• Transactions on Electrical and Electronic Materials
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• v.5 no.5
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• pp.189-193
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• 2004

Pure and Sn or Pt doped $\alpha-Fe_2O_3$ thin films were prepared on $Al_2O_3$ substrates by RF-magnetron sputtering method and the sensitivities were compared. It was found that pure $\alpha-Fe_2O_3$ thin films did not exhibit much selectivity in CO and $i-C_4H_{10}$ gases while it showed the high sensitivity in proportion to the gas concentration of $C_2H_{5}OH$ gas. Pt-doped $\alpha-Fe_2O_3$ showed to be alike sensing properties as pure $\alpha-Fe_2O_3$ thin film in $C_2H_{5}OH$ gas. However, Sn-doped $\alpha-Fe_2O_3$ thin films exhibited the excellent sensitivity and selectivity in Hz gas. After microstructure modification by plasma etching on pure $\alpha-Fe_2O_3$ thin films, the gas sensing characteristics were dramatically changed.

• 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.

• Proceedings of the KIEE Conference
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• 1991.07a
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• pp.209-212
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• 1991

Recently, oxide semiconductor gas sensors consisted of n-type semiconductor materials such as $SnO_2$, ZnO and $Fe_2O_3$ have been widely used to detect reducing gases. The advantage of thick-film technology include the possibility of mass-production and automation, that of integrating the sensing element in a hybrid circuit and that of fuctional trimming of the sensor and/or the circuit. which would enable really interchangeable transducers to be prepared. In this paper, we made ZnO and $SnO_2$ gas sensors and investigated the sensitivity to CO gas. Therefore, we compared a ZnO gas sensor with a $SnO_2$ gas sensor.

• Korean Journal of Materials Research
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• v.20 no.5
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• pp.267-270
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• 2010

Sn doped $In_2O_3$ (ITO) and ITO/Cu/ITO (ICI) multilayer films were prepared on glass substrates with a reactive radio frequency (RF) magnetron sputter without intentional substrate heating, and then the influence of the Cu interlayer on the methanol gas sensitivity of the ICI films were considered. Although both ITO and ICI film sensors had the same thickness of 100 nm, the ICI sensors had a sandwich structure of ITO 50 nm/Cu 5 nm/ITO 45 nm. The ICI films showed a ten times higher carrier density than that of the pure ITO films. However, the Cu interlayer may also have caused the decrement of carrier mobility because the interfaces between the ITO and Cu interlayer acted as a barrier to carrier movement. Although the ICI films had two times a lower mobility than that of the pure ITO films, the ICI films had a higher conductivity of $3.6{\cdot}10^{-4}\;{\Omega}cm$ due to a higher carrier density. The changes in the sensitivity of the film sensors caused by methanol gas ranging from 50 to 500 ppm were measured at room temperature. The ICI sensors showed a higher gas sensitivity than that of the ITO single layer sensors. Finally, it can be concluded that the ICI film sensors have the potential to be used as improved methanol gas sensors.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.44 no.4
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• pp.496-501
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• 1995

The N $O_{2}$ gas-detection characteristics were investigated using the functional organic Langmuir-Blodgett (LB) films of Copper-tetra-tert-butylphthalocyanine (CuTBP), Dilithium phthalocyanine (Li$_{2}$Pc), N-docosylpyridinium TCNQ(C$_{22}$Py(TCNQ)), Polyamic acid alkylamine salts (PAAS). The optimum conditions for a film deposition were obtained through a study of .pi.-.ALPHA. isotherms and the deposited film status was confirmed by electrical and optical methods such as UV/visible absortion spectra, thickness measurements by ellipsometry, and electrical capacitances. A response of the LB films to the N $O_{2}$ gas was measured by a change of the electrical conductivities when the film is exposed to the gases. The CuTBP LB film shows the biggest change of the electrical conductivities when it is exposed to the N $O_{2}$ gases. And the order of gas-detection performance is the following;Li$_{2}$Pc, $C_{22}$Py(TCNQ), and PAAS LB films. Especially, the CuTBP and Li$_{2}$Pc LB films not only show the bigger change in the electircal conductivities when exposed to the gas, but return to the original state when the gas is desorbed.d.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.20 no.5
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• pp.221-226
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• 2010

