第五十七期 2010年9月刊
 
 
 
发行人:林清富所长  编辑委员:陈奕君教授  主编:林筱文  发行日期:2010.09.03
 
 
台积电新事业部总经理蔡力行博士来访—(2010年8月27日)

台积电新事业部总经理蔡力行博士率领数位台积电高层同仁刘启光处长、曾晋晧副处长、魏烈恒经理, 于本年8月27日(星期)下午莅临本所访问,与林清富所长、林恭如副所长,以及数位本所教师如林晃岩教授、吴志毅教授、邱奕鹏教授、黄鼎伟教授等进行双方合作之意见交流,包括研究和人才培育等多层面之讨论。

 

 
 

The Correlation of Turn on Voltage and Band Alignment in Organic Light Emitting Diodes

Professor Chih-I Wu

Graduate Institute of Photonics and Optoelectronics, National Taiwan University

台湾大学光电所 吴志毅教授

Turn on voltage in the current density-voltage characteristics is one of the important factors to evaluate the performance of organic light emitting diodes (OLEDs). We report investigation of the origins of turn-on voltage, defined at where log J (current density) has a sharp rise and starts to increase dramatically. In OLEDs with NPB as the hole transport layer (HTL) and Alq3 as the electron transport layer (ETL), we find that the turn on voltage is always at 2V, regardless the cathode structures being used, such as Ca, Al, LiF/Al and Cs2CO3/Al. The turn on voltage is also independent on the thickness of organic layers (thickness varies from 30nm to 120 nm).

Beside NPB and Alq3, we also study the J-V characteristics on various OLEDs with T3/Alq3, NPB/T3, and NPB/Bphen as HTL/ETL, respectively. In all the devices mentioned above, the turn on voltage just equals to the difference between the LUMO of ETL and the HOMO of HTL, taking into consideration of vacuum level shift at organic interfaces measured from the ultraviolet photoemission spectroscopy (UPS). Combined with J-V characteristics of OLEDs and UPS measurement, we conclude that the turn on voltage of organic light emitting devices is determined by the difference between LUMO of ETL and HOMO of HTL and is independent of the cathode and thickness of organic layers. We also found that the charge transfers at the interface of ETL/HTL play an important role to the turn on voltage of OLEDs.

 

Emitting Layer Thickness Dependence of Color Stability in Phosphorescent Organic Light-Emitting Devices

Professor Jiun-Haw Lee

Graduate Institute of Photonics and Optoelectronics, National Taiwan University

台湾大学光电所 李君浩教授

We investigated the strong influence of the thickness of iridium(III)bis[(4,6-difluorophenyl) -pyridinato-N,C2’]picolinate (FIrpic) doped N,N’-dicarbazolyl-3, 5-benzene (mCP) blue emitting layer (B-EML) on color stability. The large voltage drop across the B-EML resulted in a higher sensitivity of the carrier transport and injection properties to the applied external voltage. According to carrier mobility measurements by the time-of-flight method, the electron mobility of the mCP exhibited a strong dependence on the electric field. Therefore, at a higher driving voltage, the more rapidly increasing electron mobility of the mCP and the decreasing energy barrier height on the electron transport path would extend the recombination zone from the B-EML to the tris(phenylpyridine)iridium (Ir(ppy)3) doped mCP green emitting layer (G-EML) in devices with thinner B-EMLs. Coupled with the fluctuations of the recombination zone, stronger triplet-triplet exciton annihilation occurring in the thinner B-EMLs led to an even more evident deterioration of the color stability. After circumventing these two negative factors, a green-blue organic light-emitting device (OLED) with ultra-high color stability was demonstrated, with the CIE coordinates slightly shifted from (0.256, 0.465) to (0.259, 0.467) with increased luminance from 48.7 to 12700 cd/m2. Further adding a red phosphorescent dopant into this green-blue EML backbone, we successfully fabricated a white OLED with high color stability, which exhibited a nearly invariant CIE coordinate throughout the practical luminance range from 1050 ((0.310, 0.441)) to 9120 cd/m2 ((0.318, 0.446)) and maximum efficiencies of 26.4 cd/A and 19.8 lm/W [published in Org. Electron. 11, 1500, 2010].

