• Journal of Sensor Science and Technology
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• v.18 no.1
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• pp.54-62
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• 2009

${Co_3}{O_4}$ and ${Co_3}{O_4}$-based thick films with additives such as ${Co_3}{O_4}-{Fe_2}{O_3}$(5 wt.%), ${Co_3}{O_4}-{SnO_2}$ (5 wt.%), ${Co_3}{O_4}-{WO_3}$(5 wt.%) and ${Co_3}{O_4}$-ZnO(5 wt.%) were fabricated by screen printing method on alumina substrates. Their structural properties were examined by XRD and SEM. The sensitivities to iso-${C_4}H_{10}$, $CH_4$, CO, $NH_3$ and NO gases were investigated with the thick films heat treated at $400^{\circ}C$, $500^{\circ}C$ and $600^{\circ}C$. From the gas sensing properties of the films, the films showed p-type semiconductor behaviors. ${Co_3}{O_4}-{SnO_2}$(5 wt.%) thick film heat treated at $600^{\circ}C$ showed higher sensitivity to i-${C_4}H_{10}$ and CO gases than other thick-films. ${Co_3}{O_4}-{SnO_2}$(5 wt.%) thick film heat treated at $600^{\circ}C$ showed the sensitivity of 170 % to 3000 ppm iso-${C_4}H_{10}$ gas and 100 % to 100 ppm CO gas at the working temperature of $250^{\circ}C$. The response time to i-${C_4}H_{10}$ and CO gases showed rise time of about 10 seconds and fall time of about $3{\sim}4$ minutes. The selectivity to i-${C_4}H_{10}$ and CO gases was enhanced in the ${Co_3}{O_4}-{SnO_2}$(5 wt.%) thick film.

• Korean Journal of Materials Research
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• v.16 no.6
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• pp.360-366
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• 2006

A series of ZnO thin films were grown by radio-frequency (RF) magnetron sputtering with various RF powers on $SiO_2/Si$(100) substrates at $500^{\circ}C$. Thicknesses of the investigated ZnO films were fixed to about 250nm by changing the growth time based on the changes of growth rates with RF powers. All the ZnO thin films were grown with <0001> preferred orientation. Average grain sizes of about 250nm-thick ZnO films evaluated by FE-SEM, AFM, and TEM were increased by decreasing the RF power. Structural properties addressed by FWHM values of XRD (0002) omega rocking curves and their intensities were better for the smaller grain sized ZnO films grown with high RF powers, which implies small values of tilt for smaller grain sized ZnO films. However, optical properties addressed by intensities of band edge emissions from room temperature and low temperature photoluminescence were better for the larger grain sized ZnO films with low RF power, which implies grain boundaries acted as nonradiation recombination centers.

• Journal of Surface Science and Engineering
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• v.42 no.5
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• pp.216-219
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• 2009

A surface acoustic wave (SAW) filter structure was fabricated employing $4{\mu}m$ thick nanocrystalline diamond (NCD) and $2.2{\mu}m$ thick ZnO films on Si wafer. The NCD film was deposited in an $Ar/CH_4$ gas mixture by microwave plasma chemical vapor deposition method. The ZnO film was formed over the NCD film in an RF magnetron sputter using ZnO target and $Ar/O_2$ gas. On the top of the two layers, copper film was deposited by the RF sputter and inter digital transducer (IDT) electrode pattern (line/space : $1.5/1.5{\mu}m$) was defined by the photolithography including a lift-off etching process. The fabricated SAW filter exhibited the center frequency of 1.66 GHz and the phase velocity of 9,960 m/s, which demonstrated that a giga Hertz SAW filter can be realized by utilizing the nanocrystalline diamond thin film.

• Korean Journal of Materials Research
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• v.14 no.9
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• pp.670-675
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• 2004

Glasses in the $Bi_{2}O_3-SiO_2-ZnO$ glasses system were examined as a potential replacement for lead-oxide glass frits with low firing temperature ($500\sim600^{\circ}C$) for the dielectric layer of a plasma display panel (PDP). The glasses were evaluated for glass transition temperature($T_{g}$) and thermal expansion coefficient(${\alpha}$). After forming transparent thick films by a screen-printing method, it was evaluated for the optical properties. The transmittance of thick films fired at $500-600^{\circ}C$ showed above $80\%$, which was not dependent on the firing temperature. As a result, many pores were observed at samples fired at low temperature, while the number of pores from samples prepared at high temperature decreased and the pores size increased.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.67 no.6
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• pp.753-758
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• 2018

We investigated annealing effects of seed layers on the properties of ZnO nanorods grown on the seed layers. ZnO nanorods were grown by a hydrothermal method. ~100 nm-thick ZnO films were sputtered on oxidized Si wafers and quartz as seed layers. The ZnO films were annealed at $400^{\circ}C$, $600^{\circ}C$, and $800^{\circ}C$, respectively. ZnO nanorods were grown at $90^{\circ}C$ for 3 hours in the mixed solution of zinc nitrate hexahydrate and hexamethylenetetramine. X-ray diffraction was carried out to estimate the crystallinity and strain of ZnO films and nanorods. A field emission scanning electron microscope was employed to observe the morphology of the films and nanorods. PL(photoluminescence) measurements were conducted with 266 nm light. It was found that the annealing of seed layers increase the growth rate of nanorods, and change compressive strain of nanorods to tensile strain. The intensity of PL in the UV region reduced by using the annealed seed layers.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.25 no.12
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• pp.984-989
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• 2012

