A humidity sensor with high sensitivity and low temperature coefficient of frequency based on aln surface acoustic wave and graphene oxide sensing layer

This paper reports a humidity sensor based on AlN surface acoustic wave (SAW) device coated with graphene oxide (GO) as sensing layer. Utilizing a layered structure consisted of a thin AlN layer and a highly doped Si substrate layer, the temperature coefficient of frequency (TCF) of the sensor is found to be around -22.1 ppm/°C, much smaller than conventional SAW humidity sensors. Moreover, the sensor has a wide detection range from 5% to 95%RH and shows high sensitivity up to 420.8 kHz/10%RH at 90%RH. Little hysteresis, excellent repeatability, fast response and short recovery time of the sensor are obtained. The sensor also has a good stability in a period of 28 days.