• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.35 no.3
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• pp.275-280
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• 2022

An all-solid-state electrochromic film was fabricated by laminating tungsten oxide (WO₃) and nickel oxide (NiO) thin films deposited by a reactive DC magnetron sputtering on flexible ITO films. The influence of oxygen partial pressure on the crystal structure, microstructure, optical properties, and electrochromic properties of WO₃ and NiO thin films were investigated. WO₃ and NiO films showed the best electrochromic properties under the flow of Ar:O₂=80:20 and Ar:O₂=90:10, respectively. The EC film fabricated with an optimized WO₃ and NiO films showed a high coloration efficiency, a fast response time, and a stable optical modulation. It is expected that flexible EC window films will pave the way for the next-generation energy-saving windows.

• Journal of the Korean Vacuum Society
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• v.8 no.2
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• pp.136-140
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• 1999

The stability and response time of $WO_3$ thin films for EC device are critical problems being solved. Those are affected by the species of electrolyte, preparation conditions and fabricating methods of specimen. In this paper, we compared the stabilities of three kinds of tungsten oxide film in electrolyte. Each of three films was prepared by different manufacturing conditions, that is, one is a thermal oxidation film of tungsten metal deposited on pure glass substrate, another is a $WO_3$ film made on ITO glass directly, the other is a thermally oxidized film on tungsten plate. It was observed that thermally oxidized $WO_3$ films has a remarkable stability (the lifetime was above $10^6$ cycle). From these results, we found that the stability was closely related to the stoichiometric bonding between tungsten and oxygen atoms in addition to crystallinity and density of film.

• Bulletin of the Korean Chemical Society
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• v.32 no.6
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• pp.1865-1872
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• 2011

This study investigates the sensitivity of a gas sensor to volatile organic compounds (VOCs) at various operating temperatures and catalysts. Nano-sized powdered $WO_3$ prepared by sol-gel and chemical precipitation methods was mixed with various metal oxides. Next, transition metals (Pt, Ru, Pd, and In) were doped on the surface of the mixture. Metal-$WO_3$ thick films were prepared using the screen-printing method. The physical and chemical properties of the films were studied by SEM/EDS, XRD, and BET techniques. The measured sensitivity to VOCs is defined as the ratio ($R_a/R_g$) of resistance ($R_{air}$) of $WO_3$ film in the air to resistance ($R_{gas}$) of $WO_3$ film in a VOCs test gas. The sensitivity and selectivity of the films were tested with various VOCs such as acetaldehyde, formaldehyde, methyl alcohol, and BTEX. The thick $WO_3$ film containing 1 wt % of Ru and 5 wt % of $SnO_2$ showed the best sensitivity and selectivity to acetaldehyde gas at an operating temperature of 300 $^{\circ}C$.

• Korean Journal of Materials Research
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• v.11 no.4
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• pp.272-277
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• 2001

NiO-doped $WO_3$ thick films were prepared by a screen printing technique. The electrical Property and microstructure of the films were investigated with the partial pressure of oxygen and the amount of NiO. The grain size of NiO-doped $WO_3$ was smaller than that of undoped $WO_3$ but the grain sixte of 0.1, 1, 10 mol% NiO-doped$ WO_3$ were nearly the same. The electrical conductance of the $WO_3$ thick films decreased with the oxygen partial pressure, and increased with the amount of NiO to the limit of solid solution. The variation of the electrical conductance with temperature is not so large in the extrinsic region, but it changed rapidly in the intrinsic region. The conductance decreased with adsorption of oxygen in the intermediate range between the extrinsic and intrinsic region.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1997.11a
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• pp.339-342
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• 1997

The optical properties of WO$_3$thin films deposited by RF magnetron reactive sputtering were studied. The substrate was an ITO(indium-tin-oxide) glass(100$\Omega$/ ). The optical properties are examined by different deposition conditions. RF power, substrate temperature, $O_2$concentraction. Ar flow rate, working pressure and thickness are 40~60W, 25~30$0^{\circ}C$, 10%, 54~72sccm, 5~20m7orr and 1200~2400$\AA$, respectively. All these films were colorless, light yellow and found to be amorphous in structure by X-ray diffraction analysis. When RF power, substrate temperature, $O_2$concentraction, Ar flow rate, working pressure and thickness are 40W, $25^{\circ}C$, 10%, 72sccm, 20mTorr and 2400$\AA$, respectively the values of transmittance of the WO$_3$thin films in visible region are about 80%.

