• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1998.06a
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• pp.235-238
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• 1998

Ferroelectric $LiNbO_3$ thin films were grown directly on Si(100) substrates by 13.55MHz RF magnetron sputtering system using a ceramic target ($Nb_2O_5/Li_2C0_3$ = 51.4/48.6). Because high temperature process have to avoided to prevent degradation of the interface (insulator/Si), $LiNbO_3$ thin films were deposited below $300^{\circ}C$. After as-deposited films were performed RTA treatments in an oxygen ambient at $600^{\circ}C$ for 60s, electrical measurements performed films before and after anneal treatment. In high field region, the leakage current density of the films after annealing was deceased about 4order and the resistivity of these was increased to about 5\times 10^{11} \Omega \cdot cm$ at 500kV/cm. In accumulation region of C-V curve, we calculated dielectric constant of thin film $LiNbO_3$ as 27.9 which is close to that of bulk value.

• Proceedings of the Materials Research Society of Korea Conference
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• 2003.11a
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• pp.142-142
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• 2003

The effects of film thickness on the dipolar relaxation of ferroelectric PbTiO$_3$ films were investigated in the microwave-frequency range. The dielectric constants ($\varepsilon$) and the dielectric losses (tan $\delta$) were successfully measured up to 30 ㎓ using interdigital capacitors. The PbTiO$_3$ thin films were deposited on the quartz substrate at room temperature and postannealed in oxygen atmosphere. As the film thickness increased, its grain size and tetragonality were enhanced. And the dipolar relaxation behavior began to appear in the thin films with approximately 20 nm thickness, since ferroelectric domains could not be formed hi small grains. The observed relaxation frequency (above 10 ㎓) was higher than the previous values reported in bulk ceramics. It can be correlated with the extremely small domain size of the thinfilms as shown by TEM. And, the Rayleigh constant [1] from domain wall motions was alsoinvestigated by LCR meter at 100 KHz.

• Journal of Information Display
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• v.4 no.1
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• pp.1-8
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• 2003

Recent progress in both low pretilt and high pretilt defect free C1 surface stabilized ferroelectric liquid crystal (SSFLC) devices is reviewed. First, by numerical calculation to investigate the balance between surface azimuthal anchoring energy and bulk elastic energy within the confined chevron layer geometry of C1 and C2, it is possible to achieve a zigzag free C1 state by low azimuthal anchoring alignment with a low pretilt angle. The critical azimuthal anchoring coefficient for defect free C1 state is calculated. Its relationship with elastic constant, chevron angle as well as surface topography effect are also discussed. Second, using $5^{\circ}$ oblique SiO deposition alignment method a defect free, large memory angle, high contrast ratio and bistable C1 SSFLC display, which has potential for electronic paper applications has also been developed. The electrooptical properties and bistability of this device have been investigated. Various aspects of defect control are also discussed.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.260-260
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• 2013

Multiferroic materials have attracted much attention due to their fascinating fundamental physical properties and technological applications in magnetic/ferroelectric data-storage systems, quantum electromagnets, spintronics, and sensor devices. Among single-phase multiferroic materials, $BiFeO_3 $ is a typical multiferroic material with a room temperature magnetoelectric coupling in view of high magnetic-and ferroelectric-ordering temperatures (Neel temperature $T_N$~647 K and Curie temperature $T_C$~1,103 K). Rare-earth ion substitution at the Bi sties is very interesting, which induces suppressed volatility of Bi ion and improved ferroelectric properties. At the same time, Fe-site substitution with magnetic ions is also attracting, and the enhanced ferromagnetism was reported. In this study, $Bi_{1-x}Dy_xFe_{0.95}Co_{0.05}O_3$ (x=0, 0.05 and 0.1) bulk ceramic compounds were prepared by solid-state reaction and rapid sintering. High-purity $Bi_2O_3$, $Dy_2O_3$, $Fe_2O_3$ and $Co_3O_4$ powders with the stoichiometric proportions were mixed, and calcined at $500^{\circ}C$ or 24 h to produce $Bi_{1-x}Dy_xFe_{0.95}Co_{0.05}O_3$. The samples were immediately put into an oven, which was heated up to $800^{\circ}C$ nd sintered in air for 30 min. The crystalline structure of samples was investigated at room temperature by using a Rigaku Miniflex powder diffractometer. The field-dependent magnetization measurements were performed with a vibrating-sample magnetometer. The electric polarization was measured at room temperature by using a standard ferroelectric tester (RT66B, Radiant Technologies).

• Journal of the Korean Ceramic Society
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• v.53 no.2
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• pp.178-183
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• 2016

Ferroelectric relaxor ceramics with $BaTiO_3-NaNbO_3-Bi(Mg_{1/2}Ti_{1/2})O_3$ ternary compositions (BT-NN-BMT) have been prepared by sol-gel powder synthesis and consequent bulk ceramic processing. Through the modified chemical approach, fine and single-phase complex perovskite compositions were successfully obtained. Temperature and frequency dependent dielectric properties indicated typical relaxor characteristics of the BT-NN-BMT compositions. The ferroelectric-paraelectric phase transition became diffusive when NN and BMT were added to form BT based solid solutions. BMT additions to the BT-NN solid solutions affected the high temperature dielectric properties, which might be attributable to the compositional inhomogeneity of the complex perovskite and resulting weak dielectric coupling of the Bi-containing polar nanoregions (PNRs). The temperature stability of the dielectric properties was good enough to satisfy the X9R specification. The quasi-linear P-E response and the temperature- stable dielectric properties imply the high potential of this ceramic compound for use in high temperature capacitors.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.189.1-189.1
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• 2014

