• Proceedings of the Materials Research Society of Korea Conference
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• 2010.05a
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• pp.59-59
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• 2010

ZnO는 II-VI 족 화합물 반도체로써 상온에서 큰 엑시톤 결합에너지 (~60 meV) 를 가지며 밴드갭이 3.37 eV인 직접 천이형 반도체로 잘 알려진 물질이다. 이러한 ZnO의 물리적 특성은 광학소자로 상용화된 GaN와 유사하기 때문에 LED나 LD등의 광 소자 재료로 주목 받고 있다. 또한 ZnO는 3족 원소 (In, Ga, Al)를 도핑 함으로써 전기적 특성 제어가 가능한 장점을 가지고 있다. 본 연구는 펄스레이저 증착법 (Pulsed Laser Deposition)을 이용하여 Si (111) 기판 위에 ZnO:In 박막을 성장 시켰으며, 도핑된 indium 양에 따른 ZnO 박막의 배향성 변화를 관찰 하였다. X-선 회절 분석법 (X-ray diffraction), 탐침형 원자현미경 (Atomic Force Microscope) 그리고 투과전자 현미경 (Transmission Electron Microscope)을 측정하였다. XRD 측정 결과 un-doped ZnO 박막은 (002) 방향으로 c-축 우선성장 하였다. 그러나 ZnO 박막내의 Indium 양이 증가 할수록 (002) 방향에서 (101), (102), (103) 등의 (101) 방향으로 성장이 변화 하였으며 5 at.% 이상에서는 (100) 방향의 성장이 관찰 되었다. TEM 측정 결과 un-doped ZnO 박막은 columnar 구조로 성장 되었으나, Indium 양이 증가할수록 column의 size가 감소하며, 5 at.% 이상에서 columnar 구조 성장이 거의 관찰되지 않는다. AFM 결과에서는 Indium 양이 증가 할수록 박막의 표면거칠기와 결정립 크기가 감소하였다.

• 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.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.26 no.8
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• pp.602-607
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• 2013

Concern for the TOS (Transparent Oxide Semiconductor) is increasing with the recent increase in interest for flexible device. Especially MgZnO has attracted a lot of attention. $Mg_xZn_{1-x}O$, which ZnO-based wideband-gap alloys is tuneable the band-gap ranges from 3.36 eV to 7.8 eV. In particular, the flexible substrate, the crystal structure of the amorphous as well as the surface morphology is not good. So research of MgZnO thin films growth on flexible substrate is essential. Therefore, in this study, we studied on the effects of the oxygen partial pressure on the structural and crystalline of $Mg_{0.1}Zn_{0.9}O$ thin films. MgZnO thin films were deposited on PES substrate by using pulsed laser deposition. We used XRD and AFM in order to observe the structural characteristics of MgZnO thin films. UV-visible spectrophotometer was used to get the band gap and transmittance. Crystallization was done at a low oxygen partial pressure. The crystallinity of MgZnO thin films with increasing temperature was improved, Grain size and RMS of the films were increased. MgZnO thin films showed high transmittance over 80% in the visible region.

• Journal of the Korean Magnetics Society
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• v.13 no.2
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• pp.64-69
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• 2003

Ba-ferrite thin films were prepared on Si substrate with ${\alpha}$-Fe$_2$O$_3$ underlayer by a pulsed laser deposition system and characterized by X-ray, SEM, Mossbauer spectroscopy and VSM. The appropriate conditions of pulsation in ${\alpha}$-Fe$_2$O$_3$ and Ba-ferrite were the oxygen pressure of 0.1 Torr at a substrate temperature of 400$^{\circ}C$. Ba-ferrite crystals had the forms of ellipsoidal or needle and the grains shaped the more lumps with increasing the film thickness. Mossbauer spectroscopy assured that the direction of atomic spin in Fe ion was not random but had the tendency of arrangement normal to the substrate. The coercive force and squareness of hysteresis were larger in normal than in plane to the substrate but, the magnetic saturation moment was contrary to them. The spin arrangement was strongly affected by ${\alpha}$-Fe$_2$O$_3$ underlayer and the high coercive force and squareness were influenced by this. The crystal structure was conformed to be a Magntoplumbite symmetry with the hexagonal unit cell and the lattice constant of a increased with increasing film thickness, while c decreased

• Applied Chemistry for Engineering
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• v.19 no.3
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• pp.270-276
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• 2008

$N_2$ doped $TiO_2$ nano-sized powder was prepared using a DC arc plasma jet and investigated with XRD, BET, SEM, TEM, and photo-catalytic decomposition. Recently the research interest about the nano-sized $TiO_2$ powder has been increased to improve its photo-catalytic activity for the removal of environmental pollutants. Nitrogen gas, reacting gas, and titanium tetrachloride ($TiCl_4$) were used as the raw materials and injected into the plasma reactor to synthesize the $N_2$ doped $TiO_2$ power. The particle size and XRD peaks of the synthesized powder were analyzed as a function of the flow rate of the nitrogen gas. Also, the characteristics of the photo-catalytic decomposition using the prepared powder were studied. For comparing the photo-catalytic decomposition performance of $TiO_2$ powder with that of $TiO_2$ coating, $TiO_2$ thin films were prepared by the spin coating and the pulsed laser deposition. For the results of the acetaldehyde decomposition, the photo-catalytic activity of $TiO_{2-x}N_x$ powder was higher than that of the pure $TiO_2$ powder in the visible light region. For the methylene blue decomposition, the decomposition efficiency of $TiO_2$ powder was also higher than that of $TiO_2$ film.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.9
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• pp.931-935
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• 2012

