Micromachined Silicon Cantilever Resonator-Based Humidity Sensors for Multifunctional Applications

This paper reports a piezoresistive silicon microcantilever based self-actuating and self-sensing gravimetric humidity sensor, which can be used for real-time monitoring of human activity: respiration and water evaporation on skin. A ZnO nucleation nanofilm and chitosan self-assembled monolayers (SAMs) are selectively deposited on the micromachined-cantilever as sensing materials. Thanks to the new designed geometry, in-plane electrothermal actuating can be achieved by applying an AC voltage to a p-diffused heating resistor, and the resonant frequency (RF) shifts induced by the mass adsorption on the sensing nanostructure of high surface-area-to-volume ratio can be read out directly by a p-diffused full Wheatstone bridge at the clamped end of the cantilever. The fabricated microsensor represents a combination of high sensitivity and fast response/recovery to an almost full range of relative humidity levels (0% - 97.3%), facilitating their potential applications in personal health monitoring as well as environmental monitoring.