• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.11a
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• pp.108-111
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• 2004

An efficiency and brightness of the Organic Light-emitting Diodes(OLEDs) by insertion of the novel layer between a singlet emitter and an electron transporting layer without doping processes, has been improved. The novel layers named as the K-M1 and K-M2 layers have shown the excellent improvement in the carrier balance and recombination efficiency. New devices using the K-M1 and K-M2 layers have shown a high efficiencies of over 15cd/A and 61m/W$(at\;20mA/cm^2)$, and brightness of over $16,000cd/m^2(at\;100mA/cm^2)$, respectively.

• Journal of the Semiconductor & Display Technology
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• v.12 no.4
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• pp.49-54
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• 2013

In this study, we have investigated the effect of the substrate temperature and oxygen flow rate on the characteristics of IZO thin films for the OLED (organic light emitting diodes) devices. For this purpose, IZO thin films were deposited by RF magnetron sputtering at room temperature and $300^{\circ}C$ with various $O_2$ flow rate. In order to investigate the influences of the oxygen, the flow rate of oxygen in argon mixing gas has been changed from 0.1sccm to 0.5sccm. IZO thin films deposited at room temperature show amorphous structure, whereas IZO thin films deposited at $300^{\circ}C$ show crystalline structure having an (222) preferential orientation regardless of $O_2$ flow rate. The electrical resistivity of IZO film increased with increasing flow rate of $O_2$ under Ar+$O_2$. The change of electrical resistivity with increasing flow rate of $O_2$ was mainly interpreted in terms of the charge carrier concentration rather than the charge carrier mobility. The electrical resistivity of the amorphous-IZO films deposited at R.T. was lower than that of the crystalline-IZO thin films deposited at $300^{\circ}C$. The change of electrical resistivity with increasing substrate temperature was mainly interpreted in terms of the charge carrier mobility rather than the charge carrier concentration. All the films showed the average transmittance over 85% in the visible range. The current density and the luminance of OLED devices with IZO thin films deposited at room temperature in 0.1sccm $O_2$ ambient gas are the highest amongst all other films. The optical band gap energy of IZO thin films plays a major role in OLED device performance, especially the current density and luminance.

• Journal of IKEEE
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• v.24 no.3
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• pp.719-726
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• 2020

A threshold-voltage sensing circuit is proposed to compensate for pixel aging in active matrix organic light-emitting diodes. The proposed threshold-voltage sensing circuit consists of sample-hold (S/H) circuits and a single-ended successive approximation register (SAR) analog-to-digital converter (ADC) with a resolution of 10 bits. To remove a scale down converter of each S/H circuit and a voltage gain amplifier with a signl-to-differentail converter, the middle reference voltage calibration and input range calibration for the single-ended SAR ADC are performed in the capacitor digital-to-analog converter and reference driver. The proposed threshold-voltage sensing circuit is designed by using a 180-nm CMOS process with a supply voltage of 1.8 V. The ENOB and power consimption of the single-ended SAR ADC are 9.425 bit and 2.83 mW, respectively.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.41 no.6
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• pp.525-532
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• 2017

The development of an inkjet-based manufacturing machine for the production of next-generation displays using organic and quantum-dot light emitting diodes at a low cost has been conducted. To employ inkjet printing in production lines of displays, the development of a high-speed inkjet-monitoring device to verify the reliable droplet jetting status from multiple nozzles is required. In this study, an inkjet monitoring device using a rotatable mirror with rotary and linear ultrasonic motors is developed in place of a conventional, linear reciprocating, motion-based inkjet monitoring device. Its performance is also demonstrated. The measurements of circular patterns with diameters of $10{\mu}m$, $30{\mu}m$, and $50{\mu}m$ are performed with the accuracies of $0.5{\pm}1.0{\mu}m$, $-1.2{\pm}0.3{\mu}m$, and $0.2{\pm}0.5{\mu}m$, respectively, within 17 sec. By optimizing the control program, the takt time can be reduced to as short as 8.6 sec.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.207-207
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• 2011

