Processes to achieve vibrating beams for an angular rate measurement sensor

Vibrating beam structures may be used as sensing elements in an angular rate measurement sensor. Achieving a square cross-sectional area with smooth vertical side walls and sharp edges is necessary for these beams. In this work, fabrication of beams with reasonably smooth vertical sidewalls and accurate dimensions, using anisotropic etching of silicon in TMAH, has been investigated. Beams with various thicknesses (500-100 microns) are fabricated. It is shown that by carefully aligning the mask at 45° from the ⟨110⟩ wafer flat, and by maintaining the concentration of TMAH at 25%, it is possible to achieve smooth vertical sidewalls with good uniformity along the length of the beam. Adequate control over the beam lateral dimension is achieved by etching in a 2-step procedure with the second step at a lower temperature (lower etch rate). Single-sided and double-sided masking techniques are investigated in order to fabricate the beams. An alternative design is presented to form the beams using a standard CMOS process