Micromachined mirrors

This dissertation discusses the fundamental limits of scanning mirror design, focusing on the limitations due to the interaction between mechanical properties (mirror flatness and dynamic deformation), and optical properties (beam divergence and optical resolution). The performance criteria for both resonant-scanning mirrors and steady-state, beam-positioning mirrors are related to the mirror geometries, desired optical resolution, material properties, and mechanical resonant frequencies. The optical resolution of the scanning mirror is linearly dependent on the mirror length, so longer mirrors should provide higher-resolution scanners. However, when undergoing an angular acceleration mirrors exhibit dynamic deformation, which is shown to be proportional to the fifth power of the length.; Two different implementations of MEMS scanning mirrors are presented: polysilicon surface-micromachined mirrors and a new design we call the Staggered Torsional Electrostatic Combdrive (STEC) micromirror. The surface-micromachined mirrors are shown to be capable of reliable operation, but they have significant performance limitations caused by the limited thickness obtainable with the LPCVD-polysilicon structures. Calculations show that surface-micromachined mirrors of thickness 1.5 μm and diameter 550 μm are only capable of scanning ±10 degrees at 251 Hz while retaining diffraction-limited optical performance.; The STEC micromirrors, designed to overcome the limitations of the surface-micromachined mirrors, are capable of much higher-speed scanning (up to 61 kHz) without performance-limiting dynamic deformation of the mirror surface.; The STEC micromirror fabrication process is extended to create Tensile Optical Surface (TOS) micromirrors—mirrors with thick silicon rib support structures and thin membranes that provide the reflective surface.; An application of scanning mirrors is presented: a raster-scanning video display. This demonstration uses two surface-micromachined mirrors scanning in orthogonal directions to reflect a modulated laser beam in a raster pattern. By interfacing this raster-scanning system with a computer video card, we demonstrate a full-motion video system with resolution of 41 x 52 pixels and grayscale capability.{09}The dynamic deformation of the surface-micromachined MEMS mirrors used in this video display is shown to be the factor that limits its optical resolution. (Abstract shortened by UMI.)...