Browsing by Author "Morgan, Brian C."
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Item Development and Optimization of Integrative MEMS-Based Gray-Scale Technology In Silicon For Power MEMS Applications(2004) Ghodssi, Reza; Waits, Christopher M.; Morgan, Brian C.; Ghodssi, Reza; ISRAs the field of micro-electro-mechanical systems (MEMS) has diversified, a growing number of applications are limited by the current planar technology available for fabrication. Gray-scale technology offers a method of fabricating 3-D structures in MEMS utilizing a single lithography step. Before gray-scale technology can be accepted as a universal/standard fabrication technique, methods for controlling the silicon profiles and integrating the necessary process steps must be developed. Here, an optical mask design method is outlined by which an arbitrary profile may be defined in a photoresist film, and a study is presented regarding the control of etch selectivity during deep reactive ion etching (DRIE). These results are then used to develop large controlled gradient silicon structures for the MIT micro-engine device that may be integrated into an existing process flow.Item Development of a Deep Silicon Phase Fresnel Lens Using Grayscale Lithography and Deep Reactive Ion Etching(2004) Morgan, Brian C.; Ghodssi, Professor Reza; ISRA phase Fresnel lens (PFL) could achieve higher sensitivity and angular resolution in astronomical observations than the current generation of gamma and hard x-ray instruments. For ground tests of a PFL system, silicon lenses must be fabricated on the micro-scale with controlled profiles to enable high lens efficiency. Thus, two MEMS-based technologies, gray-scale lithography and deep reactive ion etching (DRIE), are extended to create multiple controlled step heights in silicon on the necessary scale. A Gaussian approximation is introduced as a method of predicting a photoresist gray level height given the amount of transmitted light through a gray-scale optical mask. Etch selectivity during DRIE is then accurately controlled by introducing an oxygen-only step to a standard Bosch cycle to produce the desired scaling factor between the photoresist and silicon profiles. Finally, a profile evaluation method is developed to calculate the expected efficiency of measured silicon profiles. Calculated efficiencies above 87% have been achieved.