| 3D imaging laser radar has a broad application prospect in many areas, and its miniaturization is an important development direction. MEMS scanning mirror has the advantages of small size, low cost, high scanning frequency, and fast response. Recent years it became an important research direction of the miniaturized 3D imaging laser radar.The basic theory, working principle, structure design, process and performance test of the MEMS scanning mirror are deeply researched in this thesis. The main research content is as follows:1. Research on the basic theory of the electrostatic drive MEMS scanning mirror. Residual stress and self-assembly method are analyzed and discussed; the influence of residual stress on the mirror, mirror surface profile control and multilayer thin mirror structure model are analyzed and discussed; the three key parameters, mirror size, maximum scanning angle and scanning frequency of MEMS scanning mirror are discussed.2. Research on MEMS scanning mirror. An electrostatic driven MEMS scanning mirror based on residual stress is proposed. The scanning mirror is made up of the centre mirror, elastic torsion beam and cantilever beam. The cantilever beam with residual stress can increase the height of the mirror and increase the scanning angle. A sample is fabricated by the surface micromachining process, and then a thermal annealing technology is performed to introduce the tensile stress in the gold layer and further enhance the height of the mirror. Through a series of thermal annealing experiment, the residual stress value with different temperature of thermal annealing treatment is obtained; the stress formula of polysilicon cantilever beam structure is derived. After a thermal annealing treatment under the temperature of 200℃, a maximum scanning angle of ±3.6° under 145 V driving voltage is obtained.3. Research on MEMS scanning mirror array. A kind of electrostatic driven MEMS scanning mirror array is proposed. The array is made up of 37 hexagonal scan mirror units and all units are arranged hexagon. Each scanning mirror unit can realize the function of two-dimensional scanning. Through uniform control, the array can realize the function of two-dimensional scanning. Scanning mirror unit consists of two parts, actuator and mirror. Actuator use the self-assembly method and has the function of tilt and piston movement. Firstly the actuator array and mirror array are fabricated by a surface micromachining process, and then they are bonded together by a bulk micromachining process. At last the scanning mirror array is obtained by a releasing process. After a thermal annealing treatment under the temperature of 200℃, a maximum piston displacement of 4.05μm is obtained, under a driving voltage of 45 V. A maximum deflection angle of 0.8° under a driving voltage of 60 V is obtained.The results in this paper have important value on the structure design, processing technology and experimental test of MEMS scanning mirror, and can promote the development of 3D imaging laser radar technology in our country. |
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