NOVEL MEMS ACTUATOR BASED ON METAL-INSULATOR TRANSITION

Rare earth nickelate exhibits a series of fantastic properties based on its abnormal metal-insulator transition (MIT) phenomenon, which has attracted huge concerns from different areas since 1970s. Except for traditional thermally driven method for phase transition materials, electron doping is found to be another effective driving mechanism which origins from the strong correlation of electrons in the $e_g$ orbital of Ni\textsuperscript{2+} cation. Giant changes of resistivity and lattice parameter are observed during the phase transition. Although there is no record of perovskite materials utilized in actuation area, NNO is a strong candidate based on its unique properties such as high induced strain, giant resistivity change, and fast phase transition speed. In this work, the crystal structures and phase transition mechanisms of perovskite nickelates is being discussed, and based on their performance, NdNiO\textsubscript{3} (NNO) is selected to be the core material for MicroElectroMechanical Systems (MEMS) actuators. Synthesis as well as characterization method are also introduced to further understand and utilize its unique properties in actuators. actuators with 3 different layer stack are fabricated and tested. Traditional actuation materials are being discussed in details and are compared with NNO. This study also offers us an opportunity to explore the mechanical properties of perovskite nickelates associated with the phase transition, and their application in MEMS.

Besides, a vertical multilayer VO\textsubscript{2} MEMS actuator is fabricated to understand the vertical structure performance. Equivalent thermal circuit is developed with a thermal response time of 0.39 ms, and COMSOL finite element analysis is performed to determine spatial distribution of current flow and temperature profile, and to verify experimental measurements of strain induced bending in this multilayer vertical structure. The obtained experimental result shows a good fit with simulation analysis, which can in future be utilized to develop a generic understanding of such vertical MEMS devices.