• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.465-465
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• 2013

Inorganic 물질인 SiO2 dielectric 위에 organic dielectric PVP (4-vinyphenol)를 spin coating으로 올려, inorganic/organic dielectric 형태의 double layer구조로 High-performance amorphous indiumgallium zinc oxide thin-film transistors (IGZO TFT)를 제작하여 보았다. SiO2 dielectric을 buffer layer로 80 nm, PVP는 10Wt% 400 nm로 구성하였으며, 200 nm single SiO2 dielectric과 동일한 수준의 leakage current 특성을 MIM Capacitor 구조를 통해서 확인할 수 있었다. 이 소자의 장점은 용액공정의 도입으로 공정 시간의 단축 및 원가 절감을 이룰 수 있으며, dielectric과 channel 사이의 균일한 interface의 형성으로 interface trap 개선 및 Yield 향상의 장점을 갖는다. 우리는 실험을 통해서 SiO2 buffer layer가 수직 electric field에 의한 leakage current을 제어하고, PVP dielectric은 interface를 개선하는 것을 확인하였다. Vth의 negative shift 및 slope의 향상으로 구동전압이 줄어들고, 균일한 I-V Curve 형성을 통해서 Process Yield의 향상을 확인하였다.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.08a
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• pp.249-249
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• 2011

투명전도성산화물(transparent conducting oxides, TCOs) 박막은 전기 전도성과 광투과성이 우수하여 유기발광다이오드(organic light-emitting diode, OLED), 태양전지(solar cell), 발광다이오드(LED) 등의 광전자 소자에 널리 응용되고 있다. 특히 LED에서 p-GaN층에서 전류가 층안에서 충분하게 확산되지 않기 때문에, TCO는 균일하게 전류를 흘려보내기 위해서 전류확산층(current spreading layer)으로 사용된다. 그 중 널리 쓰이는 산화인듐주석(indium tin oxide, ITO)은 고가의 indium가격과 인체에 유해한 독성 등이 문제점으로 지적되고 있다. 따라서 indium의 함량을 저감하거나 함유하지 않은 새로운 조성의 친환경적 대체 TCO 개발에 대한 연구가 많이 진행되고 있다. 이러한 반도체 재료 중 하나인 AZO (Al-doped zinc oxide, Al2O3 : 2wt.%)는 3.3 eV의 넓은 에너지 밴드갭을 가지며, 가시광선 및 근적외선 파장영역에서 높은 투과율을 나타낸다. 따라서 본 연구에서는 GaN기반 LED 응용을 위한 전류확산층으로 ITO 대신 AZO의 특성을 연구하였다. 박막 증착율이 높고, 제작과정의 조정이 용이한 RF magnetron 스퍼터를 이용하여 glass기판 위에 AZO, Ni/AZO, NiOx/AZO를 증착하였다. 이어서 $N_2$ 분위기에서 다양한 온도 조건에서 열처리(rapid thermal annealing, RTA)하여 전기적 광학적 특성에 대하여 비교 분석하였다.

• 한국신재생에너지학회:학술대회논문집
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• 2011.05a
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• pp.121.2-121.2
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• 2011

Aluminum-doped Zinc Oxide (AZO) is considered as an excellent candidate to replace Indium Tin Oxide (ITO), which is widely used as transparent conductive oxide (TCO) for electronic devices such as liquid crystal displays (LCDs), organic light emitting diodes (OLEDs) and organic solar cells (OSCs). In the present study, AZO thin film was applied to the transparent electrode of a channel-shaped flexible organic solar cell using a low-temperature selective-area atomic layer deposition (ALD) process. AZO thin films were deposited on Poly-Ethylene-Naphthalate (PEN) substrates with Di-Ethyl-Zinc (DEZ) and Tri-Methyl-Aluminum (TMA) as precursors and $H_2O$ as an oxidant for the atomic layer deposition at the deposition temperature of $130^{\circ}C$. The pulse time of TMA, DEZ and $H_2O$, and purge time were 0.1 second and 20 second, respectively. The electrical and optical properties of the AZO films were characterized as a function of film thickness. The 300 nm-thick AZO film grown on a PEN substrate exhibited sheet resistance of $87{\Omega}$/square and optical transmittance of 84.3% at a wavelength between 400 and 800 nm.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1999.05a
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• pp.193-196
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• 1999

Organic electroluminescent devices have attracted a great deal of attention due to thier potential application to full-color flat-panel displays. The 8-hydroxyquinollne Zinc(Znq$_2$) were synthesized successfully from zinc chloride(ZnCl$_2$) and zinc acetate(Zn(C$_2$H$_3$O$_3$)$_2$) as green omitting material. A double-layer ELD consist of an emitting layer of B-hydroxyquinoline Zinc(Znq$_2$) and a hole-transport layer of tai-phenylene diamine(TPD) derivatives sandwiched between an Aluminium(Al) and Indium-Tin-Oxide(ITO) electrodes omitted green light resulting from Znq$_2$. The electroluminescent devices (ELD) exhibited a maximum luminance of 1000cd/$\textrm{cm}^2$ at a driving voltage of 8V and a driving current density of 0.4mA/$\textrm{cm}^2$.

