• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1998.11a
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• pp.101-104
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• 1998

A new planar-type micro gas sensor was designed and fabricated on silicon substrate and the operating characteristics of the sensor were investigated. The thin sensitive film of the sensor was fabricated by spin-coating of the SnO$_2$ sol solution which was synthesized by hydrothermal method. The spin-coating method for preparation of sensing layer was adopted to improve the long-term stability of the fabricated sensing film instead of physical methods such as rf sputtering and thermal evaporation. The fabricated microsensor showed a fairly good sensing performance for CO gas in air at 250$^{\circ}C$ The sensitivity(S=Ra/Rg) was shown to be about 5 to 2000ppm CO with heating power of 50mW.

• Journal of the Korean Ceramic Society
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• v.37 no.8
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• pp.817-823
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• 2000

A solid-state electrochemicall cell for sensing CO2 gas was fabricated using a solid electrolyte of Li2CO3-Li3PO4-Al2O3 mixture and a reference electrode of LiMn2O4. The e.m.f. (electromotive force) of sensor showed a good accordance with theoretical Nernst slope (n=2) for CO2 gas concentration range of 100-10000 ppm above 35$0^{\circ}C$. The e.m.f. of sensor was constant regardless of oxygen partial pressure at the high temperature above 0.1 atm. It was, however, a little depended on oxygen partial pressure as the pressure decreased below 0.1 atm. The oxygen-dependency of our sensor gradually disappeared as the operating temperature increased. The sensing behavior of our CO2 sensor was affected by the presence of water vapor, but its effect was small comparing with other sensors.

• Journal of Sensor Science and Technology
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• v.30 no.2
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• pp.94-98
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• 2021

In this study, pure and Co3O4/CoFe2O4-loaded Indium oxide (In2O3) nanofibers were synthesized by the electrospinning of an Indium/Polyvinylpyrrolidone precursor solution containing cobalt and iron bimetallic zeolitic imidazolate frameworks and subsequent heat treatment. The ethanol, toluene, p-xylene, benzene, carbon monodxide, and hydrogen gas sensing characteristics of the solution were measured at 250-400 ℃. 0.5 at%-Co3O4/CoFe2O4-loaded In2O3 nanofibers exhibited extreme response (resistance ratio - 1) to 5 ppm of ethanol (210.5) at 250 ℃ and excellent selectivity over the interfering gases. In contrast, pure In2O3 nanofibers exhibited relatively low responses to all the analyte gases and low selectivity above 250-400 ℃. The superior response and selectivity toward ethanol is explained by the catalytic roles of Co3O4 and CoFe2O4 in gas sensing reaction and the electronic sensitization induced by the formation of p (Co3O4/CoFe2O4)-n (In2O3) junctions.

• Journal of Sensor Science and Technology
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• v.18 no.1
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• pp.54-62
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• 2009

${Co_3}{O_4}$ and ${Co_3}{O_4}$-based thick films with additives such as ${Co_3}{O_4}-{Fe_2}{O_3}$(5 wt.%), ${Co_3}{O_4}-{SnO_2}$ (5 wt.%), ${Co_3}{O_4}-{WO_3}$(5 wt.%) and ${Co_3}{O_4}$-ZnO(5 wt.%) were fabricated by screen printing method on alumina substrates. Their structural properties were examined by XRD and SEM. The sensitivities to iso-${C_4}H_{10}$, $CH_4$, CO, $NH_3$ and NO gases were investigated with the thick films heat treated at $400^{\circ}C$, $500^{\circ}C$ and $600^{\circ}C$. From the gas sensing properties of the films, the films showed p-type semiconductor behaviors. ${Co_3}{O_4}-{SnO_2}$(5 wt.%) thick film heat treated at $600^{\circ}C$ showed higher sensitivity to i-${C_4}H_{10}$ and CO gases than other thick-films. ${Co_3}{O_4}-{SnO_2}$(5 wt.%) thick film heat treated at $600^{\circ}C$ showed the sensitivity of 170 % to 3000 ppm iso-${C_4}H_{10}$ gas and 100 % to 100 ppm CO gas at the working temperature of $250^{\circ}C$. The response time to i-${C_4}H_{10}$ and CO gases showed rise time of about 10 seconds and fall time of about $3{\sim}4$ minutes. The selectivity to i-${C_4}H_{10}$ and CO gases was enhanced in the ${Co_3}{O_4}-{SnO_2}$(5 wt.%) thick film.

• Journal of the Korean Ceramic Society
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• v.46 no.4
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• pp.429-435
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• 2009

In this study, we investigated microstructure and the CO gas sensing properties of Ag-CuO-$SnO_2$ thin films prepared by co-evaporation and subsequently thermal oxidation at air atmosphere. The sensitivity of a Cu-Sn films, thermally oxidized at $600^{\circ}C$, is strongly affected by the amount of Cu. At Cu:7 wt%-Sn:93 wt%, the film exhibited a maximum sensitivity of ${\sim}2.3$ to CO gas of 1000 ppm at $300^{\circ}C$. In contrast, the sensitivity of a Sn-Ag film did not change significantly with the amount of Ag. An enhanced sensitivity of ${\sim}3.7$ was observed in the film with a composition of Ag:3 wt%-Cu:4 wt%-Sn:93 wt%, when thermally oxidized at $600^{\circ}C$. In addition, this thin film shows a response time of ${\sim}80$ sec and a recovery time of ${\sim}450$ sec to 1000 ppm CO gas. The results demonstrate that the CO sensitivity of the Ag-CuO-$SnO_2$ thin films may be closely associated with coexistence of $SnO_2$ and SnO phase, decrease in average particle size, and a porous microstructure. We also suggest that co-evaporation and followed by thermal oxidation is a very simple and effective method to prepare oxide gas sensor thin films.

