Novel piezoelectric actuation mechanism for a gimbal-less mirror in 2D raster scanning applications

In this paper, we present the design, fabrication and measurement results of a 2D scanning mirror actuated by 1 x 10 piezoelectric Pb(Zr, Ti)O-3 (PZT) cantilever actuators integrated on a thin silicon beam. A combination of bulk silicon micromachining based on a silicon-on-insulator (SOI) substrate and thin-film surface micromachining on a 5 mu m thick Si device layer is used to fabricate the device. Multi-layers of Pt/Ti/PZT/Pt/Ti are deposited as electrode materials. A large silicon mirror plate (5 mm x 5 mm) and a 1 x 10 PZT cantilever array arranged in parallel are formed after the backside release process. The ten PZT cantilever actuators are electrically isolated from one another. The device can operate in three modes: bending, torsional and mixed (or combinational) modes. In bending mode, the first resonant frequency was measured to be 30 Hz and an optical deflection angle of +/- 8 degrees was obtained when all ten cantilevers were actuated at 9 V-pp. In torsional mode, the resonant frequency was measured to be 89 Hz and an optical deflection angle of +/- 4.6 degrees was obtained by applying a gradually declining ac voltage started at 8 V-pp to two sets of actuators, where each set comprises five cantilever actuators of the said 1 x 10 array, i.e. 1-5 and 6-10. A 2D raster scanning pattern was achieved in the mixed mode when the bending mode was carried out by cantilever actuators of 4-7 and the torsional modes were exercised by two different sets of cantilever actuators, i.e. 1-3 and 8-10, under opposite biasing direction. This mixed mode operation mechanism demonstrates the first 2D raster scanning mirror-driven beam actuators.