OLED外文文献翻译

1、ITO 外表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, Yong Hyuk LEE, Nam Gil CHO, Jong Tae LIM, Cheol Hee MOON and Geun Young YOMEDepartment of Materials Science & Engineering, Sungkyunkwan University, Suwon, 440-746, Korea PDP Division, Samsung SDI Co., Ltd., Cheonan, 330-300, Korea(Received Oc

2、tober 4, 2004; accepted October 28, 2004; published December 10, 2004)摘要： 本课题研究了ITO 外表经过 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/Alq 3/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

3、善后的电性能与4+碳元素的减少和ITO 外表 Sn 的聚集以及ITO 中氟元素的掺杂浓度有关，这说明外表处理后工作性能有所进步。关键词： ITO，外表处理，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本钱。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

4、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 外表预处理来改变。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 外表沉积有机材料之前进展处理是非常重要的。作为外表处理方法的低压等离子技术

5、、UV/O3 技术、和湿处理均被用于去除有机杂质和改善ITO 外表特性。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、生物材料和构造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 玻璃外表的价值。 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

6、，这些混合气体在ITO 的外表特性和形成干净的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 玻璃外表的常压等离子体设备图。如下列图，修改正的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11 / 11电和辉光放电的高电场，从而可以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2030 千赫兹、电压为 315 千伏的交流电压， 平板接地电极接地。He(10slm)/O 2(3slm)和

7、He(10 slm)/SF6(100 sccm) 的混合气体被应用于 OLED器件 ITO外表的清洗。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 体的最正确成分通过接触角和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 03 slm 的氧流速、 0500 sccm 的SF6 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/O2 和 He/SF6 等离子混合气体清洁后的ITO 外表组成用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

8、过在干净的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器件的构造为ITO/2-TNATA(60 nm)/NPD(20 nm)/Alq3(40 nm)/LiF(1onm)/Al(100 nm)。有机材料、氟化锂和铝的沉积速率分别为0.3 0.5 Ao/s 、0.1 Ao/s、0.5 5 A /s ，2器件的有效面积为4mm。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)/SF6(100 scc

9、m) 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2a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2义为发出 1 cd/m 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 s

10、lm)/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器件显示了最正确的电学性能。经过He(1

11、0 slm)/SF 6(100 sccm) 处 理的OLED器件的电特性的改善看上去与去除ITO 外表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)/O 2(3 slm)和 He(10 slm)/SF 6(100 sccm) 三种处理方法后的 ITO 外表的组成。 表中显示， 经等离子处理后， ITO 外表碳元素的含量显著的减少，而且， 经 He(10 slm)/SF 6(100 sccm) 处理后的 ITO 外表碳含量最少，因此，有机清洗后残留的有机杂质被等离子体去除了很 多，有机杂质的去除被认为改善了 OLED的性能。当 比

12、较 用 He(10 slm)/O 2(3 slm) 和 He(10 slm)/SF 6(100 sccm) 处理的ITO 外表组成时发现，在用He(10 slm)/SF6(100 sccm) 清洁的 ITO 外表的氧被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 进步空穴的注入效率。 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，而外表4+Sn 的 含 量 却 明 显 减 少 。Sn3d5/2 在峰值处可以分解成5/2Sn2+和 Sn4+的氧化物。图3 显示了将 Sn3d2+4+的峰值分解成Sn

13、 和 Sn 的 XPS窄扫描数据。如下列图，经4+过等离子体处理后的Sn 的最高值有所减小，在经He(10 slm)/SF 6(100 sccm) 处理后为最低的峰值。3+4+4+4+据报道， 通过用 In代替 Sn 的位置来减少Sn 的含量， Sn 的减少使 n 型的费米能级向中间能带改变，从而进步了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4+加氟元素和减少ITO 外表 Sn 的含量来除去碳杂质以进步工作性能有关。结论，利用常压等离子体设备使He(10 slm)/O 2(3 slm)和 He(10 slm)/SF6(10

14、0 sccm) 的混合气体来处理 ITO 玻璃的外表以及它对ITO 外表特性和 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21cd/m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 、最高的亮度在一样的电流密度下和最高的功率效率 He/SF6 处理后为0.93 Lm/W，He/O2 处理后为 0.75Lm/W，未处理的为 0.58Lm/W。 He(10 slm)/SF 6

15、(100sccm)等离子体处理的 OLED器件性能的改善与 ITO 外表有机4+杂质的去除、Sn 的含量的降低以及ITO 外表氟元素的掺杂有关，而且说明了ITO 性能的进步。因为常压等离子体不需要真空室，所以可以很容易安装负载室并应用于尺寸大于730mm*920m的m 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方案海军研究实验所的支持。参考文献1) C. W. Tang and S. A. VanSlyke: Appl.

