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

Abstract

The glass polarization effects were introduced in this paper to study the main cause of turn-on drift phenomenon of closed-loop micro-accelerometers. The glass substrate underneath the sensitive silicon structure underwent a polarizing process when the DC bias voltage was applied. The slow polarizing process induced an additional electrostatic field to continually drag the movable mass block from one position to another so that the sensing capacitance was changed, which led to an output drift of micro-accelerometers. This drift was indirectly tested by experiments and could be sharply reduced by a shielding layer deposited on the glass substrate because the extra electrical filed was prohibited from generating extra electrostatic forces on the movable fingers of the mass block. The experimental results indicate the average magnitude of drift decreased about 73%, from 3.69 to 0.99 mV. The conclusions proposed in this paper showed a meaningful guideline to improve the stability of micro-devices based on silicon-on-glass structures.

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

“…The electric field strength or direction could be modified to make the charge moves in opposite direction and attenuate the charge effect on the output voltage. Besides dielectric charging effect, glass polarization may also induce drift to the capacitive accelerometer [48]. These issues will be discussed in the future work.…”

Investigation of drift phenomena in closed-loop capacitive micro accelerometers

“…The movement of charge in glass, practically speaking, includes both polarization and migration, as shown in figure 13. The former behaviour concentrates on the charge movement underneath the sensing electrodes, which can be represented by the A-A section in figure 13 [28]. The latter mechanism involves the charge moving from one anchor to another, as depicted in B-B section.…”

“…Firstly, the absence of the effects on glass resulting from the symmetry of sensor structures in studies of oxide dielectrics. Secondly, the conclusion of [28] was based on the existence of asymmetrical errors in sensitive components. Therefore, the authors' contribution to previous work only pointed out that glass polarization could generate an additional field altering the balance of the system, but without explaining the reason why the drift of some accelerometers with an Au layer was larger than that of ones without an Au layer.…”

“…The process of charge migration is very different from polarization in terms of time, trends and level. Figure 15 shows the drift curves of accelerometers with and without an Au layer, respectively, where the layout and fabrication of the Au layer was introduced in [28]. The sputtered Au layer decreases the drift time from dozens of minutes to a few minutes because the migration is faster than the polarization of charge in glass.…”

“…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. Apart from the effects of dielectrics on electrodes, the impact of glass substrates on drift was considered by the authors in 2018 [28], but the this work only addressed the qualitative contribution of glass polarization to drift without considering the charge migration in glass substrates.…”