Endoscopic optical coherence tomographic imaging with a CMOS-MEMS micromirror

This paper reports a single-crystalline silicon (SCS) micromirror used for laser beam scanning in an endoscopic optical coherence tomography (OCT) system. The micromirror is fabricated by using a deep reactive-ion-etch (DRIE) post-CMOS micromachining process. Thin bimorph actuation structures and movable bulk silicon structures are simultaneously achieved. The micromirror is 1 mm by 1 mm in size, coated with aluminum, and thermally actuated by an integrated polysilicon heater. The radius of curvature of the mirror surface is 50 cm. The mirror has a resonance frequency of 165 Hz and rotates 17° when a 15 mA d.c. current is applied. A discontinuity in the dynamic response curve is observed. By using a white-light profilometer, we found that the discontinuity is caused by localized buckling of the bimorph actuation mesh. Cross-sectional images of 500 × 1000 pixels covering an area of 2.9 mm by 2.8 mm are acquired at 5 frames/s by using an OCT system based on this micromirror.