Thin Film Electrodes for High Temperature Surface Acoustic Wave Devices

Wireless surface acoustic wave devices based on langasite allow sensor operation in high-temperature environments. While langasite shows piezoelectric behavior up to temperatures close to its melting point of 1470 °C, the stability of thin film electrodes for excitation of acoustic waves limits the application tem- perature. Different metal and ceramic based thin films are tested regarding their applicability as electrode materials for wireless surface acoustic wave devices at temperatures above 600 °C. The devices should with- stand temperatures of 800 °C for at least several hours. The high-temperature stability of platinum, platinum- rhodium, iridium as well as lanthanum strontium manganite (LSM) based electrodes is characterized using electrical measurements, x-ray diffraction (XRD) measurements and scanning electron microscopy (SEM) imaging. SAW devices with Ti/Pt thin film electrodes are operated up to temperatures of 800 °C. LSM/Pt films exhibit a good stability up to temperatures of 800 °C. Above 600 °C its resistance is comparable to platinum films