A CMOS-MEMS Thermal-Piezoresistive Oscillator for Mass Sensing Applications

摘要

We present a thermally driven piezoresistively sensed resonator primarily consisting of backend of line (BEOL) CMOS material for mass sensing applications. A detailed analysis of the operation mechanism has been performed to develop a mathematical and an electrical equivalent model. The thermal-piezoresistive resonator (TPR) is composed predominantly of low loss materials like silicon dioxide (SiO2) and polysilicon for drive and sense. A differential configuration with drive and sense isolation was employed to significantly reduce the feedthrough level. Theoretical and simulated values are validated with experimental data. The proposed design has a resonance frequency of 5.13 MHz with a transconductance (g(m)) of 7.8 mu S in the vacuum (<10(-3) torr) for 1.2-mW bias while g(m) of 5 mu S in the atmospheric pressure for 2.7-mW bias power at 5.09 MHz. One of the highest reported quality factors (Q) of 2600 for CMOS-MEMS was achieved in air, while the same in the vacuum was >10 000. The thermal-piezoresistive oscillator (TPO) has Allan Deviation of 80 ppb and 20 ppm in ambient pressure using a lock-in amplifier with a phase-locked loop (PLL) and interface circuit using commercial amplifiers on printed circuit board (PCB), respectively. Using silver nanoparticles, the mass sensitivity of 24.96 kHzg was measured. The extracted mass resolution in air was 16.3 fg, thus having great potential to serve as an aerosol sensor.