Acoustic Bragg reflectors for Q-enhancement of unreleased MEMS resonators

This work presents the design of acoustic Bragg reflectors (ABRs) for unreleased MEMS resonators through analysis and simulation. Two of the greatest challenges to the successful implementation of MEMS are those of packaging and integration with integrated circuits. Development of unreleased RF MEMS resonators at the transistor level of the CMOS stack will enable direct integration into front-end-of-line (FEOL) processing, making these devices an attractive choice for on-chip signal generation and signal processing. The use of ABRs in unreleased resonators reduces spurious modes while maintaining high quality factors. Analysis on unreleased resonators using ABRs covers design principles, effects of fabrication variation, and comparison to released devices. Additionally, ABR-based unreleased resonators are compared with unreleased resonators enhanced using phononic crystals, showing order of magnitude higher quality factor (Q) for the ABR-based devices.