A CMOS-MEMS Thermal-Piezoresistive Oscillator Implemented for Wide-Range Pressure Sensing Applications

This work demonstrates an integrated thermally actuated piezoresistive micromechanical oscillator realized using TSMC
$0.35\ \mu \mathrm{m}$
CMOS-MEMS platform. The oscillation in ambient condition was verified with a frequency output of 1 MHz and Allan Deviation of 1.7 ppm, which corresponds to a frequency resolution of 1.7 Hz. Here we also present the application of the oscillator as a pressure sensor, showing the possibility of using this thermal piezoresistive oscillator (TPO) to sense the pressure variation in the surroundings. After a series of pressure measurements, it was confirmed that this system has the potential to become a sensor for real-time monitoring of environmental pressure, with a sensing range from 40 mTorr to 760 Torr. The linear output frequency change in this logarithmic sensing range is about 2.5 kHz. The TPO has Allan Deviation of 0.5 ppm in the low pressure regime corresponding to a frequency resolution of 0.5 Hz. The proposed TPO can potentially be integrated with other sensors, such as temperature, humidity, and aerosol sensors, in the same substrate using our mature CMOS-MEMS fabrication platform to form a fully integrated environmental sensor hub.