High temperature LGS SAW devices with Pt/WO/sub 3/ and Pd sensing films

This paper reports on the fabrication of high temperature LGS SAW devices to be used as gas sensors. SAW resonators and delay lines have been designed, fabricated, and tested up to 750/spl deg/C. An additional 7dB loss in the transmission coefficient, |S/sub 21/|, of the two port 167 MHz SAW resonators tested has been observed for operation at 750/spl deg/C with respect to room temperature. Original films have been fabricated for the two port SAW gas sensors tested from 250/spl deg/C to 550/spl deg/C. A combination of platinum/tungsten trioxide (Pt/WO/sub 3/) films has been used in the detection of C/sub 2/H/sub 4/ in N/sub 2/. In the detection of H/sub 2/ in N/sub 2/ an all palladium (Pd) metallic structure has been employed. Frequency variations up to 10 KHz for the 167 MHz high temperature SAW sensors were measured. The devices have been continuously cycled from 250/spl deg/C to 750/spl deg/C for periods up to six weeks, with degradations in the |S/sub 21/| response ranging from 2 to 7 dB. The high temperature LGS SAW devices and experiments reported in this work show the capability of these crystals to withstand prolonged exposure to temperatures ranging from 250/spl deg/C to 750/spl deg/C and to perform as high temperature gas sensors.