Micron-sized, high aspect ratio bulk silicon micromechanical devices

The fabrication of high-aspect-ratio microstructures having widths of ≈1 μm and thicknesses exceeding 10 μm for application in a variety of microsensors and microactuators is reported. The fabrication process utilizes deep etching of fine features into boron-diffused bulk silicon wafers using chlorine- and fluorine-based reactive ion etching techniques. These wafers are then electrostatically bonded to glass wafers which have been previously patterned with metal interconnect. The wafers are finally etched in an ethylenediamine pyrocatechol solution that frees the microstructures. The process requires a total of three masking steps (two for silicon and one for glass), is single-sided, and has high yield. Structures with thickness-to-width ratios greater than 10:1 have been fabricated using this process. Electrical measurements have shown that very large deflections (>7 μm) are possible at voltages as low as 25 V