• Journal of the Korean institute of surface engineering
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• v.50 no.3
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• pp.225-229
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• 2017

ZnO nanotubes were synthesized to investigate the effect of wall thickness on the ethanol gas sensing performance. The wall thickness of the nanotubes was varied from approximately 20 to 60 nm. Transmission electron microscopy, X-ray diffraction and SAED (Selected Area Electron Beam Diffraction) analyses showed that the synthesized nanotubes were polycrystalline structured ZnO with the diameter of approximately 200-300nm. The ZnO nanotubes sensor with an optimum wall thickness of 51.8nm showed approximately 8 times higher response, compared to that with 21.14nm wall thick nanotubes, to the ethanol concentration of 500 ppm at the temperature of $300^{\circ}C$. The wall thickness of 51.8nm was found to be a little larger than 46nm, which was theoretically derived Debye length. Along with the study of the wall thickness effect on the performance of the sensors, the mechanisms of gas sensing of the polycrystalline ZnO nanotubes are also discussed.

• Journal of Sensor Science and Technology
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• v.13 no.4
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• pp.292-297
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• 2004

Carbon nanotubes (CNT) were synthesized by arc-discharge method. To fabricate CNT sensor, CNT powder was dispersed in ${\alpha}$-Terpinol($C_{10}H_{17}OH$) solution. The CNT tilms were fabricated by screen printing method on the interdigitated Pt/Pd alloy electrode. The microstructure of CNT film was observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). In order to investigate the gas sensing characteristics of the film, the CNT film was experimented to measure NO response and recovery time. The CNT sensor with a heater was compared to that without a heater. And this sensor shows better reproductibility and faster recovery time than another CNT sensors. We suggest the possibility to utilize a CNT as new sensing materials for environmental monitoring.

• Journal of the Korean Ceramic Society
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• v.32 no.12
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• pp.1369-1376
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• 1995

The WO3 thin-film NOx sensor which is of practical use and includes the heater and the temperature sensor was fabricated. The WO3 thin films as a gas-sensing layer was deposited at ambient temperature in a high-vacuum resistance heated evaporator. The highest sensitivity of the WO3 thin-film sensor to NOx was obtained under the condition of the annealing temperature of 50$0^{\circ}C$ and the operating temperature of 30$0^{\circ}C$. The gas sensing characteristics of this sensor was excellent, i.e. high sensitivity (Rgas/Rair in 3 ppm NO2=53) and fast response time (4 seconds).

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.37 no.4
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• pp.347-357
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• 2024

Oxide semiconductor gas sensors are widely used for detecting toxic, explosive, and flammable gases due to their simple structure, cost-effectiveness, and potential integration into compact devices. However, their reliable gas detection is hindered by a longstanding issue known as humidity dependence, wherein the sensor resistance and gas response change significantly in the presence of moisture. This problem has persisted since the inception of oxide semiconductor gas sensors in the 1960s. This paper explores the root causes of humidity dependence in oxide semiconductor gas sensors and presents strategies to address this challenge. Mitigation strategies include functionalizing the gas-sensing material with noble metal/transition metal oxides and rare-earth/rare-earth oxides, as well as implementing a moisture barrier layer to prevent moisture diffusion into the gas-sensing film. Developing oxide semiconductor gas sensors immune to humidity dependence is expected to yield substantial socioeconomic benefits by enabling medical diagnosis, food quality assessment, environmental monitoring, and sensor network establishment.

• Journal of Sensor Science and Technology
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• v.29 no.2
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• pp.112-117
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• 2020

Xylene is a hazardous volatile organic compound that should be precisely measured to monitor indoor air quality. However, the selective and sensitive detection of ppm-level xylene using oxide-semiconductor gas sensors remains a challenge. In this study, pure and Cr-doped Co₃O₄ nanoparticles (NPs) were prepared using flame spray pyrolysis, and their gas-sensing characteristics to 5-ppm xylene at 250 ℃ were investigated. The 4 at% Cr-doped Co₃O₄ NPs exhibited a high gas response to 5-ppm xylene (resistance ratio to gas and air = 39.1) and negligible cross-responses to other representative and ubiquitous indoor pollutants such as ethanol, benzene, formaldehyde, carbon monoxide, and ammonia. In this paper, the enhancement of the gas response and selectivity of Co₃O₄ NPs to xylene by Cr doping was discussed in relation to the catalytic promotion of the gas-sensing reaction. This sensor can be used to monitor indoor xylene.

