High thermal stability of ultra-high temperature surface acoustic wave devices with multilayer composite electrodes

The main challenge to maintain high-temperature performance of surface acoustic wave (SAW) devices is to improve the high-temperature resistance of the interdigital transducers (IDT). This work reports on the development of the Pt-Rh alloy-based multilayered composite IDTs for high-temperature applications. Composite electrode-based wire-type resistors with different structures were prepared by magnetron sputtering, and their resistances and surface morphologies at temperatures up to 1600 degrees C were investigated. The proposed composite electrode has a structure of ZrO2 /Pt-Rh (10%) /Al2O3 /Pt-Rh (10%) /Al2O3 with a 40 nm ZrO2 protective layer at the top of the electrode. It has a 300 nm thickness Pt-Rh (10%) film, a 10 nm Al2O3 layer in the middle of Pt-Rh (10%) layer, and a 20 nm Al2O3 layer between the electrode and the substrate. The results showed that the composite electrodes could withstand a maximum operating temperature up to 1600 degrees C in air. The electrodes maintained excellent stability even after five cyclic thermal treatments at temperatures up to 1200 degrees C for one hour, and good stability after two cyclic thermal treatments up to 1400 degrees C for 1 h. The SAW devices based on AlN single-crystal piezoelectric film using the composite electrodes showed good stability at 1200 degrees C for 1 h.