The development of novel, functional, thin films for MEMS applications is becoming increasingly important. In particular, the shape memory effect exhibited by certain metal alloys is a promising candidate for exploitation in micro-scale devices. Combining microelectronic and micromechanical functionality appears to be a real possibility, thus opening up new areas of application.

We report the use of an ion beam sputter deposition (IBSD) process for growth of TiNi shape memory alloy (SMA) thin films and investigate growth of films with near-equiatomic composition. The IBSD process uses argon ions with energies in the range 1000 - 1500 eV produced by a Kaufman-type ion source. Current densities in the range 0.1 - 1 mA cm^-2 allow highly controllable growth conditions to be established with deposition rates controllable within 1 atomic layer s^-1. Non-alloyed targets of high purity titanium and nickel are used. Both sputtering targets and substrates are remote from the discharge plasma and deposition occurs under good vacuum of ~ 10^-6 mtorr thus producing high quality films. Furthermore, the ion beam energetics allow deposition at relatively low substrate temperatures. Typically these are < 150 °C and as-deposited films exhibited shape memory properties without high temperature annealing, which is invariably required in processes such as d.c. or r.f. magnetron deposition. In the latter case, temperatures of 500 - 700 °C are required during annealing which are incompatible with many MEMS fabrication processes.

The SMA films were characterised by electrical, x-ray and thermal measurements. Applications as microactuators and micropositioners, driven under closed loop control by direct Joule heating, in MEMS devices are discussed.