Design, Fabrication And Dynamic Testing Of Novel Si-Based MEMS Torsion-Mirror Optical Actuators

According to the detailed investigation on current research status of silicon-based MEMS torsion-mirror optical actuator and MEMS dynamic testing technique, some novel torsion-mirror optical actuators are brought forward and corresponding dynamic testing techniques are carried out to characterize the micro motions of these devices. The research work of the dissertation mainly includes four aspects as follows: theory analysis of optical and electromechanical characteristics, structure design and numerical simulation, flexible process development of silicon micromachining, precision measurement of three-dimension micro motions and so on. 1. The importance, application field, current status and development trends of the silicon-based MEMS torsion-mirror optical actuator and the MEMS dynamic testing technique are investigated and analyzed fully. 2. Firstly, the mechanical dynamics, mechanical shock, dynamic deformation and gravity are discussed theoretically to analyze the mechanical characteristics of the torsion-mirror optical actuator. Secondly, the complicated driving mechanism of electrostatic driving system with the forms of sidewall driving, base plane driving and vertical torsion comb driving are discussed theoretically to analyze the electronic characteristics of the torsion-mirror optical actuator. Thirdly, the optical coupling in application, optical scattering on the surface of micromirror and optical diffraction of etch holes for sacrificial layer release are discussed theoretically to analyze the optical characteristics of the torsion-mirror optical actuator, and then the mathematic formula for charactering the optical insertion loss induced by seven factors together is obtained for the first time. At last, the design rules of the torsion-mirror optical actuator for structure optimization are brought forward according to the theoretical analysis on the above optical and electromechanical characteristics of the device. 3. Five novel torsion-mirror optical actuators including double-beam thickness differential structure with single torsional axis, double flexible folded-beam structure with single torsional axis, double-beam vertical torsion comb structure with single torsion axis, four-beam differential compound-micromirror structure with double torsional axis and the combined structure of the four basis forms above, are brought forward. All of these devices could be fabricated by the same silicon micromachining process we have developed. The deformation compensation design with local enhancement for the thin torsional beam which is the key structure of these devices is also put forward to improve the reliability. The three-dimension solid model and two-dimension reduced order model of the torsion-mirror optical actuator are established and then the numerical simulations for evaluating the device characteristics of the statics, dynamics, electrostatic field, mechanical and electrostatic coupling, fluid and solid coupling are carried out to optimize the structure design. Furthermore, three optical fibre clamping structures which could be integrated monolithicly are designed and analyzed to improve the optical coupling capability. 4. Three flexible process flows combined with bulk silicon micromachining and surface silicon micromachining are brought forward to fabricate these novel single-crystal silicon or polysilicon torsion-mirror optical actuators by using the same lithography masks for both SOI wafer and regular silicon wafer. A series of important process experiments are carried out to optimize the process parameters and the process flows. Some novel and typical process phenomena which occurred during the microfabrication are analyzed and then the corresponding solutions are put forward. 5. A MEMS dynamic testing system which exploit blur image synthetic technique, stroboscopic image matching technique, stroboscopic mirau microscopic interferometry technique and microscopic laser dopper vibrometer technique is set up to measure three-dimension and six-freedom micro motions of any MEMS devices with nanometer resolution. Both periodic or transient micro motions and single-point or full-field micro motions could be measured by this system. Moreover, the surface roughness of the micro mirrors and the dynamic characteristics of the devices in torsion movement are measured and analyzed.