Resonant Body Transistors in IBM´s 32nm SOI CMOS technology

This work presents an unreleased CMOS-integrated MEMS resonators fabricated at the transistor level of IBM´s 32SOI technology and realized without the need for any post-processing or packaging. These Resonant Body Transistors (RBTs) are driven capacitively and sensed piezoresistively using an n-channel Field Effect Transistor (nFET). Acoustic Bragg Reflectors (ABRs) are used to localize acoustic vibrations in these resonators completely buried in the CMOS stack and surrounded by low-k dielectric. Experimental results from the first generation hybrid CMOS-MEMS show RBTs operating at 11.1-11.5 GHz with footprints <; 5μm × 3μm. The response of active resonators is shown to contrast with passive resonators showing no discernible peak. Comparative behavior of devices with design variations is used to demonstrate the effect of ABRs on spurious mode suppression. Temperature stability and TCF compensation due to complimentary materials in the CMOS stack are experimentally verified.