A CMOS-MEMS resonant gate field effect transistor

A high-frequency CMOS-MEMS resonant gate field effect transistor (RGFET) composed of a metal/oxide composite resonant-gate structure and an FET transducer has been demonstrated for the first time utilizing the conventional CMOS technology with Q > 1,700 and the signal-to-feedthrough ratio greater than 40 dB under a direct two-port measurement. As compared to the capacitive-type MEMS resonators, the proposed CMOS-MEMS RGFET features an inherent transconductance gain (g_m) offered by the FET transduction capable of enhancing the motional signal of the resonator. In this work, we designed a clamped-clamped beam resonant gate co-fabricated with a large W/L-ratio FET transducer using a standard CMOS-MEMS process to combine merits from the large electrostatic transduction areas of the resonator and the high gain of the FET. In addition, a commercially buffer was used to alleviate the impedance mismatch between the device and test facility to further preserve the FET gain. The transmission signal of the proposed RGFET can reach insertion loss of only 8 dB without any amplifier circuitry. Such a strong transmission and sharp phase transition across 0° pave a way for future RGFET-type oscillators in RF and sensor applications.