• 한국세라믹학회지
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• 제34권4호
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• pp.387-393
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• 1997

In order to apply WO3 thin films to the semiconducting NOx gas sensors as a sensing material, which have been expected to show good electrical properties, such as large sensitivity, rapid responsibility, and high selectivity, the fabrication method and their sensing characteristics were studied. The variations of surface morphologies, crystallographic orientations and crystallinity with the WO3 thin film growing methods thermal evaporation and DC sputtering methods were investigated by using scanning electron microscopy (SEM) and X-ray diffraction(XRD) analysis. As a result of sensitivity (Rgas/Rair) measurements for the 5 ppm NO2 test gas, the sensitivity values were 113 for the sputtered films and 93 for the evaporated films. It was also observed that the recovery rate of a sensing signal after measuring sensitivity was faster in the sputtered films than in the evaporated films.

• 한국세라믹학회지
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• 제30권9호
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• pp.701-708
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• 1993

Pd-doped SnO2 thin films for hydrogen gas sensing were fabricated by reactive fo magnetron sputtering and were studied on effects of film thickness and Pd doping content. Pd doping caused the optimum sensor operation temperature to reduce down to ~25$0^{\circ}C$ and also enhanced gas sensitivity, compared with undoped SnO2 film. Gas sensitivity depended on the film thickness. The sensitivity increased with decreasing the film thickness, showing maximum sensitivities at the thickness of 730$\AA$ and 300~400$\AA$ for the undoped SnO2 and the Pd-doped SnO2 film, respectively. Further decrease of the film thickness beyond these thickness ranges, however, resulted in the reduction of sensitivity again.

• The Korean Journal of Ceramics
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• 제5권2호
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• pp.110-114
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• 1999

NOx sensing properties of $Ba_2WO_5$ were investigated by varying the sintering temperature in an effort to study the effects of the neck-width on gas sensitivity. $Ba_2WO_5$ sintered at $800^{\circ}C$, which exhibits neck-controlled conduction provides highest sensitivity of 47 and 29 at $500^{\circ}C$ to NO and $NO_2$, respectively. The samples sintered beyond $800^{\circ}C$ show sintering temperature-independent gas sensitivity. This may be because the grain boundary control is dominant at lower sintering temperatures and open neck control is dominant at higher sintering temperatures than $800{\circ}C$. The NOx sensing mechanism of $Ba_2WO_5$ was briefly discussed.

• 한국세라믹학회지
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• 제27권5호
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• pp.638-644
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• 1990

The C3H8 gas sensitivities of SnO2, Pd-SnO2, Pt-SnO2 gas sensor are looked over with the impregnation method of PdCl2, H2PtCl6 solution on SnO2. The Cl- ion due to incomplete decomposition of PdCl2 at 80$0^{\circ}C$ for 30 min decrease the C3H8 gas sensitivity of SnO2, and the sensitivity is increased by the impreganation of H2PtCl6 solution on SnO2 because of its lower decomposition temperature compared with PdCl2. The C3H8 gas sensitivities of Pd-SnO2, Pt-SnO2 impregnated slightly after 1st sintering are larger than that of pure SnO2 sensor because very small amount of Cl- ion exist in sample due to smaller amount of impregnaiton.

• 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.

• Transactions on Electrical and Electronic Materials
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• 제11권2호
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• pp.77-80
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• 2010

Indium tin oxide (ITO) films with a 5 nm thick Au interlayer were prepared on glass substrates. The effects of the Au interlayer on the gas sensitivity for detecting methanol vapors were investigated at room temperature. The conductivity of the film sensor increased upon exposure to methanol vapor and the sensitivity also increased proportionally with the methanol vapor concentration. In terms of the sensitivity measurements, the ITO film sensor with an Au interlayer shows a higher sensitivity than that of the conventional ITO film sensor. This approach is promising in gaining improvement in the performance of ITO gas sensors used for the detection of methanol vapor at room temperature.

