Epitaxially-encapsulated quad mass gyroscope with nonlinearity compensation

Abstract

We present an epitaxially-encapsulated 2×2 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> quad-mass gyroscope (QMG). Relative to the earlier QMG which measured 8×8 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and required an external vacuum package and getter [1], this device is 16x smaller in area and is vacuum-sealed at the wafer-level. Due to the device's small size, high quality factor (Q) and large oscillation amplitude are required to achieve low noise. However, the device's high Q (85,000) makes it highly sensitive to mechanical nonlinearity, resulting in amplitude-frequency dependence and instability of the oscillator loop at large amplitudes. To overcome these problems, we demonstrate electrostatic compensation of the mechanical nonlinearity, enabling 10x greater amplitude and therefore scale factor (SF). Together with closed-loop amplitude control and quadrature compensation, this enables angle-random walk of 0.42 mdeg/s/VHz, comparable to the best QMG published to date. Closed-loop amplitude control and quadrature null are used to achieve a bias instability of 1.6 deg/hr.