Low Frequency ARC-
based MEMS Structures for Vibration Energy Harvesting.” Paper
presented at the 8th IEEE International Conference on Nano/
Micro Engineered and Molecular Systems, 615–8.
Apo, D. J., M. Sanghadasa, and S. Priya. 2014. “Vibration Modeling
of Arc-Based Cantilevers for Energy Harvesting Applications.”
Energy Harvesting and Systems 1:57–68.
Baek, S., J. Park, D. Kim, V. Aksyuk, R. Das, S. Bu, D. Felker,
J. Lettieri, V. Vaithyanathan, and S. Bharadwaja. 2011. “Giant
Piezoelectricity on Si for Hyperactive MEMS.” Science 334:
958–61.
Barton, D. A., S. G. Burrow, and L. R. Clare. 2010. “Energy Harvesting
From Vibrations with a Nonlinear Oscillator.” Journal of
Vibration and Acoustics 132:021009.
Bayraktar, M., A. Chopra, F. Bijkerk, and G. Rijnders. 2014.
“Nanosheet Controlled Epitaxial Growth of PbZr0.52ti0.48O3
Thin Films on Glass Substrates.” Applied Physics Letters
105:132904.
Bedekar, V., J. Oliver, and S. Priya. 2010. “Design and Fabrication of
Bimorph Transducer for Optimal Vibration Energy Harvesting.”
IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency
Control 57:1513–23.
Beeby, S. P., M. J. Tudor, and N. White. 2006. “Energy Harvesting
Vibration Sources for Microsystems Applications.”
Measurement Science and Technology 17:R175.
Bernstein, J., J. Bottari, K. Houston, G. Kirkos, R. Miller, B. Xu, Y. Ye,
and L. Cross. 1999. “Advanced MEMS Ferroelectric Ultrasound
2D Arrays.” Paper Presented at the IEEE Ultrasonics
Symposium, 1145–53.
Bertacchini, A., S. Scorcioni, D. Dondi, L. Larcher, P. Pavan,
M. Todaro, A. Campa, G. Caretto, S. Petroni, and A. Passaseo.
2011. “AlN-based MEMS Devices for Vibrational Energy
Harvesting Applications.” Paper Presented at the European
Solid-State Device Research Conference, 119–22.
Bono, D. C., A. Sliski, J. Huang, and R. C. O’handley. 2009. “High
Efficiency, Inductive Vibration Energy Harvester.” US Patent
7,569,952.
Brennecka, G. L., W. Huebner, B. A. Tuttle, and P. G. Clem. 2004.
“Use of Stress to Produce Highly Oriented Tetragonal Lead
Zirconate Titanate (PZT 40/60) Thin Films and Resulting
Electrical Properties.” Journal of the American Ceramic Society
87:1459–65.
Chandrakasan, A., R. Amirtharajah, J. Goodman, and W. Rabiner.
1998. “Trends in Low Power Digital Signal Processing.” Paper
Presented at the IEEE International Symposium on Circuits and
Systems, 604–7.
Chen, S. Y., and I. W. Chen. 1994. “Temperature–Time Texture
Transition of Pb (Zr1–xTix)O3 Thin Films: I, Role of Pb‐Rich
Intermediate Phases.” Journal of the American Ceramic Society
77:2332–6.
Choi, W., Y. Jeon, J.-H. Jeong, R. Sood, and S.-G. Kim. 2006.
“Energy Harvesting MEMS Device Based on Thin Film
Piezoelectric Cantilevers.” Journal of Electroceramics 17:
543–8.
Chopra, A., M. Alexe, and D. Hesse. 2015a. “Fabrication and
Orientation Control of Highly Cation-Ordered Epitaxial
32 S. Priya et al.: A Review on Piezoelectric Energy Harvesting
Authenticated | jhryu@kims.re.kr author's copy
Download Date | 2/2/17 7:13 AM
PbSc0.5ta0.5O3 Thin Films on Si (100.” Journal of Applied
Physics 117:044102.
Chopra, A., M. Bayraktar, F. Bijkerk, and G. Rijnders. 2015b.
“Controlled Growth of PbZr0.52ti 0.48O3 Using Nanosheet Coated
Si (001.” Thin Solid Films 589:13–16.
Chopra, A., D. Pantel, Y. Kim, M. Alexe, and D. Hesse. 2013.
“Microstructure and Ferroelectric Properties of Epitaxial Cation
Ordered PbSc0. 5ta0. 5O3 Thin Films Grown on Electroded and
Buffered Si (100.” Journal of Applied Physics 114:084107.
Chubachi, Y., K. Sato, and K. Kojima. 1984. “Reflection High Energy
Electron Diffraction and X-Ray Studies of AlN Films Grown on Si
(111) and Si (001) by Organometallic Chemical Vapour
Deposition.” Thin Solid Films 122:259–70.
Cottone, F., L. Gammaitoni, H. Vocca, M. Ferrari, and V. Ferrari. 2012.
