High temperature LGS SAW devices with Pt/WO3 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°C. An additional 7dB loss in the transmission coefficient, |S₂₁|, of the two port 167 MHz SAW resonators tested has been observed for operation at 750°C with respect to room temperature. Original films have been fabricated for the two port SAW gas sensors tested from 250°C to 550°C. A combination of platinum/tungsten trioxide (Pt/WO₃) films has been used in the detection of C₂H₄ in N₂. In the detection of H₂ in N₂ 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°C to 750°C for periods up to six weeks, with degradations in the |S₂₁| 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°C to 750°C and to perform as high temperature gas sensors.