Static and electrically actuated shaped MEMS mirrors

Fabrication limitations have forced MEMS mirror designers to employ flat mirrors for free-space optical switch applications. Curved mirrors have been avoided because it has been very hard to fabricate and to reliably reproduce their shape. In general, it would be preferable to have mirrors with analog-tunable radius of curvature or digitally-switchable flat/curved mirrors for many applications. Analog tuning would allow adaptive adjustment of the radius to a desired value. Digital tuning would allow mirrors to be flat in the highly-aligned on-state but curved in the off-state to maximally reduce coupling to undesired ports. Other potential applications for curved mirrors include reflectors in ultrasonic imagers and ultrasonic transducers, miniature microphones and speakers, and biomedical devices in human eyes, such as would be used in corneal surgery and man-made retinas.; In this thesis, electrostatically-switchable digital mirrors were designed for on-off operation between the flat on-state and curved off-state. Process development suitable to these actuatable devices was developed and devices were fabricated and tested. Because the high switch voltage is often a limitation for optical switches, an approach based on curved-electrode actuators using the ‘zipping’ effects was pursued to lower the switch voltage.; Reflective static spherical mirrors were designed and fabricated using conventional surface micromachining and the MultiPoly process, a technique for depositing multilayers of LPCVD polysilicon in order to control the overall stress and stress gradient. Axisymmetric curved micromirrors of different sizes (from 300 μm to 1000 μm in diameter) were produced with an 8-layer 5 μm-thick MultiPoly film. The resulting mirrors were measured to have radii of curvature of approximately 9 mm in agreement with design predictions.; Based upon these static mirrors, a novel digitally-actuated shaped micromirror (diameter = 500 μm, static radius of curvature = 6.4 mm) was designed for on-off optical switch applications with a relatively low pull-in voltage. This mirror was simulated using an electromechanical coupled-field model and fabricated using the MultiPoly process. Its performance was measured dynamically using an interferometer. A curved-to-flat digital actuation of the mirror was successfully achieved with a pull-in voltage of 38 V.