Thermal-Mechanical Evaluation of Plated Electro-Magnetic NiFe for MEMS Generators

In micro-electro-mechanical system (MEMS) devices that contain multi-layers of metallic, ceramic, and polymeric materials, acquiring a complete understanding of the mechanical properties and interfacial strength are critical in designing the devices. In general, these layered materials are specially fabricated with thickness of each layer on submicron and/or micron scale. Particularly, the properties of these layered materials strongly depend on the fabrication processes and subsequent treatments. In this paper, we study the magnetic metallic films, NiFe (80/20 in weight), for MEMS generator/motor applications. A set of tensile tests was conducted on the plated nickel-iron metallic films of various thicknesses and subjected to various annealing conditions. Distinctive differences in mechanical behaviors between the electroplated films and the corresponding bulk alloys were observed. Furthermore, the NiFe film as-deposited exhibits almost pure elastic deformation and brittle fracture at room temperature; whereas the NiFe film subjected to annealing exhibits strain hardening and ductile fracture when tested at room temperature. X-ray diffraction was used to capture the variation of crystalline structure and the residual stresses in the electroplated films as deposited and after annealing. An atomic force microscope was used to obtain the surface morphology of the films as deposited and after annealing.