CMOS-Integrated Electromagnetic Scanning Micromirror with Piezoresistive Sensing

• Main Authors: Lin, Yu-Tang, 林玉堂
• Other Authors: Lu, Shiang-Cheng
• Format: Others
• Language: zh-TW
• Published: 2014
• Online Access: http://ndltd.ncl.edu.tw/handle/24756449201546378755

碩士 === 國立清華大學 === 電子工程研究所 === 103 === This thesis introduces the application of scanning micromirror firstly. With the revolution of consumer electronics, people not only want their devices to be equipped with a big screen but also to be compact at the same time. Scanning micromirrors are able to satisfy the needs with a small size and the image projection capability. A electromagnetic scanning micromirror driven by Lorentz force is studied in this work. The projection system uses laser beam as the scanning light source and requires no focusing lens. To monitor the motion of the micro scanning mirror, polysilicon is embedded in each torsional beam as the piezoresistive sensor, which can be used in a feedback loop to initiate oscillation. The integrated chip contains the mechanical structure, sensing circuit, and oscillation circuit and is implemented by using the TSMC 2P4M (two-polysilicon-four-metal) 0.35μm CMOS (Complementary metal oxide semiconductors) process. The chip area is 3.5×2.8 mm2. By designing torsional beams with different thicknesses for fast and slow scans, the length of the latter can be significantly reduced to minimize the scanning mirror size. Etchant holes are placed on slow-axis beams to facilitate the silicon undercut by xenon diflouride. We develop a convenient and low-cost post fabrication process and successfully fabricate the scanning micromirror device. The latest measurement shows the resonant frequencies for fast and slow scans are 53.8 and 7.6 kHz, respectively (without xenon diflouride dry etching), which are close to the simulated values.