An electrostatically driven 2D micro-scanning mirror with capacitive sensing for projection display

Abstract

Bi-axial or two-dimensional (2D) MEMS micro-scanning mirrors (or micro-scanners) are considered the key component for laser scanning projectors. Many studies have shown the mechanical characterization of fabricated devices driven by various mechanisms. This work presents an electrostatically driven bi-axial micro-scanner with capacitive position sensing for Lissajous scanning projection. With the added sensing capability, a PLL (phase-locked loop)-based oscillator loop is developed to sustain mechanical resonance and to provide mirror position information, which are equally important for practical applications. The micro-scanner and the required circuits are implemented using bulk micromachining SOI (silicon on insulator) and 0.35-μm CMOS (complementary metal oxide semiconductor) technologies, respectively. The measured resonant frequencies of the bi-axial micro-scanner for the slow and fast-axis scans are 1.4 and 21.9kHz, and the associated optical scan angles are 22.5° and 40°, respectively, under pulse modulation of 48 and 115Vpp. The fabricated micro-scanner is adopted in a laser beam scanning projection system to achieve WVGA (852×480) display resolution.