Batch-micromachined, high aspect ratio Si mirror arrays for optical switching applications

Arrays of bulk micromachined, high aspect ratio vertical Si mirrors were designed, fabricated, and characterized for optical switching applications. These 50 μm tall vertical mirrors were fabricated by the deep etch-shallow diffusion process. This is accomplished by first dry etching Si microstructures using an electron cyclotron resonance source, followed by a shallow B diffusion to fully convert the etched microstructures to p⁺⁺ layer. A second dry etching step was then used to remove the thin p⁺⁺ layer around the bottom of the resonant elements, followed by bonding to glass and selective wet etch. The roughness on the sidewall surface of these vertical mirrors was minimized by using optimized lithography and etch conditions, as well as by diffusion and oxidation of the Si surface. The released Si mirrors have only 5 nm surface roughness along the sidewalls, indicating these mirrors are suitable for optical applications. Electrostatic comb drive was applied to actuate the mirrors supported by folded and serpentine beams. For 800 μm long, 3 μm wide, and 50 μm thick folded suspension beams, a lateral mirror movement of 34 μm was achieved by a driving voltage of 30 V. Resonant frequency of 987 Hz was obtained for similar devices at atmospheric pressure.