Fabrication of a three-axis capacitive MEMS accelerometer on a single substrate

This paper presents a new fabrication approach and a design for the fabrication of a three-axis capacitive MEMS accelerometer where differential sensing is enabled for all sense directions. In this approach, individual lateral and vertical axis accelerometers are fabricated in the same die on an SOI wafer which is eutectically bonded to a glass substrate. Differential sensing for the vertical axis accelerometer is realized by defining the proof mass of the accelerometer on the structural layer of the SOI wafer that is sandwiched between two stationary electrodes defined on the glass substrate and the handle layer of the SOI wafer. Vertical axis accelerometer has a 4 mm2 perforated proof mass area anchored to the glass substrate by four beams, and lateral axis accelerometer has a comb finger structure with a 2.7 ×4.2 mm2 device area anchored to the glass substrate by six folded beams.