• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2003.05a
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• pp.88-92
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• 2003

In this paper, the characteristics of the ZnO films deposited on AI bottom electrode and the temperature effects on the ZnO film growth are presented along with the fabrication and their evaluation of the film bulk acoustic wave resonator (FBAR) devices. All the films used in this work were deposited using a radio-frequency (RF) magnetron sputtering technique. Growth characteristics of the ZnO films are shown to have a strong dependence on the deposition temperatures ranged from room temperature to 35$0^{\circ}C$ regardless of the RF power applied for sputtering the ZnO target. In addition, according to the growth characteristics of the distinguishably different micro-crystal structures and the degree of the c-axis preferred orientation, the deposition temperatures can be divided into 3 temperature regions and 2 critical temperatures in-between. Overall, the ZnO films deposited at/below 20$0^{\circ}C$ are seen to have columnar grains with a highly preferred c-axis orientation where the full width at half maximum (FWHM) of X-ray diffraction rocking curve is 14$^{\circ}$. Based on the experimental findings, several FBAR devices were fabricated and measured. As a result, the FBAR devices show return loss of ~19.5dB at resonant frequency of ~2.05GHz.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.25 no.9
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• pp.717-722
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• 2012

In this work, we study on the effects of the oxygen pressure on the structural and crystalline of MgZnO thin films. MgZnO thin films were deposited on p-Si (111) substrates by using pulsed laser deposition. The X-ray diffraction analysis and energy-dispersive X-ray results revealed that as the oxygen pressure increased and Mg content in the MgZnO films decreased. Also Crystal structure was changed from cubic rock salt to hexagonal wurtzite. Alpha step and atomic force microscopy results showed that the thickness of the films are about 100 nm, and it has been found that the MgZnO (002) preferred orientation were deposited with increasing the oxygen pressure. Therefore, the effect of the preferred orientation, the crystallization grew in the form of the columnar; Grain size and RMS of the films were increased with increasing oxygen pressure.

• Journal of the Korean Society for Heat Treatment
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• v.23 no.2
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• pp.96-103
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• 2010

$Ni_3Al$ is known as a good high temperature structural material because of high yield strength at ambient temperature. However, it is too brittle to use as a structural material because of their weak grain boundary. In this work, orientation measurement and related mechanical properties of directionally solidified NiAl/$Ni_3Al$ two-phase alloys with various compositions (Ni-23~27 at.%Al) were investigated for developing multi-phase DS-processed alloys with the growth rates of 10, 50 and 100 ${\mu}m/s$ in a modified Bridgeman type furnace. It was found that the multi-phase microstructures such as the $\gamma$ dendrite +${\gamma}'$ matrix duplex microstructure was formed in the hypoeutectic composition of 23 at.%Al, $\beta$ dendrite +${\gamma}'$ matrix duplex microstructure in the hypereutectic composition of 26 and 27 at.%Al. And ${\gamma}'$ single phase was formed in the composition of 24.5 and 25 at.%Al. The hypoeutectic alloy including $\gamma$ dendrites with ${\gamma}'$ matrix showed a large elongation of over 70% at room temperature. However, the room-temperature tensile elongation decreased with increasing Al contents because the volume fraction of brittle $\beta$ dendrites in the ductile ${\gamma}'$ matrix increased.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.07a
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• pp.168-171
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• 2003

Bismuth layered structure, Cerium-substituted $Bi_4Ti_3O_{12}$ ($(Bi,Ce)_4Ti_3O_{12}$) thin films were prepared on the $Pt/TiO_2/SiO_2/Si$ substrates by the pulsed laser deposition method. We investigated the Ce-subsitituted effect on the grain orientation and ferroelectric properties. $Ce^{3+}$ ion substitution for $Bi^{3+}$ ion in perovskite layers of BTO decreased the deeree of c-axis orientation and increased the remanent polariation (2Pr). The structure and morphology of the films were characterized using X-ray diffraction and atomic force microscopy. The $(Bi,Ce)_4Ti_3O_{12}$ (BCT) thin films, which were annealed $700^{\circ}C\;and\;800^{\circ}C$ for 10min and 30min, showed a perovskite phase and dense microstructure. As the thickness of the BCT film was decresed that the ferroelectric properties of the BCT thin films were good.

• Korean Journal of Materials Research
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• v.1 no.1
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• pp.54-61
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• 1991

YBCO films deposited on MgO(100) and Si(100) by rf-magnetron sputtering using stoichiometric single target were annealed under oxygen atmosphere at $880^{\circ}C$ for 1 hr. The microstructure and superconducting properties of YBCO thin films depended on the composition of pre-annealed thin films. Basal planesuperconducting particles grown on MgO(100) substrate had small and rod-like shade due to preferred orientation, while superconducting film grown on the basal plane-superconducting particles showed round-shape particles. If pre-annealed thin film had nonstoichiometric composition, liquid phase was formed during the heat treatment, which made it easy for particles to grow in the preferred orientation and thus to form textured structure. But the thin films with the textured structure did not show good superconducting properties, especially $T_c$, since the liquid phase transformed into second phase in the grain boundary during the cooling. The effect of the second phase on $T_{c, \;zero}$ was greater than that on $T_{c, \;on}$.

