Understanding and Control of Compressively Buckled Semiconductor Thin Films

We report the controllable buckling of free-standing thin-film semiconductor metamaterials using a thin-walled structure spanning Au grid supports. The buckling is developed by compressing the Au grids, increasing the internal air pressure during the bonding of Au pads on the semiconductor to the grids, resulting in upward deformation. The stiffness of the free-standing semiconductor beam is controlled by the grid line spacing, as verified for a wide range of out-of-plane deformations, ranging from nearly flat to microns for grid line spacings from 20 to 150 μm, respectively. We also observe telephone-cord and domelike buckling as the grid line spacings and layer thicknesses are varied. Finite element analysis quantitatively predicts the shape and magnitude of the film deflection. We propose strategies to apply the distorted free-standing metamaterials for thermal energy harvesting, optical reflectors, and pressure sensors.