Analysis and modeling of piezoelectric resonant body transistors

Abstract

Microelectromechanical resonators are advantageous over traditional LC tanks in transceiver circuits due to their high quality factors (Q > 10000), small size and low power consumption. These characteristics enable monolithic integration of MEMS-based resonators as high-performance filters and oscillators at GHz frequencies in wireless communication technology. Similarly, they are desirable as high-precision low phase-noise clocking sources in microprocessor technology. To this end, both dielectric and piezoelectric transduction based resonators have been demonstrated as viable alternatives to their electrical counterparts. Dielectric (or electrostatic) based resonators take advantage of the cost-scaling of Silicon micromachining and the excellent mechanical properties of single crystal Silicon, leading to high- Q low cost resonators that have been extensively explored over the past two decades. However, piezoelectric based resonators have generally been preferred over these due to their high electromechanical coupling coefficients (kT2 ~ 4%) resulting in a much lower insertion loss, larger power handling defined by the breakdown voltage across piezoelectric films and ease of packing and integration into transceiver circuitry. Transistor sensing has been employed in both electrostatic and piezoelectric devices to enhance sensing efficiency. In particular, the Resonant Body Transistor (RBT) has been demonstrated as an electrostatic device which utilizes internal dielectric transduction to achieve the highest frequency acoustic resonators to date. The FET based sensing also pushes the operating frequency higher fundamentally as it is now limited only by the transistor cutoff frequency. In this work, we investigate the RBT geometry with piezoelectric transduction for more efficient and low loss drive and sense. To this end a full analytical model of the Piezoelectric RBT is presented explaining the piezoelectric drive and piezoelectricpiezoresistive mechanism-based sensing. The equivalent circuit model is presented and optimized for linearity in the AC output current to minimize harmonic distortion and for lowering the motional impedance . It is finally compared to a traditional piezoelectric resonator while discussing the tradeoffs with respect to the desired applications.