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 biaxial 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 21.9 kHz, and the associated optical scan angles are 22.5° and 40°, respectively, under pulse modulation of 48 and 115 Vpp. The fabricated micro-scanner is adopted in a laser beam scanning projection system to achieve WVGA (852 × 480) display resolution.