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

Abstract

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> This letter presents the design, fabrication, and demonstration of a CMOS–MEMS filter based on two high- <formula formulatype="inline"><tex Notation="TeX">$Q$</tex></formula> submicrometer-scale clamped–clamped beam resonators with resonance frequency around 22 MHz. The MEMS resonators are fabricated with a 0.35-<formula formulatype="inline"> <tex Notation="TeX">$\mu\hbox{m}$</tex></formula> 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 <formula formulatype="inline"><tex Notation="TeX">$ ≪ \hbox{1}$</tex></formula>-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. </para>