• Journal of Sensor Science and Technology
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• v.19 no.5
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• pp.356-360
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• 2010

Due to the high surface-to-volume ratio, the 3-dimensional(3D) nanostructures of metal oxides are regarded as the best candidate materials for the chemical gas sensors. Here we have synthesised flower-like 3D zinc oxide nanostructures through a simple hydrothermal route. Specific surface area of the 3D zinc oxide nanostructures synthesised in different pH values from 9.0 to 12.0 were evaluated by using a BET analyzer and the results were compared with that of a zinc oxide thin film fabricated by rf sputtering. Using interdigitated electrodes, superior CO gas sensing properties of the 3D zinc oxide nanostructures on the ZnO thin film to those of the ZnO thin film were demonstrated.

• Journal of Sensor Science and Technology
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• v.15 no.5
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• pp.309-316
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• 2006

The $SnO_{2}$ thin film sensors were fabricated by a thermal oxidation method. $SnO_{2}$ thin film sensors were treated in $N_{2}$ atmosphere. The sensors with $O_{2}$ treatment after $N_{2}$ treatment showed 70 % sensitivity for 1 ppm $H_{2}S$ gas, which is higher than the sensors with only $O_{2}$ treatment. The Ni metal was evaporated on Sn thin film on the $Al_{2}O_{3}$ substrate. And the sensor was heated to grow the Sn nanowire in the tube furnace with $N_{2}$ atmosphere. Sn nanowire was thermally oxidized in $O_{2}$ environments. The sensitivity of $SnO_{2}$ nanowire sensor was measured at 500 ppb $H_{2}S$ gas. The selectivity of $SnO_{2}$ nanowire sensor compared with thin film and thick film $SnO_{2}$ was measured for $H_{2}S$, CO, and $NH_{3}$ in this study.

• Transactions on Electrical and Electronic Materials
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• v.13 no.1
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• pp.27-30
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• 2012

This paper proposes a micro gas sensor for measuring $H_2S$ gas. This is based on a $SnO_2$-CuO multi-layer thin film. The sensor has a silicon diaphragm, micro heater, and sensing layers. The micro heater is embedded in the sensing layer in order to increase the temperature to an operating temperature. The $SnO_2$-CuO multi layer film is prepared by the alternating deposition method and thermal oxidation which uses an electron beam evaporator and a thermal furnace. To determine the effect of the number of layers, five sets of films are prepared, each with different number of layers. The sensitivities are measured by applying $H_2S$ gas. It has a concentration of 1 ppm at an operating temperature of $270^{\circ}C$. At the same total thickness, the sensitivity of the sensor with multi sensing layers was improved, compared to the sensor with one sensing layer. The sensitivity of the sensor with five layers to 1 ppm of $H_2S$ gas is approximately 68%. This is approximately 12% more than that of a sensor with one-layer.

• Korean Journal of Materials Research
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• v.6 no.7
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• pp.716-722
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• 1996

Effect of Film thickness on the sensing behavior of thin-film-type ags sensor has been analyzed by deriving an equation form a simple model, and the equation was applied to the sensing behavior of ${SnO}_{2}$ and CuO-${SnO}_{2}$ thin-film sensors. It was revealed, from the equation,that the gas sensing property was closely related to gas diffusivity into the film which was a function of film thickness, reactivity of the gas detected with sensing material, operating temperature, etc. The equation derived was well consistent with the experimental results from ${SnO}_{2}$ and CuO-${SnO}_{2}$ thin-film sensors and explained their different ${H}_{2}S$ sensing behaviors. Finally, a medel was suggested, explainning the effect of gas diffusivity on sensing be havior of oxide semiconductor sensor.

