Development of Shape Memory Alloy Films for Micro-Actuator - Various Characteristics by Using Ion Beam Modification -

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TiNi alloy is expected to be promising the best material for micro actuators in MEMS, because the shape recovery force per the volume is much larger than that of the other actuator materials. However, it is very hard to product thin films from the bulk by machining processes, e. g., milling, grinding and polishing. In order to fabricate two-dimensional micro actuators with shape memory alloy films, TiNi alloy films of 1 μm in thickness are sputter-deposited on Si(001) substrates by RF magnetron multi-sputtering system equipped with four separate confocal sources as well as with substrate heating. The films deposited at ambient temperature have been generally amorphous. However, we find that some films which are deposited at 773K of substrate temperature are crystalline, when we appropriately choose sputtering parameters such as source voltage and the distance between a target and the substrate. X-ray powder diffraction and pole figure measurements reveal that these films are oriented with {110}B2 parallel or inclined at 45 degree to the substrate. Furthermore, we also find that crystallized film is deposited even at 673K of substrate temperature by applying bias voltage to the substrate. The bias voltage was applied by using the pulse power supply, because the substrate temperature would be heated up to over 673K if we had used DC bias voltage. In order to realize the crystallization of deposited film at low substrate temperature of 673K, we empirically determined the pulse repetition frequency of 1 kHz. In order to generate ions for irradiating the film, inductively coupled coil was installed between target and substrate. The inductively coupled plasma was generated by RF power that was independent of sputter sources. The crystallization is confirmed at -300 V of the pulse voltage. In the results, the ion irradiation can induce crystallization of deposited TiNi films.