• Journal of the Institute of Electronics Engineers of Korea SD
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• v.44 no.5
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• pp.15-20
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• 2007

We fabricated ZnO thin films on quartz substrate using pulsed laser deposition method and investigated structural and optical properties of ZnO thin films with various substrate temperatures. Regardless of the substrate temperature variation, all ZnO thin films had grown to (002) and the thin film deposited at 400 $^{\circ}C$ exhibited an excellent crystallinity having 0.24$^{\circ}$ of Full-Width-Half-Maximum (FWHM). In the result of photoluminescence property, UV and deep-level emission peaks were observed in all ZnO films and the emission peaks were changed with various substrate temperatures. An highest UV emission was exhibited on the specimen deposited at 400 $^{\circ}C$ and the FWHM of UV peak was 14 nm. The optical transmittance was about 85 % in visible region regardless of the substrate temperature. The comparison result of the bandgap energies obtained from optical transmittance and UV emission centers, the two values were about the same. From these results, it is found that UV emission center has close relationship with near band edge emission of ZnO thin film.

• Korean Journal of Materials Research
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• v.10 no.12
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• pp.807-811
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• 2000

CeO$_2$ and SrBi$_2$Ta$_2$O$_{9}$ (SBT) thin films for MFISFET (Metal-ferroelectric-insulator-semiconductor-field effect transistor) were deposited by r.f. sputtering and pulsed laser ablation method, respectively. The effects of sputtering gas ratio(Ar:O$_2$) during deposition for CeO$_2$ films were investigated. The CeO$_2$ thin films deposited on Si(100) substrate at $600^{\circ}C$ exhibited (200) preferred orientation. The preferred orientation, Brain size and surface roughness of films decreased with increasing oxygen to argon gas ratio. The films deposited under the condition of Ar:O$_2$= 1 : 1 showed the best C- V characteristics. The leakage current of films showed the order of 10$^{-7}$ ~10$^{-8}$ A at 100kV/cm. The SBT thin films on CeO$_2$/Si substrate showed dense microstructure of polycrystalline phase. From the C-V characteristics of MFIS structure with SBT film annealed at 80$0^{\circ}C$, the memory window width was 0.9V at 5V The leakage current density of Pt/SBT/CeO$_2$/Si structure annealed at 80$0^{\circ}C$ was 4$\times$10$^{-7}$ /$\textrm{cm}^2$ at 5V.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.08a
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• pp.260-260
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• 2011

투명 비정질 산화물반도체는 디스플레이의 구동소자인 박막 트랜지스터에 채널층으로 사용된다. 또한 투명하면서 유연성이 있는 소자를 저비용으로 제작할 수 있는 장점을 가진다. 투명 산화물반도체 재료 중 IGZO는 Si 또는 GaAs와 같은 공유결합성 반도체와는 다른 전자 배치로 전도대가 금속이온의 ns 궤도에서 형성되며, 가전도대가 산소 음이온의 2p 궤도에서 형성된다. 특히 큰 반경의 금속 양이온은 인접한 양이온과 궤도 겹침이 크게 발생하게 되며 캐리어의 효과적인 이동 경로를 제공해줌으로써 다른 비정질 반도체와는 다르게 높은 전하이동도(~10 $cm^2$/Vs)를 가진다. 따라서 저온공정에서 우수한 성능의 TFT소자를 제작할 수 있는 장점이 있다. 본 연구에서는 TFT 채널층으로 사용하기 위한 a-IGZO박막의 산소분압에 따른 특성변화를 분석 하였다. a-IGZO박막은 Pulsed Laser Deposition (PLD)를 이용하여 산소분압(20~200 mTorr) 변화에 따라 Glass기판에 증착하였다. 증착된 a-IGZO 박막의 구조적 특성으로는 X-ray diffraction (XRD), Field emission scanning electron microscopy (FE-SEM), 광학적 특성은 UV-vis spectroscopy 분석을 통해서 알아보았다. TFT 채널층의 조건으로는 낮은 off-current, 높은 on-off ratio를 위해 고저항 ($10^3\;{\Omega}cm$)의 진성반도체 성질과 source/drain금속과의 낮은 접촉저항(ohmic contact) 등의 전기적 성질이 필요하다. 따라서 이러한 전기적 특성확인을 위해 transmission line method (TLM)을 사용하여 접촉저항과 비저항을 측정하였고, 채널층으로 적합한 분압조건을 확인해볼 수 있었다.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.04b
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• pp.157-160
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• 2004

