The gradient in the gravity acceleration is of great interest for planetologists when it can be measured with at least 1 E/√Hz. For this purpose several gravity gradiometer designs are considered. A MEMS-based gradiometer made from a single wafer is considered in this article. Using long springs and small attached masses it is possible to reach a sufficiently low Brownian noise level. The proposed readout for this device will be capacitive plates placed in a comb drive configuration. Trapped charges on these plates can cause noticeable errors when there are more than 0.004 electrons/μm2. Measurements show that trapped charge mobility goes down with temperature.
Flokstra, J., Cuperus, R., Wiegerink, R. J., & van Essen, M. C. (2009). A MEMS-based gravity gradiometer for future planetary missions. Cryogenics, 49(11), 665-668. [10.1016/j.cryogenics.2008.12.019]. https://doi.org/10.1016/j.cryogenics.2008.12.019