In this study, we fabricate and investigate low-temperature solid oxide fuel cells with a ceramic substrate/porous metal/ceramic/porous metal structure. To realize low-temperature operation in solid oxide fuel cells, the membrane should be fabricated to have a thickness of the order of a few hundreds nanometers to minimize IR loss. Yttrium-doped barium zirconate (BYZ), a proton conductor, was used as the electrolyte. We deposited a 350-nm-thick Pt (anode) layer on a porous substrate by sputter deposition. We also deposited a 1-${\mu}m$-thick BYZ layer on the Pt anode using pulsed laser deposition (PLD). Finally, we deposited a 200-nm-thick Pt (cathode) layer on the BYZ electrolyte by sputter deposition. The open circuit voltage (OCV) is 0.806 V, and the maximum power density is 11.9 mW/$cm^2$ at $350^{\circ}C$. Even though a fully dense electrolyte is deposited via PLD, a cross-sectional transmission electron microscopy (TEM) image reveals many voids and defects.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.11a
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• pp.196-196
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• 2008

We have investigated that the effect of post annealing on the structural and electrical properties of $Ba_{0.5}Sr_{0.5}TiO_3$ thin films. The BST thin films were deposited on n-type 4H-silicon carbide(SiC) using pulsed laser deposition (PLD). The deposition was carried out in oxygen ambient 100mTorr for 5 minutes, which results in about 300nm-thick BST films. For the BST/4H-SiC, 200nm thick silver was deposited on the BST films bye-beam evaporation. The X-ray diffraction patterns of the BST films revealed that the crystalline structure of BST thin films has been improved after post-annealing at $850^{\circ}C$ for 1 hour. The root mean square (RMS) surface roughness of the BST film measured by using a AFM was increased after post-annealing from 5.69nm to 11.49nm. The electrical properties of BST thin film were investigated by measuring the capacitance-voltage characteristics of a silver/BST/4H-SiC structure. After the post-annealing, dielectric constant of the film was increased from 159.67 to 355.33, which can be ascribed to the enhancement of the crystallinity of BST thin films.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.06a
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• pp.151-151
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• 2007

최근에 에피 성장된 ZnO는 UV-LED, 화학적-바이오센서와 투명전도 전극에 많은 관심을 받고 있다. 고 품질의 ZnO는 Metal-organic chemical vapor deposition(MOCVD), Pulsed laser deposition(PLD), molecular beam epitaxy(MBE), 그리고 마그네트론 스퍼터링법에 의해 성장이 이루어지고 있다. 대부분의 ZnO는 사파이어, 싫리콘과 같은 이종 기판 위에 성장되고 있으며, Heteroepitaxy로 성장된 ZnO 박막은 기판과 박막사이의 격자상수, 열팽창계수 차이로 인해 높은 결함 밀도를 보이고 있다. 이러한 문제점은 광전자 소자 응용에 있어 여러 가지 문제점을 야기 시킨다. 이와 같은 문제점을 해결하기 위해 박막과 기판사이에 저온 버퍼층을 사용하거나 같은 물질의 버퍼층을 사용하여 결할 밀도를 감소시키고, 높은 결정성을 가진 ZnO 박막을 성장시킨 결과들이 많이 보고되어지고 있다. 본 연구에서는 마그네트론 스퍼터링 법으로 저온 버퍼층 성장 없이 성장온도 만을 달리 하여 고품질의 ZnO 박막을 성장시켰다. ZnO 박막은 c-sapphire 기판위에 ZnO(99.9999%)의 타겟을 사용하여 $600{\sim}800^{\circ}C$ 온도에서 성장시켰고, 스퍼터링 가스로는 아르곤과 산소를 2:1 비율로 혼합하여 15mtorr의 압력에서 성장하였다. 이렇게 성장시킨 ZnO 박막은 Transmission Electron Microscopy (TEM), High-Resolution X-ray Diffraction (HRXRD), Low-temperature PL, 그리고 Atomic Force Microscopy (AFM)로 특성을 분석 하였다. ZnO 박막은 HRXRD (002) 면의 $\omega$-rocking curve운석 결과, $0.083^{\circ}$의 작은 FEHM을 얻었고, (102) 면의 $\varphi$-sacn을 통해 온도가 증가함에 따라 향상된 6-fold을 확인함으로새 에피성장됨을 알 수 있었다. 또한 TEM분석을 통해 $800^{\circ}C$에서 성장된 박막은 $6.7{\times}10^9/cm^2$의 전위밀도를 얻을 수 있었다.

• 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.

• Journal of the Microelectronics and Packaging Society
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• v.31 no.1
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• pp.43-48
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• 2024

The discovery of a two-dimensional electron gas (2DEG) at the interface of LaAlO₃ (LAO) and SrTiO₃ (STO) substrates has sparked significant interest, providing a foundation for cutting-edge research in electronic devices based on complex oxide heterostructures. However, conventional methods for producing LAO thin films, typically employing techniques like pulsed laser deposition (PLD) within physical vapor deposition (PVD), are associated with high costs and challenges in precisely controlling the La and Al composition within LAO. In this study, we adopted a cost-effective alternative approach-solution-based processing-to fabricate LAO thin films and investigated their electrical properties. By adjusting the concentration of the precursor solution, we varied the thickness of LAO films from 2 to 65 nm and determined the sheet resistance and carrier density for each thickness. After vacuum annealing, the sheet resistance of the conductive channel ranged from 0.015 to 0.020 Ω·s^-1, indicating that electron conduction occurs not only at the LAO/STO interface but also into the STO bulk region, consistent with previous studies. These findings demonstrate the successful formation and control of 2DEG through solution-based processing, offering the potential to reduce process costs and broaden the scope of applications in electronic device manufacturing.