Overview of thin film shape memory alloy applications

Abstract

Abstract This chapter discusses properties affecting thin film applications and resulting devices that have been developed since sputtered TiNi thin film with shape memory properties was first demonstrated in 1989. As the shape memory alloy technology has matured, the material has gradually gained acceptance. TiNi thin film shape memory alloy (SMA) exhibits intrinsic characteristics similar to bulk nitinol: large stress and strain, long fatigue life, biocompatibility, high resistance to chemical corrosion, and electrical properties that are well matched to joule heating applications. In addition, thin film dissipates heat rapidly so that it can be thermally cycled in milliseconds. These properties make TiNi thin film useful in making microactuators. Microelectromechanical (MEMS) processes – specifically photolithography, chemical etching, and use of sacrificial layers to fabricate complex microstructures – combine TiNi thin film with silicon to provide a versatile platform for fabrication of microdevices. A variety of microdevices have been developed in several laboratories, including valves, pumps, optical and electrical switches and intravascular devices. Interest in thin film applications is increasing as evidenced by the number of recent publications and patents issued. Intravascular medical devices are currently in clinical trials. The future for thin film devices, especially in medical devices, seems assured despite the fact that to this day no “killer application” has emerged. Introduction to TiNi thin film applications This chapter provides an overview of shape memory alloy thin film applications since TiNi thin film, developed with support from a National Aeronautics and Space Administration Small Business Innovation Research contract, was introduced at the Engineering Aspects of Shape Memory Alloy Conference in Lansing, MI in 1989.