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

由于TiNi合金的单位体积形状恢复力远大于其他微致动器材料，有望成为MEMS微致动器的最佳材料。然而，通过机械加工工艺，如球磨、研磨和抛光，很难从块体中生产出薄膜。为了制作具有形状记忆合金薄膜的二维微致动器，采用四个独立的共焦源的射频磁控多重溅射系统和衬底加热的方法在Si衬底上溅射了厚度为1μm的TiNi合金薄膜。在常温下沉积的薄膜通常是非晶态的。然而，当我们适当地选择源电压和靶与衬底之间的距离等溅射参数时，我们发现在773K的衬底温度下沉积的一些薄膜是结晶的。X射线粉末衍射和极图测量表明，这些薄膜具有与衬底成45°平行或倾斜的{110}B2取向。此外，我们还发现，即使在673K的衬底温度下，通过向衬底施加偏置电压也可以沉积结晶薄膜。由于采用直流偏置电压，衬底温度可达673K以上，因此采用脉冲电源施加偏置电压。为了在673K的低衬底温度下实现沉积薄膜的晶化，我们经验地确定了1 kHz的脉冲重复频率。为了产生用于辐照薄膜的离子，在靶材和衬底之间安装了电感耦合线圈。感应耦合等离子体是由与溅射源无关的射频功率产生的。在-300V的脉冲电压下，确认了晶体的结晶。结果表明，离子辐照可以诱导沉积的TiNi薄膜晶化。

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.