Dual-axis capacitive sensing for a 2D electrostatic comb-drive micromirror with polymer-filled isolation trenches

This paper proposes a dual-axis capacitive sensing design to synchronously obtain the amplitude and phase information of the two-axis scanning angles of a two-dimensional (2D) comb-drive micromirror for close loop control. The design uses an electromechanical amplitude modulation method with the driving combs directly used for capacitive sensing. Two carrier signals with two different high frequencies are used to extract the capacitance variations of the slow-axis and fast-axis comb-drive actuators in real time. In the driving and sensing circuit design, the drive signal coupling and feedthrough interference caused by the substrate parasitic capacitance are particularly considered. The micromirror under study has a 1 mm × 2 mm elliptical mirror plate and can scan a 2D field of view (FOV) of 30° by 40° with the electrical isolation provided by polymer filling trenches. Experimental results show that the FOV and phase detection accuracy of the slow axis are 1.4 mrad and 1°, respectively, and those of the fast axis are 1.6 mrad and 0.28°, respectively. The proposed capacitive detection scheme can accurately reconstruct the scanning trajectory of the 2D electrostatic micromirror by tracking the phase and FOV information.