MEMS -> Optical, structural roles shared on die

Optical, structural roles shared on die

Optical, structural roles shared on die
By Brent Burns, Principal Staff Scientist, John Peterson, Senior Sales Engineer, Denny K. Miu, Founder and CEO, Integrated Micromachines Inc., Monrovia, Calif., EE Times
July 12, 2001 (7:15 p.m. EST)
URL: http://www.eetimes.com/story/OEG20010712S0075

MEMS-based variable optical attenuators (VOAs) and switches with low port counts are like conventional components that are stepper-motor driven: They both have superior optical performance. Now, because of a MEMS engine, Integrated Micromachines Inc.'s MEMS components can be designed with high part-to-part uniformity, no backlash when changing from one state to another, faster switch time and a life time of more than a billion cycles.

IMM engineers have designed an electromagnetically driven MEMS shutter using the company's Elite (for extremely low-loss inductive torsional engine) technology, which replaces a conventional stepper motor in VOAs. Elite MEMS technology uses single-crystal silicon as both the structural and optical material instead of polysilicon, and electromagnetic instead of electrostatic actuation.

Elite's working principle is simple; it is identical to conventional free-space optomechanical components. It starts w ith a highquality front surface reflective mirror-in IMM's case, highly polished single-crystal silicon-and an electromagnetic motor. But with the Elite the motor is made on silicon using a batch-manufacturing scheme similar to that of semiconductor devices and is integrated with the mirror.

The advantage is that the MEMS electromagnetic motor is much smaller and therefore can sustain higher mechanical shock because of lower mass. Also, although there are moving parts, components based on Elite don't have a frictional interface because the mechanical design consists of torsional beams.

Another advantage of single-crystal silicon is that it doesn't fail because of fatigue and is surprisingly strong. It can withstand tensile stress before fracturing that is about seven times that of steel.

Essentially, the MEMS shutter is attached to the frame through serpentine tethers that both maximize strength and minimize the required drive current. Tight dimensional tolerances on the MEMS structur e are ensured by manufacturing with well-established silicon IC fabrication technology and state-of-the-art equipment. Those tight tolerances help ensure a high part-to-part uniformity.

The MEMS die is then mounted on a small permanent fixed magnet; after wire bonding it is actively aligned to the light path to ensure maximum attenuation and minimum optical loss. Utilizing the stored energy in the permanent magnet's external field helps to minimize power consumption while maintaining a very fast switch time in the Elite components.