Design, fabrication and test of a micromirror actuator for integrated optical microswitch applications

Abstract

This thesis investigates a waveguide-based optical microswitch for integrated optical transceiver applications. The microswitch is composed of rib-type silicon waveguides, gold-coated silicon micromirrors and an electrostatic curved electrode microactuators, all fabricated on an SOI wafer using ICP RIE process. The rib-type silicon wavguide supports single mode propagation. The half-field widths in the waveguide are measured as $w_x=2.76±0.01㎛$ and $w_y=1.90±0.01 ㎛$, respectively. To improve the surface roughenss of the micromirrors, we oxidize the etched side-wall and remove the silicon oxide. The micromirror loss is measured as 4.18±0.25dB. The major portion of the micromirror loss comes from the limited mirror height and the misalignment between the waveguide and the micromirror. On this basis, we present design guidelines for a low loss micromirror. We also propose and electrostatic beam microactuator for low voltage micromirror switching. The microactuator reduces inter-electrode gaps using the beam electrodes insulated by silicon nitride film. Thus the direct electrode contact of the present microactuator reduces the driving voltage to 22.6±3.2% of that of the uninsulated separated electrode design. The switching voltage can be reduced to 10 volts for a reduced residual stress of 30 MPa in the silicon nitride film.