“Piezoelectric Buckled Beams for Random Vibration Energy
Harvesting.” Smart Materials and Structures 21:035021.
Defosseux, M., M. Allain, E. Defay, and S. Basrour. 2012. “Highly
Efficient Piezoelectric Micro Harvester for Low Level of
Acceleration Fabricated with a CMOS Compatible Process.”
Sensors and Actuators A: Physical 188:489–94.
Deterre, M., E. Lefeuvre, Y. Zhu, M. Woytasik, A. Bosseboeuf,
B. Boutaud, and R. Dal Molin. 2013. “Micromachined
Piezoelectric Spirals and Ultra-Compliant Packaging for Blood
Pressure Energy Harvesters Powering Medical Implants.” Paper
Presented at the IEEE 26th International Conference on Micro
Electro Mechanical Systems (MEMS), 249–52.
Dini, M., A. Romani, M. Filippi, and M. Tartagni. 2016. “A Nanopower
Synchronous Charge Extractor IC for Low-Voltage Piezoelectric
Energy Harvesting with Residual Charge Inversion.” IEEE
Transactions on Power Electronics 31:1263–74.
Du, X.-h, J. Zheng, U. Belegundu, and K. Uchino. 1998. “Crystal
Orientation Dependence of Piezoelectric Properties of Lead
Zirconate Titanate Near the Morphotropic Phase Boundary.”
Applied Physics Letters 72:2421–3.
Dubois, M.-A., and P. Muralt. 2001. “Stress and Piezoelectric
Properties of Aluminum Nitride Thin Films Deposited Onto
Metal Electrodes by Pulsed Direct Current Reactive Sputtering.”
Journal of Applied Physics 89:6389–95.
Duffy, M., C. Wang, G. O’clock, S. McFarlane, and P. Zanzucchi. 1973.
“Epitaxial Growth and Piezoelectric Properties of A1N, GaN, and
GaAS on Sapphire or Spinel.” Journal of Electronic Materials
2:359–72.
Durou, H., G. A. Ardila-Rodriguez, A. Ramond, X. Dollat, C. Rossi, and
D. Esteve. 2010. “Micromachined Bulk Pzt Piezoelectric
Vibration Harvester to Improve Effectiveness Over Low
Amplitude and Low Frequency Vibrations.” Proceedings of
Power MEMS 27–30.
Dutoit, N. E., B. L. Wardle, and S.-G. Kim. 2005. “Design
Considerations for MEMS-Scale Piezoelectric Mechanical
Vibration Energy Harvesters.” Integrated Ferroelectrics
71:121–60.
Elfrink, R., T. Kamel, M. Goedbloed, S. Matova, D. Hohlfeld, Y. Van
Andel, and R. Van Schaijk. 2009a. “Vibration Energy Harvesting
with Aluminum Nitride-Based Piezoelectric Devices.” Journal of
Micromechanics and Microengineering 19:094005.
Elfrink, R., V. Pop, D. Hohlfeld, T. Kamel, S. Matova, C. De Nooijer,
M. Jambunathan, M. Goedbloed, L. Caballero, and M. Renaud.
2009b. “First Autonomous Wireless Sensor Node Powered by a
Vacuum-Packaged Piezoelectric MEMS Energy Harvester.”
Paper presented at the IEEE International Electron Devices
Meeting (IEDM), 1–4.
Elfrink, R., M. Renaud, T. Kamel, C. De Nooijer, M. Jambunathan,
M. Goedbloed, D. Hohlfeld, S. Matova, V. Pop, and L. Caballero.
2010. “Vacuum-Packaged Piezoelectric Vibration Energy
Harvesters: Damping Contributions and Autonomy for a
Wireless Sensor System.” Journal of Micromechanics and
Microengineering 20:104001.
Erturk, A., and D. J. Inman. 2008. “On Mechanical Modeling of
Cantilevered Piezoelectric Vibration Energy Harvesters.” Journal
of Intelligent Material Systems and Structures 19:1311–25.
Erturk, A., and D. Inman. 2011. “Broadband Piezoelectric Power
Generation on High-Energy Orbits of the Bistable Duffing
Oscillator with Electromechanical Coupling.” Journal of Sound
and Vibration 330:2339–53.
Fang, H.-B., J.-Q. Liu, Z.-Y. Xu, L. Dong, L. Wang, D. Chen, B.-C. Cai,
and Y. Liu. 2006. “Fabrication and Performance of MEMS-Based
Piezoelectric Power Generator for Vibration Energy Harvesting.”
Microelectronics Journal 37:1280–4.
Findeisen, D. 2013. System Dynamics and Mechanical Vibrations: An
Introduction. Berlin: Springer Science & Business Media.
Funakubo, H., M. Dekkers, A. Sambri, S. Gariglio, I. Shklyarevskiy,
and G. Rijnders. 2012. “Epitaxial PZT Films for MEMS Printing
Applications.” MRS Bulletin 37:1030–8.
Gardeniers, J., A. Smith, and C. Cobianu. 1995. “Characterisation of
Sol-Gel PZT Films on Pt-Coated Substrates.” Journal of
Micromechanics and Microengineering 5:153.