• 한국전기전자재료학회논문지
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• 제26권4호
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• pp.325-329
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• 2013

Carbon nanotubes(CNT) have excellent electrical, chemical stability and mechanical properties. These can be used in a variety of fields. MWCNT are extremely sensitive for minute changes in the ambient gas, namely, their sensing properties varies greatly with the absorption of gas such as NOx and $H_2$. We investigate the electrical properties of CNTs and make a NOx gas sensor based on Multi-walled carbon nanotubes (MWCNT) materials. We obtained the NOx gas sensor of MWCNT based on P-type Si wafer that has the resistivity of $1.667{\times}10^{-1}[{\Omega}{\cdot}cm]$. We knew that the sensitivity of sensor decreased with increasing of NOx gas concentration. And the sensitivity of sensor shows the largest value at $20^{\circ}C$. The sensitivity of sensor decrease with increasing the temperature. Also absorption energy of NOx gas molecule on the MWCNT surface decreases with increasing concentration of NOx gas.

• 한국전기전자재료학회논문지
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• 제25권2호
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• pp.91-95
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• 2012

ZnO thin films were deposited on p-type 4H-SiC substrate by pulsed laser deposition. ZnO nanowires were formed on p-type 4H-SiC substrate by furnace. Ti/Au electrodes were deposited on ZnO thin film/SiC and ZnO nanowire/SiC structures, respectively. Structural and crystallographical properties of the fabricated ZnO thin film/SiC and ZnO nanowire/SiC structures were investigated by field emission scanning electron microscope and X-ray diffraction. In this work, resistance and sensitivity of ZnO thin film/SiC gas sensor and ZnO nanowire/SiC gas sensor were measured at $300^{\circ}C$ with various CO gas concentrations (0%, 90%, 70%, and 50%). Resistance of gas sensor decreases at CO gas atmosphere. Sensitivity of ZnO nanowire/SiC gas sensor is twice as big as sensitivity of ZnO thin film/SiC gas sensor.

• 한국재료학회지
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• 제21권4호
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• pp.232-235
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• 2011

ZnO nanorods for gas sensors were prepared by a hydrothermal method. The ZnO gas sensors were fabricated on alumina substrates by a screen printing method. The gas-sensing properties of the ZnO nanorods were investigated for $CH_4$ gas. The effects of growth time on the structural and morphological properties of the ZnO nanorods were investigated by X-ray diffraction and scanning electron microscope. The XRD patterns of the nanocrystallized ZnO nanorods showed a wurtzite structure with the (002) predominant orientation. The diameter and length of the ZnO nanorods increased in proportion to the growth time. The sensitivity of the ZnO sensors to 5 ppm $CH_4$ gas was investigated for various growth times. The ZnO sensors exhibited good sensitivity and rapid response-recovery characteristics to $CH_4$ gas, and both traits were dependent on the growth time. The highest sensitivity of the ZnO sensors to $CH_4$ gas was observed with the growth time of 7 h. The response and recovery times were 13 s and 6 s, respectively.

• 한국세라믹학회지
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• 제25권4호
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• pp.341-348
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• 1988

Thin films of tin-oxide were prepared by chemical vapor deposition technique using the direct of SnCl4. Resistivity and carrier concentration of deposited SnO2 thin film were measured by 4-point probe method and Hall effect measurement. The results showed the remarkable dependence of electrical properties on the deposition temperature. As the deposition temperature increased, resistivity of deposited film initially decreased to a minimum value of ~10-3$\Omega$cm at 50$0^{\circ}C$, and then rapidly increased to ~10$\Omega$cm at $700^{\circ}C$. Electrical conductance of these films was measured in exposure to H2 gas. It was found that gas sensitivity was affected combination of film thickness and intrinsic resistivity of deposited film. Gas sensitivity increased with decrease of film thickness. Fairly high sensitivity to H2 gas was obtained for the film deposited at $700^{\circ}C$. Optimum operation temperature of sensing was 30$0^{\circ}C$ for H2 gas.