OLED外文文献翻译

ITO表面经过常压等离子体处理的有机发光器件的特性
Chang Hyun JEONG, June Hee LEE, Y ong Hyuk LEE, Nam Gil CHO, Jong Tae LIM,
Cheol Hee MOON and Geun Young YOME
Department of Materials Science & Engineering, Sungkyunkwan University, Suwon, 440-746, Korea PDP Division, Samsung SDI Co., Ltd., Cheonan, 330-300, Korea
(Received October 4, 2004; accepted October 28, 2004; published December 10, 2004)
摘要：本课题研究了ITO表面经过He/O2和He/SF6的常压等离子混合气体处理后的影响和有机发光器件的电学特性。

经过He/O2或He/SF6的等离子体处理后，由ITO/2-TNATA/NPD/Alq3/LiF/Al组成的OLED 器件显示出了很好的电学特性，例如：较低的导通电压，高的功率效率等等。

经过He/SF6处理的器件与He/O2处理过的相比有更卓越的电学性能。

在用He/O2和He/SF6等离子体处理后，改善后的电性能与碳元素的减少和ITO表面Sn4+的聚集以及ITO中氟元素的掺杂浓度有关，这表明表面处理后工作性能有所提高。

关键词：ITO，表面处理，常压等离子体，OLED，He/O2，He/SF6
OLED显示器件之所以能得到广泛的研究是因为他们具有非常优越的特性，例如：快速的响应时间，较低的工作电压，较高的量子效率等等。

此外，与其他的平板显示器相比，例如：液晶显示器和等离子显示器，OLED显示器有更简单的工艺流程和更低的制造成本。

目前，对于基板尺寸小于370mm*470mm 的器件，通常在一个真空腔体内利用多层蒸发技术来完成，而用于制造接近920mm*730mm的大尺寸的沉积技术目前正处于研发当中。

此外，利用喷墨打印技术代替真空蒸发技术来制作高分子有机OLED 器件正处于积极的研发阶段。

对于OLED器件，需要一种透光性高的透明导体，在各种透明导体中，具有高传导性和高透光性的ITO被广泛的应用。

为形成OLED器件，有机材料被沉积在ITO上，形成一个低阻值的欧姆接触，OLED 器件在ITO和有机材料之间形成的接触电阻可以通过ITO表面预处理来改变。

ITO是一个非化学计量化合物，化学成分可以很容易的改变。

因此，为了改善OLED器件中ITO和有机材料间的接触特性，在ITO表面沉积有机材料之前进行处理是非常重要的。

作为表面处理方法的低压等离子技术、UV/O3技术、和湿处理均被用于去除有机杂质和改善ITO表面特性。

然而，这些技术价格非常昂贵，而且低压等离子技术和UV/O3技术难以用于规模较大的基板，并且，湿处理法还存在环境问题。

为了代替低压等离子体技术和湿处理等技术，以常压等离子体，如电晕放电、电介质阻挡放电、大气等离子流体等为处理技术来处理电子材料、电极材料、生物材料和结构材料的方法正在积极地开发当中。

