A high-aspect-ratio comb actuator using UV-LIGA surface micromachining and (110) silicon bulk micromachining

Abstract

A novel micromachining process based on the UV-LIGA process and (110) silicon anisotropic etching to fabricate a high-aspect-ratio comb actuator was developed. The comb electrodes were fabricated by (110) silicon anisotropic etching and the spring structures were fabricated using a UV-LIGA micromachining process. The (110) silicon comb structure was designed considering the etch-rate-ratio between the (110) and (111) planes and the lateral etch rate of a line-type structure. The fabricated structure was 400 μm thick and 18 μm wide comb electrodes separated by 7 μm and the height–gap ratio was approximately 57. In addition, the number, width, height and length of the spring structures were designed considering resonant frequency of the comb actuator and frequency-matching between the sensing and driving mode for gyroscope application. The electroplated gold springs on both sides of the seismic mass were 15 μm wide, 14 μm thick and 500 μm long. The fabricated comb actuator had a resonant frequency at 1430 Hz, which was calculated to be 1441 Hz. The proposed fabrication process can be applied to fabricating a high-aspect-ratio comb actuator for large displacement actuators and precision sensors. Moreover, this combined process enables the fabrication of a more complex structure, which cannot be fabricated by surface or bulk micromachining alone.