Gasnier, P., J. Willemin, S. Boisseau, G. Despesse, C. Condemine,
G. Gouvernet, et al. 2014. “An Autonomous Piezoelectric Energy
Harvesting IC Based on a Synchronous Multi-Shot Technique.”
IEEE Journal of Solid-State Circuits 49:1561–70.
Ginsberg, J. H., and J. H. Ginsberg. 2001. Mechanical and Structural
Vibrations: Theory and Applications. New York: Wiley.
Guyomar, D., A. Badel, E. Lefeuvre, and C. Richard. 2005. “Toward
Energy Harvesting Using Active Materials and Conversion
Improvement by Nonlinear Processing.” IEEE Transactions on
Ultrasonics, Ferroelectrics, and Frequency Control 52:584–95.
Hajati, A. 2011. “Ultra Wide-Bandwidth Micro Energy Harvester.”
Ph. D. Dissertation in Massachusetts Institute of Technology.
Hajati, A., and S.-G. Kim. 2011. “Ultra-Wide Bandwidth Piezoelectric
Energy Harvesting.” Applied Physics Letters 99:083105.
Hajati, A., R. Xu, and S.-G. Kim. 2011. “Wide Bandwidth Piezoelectric
Micro Energy Harvester Based on Nonlinear Resonance.” Paper
presented at the PowerMEMS.
Han, G., J. Ryu, W.-H. Yoon, J.-J. Choi, B.-D. Hahn, J.-W. Kim,
D.-S. Park, C.-W. Ahn, S. Priya, and D.-Y. Jeong. 2011a. “Stress-
Controlled Pb(Zr0. 52ti0. 48)O3 Thick Films by Thermal Expansion
Mismatch Between Substrate and Pb(Zr0. 52ti0. 48)O3 Film.”
Journal of Applied Physics 110:124101.
Han, G., J. Ryu, W. H. Yoon, J. J. Choi, B. D. Hahn, and D. S. Park. 2011b.
“Effect of Film Thickness on the Piezoelectric Properties of Lead
Zirconate Titanate Thick Films Fabricated by Aerosol Deposition.”
Journal of the American Ceramic Society 94:1509–13.
Hashemi, S., M. Sawan, and Y. Savaria. 2012. “A High-Efficiency
Low-Voltage CMOS Rectifier for Harvesting Energy in
Implantable Devices.” Biomedical Circuits and Systems, IEEE
Transactions on 6:326–35.
S. Priya et al.: A Review on Piezoelectric Energy Harvesting 33
Authenticated | jhryu@kims.re.kr author's copy
Download Date | 2/2/17 7:13 AM
Heidrich, N., F. Knöbber, S. Hampl, W. Pletschen, R. E. Sah,
V. Cimalla, V. Lebedev, and O. Ambacher. 2011. AlN-Basierte
Mikroelektromechanische Strukturen Für Implantate Paper
Presented at Transducers’ 11:1642–4.
Hirasawa, T. H., Y. T.-T. Yen, P. K. Wright, A. P. Pisano, and
L. Lin. 2010. “Design and Fabrication of Piezoelectric Aluminum
Nitride Corrugated Beam Energy Harvester.” Paper presented at
PowerMEMS, 211–4.
Hwang, G.-T., V. Annapureddy, J. H. Han, D. J. Joe, C. Baek, D. Y. Park,
et al. 2015. “A Reconfigurable Rectified Flexible Energy Harvester
via Solid-State Single Crystal Grown PMN–PZT.” Adv Energy Mater
5:1500051.
Isarakorn, D., D. Briand, P. Janphuang, A. Sambri, S. Gariglio,
J. Triscone, F. Guy, J. Reiner, C. Ahn, and N. De Rooij. 2011. “The
Realization and Performance of Vibration Energy Harvesting
MEMS Devices Based on an Epitaxial Piezoelectric Thin Film.”
Smart Materials and Structures 20:025015.
Jaffe, B. 1971. Piezoelectric Ceramics. New York: Academic.
Jeon, Y., R. Sood, J.-H. Jeong, and S.-G. Kim. 2005. “MEMS Power
Generator with Transverse Mode Thin Film PZT.” Sensors and
Actuators A: Physical 122:16–22.
Jiang, L., and R. Miles. 1999. “A Passive Damper for the Vibration
Modes of the Head Actuator in Hard Disk Drives.” Journal of
Sound and Vibration 220:683–94.
Jo, S.-E., M.-S. Kim, and Y.-J. Kim. 2011. “A Resonant Frequency
Switching Scheme of a Cantilever Based on Polyvinylidene
Fluoride for Vibration Energy Harvesting.” Smart Materials and
Structures 21:015007.
Jumpertz, L., M. Carras, K. Schires, and F. Grillot. 2014. “Regimes of
External Optical Feedback in 5.6 Μm Distributed Feedback Mid-
Infrared Quantum Cascade Lasers.” Applied Physics Letters
105:131112.