本课题研究了利用常压等离子体来处理和清洁OLED器件ITO玻璃表面的价值。

作为常压等离子清洁技术，即一个修改了的DBD技术，能被用于大规模的环境中并且展现了一个比传统DBD更高密度的等离子体。

通过改变在修改的DBD混合气体，这些混合气体在ITO的表面特性和形成干净的ITO 玻璃的OLED器件电学特性方面的影响正在观察中。

图1为处理ITO玻璃表面的常压等离子体设备图。

如图所示，修改过的DBD的研究设备由代替一个平板电极作为功率电极的锥体形状的多针电极，作为接地端的另一块平板电极以及两电极间的电介质材料组成。

使用多针电极代替平板电极，通过在针的尖端形成一个类似于具有较高稳定性的电晕放
电和辉光放电的高电场，从而能够获得一个高的离子体密度和低压交流下的气体击穿。

多针功率电极连接到频率为20~30千赫兹、电压
为3~15千伏的交流电压，平板接地
电极接地。

He(10 slm)/O 2(3 slm) 和
He(10 slm)/SF 6(100 sccm)的混合
气体被应用于OLED 器件ITO 表面的
清洗。

在等离子处理前，所有的ITO
玻璃均用有机溶剂清洗过。

这些气
体的最佳成分通过接触角和ITO 基
板碳含量来选择，接触角利用专用
工具来测量，碳含量通过改变由
0~3 slm 的氧流速、0~500 sccm 的
SF 6流速以及10slm 的氦流速的X
射线光电谱线来测量。

交流电源为
25千赫兹、10千伏，持续工作30
秒。

经过He/O 2和He/SF 6等离子混合气体清洁后的ITO 表面组成用X 射线源为1486.6 eV 的X 射线光电子能谱来研究。

在没有破坏真空的条件下，通过在洁净的ITO 上OLED 材料的热分解和电极材料的顺序蒸镀制备成了OLED 器件。

研究的这个OLED 器件的结构为ITO/2-TNATA(60 nm)/NPD(20 nm)/Alq 3(40 nm)/LiF(1
nm)/Al(100 nm)。

有机材料、氟化锂和铝的沉积速率分别为0.3–0.5 A o /s 、0.1 A o /s 、0.5–5 A o
/s ，器件的有效面积为4mm 2。

OLED 器件的电学特性由电子仪器测量得到，光学特性通过使用皮安计测量OLED 器件光发射引起的光电流来得到。

图2所示为ITO 经过He(10 slm)/O 2(3 slm) 和 He(10 slm)/SF 6(100 sccm)常压等离子混合气体处理的OLED 器件的特性，例如：（a ）亮度与电压的关系、（b ）亮度与电流密度的关系、（c ）功率效率与电流密度的关系。

作为参考，图中还包括了没经过等离子处理的OLED 器件的特性。

如图2（a ）所示，经过等离子体He(10 slm)/O 2(3 slm) 和 He(10 slm)/SF 6(100 sccm)处理后的器件的开启电压（定义为发出1 cd/m 2的亮度所需的电压）分别为3.6V 和3.2V ，然而未经等离子体处理的器件的开启电压为4.2V 。

因此，经过等离子体处理后开启电压减小了，而且经He(10 slm)/O 2(3 slm)处理后的器件的开启电压比经He(10 slm)/SF 6(100 sccm)处理后的电压低。

此外，如图2（b ）所示，在同一发光强度的条件下，经He(10 slm)/SF 6(100 sccm)处理的OLED 表现出了最低的电流密度，而没经处理的OLED 器件表现出了最高的电流密度。

通过对电流密度的测量，得到了用三种方法He(10 slm)/SF 6(100 sccm)、He(10 slm)/O 2(3 slm)和未做处理的三个器件的最高功率效率分别为0.93 Lm/W 、0.75 Lm/W 和0.58Lm/W 。

因此，经过He(10 slm)/SF 6(100 sccm)处理的OLED 器件显示了最佳的电学性能。

经过He(10 slm)/SF6(100 sccm)处理的OLED
器件的电特性的改善看上去与去除ITO表面的有机杂质和经处理的ITO工作性能的改变有关。

表1显示了通过XPS测量的未经处理、He(10 slm)/O2(3 slm)和He(10 slm)/SF6(100 sccm)三种处理方法后的ITO表面的组成。

表中显示，经等离子处理后，ITO表面碳元素的含量显著的减少，而且，经He(10 slm)/SF6(100 sccm)处理后
的ITO表面碳含量最少，因
此，有机清洗后残留的有机
杂质被等离子体清除了很
多，有机杂质的去除被认为
改善了OLED的性能。

当比较用He(10
slm)/O2(3 slm) 和He(10
slm)/SF6(100 sccm)处理的
ITO表面组成时发现，在用
He(10 slm)/SF6(100 sccm)
清洁的ITO表面的氧被12%
的氟代替，然而却没有发现
硫元素。

