The Resonant Body Transistor

Abstract

Cornell University 2009With quality factors (Q) often exceeding 10,000, vibrating micromechanical resonators have emerged as leading candidates for on-chip versions of high-Q resonators used in wireless communications systems, sensor networks, and clocking sources in microprocessors. However, extending the frequency of MEMS resonators generally entails scaling of resonator dimensions leading to increased motional impedance. In this dissertation, I introduce a new transduction mechanism using dielectric materials to improve performance and increase frequency of silicon-based RF acoustic resonators.Traditionally, electrostatically transduced mechanical resonators have used air-gap capacitors for driving and sensing vibrations in the structure. To increase transduction efficiency, facilitate fabrication, and enable GHz frequencies of operation, it is desirable to replace air-gap transducers with dielectric films.In my doctoral work, I designed, fabricated, and demonstrated dielectrically transduced silicon bulk-mode resonators up to 6.2 GHz, marking the highest acoustic frequency measured in silicon to date. The concept of internal dielectric transduction is introduced, in which dielectric transducers are incorporated directly into the resonator body. With dielectric films positioned at points of maximum strain in the resonator, this transduction improves in efficiency with increasing frequency, enabling resonator scaling to previously unattainable frequencies. Using internal dielectric transduction, longitudinal-mode resonators exhibited the highest frequency-quality factor ( f Q) product in silicon to date

Acoustic Bragg reflectors for Q-enhancement of unreleased MEMS resonators

“…These structures were fabricated from a released resonator design in previous work at Cornell [19]. The original, released RBT fabrication relies on a SOI process in which the fin is etched out of the SOI wafer's device layer, followed by dielectric deposition and deposition of poly-silicon gate.…”

A 440pJ/bit 1Mb/s 2.4GHz multi-channel FBAR-based TX and an integrated pulse-shaping PA

“…High-Q FBAR based LO generation is extended to three-channel operation. Integrated on-chip resonators [5] will enable area-efficient expansion to larger number of channels.…”

Multi-channel 180pJ/b 2.4GHz FBAR-based receiver

“…The LNA architecture provides efficient multiplexing to obtain channel selection, permitting the use of a lowpower ring oscillator for down-conversion and low power circuits for gain and detection. In this work, the packaging space consumed by single wirebonded resonators limits the design to a handful of channels, however, flip-chip bonding to an array of binary mass-loaded FBARs, or future integration of resonators in CMOS processes [8] could allow area-efficient expansion of the ideas presented here to many additional channels. …”