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Abstract
In this thesis, the development of a novel electro-thermally actuated bi-stable out-of-plane two way actuated buckled micro-bridge for a potential application in optical switching is presented.
The actuator consists of a bridge supported by 'legs' and springs at its four corners. The springs and the bridge are made of a tri-layer structure comprising of 2.5µm thick low-stress PECVD oxide, 1µm thick high-stress PECVD oxide and 2µm thick heavily phosphorus doped silicon. The legs, on the other hand, are 2µm thick single layer heavily phosphorus doped silicon. Both legs and springs provide elastically constrained boundary conditions at the supporting ends, without of which important features of the micro-bridge actuator could not have been achieved. This microbridge actuator is designed, simulated using ANSYS, fabricated and tested. The results from the testing have shown a good agreement with analytical prediction and ANSYS simulation. The actuator demonstrated bi-stability, two-way actuation and 31µm out-of-plane movement between the two-states using low voltage drive. Buckled shape model, design method for bi-stability and thermo-mechanical model are developed and employed in the design of the micro-bridge.
These models are compared with Finite Element (FE) based ANSYS simulation and measurements from the fabricated micro-bridge and have shown a good agreement. In order to demonstrate the potential application of this actuator to optical switching, ANSYS simulation studies have been performed on a micro-mirror integrated with the micro-bridge actuator. From these studies, the optimum micro-mirror size that is appropriate for the integration has been obtained. This optimal mirror size ensures the important features of the actuator. Mirror fabrication experiments in (110) wafer have been carried out to find out the appropriate compensation mask size for a given etch depth and the suitable wafer thickness that can be used to fabricate the integrated system.