An electromagnetically actuated micromirror with precise angle control for harsh environment optical switching applications

• The design, fabrication, and characterization of an electromagnetically actuated micromirror with precise angle control, suitable for harsh environment optical switching applications, are reported.
• Processes have been developed to accurately produce the frontside/backside structure overlap for angle fixing.
• The device is packaged with a textured silicon encapsulation to promote high contrast and better vibration resistance.
• The nonlinear magnetic response and dynamic behavior have been incorporated into the analytical model.
• A pulsed voltage driving circuit is used to increase the electromagnet response speed.

An electromagnetically actuated micromirror with precise tilt angle control for application as a bi-stable optical switch is reported. A tilt angle control of ±2.3° is achieved by utilizing the 4 μm buried oxide (BOX) layer thickness of an SOI wafer together with a carefully controlled pulsed low frequency deep silicon backside etch to construct precise mechanical stoppers, while maximizing the torsion beam out-of-plane stiffness for angle fixing. The device is packaged with a KOH etched textured silicon encapsulation, which prevents reflection from the back cavity to promote high contrast, and also increases vibration resistance. By incorporating the magnetization response of the permalloy material, a compact analytical model for the quasi-static/dynamic analysis of the device was constructed, which corresponds well with the measured tilt angle versus applied magnetic field, frequency response, and switching time. A pulsed voltage driving circuit was also applied to increase the electromagnet response speed. Latchability can be easily established by employing an electro-permanent magnet or electrostatic clamping between the stoppers. The mirror reflectivity was measured to be 87.2% (0.6 dB) at a wavelength of 632.8 nm, and the static and dynamic deformation of the mirror was also measured and reported. The device is suitable for optical telecommunication in harsh environments that do not permit any electrical sparks.