Integrated position sensing for control of XY actuator

We present an integrated capacitance based sensor and electronics system for measuring the position of a two axis microelectromechanical (MEMS) stage. Integrated position sensing enables closed-loop operation of the stage, greatly increasing system performance compared to previous micro-stages. The 2 mm square stage is fabricated in a bonded wafer process and is actuated using a bipolar, electrostatic surface drive. Sensor and actuator electrodes are positioned on the bottom of the stage increasing the available moving area of the stage to 50% of the chip size. Individual sensors for each axis and high aspect ratio flexures minimize sensor crosstalk from in-plane motion. The sensor electronics rejects signals from out-of-plane motion of the stage or sensors. The stage is capable of 50 /spl mu/m of travel in each axis with maxima for velocity and acceleration of 40 mm/s and 200 m/s/sup 2/, respectively. Sensor resolution has been measured at 2 /spl Aring/ in a 10 Hz bandwidth, giving the system near part-per-million position resolution.