• Solar Energy
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• v.12 no.2
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• pp.18-27
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• 1992

Multilayer coatings of $WO_3$ were deposited by the sol-gel technique on microscope slide glass and ITO coated glass. These films were characterized optically, chemically, and structurally by XRD, spectro-photometry, DTA/TGA, SEM/EDAX and RBS. Uniform $WO_3$ sol-gel films were dip coated on slide glass at dipping speed of 5mm/s. This sample indicated a low near IR transmittance in optical properties as a result of coloration using a dilute HCI electrolyte as the $H^+$ion sources. Differential thermal analysis results have allowed the accurate determination of the formation temperature of the $WO_3$ crystalline phase from the gel data in the range of $380^{\circ}C{\sim}500^{\circ}C$, consistent with crystallization temperature of sol-gel film. RBS spectrometry was performed on the uncolored $WO_3$ sol-gel film, yielding a chemical composition of $WO_3$.

• Journal of the Korean Ceramic Society
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• v.32 no.12
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• pp.1369-1376
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• 1995

The WO3 thin-film NOx sensor which is of practical use and includes the heater and the temperature sensor was fabricated. The WO3 thin films as a gas-sensing layer was deposited at ambient temperature in a high-vacuum resistance heated evaporator. The highest sensitivity of the WO3 thin-film sensor to NOx was obtained under the condition of the annealing temperature of 50$0^{\circ}C$ and the operating temperature of 30$0^{\circ}C$. The gas sensing characteristics of this sensor was excellent, i.e. high sensitivity (Rgas/Rair in 3 ppm NO2=53) and fast response time (4 seconds).

• Proceedings of the IEEK Conference
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• 1998.10a
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• pp.601-604
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• 1998

NOX detecting gas sensors using TiO2 doped tungsten oxide semiconductor were prepared and their electrical and sensing characteristics have been investigated. In normal air condition, the sensors of WO3, TiO2 doped WO3 show grain boundary heights of 0.34 eV, 0.25 eV, respectively. The grain boundary barrier energy variation was increased by doping TiO2 into large variation of resistance to NOX gases. And doping the TiO2 4 wt.%, the particle size of WO3 polycrystal films showed higher sensitivity and better sorption characteristics to NOX gas than the pure WO3 films material in air at operating temperature of $350^{\circ}C.$ The TiO2 doped WO3 semiconductor gas sensor shows nano-sized particle size and good sensitivity to sub-ppm concentration of NOX.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.07a
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• pp.536-539
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• 2000

The effects of annealing on the electrical and structural characteristics for the rf sputter deposited WO$_3$thin film. The sputtered thin films are annealed at 773K for 1 hour in air atmosphere. Oxygen flow rate were changed from 0 to 70% during sputtering. It is observed from the results of the AFM measurement that the average roughness for the rf sputter deposited WO$_3$thin film would be increased from 2.45 angstrom to 152 angstrom by annealing. The sheet resistance of the sputtered WO$_3$film is changed from insulting to MOhm after annealing. According to the results of the XRD, the as-deposited films revealed the amorphous state whereas the peaks of X-ray diffraction at 2 theta= 28 degrees and 2 theta = 25 degrees corresponding to the (111) and (200) plane of the WO$_3$film respectively are observed after annealing.

• Proceedings of the Materials Research Society of Korea Conference
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• 2005.05a
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• pp.145-145
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• 2005