Abstract
We report a thermally driven and piezoresistively sensed CMOS-microelectromechanical systems (MEMS) resonator with quality factor Q >10 000 and stopband rejection of 15 dB under CMOS-compatible bias voltage. The bias voltage requirement of this letter is two orders of magnitude lower than that of the previous CMOS-MEMS capacitively transduced resonators. In addition, the combination of the bulk-mode resonator design and high-Q SiO <sub>2</sub> /polysilicon structural material leads to resonator Q >10 000, a key index for low-phase-noise oscillators and low-insertion-loss filters. The resonator with a center frequency at 5.1 MHz was fabricated using a standard 0.35 μm 2-poly-4-metal CMOS process, featuring low cost, batch production, fast turnaround time, easy prototyping, and MEMS/IC integration. To resolve the feedthrough issue often seen in conventional thermal-piezoresistive resonators: 1) separation of the heater and piezoresistor is first adopted because of the routing flexibility of the structural configuration offered by CMOS back-end-of-line materials and 2) fully differential measurement scheme is then applied to the proposed device, both of which enable a low-feedthrough level with 65-dB improvement as compared with its single-ended counterpart.