TiNi is well known as a typical shape-memory alloy, and is expected to be a promising material for micro actuators. In order to realize micro electro mechanical systems (MEMS) with this material, we have to get thin crystal film of the material, since the shape-memory property appears only when the structure is crystalline. Until recently, the material has been formed as amorphous film by single-target sputtering deposition at first and then crystallized by annealing at high temperature of over 773 K. However, if we try to make the micro actuators on a substrate of low heat resistance such as polymer-based materials, the temperature should be lowered below 473K. In our previous studies [1] we have found that deposited film can be crystallized at very low temperature without annealing but with simultaneous irradiation of Ar ions. We have identified shape-memory effect with the TiNi film made by the new process.

In order to investigate what parameters of the process contribute　to the low-temperature crystallization, we have focused to the ion fluence of the ion irradiation. For correct measurement of the ion fluence, a quadrupole mass spectrometer (QMS) for measuring ion current as well as a double probe for measuring plasma density was utilized. Resultantly, it was found that the transition from amorphous structure to crystal one has a threshold value of ion fluence.

[1] Y. Kishi, N. Ikenaga, N. Sakudo and Z. Yajima, Transforamation Behavior of Low Temperature Crystallized TiNi Shape Memory Alloy Films, published by EDP Sciences, DOI:10.1051/esomat/200902012