Study of tantalum and iridium as adhesion layers for Pt/LGS high temperature SAW devices

TL;DR

This study investigates tantalum and iridium as adhesion layers for platinum electrodes in high-temperature LGS-based SAW devices, highlighting tantalum's superior adhesion and device longevity at 1000°C.

Contribution

It demonstrates tantalum's better adhesion properties and device lifetime compared to iridium and explores the intrinsic limitations of platinum films at high temperatures.

Findings

Tantalum provides stronger adhesion than iridium.

Device lifetime at 1000°C is limited by platinum film deterioration.

Platinum film degradation is intrinsic, regardless of adhesion layer.

Abstract

In this paper, we report on the use of tantalum and iridium as adhesion layers for platinum electrodes used in high temperature SAW devices based on langasite substrates (LGS). Unlike iridium, tantalum exhibits a great adhesive strength, and a very low mobility through the Pt film, ensuring a device lifetime of at least half an hour at 1000{\textdegree}C. The latter is limited by morphological modifications of platinum, starting by the apparition of crystallites on the surface, and followed by important terracing and breaking of the film continuity. SNMS and XRD measurements allowed us to show that these phenomena are likely intrinsic to platinum film, whatever be the nature of the adhesion layer. Finally, after having outlined a possible scenario leading to this deterioration, we consider some solutions that could replace platinum in order to increase the lifetime of LGS-based SAW devices in high temperatures conditions.