Kang, M.-G., W.-S. Jung, C.-Y. Kang, and S.-J. Yoon. 2016. “Recent
Progress on PZT Based Piezoelectric Energy Harvesting
Technologies.” Actuators 5:5.
Kanno, I., S. Fujii, T. Kamada, and R. Takayama. 1997. “Piezoelectric
Properties of c-Axis Oriented Pb(Zr,Ti)O3 Thin Films.” Applied
Physics Letters 70:1378–80.
Kanno, I., T. Ichida, K. Adachi, H. Kotera, K. Shibata, and T. Mishima.
2012. “Power-Generation Performance of Lead-Free (K, Na)NbO3
Piezoelectric Thin-Film Energy Harvesters.” Sensors and
Actuators A: Physical 179:132–6.
Kim, H.-U., W.-H. Lee, H. R. Dias, and S. Priya. 2009. “Piezoelectric
Microgenerators-Current Status and Challenges.” IEEE
Transactions on Ultrasonics, Ferroelectrics, and Frequency
Control 56:1555–68.
Kim, H., S. Priya, H. Stephanou, and K. Uchino. 2007. “Consideration
of Impedance Matching Techniques for Efficient Piezoelectric
Energy Harvesting.” IEEE Transactions on Ultrasonics,
Ferroelectrics, and Frequency Control 54:1851–9.
Kong, N., T. S. Deyerle IV, and D. S. Ha. 2011. “Universal Power
Management IC for Small-Scale Energy Harvesting with
Adaptive Impedance Matching.” Paper presented at the IEEE
Energy Conversion Congress and Exposition (ECCE), 3859–63.
Kong, N., and D. S. Ha. 2012. “Low-Power Design of a Self-Powered
Piezoelectric Energy Harvesting System with Maximum Power
Point Tracking.” IEEE Transactions on Power Electronics
27:2298–308.
Kong, N., D. S. Ha, A. Erturk, and D. J. Inman. 2010. “Resistive
Impedance Matching Circuit for Piezoelectric Energy
Harvesting.” Journal of Intelligent Material Systems and
Structures 31:1293–302.
Krulevitch, P., A. P. Lee, P. B. Ramsey, J. C. Trevino, J. Hamilton, and
M. A. Northrup. 1996. “Thin Film Shape Memory Alloy
Microactuators.” Journal of Microelectromechanical Systems
5:270–82.
Kuwata, J., K. Uchino, and S. Nomura. 1982. “Dielectric and
Piezoelectric Properties of 0.91pb(Zn1/3nb2/3)O3-0.09PbTiO3
Single Crystals.” Japanese Journal of Applied Physics 21:1298.
Lam, Y.-H., W.-H. Ki, and C.-Y. Tsui. 2006. “Integrated Low-Loss
CMOS Active Rectifier for Wirelessly Powered Devices.” IEEE
Transactions on Circuits and Systems II: Express Briefs
53:1378–82.
Le, T. T., J. Han, A. Von Jouanne, K. Mayaram, and T. S. Fiez. 2006.
“Piezoelectric Micro-Power Generation Interface Circuits.” IEEE
Journal of Solid-State Circuits 41:1411–20.
Ledermann, N., P. Muralt, J. Baborowski, S. Gentil, K. Mukati,
M. Cantoni, A. Seifert, and N. Setter. 2003. “{1 0 0}-Textured,
Piezoelectric Pb(Zrx, Ti1− x)O3 Thin Films for MEMS: Integration,
Deposition and Properties.” Sensors and Actuators A: Physical
105:162–70.
Lee, B., S. Lin, W. Wu, X. Wang, P. Chang, and C. Lee. 2009.
“Piezoelectric MEMS Generators Fabricated with an Aerosol
Deposition PZT Thin Film.” Journal of Micromechanics and
Microengineering 19:065014.
Lefeuvre, E., A. Badel, C. Richard, and D. Guyomar. 2005.
“Piezoelectric Energy Harvesting Device Optimization by
Synchronous Electric Charge Extraction.” Journal of Intelligent
Material Systems and Structures 16:865–76.
Lefeuvre, E., S. Risquez, J. Wei, M. Woytasik, and F. Parrain. 2014.
“Self-Biased Inductor-Less Interface Circuit for Electret-Free
Electrostatic Energy Harvesters.” Journal of Physics: Conference
Series, PowerMEMS 557:012052.
Lefki, K., and G. Dormans. 1994. “Measurement of Piezoelectric
Coefficients of Ferroelectric Thin Films.” Journal of Applied
Physics 76:1764–7.
Lei, A., R. Xu, A. Thyssen, A. C. Stoot, T. L. Christiansen, K. Hansen,
R. Lou-Moller, E. V. Thomsen, and K. Birkelund. 2011. “MEMS-
based Thick Film PZT Vibrational Energy Harvester.” Paper
presented at the IEEE International Conference on Micro Electro
Mechanical Systems (MEMS), 125–8.