• Korean Journal of Materials Research
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• v.34 no.5
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• pp.235-241
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• 2024

Gas identification techniques using pattern recognition methods were developed from four micro-electronic gas sensors for noxious gas mixture analysis. The target gases for the air quality monitoring inside vehicles were two exhaust gases, carbon monoxide (CO) and nitrogen oxides (NO_x), and two odor gases, ammonia (NH₃) and formaldehyde (HCHO). Four MEMS gas sensors with sensing materials of Pd-SnO₂ for CO, In₂O₃ for NO_X, Ru-WO₃ for NH₃, and hybridized SnO₂-ZnO material for HCHO were fabricated. In six binary mixed gas systems with oxidizing and reducing gases, the gas sensing behaviors and the sensor responses of these methods were examined for the discrimination of gas species. The gas sensitivity data was extracted and their patterns were determined using principal component analysis (PCA) techniques. The PCA plot results showed good separation among the mixed gas systems, suggesting that the gas mixture tests for noxious gases and their mixtures could be well classified and discriminated changes.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.24 no.3
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• pp.215-218
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• 2011

A novel design of gas sensor using Ga-doped ZnO (GZO) thin films which are deposited on low temperature co-fired ceramic (LTCC) substrates is presented. The LTCC substrates with thickness of 400 ${\mu}m$ are fabricated by laminating 12 green tapes which consist of alumina and glass particle in an organic binder. The GZO thin films with different thickness are deposited on LTCC substrates, by RF magnetron sputtering method. The microstructure and sensing properties of GZO gas sensing films are analyzed as a function of the film thickness. The films are well crystallized in the hexagonal (wurzite) structure with increasing thickness. The maximum sensitivity of 3.49 is obtained at 100 nm film thickness and the fastest 90% response time of 27.2 sec is obtained at 50 nm film thickness for the operating temperature of $400^{\circ}C$ to the $NO_2$ gas.

• Journal of the Korean Institute of Telematics and Electronics
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• v.26 no.11
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• pp.1691-1698
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• 1989

Gas sensing effects produced by adsorptive reaction between specimen surface and gases are expected to be influenced greatly by the state of the speimen surface. In this study, Co1-xMgxO ceramics oxygen sensors were prepared by pressing at 0.3-1.5ton/cm\ulcornerwith or without binder, intending to change porosity and average grain size on the surface purposely. The composition ratio of CoO to MgO was fixed at 1:1(mol.%). Microstructure of prepared Co0.5Mg0.5O ceramics were observed, the electrical properties and the sensitivity characteristics for oxygen gas were investigated in the device temperature range of 700-1000\ulcorner and for oxygen partical pressure range of 1-10**-4 atm. Temperature dependence of the resistivity of the specimen showed NTC behavior, average grain size increased and porosity decreased with increasing compaction pressure. The slope of the resistivity of the specimen on the oxygen partial pressure decreased with increasing average grain size and with decreasing porosity. Particularly, specimen pressed by 0.3 and 0.5 ton/cm\ulcornershowed the highest sensitivity to oxygen gas.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.30 no.5
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• pp.288-293
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• 2017

$Fe_2O_3$ is one of the most important metal oxides for gas sensing applications because of its low cost and high stability. It is well-known that the shape, size, and phase of $Fe_2O_3$ have a significant influence on its sensing properties. Many reports are available in the literature on the use of $Fe_2O_3$-based sensors for detecting gases, such as $NO_2$, $NH_3$, $H_2S$, $H_2$, and CO. In this paper, we investigated the gas-sensing performance of a Pt-doped ${\varepsilon}$-phase $Fe_2O_3$ gas sensor. Pt-doped $Fe_2O_3$ nanoparticles were synthesized by a Sol-Gel method. Platinum, known as a catalytic material, was used for improving gas-sensing performance in this research. The gas-response measurement at $300^{\circ}C$ showed that $Fe_2O_3$ gas sensors doped with 3%Pt are selective for $NO_2$ gas and exhibita maximum response of 21.23%. The gas-sensing properties proved that $Fe_2O_3$ could be used as a gas sensor for nitrogen dioxide.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1997.11a
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• pp.347-349
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• 1997

In order to investigate CO sensing property of a SnO$_2$-WO$_3$composite ceramic. we prepared pure SnO$_2$and WO$_3$added SnO$_2$compostie ceramics. Using XRD and SEM, a phase analysis and microstructure were investigated. The resistances as a function of gas atmosphere were measured by High Voltage Measure/source Unit. The measured 1000ppm CO gas sensitivity of SnO$_2$-WO$_3$composite ceramics were smaller than that of pure SnO$_2$.