New 3-D Structures Fabricated on Si (hkl) Substrates by Bulk Micromachining

The paper deals with the new 3D structures fabricated by the bulk micromachining of (110), (112), and (522) silicon substrates. The structures employ a specific arrangement of {111} planes on these substrates and are entirely bounded by these slowly etching planes. Design rules and complete structures of new seismic-mass systems, suspended on two or four beams, composed of the {111} planes, are presented. The beams supporting the masses are inclined toward the substrate at different angles, which can be adjusted by an appropriate selection of crystallographic orientation of the etched substrate. The structures seem to be interesting as structural components of multiaxes accelerometers. Slanted membranes fabricated by the double-sided etching of (112) and (552) substrates have also been presented. The structures utilize the {111} planes, inclined at a low angle toward the etched substrate, both as structural elements, as well as a natural etch stop. It can be claimed that the application of Si substrates with unconventional crystallographic orientations opens new possibilities in the micromachining of 3D structures.