Resonant micro-mirror excited by a thin-film piezoelectric actuator for fast optical beam scanning

A silicon resonant torsional micro-mirror excited by piezoelectric bimorph actuators is presented. The bimorph actuators consist of a single-crystal silicon flexible beam or membrane and a PZT thin film. The mechanical elements are etched in the 20 μm thick superficial layer of a SOI substrate, thereby ensuring the flatness of the 500 μm-diameter gold-coated mirror. This device achieves optical beam scanning with large angular deflection at high frequency. In air, we have measured scanning up to 19.8° at 1.8 kHz, 99.1° at 10.6 kHz and 40.8° at 25.4 kHz. The applied driving voltage is sinusoidal with an amplitude under 42 VPP and with a 6 VDC bias voltage. At large oscillation amplitude, a non-linear hard-spring effect has been observed. In vacuum, a 78° optical scanning has been obtained with less than 1 VPP.