This study aims to develop a new fabrication process to create high-precision patterned shape memory alloy (SMA) bimorph micro-actuators by the e-beam evaporation technique. To examine the effect of the annealing process on nitinol (NiTi) thin film characteristics, the as-deposited and annealed NiTi thin films are, respectively, investigated. X-ray diffraction (XRD) results demonstrate the crystallization of NiTi thin films after annealing at 600 °C. The transformation behaviors of NiTi thin films during heating and cooling are studied using the differential scanning calorimeter (DSC). Furthermore, scanning electron microscopy (SEM) images indicate that SMA bimorph micro-actuators with high-precision features can be fabricated by the lift-off process, without any wet or dry etching procedures, and their thermomechanical behaviors are experimentally verified by comparing them with that of finite element analysis simulation results.

Lightweight microstructures with high area-to-mass ratios, or low surface densities, show great potential applications in microrobots, soft electronics, medical devices, and solar sailing. However, the bending stiffness of such microstructures is usually too low to work effectively. In order to obtain active microstructures with enhanced bending stiffness, a new design for thermally actuated multilayered metallic microstructures with high area-to-mass ratios is presented in this article. The microstructures made of aluminum and NiTi alloy are fabricated to demonstrate the feasibility of vertical deployment of such microstructures under thermal actuation. The concept design and working principle of designed multilayered metallic microstructures are based on symmetrical deposition of metals Al\NiTi\NiTi\Al, followed by practical microfabrication processes, such as photolithography, physical vapor deposition (PVD), and dry etch. The area-to-mass ratios of such microstructures could be up to 400 m2/kg. Then, experiments for electrical characterization are set up for thermal actuation or Joule heating. Besides that, the equivalent resistances of such microstructures with regard to temperatures are calibrated, allowing for the determination of in situ temperatures of deformed microstructures when being heated in the vacuum chamber of scanning electron microscope (SEM). Finally, vertical deployment of such thin microstructures is detected and measured, which validates the feasibility of stiffness enhancement through the symmetrical design and thermal actuation.