• Korean Journal of Materials Research
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• v.15 no.8
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• pp.518-520
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• 2005

Effects of the $O_2/Ar$ flow ratio in the sputtering process on the crystallinity, surface roughness, carrier concentration, carrier mobility, and optical properties of Al-doped ZnO thin films deposited on sapphire (001) substrates by RF magnetron sputtering were investigated. XRD spectra showed a preferred orientation along the c-axis and a minimum FWHM of the (002) XRD intensity peak for the $O_2/Ar$ flow ratio of 0.5. The (101)peak also appeared and the degree of preferred orientation decreased as the $O_2/Ar$ flow ratio increased from 0.5 to 1.0. AFM analysis results showed that the surface roughness was lowest at the $O_2/Ar$ flow ratio of 0.5 and tended to increase owing to the increase of the grain size as the $O_2/Ar$ flow ratio increased further. According to the Hall measurement results the carrier concentration and carrier mobility of the fan decreased and thus the resistivity increased as the $O_2/Ar$ flow ratio increased. The transmittance of the ZnO:Al film deposited on the glass substrate was characteristic of a standing wave. The transmittance increased as the $O_2/Ar$ flow ratio in-RF magnetron sputtering increased up to 0.5. Considering the effects of the $O_2/Ar$ flow ratio on the surface roughness, electrical resistivity and transmittance properties of the ZnO:Al film the optimum $O_2/Ar$ flow ratio was 0.5 in the RF magnetron sputter deposition of the ZnO:Al film.

• Journal of the Korean Ceramic Society
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• v.50 no.6
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• pp.551-556
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• 2013

AlN films with c-axis orientation and thermal conductivity characteristics were deposited by using Pulsed Laser Deposition and the films were characterized by changing the deposition conditions. In particular, we investigated the optimal conditions for the application of a heat sinking plane AlN thin film. Epitaxial AlN films were deposited on sapphire ($c-Al_2O_3$) single crystals by pulsed laser deposition (PLD) with an AlN target. AlN films were deposited at a fixed pressure of $2{\times}10^{-5}$ Torr, while the substrate temperature was varied from 500 to $700^{\circ}C$. According to the experimental results of the growth temperature of the thin film, AlN thin films were confirmed with a highly c-axis orientation, maximum grain size, and high thermal conductivity at $650^{\circ}C$. The thermal conductivity of the AlN thin film was found to increase compared to bulk AlN near the band gap value of 6.2 eV.

• Korean Journal of Crystallography
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• v.6 no.1
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• pp.14-26
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• 1995

The growth mechanism of diamond thin films, deposited by Hot Filament CVD, was investigated through observation of changes in their surface morphology as a function of the substance temperature and deposition time. Amorphous carbon or DLC thin films were deposited at low substrate temperature. Diamond films consisting of square-shaped particles, whose surfaces are (100) planes, were deposited at an intermedate temperature. At high substrate temperatures, diamond films consisting of the particles showing both (100) and (111) plane were deposited. The (100) proferred orientation of the diamond films are believed to be due to a relatively high supersaturation during deposition, and the growth condition for the diamond films having (100) preferred orientation can be applied to the single crystal growth since no twins are generated on the (100) plane. The grain size of the diamond films did not change with increasing temperature and its increasing rate with increasing deposition time was the same irrespective of the substrate temperature. However, the nucleation density increased with substrate temperature and its increasing rate with deposition time was much higher for the films deposited at higher substrate temperature.

• Journal of the Korean Society for Heat Treatment
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• v.31 no.2
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• pp.41-48
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• 2018

In this study, microstructural changes due to extrusion, rolling and heat treatment were studied to fabricate Al-4.0wt%Zn-1.5wt%Mg-0.9wt%Cu alloys with homogeneous microstructure suitable for metal cases of smart phones and electronic products fabricated through plastic working. After extrusion microstructure and texture were developed very differently on the surface and inside. Inside, coarse grains were formed and a strong Cube component orientation was developed. On the surface, a weak texture was developed with small grains. After 72% cold rolling the intensity of the Cube component orientation was lower, and uniform texture was developed in all the layers and the R-value was uniformly predicted. After recrystallization, the grain size difference between at the surface and the inside is smaller, when 72% rolling was performed, indicating that a uniform structure is formed. Texture develops almost randomly after recrystallization and exhibits uniform R-values at all layers.

• Korean Journal of Metals and Materials
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• v.49 no.2
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• pp.93-103
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• 2011

Precipitation behavior of high-nitrogen duplex Fe-24Cr-7Mn-4Ni-4Mo-0.43N stainless steel aged at $850^{\circ}C$ was investigated using scanning transmission electron microscopy. Based on the analyses of selected area diffraction patterns, four kinds of precipitates (intermetallic sigma (${\sigma}$) and chi (${\chi}$), $Cr_2N$ and secondary austenite) were identified. At the ferrite/austenite phase boundary, the ${\sigma}$ phase and secondary austenite were formed via ${\alpha}{\rightarrow}{\gamma}+{\sigma}$ eutectoid reaction. The precipitation of $Cr_2N$ occurred at the austenite grain boundary as well as the interior of the ferrite. The intermetallic ${\chi}$ phase also formed within the ferrite and showed a cube-cube orientation relationship with the ferrite. Further aging produced a lamellar structure composed of $Cr_2N$ and austenite along the ferrite/austenite boundary and enhanced the precipitation of the ${\chi}$ phase. The crystallographic features of the precipitates were also examined in terms of the orientation relationship with the austenite or ferrite matrix.