Improved Electrical and Mechanical Properties of Niti/TiOx/PZT/TiOx Thin Film Heterostructures

Nickel-titanium (NiTi) alloys are high-performance shape memory alloy actuator materials [1]. These alloys are metals possessing a memory, which can be triggered thermally or mechanically. Thin film of nickel-titanium shape memory alloy (SMA) is an excellent candidate for micro electric mechanical systems (MEMS). On the other hand, PZT is well known for its superior ferroelectric, dielectric and piezoelectric properties [2]. Integrating a ferroelectric (PZT) with ferroelastic (NiTi) material is technically interesting as the resulting heterostructure may then produce the properties associated with both of the materials and enhances the performance of MEMS based devices [3]. An important issue in the synthesis of NiTi/PZT hybrid heterostructure is the formation of appropriate crystalline phases of each material. The interdiffusions present at the interface of NiTi and PZT layer makes it difficult to obtain the optimal properties of both the components suitably at lower thickness values. With the miniaturization of active thin film devices, particularly for MEMS applications, it is desirable to obtain the best properties at lower thickness values. Therefore, in the present study, we have tried to lower the thickness of top NiTi films with the help of thin TiOx buffer layer between PZT and NiTi films. As expected, the excellent structural, electrical and mechanical properties of the NiTi/PZT heterostructure were achieved at lower thickness values.