A Miniaturized PM2.5 Sensor Module Based on a Thin-Film Piezoelectric-on-Silicon MEMS Oscillator

Abstract

This study reports on a miniaturized PM2.5 sensor module utilizing a thin-film piezoelectric-on-silicon (TPoS) MEMS oscillator with real-time detection and high mass resolution. An aerosol impactor is used to serve as a particle size-selective sampler. A TPoS MEMS resonator utilizes a length-extensional mode with a quality factor (Q) of 1109 and a resonant frequency of 5.79 MHz in air. A transimpedance amplifier (TIA) interface circuit using UMC 0.18 μm CMOS technology is implemented, having an impedance gain of 81.64 dB□. To demonstrate a miniaturized mass sensor module, a board-level oscillator is integrated by a TPoS resonator, an in-house designed TIA IC interface circuit, an all-pass filter based phase shifter, buffer circuits, and a band-pass filter to fulfill Barkhausen criteria. For a carrier frequency of 5.79 MHz, a phase noise of -102.54 dBc/Hz at 1 kHz offset in air is recorded while the mass resolution of 0.21 pg for the PM2.5 sensor is demonstrated in this study. Finally, the aerosol measurement results within the concentration of 10 μg/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> to 1000 μg/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> show the coefficient of determination (R <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ) of 0.84 between the frequency slope and the environment concentration of aerosol.