High temperature stability of langasite surface acoustic wave devices

High temperature acoustic wave (AW) devices capable of operating above 600degC and in hostile environments have opened potential applications for monitoring industrial processes, power plants, and aerospace systems. The authors have reported on the development of thin film electrodes and protective ceramic layers to allow surface acoustic wave (SAW) device operation up to 800degC on langasite (LGS) crystals. This success motivated further study of the electrode material and protective ceramic overlayer, as well as investigations of long term performance, temperature cycling and shock behavior, which are reported in this work. Among the results reported are: behavior of a co-deposited Pt/Rh/ZrO₂ composite electrode structure up to 1000degC; investigation of oxygen rich and nitrogen rich SiAlON protective ceramic layers; long term (4080 hours, or about 5frac12 months) operation of a two-port SAW resonator at 800degC; cyclical thermal tests between room temperature and 850degC; and thermal shock tests of crystals between 700degC and room temperature.