MEMS high-quality micromirrors for optical interconnect and optical pick-up heads

In this dissertation, I will first discuss a new type of MEMS actuators based on electrostatic force. A surface-micromachined electrostatic domino actuator (EDA) has been successfully demonstrated. The EDA consists of N stages of gap-closing actuators with linearly increasing gap spacing. Large displacement and large force are achieved by the domino effect created by successive pull-in of the gap-closing actuator array. Experimentally, a displacement of 24 μm (bi-directional) at 35 V bias has been successfully achieved by a four-stage EDA.; After that, two novel silicon surface micromachined devices, scanning mirrors and mirror arrays, for applications in optical interconnect and optical data storage, respectively. The 2D MEMS scanning mirror is self-assembled by either scratch drive actuator or stress-induced bimorph structure without any external manual feed. The scanning angle ±5.7° has been successfully demonstrated. The scanning micromirror can be inserted into optical path to perform active alignment and dynamic tracking for optical interconnect application. The micromirror arrays with two different motion, piston motion and tip-tilt motion, have been investigated. By using novel micro-elevator-by-self-assembly (MESA), strokes as large as 12 μm have been successfully achieved without using bulk etching or thick sacrificial layers. The large strokes and the batch fabrication process make this micromirror arrays an attractive candidate for low-cost optical pick-up heads in high-capacity optical disc storage application.; However, micromirror fabricated by standard surface micromachining process (e.g. Multi-User MEMS Process, or MUMPs™, by CRONOS) will have significant curvature due to residual stress and stress gradient in the deposited polysilicon thin film. For most applications, flat micromirrors with radius of curvature >30 cm and surface roughness <λ/10 are required. We have developed a novel hybrid bulk-/surface-micromachining bonding process to fabricate high-performance micromirror on MUMPS chips. The micromirrors are formed on thick (>10μm) silicon-on-insulator (SOI) and then bonded to surface-micromachined actuators. This wafer-scale process takes advantages of flatness achievable with stress-free single crystalline silicon micromirrors without sacrificing the design flexibility of the standard polysilicon surface-micromachining process.