Amorphous transparent oxide semiconductors (a-TOS) have been widely studied for many optoelectronic devices such as AM-OLED (active-matrix organic light emitting diodes). Recently, Nomura et al. demonstrated high performance amorphous IGZO (In-Ga-Zn-O) TFTs.1 Despite the amorphous structure, due to the conduction band minimum (CBM) that made of spherically extended s-orbitals of the constituent metals, an a-IGZO TFT shows high mobility.2,3 But IGZO films contain high cost rare metals. Therefore, we need to investigate the alternatives. Because Aluminum has a high bond enthalpy with oxygen atom and Alumina has a high lattice energy, we try to replace Gallium with Aluminum that is high reserve low cost material. In this study, we focused on the electrical properties of IZO:Al thin films as a channel layer of TFTs. IZO:Al were deposited on unheated non-alkali glass substrates (5 cm ${\times}$ 5 cm) by magnetron co-sputtering system with two cathodes equipped with IZO target and Al target, respectively. The sintered ceramic IZO disc (3 inch ${\phi}$, 5 mm t) and metal Al target (3 inch ${\phi}$, 5 mm t) are used for deposition. The O2 gas was used as the reactive gas to control carrier concentration and mobility. Deposition was carried out under various sputtering conditions to investigate the effect of sputtering process on the characteristics of IZO:Al thin films. Correlation between sputtering factors and electronic properties of the film will be discussed in detail.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.450-450
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• 2012

In recent days, advances in ZnO-based oxide semiconductor materials have accelerated the development of thin-film transistors (TFTs), which are the building blocks for active matrix flat-panel displays including liquid crystal displays (LCD) and organic light-emitting diodes (OLED). In particular, the development of high-mobility ZnO-based channel materials has been proven invaluable; thus, there have been many reports of high-performance TFTs with oxide semiconductor channels such as ZnO, InZnO (IZO), ZnSnO (ZTO), and InGaZnO (IGZO). The reliability of oxide TFTs can be improved by examining more stable oxide channel materials. In the present study, we investigated the effects of an ALD-deposited water vapor permeation barrier on the stability of ZnO and HfZnO (HZO) thin film transistors. The device without the water vapor barrier films showed a large turn-on voltage shift under negative bias temperature stress. On the other hand, the suitably protected device with the lowest water vapor transmission rate showed a dramatically improved device performance. As the value of the water vapor transmission rate of the barrier films was decreased, the turn-on voltage instability reduced. The results suggest that water vapor related traps are strongly related to the instability of ZnO and HfZnO TFTs and that a proper combination of water vapor permeation barriers plays an important role in suppressing the device instability.

• Journal of the Semiconductor & Display Technology
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• v.11 no.4
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• pp.25-30
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• 2012

In this study, we have investigated the effect of the substrate temperature and oxygen flow rate on the characteristics of IZO thin films for the organic light emitting diodes (OLED) devices. For this purpose, IZO thin films were deposited by RF magnetron sputtering at room temperature and $300^{\circ}C$ with various $O_2$ flow rate. In order to investigate the influences of the oxygen, the flow rate of oxygen in argon mixing gas has been changed from 0.1sccm to 0.5sccm. IZO thin films deposited at room temperature show amorphous structure, whereas IZO thin films deposited at $300^{\circ}C$ show crystalline structure having an (222) preferential orientation regardless of $O_2$ flow rate. The electrical resistivity of IZO film increased with increasing flow rate of $O_2$ under $Ar+O_2$. The change of electrical resistivity with increasing flow rate of $O_2$ was mainly interpreted in terms of the charge carrier concentration rather than the charge carrier mobility. The electrical resistivity of the amorphous-IZO films deposited at R.T. was lower than that of the crystalline-IZO thin films deposited at $300^{\circ}C$. The change of electrical resistivity with increasing substrate temperature was mainly interpreted in terms of the charge carrier mobility rather than the charge carrier concentration. All the films showed the average transmittance over 83% in the visible range.

• Proceedings of the Materials Research Society of Korea Conference
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• 2012.05a
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• pp.110.1-110.1
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• 2012

Recently, advances in ZnO based oxide semiconductor materials have accelerated the development of thin-film transistors (TFTs), which are the building blocks for active matrix flat-panel displays including liquid crystal displays (LCD) and organic light-emitting diodes (OLED). However, the electrical performances of oxide semiconductors are significantly affected by interactions with the ambient atmosphere. Jeong et al. reported that the channel of the IGZO-TFT is very sensitive to water vapor adsorption. Thus, water vapor passivation layers are necessary for long-term current stability in the operation of the oxide-based TFTs. In the present work, $Al_2O_3$ and $TiO_2$ thin films were deposited on poly ether sulfon (PES) and $SnO_x$-based TFTs by electron cyclotron resonance atomic layer deposition (ECR-ALD). And enhancing the WVTR (water vapor transmission rate) characteristics, barrier layer structure was modified to $Al_2O_3/TiO_2$ layered structure. For example, $Al_2O_3$, $TiO_2$ single layer, $Al_2O_3/TiO_2$ double layer and $Al_2O_3/TiO_2/Al_2O_3/TiO_2$ multilayer were studied for enhancement of water vapor barrier properties. After thin film water vapor barrier deposited on PES substrate and $SnO_x$-based TFT, thin film permeation characteristics were three orders of magnitude smaller than that without water vapor barrier layer of PES substrate, stability of $SnO_x$-based TFT devices were significantly improved. Therefore, the results indicate that $Al_2O_3/TiO_2$ water vapor barrier layers are highly proper for use as a passivation layer in $SnO_x$-based TFT devices.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.163-163
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• 2013

