Byeoung Ju Ha

A Capacitive Silicon Microaccelerometer With Force Balancing Electrodes

A surface micromachined accelerometer, which senses an inertial motion with an area variation, has been developed. The accelerometer is designed as an interdigital rib structure that has a differential capacitor arrangement. The movable electrodes are mounted on a mass of 7 µm thick polysilicon and a pair of stationary electrodes is formed under the mass with a 1.5 µm gap. Both sides of the movable electrodes are fixed on the mass, and the stationary electrode is formed on the substrate without being suspended. As a result, the mechanical stress and the electrical pulling effects can be reduced in comparison to the comb-type capacitor arrangement. In order to improve the dynamic range and the linearity, a pair of comb-shaped force-balancing electrodes is placed on both sides of the mass. The force-balancing electrodes are fabricated on the same layer as the mass and anchored on a silicon substrate. In particular, differential feedback electrodes enable linear control of mass repositioning.

Microscopy Studies for the Deep-Anisotropic Etching of (100) Si Wafers

Several etching phenomena appeared during the Si membrane process were observed and analyzed. In case of deep etching to above 300 µm depth, the etch-defects existed at the etched surface could be classified into three categories such as hillocks, adhered reaction products and white residues. It was known that the hillocks had a pyramidal shape or trapizoidal hexahedron structures depending on the density and size of the reaction products. Also, the existence of etch-defects and the etch rate distribution over a whole 4-inch wafers were investigated when the surfaces to be etched were downward, upward horizontally and erective for the stirring bar in the solution. As the results, the downward and erected postures were favorable in the etch rate uniformity and the etch-defect removal, respectively.