Stabilized Pt Interdigitated Electrodes for High-Temperature SAW Sensors

The standard working temperature of Surface Acoustic Wave (SAW) device does not exceed 150°C, although high-temperature device demand is increasing. Commonly, Interdigitated Transducers (IDTs) for high-temperature SAW devices are fabricated by means of deposition of metal films by evaporation at room temperature and lift-off process. A bunch of different stacks of materials has been tested in order to optimize IDT stability at high-temperature: adhesion layer/noble metals, interlayering oxide/noble metal IDTs, composite with oxide particles incorporated in noble metal, metal alloys (note that a capping layer is also usually used). Such heterostructure implies many structural defects, small grains, and chemical instability which favor agglomeration, recrystallization and interdiffusion during annealing. Our previous work demonstrating a complete elimination of interdiffusion issues by direct growth of Pt IDTs onto Langasite (LGS) without adhesion layer. In this work, the growth of Pt films at high temperature was considered including the development of entire microfabrication process to demonstrate the feasibility of stable pure Pt electrodes.