Monolithically integrated out-of-plane micro-mirror

Abstract

This paper describes the monolithic integration of vertical micro-mirror onto a central portion of a novel micro-bridge without compromising the requirements of bi-stability, bi-directionality, large initial out-of-plane deflection and low operational voltage for optical switching application. Analytical models describing initial out-of-plane deflection and bi-stability of the micro-bridge have been modified to include the integration of a micro-mirror. Theoretical formulations to estimate the resonance frequencies of the micro-bridge and its integration with micro-mirror have also been presented. The theoretical results have been substantiated by ANSYS simulations. TMAH anisotropic wet-etch of (110) silicon substrate has been used to realize the vertical micro-mirror with the aid of convex corner compensation features in the mask design. Experiments on anisotropic TMAH etch have been carried out to establish a relationship between the sizes of convex corner compensation features and etched depth. Based on the analytical models and wet anisotropic etch experiments, the micro-mirror actuator was designed, fabricated and tested. An initial out-of-plane deflection of 27μm was obtained. Free space optical path is established by micro-positioning optical fibers on the surface of the wafer in etched grooves to demonstrate the actuation of the micro-mirror, its bi-stability, bi-directionality and measure its optical performances. The micro-mirror is actuated between the ON and OFF positions with switching times of 2.5ms and 1.7ms respectively. It was operated continuously for over 10 million cycles without failure and shows robustness in maintaining its state against vibrations of up to 110g amplitude. The insertion, isolation, and polarization dependent losses of the micro-mirror switch at 633nm were 1.3dB, >60dB, <0.12dB, respectively. Lower insertion loss of 0.9dB was obtained at 1300nm wavelength.