Li, J., J. Slutsker, J. Ouyang, and A. Roytburd. 2004. “Contribution of
Substrate to Converse Piezoelectric Response of Constrained
Thin Films.” Journal of Materials Research 19:2853–8.
Li, X., and T. Tansley. 1990. “Laser‐Induced Chemical Vapor
Deposition of AlN Films.” Journal of Applied Physics 68:
5369–71.
Liu, H., C. Lee, T. Kobayashi, C. J. Tay, and C. Quan. 2012.
“Piezoelectric MEMS-Based Wideband Energy Harvesting
Systems Using a Frequency-up-Conversion Cantilever Stopper.”
Sensors and Actuators A: Physical 186:242–8.
Lu, C., C.-Y. Tsui, and W.-H. Ki. 2011. “Vibration Energy Scavenging
System with Maximum Power Tracking for Micropower
Applications.” IEEE Transactions Very Large Scale Integrated
VLSI System 19:2109–19.
Mann, B., and N. Sims. 2009. “Energy Harvesting From the Nonlinear
Oscillations of Magnetic Levitation.” Journal of Sound and
Vibration 319:515–30.
Mansour, M. O., M. H. Arafa, and S. M. Megahed. 2010. “Resonator
with Magnetically Adjustable Natural Frequency for Vibration
34 S. Priya et al.: A Review on Piezoelectric Energy Harvesting
Authenticated | jhryu@kims.re.kr author's copy
Download Date | 2/2/17 7:13 AM
Energy Harvesting.” Sensors and Actuators A: Physical
163:297–303.
Marin, A. 2013. “Mechanical Energy Harvesting for Powering
Distributed Sensors and Recharging Storage Systems.”
Ph. D. Dissertation in Virginia Tech.
Marin, A., S. Bressers, and S. Priya. 2011. “Multiple Cell
Configuration Electromagnetic Vibration Energy Harvester.”
Journal of Physics D: Applied Physics 44:295501.
Marin, A., and S. Priya. 2012. “Multi-Mechanism Vibration Harvester
Combining Inductive and Piezoelectric Mechanisms.” Paper
presented at the SPIE Smart Structures and Materials+
Nondestructive Evaluation and Health Monitoring, 83411L-L–11.
Marinkovic, B., and H. Koser. 2009. “Smart Sand-a Wide Bandwidth
Vibration Energy Harvesting Platform.” Applied Physics Letters
94:103505.
Martin, F., P. Muralt, M.-A. Dubois, and A. Pezous. 2004. “Thickness
Dependence of the Properties of Highly c-Axis Textured AlN
Thin Films.” Journal of Vacuum Science & Technology A
22:361–5.
Marzencki, M., Y. Ammar, and S. Basrour. 2007. “Design, Fabrication
and Characterization of a Piezoelectric MEMS, Vibration Energy
Scavenging.” Paper presented at the Symposium on Design,
Test, Integration and Packaging of MEMS/MOEMS (DTIP’07),
350–3.
Massaro, A., S. De Guido, I. Ingrosso, R. Cingolani, M. De Vittorio,
M. Cori, A. Bertacchini, L. Larcher, and A. Passaseo. 2011.
“Freestanding Piezoelectric Rings for High Efficiency Energy
Harvesting at Low Frequency.” Applied Physics Letters
98:053502.
Meng, W., J. Heremans, and Y. Cheng. 1991. “Epitaxial Growth of
Aluminum Nitride on Si (111) by Reactive Sputtering.” Applied
Physics Letters 59:2097–9.
Miller, L. M., E. Halvorsen, T. Dong, and P. K. Wright. 2011.
“Modeling and Experimental Verification of Low-Frequency
MEMS Energy Harvesting From Ambient Vibrations.” Journal of
Micromechanics and Microengineering 21:045029.
Mitcheson, P. D., E. K. Reilly, T. Toh, P. K. Wright, and E. M. Yeatman.
2007. “Performance Limits of the Three MEMS Inertial Energy
Generator Transduction Types.” Journal of Micromechanics and
Microengineering 17:S211.
Morimoto, K., I. Kanno, K. Wasa, and H. Kotera. 2010. “High-
Efficiency Piezoelectric Energy Harvesters of c-Axis-Oriented
Epitaxial PZT Films Transferred Onto Stainless Steel
Cantilevers.” Sensors and Actuators A: Physical 163:428–32.
Muralt, P., M. Marzencki, B. Belgacem, F. Calame, and S. Basrour.
2009a. “Vibration Energy Harvesting with PZT Micro Device.”
Procedia Chemistry 1:1191–4.
Muralt, P., R. Polcawich, and S. Trolier-McKinstry. 2009b.
“Piezoelectric Thin Films for Sensors, Actuators, and Energy
Harvesting.” MRS Bulletin 34:658–64.
Norton, M. G., P. G. Kotula, and C. B. Carter. 1991. “Oriented
Aluminum Nitride Thin Films Deposited by Pulsed‐Laser
Ablation.” Journal of Applied Physics 70:2871–3.
