Material and process development of thin-film shape memory alloy for MEMS actuator

International Conference on Smart Materials & Structures

June 15 -17, 2015 Las Vegas, USA

Cory R Knick and Christopher J Morris

Posters-Accepted Abstracts: J Material Sci Eng

Abstract :

In this work we discuss the design and fabrication of a cantilever that may be actuated by utilizing the martensite to austenite phase transformation of a sputtered thin film of equiatomicNiTi shape memory alloy (SMA). The cantilever devices were fabricated on a silicon wafer using standard micro fabrication techniques, and may therefore be applicable to Micro-Electro- Mechanical Systems (MEMS) switch or actuator applications. This paper details the development of a co-sputtering process to yield a SMA film with controllable composition of Ni50Ti50 and transformation temperature around 60°C. Shape memory effects were characterized using Differential Scanning Calorimetry (DSC), for which we demonstrated martensite-austenite phase change at 57°C for 1-3 μm films, annealed at 600°C. We used wafer stress versus temperature measurements as additional confirmation for the repeatable measurement of reversible phase transformation peaking at 73°C upon heating. Up to 62 MPa was available for actuation during the thermally induced phase change. After exploring multiple approaches to a frontside wafer release process, we were successful in patterning and fabricating freestanding NiTi cantilevers that exhibited out of plane curling upon heating.