A high performance humidity sensor based on surface acoustic wave and graphene oxide on AlN/Si layered structure

A surface acoustic wave (SAW) humidity sensor based on AlN/Si (doped) layered structure and graphene oxide (GO) sensing layer is proposed for high sensitivity and low temperature coefficient of frequency. With the GO thin film, the sensitivity of the humidity sensor is increased to 42.08 kHz/RH% when the relative humidity is greater than 80%RH. The humidity sensor performs well even at both very low (≤10%RH) and very high (≥90%RH) detection range of humidity. The present sensor has low hysteresis, excellent short term repeatability and long term stability (variation less than ± 2%). The sensor also shows a fast response and short recovery time. Moreover, using the AlN/Si (doped) layered structure, the thermal stability of the sensor is significantly improved. After being covered with GO thin film, the temperature coefficient of frequency (TCF) of the sensor is further reduced to −22.1 ppm/°C, much smaller than the previously reported SAW humidity sensors.