Origins and Mechanisms of Bias Instability Noise in a Three-Axis Mode-Matched MEMS Gyroscope

In this paper, we examine the origins of bias instability in three-axis, mode-matched MEMS gyroscopes. Reducing this drift phenomenon is crucial for highly accurate navigation in applications, such as automated driving or indoor localization. We show that for a typical MEMS gyroscope, bias instability noise becomes the dominant orientation error component after less than 10 s of integration time. A model-based approach summarizing the most common sources of zero-rate offset is combined with a detailed experimental analysis. We find naturally occurring flicker noise acting on the frequency tuning electrodes to be the dominant source of bias instability for the in-plane axis. By controlling the frequency tuning state, we establish an unprecedented value for bias instability of an automotive-type MEMS gyroscope of lower than 0.1 dph-more than a factor 10 improvement from its performance in ordinary operation. Furthermore, we analyze the so far sparsely studied effect of scale-factor instability, which is an increase of drift that scales with applied angular rate. This phenomenon is particularly important for applications, where high angular rates are common, such as dead-reckoning with smart-phones. As out-of-plane MEMS gyroscopes are significantly more challenging to manufacture, their performance has been studied much less. The out-of-plane axes in this paper are shown to exhibit a complex composition of bias instability sources with a total level as low as 0.7 dph. The presented gyroscopes were furthermore designed for ultra-low white noise. The angle random walk (ARW) is lower than 2.5 md/s/rtHz in all three axes.