Thermally modulated CMOS compatible particle sensor for air quality monitoring

Combating the health effects of particulate matter pollution requires affordable and reliable real-time air quality monitoring. The potential for large-scale manufacturing of acoustic wave-based sensors makes them an interesting option for low-cost, low-power particle sensing applications. This paper demonstrates a solidly mounted resonator particulate matter sensor with improved sensitivity through thermal modulation of the device. A novel, CMOS compatible solidly mounted resonator with an integrated microheater was designed, manufactured, and tested. In simulations, it was found that particle deposition increases both the heat loss and the thermal time constant of the solidly mounted resonator. The effect of this on the resonant frequency shift of the device caused by particle deposition is investigated closely in this work. The sensitivity of the devices to particle deposition was tested experimentally with and without temperature modulation by placing the device in a test chamber and allowing the randomised settling of aerosolised particles on its surface. The unmodulated sensor demonstrated a particle mass sensitivity of ~ 40 Hz/ng whilst the mass sensitivity of the temperature-modulated device was shown to improve by a factor of nearly × 5 to 190 Hz/ng. Temperature modulation also improved the detection limit from 100 ng to 50 ng. Further experiments were conducted by adding an impactor mechanism to have a more controlled measurement set up. To this effect a thermophoretic particle deposition mechanism was added to the device to enhance its performance. It was demonstrated that the repeatability of measurements was significantly improved, making the device a promising low-cost technology for air quality monitoring