• Journal of the Korean Society for Heat Treatment
• /
• v.28 no.3
• /
• pp.121-125
• /
• 2015

GZO single layer, Ni buffered GZO(GZO/Ni), Ni intermediated GZO (GZO/Ni/GZO) and Ni capped GZO (Ni/GZO) films were prepared on poly-carbonate (PC) substrates by RF and DC magnetron sputtering without intentional substrate heating and then the influence of the Ni (2 nm thick) thin film on the optical, electrical and structural properties of GZO films were investigated. As deposited GZO single layer films show the optical transmittance of 81.3% in the visible wavelength region and a resistivity of $1.0{\times}10^{-2}{\Omega}cm$, while GZO/Ni/GZO trilayer films show a lower resistivity of $6.4{\times}10^{-4}{\Omega}cm$ and an optical transmittance of 74.5% in this study. Based on the figure of merit, it can be concluded that the intermediated Ni thin film effectively enhances the opto-electrical performance of GZO films for use as transparent conducting oxides in flexible display applications.

• Transactions on Electrical and Electronic Materials
• /
• v.16 no.6
• /
• pp.303-307
• /
• 2015

Multilayered films of ITO (In₂O₃:SnO₂ = 9:1)/SiO₂ were deposited on soda-lime glass by RF/DC magnetron sputtering at 500℃ to improve the energy conversion efficiency of dye-sensitized solar cells (DSSCs). The light absorption of the dye was improved by decrease in light reflectance from the surface of the DSSCs by using an ITO film. In order to estimate the optical characteristics and compare them with experimental results, a simulation program named EMP (essential macleod program) was used. EMP results revealed that the multilayered thin films showed high transmittance (approximate average transmittance of 79%) by adjusting the SiO₂ layer thickness. XRD results revealed that the ITO and TiO₂ films exhibited a crystalline phase with (400) and (101) preferred orientations at 2 θ = 26.24° and 35.18°, respectively. The photocurrent-voltage (I-V) characteristics of the DSSCs were measured under AM 1.5 and 100 mW/cm² (1 sun) by using a solar simulator. The DSSC fabricated on the ITO film with a 0.1-nm-thick SiO₂ film showed a Voc of 0.697 V, J_sc of 10.596 mA/cm² , FF of 66.423, and calculated power conversion efficiency (η_AM1.5) of 5.259%, which was the maximum value observed in this study.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2015.08a
• /
• pp.169.2-169.2
• /
• 2015

$VO_2$ is a well-known a metal-to-insulator-transition (MIT) material, accompanied with a first order structural phase transition near room temperature. Because of the structural phase transition and the MIT occur near a same temperature, there is an ongoing argument whether the MIT is induced by the structural phase transition. $VO_2$ exhibits a relatively weak anti-oxidization ability and can be oxidized to higher-valence oxides (e.g., $V_4$ $O_7$ or $V_2$ $O_5$) when annealed at a high temperature in an oxygen-rich atmosphere. We fabricated $VO_2$ films on $Al_2$ $O_3$ (0001) substrates using a DC magnetron sputtering deposition process with carefully control the $O_2$ percentage in an atmosphere. X-ray diffraction measurements from the films showed only (0l0) peaks with no extra peaks, indicating b-oriented films. The temperature-dependent local structural properties of $VO_2$ films were investigated by using in-situ X-ray absorption fine structure (XAFS) measurements at the V K edge. XAFS revealed that the structural phase transition was occurred nearly $70^{\circ}C$ for heating process and reproducible. Resistance measurements as a function of temperature (R-T) demonstrated that the resistance of $VO_2$ films was changed by a factor of 4 near $75^{\circ}C$ which was higher than $68^{\circ}C$ reported from a $VO_2$ bulk. We will discuss the MIT of $VO_2$ films, comparing with the local structural properties determined by XAFS measurements.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2015.08a
• /
• pp.181.1-181.1
• /
• 2015

