• Journal of Sensor Science and Technology
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• v.25 no.3
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• pp.184-188
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• 2016

Highly ordered $SnO_2$ and NiO nanocolumns have been successfully achieved by glancing-angle deposition (GLAD) using an electron beam evaporator. Nanocolumnar $SnO_2$ and NiO sensors exhibited high performance owing to the porous nanostructural effect with the formation of a double Schottky junction and high surface-to-volume ratios. When all gas sensors were exposed to various gases such as $C_2H_5OH$, $C_6H_6$, and $CH_3COCH_3$, the response of the highly ordered $SnO_2$ nanocolumn were over 50 times higher than that of the $SnO_2$ thin film. This work will bring broad interest and create a strong impact in many different fields owing to its particularly simple and reliable fabrication process.

• Journal of the Korean Society for Heat Treatment
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• v.25 no.6
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• pp.279-282
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• 2012

$SnO_2$ thin films were prepared on the Si substrate by radio frequency (RF) magnetron sputtering and then surface of the films were irradiated with intense Ar ion beam to investigate the effect of Ar ion irradiation on the properties and hydrogen gas sensitivity of the films. From atomic force microscope observation, it is supposed that intense Ar bombardments promote rough surface and increase gas sensitivity of $SnO_2$ films for hydrogen gas. The films that Ar ion beam irradiated at 6 keV show the higher sensitivity than the films were irradiated at 3 keV and 9 keV. These results suggest that the $SnO_2$ thin films irradiated with optimized Ar ion beam are promising for practical high-performance hydrogen gas sensors.

• Fire Science and Engineering
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• v.10 no.2
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• pp.40-51
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• 1996

A synthesis process for PZT powder using NH$_3$ gas as a precipitator in a bubble column reactor was experimentally successful in develope a production process of Piezoelectric ceramic PZT powder. Also as a reaction by coprecipitation, the crystalized PZT ceramic powder at the condition of over pH 9 could be attained. The time needed for reaction on the condition of NH$_3$ gas flow rate=0.5 1/min, Ar gas flow rate=2.0 1/min, Feed flow rate=2.33 ml /sec was less than five minutes, so it could synthesize PZT powder for such a few moments. And the synthesized PZT powder was 0.17${\mu}{\textrm}{m}$ in diameter on an average.

• Journal of the Korean Society for Heat Treatment
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• v.25 no.5
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• pp.239-243
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• 2012

$SnO_2$ thin films were prepared on the Si substrate by radio frequency (RF) magnetron sputtering and then post deposition vacuum annealed to investigate the effect of annealing temperature on the structural properties and hydrogen gas sensitivity of the films. The films that annealed at $300^{\circ}C$ show the higher sensitivity than the other films annealed at $150^{\circ}C$. From atomic force microscope observation, it is supposed that post deposition annealing promotes the rough surface and also, increase gas sensitivity of $SnO_2$ films for hydrogen gas. These results suggest that the vacuum annealed $SnO_2$ thin films at optimized temperatures are promising for practical high-performance hydrogen gas sensors.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.222-222
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• 2012

Metal oxide gas sensors based on semiconductor type have attracted a great deal of attention due to their low cost, flexible production and simple usability. However, most works have been focused on n-type oxides, while the characteristics of p-type oxide gas sensors have been barely studied. An investigation on p-type oxides is very important in that the use of them makes possible the novel sensors such as p-n diode and tandem devices. Monoclinic cupric oxide (CuO) is p-type semiconductor with narrow band gap (~1.2 eV). This is composed of abundant, nontoxic elements on earth, and thus low-cost, environment-friendly devices can be realized. However, gas sensing properties of neat CuO were rarely explored and the mechanism still remains unclear. In this work, the neat CuO layers with highly ordered mesoporous structures were prepared by a template-free, one-pot solution-based method using novel ink solutions, formulated with copper formate tetrahydrate, hexylamine and ethyl cellulose. The shear viscosity of the formulated solutions was 5.79 Pa s at a shear rate of 1 s-1. The solutions were coated on SiO2/Si substrates by spin-coating (ink) and calcined for 1 h at the temperature of $200{\sim}600^{\circ}C$ in air. The surface and cross-sectional morphologies of the formed CuO layers were observed by a focused ion beam scanning electron microscopy (FIB-SEM) and porosity was determined by image analysis using simple computer-programming. XRD analysis showed phase evolutions of the layers, depending on the calcination temperature, and thermal decompositions of the neat precursor and the formulated ink were investigated by TGA and DSC. As a result, the formation of the porous structures was attributed to the vaporization of ethyl cellulose contained in the solutions. Mesoporous CuO, formed with the ink solution, consisted of grains and pores with nano-meter size. All of them were strongly dependent on calcination temperature. Sensing properties toward H2 and C2H5OH gases were examined as a function of operating temperature. High and fast responses toward H2 and C2H5OH gases were discussed in terms of crystallinity, nonstoichiometry and morphological factors such as porosity, grain size and surface-to-volume ratio. To our knowledge, the responses toward H2 and C2H5OH gases of these CuO gas sensors are comparable to previously reported values.

