Design of a tunable resonant micromirror

Abstract

This paper presents the concept, theoretical analysis, microfabrication processes and experimental characterization of a micromirror with tunable resonant frequency. For scanning applications where a large scanning angle is required, comb-drive based micromirrors are typically operated at resonance due to the limited force/energy density of electrostatic actuators. However, errors in microfabrication processes often cause natural frequencies to offset from the design value. This issue may be resolved by a frequency-tunable micromirror. In our design, the shifting of the resonant frequency is achieved by adjusting the axial stress of the micromirror's torsion hinge via integrated chevron thermomechanical actuators. The scanning motion of the micromirror is generated by double silicon-on-insulator (SOI) wafer-based electrostatic comb-drive actuators. The experimental results show that the micromirror has achieved a frequency tuning range of approximately 3%, which is close to the analytic model. With precise frequency control, the micromirror may compensate the undesired frequency shift due to fabrication errors, which is useful for applications requiring precise scanning synchronization such as the laser scanning endomicroscope systems.