• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.11a
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• pp.45-48
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• 2000

High dielectric (Ba,Sr)TiO$_3$ thin films were etched in an inductively coupled plasma (ICP) as a function of C1$_2$/Ar gas mixing ratio. Under Cl$_2$(20)/Ar(80), the maximum etch rate of the BST films was 400$\AA$/min and selectivities of BST to Pt and PR were obtained 0.4 and 0.2, respectively. We investigated the etched surface of BST by x-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and x-ray diffraction (XRD). From the result of XPS analysis, we found that residues of Ba-Cl and Ti-Cl bonds remained on the surface of the etched BST for high boiling point. The surface roughness decreased as Cl$_2$ increases in Cl$_2$/Ar plasma because of non-volatile etching products. This changed the nature of the crystallinity of BST. From the result of XRD analysis, the crystalliility of etched BST film maintained as similar to as-deposited BST under Ar only and Cl$_2$(20)/Ar(80). However, (100) orientation intensity of etched BST film abruptly decreased at Cl$_2$ only plasma. It was caused that Cl compounds were redeposited on the etched BST surface and damaged to crystallinity of BST film during the etch process.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.11a
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• pp.309-312
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• 2002

Ferroelectric $Sr_{0.3}Ba_{0.7}Nb_{2}O_{6}$ (SBN30) thin films were deposited on Pt/Ti/$SiO_{2}$/Si(100) substrates by ion beam sputtering. During annealing treatment at $750^{\circ}C$, poling was attempted by applying dc voltage bias across polished surfaces. Phase relation, microstructure and crystallization behavior were examined using XRD and FE-SEM. Ferroelectric hysteresis characteristics were also determined where both remanent polarization and coercive values decreased with the increase of bias voltage. The measured remanent polarization and coercive field values at 5 V and 10 V bias were $36{\mu}C/cm^2$, $10{\mu}C/cm^2$ and 100kV /cm, 80kV /cm, respectively.

• Journal of Sensor Science and Technology
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• v.10 no.6
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• pp.295-303
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• 2001

White emission thin film electroluminecent device was fabricated with ZnS for phosphor layers and BST ferroelectric thin film for insulating layers. The ZnS:Mn and $ZnS:SmF_3$ layers were used for emission of red color. Also the $ZnS:TbF_3$ and $ZnS:AgF_3$ layers were used to emission of green and blue color, respectively. And the fabrication conditions of the BST insulating layers were followings, that is, the composition ratio of target, substrate temperature, working pressure and operating gas ratio were $Ba_{0.5}Sr_{0.5}Ti_{0.3}$, $400^{\circ}C$, 30 mTorr and 9:1, respectively. The thickness of phosphor were 150 nm for each layers and the insulating layers of upper and bottom were 400 nm and 200 nm, respectively. The luminesence threshold voltage was $75\;V_{rms}$ and the maximum brightness of the thin film electroluminecent device was $3200\;cd/m^2$ at $100\;V_{rms}$.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.07a
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• pp.393-396
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• 2004

본 논문에서는 완충층용 MgO 박막을 P-type(100)Si 기판위에 작업가스 $Ar:O_2=80:20$, RF 파워 50W, 기판온도 $400^{\circ}C$, 10mtorr의 작업진공에서 $500{\AA}$ 증착하였다. 제작된 MgO/Si 기판위에 RF Magnetron sputtering법으로 작업가스 $Ar:O_2$의 비율을 90:10, 80:20, 70:30으로 변화하면서 $BST(Ba_{0.5}Sr_{0.5}TiO_3)$ 박막을 약 $2000{\AA}$ 증착하였다. XRD 측정결과 작업가스비의 변화에 관계없이(110)BST와 (111)BST 피크만이 관찰되었으며 작업가스 $Ar:O_2=80:20$에서 가장 양호한 결정성을 나타내었다. I-V 측정결과 인가전계 ${\pm}100kV/cm$에서 $10^{-7}A/cm^2$이하의 양호한 누설전류 특성을 보여주고 있으며 C-V 측정결과 작업가스 $Ar:O_2$의 비율 90:10, 80:20, 70:30에서의 비유전율은 각각 283, 305, 296으로서 작업가스비 80:20에서 제작된 박막의 특성이 가장 우수하였다. 작업가스비 80:20에서 제작된 박막의 SEM 측정결과 결정이 성장되었음을 확인할 수 있었고 그레인의 크기는 약 10nm였다.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.07b
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• pp.623-626
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• 2004

[ $Ba_{0.6}Sr_{0.4}TiO_3$ ] (BST) dielectric thin films doped by Cr were prepared using an alkoxide-based sol-gel method on the Pt/Ti/SiO2/Si substrate. Atomic force microscopy and x-ray diffraction analysis showed that increasing the Cr doping ratio causes increased grain size while the surface remains smooth and crack-free. It was also found that compared with undoped films the increase of Cr content in BST improves the dielectric constant and the leakage-current characteristics. The figure of merit reached the maximum value of 72.3 at the 5 mol % of Cr doping. This composition showed the dielectric constant of 426, the loss factor of 0.0065, tenability of 47.7%, and leakage-current density (at the electric field of 100 kV/cm) of $5.31{\times}10^{-8}A/cm^2$. The results show that the Cr-doped BST thin films are prospective candidates for applications in tunable devices.

