Vertical Deployment of Multilayered Metallic Microstructures With High Area-to-Mass Ratios by Thermal Actuation

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.