A large-scanning-angle, electrothermal SCS micromirror for biomedical imaging

Abstract

This paper reports a 1mm-by-1mm single-crystal silicon (SCS)-based aluminum-coated micromirror (Fig. 1) that rotates 36° at a 7.5 mA d.c. current. Large, flat micromirrors with large scanning angles are required by applications such as medical imaging and interferometer systems. SCS micromirrors have been explored because of the manufacturability and flatness of SCS-based microstructures [1,2,3]. A previous SCS micromirror rotated 17° at 15 mA (d.c.) [3]. However, the buckling of the employed bimorph mesh structure resulted in a discontinuity in the angle versus current curve, which limited the usable scanning range to about 5°. From FEM simulation (Coventorware) we found that the orientation of the embedded poly-silicon resistor significantly changes the temperature behavior of the micromirror. Fig. 2 illustrates the difference between a previous design and the new design. The new design (Fig. 2(c)) has a transversely oriented serpentine poly-silicon resistor to obtain uniform heating along the transverse direction. This results in a continuous response curve (Fig. 2), and an even larger rotation angle. The micromirror is fabricated using deep reactive-ion-etch (DRIE) CMOS-MEMS processing [4].