Semiconducting metal oxides are widely used for gas sensors. The resulting chemiresistor devices, however, suffer from non-linear responses, signal fluctuations and gas cross-sensitivities, which limits their use in demanding applications of air-quality monitoring. Here, we show that conventional semiconducting metal oxide materials can provide high-performance sensors using an impedance measurement technique. Our approach is based on dielectric excitation measurements and yields sensors with a linear gas response (R2 > 0.99), broad dynamic range of gas detection (six decades of concentrations) and high baseline stability, as well as reduced humidity and ambient-temperature effects. We validated the technique using a range of commercial sensing elements and a range of gases in both laboratory and field conditions. Our approach can be applied to both n- and p-type semiconducting metal oxide materials, and we show that it can be used in wireless sensor networks, and drone-based and wearable environmental and industrial gas monitoring.
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Different phases of this project were funded by GE Research Innovation Fund, GE Services, National Institute for Occupational Safety and Health Contracts 211-2015-63806 and 75D30118C02617, GE Renewable Energy and BHGE. The findings and conclusions in this study should not be construed to represent any determination or policy of the US Government. The content of this report does not necessarily reflect the position or the policy of the US Government. Certain commercial equipment, instruments or materials are identified in this paper to foster understanding. Such identification does not imply recommendation or endorsement by the National Institute for Occupational Safety and Health and the National Institute of Standards and Technology, nor does it imply that the materials or equipment identified are necessarily the best available for the purpose.
The authors declare no competing interests.
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Extended Data Fig. 1 Spectral details of dielectric excitation measurements of response of a SMOX sensing element to different concentration ranges of methane.
a, 0–10 ppm, b, 0–100 ppm, c, 0–1,000 ppm, and d, 0–10,000 ppm. Each panel (a–d) has the top graph of Z′(f) spectra, middle graph of Z″(f) spectra and the bottom graph is the zoomed-in region of Z″(f) spectra with the spectral region of the linear sensor response to methane (dotted lines). Different colors in spectra in (a–d) are labeled as 0 to 16 as the respective methane gas concentration steps depicted in Fig. 1g–n and plotted as a blank (0) and every other spectrum (2–16).
Extended Data Fig. 2 Broad range of gas-response linearity achieved with dielectric excitation measurements.
a, Detection of methane at sub-ppm and low-ppm concentrations with the achieved LOD of 0.02 ppm. b, Detection of methane from 0 to 11 % vol.
Extended Data Fig. 4 Dielectric excitation measurements with a p-type SMOX material using a VOCM31 sensing element (see Supplementary Table 1).
Ethanol was used as a model analyte. Monitoring of ethanol concentrations using a, conventional resistance and b, dielectric excitation measurements. c, Z′(f) and d, Z″(f) spectra and e, Nyquist plots of sensor response. f, Frequency dependence of the R2 values of the linear fit. Inset, low-frequency range. Ethanol vapour concentrations: 0, 300, 600, 900, 1200, 1500, and 1800 ppm. For details about the VOCM31 sensing element (see Supplementary Table 1).
Extended Data Fig. 5 Rules for dielectric excitation measurements to achieve linear gas-sensing response in n- and p-type SMOX materials.
a, Response of n-type materials to increasing concentrations of reducing volatiles where Z″(f) spectra follow the increasing gas concentrations with the high-frequency shifts. b, Response of p-type materials to increasing concentrations of reducing volatiles where Z″(f) spectra follow the increasing gas concentrations with the low-frequency shifts. Thus, for both, n- and p-type SMOX materials the linear Z″(f) gas responses were observed on the front-edge shoulder of the relaxation peak that followed the gas concentrations. For n- and p-type materials, the front-edge shoulder was the high- or low-frequency regions of the relaxation peak, respectively.
a, Conventional chemiresistor mode, b, Dielectric excitation measurement mode.
a, Boards for sensor data acquisition, b, Boards for sensor data acquisition and wireless data communication. c, Assembled sensor node. d, Sensor nodes in a chamber for gas calibration. e, Field data collection unit, paper coffee cup shown for scale.
Extended Data Fig. 8 Benchmarking of the performance of the developed wireless sensor node against a tunable diode laser absorption spectroscopy (TDLAS) system in dynamic detection of methane under ambient wind conditions.
a, Test layout. Dynamic responses of b, TDLAS and c, developed sensor system.
Extended Data Fig. 9 Summary of calibration stability of several sensor nodes after 407 days as percent of sensitivity change of the sensors.
a, b, Z′ measurements and histogram for all nodes. c, d, Z″ measurements and histogram for all nodes. e, Summary for all nodes demonstrating Z′ calibration stability from–3% to 3% and Z″ calibration stability from – 15% to - 3%. Node 7 was not tested.
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Potyrailo, R.A., Go, S., Sexton, D. et al. Extraordinary performance of semiconducting metal oxide gas sensors using dielectric excitation. Nat Electron 3, 280–289 (2020). https://doi.org/10.1038/s41928-020-0402-3
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