ITO中氟的掺杂提
高了ITO的电学特性，从而
推理出氧化锡中掺杂氟可以
提高空穴的注入效率。

此外，
X射线电子谱线数据显示，
即使在等离子处理后，锡铟
比值没有显著变化，而表面
Sn4+的含量却明显减少。

Sn3d5/2在峰值处可以分解成
Sn2+和Sn4+的氧化物。

图3显示了将Sn3d5/2的峰值分解成Sn2+和Sn4+的XPS窄扫描数据。

如图所示，经过等离子体处理后的Sn4+的最高值有所减小，在经He(10 slm)/SF6(100 sccm)处理后为最低的峰值。

据报道，通过用In3+代替Sn4+的位置来减少Sn4+的含量，Sn4+的减少使n型的费米能级向中间能带改变，从而提高了ITO的工作性能。

因此，经用He(10 slm)/SF6(100 sccm)处理的OLED器件的改善也与增加氟元素和减少ITO表面Sn4+的含量来除去碳杂质以提高工作性能有关。

结论，利用常压等离子体设备使He(10 slm)/O2(3 slm) 和 He(10 slm)/SF6(100 sccm)的混合气体来处理ITO玻璃的表面以及它对ITO表面特性和ITO经过处理的OLED器件的特性的影响已经得到了研究。

经过He (10 slm)/SF6(100 sccm)处理的OLED器件拥有最好的电学特性，例如：最低的开启电压（在亮度均为
1cd/m2的前提下，
He/SF6处理后为
3.2V，He/O2处理后为
3.6V，未处理的为
4.2V）、最高的亮度
（在相同的电流密度
下）和最高的功率效
率（He/SF6处理后为
0.93Lm/W，He/O2处理
后为0.75Lm/W，未处
理的为0.58Lm/W）。

He(10 slm)/SF6(100
sccm)等离子体处理
的OLED器件性能的
改善与ITO表面有机
杂质的去除、Sn4+的
含量的降低以及ITO表面氟元素的掺杂有关，而且表明了ITO性能的提高。

因为常压等离子体不需要真空室，所以能够很容易安装负载室并应用于尺寸大于730mm*920mm的基板，常压等离子体可以成功的应用于商业制造OLED中ITO的清洗环节。

