Dual-mode piezo-on-silicon resonant temperature and humidity sensor for portable air quality monitoring systems

Abstract

This paper demonstrates a dual-mode, micromachined temperature and relative humidity (RH) sensor platform using two ZnO-on-silicon, lateral-mode bulk acoustic wave (BAW) resonators. A moisture-insensitive reference resonator is utilized in conjunction with an identical, humidity-functionalized resonator to yield a thermally compensated RH sensor. The reference sensor exploits the dual-mode response of fundamental and higher order in-plane resonance modes in the range of 30–100 MHz to eliminate the RH sensor dependence on temperature. Hygroscopic polyethyleneimine (PEI) is deposited on annexed sensing platforms of the BAW resonator to enable operation from 20 to 92 %RH with high Q in air. A humidity sensitivity of 1.2 kHz/%RH from 20 to 60 %RH and 14 kHz/%RH from 60 to 92 %RH is measured at room temperature for the RH sensor which, combined with the reference sensor, occupies a total area of .053 mm2.