Applications of microaccelerometers cover a wide range from those which require low/medium sensitivity sensors, to those used in inertial navigation/guidance systems, seismometry, or microgravity measurements, which demand high sensitivity with very low noise floor. Among various sensing methods, the capacitive sensing technique has recently gained attention as it provides high sensitivity, low noise performance, low temperature sensitivity, and low power dissipation. While most commercialized or developed lateral capacitance microaccelerometers utilize a cantilever-type electrode configuration to achieve a higher dynamic range and sensitivity, the cantilever-type configuration does not provide adequate stiffness if the proofmass is heavy such that it requires a large force to move, which is the case for a high performance device.
Researchers at the University of Michigan have developed a micromachined in-plane (lateral) accelerometer, which utilizes a combined surface and bulk micro-machining technology. Unlike other accelerometers, this accelerometer uses a very large proofmass (full wafer thick) and high aspect ratio sensing gap, which results in high sensitivity and low noise. It also uses a bridge-type configuration for a stable operation, wherein its proofmass itself forms one plate of the parallel-plate capacitor and electrodes the other plate anchored at its ends. One side of the proofmass forms the sense capacitor with the sense/drive electrodes, while the other side of the proofmass is etched and does not form a capacitor with the electrodes, to ensure that the sensitivity of the device is not compromised when the proofmass moves.