Development of an optical waveguide cantilever scanner
Design, fabrication, and testing of a micromachined cantilever beam that is optically transmissive and mechanically resonant is presented with application as a micro-optical scanner. An optical waveguide is formed from a 2.2μm 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 technique, a cavity is back-etched in the silicon to release the 30-40μm thick and 0.5-1.5 mm long cantilevers from the wafer. An etch rate of 2.0-2.2μm/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 16-52 kHz with response amplitudes ranging from 80 to 420 mm. Optical throughput is visible, but greatly diminished 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 may be used for image acquisition and display.
This paper was published in SPIE Proceedings Vol. 4876