An Ultrafast Capacitive Humidity Sensor With Excellent Static and Dynamic Characteristics

Humidity sensors are widely used in many applications including health care, pharmaceutical, metrological, food, agricultural, industrial fields, etc. This article presents a unique application of a surface acoustic wave (SAW) resonator for developing a capacitive humidity sensor. A single port resonator has a planar interdigital electrode (IDE) on a piezoelectric substrate. A hydrophilic thin sensing film of titanium dioxide (TiO2) is deposited on the IDE to measure relative humidity (%RH) in a moist gas over a wide dynamic range. Keysight LCR meter (U1733C) is used to measure the electrical static and dynamic response parameters in the presence of humidity at 1 kHz frequency. The sensor with TiO2 film has excellent sensing performances, such as high sensitivity (1.3 pF/%RH), very fast response/recovery time (400/900 ms), as well as excellent precision for a humidity range of 5%RH–95%RH. Experimental results show that the output is consistent and repeatable (0.5%). The device can be used for wireless humidity measurement. The performances are competitive with those described in the literature. The small size, high sensitivity, very fast response, low fabrication cost, and broad dynamic range are all notable advantages of the sensor.