SF6低压等离子体处理和常压等离子体处理对ITO的影响
正在进一步观察中。

这个课题得到了商务部、工业和能源部以及韩国科技部的国家研究实验室计划（海军研究实验所）的支持。

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Characteristics of Organic Light-Emitting Devices by the Surface Treatment of Indium Tin Oxide Surfaces Using Atmospheric Pressure
Plasmas
Chang Hyun JEONG, June Hee LEE, Y ong Hyuk LEE, Nam Gil CHO, Jong Tae LIM,
Cheol Hee MOON and Geun Young YOME
Department of Materials Science & Engineering, Sungkyunkwan University, Suwon, 440-746, Korea PDP Division, Samsung SDI Co., Ltd., Cheonan, 330-300, Korea
(Received October 4, 2004; accepted October 28, 2004; published December 10, 2004)
ABSTRACT：This study examined the effects of a He/O2 and He/SF6 atmospheric pressure plasma surface treatment of indium tin oxide(ITO) glass on the ITO surface and electrical characteristics of organic light emitting diodes (OLEDs). The OLEDs composedof ITO glass/2-TNATA/NPD/Alq3/LiF/Al showed better electrical characteristics, such as lower turn-on voltage, higher power efficiency, etc., after the He/O2or He/SF6 plasma treatment. The He/SF6 treatment resulted in superior electrical characteristics compared with the He/O2 treatment. The electrical improvement as a result of the He/SF6 and He/O2 plasma treatments is related to the decrease in the carbon and Sn4t concentration on the ITO surface and fluorine doping of the ITO possibly indicating a change in the work function as a result of the treatments. [DOI: 10.1143/ KEYWORDS：ITO, surface treatment, atmospheric pressure plasma, OLED, He/O2, He/SF6 Organic light emitting diode (OLED) displays have been extensively studied due to their superior properties such as faster response time, lower operating voltage, higher quantum efficiency, etc. in addition to the simpler deposition processing and lower manufacturing cost compared with other flat panel displays such as liquid crystal displays and plasma display panels.1–3) Currently, these devices are manufactured in a high vacuum chamber for substrate areas smaller than 370mm×470mm using a multilayer evaporation technique for monomer organics, and deposition techniques for the large area substrates close to 920mm×730mm are currently under development. In addition, OLED displays utilizing polymer organics, which use inkjet printing instead of vacuum evaporation, are actively being studied.4,5)
On OLED devices, a transparent conductor is used for the higher optical transparency, and among the various transparent conductors, indium tin oxide (ITO) is the most widely used due to its high conductivity and transparency. In order to form OLED devices, the organic monomers are deposited on patterned ITO glass for the formation of a low resistive ohmic contact. The contact resistance between the ITO and organic materials of the OLED devices can be altered by the ITO surface preparation due to the organic materials on the ITO glass surface and the change in the ITO composition as a result of the ITO surface preparation method. ITO is a nonstoichiometric compound. Therefore, the chemical composition can be easily changed.6) Consequently, in order to improve the contact properties between the ITO and the organic material of the OLED, the surface treatment of the patterned ITO before depositing the organic materials is very important.6–13) As surface treatment methods, low pressure plasma techniques,6–10,12) UV/O3 techniques,9–11) and wet treatments12,13)have been used to remove the organic materials and improve the ITO surface properties. However, these techniques are expensive and difficult to scale to large areas using low pressure plasma and UV/O3 techniques. In addition, there are environmental issues in the case of wet treatment.
Atmospheric pressure plasma such as a corona discharge,14)dielectric barrier discharge (DBD),15,16) atmospheric plasma jet,17) etc. for the treatment of various surfaces applied to electric materials, electronic materials, biomaterials, structural materials, etc. have been actively studied in order to replace low pressure plasma techniques, wet processing, etc. This study examined the potential of using atmospheric pressure plasma for the surface treatment and cleaning of ITO glass for OLED devices. As an atmospheric pressure plasma cleaning technique, a modified DBD, which can be scaled to large areas and show a higher plasma density than conventional DBD, was used. By varying the gas mixture in the modified DBD, the effects of the gas mixture on the characteristics of the ITO surface and on the electrical properties of the OLED devices formed on the cleaned ITO glass were investigated.
