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.

Fluctuations During Anisotropic Etching: Local Recalibration and Application to Si{110}

“…For step flow to occur the site-specific removal rates of these three atom types must be much larger than for the {111} terraces. Apart from this requirement, the removal rates of the three atom types can be freely modified, thus affecting (controlling) the overall etch rate of facet C. Similarly, the light blue circles on facet D represent the atoms located on {100} terraces while the highlighted atoms (1,1,3,4) and (1,2,2,5) are located at the steps between those terraces. Thus, the overall etch rate of facet D can be controlled by adjusting the site-specific removal rates of these two atoms.…”

“…A NISOTROPIC wet chemical etching of silicon in alkaline solutions, such as potassium hydroxide (KOH) and tetramethyl ammonium hydroxide (TMAH), is a fundamental technique for the fabrication of microelectromechanical systems (MEMS) [1]- [12]. Typically, the process consists in covering selected regions of a silicon wafer using an etch-resistant layer (or mask) and immersing the sample in a KOH or TMAH solution, whereby the exposed silicon is progressively removed.…”

Fabrication of a 2-D in-plane micro needle array integrated with microfluidic components using crystalline wet etching of (110) silicon

“…The deposited Si 3 N 4 film was used as an etch mask for the crystalline wet etching process. To accurately find the vertical (111) plane of (110) silicon, a fan-shaped align mark was employed (Kim et al 2002). The fan-shaped pattern was formed on the photoresist (PR) by DUV photolithography process and was transferred onto the Si 3 N 4 film by the reactive ion etching (RIE) process.…”

MEMS components with perfectly protected edges and corners in Si{110} wafers

“…Wet chemical-based micromachining in {l1O}Si provides uniquely shaped stationary and movable microstructures [1][2][3]. There are six {111} planes that can be exposed and intersect with the {II O} surface.…”