Park, J. C., J. Y. Park, and Y.-P. Lee. 2010. “Modeling and
Characterization of Piezoelectric-Mode MEMS Energy
Harvester.” Journal of Microelectromechanical Systems
19:1215–22.
Park, S., and T. R. Shrout. 1997. “Ultrahigh Strain and Piezoelectric
Behavior in Relaxor Based Ferroelectric Single Crystals.”
Journal of Applied Physics 82:1804–11.
Potrepka, D. M., G. R. Fox, L. M. Sanchez, and R. G. Polcawich. 2011.
“Pt/TiO2 Growth Templates for Enhanced PZT Films and MEMS
Devices.” Paper presented at the MRS, 67–72.
Priya, S. 2007. “Advances in Energy Harvesting Using Low Profile
Piezoelectric Transducers.” Journal of Electroceramics 19:
167–84.
Priya, S. 2010. “Criterion for Material Selection in Design of Bulk
Piezoelectric Energy Harvesters.” IEEE Transactions on
Ultrasonics, Ferroelectrics, and Frequency Control 57:
2610–12.
Priya, S., and D. J. Inman. 2009. “Energy harvesting technologies”
Springer.
Qi, Y., J. Kim, T. D. Nguyen, B. Lisko, P. K. Purohit, and
M. C. McAlpine. 2011. “Enhanced Piezoelectricity and
Stretchability in Energy Harvesting Devices Fabricated From
Buckled PZT Ribbons.” Nano Letters 11:1331–6.
Ramadass, Y. K., and A. P. Chandrakasan. 2010. “An Efficient
Piezoelectric Energy Harvesting Interface Circuit Using a Bias-
Flip Rectifier and Shared Inductor.” IEEE Journal of Solid-State
Circuits 45:189–204.
Reilly, E. K., L. M. Miller, R. Fain, and P. Wright. 2009. “A Study of
Ambient Vibrations for Piezoelectric Energy Conversion.” Proc.
PowerMEMS 2009:312–15.
Renaud, M., K. Karakaya, T. Sterken, P. Fiorini, C. Van Hoof, and
R. Puers. 2008. “Fabrication, Modelling and Characterization of
MEMS Piezoelectric Vibration Harvesters.” Sensors and
Actuators A: Physical 145:380–6.
Rincón-Mora, G. A., and S. Yang. 2016. “Tiny Piezoelectric
Harvesters: Principles, Constraints, and Power Conversion.”
IEEE Trans on Circuits and Systems I: Regular Papers 63:
639–49.
Roundy, S., and P. K. Wright. 2004. “A Piezoelectric Vibration Based
Generator for Wireless Electronics.” Smart Materials and
Structures 13:1131.
Roundy, S., P. K. Wright, and J. Rabaey. 2003a. “A Study of Low
Level Vibrations as a Power Source for Wireless Sensor Nodes.”
Computer Communications 26:1131–44.
Roundy, S., P. K. Wright, and J. Rabaey. 2003b. Energy Scavenging
for Wireless Sensor Networks. Kluwer Academic Publishers.
Ryu, J., J.-J. Choi, B.-D. Hahn, D.-S. Park, W.-H. Yoon, and K.-H. Kim.
2007. “Fabrication and Ferroelectric Properties of Highly Dense
Lead-Free Piezoelectric (K0.5na0.5) NbO3 Thick Films by Aerosol
Deposition.” Appl. Phys. Lett 90:152901.
Ryu, J., G. Han, T. K. Song, A. Welsh, S. Trolier-McKinstry, H. Choi,
J.-P. Lee, J.-W. Kim, W.-H. Yoon, and J.-J. Choi. 2014. “Upshift of
Phase Transition Temperature in Nanostructured PbTiO3 Thick
Film for High Temperature Applications.” ACS Applied Materials
& Interfaces 6:11980–7.
Saggini, S., S. Giro, F. Ongaro, and P. Mattavelli. 2010.
“Implementation of Reactive and Resistive Load Matching for
Optimal Energy Harvesting from Piezoelectric Generators.”
Paper presented at the IEEE Workshop on Control and Modeling
for Power Electronics (COMPEL), 1–6.
Sanchez, L. M., D. M. Potrepka, G. R. Fox, I. Takeuchi, K. Wang,
L. A. Bendersky, and R. G. Polcawich. 2013. “Optimization of
PbTiO3 Seed Layers and Pt Metallization for PZT-Based
piezoMEMS Actuators.” J. Mater. Res 28:1920–31.
Sankman, J., and D. Ma. 2014. “A 12-µw to 1.1-mW AIM Piezoelectric
Energy Harvester for Time-Varying Vibrations with 450 nA IQ.”
IEEE Trans. Power Electron 30:632–43.
S. Priya et al.: A Review on Piezoelectric Energy Harvesting 35
Authenticated | jhryu@kims.re.kr author's copy
Download Date | 2/2/17 7:13 AM
Saxler, A., P. Kung, C. Sun, E. Bigan, and M. Razeghi. 1994. “High
Quality Aluminum Nitride Epitaxial Layers Grown on Sapphire
Substrates.” Applied Physics Letters 64:339–41.