 

Effects of Gate Bias and Thermal Stress on ZnO Thin Film Transistors

Professor Jian-Jang Huang

Graduate Institute of Photonics and Optoelectronics, National Taiwan University

台湾大学光电所 黄建璋教授

The effects of gate bias and thermal stress on the threshold voltage shift were examined for ZnO TFTs fabricated on the glass substrate. We compared three samples with various post ZnO growth annealing durations. The results show that the threshold voltage shift (ΔVth) is only 2.2V after a 1.3×104s stress at the gate bias 20V for device C. And the threshold voltage shift can be correlated to the stress time following the charge trapping mechanism. The characteristic trapping time τ of device C was calculated to be 1.26×106 s. Further comparisons of the trap states and off currents reveal that device C has a better ZnO crystalinity and a better ZnO/SiNx interface quality. Finally, the characteristic trapping time was extracted at different temperatures for device C. We obtain an average effective energy barrier Eτ of 0.57eV. The results presented in this work suggested that excellent τ and Eτ can be obtained from ZnO TFTs on the glass substrate following our fabrication steps.

Fig. 1: Layer structure of the ZnO TFT on the glass substrate.

Fig. 2: Transfer curves at different stress time for device A(a), B(b) and C(c). The bias gate voltage is 20V.

Fig. 3: Time dependent ΔVth of device A, B and C under a gate bias 20V.

Fig. 4: Time evolution of transfer curve during the recovery phase of device C. The inset shows the ΔVth versus relaxation time.

Fig. 1  

Fig. 2(a) Fig. 2(b) Fig. 2(c)

Fig. 3 Fig. 4

 

 
 
论文题目:临床倍频显微术—皮肤之光学虚拟切片

姓名:陈思妤   指导教授:孙启光教授

 

摘要

倍频显微术结合了二倍频及三倍频显微术,并以一铬贵橄榄石为激发光源,因其同时拥有非侵入性、高分辨率及高穿透度等优点,在医学应用上,为一可用来进行非侵入性虚拟光学切片的新技术。在皮肤里,三倍频的信号来自于物质的非同构型、细胞胞器、脂质、血红素及黑色素;而二倍频信号的主要来源则是第一型的胶原蛋白,基于丰富多样的信号来源,倍频显微术可被用来观察细胞型态或是胶原蛋白纤维结构上的病变,此技术很适合应用于皮肤的临床诊断。

图一、本图为在健康受试者前臂皮肤表皮真皮交界处所取得之倍频影像,影像大小为240mm×240mm,三倍频及二倍频分别以紫色及绿色表示,透过三倍频可清楚得到表皮层基底细胞的型态结构(箭头),而透过二倍频则可见真皮层胶原蛋白纤维的结构(箭号)。

图二、本图为在健康受试者前臂皮肤真皮层所取得之倍频影像,影像大小为240mm×240mm,三倍频及二倍频分别以紫色及绿色表示,透过三倍频可清楚看到微血管内红血球的流动(箭头),而透过二倍频则可见真皮层胶原蛋白纤维的结构。

 

论文题目:氯化硼亚菁应用于有机光电半导体之电子结构与接口特性探讨

姓名:陈裕宏   指导教授:吴志毅教授


摘要

菁衍生物因为其特殊的物理与化学性质,在化学工业与光电产业中被广泛的利用。本论文中,首次将氯化硼亚菁(SubPc)成功的应用至有机发光二极管内,并探讨SubPc应用至有机半导体组件上所扮演的角色。首先,针对有机发光二极管的组件架构做简单介绍,并讨论应用至各层时,有机材料所应该具备的相关物理与化学特性。接口特性探讨上,对于半导体接口上所适用的理论来简单的介绍。最后,文献探讨部分将对于酞菁衍生物的发展历程有初步的介绍。并且对于应用至阳极注入时,菁衍生物在电洞注入与传输接口上所扮演的角色跟运作原理做进一步的说明。

