• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제54권5호
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• pp.232-237
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• 2005

In this paper, we fabricated $CO_2$ gas sensor based on the MEMS infrared sensor and characterized its electrical and $CO_2$-sensing properties. The fabricated $CO_2$ gas sensor by MEMS technique has many advanges over NDIR(nondispersive) $CO_2$ sensor such as monolithic fabrication, very high selectivity on $CO_2$, low power consumption and compact system. Microbolometer by surface micromachining was fabricated for gas detector and $CO_2$ filter chip by bulk micromachining was fabricated for signal referencing. By using the proposed and fabricated gas sensor, we are expected to measure $CO_2$ concentration more accurately with high reliability.

• 한국자동차공학회논문집
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• 제8권2호
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• pp.41-49
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• 2000

To understand the signal fluctuation of a wide-range oxygen sensor installed at the exhaust confluence point, when a misfiring is triggered in a cylinder, the steady state and the transient response characteristics of the sensor to the flow of the misfired gas were investigated quantitatively. It was recognized that the steady state output voltage of the sensor increased higher when it contacted the misfired gas even though the fueling condition was the same as the normal combustion case and this characteristic enabled the application of the wide-range oxygen sensor for the misfire detection. The transient response was compared at different engine speeds and it was found that the response speed increased with the engine speed. The signal fluctuation was also estimated quantitatively, using these steady state and transient response of the sensor, and the estimated signal showed satisfactory correlation with the measurements.

• 한국재료학회지
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• 제34권5호
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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.

• 공업화학
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• 제25권2호
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• pp.193-197
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• 2014

피치계 활성탄소섬유의 유해가스 감응특성을 알아보고자 피치계 활성탄소섬유와 폴리비닐알코올(PVA)을 이용하여 가스센서용 전극을 제조하였다. 제조된 가스센서용 활성탄소섬유 전극의 물리화학적 특성은 주사전자현미경(SEM) 및 비표면적 측정기(BET)를 이용하여 분석하였다. 또한, 전극의 유해가스 감응특성은 $NH_3$, NO 및 $CO_2$와 같은 여러 유독가스를 이용하여 확인하였다. 가스센서용 활성탄소섬유 전극의 비표면적은 바인더인 PVA에 의하여 활성탄소섬유보다 33% 감소하였지만, 전극의 기공크기분포는 PVA에 의하여 크게 영향을 받지 않았다. 가스센서용 활성탄소섬유 전극은 반도체 기반 가스센서와는 다르게 전자도약에 의해서 유해가스를 감응하였다. 본 연구에서, 활성탄소섬유 전극의 저항은 100 ppm의 $NH_3$ 유해가스에 대하여 7.5% 감소하였으며, 그 $NH_3$ 가스 감응특성이 다른 유해가스보다 뛰어남을 확인하였다.

• 센서학회지
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• 제29권6호
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• pp.420-426
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• 2020

A metal oxide semiconductor gas sensor is operated by measuring the changes in resistance that occur on the surface of nanostructures for gas detection. ZnO, which is an n-type metal oxide semiconductor, is widely used as a gas sensor material owing to its high sensitivity. Various ZnO nanostructures in gas sensors have been studied with the aim of improving surface reactions. In the present study, the sol-gel and vapor phase growth techniques were used to fabricate nanostructures to improve the sensitivity, response, and recovery rate for gas sensing. The sol-gel method was used to synthesize SnO₂ nanoparticles, which were used as the seed layer. The nanoparticles size was controlled by regulating the process parameters of the solution, such as the pH of the solution, the type and amount of solvent. As a result, the SnO₂ seed layer suppressed the aggregation of the nanostructures, thereby interrupting gas diffusion. The ZnO nanostructures with a sol-gel processed SnO₂ seed layer had larger specific surface area and high sensitivity. The gas response and recovery rate were 1-7 min faster than the gas sensor without the sol-gel process. The gas response increased 4-24 times compared to that of the gas sensor without the sol-gel method.

