Impedance model for a high-temperature ceramic humidity sensor

Abstract. We present an equivalent circuit model for a titanium dioxide-based humidity sensor which enables discrimination of three separate contributions to the sensor impedance. The first contribution, the electronic conductance, consists of a temperature-dependent ohmic resistance. The second contribution arises from the ionic pathway, which forms depending on the relative humidity on the sensor surface. It is modeled by a constant-phase element (CPE) in parallel with an ohmic resistance. The third contribution is the capacitance of the double layer which forms at the blocking electrodes and is modeled by a second CPE in series to the first CPE. This model was fitted to experimental data between 1 mHz and 1 MHz recorded at different sensor temperatures (between room temperature and 320 ∘C) and different humidity levels. The electronic conductance becomes negligible at low sensor temperatures, whereas the double-layer capacitance becomes negligible at high sensor temperatures in the investigated frequency range. Both the contribution from the ionic pathway and from the double-layer capacitance strongly depend on the relative humidity and are, therefore, suitable sensor signals. The findings define the parameters for the development of a dedicated Fourier-based impedance spectroscope with much faster acquisition times, paving a way for impedance-based high-temperature humidity sensor systems.

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Structure of the Electrical Double Layer in High-Temperature Superconductors. Origin of the Dip in the Double-Layer Capacitance near the Superconducting Transition

The Journal of Physical Chemistry B ◽

10.1021/jp971026o ◽

1997 ◽

Vol 101 (36) ◽

pp. 7095-7099 ◽

Cited By ~ 2

Author(s):

Leonid D. Zusman ◽

David N. Beratan

Keyword(s):

High Temperature ◽

Double Layer ◽

Electrical Double Layer ◽

High Temperature Superconductors ◽

Superconducting Transition ◽

Double Layer Capacitance

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Investigation of the Effect of Native Oxide Layer on Performance of Interdigitated Impedance-Based Silicon Biochemical Sensors

Volume 1: 14th International Conference on Micro- and Nanosystems (MNS) ◽

10.1115/detc2020-22207 ◽

2020 ◽

Author(s):

Nadia Ebrahimpour Tolouei ◽

Shima Ghamari ◽

Mohammad Shavezipur

Keyword(s):

Oxide Layer ◽

Double Layer ◽

Electrode Materials ◽

Low Frequency ◽

Native Oxide ◽

Native Oxide Layer ◽

Double Layer Capacitance ◽

Biochemical Sensors ◽

Electrode Surfaces ◽

In Series

Abstract Chemical and biological detection using Electrochemistry Impedance Spectroscopy (EIS) highly depends on the electrical characteristics of the electrodes used in the measurement process. In this work, the effect of surface coating on behavior of interdigitated impedance-based biochemical sensors is studied. Two interdigitated sensors with the same geometry and different electrode materials are fabricated using a standard process. One electrode is made of gold and the other electrode is made of polycrystalline silicon covered with a thin layer of native silicon dioxide. Different concentrations of di(2-ethylhexyl) phthalate (DEHP) in water are used and the Nyquist responses of the two sensors exposed to these solutions are obtained. The measurement results show that at high frequency both sensors form double-layer capacitance values on their electrode surfaces, however, the silicon sensor has a much lower double-layer capacitance values, because formation of oxide layer adds to the gap between charges at the interface of the electrode and the solution. Moreover, comparing the low frequency regions of the Nyquist plots for two sensors shows that the presence of oxide layer affects the Warburg effect and the charge diffusion near the surface of the electrode, creating an extra capacitive element in series with the diffusion effect. The results of this work may be extended to other interdigitated biochemical sensors that may have other sources of contamination on their surfaces.

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