Micromachined optical waveguide cantilever as a resonant optical scanner

Design, fabrication, and testing of a micromachined cantilever beam that is optically transmissive and operates in the resonant mode is presented with application as a micro-optical scanner. An optical waveguide is formed from a 2.2 mum thick SiO2 layer deposited on a single crystal silicon wafer and etched to yield a SiO2/Si composite slab cantilever. Using a novel capacitively coupled reactive ion etching (RIE) technique, a cavity is back-etched in the silicon to release the 30-40 mum thick and 0.5-1.5 mm long cantilevers from the wafer. An etch rate of 2.0-2.2 mum/min in Si, an anisotropy of 0.5 and selectivity to thermal oxide (Si:SiO2 = 10:1) and to photoresist (Si:+PR = 8.6:1) are reported. Evaporated aluminum film is used as a passivation material. Optical and mechanical tests are performed on these microfabricated structures. The first mode resonances are found between 16 and 52 kHz with response amplitudes ranging from 62.5 to 420 mum. Optical throughput was estimated at 10 nW, but this was greatly diminshed due to scattering losses, primarily at the edges of the waveguide. Since cantilever waveguides with resonant frequencies above 20 kHz are potentially suitable for video rate scanning, these devices maybe used for image acquisition and display. (C) 2002 Elsevier Science B.V. All rights reserved.