• Proceedings of the KIEE Conference
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• 2011.07a
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• pp.25-26
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• 2011

In this paper, we investigated the effect of various annealing processes on the electrical characteristics of oxide thin film transistors (TFTs). When we annealed the TFT devices before and after source/drain (S/D) process, we could observe the different electrical characteristics of oxide TFTs. When we annealed the TFTs after deposition of transparent indium zinc oxide S/D electrodes, the annealing process decreased the contact resistance but increased the resistivity of S/D electrodes. The field effect mobility, subthreshold slope and threshold voltage of the oxide TFTs annealed before and after S/D process were 5.83 and 4.47 $cm^2$/Vs, 1.20 and 0.82 V/dec, and 3.92 and 8.33 V respectively. To analyze the differences, we measured the contact resistances and the carrier concentrations using transfer length method (TLM) and Hall measurement.

• Transactions on Electrical and Electronic Materials
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• v.17 no.4
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• pp.235-237
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• 2016

Oxide/metal/oxide (OMO) thin films were fabricated using amorphous indium-gallium-zinc-oxide (a-IGZO) and an Ag metal layer on a glass substrate at room temperature. The optical and electrical properties of the a-IGZO/Ag/a-IGZO samples changed systemically depending on the thickness of the Ag layer. The transmittance in the visible range tends to decrease as the Ag thickness increases while the resistivity, carrier concentration, and Hall mobility tend to improve. The a-IGZO/Ag (13 nm)/a-IGZO thin film with the optimum Ag thickness showed an average transmittance (T_av) of 71.7%, resistivity of 6.63 × 10⁻⁵ Ω·cm and Hall mobility of 15.22 cm²V⁻¹s⁻¹.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.347.1-347.1
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• 2014

최근, 박막 트랜지스터는 빠른 동작 속도, 낮은 공정비용 그리고 저온공정 등의 특성을 필요로 하고 있다. 그 중 indium-zinc oxide (InZnO)는 높은 전기적 특성, 높은 광 투과도 그리고 우수한 안정성 때문에 기존의 반도체를 대체할 수 있을 것으로 기대된다. InZnO의 경우 indium과 zinc의 조성비에 따라 특성 변화의 차이가 크기 때문에 다양한 조성비에 대한 연구가 보고되고 있는데, 기존의 InZnO 박막을 증착하는 방법의 경우에 조성비의 변화 과정에 많은 공정상의 어려움이 있다. 이 같은 문제점 때문에 조성비의 변화를 용이하게 할 수 있는 용액공정을 이용한 연구가 진행되고 있다. 또한 용액공정은 높은 균일성, 공정 시간 및 비용 감소 그리고 대면적화가 가능한 장점을 가지고 있다. 한편, 용액공정을 기반으로 한 InZnO의 경우에 용액 상태에서 고체 상태의 순수한 금속 산화물 상태로 바꾸기 위해 post-treatment 가 필요하다. 일반적으로 furnace 열처리 방법을 사용하는데, 이 경우 낮은 열효율 및 고비용 등의 문제점을 가지고 있다. 특히 glass 또는 flexible 기판의 경우 열처리 온도에 대한 제약이 있다. 이러한 문제를 해결하기 위한 방법으로 최근에 microwave irradiation를 이용한 저온 post-treatment 방법이 보고되고 있다. Microwave irradiation는 짧은 공정시간 및 열 균일성 등의 장점이 있다. 따라서 본 연구에서는 다양한 indium과 zinc의 조성비를 갖는 용액을 제작한 후 spin coating을 이용하여 증착한 InZnO 기반의 박막 트랜지스터를 제작하였다. Furnace와 microwave 방식으로 post-treatment 하여 비교 평가한 결과 microwave irradiation 한 경우 furnace 열처리 한 경우 보다 더 안정된 동작 전압을 가지는 것으로 나타났다. 따라서 저온공정이 가능한 microwave irradiation 방법으로 post-treatment 한다면 차세대 산화물 반도체로서의 적용이 가능할 것으로 기대된다.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.28 no.3
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• pp.185-190
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• 2015