• 센서학회지
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• 제19권6호
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• pp.462-468
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• 2010

A low power gas sensor with microheater was fabricated by MEMS technology. In order to heat up the gas sensing material to a operating temperature, a platinum(Pt) micro heater was built on to the micromachined Si substrate. The width and gap of microheater were $20\;{\mu}m$ and $4.5\;{\mu}m$, respectively. ZnO nanowhisker arrays were fabricated on a sensor device by hydrothermal method. The sensor device was deposited with ZnO seeds using PLD systems. A 200 ml aqueous solution of 0.1 mol zinc nitrate hexahydrate, 0.1 mol hexamethylenetetramine, and 0.02 mol polyethylenimine was used for growthing ZnO nanowhiskers. The power consumption to heat up the gas sensor to a operating temperature was measured and temperature distribution of sensor was analyzed by a Infrared Thermal Camera. The optimum temperature for highest sensitivity was found to be $250^{\circ}C$ although relatively high(64 %) sensitivity was obtained even at as low as $150^{\circ}C$. The power consumption was 72 mW at $250^{\circ}C$ and was only 25 mW at $150^{\circ}C$.

• Journal of Biosystems Engineering
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• 제23권4호
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• pp.359-364
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• 1998

A PC based measurement system was developed and it consisted of ammonia sensor(TS-1000), AMP & MUX Board, A/D Converter, and personal computer. The results obtained from the study are summarized as follows : 1. The relationship of outputs(V) of ammonia sensor(AS) and concentrations(ppm) of ammonia gas was analyzed by the linear regression analysis and the output values were very accurate when compared with standard ammonia gas. 2. The test results showed that the performance of ammonia gas sensor was not 31B3c1e4 by temperatures and humidities 3. The developed ammonia gas measurement system was proved to be practically uesful for measuring concentrations of ammonia gas in pig housing.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1999년도 추계학술대회 논문집 학회본부 C
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• pp.1011-1014
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• 1999

An on-board monitoring system for an automobile emission gas has a test chamber remote from the automobile's engine exhaust gas stream: apparatus for supplying the chamber with sampled exhaust gases. A single hydrocarbon sensor exposed to the exhaust gas in the chamber to render a signal responsive to the hydrocarbon. The conductive ions in emission gas was checked by the HC sensor in test chamber. A preferred application includes hydrocarbons in an automotive exhaust gas stream by exposing a transition porous alumina($Al_{2}O_{3}$) ceramic based sensor to the same exhaust gas stream. By combining the electrical signal, a measure of hydrocarbons can be provided.

• 센서학회지
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• 제29권1호
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• pp.14-18
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• 2020

This study investigates the nitrogen dioxide (NO₂) sensing characteristics of an Si MOSFET gas sensor with a tungsten trioxide (WO₃) sensing layer deposited using the sputtering method. The Si MOSFET gas sensor consists of a horizontal floating gate (FG) interdigitated with a control gate (CG). The WO₃ sensing layer is deposited on the interdigitated CG-FG of a field effect transistor(FET)-type gas sensor platform. The sensing layer is deposited with different thicknesses of the film ranging from 100 nm to 1 ㎛ by changing the deposition times during the sputtering process. The sensing characteristics of the fabricated gas sensor are measured at different NO₂ concentrations and operating temperatures. The response of the gas sensor increases as the NO₂ concentration and operating temperature increase. However, the gas sensor has an optimal performance at 180℃ considering both response and recovery speed. The response of the gas sensor increases significantly from 24% to 138% as the thickness of the sensing layer increases from 100 nm to 1 ㎛. The sputtered WO₃ film consists of a dense part and a porous part. As reported in previous work, the area of the porous part of the film increases as the thickness of the film increases. This increased porous part promotes the reaction of the sensing layer with the NO₂ gas. Consequently, the response of the gas sensor increases as the thickness of the sputtered WO₃ film increases.

• 센서학회지
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• 제30권3호
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• pp.175-180
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• 2021

In this paper, methods for improving the sensitivity of gas sensors to NO₂ gas are presented. A gas sensor was fabricated based on an SnO₂ nanowire network using the vapor-phase-growth method. In the gas sensor, the Au electrode was replaced with a fluorinedoped tin oxide (FTO) electrode, to achieve high sensitivity at low temperatures and concentrations. The gas sensor with the FTO electrode was more sensitive to NO₂ gas than the sensor with the Au electrode: notably, both sensors were based on typical SnO₂ nanowire network. When the Au electrode was replaced by the FTO electrode, the sensitivity improved, as the contact resistance decreased and the surface-to-volume ratio increased. The morphological features of the fabricated gas sensor were characterized in detail via field-emission scanning electron microscopy and X-ray diffraction analysis.