Single-Crystal PMN-PT MEMS Deformable Mirrors

This paper describes microelectromechanical systems deformable mirrors (DMs) fabricated from Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃ single crystal (PMN-PT) for use in ocular adaptive optics. The DM is a piezoelectric unimorph with 35 actuators on a 13-mm circular membrane. Each actuator inside the 8-mm pupil achieves a static stroke of over 5 μm at 10 V. Dynamic measurements prove that the DM can be operated up to a 2.27-kHz bandwidth. The large stroke with low driving voltage and high operating bandwidth confirm that the DM is a promising candidate for use as a wavefront corrector in vision science applications. The measured piezoelectric properties of the PMN-PT are in close agreement with factory specifications, demonstrating that the piezoelectric properties of single-crystal PMN-PT are not degraded by the bonding and lapping process used here. The large 13-mm-diameter 30-μm-thick membrane is produced by constructing silicon rings to protect the membrane from the considerable compressive stress present in the SiO₂ layer of a silicon-on-insulator wafer. In the prototype mirror, residual stress in the electrode metal results in an initial peak-to-valley surface flatness of 3.3 μm which is reduced to 0.7 μm by iterative computation of the control voltages applied to the electrodes.