CMOS-MEMS Based Optical Electrostatic Phase Shifter Array With Low Driving Voltage and High Fill Factor

Abstract—This work develops a novel 4 4 optical phase shifting micromirror array that achieves a vertical displace-ment and makes the mirror peak-to-valley deformation within (514 nm light source). Each individual micromirror pixel is controllable and driven by an electrostatic parallel plate actuator. The mirror reflective surface is an aluminum layer with a high optical reflectivity exceeding 90%. This device achieves a high fill factor of more than 90 % without an additional flip-chip bonding process due to the parallel plate actuator and the hidden suspen-sion beam structures. The phase shifter array is fabricated using the Taiwan Semiconductor Manufacturing Company (TSMC) 0.35 2p4m CMOS process and post-CMOS process. An in-house post-process is utilized to reserve a 40 thick bulk-sil-icon under the 200 200 mirror. This eliminates mirror deformation from residual stress after the device is released. The micromirror demonstrates a vertical displacement of at only 3 V and the resonant frequency is 3.6 kHz. Industry can use this phase-shifting micromirror array as a spatial light modulator in holographic data storage systems in the future. Index Terms—CMOS MEMS, MEMS, micromirror, MOEMS, phase shifter. I