A micromachined 2D positioner with electrothermal actuation and sub-nanometer capacitive sensing

This paper reports on a multi-purpose two-axis micropositioner with sub-nanometer position sensing for precise feedback control. Along each axis it has an electrothermal actuator, a capacitive position sensor and a displacement amplifier that provides a gain of 3.37 for the sensor. It is fabricated from custom SOI wafers using dry etching, and each component is electrically and thermally isolated by silicon nitride. For a fabricated device of 65 Am thickness, the measured displacement sensitivity is 0.333 fF nm(-1), which corresponds to 0.3 nm resolution with available laboratory instrumentation. The range is approximate to19 mum along each axis for the positioner, which corresponds to 66 mum travel in the sense combs. Using an external parallel inductor, a positioning displacement of 9.6 mum offers a shift 1 of 240 kHz in L-C resonance, corresponding to a sensitivity of 25 Hz nm(-1).