The Finite Element Analysis And Fabrication Of Self-assembled Micro Mirror

Micro Opto-Electronic Mechanical System (MOEMS) have received more and more attention because of their many applications. Its significance lies not only in reducing the size and the volume of mechanical and electrical systems, but also lies in exploring new principles and new features of the devices and systems based on its miniaturization, integration and intelligentization. In its development process, using precision processing techniques to process micro/nano structures and systems, micromaching technology became the basis for MOEMS fabrication.In this paper, self-assembly method is introduced to fabricate MOEMS components, which using the driven stress created by lattice mismatch between epitaxial bilayer. Finite element method (FEM) is introduced to analysis those MOEMS devices and related experiment have been done. The main contents of this thesis are as follows:1. The development, characteristics and prospects of MOEMS are introduced systematically. The main MOEMS processing technology and thin film growth methods are also discussed.2. The two types of the elastic plane problems and the procedure of finite element analysis are described. As a practical numerical analysis method, FEM received extensive attention in engineering in recent years, and became a powerful tool for analysis of the continuum. Compared with finite difference method and boundary element method, which are other two common used numerical methods in elasticity problem, FEM is suited to solve nonlinear-non-homogeneous problem and bounded domain without singularity problem. Furthermore, FEM have high accuracy for the narrow region. Because of its universality, efficiency and reliability, FEM turn into the most appropriate method in solving the geometrically nonlinear elasticity problem in this article.3. The fabrication process of using the self-assembly method to fabricate the micro mirror are described. The micro mirror can be fabricated by self-assembly technique using the strain in lattice-mismatched epitaxial layers. A self-assembly micro mirror can be fabricated by photolithography and selective etching. Apply FEM to make theoretical modeling and simulation analysis. Finally, the impact factors for the mirror rotation angle are discussed. The result shows that using self-assembly method to fabricate three-dimensional micro/nano devices can preset the mirror rotation angle.4. Sample grown using the V90 GSMBE system. GaAs is used as a substrate. Starting from the substrate, the multilayer material consists of a 600nm GaAs buffer layer, a 80nm A10.58Ga0.42As/AlAs digital alloy sacrificial layer, a 7nm In0.22Ga0.78As and 34nm GaAs strain bilayer, a 150nm A10.58Ga0.42As etch-stop layer, a 450nm GaAs layer, a 15nm In0.22Ga0.78As strain-compensated layer, and a 20nm GaAs cap layer. After growth, the epitaxial layer needs to through the following steps:the wafer cleaning, graphics photolithography of micro hinge, etching of the hinge, graphics photolithography of mirror, and etching of the mirror to fabricate the micro mirror.5. Successful theoretical design and simulate micro corner cube reflectors (CCR). CCR has features of microminiaturize, high performance, low power consumption, and can easy integrate with sensors, solar cells and CMOS control circuitry et al, making the CCR as the key components in the micro self-transmission devices. Furthermore, mirrors with different angels and a micro-cube box are also successfully simulated.The success of the simulation and experiment demonstrated that the self-assembly method is a very effective way to fabricate MOEMS components and have a good prospects for development.