Design and modelling of solidly mounted resonators for low-cost particle sensing

This work presents the design and fabrication of Solidly Mounted Resonator (SMR) devices for the detection of particulate matter (PM2.5 and PM10) in order to develop a smart low-cost particle sensor for air quality. These devices were designed to operate at a resonant frequency of either 870 MHz or 1.5 GHz, employing zinc oxide as the piezoelectric layer and an acoustic mirror made from molybdenum and silicon dioxide layers. Finite element analysis of the acoustic resonators was performed using COMSOL Multiphysics software in order to evaluate the frequency response of the devices and the performance of the acoustic mirror. The zinc oxide based acoustic resonators were fabricated on a silicon substrate using a five mask process. The mass sensitivity of the acoustic resonators was estimated using a 3D finite element model and preliminary testing has been performed. The theoretical and observed mass sensitivity were similar at ca. 145 kHz ng-1 for the 870 MHz resonator when detecting PM2.5 suggesting that SMR devices have potential to be used as part of a miniature smart sensor system for airborne particle detection