Batch-fabricated milli-actuators

The authors describe the design, process and characterization of microfabricated structures with dimensions an order of magnitude larger than conventional structures in all three dimensions, while still keeping the minimum in-plane features. Some special considerations, such as low intrinsic stress, become very important in millimeter-sized structures for controlling minimum feature distortion between stress-released and unreleased parts. Electrostatically driven flexures 20-μm thick and up to 3 mm in size are made with this process. The air gaps between electrodes are less than 2 μm. Laser Doppler velocimetry (LDV) is applied to measure the in-plane motion to better than 5-nm resolution. Small-scale linearization is used for the square-law electrostatic actuator, and frequency response functions are measured using LDV for open-loop and closed-loop servo configuration. The first resonance is electronically damped in the closed-loop case