Figure 1 shows a schematic diagram of the atmospheric pressure plasma equipment used in this study for
the surface treatment of ITO glass. As shown in the figure, the modified DBD used in this study was composed of a pyramid shaped multi-pin electrode as the power electrode instead of a plate electrode, a plate electrode as the ground electrode, and dielectric materials on both electrodes. Using the multi-pin electrode instead of a blank plate electrode, a higher plasma density and gas breakdown at a lower AC voltage could be obtained by forming a high electric field on the tip of the pins similar to the corona discharge with a higher stability and glow discharge shape instead of a filamentary discharge shape. The AC voltage in the range from 3 to 15 kV with a frequency of 20–30 kHz was connected to the multi-pin power electrode and the ground was connected to the plate ground electrode.
Fig. 1. Schematic diagram of the atmospheric pressure plasma equipmentused for the surface treatment of ITO
glass.
He(10 slm)/O2(3 slm) and He(10 slm)/SF6(100 sccm) were used as the ITO surface cleaning gas mixtures for the OLED devices. Before the plasma treatment, all the ITO glasses were cleaned with an organic solvent. These optimum gas compositions were selected after measuring the contact angle by a contact angle measuring tool and the carbon contents on the ITO surface by X-ray photoelectron spectroscopy (XPS, VG Microtech Inc., ESCA2000) after varying the O2 flow rate from 0 to 3 slm and the SF6 flow rate from 0 to 500 sccm with a He flow rate of 10 slm. The AC voltage used was 10 kV at 25 kHz and the processing time was 30 seconds. The composition of the ITO surface after cleaning with the He/O2and He/SF6plasma was investigated by XPS using Al KX-ray source of 1486.6 eV.
The OLED devices were fabricated on the cleaned ITO by the thermal evaporation of the OLED materials andelectrode materials sequentially without breaking the vacuum.The OLED structure used in this study was ITO glass/2-TNATA(60 nm)/NPD(20 nm)/Alq3(40 nm)/LiF(1 nm)/Al(100 nm). The deposition rates of the organic materials, LiF, and Al were 0.3–0.5Å /s, 0.1 Å /s, and 0.5–5 Å /s, respectively. The fabricated device active area was 4mm2. The electrical characteristics of the fabricated OLED devices were measured using an electrometer (Keithley 2400) and the luminescence characteristics were determined by measuring the photocurrent induced by light emission from the OLEDs using a picoammeter (Keithley 485).
Figure 2 shows the characteristics of the OLEDs fabricated on the ITO glass cleaned by the atmospheric pressure plasma using the He(10 slm)/O2(3 slm) and He(10 slm)/SF6(100 sccm) gas mixtures such as (a) luminescencevoltage, (b) luminescence-current density, and (c) power efficiency-current density. As a reference, the characteristics of the OLED device fabricated without plasma cleaning were included. As shown in Fig. 2(a), the turn-on voltages of the devices (defined as the voltage required to deliver a luminescence of 1 cd/m2) after the He(10 slm)/O2(3 slm) and He(10 slm)/SF6(100 sccm) treatment were 3.6V and 3.2 V, respectively, while the turn-on voltage of
the device without the plasma treatment was 4.2 V.
Therefore, after the plasma treatment, the turn-on
voltage was decreased and the He(10 slm)/O2(3 slm)
treatment showed a lower turn-on voltage than the
He(10 slm)/SF6(100 sccm) treatment. In addition, as
shown in Fig. 2(b), the OLED treated by He(10
slm)/SF6(100 sccm) showed the lowest current
density at the same emission intensity while the OLED fabricated without the plasma treatment showed the highest current density. When the power efficiency was measured as a function of the current density, the highest power efficiencies were ~0.93 Lm/W, ~0.75 Lm/W, and ~0.58 Lm/W for the He(10 slm)/SF6(100 sccm) treated sample, He(10 slm)/O2(3 slm) treated sample, and the non-treated sample, respectively. Therefore, after the He(10 slm)/SF6-(100 sccm) treatment, the device showed the best electrical performance. Fig. 2. Characteristics of the OLEDs fabricated on the ITO glass cleaned by the atmospheric pressure plasma using He(10 slm)/O2(3 slm) and He(10 slm)/SF6(100 sccm) gas mixtures. (a) luminescence-voltage, (b)luminescence-current density, and (c) power efficiency-current density.As a reference, the characteristics of
the OLED device fabricated withoutplasma cleaning are included.
