A miniaturized aerosol sensor implemented by a silicon-based MEMS thermal-piezoresistive oscillator

A real-time aerosol sensor utilizing an SOI-MEMS thermal-piezoresistive oscillator (TPO) has been demonstrated in this work with sensor calibration using a commercial optical aerosol sensor (OAS). As compared to the self-sustained TPO [1], the DC power and operating temperature of the device can be significantly reduced by integrating the MEMS resonators and sustaining circuits, which leads to a longer lifetime and better reliability with lower power consumption and makes it a viable candidate for environmental sensing applications. The mass resolution of the proposed device is 3.34 fg extracted from a measured Allan deviation of 35 ppb, which is orders of magnitude higher than the commercially available quartz crystal microbalance (QCM). In addition, the proposed TPO technology also benefits cost reduction through the SOI-MEMS batch process as compared to its optical counterparts. Finally, the particulate matter (PM) sensing measurement under oxide (solid-phase PM
₁
, μm diameter) and smoke (liquid-phase PM
₁
, μm diameter) has shown a high correlation between the frequency slope of the TPO and the calibrated readings from the OAS.