Comparison of Two Alternative Fabrication Processes for a Three-Axis Capacitive MEMS Accelerometer

This paper presents a three-axis capacitive MEMS accelerometer implemented by fabricating lateral and vertical accelerometers in a same die with two alternative processes: a double glass modified dissolved wafer (DGM-DWP) and a double glass modified silicon-on-glass (DGM-SOG) processes. The accelerometers are implemented with a 35 μm structural layer, and the three-axis accelerometer die measures 12mmx7mmx1 mm in each process. Each process includes a second glass wafer which, not only allows implementing a top electrode for the vertical accelerometer, but also forms an inherent cap for the entire structure. Thanks to the stress-free structural layer coming from the SOI wafer, the DGM-SOG process allows obtaining the same rest capacitance values in each side of the accelerometer, which is one of the most important challenges for a functional high performance operation.