Flash evaporation of TiNi shape memory thin film for microactuators

Abstract

The flash evaporation, with which material for deposition is repeatedly evaporated in very small volumes, was investigated for formation of TiNi shape memory alloy thin film. Along with the flash method itself, the timing for opening the shutter proved a crucial factor in controlling thin film composition. Using our evaporation system, a thin film with a composition of around 50 at.% Ti-50 at.% Ni was obtained with an interval of about 5 s between the beginning of material evaporation and opening of the shutter. The deposited thin film had a lamella structure, corresponding to repeated deposition cycles, and showed small fluctuations in alloy composition in each deposition cycle. However, these effects on its shape memory properties could be considered tolerable. The deposited thin film showed martensitic (monoclinic structure) and reverse martensitic (B2 parent structure) transformation during cooling and heating cycles, respectively. In particular, thin film with a composition of 45–50 at.% Ni showed martensitic transformation at near room temperature and reverse martensitic transformation at about 70°C. This means that such thin film could be used as material for microactuators driven at room temperature without requiring any special cooling device.