Design and Fabrication of Bulk Micro-machined, High Resilience, High-Q, High Tilt Angle, Low Driving Voltage, Flexure Beam Micro-mirrors on Mono-crystalline Silicon

Abstract

We report the design, fabrication and characterization of electrically tunable, bulk micro machined, doubly clamped, circular cross-section flexure based square-plate Metal-On-Oxide, DC bias tension applied, resonant micro-mirrors for different frequencies starting from 1 kilohertz to 172 kilohertz on silicon {100} oriented wafers with high Q factors in the air, that have high resilience. Though silicon shows inherent reflective behavior, the surface quality of the top-deposited metal layer is treatment specific. The sputtered chrome-gold films have good light scattering properties, for precise measurements within 6 ×6 ROI matrixes for vibrometry and AFM. We introduce novel circular cross-section flexure hinges with the advantages of compact design, 5 fold better precision of rotation compared to similar constant cross-section flexure, lesser stiffness, and beam length and beam width that are less decisive for the micro-manufacture. We have fabricated the device, with a double mask, replacing torsion beams with flexure beams. These suspended-in-air-in-trapezoidal-cavity square plate micro-mirrors fabricated on the silicon {100} oriented wafers, are electrically tunable at ±30 Volts, with onset of motion at as low as 3 Volts electrical potential, with the largest achieved tilt angle as high as 11 degrees and parabolic capacitance-voltage characteristics, that confirm the motion of the device in a cavity. The motion of these devices was recorded as a Doppler frequency shift. The result shows a slight improvement in mirror surface quality when resonant micro-mirrors are applied with bias tension, that deviates from the results presented in prior art. The micro-mirrors initially show inactivity in motion, which was stabilizes later. The exact mechanism responsible for this initial inactivity is not known, we attribute it to the sluggish behavior of joined mechanical elements with large time constants, which slow down the vibrancy.