III-V vertical nanowire transistor for ultra-low power applications
Author(s)Zhao, Xin, Ph. D. Massachusetts Institute of Technology
Massachusetts Institute of Technology. Department of Materials Science and Engineering.
Jesús A. del Alamo.
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Combining the superior carrier transport properties and flexible band structure engineering from III-V materials and ultimate scalability of vertical nanowire (VNW) device architecture, III-V VNW transistors are promising to extend Moore's law further than any other device technology. In this thesis, III-V VNW transistor technology has been pioneered via a top down approach for logic applications in future ultra-low power systems. Process flow and critical modules for sub-10 nm VNW transistors are developed from scratch. A novel dry etch technique based on BCl₃/SiCl₄/Ar chemistry for fabricating sub-20 nm III-V nanostructures with smooth, vertical sidewall and high aspect ratio (> 10) is developed. Digital etch (DE) is shown to mitigate the dry etch damage and reduce NW diameter below 10 nm in a controllable fashion while preserving the sidewall roughness and NW shape. Top-down InGaAs VNW MOSFET is demonstrated for the first time. Record Ion of 224 μA/μm is obtained at Ioff = 100 nA/μm with Vdd = 0.5 V in third generation devices. With novel solvent-based, switching characteristics are observed in devices with diameter as small as 14 nm. The impact of the intrinsic source/drain asymmetry on the device electrical characteristics is studied in detail, highlighting the importance of uniform NW diameter. The first experimental demonstration of III-V VNW TFETs with an InGaAs/InAs heterojunction fabricated by a top-down approach is introduced. Second generation TFETs demonstrate sub-thermal subthreshold characteristics over two orders of magnitude of current and a record high I60 in any experimental TFETs for Vds < 1 V at the time of device fabrication. The comparison of two generations of TFETs confirms oxide/semiconductor interface trapassisted tunneling as the source of significant temperature dependence in the first device generation. Detailed analysis on the conductance-voltage characteristics on both generations of devices reveal a 100-120 mV/dec steepness of Urbach tails in the VNW TFETs.
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2017.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Cataloged from student-submitted PDF version of thesis.Includes bibliographical references (pages 156-166).
DepartmentMassachusetts Institute of Technology. Department of Materials Science and Engineering.
Massachusetts Institute of Technology
Materials Science and Engineering.