The effects of process-induced stress on the microstructures and the phase transformation characteristics of sputtered titanium-nickel thin-film shape-memory alloys

Abstract

The microstructures and the phase transformation temperatures of sputtered titanium-nickel (TiNi) thin films, both free-standing and attached on different underlying multi-layer substrates, have been studied. Differences in the microstructures, such as the lattice constants and relative concentrations of TiNi, Ti 2 Ni and TiNi 3 phases, have been observed among the free-standing and the attached films, among the films attached on different underlying multi-layers and among the films with different relative orders of ageing and release. Not surprisingly, the corresponding phase transformation temperatures are also different. It is proposed that both process-and substrate-induced stresses affect the microstructures, hence the phase transformation characteristics, of the resulting shape-memory thin films.

Effects of deposition and annealing conditions on the crystallisation of NiTi thin films by e‐beam evaporation

“…When the temperature of NiTi thin film drops below , all of the crystal structures of NiTi will be monoclinic structures (martensite B19′). The DSC results of A s , A f , M s , and M f are in agreement with the reported values of Ni‐rich NiTi thin films deposited by other methods [4, 24, 27]. The results shown in Fig.…”

Residual stress-loaded titanium$ndash$nickel shape-memory alloy thin-film micro-actuators

“…levels. This is consistent with the dependence of stress on d [2,3,12,14,16,17]. When d is small, the necks of beams B L and B R will significantly overlap with that of beam B C .…”

“…Finally, the Cr and poly-Si sacrificial layers were removed and the actuation structures released ( figure 2(c)). Subsequently, the devices were crystallized at 750 • C for 30 min and aged [2,3,9,14] at 500 • C for 100 h in a 0.44 µTorr vacuum. The displacement of the micro-tweezers was measured using an optical microscope at a magnification of 1000×.…”

Thin film shape memory alloys and microactuators

“…The force and displacement generated can be very large. Another gripper design is in-plane mode, in which the deformation of two arms (using free-standing TiNi films or TiNi/Si beams) is within a plane realised by compliant structure design (Wang et al, 2002). The problems associated with this design include: small force generated and out-of-plane bending caused by intrinsic film stress.…”