Development of an optical waveguide cantilever scanner

Abstract

The work is devoted to 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. The building block of the suspended waveguide comprses a 2.2 μm thick SiO2 layer on a 30μm thick single crystal silicon beam. Using a novel capacitively-coupled reactive ion etching technique, a cavity is back-etched in the silicon to release the 30-40 μm thick and 0.5-1.5 mm long cantilevers from the wafer. An etch rate of 2.0-2.2 μm/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 62.5 to 420 μm. Optical throughput was estimated at 10 nW, but this was greatly diminshed due to scattering losses, primarily at the edges of the waveguide. A 100μm wide one dimension scanning pattern has been realized. 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.