Investigations of humidity properties of on indium oxide thin films coated quartz crystal microbalances

Indium oxide thin films prepared by the chemical solution-based process have been investigated for humidity sensing application. The physical properties of thin films have been first characterized by various techniques such as scanning electron microscopy (SEM) to obtain morphological information of the layers. Humidity sensors were featured by combination of quartz crystals as transducers and indium oxide thin films as sensing elements. The coated crystal is used as a resonator in an oscillator circuit, the frequency of which varies as a function of the change in mass. The established sensor had a nonlinear frequency shift-humidity relationship and can respond to the humidity ranging from 40% to 80% relative humidity (RH). The maximum frequency sensitivity is50Hz/RH with the response time of ∼30s. The sensor has potential for use as a hygrometer, provided that the appropriate coating is chosen for a specific application.