Surface acoustic wave sensors for high-temperature applications

Results of investigations of surface acoustic wave (SAW) devices working at high temperatures are presented in this paper. The considered substrate materials are lithium niobate (LiNbO₃), quartz and langasite (La₃Ga₅SiO₁₄). In addition, electrode materials and assembly, interconnect and packaging strategies are discussed or examined. Delay lines on LiNbO₃ had low SAW attenuation up to approx. 550°C. The frequency response disappeared completely at about 800°C. Delay lines on quartz had low SAW attenuation up to 500°C, a temperature being significantly below the phase transition from α- to β-quartz at 573°C. Delay lines on La₃Ga₅SiO₁₄ withstand extreme temperatures: a SAW response was observed up to destruction of the packages used in these tests, however, resulted in a degradation of the device performance starting at about 600°C. An identification (ID) tag on La₃Ga₅SiO₁₄, could be used as a wireless passive thermometer for measuring high temperatures in industrial process control applications