Ferroelectric $(Ba_xSr_{1-x})TiO_3$ (BST) thin films have been deposited on (001) MgO single crystals by a pulsed laser deposition (PLD) method. The structure of deposited BST thin films were investigated by an x-ray diffractometer. Calculated c-axis lattice parameters of the BST films exhibit a strong lattice distortion, which was not observed in ceramic BST at room temperature. This lattice distortion of BST has been attributed to strains caused by lattice constant difference between film and substrate, oxygen vacancies in BST film, and thermal expansion difference between film and substrate. Ferroelectric properties at 10 GHz have been measured using a HP 8510C vector network analyzer. Dielectric properties, capacitance tunability and quality factor, of the interdigitaed capacitors fabricated on BST films were calculated from the measured s-parameters. Two distinct behaviors in structural, opitical, and microwave properties of BST films were observed; below and above 200 mTorr of oxygen pressure in the deposition chmber.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.17 no.11
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• pp.1241-1245
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• 2004

Continuous physical vapor deposition (PVD) method is one of many processes to fabricate long length coated conductor which is required for successful large-scale application of superconducting power devices. Three film deposition systems (pulsed laser deposition, sputtering, and evaporation) equipped with reel-to-reel(R2R) metal tape moving apparatus were installed and used to deposit multi-layer oxide thin films. Both RABiTS and IBAD texture templates are used. IBAD template consists of CeO$_2$(PLD)/YSZ(IBAD) on stainless steel(SS) metal tape, and RABiTS template has the structure of CeO$_2$/YSZ/Y$_2$O$_3$ which was continuously deposited on Ni-alloy tape using R$_2$R evaporation and DC reactive sputtering in a deposition system designed to do both processes. 0.4 m-long coated conductor with Ic(77 K) of 34 A/cm was fabricated using RABiTS template. 0.5 m and 1.1 m-long coated conductor with Ic(77 K) of 41 A/cm and 26 A/cm were fabricated using IBAD template.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 2003.02a
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• pp.287-290
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• 2003

For microwave device applications, c-axis oriented high temperature superconducting YBa$_2$Cu$_3$O$_{7-{\delta}}$ (HTS-YBCO) epitaxial thin films on the r-cut sapphire substrate(Al$_2$O$_3$) were prepared. In order to reduce the lattice mismatch with a substrate and to enhance the crystallity of HTS thin films, CeO$_2$ buffer layer on the r-cut sapphire substrate was grown by the RF-magnetron sputtering. The YBCO films on the CeO$_2$ buffer layer were deposited using the pulsed-laser deposition (PLD) method. These HTS YBCO /CeO$_2$/Al$_2$O$_3$ multilayer thin films(30 $\times$ 30 mm$^2$) routinely exhibited a critical temperature(T$_{c}$) of 89 K from the R-T measurement. Using HTS YBCO/CeO$_2$ /Al$_2$O$_3$ multilayer thin film. We fabricated and characterized the microwave passive devices (planar type filters) with cryopack-age such as the coupled -line type low-pass filter (LPF) and the open-loop meander type bandpass filter (BPF).filter (BPF).).

• Progress in Superconductivity
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• v.14 no.1
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• pp.30-33
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• 2012

We have grown $MgB_2$ superconducting thin films on the SiC buffer layers by means of hybrid physical-chemical vapor deposition (HPCVD) technique. Prior to that, SiC was first deposited on $Al_2O_3$ substrates at various temperatures from room temperature to $600^{\circ}C$ by using the pulsed laser deposition (PLD) method in a vacuum atmosphere of ${\sim}10^{-6}$ Torr pressure. All samples showed a high transition temperature of ~40 K. The grain boundaries of $MgB_2$ samples with SiC layer are greater in amount, compare to that of the pure $MgB_2$ samples. $MgB_2$ with SiC buffer layer samples show interesting change in the critical current density ($J_c$) values. Generally, at both 5 K and 20 K measurements, at lower magnetic field, all $MgB_2$ films deposited on SiC buffer layers have low $J_c$ values, but when they reach higher magnetic fields of nearly 3.5 Tesla, $J_c$ values are enhanced. $MgB_2$ film with SiC grown at $600^{\circ}C$ has the highest $J_c$ enhancement at higher magnetic fields, while all SiC buffer layer samples exhibit higher $J_c$ values than that of the pure $MgB_2$ films. A change in the grain boundary morphologies of $MgB_2$ films due to SiC buffer layer seems to be responsible for $J_c$ enhancements at high magnetic fields.

