A Self-Sustained Mass Sensor With Physical Closed Loop Based on Thermal-Piezoresistive Coupled Resonators

This article reports a mode-localized mass sensor based on thermal-actuation piezoresistive-detection self-oscillated weakly coupled resonators. Detailed theoretical models and simulations of the self-oscillation of the coupled resonators were established and were also verified using optical and electrical measurements. The sensor was fabricated and characterized in terms of stability, linearity, sensitivity, and resolution. Supplied with only a constant direct current (DC), the resonant mass sensor could oscillate at its resonant frequency with an ultrahigh quality factor of 95 k in air. By implementing the principle of the mode localization phenomenon, ~200 times parametric sensitivity improvement with amplitude ratio output was implemented compared to the traditional frequency output metric. A real-time mass detector with 84-fg resolution and larger than ~700-pg linear measurement range was obtained.