Abstract
An electromagnetic scanning micromirror driven by Lorentz force is studied in this thesis for application in a laser beam scanning projector. In order to produce repetitive scanning at the resonance, polycrystalline silicon deposited on the torsion axis is used to provide piezoresistive sensing of the motion. The integrated chip containing the mechanical structure, sensing and compensation circuit, is implemented by using the TSMC 2P4M 0.35μm CMOS process. The chip area is 3.5 × 3.6 mm2. By designing torsional beams with different thicknesses for fast and slow scans, the length of the latter can be reduced to minimize the overall scanning mirror size. In addition, the design for the slow axis of three springs can reduce stress and avoid damage to the chip when the larger current driving. We develop a convenient and low-cost post fabrication process and successfully fabricate the scanning micromirror device. The fabricated micromirror structure designed for SXGA resolution (1280×1024) shows the measured resonant frequencies at 36.6 and 4.3 kHz, respectively, for fast and slow-axis scans. The results are close to the simulated values. Electromagnetic actuation is used for the driving. The Lorentz’s force driving the scanner is created by an external magnet and a current carrying coil. The magnet is placed at 45 degrees relative to the both scan axes. The piezoresistive sensing circuit contains a Wheatstone bridge and a differential-to-single-ended circuit. Through proper gain and phase compensation, sustained oscillation with respect to the fast scan axis is successfully achieved. The optical angle was measured to be 3.4 degrees at 6.1 mArms.