Optical MEMS

Si Micromirror is the topic for both internal core and industry research projects in IME targeting for Optical Coherent Tomography (OCT) imaging, TV display applications, and CMOS-MEMS integration applications etc.

Strategy & Focus

• Platform technology for MEMS and Si Photonics integration. Wafer level integration of photonic waveguides with MEMS optical switch, further leading to integration of Si modulator and MEMS tunable laser
• 3D scanning micromirror integrated optical probe for optical coherent tomography (OCT) imaging
• CMOS-MEMS integrated micromirror array for projection TV
• CMOS-MEMS integrated optical modulator

Significant Results

3D scanning micromirror integrated optical probe for bio imaging applications

Micromirror development started back in year 2000 at IME. This project was the first of its kind in developing an application-oriented workable prototype which would go for animal model trials at the National Cancer Centre.

The project team has made several key developments. The first objective was to demonstrate feasibility of using 3D micromirror for OCT bio imaging, which was accomplished in December 2005 by (1) demonstrating linear scanning repeatability at the OCT imaging scan rate of about 20 Hz, and (2) obtaining OCT image of a standard sample and also of onion tissues. The size of the mirror then was 2.5 mm x 2.5 mm, which resulted in an optical probe with diameter close to 6 mm. The process was reengineered by eliminating steps, which contributed to dead space on the chip such as anisotropic alkaline etching of silicon from backside and by including high aspect ratio etch steps such as DRIE of silicon. Actuator and spring geometries were also redesigned and most of the dead space on the chip was eliminated.

New compact size chip was developed and demonstrated in September 2006. The mirror devices with curved actuators and springs also demonstrated a tilt angle up to 17 degrees, while the mirrors with linear actuators could provide a tilt of 10 degrees. Mirror chip package with alignment optics components (GRIN lens and Fiber) was the last and most tedious part. The team came out with a novel silicon optical bench (SiOB) package, which provided optical alignment slots for the mirror, GRIN lens and fiber, and also provided electrical connectivity to the mirror. The SiOB concept and package development was successfully completed by demonstrating a very good optical alignment through optical tests. Micromirror has also been demonstrated to work in SiOB package for scanning. The final OCT imaging testing is still ongoing.

Optical and SEM micrographs of realised compact 3D scanning thermally actuated single crystal silicon micromirrors

Silicon optical bench probe and assembly

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