Ion Beam Machining to Eliminate Stress-Induced Curvature in Microelectromechanical Systems (MEMS) Optical Devices

Trustees Of Boston University, Boston

Investigators

Abstract

The objective of this research project is to develop a post-processing technique to planarize curved freestanding thin film microelectromechanical systems (MEMS) devices by means of controlled exposure to a neutral ion beam. The method works by (1) affecting a thin highly stressed layer in the first few seconds of ion beam exposure through atomic rearrangement near the surface of the film; and, (2) removing initially stressed material in the film after several additional minutes of ion beam exposure. These effects can be combined in a controlled way to offset the initial relaxation curvature in the micro-mirror. MEMS micro-mirrors are important components in several next-generation optical communications devices. Freestanding MEMS micro-mirrors are often fabricated in a layer-by-layer process before being released from a host substrate; through-thickness dimensions may be as small as one micron or less. Once these thin structures are released, residual stresses due to processing are relaxed by transverse curvatures large enough to render the devices optically useless. The program includes both theoretical and experimental work. Using analytical and numerical models, the effects of various processing parameters will be studied; experiments will be carried out to test these parameters, and the quality of the resulting planarized mirrors will be characterized.