Micromachined mirrors in a raster scanning display system

This paper describes a 2D raster scanning system incorporating two surface-micromachined mirrors fabricated on separate chips: a fast mirror for horizontal and a slow mirror for vertical scanning. The mirrors are tilted out-of-plane on polysilicon hinges and are connected to their supporting frames with torsional polysilicon beams. The tilt-up mirror design accommodates large mirror areas and allows integration of optical components on the same chip. Prior work on tilt-up micromirrors has demonstrated the feasibility of resonant mirrors for 1-D barcode scanning. The raster scanning mirrors are nearly circular, measuring 565 /spl mu/m along the scan axis and 500 /spl mu/m along the perpendicular axis. The mirror surfaces are linked to comb drive actuators, and both have a resonant frequency of 4.54 kHz. The measured optical scan angle of the fast mirror is 5.3/spl deg/ when operated at resonance, driven with a 116 Vpp sine wave and zero DC offset. The scan axis of the fast mirror is oriented perpendicular to the slow mirror. The slow mirror is identical to the fast mirror, except bidirectional comb drives allow it to be driven in opposing directions. Triangular voltage waveforms at 167 Vpp rotate the mirror, deflecting the optical beam through 5.7/spl deg/. The slow mirror governs the image refresh rate.