Dynamic Properties of Angular Vertical Comb-Drive Scanning Micromirrors With Electrothermally Controlled Variable Offset

This paper presents the investigation of a variable angular vertical comb-drive (AVC) actuated MEMS scanning micromirror, focusing on the influence of the initial comb offset on the dynamic scan characteristics. Continuous control of the fixed comb initial vertical offset is achieved using an electrothermal actuator integrated in the AVC. Electro-thermomechanical simulations and experiments of the AVC structure show good agreement, with the initial vertical offset of the fixed comb reducing theoretically from 10.8 μm (0 mW to actuator) to 6.0 μm (500 mW to actuator) and experimentally from 10.4 μm (0 mW to actuator) to 4.9 μm (510 mW to actuator). Experimentally, a change of the initial vertical comb-offset from 10.4 μm to 4.9 μm leads to a reduction of the measured dynamic total optical scan angle (TOSA) from 27° to 19° for 100 V ac actuation. In addition, a mechanically assisted deflection of the AVC actuators to achieve an almost in-plane comb configuration further reduces the measured dynamic TOSA to about 3°. The overall device behavior is modeled using a hybrid simulation approach combining FEM analysis of the AVC capacitance with an analytical solution of the motion equation of the scanner. The analysis show good agreement, with the experimentally measured characteristics; overall showing an increased TOSA with higher initial comb offsets.