Statics and Dynamics of Electrothermal Micromirrors
This event is part of the Departmental Seminars.
Dissertation Committee: David Bishop, Tom Little, David Campbell, Shyam Erramilli, John Butler
Modern fabrication techniques are enabling the adoption of microelectromechanical systems (MEMS) devices in commodity applications never anticipated. Low-cost lighting systems can exploit micromirrors both to enable directed or sculpted light and to support short-range optical communications. We have developed a novel MEMS mirror, an SEM image of which is shown in the figure. The mirror fully integrates variable focus and dynamic beam steering providing unique advantages in connected lighting systems.
The fabrication process is fixed by using a commercial foundry process, PolyMUMPs by MEMSCAP, providing a reliable and reproducible system that can be commercialized easily. The mirror uses electrothermal actuation to both steer the light and tune the focal length. Residual stresses in the deposited layers during the fabrication process provide an initial curvature that projects the system from the substrate. The curvature of a bimorph can be tuned using Joule heating. A large electrical and thermal impedance mismatch allows independent heating of the mirror and the bimorph legs.
An in-depth characterization of the dynamics of such a system provides insight into tunable mechanical properties such as the resonant frequency and quality factor. The degenerate resonant modes can be separated significantly. As a result, the system can be scanned at increasingly large angles. In other words, nonlinearities and coupled mechanical modes allow variable damping and amplification.