Effect of heat treatment temperature on the microstructure and actuation behavior of a Ti–Ni–Cu thin film microactuator

Ti–Ni–Cu/SiO2 two layer diaphragm-type microactuators were fabricated by sputter deposition and micromachining. The influence of heat treatment temperature on the actuation behavior was investigated under quasi-static conditions. The interfacial structure of Ti–Ni–Cu/SiO2 and internal structure of the Ti–Ni–Cu layer were also investigated using transmission electron microscopy. The reaction layer formed between the Ti–Ni–Cu and SiO2 layers, and preferentially grew into the SiO2 side. The reaction layer formed at 1023 K mainly consisted of Ti4(Ni,Cu)2O. The maximum height of the diaphragm decreased with increasing heat treatment temperature. The growth of the reaction layer also affected the microstructure of the Ti–Ni–Cu layer. The density of fine platelets and Ti2Ni precipitates decreased with increasing heat treatment temperature from 873 to 923 K, and they disappeared at 973 K due to the fact that the reaction layer mainly consisted of a Ti-rich phase. The microactuator heat treated at 973 K showed the highest transformation temperature with the lowest transformation temperature hysteresis, which is attractive for high speed actuation.