A CMOS–MEMS RF-Tunable Bandpass Filter Based on Two High- $Q$ 22-MHz Polysilicon Clamped-Clamped Beam Resonators

This letter presents the design, fabrication, and demonstration of a CMOS–MEMS filter based on two high- $Q$ submicrometer-scale clamped–clamped beam resonators with resonance frequency around 22 MHz. The MEMS resonators are fabricated with a 0.35- $\mu\hbox{m}$ CMOS process and monolithically integrated with an on-chip differential amplifier. The CMOS–MEMS resonator shows high-quality factors of 227 in air conditions and 4400 in a vacuum for a bias voltage of 5 V. In air conditions, the CMOS–MEMS parallel filter presents a programmable bandwidth from 100 to 200 kHz with a $ ≪ \hbox{1}$-dB ripple. In a vacuum, the filter presents a stop-band attenuation of 37 dB and a shape factor as low as 2.5 for a CMOS-compatible bias voltage of 5 V, demonstrating competitive performance compared with the state of the art of not fully integrated MEMS filters.