• Proceedings of the Materials Research Society of Korea Conference
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• 2011.05a
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• pp.25.2-25.2
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• 2011

The tungsten oxide wire-like nanostructure is fabricated by deposition and thermal oxidation of tungsten metal on porous single wall carbon nanotubes (SWNTs). The morphology and crystalline quality of materials are investigated by SEM, TEM, XRD and Raman analysis. The results prove that $WO_3$ wire-like nanostructure fabricated on SWNTs show highly porous structures. Exposure of the sensors to NH3 gas in the temperature range of 150~300$^{\circ}C$ resulted in the highest sensitivity at $250^{\circ}C$ with quite rapid response and recovery time. Response time as a function of test concentrations and NH3 gas sensing mechanism is reported and discussed.

• Journal of Sensor Science and Technology
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• v.15 no.6
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• pp.457-461
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• 2006

To use the porous silicon as gas sensors, we made the MOPS structure from the porous silicon with Al evaporation and investigated the sensing characteristic of ethanol. When the MOPS structure is in contact with ethanol gas, the maximum peak of PL changes and it return to original intensity without contact. The MOPS structure had response time 0.78s and recovery time 4.13s when it is in contact with ethanol, which satisfied the required sensor standards. Further complimentary researches, however, are required to investigate the contact mechanism between MOPS structure and ethanol and to solve the surface contamination problem.

• Journal of Sensor Science and Technology
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• v.17 no.3
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• pp.183-187
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• 2008

A sub-ppm level MEMS gas sensor that can be used for the detection of formaldehyde (HCHO) is presented. It is realized by using a zinc oxide (ZnO) thin-film material with a Ni-seed layer as a sensing material and by bulk micromachining technology. To enhance sensitivity of the MEMS gas sensor with Ni-seed layer was embedded with ZnO sensing material and sensing electrodes. As experimental results, the changed sensor resistance ratio for HCHO gas was 9.65 % for 10 ppb, 18.06 % for 100 ppb, and 35.7 % for 1 ppm, respectively. In addition, the minimum detection level of the fabricated MEMS gas sensor was 10 ppb for the HCHO gas. And the measured output voltage was about 0.94 V for 10 ppb HCHO gas concentration. The noise level of the fabricated MEMS gas sensor was about 50 mV. The response and recovery times were 3 and 5 min, respectively. The consumption power of the Pt micro-heater under sensor testing was 184 mW and its operating temperature was $400^{\circ}C$.

• Journal of the Microelectronics and Packaging Society
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• v.6 no.2
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• pp.63-68
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• 1999

We have fabricated $WO_3$ thick film gas sensor under various firing conditions in order to study gas sensing properties in terms of the variation of microstructure and non-stoichiometric structure of gas sensing layer. $WO_3$ paste mixed homogeneously with organic vehicle was coated by screen printing method on alumina substrate composed of Au electrode and $RuO_2$heater on each side. To change filing condition, sensing materials were fared at 600-$800^{\circ}C$ for 1 hour and refired at $700^{\circ}C$ for 1 hour in the mixtures of $_Ar/O2$gas. In the result of heat-treatment, $WO_3$ gas sensor fared at $700^{\circ}C$ showed best gas sensing properties of 210 gas sensitivity and 2 second response time and the best firing environment was 40-50% of $Ar/O_2$gas.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.17 no.3
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• pp.294-298
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• 2004

Carbon nanotubes(CNTs) were synthesized by thermal chemical vapor deposition(CVD) method. To fabricate CNT gas sensor, catalyst metal layer was deposited on microstructure. The CNT gas detecting layer was grown by thermal CVD method on the catalyst metal layer. In order to investigate the gas sensing characteristics of the fabricated CNT gas sensor, it was exposed in NO$_2$ gas and sensitivity, response, and recovery time were measured. As the result, this sensor has better reproductibility and faster recovery time than another CNT gas sensors.