A Thermal-Piezoresistive Self-Sustained Resonant Mass Sensor with High-Q (>95k) in Air

This paper demonstrates, for the first time, a high sensitivity mass sensor based on thermal-actuation piezoresistive-detection coupled resonators with a self-sustained oscillation. In-plane-vibration resonators are actuated by thermal expansion and contraction of the nanobeams, while the vibration displacements are detected by changes in resistance. Due to the combination of the negative piezoresistive coefficient of the phosphorus-doped structural silicon layer and the thermal expansion/contraction effect, a constant direct current (DC) through the nanobeam produces a periodic resistance variation in the beam at the fundamental modal frequency as the resonator, thus a self-sustained oscillation is generated. An ultra-high quality factor of 95k in air is obtained. Linear response with respect to mass perturbations for both amplitude ratio (of the two coupled resonators) and frequency shift readouts are observed from the proposed self-oscillating, mode-localized mass sensor. The measured sensitivity of the amplitude ratio (162 ppm/pg) is 100 × higher than that of a shift in the normalized resonant frequency.