Metals and Alloys

Abstract

The continued development of microelectromechanical systems (MEMS) devices is dependent on continued innovation in materials development for application on the micrometer scale. The application of materials other than silicon is required to develop high-performance MEMS devices. Metals and alloys have a wide variety of mechanical properties (elastic modulus, strength, fracture toughness, and fatigue properties) and functional properties (electric and magnetic properties). This indicates that the use of metallic materials is promising to realize MEMS devices with higher performances. For designing MEMS devices, materials selection is important to enable durable MEMS devices, and it is required to know the mechanical properties of freestanding metallic thin films on the micrometer scale. In this chapter, mechanical properties of metallic thin films, which have been and will be used in MEMS devices, will be described. In the past decade, shape-memory alloy (SMA) thin films formed by sputter deposition have attracted considerable attention as a powerful microactuator. Current intensive research demonstrates that superior shape-memory characteristics are achieved in comparison to bulk materials due to unique fine microstructures. Simultaneously, much effort has been undertaken to develop and fabricate microdevices actuated by SMA thin films. This article reviews the research to date on shape-memory behavior and the mechanical properties of SMA thin films in connection with their peculiar microstructures. Promising applications such as microvalves are demonstrated, along with a focused discussion on process-related problems. All of the results indicate that thin-film shape-memory actuators are ready to contribute to the development of MEMS.