HVEM of crystallization of amorphous TiNi shape memory films

Abstract

TiNi alloys, well-known for their shape memory properties that arise due to a martensitic transformation, have recently been considered for application as thin film actuators. Although various methods of thin film preparation have been considered, deposition via d.c. magnetron ion sputtering provides for reproducible film formation as well as possible integration of a TiNi film as a micromachine with a semiconductor device. When sputter deposited at room temperature, the as-deposited films have an amorphous structure. These films can be bent into a particular macroscopic shape prior to crystallization, thereby setting the parent (memory) shape. When used as thin film actuators, TiNi shape memory alloys are quite cost efficient, as compared to the prohibitive manufacturing costs typical when producing bulk shape memory devices. In addition, thin film shape memory devices may be cooled much more quickly than a bulk part, and reversible transformation cycles are achieved in only milliseconds. Applications being considered for these shape memory thin films are as microactuators in optical storage devices and as microvalves in portable gas chromatographs.