Post-CMOS Compatible Aluminum Nitride MEMS Filters and Resonant Sensors

This paper reports post-CMOS compatible aluminum nitride (AlN) MEMS resonators, filters, and resonant sensors for the miniaturization of radio-frequency transceivers and sensor systems. Utilizing a resonator with two closely spaced modes, 2^nd order MEMS filters occupying 0.06 mm² have been realized in a single device. Methods for tuning the bandwidth and center frequency of these filters lithographically have been demonstrated. A 0.5% bandwidth, 108.4 MHz dual mode filter has a measured insertion loss of 9.4 dB with 50 Omega termination which can be reduced to 4.7 dB by terminating the filter with 75 Omega. In order to scale MEMS resonators to higher frequencies without increasing the size or impedance, resonators selectively driven at a harmonic determined by interdigitated drive and sense electrodes have been demonstrated reaching frequencies of 796 MHz with impedances of approximately 100 Omega and quality factors in excess of 750 in air. In the same process resonant sensors based on AlN double-ended tuning fork (DETF) sensing beams have been demonstrated at 727 kHz with quality factors of 2160. An oscillator based on the DETF sensing beams achieves a phase noise of -81 dBc/Hz at 275 Hz offset from the carrier. A 100 ng mass coupled to a pair of DETF sensors achieves an acceleration sensitivity of 565 mG/radicHz for accelerations from 275 to 1100 Hz.