Rotary electrostatic micromirror switches using wafer-scale processing and assembly

The design, micromachining process, wafer-scale assembly, and experimental characterization of our rotary electrostatic micromirrors for optical switching applications are reported in this paper. Some of the proposed microelectromechanical systems (MEMS) optical switches utilize surface-micromachined thin films as the reflection micromirrors which might result in optical degradation due to dynamic warping. Some of these devices fabricated by bulk micromachining highly rely on a delicate post-assembly process to assemble the micromirrors onto the top of MEMS actuators. In this research, we focus on developing rotary electrostatic micromirror switches without the requirement of delicate post-assembly processes. We use the spin-on-glass, which is used as an intermediate layer in a 280°C low-temperature wafer-bonding process, to fabricate our rotary optical switches with a wafer-scale assembly process. The rotary electrostatic actuator and the vertical micromirror are fabricated simultaneously by the same deep RIE process in our design. We have successfully demonstrated the rotary electrostatic micromirror switches via the wafer-scale assembly process with a yield rate of above 70%. Experimental results show that our rotary vertical micromirrors rotate about 1.5° under an applied voltage of 150 V for steady-state measurements. For dynamic measurements, the rotary vertical micromirrors rotate about 3.6° under an applied voltage of 30 V at the resonant frequency. The first vibration mode of our rotary switch is an in-plane rotational mode and appears around 3.4 kHz, which is characterized via a Polytec laser doppler vibrometer.