Fabrication of vertical digital silicon optical micromirrors on suspended electrode for guided-wave optical switching applications

This paper presents a novel technological and design study of optical guided-wave MicroElectroMechanical Systems (MEMS) switch. We work on a concept of hermetic assembly in which a MEMS wafer is covered (top-down) by a crossing optical waveguide wafer. The mirrors are designed to be pulled up and inserted at waveguide intersection for N × N optical switching. Vertical micromirrors have been fabricated in SU8 photopolymer or in single crystalline silicon (on SOI substrate). The SU8 mirrors, coated with gold layer, exhibit vertical and smooth sidewalls that will be sufficient for optical use. For integration of silicon mirrors, we have developed a new simple two-step deep reactive ion etching (DRIE) pattern transfer that allow simultaneous fabrication of good quality silicon mirrors (20 μm height and 2 μm thickness) and of recessed mechanical platform (5 μm thick). The platform has been analysed through its resonance behaviour. The strong effect of mechanical non-linearity which is observed in clamped suspension can be exploited to increase the control range of the electrostatic actuator.