Comparison between Ir, Ir_0.85Rh_0.15 and Ir_0.7Rh_0.3 thin films as electrodes for surface acoustic waves applications above 800 °C in air atmosphere

In this paper, we investigate the suitability of Ir, Ir_0.85Rh_0.15 and Ir_0.7Rh_0.3 thin films as electrodes for surface acoustic waves (SAW devices) applications taking place above 800 °C in air atmosphere. As expected, all films oxidize from 800 °C in IrO₂ or Ir_xRh_1-xO₂ phase. The electrical properties of the latter remain compatible with the design of SAW devices, with a specific electrical resistance of 151 and 100 μΩ·cm for x = 0.7 and x = 0.85 respectively. Moreover, we observe that the Ir_xRh_1-xO₂ phase is much more stable regarding sublimation effect than the IrO₂ phase, highlighting the interest of alloying Ir with Rh for high-temperature applications. SAW devices based on langasite substrate and Ir_0.85Rh_0.15 electrodes show a very good stability for at least several days at 800 °C in air. In the case of Ir_0.7Rh_0.3 electrodes, this stability is extended to temperatures up to 900 °C.