Deposition and Characterization of NiTi Thin Films On Full Wafer

Shape Memory alloys are often used in actuation applications, having the advantage of producing the highest work-output per unit volume amongst all other actuation methods. Thin films of NiTi SMA have the potential to be integrated into Micro Electrical Mechanical Systems (MEMS) devices since they can be patterned with standard lithography techniques and are compatible with standard MEMS processes.

In this work, we present a comprehensive analysis of NiTi uniformity on 4 inch wafers and investigate the effects of deposition and heat treatment conditions on the resulted properties. After the heat treatment, a repeatable and stable ring patter is observed, in which different NiTi phases appear in different rings on the wafer. We show that this non-uniformity effect is not related to composition changes. Instead, it is attributed to differences in the kinetic energy of the deposited atoms when impacting the surface. In particular, we identify a unique phenomenon of stabilized austenite phase, which is stable on the wafer under a temperature lower by at least 60^oC than the martensitic finish temperature, M_f.

For actuation applications, it is crucial to have a martensite phase at room temperature. Therefore, the effect of different deposition conditions is studied and ways for obtaining a stable martensitic phase at room temperature on all wafer regions are demonstrated.