This dissertation examines a class of electrostatically driven micro-shutters. These micro-shutters are surface micromachined using silicon related materials and techniques similar to those used to fabricate integrated circuits. Analytic tools and experimental methods are developed to facilitate the analysis, design, and testing of these micro-shutters. The ultimate objective of this examination is an understanding of micro-shutter operation, and the development of analyses and design guidelines for future micro-shutters.
Electronic display devices play a bridging role (man-machine interface) and have become increasingly important with progress towards the information society, development of new media, and the spread of electronic systems. Demand for such devices continues to expand and diversify. Various types of flat panel type electronic display devices of the active and passive types, characterized by small depth and light weight, with low voltage and low power, have attracted attention as novel electronic devices adapted to this new situation.
The Electrostatically driven Micro-Shutter(EMS) is a new transmissive type spatial light modulator developed by using the microelectromechanical system (MEMS) technology. The micromachined thin film electrostatic actuators are used to control the tilting angle of micro-shutters. This dissertation describes the principle, design, fabrication and the evaluation of the EMS module for direct view displays. Currently, the mainstream direct view technology for flat panel displays is the transmissive active matrix addressed liquid crystal display (LCD)technology. However, the light polarization result in poor efficiency(about 5%) of light utilization. The EMS doesn't require the polarizer, so that it has higher optical efficiency. A comb shaped double layer microstructure provides the function of on/off for the light.
Movable structures with dimensions measured in micrometers have been fabricated using silicon microfabrication technology. These micromechanical structures are batch-fabricated in an IC-compatible process. The movable mechanical elements are built on layers that are later removed so that they freed for translation and rotation.
A new method for dry etching of silicon dioxide for surface micromachining is presented to obtain very compliant polysilicon microstructures with negligible stiction problem and to greatly simplify the overall releasing procedure as well. By etching the sacrificial silicon dioxide with hydrofluoric acid (HF) vapor instead of conventional aqueous HF solution, the need for subsequent rinsing and an elaborate drying procedure is eliminated. Condensation of water on the etch surface is first identified as the cause that prevented the success of HF vapor release in the past. Use of an anhydrous HF/$CH_3OH$ mixture under low pressure solves the problem of water condensation and enables us to take advantage of vapor-phase etching(VPE) for surface micromachining. The mechanism of oxide etching with the HF/$CH_3OH$ mixture is explained. Polysilicon cantilevers up to 1200㎛ in length are successfully released with this HF VPE technique. The beams tested are 2 ㎛ thick with a 2 ㎛ gap from the substrate, and no antistiction dimples are used. The fabricated structures are observed using both scanning electron microscopy(SEM) and an optical profilometer. The reported VPE technique provides a robust releasing method for polysilicon microstructures and is compatible with integrated circuit (IC) fabrication, even including cluster processors.