• Journal of Sensor Science and Technology
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• v.16 no.6
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• pp.407-412
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• 2007

For $VO_{2}$ sensors applicable to temperature measurement by using the nature of semiconductor to metal transition, the crystallinity, microstructure, and temperature vs. resistance characteristics were investigated systematically as a function of the annealing condition. The starting materials, vanadium pentoxide ($V_{2}O_{5}$) powders, were mixed with vehicle to form paste. This paste was screen-printed on $Al_{2}O_{3}$ substrates and then $VO_{2}$ thick films were heat-treated at $450^{\circ}C$ to $600^{\circ}C$, respectively, for 1 hr in $N_{2}$ gas atmosphere for the reduction. As results of the temperature vs. resistance property measurements, the electrical resistance of the $V_{2}O_{5}$ sensor in phase transition range was decreased by $10^{3.9}$ order. The presented critical temperature sensor could be used in fire-protection and control systems.

• Journal of Sensor Science and Technology
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• v.12 no.1
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• pp.34-43
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• 2003

In this study, we implemented the measurement of pH, $pO_2$, $pCO_2$ of the arterial blood on a portable blood gas analysis system. This system is consist of two parts of hardware and software. The hardware part is divided into a fluidic mechanism and an electronic circuit unit. The system program is composed of operating, washing, correcting, and measuring routines. Both of 1-point and 2-point calibration schemes were used to enhance the accuracy of the measurement. In order to evaluate the performance of the developed system, we measured and performed statistical analysis on the characteristics of the sensing electrode response. As a result, coefficient variation was within 1.12, and maximum error was within 1.298%. We confirmed development possibility of portable blood gas analyzer.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.48 no.2
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• pp.69-75
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• 1999

The characteristics of $H_2$ gas detection have been investigated using the Pt-MIS capacitor composed of the LPCVD nitride on the oxide. The flat band voltage shift is measured as 0.1 V in 1,000 ppm $H_2$ gas ambient and to be independent of Pt catalyst thickness. It is found that the flatband voltage shift is proportional to the hydrogen concentrations. The response and recovery time of Pt-MIS capacitor are 5 mins and 25 mins respectively. The samples of 30nm thick Pt revealed much higher sensitivity than that of 150nm samples. The samples of 150nm Pt showed that the flatband voltage shift of the device is due to the formation of the dipole layer of the adsorbed hydrogen atoms at the Pt-insulator interface.

• Korean Journal of Materials Research
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• v.13 no.2
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• pp.106-110
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• 2003

Nano-sized powders of Indium Tin Oxide(ITO) were synthesized by a coprecipitation method. In order to investigate the gas sensing characteristics in the nanocrystalline ITO thick films with various particle sizes, ITO powders with the average particle diameter of 15, 30, and 70 nm respectively were synthesized. And the sensitivity of ITO thick films was measured upon exposure to a target gas($C_2$$H_{5}$ /OH) and some other Volatile Organic Compounds(VOCs), such as, toluene, methanol, benzene, chloroform. As a result, ITO thick films had high sensitivity for ethanol and higher sensitivity with smaller particle size.

• Korean Journal of Materials Research
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• v.10 no.11
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• pp.778-783
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• 2000

Effects of the $Al_2$O$_3$surface protective layer, deposited on the SnO$_2$sensing layer by aerosol flame deposition (AFD) method, on the sensing properties of SnO$_2$thin film ags sensors were investigated.Effects of Pt doping to the $Al_2$O$_3$surface protective layer on the selectivity of CH$_4$ gas were also investigated. 0.3$\mu\textrm{m}$ thick SnO$_2$thin sensing layers on Pt electrodes were prepared by R.F. magnetron sputtering with R.F. power of 50 W, at working pressure of 4mTorr, and at 20$0^{\circ}C$ for 30 min. $Al_2$O$_3$surface protective layers on SnO$_2$layers were prepared by AFD using a diluted aluminum nitrade (Al(NO$_3$).9$H_2O$) solution. The sensitivity of CO gas in the SnO$_2$gas sensor with an $Al_2$O$_3$surface protective layer was significantly decreased. But that of CH$_4$gas remained almost same with pure SnO$_2$gas sensor. This result shows that the selectivity of CH$_4$gas is increased because of the $Al_2$O$_3$surface protective layer. In the case of SnO$_2$gas sensors with Pt-doped $Al_2$O$_3$surface protective layers, low sensing property to CO gas and high sensing property to CH$_4$were observed. This results in the increasing of selectivity of CH$_4$gas selectivity are discussed.