We have investigated the structural, electrical and optical properties of Ga-doped ZnO (GZO) thin films prepared by RF magnetron sputtering with laboratory-made ZnO targets containing 1, 3, 5, 7 wt% of $Ga_2O_3$ powder as a doping source. The GZO thin films show the typical crystallographic orientation with c-axis regardless of $Ga_2O_3$ content in the targets. The $3,000{\AA}$ thick GZO thin films with the lowest resistivity of $7{\times}10^{-4}{\Omega}{\cdot}cm$ are obtained by using the GZO ($Ga_2O_3$= 5 wt%) target. Optical transmittance of all films shows higher than 80% at the visible region. The optical energy band gap for GZO films increases as the carrier concentration ($n_e$) in the film increases.

• Journal of IKEEE
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• v.23 no.2
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• pp.375-379
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• 2019

$ZnO-SnO_2(ZTO)$ was deposited by RF magnetron sputtering using a ceramic target whose Zn atomic ratio to Sn is 2:1 as a target, and the crystal structure variation with thermal treats was investigated. Transparent thin film transistors (TTFT) were fabricated using the ZTO films as active layers. About 100 nm-thick $Si_3N_4$ film grown on 100 nm-thick $SiO_2$ film was adopted as gate dielectrics. The mobility, threshold voltage, $I_{on}/I_{off}$, and interface trap density were obtained from the transfer characteristics of ZTO TTFTs. The effects of substrate temperature, and post-annealing on the property variation of ZTO TTFT were analyzed.

• Korean Journal of Materials Research
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• v.14 no.5
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• pp.328-333
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• 2004

Transparent ZnO:Al conductor films for the optoelectronic devices were deposited by using the capacitively coupled DC magnetron sputtering method. The effect of Al doping concentration and discharge power on the electrical and optical properties of the films was studied. The film resistivity of $8.5${\times}$10^{-4}$ $\Omega$-cm was obtained at the discharge power of 40 W with the ZnO target doped with 2 wt% $Al_2$$_O3$. The transmittance of the 840 nm thick film was 91.7% in the visible waves. Increasing doping concentration of 3 wt% $Al_2$$O_3$ in ZnO target results in significant decrease of film resistivity, which may be due to the formation of $Al_2$$O_3$ particles in the as-deposited ZnO:Al film and the reduced ZnO grain sizes. Increasing DC power from 40 to 60 W increases deposition rate by more than 50%, but can induce high defect density in the film, resulting in higher film resistivity.

• Journal of the Korean Vacuum Society
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• v.20 no.1
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• pp.50-56
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• 2011

In this study, the effects of ZnO buffer layer thickness and annealing temperature on the heterojunction diode, ZnO/b-ZnO/p-Si(111), were reported. The effects of those on the structural and electrical properties of zinc oxide (ZnO) films on ZnO buffered p-Si (111) substrate were also studied. Structural properties of ZnO thin films were studied by X-ray diffraction and I-V characteristics were measured by a semiconductor parameter analyzer. ZnO thin films with 70 nm thick buffer layer and annealing temperature of $700^{\circ}C$ showed the best c-axis preferred orientation. The best electrical property was found at the condition of buffer layer annealing temperature of $700^{\circ}C$ and 50nm thick ZnO buffer layer (resistivity: $2.58{\times}10^{-4}[{\Omega}-cm]$, carrier concentration: $1.16{\times}1020[cm^{-3}]$). The I-V characteristics for ZnO/b-ZnO/p-Si(111) heterojunction diode were improved with increasing buffer layer thickness at buffer layer annealing temperature of $700^{\circ}C$.

• KIEE International Transactions on Electrophysics and Applications
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• v.2C no.6
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• pp.314-320
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• 2002

Three different ZnO nanomaterials (nanobelts, nanorods, and nanowires) were synthesized at 138$0^{\circ}C$ from ball-milled ZnO powders by a thermal evaporation procedure with an argon carrier gas without any catalysts. Transmission electron microscopy (TEM) revealed that the ZnO nanobelts are single crystalline with the growth direction perpendicular to the (010) lattice plane, and that the ZnO nanorods and nanowires are single crystalline with the growth directions perpendicular to the (001) and (110) lattice Planes, respectively. In cathodoluminescence (CL), the energy Position of the near band-edge (NBE) peak is 3.280 eV for the 100-, 250-, and 500-nm thick nanobelts, 3.262 eV for the 100- and 250-nm thick nanorods, and 3.237 eV for the 500-nm thick nanorods. The synthesized ZnO nanorods were coated conformally with aluminum oxide (Al$_2$O$_3$) material by atomic layer deposition (ALD). $Al_2$O$_3$films were then deposited on these ZnO nanorods by ALD at a substrate temperature of 300 $^{\circ}C$ using trimethylaluminum (TMA) and distilled water ($H_2O$). Transmission electron microscopy (TEM) images of the deposited ZnO nanorods revealed that 40nm-thick $Al_2$O$_3$ cylindrical shells surround the ZnO nanorods.