Biaxial scanning mirror activated by bimorph structures for medical applications

Abstract We present here a micromachined scanning mirror as part of a keratotomy system which should be small enough to be set directly on the eye ball and thus follow its movement. The bimorph actuation type used here has the advantage of IC-compatible fabrication steps, high mechanical stiffness and a force independent of position. Beam and plate combinations of various sizes were fabricated to check the basic behaviour. The biaxial elements consist of a mirror plate and at least two independent actuators. The technological challenge of this device was to obtain a relatively thin silicon beam covered by a relatively thick aluminium layer. Doping of the silicon reduces the resistance and allows a guided current path, which is needed to drive the multiple actuator devices correctly. The insulation diodes show leakage currents of about 100 nA at 20 V. The dynamic range rises at least to 50 Hz which is sufficient for this device.