• Proceedings of the KIEE Conference
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• 1997.11a
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• pp.291-293
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• 1997

In this study, Sol-Gel derived $(Ba_{0.7}Sr_{0.3})TiO_3$ thin films were fabricated and investigated. The stock solution was synthesized and spin-coated on Pt/Ti/$SiO_2$/Si substrate at 4000(rpm] and then, annealed at $650{\sim}750[^{\circ}C]$. Crystallization condition, microstructural properties and interfacial structure were observed by XRD, AFM, SEM and TEM. It was found that the BST thin films were completely crystallized at 750[$^{\circ}C$] and showed nano-sized grains. The dielectric constant and loss of the BST thin films were 220, 0.01 at 1[kHz] respectively. Increasing the temperature, the dielectric constant and loss characteristics were not varied widely. At the applied voltage of 1.5[V], the leakage current density was under the $10^{-9}[A/cm^2]$.

• Progress in Superconductivity
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• v.11 no.1
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• pp.47-51
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• 2009

For many large-scale applications of high-temperature superconducting materials, large critical current density ($J_c$) in high applied magnetic fields are required. A number of methods have been reported to introduce artificial pinning centers in $YBa_2Cu_3O_{7-{\delta}}$ films for enhancement of their $J_c$. We studied the microstructures and characteristic of $YBa_2Cu_3O_{7-{\delta}}$ films fabricated on $SrTiO_3$ (100) substrates with ZnO nanorods as pinning centers. Au catalyst nanoparticles were synthesized on STO substrates with self assembled monolayer to control the number of ZnO nanorods. The density of Au nanoparticles is approximately $240{\sim}260{\mu}m^{-2}$ with diameters of $41{\sim}49nm$. ZnO nanorods were grown on STO by hot-walled PLD with Au nanoparticles. Typical size of ZnO nanorod was around 179 nm in diameter and $2{\sim}6{\mu}m$ in length respectively. YBCO films deposited directly on STO substrates show the c-axis orientation, while YBCO films with ZnO nanorods exhibit any mixed phases without any typical crystal orientation.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.07a
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• pp.22-25
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• 2002

In this paper, we deposited MgO buffer layer on p-type (100)Si substrate in the condition of substrate temperature 400$^{\circ}C$, working gas ratio Ar:O$_2$=80:20, RF Power 50W, working pressure 10mtorr, and the thickness of the film was about 300${\AA}$. Then we deposited Ba$\sub$0.5/Sr$\sub$0.5/TiO$_3$ thin film using RF Magnetron sputtering method on the MgO/Si substrate in various RF power of 25W, 50W, 75W. The film deposited in 50W showed the best crystalline from the XRD measurement. To know the electrical properties of the film, we manufactured Al/BSTMgO(300${\AA}$)/Si/Al structure capacitor. In the result of I-V measurement, The leakage current density of the capacitor was lower than 10$\^$-7/A/$\textrm{cm}^2$ at the range of ${\pm}$150kV/cm. From C-V characteristics of the capacitor, can calculate the dielectric constant and it was 305. Finally we deposited BST thin film on bare Si substrate and (100)MgO substrate in the same deposition condition. From the comparate of the properties of these samples, we found the properties of BST thin film which deposited on MgO/Si substrate were better than on bare Si substrate and similar to on MgO substrate.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.17 no.10
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• pp.1061-1067
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• 2004

In this study, ferroelectric (Ba,Sr)TiO$_3$ and high temperature superconductor YBCO thin films were fabricated by PLD (Pulsed Laser Deposition) method and tuneable bandstop filters were implemented with two different IDC(Interdigital Capacitance) gap patterns, 20${\mu}{\textrm}{m}$ and 30${\mu}{\textrm}{m}$ using these two thin film layers. The resonant frequency was changed by DC bias voltage. By comparing measured results with simulation, the dielectric properties of ferroelectric thin film have been extracted. The permittivity was 820 ～ 900 at 30 K and had an acceptable error range but the loss tangent had a great difference, 0.018 in 30${\mu}{\textrm}{m}$ IDC gap pattern and 0.037 in 20 ${\mu}{\textrm}{m}$.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.05b
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• pp.34-38
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• 2000

Recently, the ceramics of high permittivity are applied to DRAM and FRAM. In this study, (Ba, Sr)$TiO_3$ (BST) ceramics thin films were prepared by Sol-Gel method. BST solution was made and spin-coated on Pt/$SiO_2$/Si substrate at 4000 [rpm] for 10 seconds. Coated specimens were dried at $150[^{\circ}C]$ for 5 minutes. Coating process was repeated 3 times and then sintered at $750[^{\circ}C]$ for 30 minutes. Each specimen was analyzed structure and electrical characteristics by Fractal Process. Thickness of BST ceramics thin films are about $2000{\AA}$. Dielectric constant and loss of thin films was little decreased at 1[KHz] - 1[MHz]. Dielectric constant and loss to frequency were 250 and 0.02 in BST3. The property of leakage current as the realation between the current and the voltage was that change of the leakage current was stable when the applied voltage was 0~3[V].