Effects of dielectric charging on the output voltage of a capacitive accelerometer

Abstract

Output voltage drifting observed in one typical capacitive microelectromechanical system (MEMS) accelerometer is discussed in this paper. Dielectric charging effect is located as one of the major determinants of this phenomenon through a combination of experimental and theoretical studies. A theoretical model for the electromechanical effects of the dielectric surface charges within the electrode gap is established to analyze the dielectric charge effect on the output voltage. Observations of output voltage drift against time are fitted to this model in order to estimate the possible dielectric layer thickness. Meanwhile, Auger electron spectroscopy is carried out to analyze the electrode surface material composition and confirms a mixture layer of dielectric SiO 2 and Si with a thickness about 5 nm, which is very close to the model estimation. In addition, observation of time-varing output drift in the variable bias voltage experiment indicates the movement of dielectric charge can be controlled by the applied electric field.

Investigation of drift phenomena in closed-loop capacitive micro accelerometers

“…Similarly to closed-loop accelerometers, a DC bias voltage is applied to generate a feedback electrostatic force [29], and the dielectric material includes the silicon oxide on the electrode surface and glass. The former is confirmed by Auger electron spectroscopy [25,56] and the latter is utilized to mount the Au wire and silicon structures.…”

“…In addition, the residual stress generated in micro-machining can be released during the heating process to generate output drift [23,24]. However, only the amplitude or level of drift were discussed in published research, except for the authors' study, which was the first one to discuss the period of drift [25]. That study concluded that the drift observed over dozens of minutes was similar to the process of dielectric charging, as identified and proved by both experimental and theoretical work on micro-switches [26] and micro-resonators [27], but it mainly focused on the materials analysis and only utilized charging principle to predict the influence of charging on four sensors without a comparison between the theoretical results and the test data.…”

Glass Polarization Induced Drift of a Closed-Loop Micro-Accelerometer

“…It was indicated that the average magnitude of drift decreased from 3.69 to 0.99 mV because the glass polarization-induced drift had been eliminated by the shielding layer, which led the polarized charges to the ground and no additional electrostatic field formed to disturb the current balance. Nevertheless, the remaining drift existing in the tests was related to the charge movement of other components [ 12 ].…”

“…The measurement results showed the dielectric layers on silicon electrodes are very thin, normally in the range of sub-nanometers. This layer certainly formed an additional electrical field to disturb the static balance sustained by the mechanical domain and the electrostatic domain and induced a specific level drift [ 12 ], but the drift amount and level were much smaller than that observed in experiments.…”

Fabrication of a printed capacitive air-gap touch sensor

“…Etching, in particular, is needed to fabricate sensors with air gaps, such as pressure sensors and accelerometers. [10][11][12][13][14] In contrast, printed electronics offers many advantages but it does not employ etching, which makes it difficult to fabricate air-gap based electronic devices.…”