A new micro SMA thin film actuator prestrained by polyimide

Micro SMA (shape memory alloy) thin film is a good material for a microactuator of a micromachine on silicone wafer, because of it merits: i) low driving voltage, ii) big force per volume and weight, iii) faster response compared to bulk SMA actuator. However there is a problem in fabricating micro SMA thin film actuator on silicone wafer; that is, how to prestrain automatically. We propose to use polyimide that shrinks to about one-half of the original size following heat treatment as a material to prestrain SMA thin films. Trial productions of bending type SMA thin film actuators were made. This actuator curls at room temperature and becomes straight at a high temperature of about 80/spl deg/C.