High-Q Low-Impedance MEMS Resonators

Permission to make digital or hard copies of all or part of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for profit or commercial advantage and that copies bear this notice and the full citation on the first page. To copy otherwise, to republish, to post on servers or to redistribute to lists, requires prior specific permission. Acknowledgement I am indebted to Prof. Nguyen for his generous support and guidance. I would like to thank Prof. King Liu and Prof. Lin for serving on my qualifying exam and dissertation committees, as well as Prof. Alon for serving on my qualifying exam committee. (Qualcomn). They have provided me timely help when I needed them and valuable feedback to better my research. I thank my current group members for their friendship and technical supports. I thank all of the BSAC directors and researchers for their endless efforts to make BSAC an even better environment for graduate students to learn and to grow professionally. The deepest thanks go to my family. The ever increasing need for regional and global roaming together with continuous advances in wireless communication standards continue to push future transceivers towards an ability to support multi-mode operation with minimal increases in cost, hardware complexity, and power consumption. RF channel-select filter banks pose a particularly attractive method for achieving multiband reconfigurability, since they not only provide the needed front-end reconfigurability, but also allow for power efficient and versatile transceiver designs, e.g., software-defined radio. Such channel-select filters, however, impose requirements on their constituent resonators that are not yet achievable on the micro-scale. Specifically, capacitively-transduced micromechanical resonators achieve high Q, but suffer from high impedance; while piezoelectric micromechanical resonators offer low impedance, but with insufficient Q. This dissertation demonstrates four new techniques to address the issues in both technologies. Two of the methods recognize that sub-30 nm gap spacing enables electrostatic resonators to achieve acceptably low impedance. Unfortunately, however, such small gaps with the needed high aspect ratios are difficult to achieve via wafer-level batch processing. Two new methods are proposed and experimentally verified for forming sub-30 nm gaps: 1) partial-filling of electrode-to-resonator gaps with atomic layer deposition (ALD) of high-k dielectric; and 2) generating gaps via the volume reduction associated with a silicidation reaction. Among the many benefits provided by a silicide-based approach to gap formation is speed of release, where …