Humidity sensors based on AlN microcantilevers excited at high-order resonant modes and sensing layers of uniform graphene oxide

Abstract Resonant humidity sensors base on interdigital transducers (IDTs) excited microcantilevers are proposed for high sensitivity. The microcantilevers are coated with uniform graphene oxide (GO) thin films as sensing layers. For the first time, IDTs are used to excite piezoelectric microcantilevers to operate at very high-order resonant modes with intense signal. A small temperature coefficient of frequency (-23.6 ppm/˚C) of the microcantilvers is obtained by using AlN/Si (surface highly doped) layered structure. Uniform and thickness-controllable GO films covering the surface of microcantilevers are formed by vacuum filtration. Compared with the normal electrodes excited sensor with the same structure size, the sensitivity of the IDTs excited sensor is increased from 9.67 to 84.41 Hz/%RH. The thicker GO film, the higher sensitivity of the humidity sensor. Very little humidity hysteresis (