Quartz crystal microbalance (QCM) gas sensor to detect methyl mercaptan ($CH_3SH$) gas was fabricated by depositing $TiO_2$ nanoparticles and polyelectrolyte on the electrode of QCM. The $TiO_2$/poly(sodium 4-styrenesulfonate) (PSS) thin film fabricated by a layer-by-layer self-assembly (LBL-SA) method showed a high surface area and increased the sensitivity of gas sensor. When the QCM sensors coated with triethanolamine (TEA) or ($TiO_2$/PSS) were exposed to methyl mercaptan gas (1.0 ppm), the frequency shifts of QCM with TEA casting film and $TiO_2$/PSS thin film were ca. 9 Hz and ca. 24 Hz, respectively. As the bilayer number of ($TiO_2$/PSS) increased, the frequency shift of QCM sensor with ($TiO_2$/PSS) thin film was gradually increased. In addition, the frequency shift of QCM sensor was gradually increased as the concentration of methyl mercaptan gas increased from 0.5 ppm to 2.0 ppm. In this study, the surface morphology and sensor property of QCM sensor coated with ($TiO_2$/PSS) thin film were measured.

• Journal of the Korean Ceramic Society
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• v.26 no.2
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• pp.235-241
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• 1989

A study on the APCVD(atmospheric pressure chemical vapor deposition) Al2O3 was done by using the aluminum-tri-isopropoxide/N2 reaction system at 40$0^{\circ}C$. When the flow rate of the carrier gas(N2) was over 2SLPM, heterogeneous reaction was observed. However, when the flow rate of the carrier gas was below 2SLPM, a porously deposited film or powder formation was observed. The film formed by a heterogeneous reaction was optically dense. The dense film is thought to be a kind of a hydrated alumina. After a thermal treatment of the film in the range of temperature from $600^{\circ}C$ to 1, 20$0^{\circ}C$, properties of the film seems to be changed due to dehydration and densification process. In the case of the powder on heat treatment(600~1, 20$0^{\circ}C$), both a phase transformation and the change of OH peak was observed.

• Transactions of the Korean hydrogen and new energy society
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• v.16 no.4
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• pp.386-390
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• 2005

Al film(135.5 nm thick) with Pd film(39.6 nm thick) on the top of it was made by thermal evaporation method. Electrical resistance change due to hydrogen absorption and desorption was measured by four point measurement method. The sample was activated by hydrogen absorption and desorption cycling at room temp. Hydrogen was introduced into the film by increasing hydrogen gas pressure step by step up to 640 torr at room temp. The resistance change ratio was decreased to 12 % with increasing hydrogen pressure in contrast to normal metal behavior. This strange tendency was not understood yet. Further study is needed to find out the mechanism of hydrogen absorption in Al in Al/Pd film.

• Journal of information and communication convergence engineering
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• v.5 no.3
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• pp.215-218
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• 2007

In this paper, amorphous semiconductor and insulator thin film are etched using reactive ion etcher. At that time, we experiment in various RIE conditions (chamber pressure, gas flow rate, rf power, temperature) that have effects on quality of thin film. The using gases are $CF_4,\;CF_4+O_2,\;CCl_2F_2,\;CHF_3$ gases. The etching of a-Si:H thin film use $CF_4,\;CF_4+O_2$ gases and the etching of $a-SiO_2,\;a-SiN_x$ thin film use $CCl_2F_2,\;CHF_3$ gases. The $CCl_2F_2$ gas is particularly excellent because the selectivity of between a-Si:H thin film and $a-SiN_x$ thin film is 6:1. We made precise condition on dry etching with uniformity of 5%. If this dry etching condition is used, that process can acquire high yield and can cut down process cost.

• Journal of the Korean Ceramic Society
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• v.35 no.8
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• pp.795-800
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• 1998