Ethanol sensor based on layered WO/sub 3//ZnO/36/spl deg/ LiTaO/sub 3/ SAW devices

Layered surface acoustic wave (SAW) devices for the detection of ethanol in dry and humid air were fabricated on 36/spl deg/ YX LiTaO/sub 3/ utilizing a 1.2 /spl mu/m zinc oxide (ZnO) intermediate layer. A 150 nm tungsten trioxide (WO/sub 3/) sensing layer was deposited via r.f. sputtering. Sensor performance was analyzed in terms of response magnitude as a function of operational temperature. Different relative humidity (RH) levels for various ethanol concentrations were investigated. Frequency shifts of 119 kHz, 90 kHz and 86 kHz towards 500 ppm of ethanol in air were observed for 0%, 25% and 50% RH, measured at 20 /spl deg/C, respectively. The effect of elevated temperatures on the sensors' surface morphology is presented. The influence of humidity on sensitivity is investigated at different operating temperatures. At the highest sensor operating temperature of 300 /spl deg/C, the largest response was observed.