용액 공정을 이용한 Resistive random access memory (ReRAM)은 간단한 공정 과정, 대면적화, 저렴한 가격 등의 장점으로 인해 큰 관심을 받고 있으며, HfOx, TiOx, AlOx 등의 산화물이 ReRAM 절연 막으로 주로 연구되고 있다. 더 나아가 최근에는 organic 물질을 메모리 소자로 사용한 연구가 보고되고 있다. 이는 경제적이며, wearable 또는 flexible system에 적용이 용이하다. 그럼에도 불구하고, organic 물질을 갖는 메모리 소자는 기존의 산화물 소자에 비해 열에 취약하며 전기적인 특성과 신뢰성이 우수하지 못하다는 단점을 가지고 있다. 이를 위한 방안으로 본 연구에서는 AlOx - polymethylmethacrylate (PMMA) blended thin film ReRAM을 제안하였다. 이는 organic물질의 전기적 특성을 개선시킬 뿐 아니라, inorganic 물질을 wearable 소자에 적용했을 때 발생하는 crack과 같은 기계적 물리적 결함을 해결할 수 있는 새로운 방법이다. 먼저, P-type Si 위에 습식산화를 통하여 SiO2 300 nm 성장시킨 기판을 사용하여 electron beam evaporation으로 10 nm의 Ti, 100 nm의 Pt 층을 차례로 증착하였다. 그리고 PMMA 용액과 AlOx 용액을 초음파를 이용하여 혼합한 뒤, 이 용액을 Pt 하부 전극 상에서 spin coating방법으로 1000 rpm 10초, 5000 rpm 30초의 조건으로 증착하였다. Solvent 및 불순물 제거를 위하여 150, 180, $210^{\circ}C$의 온도로 30 분 동안 열처리를 진행하였고, shadow mask를 이용하여 상부 전극인 Ti를 sputtering 방식으로 100 nm 증착하였다. 150, 180, $210^{\circ}C$로 각각 열처리한 AlOx - PMMA blended ReRAM의 전기적 특성은 HP 4156B semiconductor parameter analyzer를 이용하여 측정하였다. 측정 결과 제작된 소자 전부에서 2 V이하의 낮은 동작전압, 안정된 DC endurance (>150cycles), 102 이상의 높은 on/off ratio를 확인하였고, 그 중 $180^{\circ}C$에서 열처리한 ReRAM은 더 높은 on/off ratio를 갖는 것을 확인하였다. 결론적으로 baking 온도를 최적화하였으며 AlOx - PMMA blended film ReRAM의 우수한 메모리 특성을 확인하였다. AlOx-PMMA blended film ReRAM은 organic과 inorganic의 장점을 갖는 wearable 및 system용 비휘발성 메모리소자에 적용이 가능한 경제적인 기술로 판단된다.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2015.08a
• /
• pp.86.2-86.2
• /
• 2015

Cu2ZnSn(S,Se)4 thin film solar cells have been fabricated using sputtered Cu/Sn/Zn metallic precursors on Mo coated sodalime glass substrate without using a toxic H2Se and H2S atmosphere. Cu/Sn/Zn metallic precursors with various thicknesses were prepared using DC magnetron sputtering process at room temperature. As-deposited metallic precursors were sulfo-selenized inside a graphite box containing S and Se pellets using rapid thermal processing furnace at various sulfur to selenium (S/Se) compositional ratio. Thin film solar cells were fabricated after sulfo-selenization process using a 65 nm CdS buffer, a 40 nm intrinsic ZnO, a 400 nm Al doped ZnO, and Al/Ni top metal contact. Effects of sulfur to selenium (S/Se) compositional ratio on the microstructure, crystallinity, electrical properties, and cell efficiencies have been studied using X-ray diffraction, Raman spectroscopy, field emission scanning electron microscope, I-V measurement system, solar simulator, quantum efficiency measurement system, and time resolved photoluminescence spectrometer. Our fabricated Cu2ZnSn(S,Se)4 thin film solar cell shows the best conversion efficiency of 9.24 % (Voc : 454.6 mV, Jsc : 32.14 mA/cm2, FF : 63.29 %, and active area : 0.433 cm2), which is the highest efficiency among Cu2ZnSn(S,Se)4 thin film solar cells prepared using sputter deposited metallic precursors and without using a toxic H2Se gas. Details about other experimental results will be discussed during the presentation.

• Proceedings of the Materials Research Society of Korea Conference
• /
• 2009.11a
• /
• pp.30.1-30.1
• /
• 2009

정보화가 급속히 진전됨에 따라 보다 많은 양의 정보를 전송, 처리, 저장하게 되면서 이를 위해 대용량, 고속, 비휘발성의 특징을 갖는 차세대 메모리의 개발이 절실히 요구되고있다. 이 중 저항 변화 메모리(ReRAM)는 일반적으로 TiO2, Al2O3, NiO2, HfO2, ZrO2 등의 전이금속산화물을 이용한 MIM 구조로서 적당한 전기 신호를 가하면 저항이 높아서 전도되지 않는 상태(Offstate)에서 저항이 낮아져 전도가 가능한 상태(On state)로 바뀌는 메모리 특성을가진다. ReRAM은 비휘발성 메모리이며 종래의 비휘발성 기억소자인 Flash memory 보다 access time 이105 배 이상 빠르고, 5V 이하의 낮은 전압에서도 동작이 가능하다. 또한 구조가 간단하여 공정 단순화가 가능하고 소자의 집적화도 쉽다는 점 등 많은 장점들이 있어서 Flash memory를 대체할 수 있는 유력한 후보로 여겨지고 있다. 본연구에서는 DC-magnetron Sputtering 방법으로 전이금속 박막을 증착하고, Dry furnace로 산화시켜 전이금속산화물 박막을 제작한 후 저항변화 특성을 연구하였다. 두 개의 전이금속산화물 박막을 dual-layer로 형성시켜 저항변화특성을 관찰하였으며 또한, 전이금속산화물 박막의 조성을 달리 하여 저항변화를 관찰 하였다. 전이금속산화물 박막의 전기적 특성을 알아보기 위해 Si(100) wafer 위에 Pt를 이용 MIM 형태로 capacitor 시편을 제작 하여, probe station으로 I-V 측정을 하였고 조성 및 표면 분석을 위해서는 AES와 AFM을, 미세구조를 분석을 위해서는 TEM과 SEM 을 사용하였다.