The improved electrical characteristics shown for the OLED after the He(10 slm)/SF6(100 sccm) treatment appeared to be related to the removal of the remaining contaminants on the ITO surface and the change in the work function of the ITO as a result of the plasma treatment. Table I shows the composition of the non-treated (as is) and He(10 slm)/O2(3 slm) and He(10 slm)/SF6(100 sccm) treated ITO surface measured by XPS. As shown in the table, carbon contamination on the surface decreased significantly as a result of the plasma treatment and the ITO surface after the He(10 slm)/SF6(100 sccm) treatment showed the lowest carbon content on the surface. Therefore, the organic contaminants remaining after organic cleaning were removed further after the plasma cleaning, and the removal of the organic contaminants is believed to be partially responsible for the improved OLED performance.
Table I. Composition of the ITO surfaces not treated (as is) and treated with He(10 slm)/O2(3 slm) and He(10
slm)/SF6(100 sccm) measured by XPS.
In the case of the He(10 slm)/SF6(100 sccm) cleaning, 12% of fluorine (F1s 685 eV) was detected on the ITO surface, which replaced oxygen on the surface when comparing the surface compositions of the ITO cleaned by the He(10 slm)/O2(3 slm) and that by the He(10 slm)/ SF6(100 sccm). However, sulfur (S2p 164 eV) was not detected on the ITO surface as a result of the He(10 slm)/ SF6(100 sccm) treatment. The doping of fluorine on the ITO is known to improve the electrical properties of ITO similar to the doping of fluorine on SnO2 by increasing the level of hole injection to the device.8,19) In addition, in the XPS data, even though the Sn to In ratio was not significantly altered by the plasma treatment, the surface concentration of Sn4+was deceased significantly by the plasma treatment. The Sn3d5/2 peak can be deconvoluted into the: Sn2+(486.3 eV) and Sn4+ (487.3 eV) oxidation states7) and Fig. 3 shows the narrow scan XPS data of the deconvoluted Sn2+ and Sn4+ peaks of Sn3d5/2 peak are shown in. As shown in the figure, the Sn4+ peak intensity was deceased by the plasma treatment and showed the lowest peak for the He(10 slm)/ SF6(100 sccm) treatment. It was reported that the substitution of an In3+site by Sn4+ decreases the Sn4+ content and the decrease in Sn4+increases the work function of ITO by changing the n-type Fermi level toward the middle of the band gap.18) Therefore, the improvement in the OLED devices treated with the He(10 slm)/SF6(100 sccm) is also related to the increase in the work function by the fluorination and the decrease in the Sn4+level of the ITO in addition to the removal of carbon contaminants on the ITO surface.
Fig. 3. Narrow scan XPS data of the deconvoluted Sn2+ and Sn4+ peaksfrom the Sn3d5/2 peaks of the ITO surface treated with He(10 slm)/O2(3 slm) and He(10 slm)/SF6(100 sccm). The XPS data of the ITO surface
not treated by the plasma is also included.
In conclusion, the ITO glass surfaces were treated with He(10 slm)/O2(3 slm) and He(10 slm)/SF6(100
sccm) gas mixtures using an atmospheric pressure plasma equipment composed of a multi-pin type DBD and its effects on ITO surface properties and the characteristics of the OLED devices fabricated on the treated ITO were investigated. The OLED devices treated with the He(10 slm)/SF6(100 sccm) plasma showed the best electrical properties such as the lowest turn-on voltage (He/SF6plasma treatment: 3.2 V, He/O2plasma treatment: 3.6V, non-treatment: 4.2V at the luminescence of 1 cd/m2), highest luminescence at the same current density, and the highest power efficiency (He/SF6plasma treatment: 0.93 Lm/W, He/O2plasma treatment: 0.75 Lm/W, non-treatment: 0.58 Lm/W). The improved properties of the OLED devices after the ITO treatment using He(10 slm)/SF6(100 sccm) appear to be related to the removal of the organic contaminants remaining on the ITO surface, the decrease in the Sn4+ level, and the fluorine doping on the ITO surface possibly indicating an increase in the work function of the ITO. Because atmospheric pressure plasma does not require a vacuum chamber, it can be installed easily in the loading chamber, and be scaled to substrates larger than 730mm×920mm in size. It is believed that the use of He(10 slm)/SF6(100 sccm) atmospheric pressure plasma can be successfully applied to a commercial OLED system requiring ITO cleaning. The effects of SF6 on the ITO cleaning in low pressure plasma systems and a comparison with the data of the atmospheric pressure system are currently under investigation.
This work was supported by the Ministry of Commerce, Industry and Energy, and National Research Laboratory Program (NRL) by the Korea Ministry of Science and Technology.
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