An electrostatic scanning micromirror with diaphragm mirror plate and diamond-shaped reinforcement frame

We present the design, fabrication and measurement results of a comb-driven electrostatic scanning micromirror. Instead of a conventional micromirror having uniform thickness across the entire reflective surface, a diaphragm mirror plate supported by an array of diamond-shaped frame structures is fabricated monolithically. The fabrication process is a simple sequence of silicon deep etch processes on both sides of the silicon-on-insulator (SOI) substrate without the substrate bonding process. The micromirror is fabricated on the device layer of the substrate. The mirror plate undergoes a rotational motion by an electrostatic force between the movable comb electrodes connected to the micromirror and stationary comb electrode formed on the handle wafer. A scanning micromirror with a 10 µm thick diaphragm mirror plate, having a planar dimension of 1.5 × 1.5 mm2, supported by an array of 110 µm thick rhombic support frames, was fabricated and tested. A mechanical deflection angle of 8.5° at a resonance frequency of 19.55 kHz and a pressure of 7 mTorr was obtained. A prototype of the raster scanning laser projection display system was developed using the fabricated micromirror as the horizontal scanner and a galvanomirror as the vertical scanner, respectively.