Structuring of sputtered superelastic NiTi thin films by photolithography and etching

The binary Ni-49 at.% Ti shape memory alloy was sputter deposited on micro-machined oxidized Si(1 0 0) substrates. Typical deposition rates of 13 μm/h at a deposition temperature of 450 °C allowed the fabrication of thick films which can be removed mechanically from the substrate. A remarkable high mechanical stability was achieved in these films revealing an ultimate tensile strength of 1180 MPa at a maximum strain of 11.5%. At 36 °C, superelastic properties were demonstrated showing a closed-loop hysteresis in tensile testing with 6% superelastic strain. Photolithography and etching technology were applied in order to fabricate planar thin film devices. Achievable structure sizes range in the order of the NiTi film thickness, i.e. typically between 5 and 15 μm.