实验部分,经由组件的制作,成功的实现了以SubPc跟NPB为电洞注入层的有机发光二极管组件。光电子能谱的实验上,SubPc以极低蒸镀速率镀到NPB,蒸镀过程中量测价带能谱与核电子能谱。如图一所示,经由能谱上的变化,推论出NPB与SubPc两者于接口上的反应方式。并且藉由前述的第一原理,先模拟分子结构至最低能量,进而获得模拟的价带能谱与分子轨域图样。如图二所示,藉由理论与实验能谱的对照,进一步左证在实验结果上所获得的推论。阴极结构的应用上,将SubPc与LiF以适当的比例运用至电子注入层,实现了组件电性的提升。个别的针对阴极结构的Alq3\SubPc与SubPc\LiF\Al的能谱来解释组件电性提升的原因。除此之外,碱金属与有机半导体材料在接口间的变化也是近年来相当有趣的课题。因此,本论文也会对锂原子与SubPc 接口间,在价带能谱与核电子能谱上的变化来讨论。

图一、NPB与SubPc接口间的连续能隙能态(价带与HOMO peak)。

图二、实验能谱与理论能谱之对照,与连续能隙能态的理论与实验对照。

 

 
 
 

— 数据提供:影像显示科技知识平台 (DTKP, Display Technology Knowledge Platform) —

— 整理:林晃岩教授、康誉龄 —

麻省理工开发出新型锂电池

美国麻省理工学院(MIT)开发出了正极材料采用包括碳奈米管在内的混合材料之锂离子充电电池。开发该电池的是MIT化学工程系教授Paula T. Hammond与该校机械工程系兼材料科学与工程系教授杨少红领导的研究小组。该电池同时兼顾锂离子充电电池及电容器二者的性能。具体而言,输出密度是普通锂离子充电电池的10倍,能量密度是普通电容器的5倍。论文已刊登在2010年6月20的《Nature Nanotechnology》上。

 

此次发表的电池,正极采用多层碳奈米管(MWNT)和有机材料的混合材料,负极采用钛酸锂(Li4Ti5O12:LTO)。这应该是首次在正极上采用MWNT(图一~三)。 正极的构造如下:透过将电极反复浸泡在两种不同的溶液中,交替形成MWNT和羧基相结合的MWNT-COOH层与MWNT和氨基相结合的MWNT-NH2层。MWNT-COOH层和MWNT-NH2层的层数由小于100层到最大400层(将2层作为1组时,最大200组)。由于两层分别带正电及负电,所以透过层积方法可使其牢固地结合在一起。

 

这种电池的特点是可实现非常高的功率输出,并且此时的能量密度也较高。在低功率输出时的能量密度虽然与普通锂离子充电电池没什么差别,但在高功率输出时,此次发表的电池显示出了更高的性能特性。

 

此次发表的电池在输出密度为100kW/kg时,单位重量的能量密度为200Wh/kg;低功率输出时的最大能量密度约为500Wh/kg。不过,这些数值是相对于电极的重量计算的。如果相对于电池整体的重量计算,将会是这些数值的1/5,亦即输出密度约为20kW/kg时,能量密度约为40Wh/kg,低功率输出时的最大能量密度约为100Wh/kg。相较而言,普通锂离子充电电池在输出密度为1kW/kg时,相对于电池重量的能量密度为150Wh/kg;普通电容器在电力密度为10kW/kg时,相对于电容器重量的能量密度为5Wh/kg。与这些普通的电池及电容器相比,此次发表的电池拥有输出密度是锂离子充电电池的5倍左右、能量密度是电容器的10倍左右的性能。

 

电池的充放电周期特性方面,论文表示即使反复充放电1000次以上,性能也不会发生劣化。

 

图一、LBL-MWNT电极的能量储存机制

图二、不同层组数MWNT 电极在ITO镀膜玻片上

图三、MWNT 电极的SEM和TEM的扫描影像

 

中文新闻来源:

http://big5.nikkeibp.com.cn/news/elec/52028-20100623.html

英文新闻来源

http://www.eetimes.com/electronics-news/4200509/MIT-Resarch-Squezzes-Power-Carbon-Li-ion-

论文来源:

“High-power lithium batteries from functionalized carbon-nanotube electrodes”, Nature Nanotechnology v.5, pp.531 - 537 (2010), Seung Woo Lee, Naoaki Yabuuchi, Betar M. Gallant, Shuo Chen, Byeong-Su Kim, Paula T. Hammond and Yang Shao-Horn

   
 
 
 
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