Chip-scale IMU using folded-mems approach

This paper reports a new approach to design and fabrication of chip-level inertial measurement units (IMUs). The folded-chip method utilizes a 3-D foldable silicon-on-insulator (SOI) backbone suitable for high-aspect ratio sensor fabrication. Assembly is done on the wafer level forming a compact rigid 6-axis system of sensors. Accelerometers and gyroscopes are fabricated in parallel with the folded structure on the same substrate, and are electrically and mechanically interfaced through integrated flexible polyimide film hinges and interlocking silicon latches. To demonstrate feasibility of the approach, folded IMUs are fabricated containing resonant capacitive accelerometers and gyroscopes. The value of the scale factor of the accelerometers is tunable over a range from 1.75 Hz/g to 3.7 Hz/g. Driving the gyroscope on the pyramid sidewall with 1.5 kHz operational frequency, the rotation rate is characterized in air to demonstrate operation with a scale factor of 0.43 mV/(deg/sec). Structural rigidity was verified by subjecting the IMU to oscillations from 50 Hz - 3.5 kHz over an amplitude range of 5-25 g. The results confirm feasibility of the proposed folded MEMS IMU approach, and may enable new integrated architectures for other multi-axis dynamic sensors, such as 3-D microphones, hydrophones, and ultrasonic transducers.