Sessler, G. M. 2001. “Electrets: Recent Developments.” Journal of
Electrostatics 51–52:137–45.
Sharpes, N., A. Abdelkefi, and S. Priya. 2015. “Two-Dimensional
Concentrated-Stress Low-Frequency Piezoelectric Vibration
Energy Harvesters.” Applied Physics Letters 107:093901.
Shen, D., J.-H. Park, J. Ajitsaria, S.-Y. Choe, H. C. Wikle III, and D.-J.
Kim. 2008. “The Design, Fabrication and Evaluation of a MEMS
PZT Cantilever with an Integrated Si Proof Mass for Vibration
Energy Harvesting.” Journal of Micromechanics and
Microengineering 18:055017.
Shibata, K., K. Suenaga, K. Watanabe, F. Horikiri, A. Nomoto, and
T. Mishima. 2011. “Improvement of Piezoelectric Properties of
(K, Na)NbO3 Films Deposited by Sputtering.” Japanese Journal
of Applied Physics 50:041503.
Shim, M., J. Kim, J. Jeong, S. Park, and C. Kim. 2015. “Self-Powered
30 µw to 10 mW Piezoelectric Energy Harvesting System with
9.09 Ms/V Maximum Power Point Tracking Time.” IEEE J. Solid-
State Circuits 50:2367–79.
Shiosaki, T., T. Yamamoto, T. Oda, and A. Kawabata. 1980. “Low‐
Temperature Growth of Piezoelectric AlN Film by Rf Reactive
Planar Magnetron Sputtering.” Applied Physics Letters 36:
643–5.
Sorimachi, A., H. Takahashi, and S. Tokonami. 2009. “Influence of
the Presence of Humidity, Ambient Aerosols and Thoron on the
Detection Responses of Electret Radon Monitors.” Radiation
Measurements 44:111–15.
Stevens, K., A. Ohtani, M. Kinniburgh, and R. Beresford. 1994.
“Microstructure of AlN on Si (111) Grown by Plasma‐Assisted
Molecular Beam Epitaxy.” Applied Physics Letters 65:321–3.
Stoppel, F., C. Schröder, F. Senger, B. Wagner, and W. Benecke.
2011. “AlN-Based Piezoelectric Micropower Generator for Low
Ambient Vibration Energy Harvesting.” Procedia Engineering
25:721–4.
Tabesh, A., and L. G. Fréchette. 2010. “A Low-Power Stand-Alone
Adaptive Circuit for Harvesting Energy From a Piezoelectric
Micropower Generator.” Industrial Electronics, IEEE
Transactions on 57:840–9.
Takeda, F., T. Mori, and T. Takahashi. 1981. “Effect of Hydrogen Gas
on c-Axis Oriented AlN Films Prepared by Reactive Magnetron
Sputtering.” Japanese Journal of Applied Physics 20:L169.
Ting-Ta, Y., T. Hirasawa, P. Wright, A. Pisano, and L. Liwei. 2011.
“Corrugated Aluminum Nitride Energy Harvesters for High
Energy Conversion 26. Effectiveness.” J. Micromech. Microeng
21:085037.
Trolier-McKinstry, S., and P. Muralt. 2004. “Thin Film Piezoelectrics
for MEMS.” Journal of Electroceramics 12:7–17.
Tsubouchi, K., and N. Mikoshiba. 1985. “Zero-Temperature-
Coefficients SAW Devices on AlN Epitaxial Films.” IEEE
Transactions on Sonics and Ultrasonics 32:634–44.
Tsujiura, Y., E. Suwa, H. Hida, K. Suenaga, K. Shibata, and I. Kanno.
2013. “Lead-Free Piezoelectric MEMS Energy Harvesters of
Stainless Steel Cantilevers.” Paper Presented at the
Transducers & Eurosensors XXVII: The 17th International
Conference on Solid-State Sensors, Actuators and
Microsystems, 474–7.
Tuttle, B., J. A. Voigt, T. J. Garino, D. C. Goodnow, R. W. Schwartz,
D. L. Lamppa, T. J. Headley, and M. O. Eatough. 1992. “Chemically
Prepared Pb(Zr,Ti)O3 Thin Films: The Effects of Orientation and
Stress.” Paper presented at the IEEE International Symposium on
Applications of Ferroelectrics, 344–8.
Uchino, K. 2009. Ferroelectric Devices, 2nd ed. CRC press.
Van Schaijk, R., R. Elfrink, T. Kamel, and M. Goedbloed. 2008.
“Piezoelectric AlN Energy Harvesters for Wireless Autonomous
Transducer Solutions.” Paper presented at the IEEE Sensors,
45–8.
Varghese, R. P. 2013. “MEMS Technologies for Energy Harvesting
and Sensing.” Ph. D. Disseration in Virginia Tech.
Varghese, R., M. Williams, S. Gupta, and S. Priya. 2011.
