Wafer level vacuum encapsulated tri-axial accelerometer with low cross-axis sensitivity in a commercial MEMS Process

We present the design, fabrication and testing of a novel integrated tri-axial capacitive accelerometer with low cross-axis sensitivity. The accelerometer is fabricated in MEMS Integrated Design for Inertial Sensors (MIDIS), a process recently introduced by Teledyne DALSA Semiconductor Inc. (TDSI). The MIDIS process is based on high aspect ratio bulk micromachining of single-crystal silicon wafer that is vacuum encapsulated between two other silicon wafers. The fabrication process includes Through Silicon Vias (TSVs) with sealed anchors for compact flip-chip integration with microelectronic signal processing circuitry. The proposed accelerometer is designed to provide simultaneous detection of the input accelerations along the 3 principle axes enabling high-g measurement up to ±50 g. The integrated structure design uses decoupled frames supported by strategically designed springs and employs capacitive compensators for the purpose of achieving low cross-axis sensitivity. The capacitive transduction is based on differential measurement along X- and Y- axis and absolute measurement along the Z-axis. The initial measured capacitances are 2.18 pF, 2.4 pF and 1.14 pF along X, Y and Z-axis, respectively. The dynamic specifications of the accelerometer are characterized by its lowest-order operating mode at 4 kHz.