Study of a Nanostructured Co-Doped SnO2 Sensor for Hydrogen Peroxide Vapor Detection Using Impedance Spectroscopy

Abstract

A hydrogen peroxide vapor (HPV) sensor based on SnO₂ doped with 1.3 at. % Co thin film has been fabricated using the high-frequency magnetron sputtering method. The thickness of the SnO₂ ⟨Co⟩ thin film was measured and the surface morphology was examined using the thickness measurement profilometer and scanning electron microscopy, respectively. The crystalline properties of the sensing material were revealed by transmission electron microscopy. The response, current-voltage, and impedance characteristics of the sensor were measured in the air and in the presence of various concentrations of HPV at 25-200 °C. An equivalent electrical circuit for the manufactured sensor structure was proposed, and the parameters of its constituent elements were determined. Furthermore, fitting frequency dependences of impedance were calculated. It was shown that charge transfer in the SnO₂ ⟨Co⟩ thin film was regulated by the processes mainly occurring at the grain boundaries of the gas-sensing film.

Figure 1

(a) Actual photo of the polycrystalline SnO₂ ⟨Co⟩ target, (b) SEM image of the target, and (c) XRF analysis data of the target.

Figure 2

(a) Schematic representation of the multisensor platform and (b) profile of IDEs.

Figure 3

Illustration of the experimental setup.

Figure 4

(a) Thickness measurement results, (b) SEM and (c) TEM images, and (d) SAED pattern of the SnO₂ ⟨Co⟩ film.

Figure 5

(a,b) Current–voltage characteristics of the sensor in the air at different temperatures, (c) dependence of the sensor resistance on the temperature, and (d) activation energy of the conductivity.

Figure 6

(a) Frequency dependencies of real (Z_sub^′) and imaginary (Z_sub^″) components of the substrate impedance (dotted values are experimental data and solid lines are theoretical calculations), (b) equivalent electrical circuit of the substrate, and frequency dependencies of the real (c) and imaginary (d) components of complex impedance at different temperatures.

Figure 7

(a) Nyquist curves the SnO₂ ⟨Co⟩ film in the frequency range above 100 Hz at different temperatures in the air (experimental data: dotted values, fitting data: solid lines), (b) equivalent electrical circuit of the sensor structure in the general case, (c) the equivalent electrical circuit for the SnO₂ ⟨Co⟩ sensor at the high-frequency range, and (d) dependence of the sensor resistance (R) on the temperature.

Figure 8

(a) Equivalent electrical circuit of the SnO₂ ⟨Co⟩ sensor for the whole frequency range, (b) frequency dependencies of real and imaginary components of impedance at 125 °C in the air (the dotted values represent the experimental data, and the solid lines are fitting curves), and (c) distribution of the fitting absolute error.

Figure 9

(a) Current–voltage characteristics and (b) real-time resistance change of the SnO₂ ⟨Co⟩ sensor in the air and the presence of 100 ppm of HPV at 125 ^°C.

Figure 10

Schematic block diagram of the HPV-sensing mechanism.

Figure 11

Frequency dependencies of (a) real and (b) imaginary components of impedance in the air and the presence of 100 ppm of HPV at 100 °C, (c) Nyquist curves of the sensor in the presence of 100 ppm of HPV at different temperatures, and (d) Nyquist curves of the sensor for different concentrations of HPV at 50 °C (dotted values: experimental data; solid lines: fitting curves).

Figure 12

(a) Response vs frequency at different temperatures and (b) response vs HPV concentration at 50 °C.