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

Abstract

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 μm 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 ≈19 μm along each axis for the positioner, which corresponds to 66 μm travel in the sense combs. Using an external parallel inductor, a positioning displacement of 9.6 μm offers a shift of 240 kHz in L–C resonance, corresponding to a sensitivity of 25 Hz nm−1.