• Korean Journal of Materials Research
• /
• v.20 no.11
• /
• pp.611-616
• /
• 2010

A cobalt oxide - tin oxide nanocomposite based gas sensor on an $SiO_2$ substrate was fabricated. Granular thin film of tin oxide was formed by a rheotaxial growth and thermal oxidation method using dc magnetron sputtering of Sn. Nano particles of cobalt oxide were spin-coated on the tin oxide. The cobalt oxide nanoparticles were synthesized by polymer-assisted deposition method, which is a simple cost-effective versatile synthesis method for various metal oxides. The thickness of the film can be controlled over a wide range of thicknesses. The composite structures thus formed were characterized in terms of morphology and gas sensing properties for reduction gas of $H_2$. The composites showed a highest response of 240% at $250^{\circ}C$ upon exposure to 4% $H_2$. This response is higher than those observed in pure $SnO_2$ (90%) and $Co_3O_4$ (70%) thin films. The improved response with the composite structure may be related to the additional formation of electrically active defects at the interfaces. The composite sensor shows a very fast response and good reproducibility.

• Korean Journal of Materials Research
• /
• v.24 no.12
• /
• pp.694-699
• /
• 2014

We report the chemical vapor deposition growth characteristics of graphene on various catalytic metal substrates such as Ni, Fe, Ag, Au, and Pt. 50-nm-thick metal films were deposited on $SiO_2/Si$ substrates using dc magnetron sputtering. Graphene was synthesized on the metal/$SiO_2$/Si substrates with $CH_4$ gas (1 SCCM) diluted in mixed gases of 10% $H_2$ and 90 % Ar (99 SCCM) using inductively-coupled plasma chemical vapor deposition (ICP-CVD). The highest quality of graphene film was achieved on Ni and Fe substrates at $900^{\circ}C$ and 500 W of ICP power. Ni substrate seemed to be the best catalytic material among the tested materials for graphene growth because it required the lowest growth temperature ($600^{\circ}C$) as well as showing a low ICP power of 200W. Graphene films were successfully grown on Ag, Au, and Pt substrates as well. Graphene was formed on Pt substrate within 2 sec, while graphene film was achieved on Ni substrate over a period of 5 min of growth. These results can be understood as showing the direct CVD growth of graphene with a highly efficient catalytic reaction on the Pt surface.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.23 no.9
• /
• pp.681-684
• /
• 2010

The $TiO_2$/ZnS/Ag/ZnS/$TiO_2$ multilayered structure for the transparent electrodes in plasma display panel was designed by essential macleod program (EMP) and the multilayered film was deposited on a glass substrate by direct-current (DC)/radio-frequency (RF) magnetron sputtering system. During film deposition process, the Ag layer in $TiO_2$/Ag/$TiO_2$ structure became oxidized and the filter characteristic was degraded easily. In this study, ZnS layer was adopted as a diffusion blocking layer between $TiO_2$ and Ag to prevent the oxidation of Ag layer efficiently in $TiO_2$/ZnS/Ag/ZnS/$TiO_2$ structure. Based on the AES depth profiling analysis, the Ag layer was effectively protected by the ZnS layer as compared with the $TiO_2$/Ag/$TiO_2$ multilayered films without ZnS as an antioxidant layer. The 3 times stacked $TiO_2$/ZnS/Ag/ZnS/$TiO_2$ films have low sheet resistance of $1.22{\Omega}/{\square}$ and luminous transmittance was as high as 62% in the visible ranges.

• Transactions on Electrical and Electronic Materials
• /
• v.14 no.6
• /
• pp.321-323
• /
• 2013

100 nm thick Ga doped ZnO (GZO) thin films were deposited with DC and RF magnetron sputtering at room temperature on glass substrate and Al coated glass substrate, respectively. and the effect of the Al underlayer on the optical and electrical properties of the GZO films was investigated. As-deposited GZO single layer films had an optical transmittance of 80% in the visible wavelength region, and sheet resistance of 1,516 ${\Omega}/{\Box}$, while the optical and electrical properties of GZO/Al bi-layered films were influenced by the thickness of the Al buffer layer. GZO films with 2 nm thick Al film show a lower sheet resistance of 990 ${\Omega}/{\Box}$, and an optical transmittance of 78%. Based on the figure of merit (FOM), it can be concluded that the thin Al buffer layer effectively increases the performance of GZO films as a transparent and conducting electrode without intentional substrate heating or a post deposition annealing process.