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22、e Treatment of Indium Tin Oxide Surfaces Using Atmospheric PressurePlasmasChang Hyun JEONG, June Hee LEE, Yong Hyuk LEE, Nam Gil CHO, Jong Tae LIM, Cheol Hee MOON and Geun Young YOMEDepartment of Materials Science & Engineering, Sungkyunkwan University, Suwon, 440-746, Korea PDP Division, Samsung SD

23、I 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/O 2 and He/SF6 atmospheric pressure plasma surface treatment of indium tin oxide(ITO)glass on the ITO surface and electrical charact

24、eristics of organic light emitting diodes (OLEDs). The OLEDs composedof ITO glass/2-TNATA/NPD/Alq3/LiF/Alshowed betterelectrical characteristics, such as lower turn-on voltage, higher power efficiency,etc., after the He/O 2 or He/SF6 plasma treatment. The He/SF6 treatment resulted in superior electr

25、ical characteristics compared with the He/O2 treatment. The electrical improvement as a result of the He/SF6 and He/O 2 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 functio

26、n as a result of the treatments. DOI: 10.1143/KEYWORDS： ITO, surface treatment, atmospheric pressure plasma, OLED, He/O2, He/SF6Organic light emittingdiode (OLED)displays have been extensively studied due to their superior properties such as faster response time, lower operating voltage, higher quan

27、tum 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. 13) Currently, these devices are manufactured in a highvacuum chamber for substrate areas smaller than

28、 370mm 470mm usinga multilayer evaporation techniquefor 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

29、actively being studied4.,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 conductivityand transparency. In order to form OLED devices, the organic monom

30、ers are deposited on patterned ITO glassfor the formation of a lowresistive 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 co

31、mposition as a result of the ITO surface preparation method. ITOis 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 ofthe patt

32、erned ITObefore depositingthe organic materials isvery important.613) As surface treatment methods, low pressure plasma techniques, 610,12) UV/O 3 techniques,911) and wet treatments12,13) have been used to remove the organic materials and improve the ITO surface properties. However, these techniques

33、 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,1

34、7) 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 press

35、ure 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,

36、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 forthe surface treatment

37、of ITOglass. As shown in the figure, the modifiedDBDused 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 inste

38、ad 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 v

39、oltage 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 ITOglass.He(10 slm)/O2(3

40、 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 measuri

41、ng tool and the carbon contents on the ITO surface by X-ray photoelectron spectroscopy (XPS, VG Microtech Inc., ESCA2000) after varying the O 2 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

42、 time was30 seconds. The composition of the ITO surface after cleaning with the He/O2 and He/SF6 plasma 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

43、 without breaking the vacuum.The OLED structure used in this study was ITO glass/2-TNATA(60 nm)/NPD(20 nm)/Alq 3(40 nm)/LiF(1 nm)/Al(100 nm). The depositionrates of the organic materials, LiF, and Alwere 0.30.5?/s, 0.1 ? /s, and 0.55 ? /s, respectively. Thefabricated device active area was 4mm2. The

44、 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 characteris

45、tics of the OLEDs fabricated on the ITO glass cleaned by the atmospheric pressure plasma using the He(10 slm)/O 2(3 slm) and He(10 slm)/SF6(100 sccm) gas mixtures such as (a) luminescencevoltage, (b)luminescence-current density, and (c)power efficiency-currentdensity. Asa reference, the characterist

46、ics of the OLEDdevice fabricated without plasma cleaning were included. As shown in Fig. 2(a), the turn-on voltages ofthe devices (defined as the voltage required to deliver a luminescence of 1 cd/m2) after the He(10 slm)/O 2(3 slm) and He(10 slm)/SF6(100 sccm) treatment were 3.6V and 3.2 V, respect

47、ively, while the turn-on voltage ofthe 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)/SF 6(100 sccm) treatment. In addition, as shown in

48、Fig. 2(b), the OLED treated by He(10 slm)/SF6(100 sccm) showed the lowest current density at the same emission intensity while theOLEDfabricated withoutthe plasma treatment showed the highest current density. Whenthe power efficiency was measured as a function of the current density, the highest pow

49、er 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)/SF 6-(100 sccm) treatment, the device showed the best electricalperformance.Fig. 2.

50、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 characteris

51、tics of the OLED device fabricated withoutplasma cleaning are included.The improved electrical characteristics shown forthe OLEDafter 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 t

52、he 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

53、 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

54、 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

55、on the ITO surface, which replaced oxygen on the surface when comparing the surface compositions of the ITO cleaned by the He(10 slm)/O 2(3 slm) and that by the He(10 slm)/ SF 6(100 sccm). However, sulfur (S2p 164 eV) was not detected on the ITO surface as a result of the He(10 slm)/ SF 6(100 sccm)

56、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 significantlyaltered by the

57、plasma treatment, the surface concentration of Sn4+was deceased significantly by the plasma treatment. The S3nd5/2 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 Sn 2+ and Sn4+ peaks of Sn3d5/2 peak are shown in. As shown in the figure, the Sn 4+ peak intensity was deceased by the plasma treatment and showed the lowest peak for the He(10 slm)/ SF6(100 sccm