Solid state RF MEMS resonators in standard CMOS

This paper presents a review of our work in CMOS-MEMS resonators fabricated in Front-End-of-Line (FEOL) processing of standard CMOS technology with no need for post-processing or special packaging. Acoustic resonators composed of Si and SiO₂ found in the CMOS stack are demonstrated, confined by Acoustic Bragg Reflectors and sensed using a standard transistor embedded inside the acoustic resonant cavity. The merits of active transistor sensing of MEMS resonators at high frequencies are discussed, leading to the principle of the Resonant Body Transistors (RBTs) described in this work. RBTs realized in IBM´s 32nm SOI process are demonstrated with resonance frequency above 11 GHz and Q~30, spanning a footprint of less than 15 μm². Finally, thermal stability of <;3 ppm/K is shown for these CMOS-integrated devices. The CMOS-MEMS resonators presented here offer building blocks for RF circuit design which can be integrated seamlessly with supporting circuits for on-chip clocking and signal processing.