第五十七期 2010年9月刊
 
 
 
發行人:林清富所長  編輯委員:陳奕君教授  主編:林筱文  發行日期:2010.09.03
 
 
台積電新事業部總經理蔡力行博士來訪—(99年8月27日)

台積電新事業部總經理蔡力行博士率領數位台積電高層同仁劉啟光處長、曾晉晧副處長、魏烈恒經理, 於本年8月27日(星期)下午蒞臨本所訪問,與林清富所長、林恭如副所長,以及數位本所教師如林晃巖教授、吳志毅教授、邱奕鵬教授、黃鼎偉教授等進行雙方合作之意見交流,包括研究和人才培育等多層面之討論。

 

 
 

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

臺灣大學光電所 吳志毅教授

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

臺灣大學光電所 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

臺灣大學光電所 黃建璋教授

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

 

 
 
論文題目:臨床倍頻顯微術—皮膚之光學虛擬切片

姓名:陳思妤   指導教授:孫啟光教授

 

摘要

倍頻顯微術結合了二倍頻及三倍頻顯微術,並以一鉻貴橄欖石為激發光源,因其同時擁有非侵入性、高解析度及高穿透度等優點,在醫學應用上,為一可用來進行非侵入性虛擬光學切片的新技術。在皮膚裡,三倍頻的信號來自於物質的非同質性、細胞胞器、脂質、血紅素及黑色素;而二倍頻信號的主要來源則是第一型的膠原蛋白,基於豐富多樣的信號來源,倍頻顯微術可被用來觀察細胞型態或是膠原蛋白纖維結構上的病變,此技術很適合應用於皮膚的臨床診斷。

圖一、本圖為在健康受試者前臂皮膚表皮真皮交界處所取得之倍頻影像,影像大小為240mm×240mm,三倍頻及二倍頻分別以紫色及綠色表示,透過三倍頻可清楚得到表皮層基底細胞的型態結構(箭頭),而透過二倍頻則可見真皮層膠原蛋白纖維的結構(箭號)。

圖二、本圖為在健康受試者前臂皮膚真皮層所取得之倍頻影像,影像大小為240mm×240mm,三倍頻及二倍頻分別以紫色及綠色表示,透過三倍頻可清楚看到微血管內紅血球的流動(箭頭),而透過二倍頻則可見真皮層膠原蛋白纖維的結構。

 

論文題目:氯化硼亞菁應用於有機光電半導體之電子結構與介面特性探討

姓名:陳裕宏   指導教授:吳志毅教授


摘要

菁衍生物因為其特殊的物理與化學性質,在化學工業與光電產業中被廣泛的利用。本論文中,首次將氯化硼亞菁(SubPc)成功的應用至有機發光二極體內,並探討SubPc應用至有機半導體元件上所扮演的角色。首先,針對有機發光二極體的元件架構做簡單介紹,並討論應用至各層時,有機材料所應該具備的相關物理與化學特性。介面特性探討上,對於半導體介面上所適用的理論來簡單的介紹。最後,文獻探討部分將對於酞菁衍生物的發展歷程有初步的介紹。並且對於應用至陽極注入時,菁衍生物在電洞注入與傳輸介面上所扮演的角色跟運作原理做進一步的說明。

實驗部分,經由元件的製作,成功的實現了以SubPc跟NPB為電洞注入層的有機發光二極體元件。光電子能譜的實驗上,SubPc以極低蒸鍍速率鍍到NPB,蒸鍍過程中量測價帶能譜與核電子能譜。如圖一所示,經由能譜上的變化,推論出NPB與SubPc兩者於介面上的反應方式。並且藉由前述的第一原理,先模擬分子結構至最低能量,進而獲得模擬的價帶能譜與分子軌域圖樣。如圖二所示,藉由理論與實驗能譜的對照,進一步佐證在實驗結果上所獲得的推論。陰極結構的應用上,將SubPc與LiF以適當的比例運用至電子注入層,實現了元件電性的提升。個別的針對陰極結構的Alq3\SubPc與SubPc\LiF\Al的能譜來解釋元件電性提升的原因。除此之外,鹼金屬與有機半導體材料在介面間的變化也是近年來相當有趣的課題。因此,本論文也會對鋰原子與SubPc 介面間,在價帶能譜與核電子能譜上的變化來討論。

圖一、NPB與SubPc介面間的連續能隙能態(價帶與HOMO peak)。

圖二、實驗能譜與理論能譜之對照,與連續能隙能態的理論與實驗對照。

 

 
 
 

— 資料提供:影像顯示科技知識平台 (DTKP, Display Technology Knowledge Platform) —

— 整理:林晃巖教授、康譽齡 —

麻省理工開發出新型鋰電池

美國麻省理工學院(MIT)開發出了正極材料採用包括碳奈米管在內的混合材料之鋰離子充電電池。開發該電池的是MIT化學工程系教授Paula T. Hammond與該校機械工程系兼材料科學與工程系教授楊少紅領導的研究小組。該電池同時兼顧鋰離子充電電池及電容器二者的性能。具體而言,輸出密度是普通鋰離子充電電池的10倍,能量密度是普通電容器的5倍。論文已刊登在2010年6月20的《Nature Nanotechnology》上。

 

此次發表的電池,正極採用多層碳奈米管(MWNT)和有機材料的混合材料,負極採用鈦酸鋰(Li4Ti5O12:LTO)。這應該是首次在正極上採用MWNT(圖一~三)。 正極的構造如下:透過將電極反覆浸泡在兩種不同的溶液中,交替形成MWNT和羧基相結合的MWNT-COOH層與MWNT和氨基相結合的MWNT-NH2層。MWNT-COOH層和MWNT-NH2層的層數由小於100層到最大400層(將2層作為1組時,最大200組)。由於兩層分別帶正電及負電,所以透過層積方法可使其牢固地結合在一起。

 

這種電池的特點是可實現非常高的功率輸出,並且此時的能量密度也較高。在低功率輸出時的能量密度雖然與普通鋰離子充電電池沒什麼差別,但在高功率輸出時,此次發表的電池顯示出了更高的性能特性。

 

此次發表的電池在輸出密度為100kW/kg時,單位重量的能量密度為200Wh/kg;低功率輸出時的最大能量密度約為500Wh/kg。不過,這些數值是相對於電極的重量計算的。如果相對於電池整體的重量計算,將會是這些數值的1/5,亦即輸出密度約為20kW/kg時,能量密度約為40Wh/kg,低功率輸出時的最大能量密度約為100Wh/kg。相較而言,普通鋰離子充電電池在輸出密度為1kW/kg時,相對於電池重量的能量密度為150Wh/kg;普通電容器在電力密度為10kW/kg時,相對於電容器重量的能量密度為5Wh/kg。與這些普通的電池及電容器相比,此次發表的電池擁有輸出密度是鋰離子充電電池的5倍左右、能量密度是電容器的10倍左右的性能。

 

電池的充放電週期特性方面,論文表示即使反覆充放電1000次以上,性能也不會發生劣化。

 

圖一、LBL-MWNT電極的能量儲存機制

圖二、不同層組數MWNT 電極在ITO鍍膜玻片上

圖三、MWNT 電極的SEM和TEM的掃描影像

 

中文新聞來源:

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

英文新聞來源

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

論文來源:

“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

   
 
 
 
版權所有 國立臺灣大學電機資訊學院光電工程學研究所 http://gipo.ntu.edu.tw/
歡迎轉載 但請註明出處 http://gipo.ntu.edu.tw/monthly.htm/