“Temperature-Time Transformation Diagram for Pb(Zr, Ti)O3
Thin Films.” Journal of Applied Physics 110:014109.
Wang, Q.-M., X.-H. Du, B. Xu, and L. E. Cross. 1999.
“Electromechanical Coupling and Output Efficiency of
Piezoelectric Bending Actuators.” IEEE Transactions on
Ultrasonics, Ferroelectrics, and Frequency Control 46:
638–46.
Wang, X.-Y., C.-Y. Lee, Y.-C. Hu, W.-P. Shih, C.-C. Lee, J.-T. Huang,
and P.-Z. Chang. 2008. “The Fabrication of Silicon-Based PZT
Microstructures Using an Aerosol Deposition Method.” Journal
of Micromechanics and Microengineering 18:055034.
Wang, Z. L., and J. Song. 2006. “Piezoelectric Nanogenerators Based
on Zinc Oxide Nanowire Arrays.” Science 312:242–6.
Wu, L., X.-D. Do, S.-G. Lee, and D. S. Ha, A Self-Powered and Optimal
SSHI Circuit Integrated with an Active Rectifier for Piezoelectric
Energy Harvesting to appear in IEEE Trans. on Circuits and
Systems I.
Xu, R. 2012. “The Design of Low-Frequency, Low-G Piezoelectric
Micro Energy Harvesters.” Ph. D. Dissertation in Massachusetts
Institute of Technology.
Xu, R., and S. Kim. 2012. “Figures of Merits of Piezoelectric Materials
in Energy Harvesters.” Paper presented at the Power MEMS.
Xu, R., and S. Kim. 2015. “Low-Frequency, Low-G MEMS Piezoelectric
Energy Harvester.” Paper presented at the Power MEMS,
012013.
Xu, R., A. Lei, C. Dahl-Petersen, K. Hansen, M. Guizzetti,
K. Birkelund, E. V. Thomsen, and O. Hansen. 2012a.
“Fabrication and Characterization of MEMS-Based PZT/PZT
Bimorph Thick Film Vibration Energy Harvesters.” Journal of
Micromechanics and Microengineering 22:094007.
Xu, R., A. Lei, C. Dahl-Petersen, K. Hansen, M. Guizzetti,
K. Birkelund, E. V. Thomsen, and O. Hansen. 2012b. “Screen
Printed PZT/PZT Thick Film Bimorph MEMS Cantilever Device for
Vibration Energy Harvesting.” Sensors and Actuators A:
Physical 188:383–8.
Yen, T.-T., T. Hirasawa, P. K. Wright, A. P. Pisano, and L. Lin. 2011.
“Corrugated Aluminum Nitride Energy Harvesters for High
Energy Conversion Effectiveness.” Journal of Micromechanics
and Microengineering 21:085037.
Yeo, H. G., and S. Trolier-McKinstry. 2014. “{001} Oriented
Piezoelectric Films Prepared by Chemical Solution Deposition
on Ni Foils.” Journal of Applied Physics 116:014105.
Yokoyama, S., T. Ozeki, T. Oikawa, and H. Funakubo. 2002.
“Preparation of Orientation-Controlled Polycrystalline Pb(Zr, Ti)
O3 Thick Films on (100) Si Substrates by Metalorganic Chemical
Vapor Deposition and Their Electrical Properties.” Japanese
Journal of Applied Physics 41:6705.
Zhang, W., Y. Someno, M. Sasaki, and T. Hirai. 1993. “Low-
Temperature Epitaxial Growth of AlN Films on Sapphire by
36 S. Priya et al.: A Review on Piezoelectric Energy Harvesting
Authenticated | jhryu@kims.re.kr author's copy
Download Date | 2/2/17 7:13 AM
Electron Cyclotron Resonance Plasma-Assisted Chemical Vapor
Deposition.” Journal of Crystal Growth 130:308–12.
Zhou, Y., D. J. Apo, and S. Priya. 2013a. “Dual-Phase Self-Biased
Magnetoelectric Energy Harvester.” Applied Physics Letters
103:192909.
Zhou, Q., S. Lau, D. Wu, and K. K. Shung. 2011. “Piezoelectric Films
for High Frequency Ultrasonic Transducers in Biomedical
Applications.” Progress in Materials Science 56:139–74.
Zhou, Y., C.-S. Park, C.-H. Wu, D. Maurya, M. Murayama, A. Kumar,
R. Katiyar, and S. Priya. 2013b. “Microstructure and
Surface Morphology Evolution of Pulsed Laser Deposited
Piezoelectric BaTiO3 Films.” Journal of Materials Chemistry C
1:6308–15.
Zhu, D., S. Roberts, J. Tudor, and S. Beeby. 2008. “Closed Loop
Frequency Tuning of a Vibration-based Micro-Generator.” Paper
presented at the Power MEMS, 229–32.
S. Priya et al.: A Review on Piezoelectric Energy Harvesting 37
Authenticated | jhryu@kims.re.kr author's copy
Download Date | 2/2/17 7:13 AM
View publication stats