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We report an improved electrostatically-driven micro torsion mirror which is suitable to be integrated monolithically to form large scale optical switch arrays. The mirror is fabricated by combining surface silicon micromachining techniques and bulk silicon micromachining techniques. In addition, a self-alignment technique is employed in aligning the optical fibers to the mirror. The micro mirror covered with Au on its surface is supported by the torsion beam, and will rotate inward by 90 degrees to reflect the incident light in a free-space when a big enough bias is applied. The practical threshold voltage of driving the mirror to rotate by 90 degrees is about 200 V, very much higher than its theoretical value which is less than 100 V The big difference is due to the surface stress that makes the mirror surface tilt upwards away from the other plate electrode. A way to lower the driving voltage versus large rotating angle is analyzed.