A highly symmetrical capacitive micro-accelerometer with single degree-of-freedom response

It is shown how a micromachined capacitive sensor can be constructed that is able to perform acceleration measurements with over 80 dB dynamic range at less than 1% nonlinearity. Mechanical symmetry alone, without any electrical compensation, accounts for extremely low off-axis and rotational sensitivities. Viscous flow of helium gas controls damping, and the gas pressure can be used to set bandwidth, which is typically on the order of 500 Hz for a 50 G device. The main device characteristics are the exclusive response to a translational acceleration component in a single axis, maximized sensitivity for a given chip area, and improved linearity by suppression of error sources such as fringing field effects, stray capacitances, leakage resistances, and electrostatic pressure. Typical applications are the medium to low frequency, high-sensitivity areas where a uniaxial response is imperative. Robot endpoint control and space or airborne navigation are examples of such areas.<>