J. Foltz, D. S. Grummon, Y. Zhang, Michigan State University, East Lansing, MI
While much attention has been paid to shape-memory thin films for actuators in silicon-based micromachines, less thought has been given to the potential for sputtered films to replace wires in more macroscopic applications. The cross-sectional area of a 2.5 mm wide by 5-micron thick sputtered film is the same as that of an .005-inch diameter wire, but the film has a 10-fold advantage in surface-to-volume ratio. It therefore has much better heat transfer characteristics, and the form-factor offers a broad and flat surface for mechanical and electrical attachment. In this paper we show how sputtered thin-film actuator materials can be made in large quantity, and at low cost, through the use of thin polyimide substrates. Furthermore we have developed a method to cold-deform large sheets of these materials, in uniaxial and/or unbalanced biaxial tension. This discovery has several important implications for thin-film actuators: First, cold-deformation of the austenite will permit the development of very high strength as well as the favorable crystallographic textures found in conventional wrought SMAs. Secondly, cold-deformation of the martensite will allow production of “pre-programmed” shape-memory elements that will be easy to integrate with other mechanisms, and which need not rely on additional mechanical elements for biasing. This suggests a very wide range of potential applications, from low-cost discrete linear or planar multiaxial actuators, to highly functional “smart-membrane” materials.
Summary: This paper describes fabrication methods and applications of pre-deformed NiTi thin films on polyimide substrates for low-cost actuators and functional membranes