Characterization of TiAl alloy films for potential application in MEMS bimorph actuators

In this letter, we demonstrate the feasibility of applying TiAl alloy film for the fabrication of bimorph actuators. The TiAl alloy films were prepared by thermal annealing at 400°C of Ti/Al multilayers, which were deposited by DC magnetron sputtering from Ti and Al targets. The microstructure and surface morphology of TiAl alloy films were analyzed by X-ray diffraction and scanning electron microscopy, which showed that TiAl alloy film is formed in the mixed phases of TiAl₃ and Ti₃₆Al₆₄, depending on the deposition conditions. The resistivity of TiAl film is about 9 μΩ cm, and the stress is about 200 MPa. Our nano-indentation measurements showed that the Young's modulus and hardness of TiAl alloy films are 175 and 6.5 GPa, respectively, which are larger than that of Al and comparable to Si. We have successfully fabricated the bimorph actuators based on the TiAl alloy films and our test cantilevers up to 500 μm long showed very straight with tip bending as small as ±5 μm, indicating negligible stress gradient in TiAl film. Our preliminary testing results indicated that TiAl alloy film has potential application for bimorph actuators.