In this study, we fabricated the indium gallium zinc oxide (IGZO), zinc oxide (ZnO), aluminum zinc oxide (AZO). oxide and silver are deposited by magnetron sputtering and thermal evaporator, respectively transparency and energy bandgap were changed by the thickness of silver layer. To fabricate metal oxide metal (OMO) structure, IGZO sputtered on a corning 1,737 glass substrate was used as bottom oxide material and then silver was evaporated on the IGZO layer, finally IGZO was sputtered on the silver layer we get the final OMO structure. The radio-frequency power of the target was fixed at 30 W. The chamber pressure was set to $6.0{\times}10^{-3}$ Torr, and the gas ratio of Ar was fixed at 25 sccm. The silver thickness are varied from 3 to 15 nm. The OMO thin films was analyzed using XRD. XRD shows broad peak which clearly indicates amorphous phase. ZnO, AZO, OMO show the peak [002] direction at $34^{\circ}$. This indicate that ZnO, AZO OMO structure show the crystalline peak. Average transmittance of visible region was over 75%, while that of infrared region was under 20%. Energy band gap of OMO layer was increased with increasing thickness of Ag layer. As a result total transmittance was decreased.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.423-423
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• 2011

Zinc oxide is metal oxide semiconductor with the 3.37 eV bandgap energy. Zinc oxide is very attractive materials for many application fields. Zinc Oxide has many advantages such as high conductivity and good transmittance in visible region. Also it is cheaper than other semiconductor materials such as indium tin oxide (ITO). Therefore, ZnO is alternative material for ITO. ZnO is attracting attention for its application to transparent conductive oxide (TCO) films, surface acoustic wave (SAW), films bulk acoustic resonator (FBAR), piezoelectric materials, gas-sensing, solar cells and photocatalyst. In this study, we synthesized ZnO nanoparticles and defined their physical and chemical properties. Also we studied about the application of ZnO nanoparticles as a photocatalyst and try to find a enhancement photocatalytic activity of ZnO nanorticles.. We synthesized ZnO nanoparticles using spray-pyrolysis method and defined the physical and optical properties of ZnO nanoparticles in experiment I. When the ZnO are exposed to UV light, reduction and oxidation (REDOX) reaction will occur on the ZnO surface and generate O2- and OH radicals. These powerful oxidizing agents are proven to be effective in decomposition of the harmful organic materials and convert them into CO2 and H2O. Therefore, we investigated that the photocatalytic activity was increased through the surface modification of synthesized ZnO nanoparticles. In experiment II, we studied on the stability of ZnO nanoparticles in water. It is well known that ZnO is unstable in water in comparison with TiO2. Zn(OH)2 was formed at the ZnO surface and ZnO become inactive as a photocatalyst when ZnO is present in the solution. Therefore, we prepared synthesized ZnO nanoparticles that were immersed in the water and dried in the oven. After that, we measured photocatalytic activities of prepared samples and find the cause of their photocatalytic activity changes.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.252-253
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• 2011

ZnO-based thin film transistors (TFTs) are of great interest for application in next generation flat panel displays. Most research has been based on amorphous indium-gallium-zinc-oxide (IGZO) TFTs, rather than single binary oxides, such as ZnO, due to the reproducibility, uniformity, and surface smoothness of the IGZO active channel layer. However, recently, intrinsic ZnO-TFTs have been investigated, and TFT- arrayss have been demonstrated as prototypes of flat-panel displays and electronic circuits. However, ZnO thin films have some significant problems for application as an active channel layer of TFTs; it was easy to change the electrical properties of the i-ZnO thin films under external conditions. The variable electrical properties lead to unstable TFTs device characteristics under bias stress and/or temperature. In order to obtain higher performance and more stable ZnO-based TFTs, HZO thin film was used as an active channel layer. It was expected that HZO-TFTs would have more stable electrical characteristics under gate bias stress conditions because the binding energy of Hf-O is greater than that of Zn-O. For deposition of HZO thin films, Hf would be substituted with Zn, and then Hf could be suppressed to generate oxygen vacancies. In this study, the fabrication of the oxide-based TFTs with HZO active channel layer was reported with excellent stability. Application of HZO thin films as an active channel layer improved the TFT device performance and bias stability, as compared to i-ZnO TFTs. The excellent negative bias temperature stress (NBTS) stability of the device was analyzed using the HZO and i-ZnO TFTs transfer curves acquired at a high temperature (473 K).