Characterizing deflectable microstructures via a high-resolution laser-based measurement system

Abstract

We have developed a high-resolution, laser-based system capable of real-time angular deflection measurement and have used it to characterize non-invasively micromechanical actuators with reflective surfaces. The angular resolution of this system is better than 0.0005° and the measurement bandwidth is 100 kHz. The linear range can be as high as ± 1.5° from any bias angle up to ± 30°. Steady-state deflection measurements of electrostatic torsional aluminum actuators show the expected nonlinear dependence on input voltage, while small-signal frequency response measurements show the characteristic response of a dominant second-order system. Thermally sensitive resonance modes were seen in some devices. The statistical spread in device natural frequency is used as a quantifier for process variations while device lifetime is confirmed beyond one billion cycles by the absence of discernible natural frequency shifts after repeated cycling. The system has also been used to demonstrate optically-based closed-loop control as a precursor to an integrated capacitive solution.