Lead zirconium titanate (PZT) is usually used as bulk and thin films. Due to high flexibility and piezoelectric, ferroelectric and pyroelectric properties, PZT fiber has attracted in a variety of fields such as sensor devices, non-electromechanical systems and non-volatile ferroelectric memory devices. And PZT fiber can be numerously synthesized and almost with the diameter of PZT fiber thicker than $10{\mu}m$. However, the electrospinnig method is cost effective and convenient. PZT obtained by electrospinning methodhas the diameter from sub-micro to nanometer. In this paper, the PZT/PVP nanofibers were synthesized with three precursors, lead nitrate, zirconium ethoxide and titanium isopropoxide. And the PZT nanofibers were fabricated after removal of PVP by annealing process at various temperature. The obtained PZT nanofibers were characterized by means of X-ray photoelectron spectroscopy (XPS) for chemical properties, X-ray diffraction (XRD) for crystallinity and phase, scanning electron microscopy (SEM) for morphologies. The diameter of PZT nanofibers were measured with SEM. From the SEM images, we confirmed that diameter of PZT nanofibers was hundreds of nanometers and decreased with increasing the annealing temperature. When the annealing temperature increased, the crystallinity of PZT nanofibers changed from pyrochlore to perovskite structure.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.533-534
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• 2006

1mm-thick BLT ceramics were sintered in accordance with a bulk ceramic fabrication process. All XRD peaks detected in the sintered ceramics were indexed as the Bi-layered perovskite structure without secondary phases. Density was increased with increasing the sintering temperature up to $1050\;^{\circ}C$ and the maximum value was about 98% of the theoretical density. The remanent polarization (2Pr) value of BLT ceramic sintered at $1050\;^{\circ}C$ was approximately $6.5\;{\mu}C/cm^2$ at the applied voltage of 4.5kV. From these results, a BLT ceramic target for plused laser deposition (PLD) system was successfully fabricated.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.06a
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• pp.276-277
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• 2006

1mm-thick BLT ceramics were sintered in accordance with a bulk ceramic fabrication process. AII XRD peaks detected in the sintered ceramics were indexed as the Bi-layered perovskite structure without secondary phases. Density was increased with increasing the sintering temperature up to $1050^{\circ}C$ and the maximum value was about 98% of the theoretical density. The remanent polarization (2Pr) value of BLT ceramic sintered at $1050^{\circ}C$ was approximately $6.5\;{\mu}C/cm^2$ at the applied voltage of 4.5 kV. The calculated electromechanical coupling factor ($k_t$) of it was about 5% and the mechanical quality factor (Qm) was about 2200. From these results, a BLT ceramic target for pulsed laser deposition (PLD) system was successfully fabricated.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.139.1-139.1
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• 2016

Multiferroic materials are of great interest because of its potential applications in the design of devices combining magnetic, electronic and optical functionalities. Among various multiferroic materials, $BiFeO_3$(BFO) is known to be one of the intensively focused mainly due to the possibility of multiferroism at device working temperature (> $200^{\circ}C$). However, leakage current and weak polarization resulting from oxygen deficiency and crystalline defect should be resolved. Furthermore the magnetic ordering of pure BFO mainly prefers to have antiferromagnetic coupling. Up to now many attempts have been performed to improve the ferromagnetic and the ferroelectric properties of BFO by doping. In this work, we investigated the effects of Ni substitution on the multiferroism of bulk BFO. Four BFO samples (a pure BFO and three Ni-doped BFO's; $BiFe_{0.99}Ni_{0.01}O_3$, $BiFe_{0.98}Ni_{0.02}O_3$ and $BiFe_{0.97}Ni_{0.03}O_3$) were synthesized by the standard solid-state reaction and rapid sintering technique. The XRD results reveal that Ni atoms are substituted into Fe-sites and give rise to phase transition of cubic to rhombohedal. By using vibrating sample magnetometer and standard ferroelectric tester, the multiferroic properties at room temperature were characterized. We found that the magnetic moment of Ni-doped BFO turned out to be maximized for 3% of Ni dopant.

• Proceedings of the KIEE Conference
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• 1998.07d
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• pp.1352-1354
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• 1998

$LiNbO_3$ transistor showed relatively stable characteristic, low interface trap density, and large remanent polarization. This paper reports ferroelectric $LiNbO_3$ thin films grown directly on p-type Si(100) substrates by 13.56 MHz rf magnetron sputtering system for FRAM applications. To take advantage of low temperature requirement for growing films, we deposited $LiNbO_3$ films lower than $300 ^{\circ}C$. RTA(Rapid Thermal Anneal) treatment was performed for as-deposited films in an oxygen atmosphere at $600^{\circ}C$ for 60 sec. We learned from X-ray diffraction that the RTA annealed films were changed from amorphous to poly-crystalline $LiNbO_3$ which exhibited (012), (015), and (022) orientations. The I-V characteristics of $LiNbO_3$ films before and after anneal treatment showed that RTA improved the leakage current of films. The leakage current density of films decreased from $10^{-5}$ to $10^{-7} A/cm^2$ at room temperature measurement. Breakdown electric field of the films exhibited higher than 500 kV/cm. The C-V curves showed the clockwise hysteresis represents ferroelectric switching characteristics. From C-V curves, we calculated dielectric constant of thin film $LiNbO_3$ as 27.5 which is close to that of bulk value.