Integrated HF CMOS-MEMS square-frame resonators with on-chip electronics and electrothermal narrow gap mechanism

A fully differential square frame resonator (SFR), operating at resonant frequencies of 6.184MHz and 17.63MHz for the fundamental and 2^nd harmonic, respectively, is introduced, which is the highest resonant frequency reported to date in CMOS-MEMS technology. In-plane CMOS-MEMS resonators have been fabricated directly on a conventional CMOS substrate with on-chip differential amplifiers. To enhance the output motional current, an electrothermal-actuated electrode is designed to reduce the input/output capacitive gap. A 5μm-thick, 4 μm-wide, 63 μm-long SFR with fixed electrodes exhibits a quality factor of 996 in vacuum at 6.18MHz.