Stress relaxation and creep analysis of high temperature thin film materials on CTGS substrates

了解薄膜在高温下的热机械行为是材料科学的基本兴趣，也是提高现代高温表面声波（SAW）器件工作温度、可靠性和寿命的关键方面。对于叉指换能器的高熔点BCC金属电极中发生的过程缺乏基本知识，特别是对于350 °C以上的高温应用的压电基板，因此这是SAW技术面临的关键挑战。该项目的主要目标是研究溅射沉积的高温稳定的BCC的W和Mo的金属薄膜的Ca 3 TaGa 3Si 2 O 14衬底（Catangasite，CTGS）的热机械行为。CTGS是一种相对较新的具有高热稳定性的压电材料，使其适用于创新的高温SAW温度传感器。然而，没有关于CTGS上的这种薄金属膜的热机械行为的基本研究，这对于理解这种SAW传感器在高温范围内的操作或退化行为是必不可少的。因此，在薄膜生长期间和沉积过程后，将通过基于激光的曲率测量方法（弯曲束）研究薄膜-基底复合材料上的薄膜应力演变以及应力松弛热循环高达约700 °C的温度。由于对这些平均晶粒尺寸< 100 nm的技术上适用的纳米晶材料中可能发生的破坏过程的担忧，计划对微观结构演变及其对膜应力的影响进行详细研究。为此，将通过不同的分析方法，如薄膜X射线衍射，扫描和透射电子显微镜，聚焦离子束技术，原子力显微镜来证实微观结构。研究的重点是从根本上理解和模拟薄膜-基体复合材料中的变形和蠕变过程，这取决于沉积参数或更确切地说是内应力和温度，基于W. D. Nix，E.阿尔兹特角V. Thompson，H.高和其他人。

The understanding of the thermomechanical behaviour of thin films at high temperatures is of fundamental interest in material science and a crucial aspect for improving the operation temperature, reliability and lifetime of modern high-temperature surface acoustic wave (SAW) devices. There is a lack of fundamental knowledge about the processes occurring in high melting BCC metal electrodes for interdigital transducers especially on piezoelectric substrates for high-temperature application above 350 °C and as such is the key challenge faced in SAW technology. The main goal of this project is to study the thermomechanical behaviour of sputter deposited high-temperature-stable metallic thin films of BCC W and Mo on Ca3TaGa3Si2O14-substrates (Catangasite, CTGS). CTGS is a relatively new piezoelectric material of high thermal stability that makes it suitable for innovative high-temperature SAW based temperature sensors. However, there is no fundamental study regarding the thermo-mechanical behaviour of such thin metallic film on CTGS which is essential for understanding the operation or degradation behaviour of such SAW sensors in the high temperature range. For this reason the film stress evolution as well as stress relaxation will be studied on the film-substrate composites by means of a laser-based curvature measuring method (bending-beam) both during the film growth and after the deposition process upon thermal cycling up to a temperature of about 700 °C. A detailed study of the microstructural evolution and its effect on the film stresses is planned owing to concerns regarding damaging processes that can occur in these technologically applicable nanocrystalline materials with average grain size < 100 nm. For this purpose, the microstructure will be corroborated by means of different analytical methods such as thin film X-ray diffraction, scanning and transmission electron microscopy, focussed ion beam technique, atomic force microscopy. The focus of the study is to understand fundamentally and to model the deformation and creep processes in the film-substrate composites in dependence of both deposition parameters or rather intrinsic stress and temperature based on the years of work of W. D. Nix, E. Arzt, C. V. Thompson, H. Gao and others.