Self-Packaged Three Axis Capacitive Mems Accelerometer

This paper presents the design, fabrication, and characterization of a self-packaged three axis capacitive MEMS accelerometer fabricated by using only four masks that is capable of differentially sensing the externally applied accelerations in three orthogonal axes. Individual lateral and vertical axis accelerometers are fabricated in the same die on a SOI wafer, which is eutectically bonded to a silicon substrate. Handle layer of the SOI wafer is both used as the top electrode for the vertical axis accelerometer, and a capping layer for all accelerometers. Vertical axis accelerometer has a 2 mm
²
perforated electrode area anchored to the Si substrate by four beams. The lateral axis accelerometers on the other hand, have comb finger structures with a
$2.4 \times 1.9\ \mathrm{mm}^{2}$
device area and anchored to the Si substrate by four folded beams. Three axis accelerometer has a dimension of
$8.45 \times 4.0 \times 0.84\ \mathrm{mm}^{3}$
. Rest capacitance of the vertical axis accelerometer is designed to be 12 pF, and it is 10 pF for the lateral axis accelerometers.