• Progress in Superconductivity and Cryogenics
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• v.18 no.4
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• pp.1-4
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• 2016

We investigated the relation between the Cu-O bond length and the superconducting properties of $BaSnO_3$ (BSO)-added $GdBa_2Cu_3O_{7-x}$ (GdBCO) thin films by using extended x-ray absorption fine structure (EXAFS) spectroscopy. 4 wt.% $BaSnO_3$ (BSO) added $GdBa_2Cu_3O_{7-x}$ (GdBCO) thin films with varying thickness from $0.2{\mu}m$ to $1.0{\mu}m$ were fabricated by using pulsed laser deposition (PLD) method. The transition temperature ($T_c$) and the residual resistance ratio (RRR) of the GdBCO films increased with increasing thickness up to $0.8{\mu}m$, where the crystalline BSO has the highest peak intensity, and then decreased. This uncommon behaviors of $T_c$ and RRR are likely to be created by the addition of BSO, which may change the ordering of GdBCO atomic bonds. Analysis from the Cu K-edge EXAFS spectroscopy showed an interesting thickness dependence of ordering behavior of BSO-added GdBCO films. It is noticeable that the ordering of Cu-O bond and the transition temperature are found to show opposite behaviors in the thickness dependence. Based on these results, the growth of BSO seemingly have evident effect on the alteration of the local structure of GdBCO film.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.330-332
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• 2013

소 분위기에서 플라즈마 표면 처리의 경우 기판 표면에 존재하는 수소와 탄소 유기물들이 산소와 반응하여 $H_2O$와 $CO_2$ 등으로 제거되며 표면에 오존 결합을 유도하여 표면 에너지를 증가시키는 것으로 알려져 있다. ZnO 나노구조물을 성장시키는 방법으로는 MOCVD (Metal-Organic Chemical Vapor Deposited), PLD (Pulsed Laser Deposition), VLS (Vapor-Liquid-Solid), Sputtering, 습식화학합성법(Wet Chemical Method) 방법 등이 있다. 그중에서도 습식화학합성법은 쉽게 구성요소를 제어할 수 있고, 저비용 공정과 낮은 온도에서 성장 가능하며 플렉서블 소자에도 적용이 가능하다. 그러므로 본 연구에서는 플라즈마 표면처리에 따라 표면에너지를 변화하여 습식화학합성법으로 성장시킨 ZnO nanorods의 밀도를 제어하고 photolithography 공정 없이 패터닝 가능성을 유 무를 판단하는 연구를 진행하였다. 기판은 Si wafer (100)를 사용하였으며 세척 후 표면에너지 증가를 위한 플라즈마 표면처리를 실시하였다. 분위기 가스는 Ar/$O_2$를 사용하였으며 입력전압 400 W에서 0, 5, 10, 15, 60초 동안 각각 실시하였다. ZnO nanorods의 seed layer를 도포하기 위하여 Zinc acetate dehydrate [Zn $(CH_3COO)_2{\cdot}2H_2O$, 0.03 M]를 ethanol 50 ml에 용해시킨 후 스핀코팅기를 이용하여 850 RPM, 15초로 5회 실시하였으며 $80^{\circ}C$에서 5분간 건조하였다. ZnO rods의 성장은 Zinc nitrate hexahydrate [$Zn(NO_3)_2{\cdot}6H_2O$, 0.025M], HMT [$C6H_{12}N_4$, 0.025M]를 deionized water 250 ml에 용해시켜 hotplate에 올리고 $300^{\circ}C$에서 녹인 후 $200^{\circ}C$에서 3시간 성장시켰다. ZnO nanorods의 성장 공정은(Fig. 1)과 같다. 먼저 플라즈마 처리한 시편의 표면에너지 측정을 위해 접촉각 측정 장치[KRUSS, DSA100]를 이용하였다. 그 결과 0, 5, 10, 15, 60 초로 플라즈마 표면 처리했던 시편이 각각 Fig. l, 2와 같이 $79^{\circ}$, $43^{\circ}$, $11^{\circ}$, $6^{\circ}$, $7.8^{\circ}$로 측정되었으며 이것을 각각 습식화학합성법으로 ZnO nanorods를 성장 시켰을 때 Fig. 3과 같이 밀도 차이를 확인할 수 있었다. 이러한 결과를 바탕으로 기판의 표면에너지를 제어하여 Fig. 4와 같이 나타나며 photolithography 공정없이 ZnO nanorods를 패터닝을 할 수 있었다. 본 연구에서는 플라즈마 표면 처리를 통하여 표면에너지의 변화를 제어함으로써 ZnO nanorods 성장의 밀도 차이를 나타냈었다. 이러한 저비용, 저온 공정으로 $O_2$, CO, $H_2$, $H_2O$와 같은 다양한 화학종에 반응하는 ZnO를 이용한 플렉시블 화학센서에 응용 및 사용될 수 있고, 플렉시블 디스플레이 및 3D 디스플레이 소자에 활용 가능하다.