• Korean Journal of Materials Research
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• v.25 no.7
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• pp.358-363
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• 2015

We present an excellent detection for nitrogen monoxide (NO) gas using polycrystalline ZnO wire-like films synthesized via a simple method combined with sputtering of Zn metallic films and subsequent thermal oxidation of the sputtered Zn nanowire films in dry air. Structural and morphological characterization revealed that it would be possible to synthesize polycrystalline hexagonal wurtzite ZnO films of a wire-like nanostructure with widths of 100-150 nm and lengths of several microns by controlling the sputtering conditions. It was found from the gas sensing measurements that the ZnO wire-like thin film gas sensor showed a significantly high response, with a maximum value of 29.2 for 2 ppm NO at $200^{\circ}C$, as well as a reversible fast response to NO with a very low detection limit of 50 ppb. In addition, the ZnO wire-like thin film gas sensor also displayed an NO-selective sensing response for NO, $O_2$, $H_2$, $NH_3$, and CO gases. Our results illustrate that polycrystalline ZnO wire-like thin films are potential sensing materials for the fabrication of NO-sensitive high-performance gas sensors.

• Journal of Sensor Science and Technology
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• v.5 no.5
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• pp.39-46
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• 1996

The Pd or Pt-doped $WO_{3}$ thin-film NOx sensor was fabricated. The $WO_{3}$-based thin films as a gas-sensing layer were deposited at ambient temperature in a high-vacuum resistance heated evaporator and annealed at $500^{\circ}C$. The gas sensitivity ($R_{gas}/R_{air}$) to 5 ppm $NO_{2}$ measured at the operating temperature of $300^{\circ}C$ was 50 (highest sensitivity) for the 0.5 wt.% $Pt-WO_{3}$ sensor.

• 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 $400^{\circ}C$.

• Korean Journal of Materials Research
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• v.25 no.4
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• pp.171-176
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• 2015

We present the detection characteristics of nitrogen monoxide(NO) gas using p-type copper oxide(CuO) thin film gas sensors. The CuO thin films were fabricated on glass substrates by a sol-gel spin coating method using copper acetate hydrate and diethanolamine as precursors. Structural characterizations revealed that we prepared the pure CuO thin films having a monoclinic crystalline structure without any obvious formation of secondary phase. It was found from the NO gas sensing measurements that the p-type CuO thin film gas sensors exhibited a maximum sensitivity to NO gas in dry air at an operating temperature as low as $100^{\circ}C$. Additionally, these CuO thin film gas sensors were found to show reversible and reliable electrical response to NO gas in a range of operating temperatures from $60^{\circ}C$ to $200^{\circ}C$. It is supposed from these results that the p-type oxide semiconductor CuO thin film could have significant potential for use in future gas sensors and other oxide electronics applications using oxide p-n heterojunction structures.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.11 no.11
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• pp.1001-1006
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• 1998

$WO_3$ based semiconduction sensor have been reported to have excellent sension properties to $NO_x$ gases by many researchers. In this study appropriate $WO_3$ precursor have been chosen and thin film sensors were fabricated by metallo organic deposition process. Their sensing characteristics were investigated as a function of NO concentration, heat treatment, and measuring temperature. Tungsten dichloro triethoxide was found to be a good precursor for $WO_3$ thin film in this method. Samples heat treated at $600^{\circ}C$ showed sensitivity (S) 200 to 50 ppm NO gas when measuring temperature was $150^{\circ}C$.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.29 no.4
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• pp.272-278
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• 1993

The trimethylamine-sensing characteristics of ZnO based thin film semiconductors and the sensitivity enhancement by squttering conditions have been investigated to develop a new type sensor for detecting fish freshness. The sensor fabricated with a 300nm of ZnO thin film with 4 wt% Al sub(2) O sub(3) and 1 wt% TiO sub(2) exhibited the highest sensitivity of 155 at 30$0^{\circ}C$ of working temperature and to the 240 ppm TMA gas. Deposition of ZnO thin film using a RF magnetron sputter was carried out at a pressure of 10 super(-2) Torr in pure oxygen gas with an RF power of 100W. The sensor exhibited a large response to the actual gases produced by a mackerel at an early stage of decomposition.