Resonant Inductive Coupling-Based Piston Position Sensing Mechanism for Large Vertical Displacement Micromirrors

Abstract

This paper serves to demonstrate resonant inductive coupling-based eddy current sensing as a promising piston position sensing mechanism for large vertical displacement micromirrors that exhibit piston scan ranges above 100 μm. The sensor consists of two microfabricated coils packaged underneath the mirror plate of an electrothermally actuated piston scanning micromirror. For this paper, position sensing is achieved through the amplitude detection of the sensor oscillation signal due to the change in inductive coupling between the coils when the mirror plate undergoes its piston scan. Two sensing regions could be obtained: a front slope region that has a larger piston sensing range of 1 mm with a 280-nm resolution and a back slope region that has higher sensitivity over a smaller piston sensing range of ~130 μm with a 20-nm resolution. For demonstration purpose, the sensing coils are designed to oscillate at 9.4 MHz through a regenerative circuit and a readout circuit was used to extract the piston position information, with which the static, dynamic, and frequency response of the micromirror were measured. This paper also presents the fundamental electromagnetic analytical modeling for the sensor performance.