최근 들어서 유연 OLED (Organic Light-Emitting Diodes) 소자에 대한 연구가 증가하면서 전통적인 ITO 전극을 대체할 수 있는 전극물질 후보로 그래핀이 많은 주목을 받고 있다. 그 중에 CVD 방법으로 합성된 다층 그래핀(Few layer graphene, FLG)은 실제 상용화되는 소자에 응용이 될 가능성이 높아 많은 연구가 이 방향으로 진행되고 있다. 이 연구에서는 다층 그래핀과 유기물질 사이의 계면을 전자분광학 분석을 이용해 각 분자층 사이의 에너지 준위 변화에 대해 분석했다. 에너지 준위 정렬을 이용하면 각 분자층간의 정공주입 에너지장벽을 알 수 있는데 이 에너지 장벽은 소자의 효율에 직접적으로 연관되는 값이다. 정공 주입층 물질로는 TAPC 1,1- Bis[4-[N,N'-di(p-tolyl)amino]phenyl]cyclohexane (TAPC)를 사용했고, 다층 그래핀과 TAPC층 사이의 에너지 준위 정렬을 분석한 결과 다층 그래핀과 TAPC층 사이에는 ~1.4 eV의 에너지 장벽이 존재함을 확인했다. 하지만 OLED 소자로 활용하기 위해서는 이보다 더 낮은 에너지 장벽을 필요로 하기 때문에 두 물질 사이에 4,4'-bis(N-phenyl-1-naphthylamino)biphenyl (NPB), 1,4,5,8,9,11-hexaazatriphenylene-hexacarbonitrile (HAT-CN)을 삽입하여 에너지 장벽을 낮추기 위한 시도를 해 보았다. 그래핀과 TAPC 사이에 중간층으로 NPB를 사용했을 때의 에너지 장벽은 0.55 eV, HAT-CN을 사용했을 때는 0.4 eV로 TAPC만 사용했을 때보다 ~1 eV정도 에너지 장벽을 낮추는 효과를 보여줬다. 이 연구를 통해 다층 그래핀을 OLED 소자의 전극으로 활용할 수 있는 가능성을 볼 수 있었다.

• Bulletin of the Korean Chemical Society
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• v.31 no.10
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• pp.2955-2960
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• 2010

Spiro-type orange phosphorescent host materials, 9-diphenylphosphine oxide-spiro[fluorene-7,9'-benzofluorene] (OPH-1P) and 5-diphenylphosphine oxide-spiro[fluorene-7,9'-benzofluorene] (OPH-2P) were successfully prepared by a lithiation reaction followed by a phosphination reaction with diphenylphosphinic chloride. The EL characteristics of OPH-1P and OPH-2P as orange host materials doped with iridium(III) bis(2-phenylquinoline)acetylacetonate ($Ir(pq)_2acac$) were evaluated. The electroluminescence spectra of the ITO (150 nm)/DNTPD (60 nm)/NPB (30 nm)/OPH-1P or OPH-2P: $Ir(pq)_2acac$ (30 nm)/BCP (5 nm)/$Alq_3$ (20 nm)/LiF (1 nm)/Al (200 nm) devices show a narrow emission band with a full width at half maximum of 75 nm and $\lambda_{max}$ = 596 nm. The device obtained from OPH-1P doped with 3% $Ir(pq)_2acac$ showed an orange color purity of (0.580, 0.385) and an efficiency of (14 cd/A at 7.0 V). The ability of the OPH-P series to combine a high triple energy with a low operating voltage is attributed to the inductive effect of the P=O moieties and subsequent energy lowering of the LUMO, resulting in the enhancement of both the electron injection and transport in the device. The overall result is a device with an EQE > 8% at high brightness, but operating voltage of less than 6.4 V, as compared to the literature voltages of ~10 V.