儲存環境因子對於含烷基的低聚?吩有機薄膜電晶體偏壓應力的可靠度測試與評估探討; Study of environmental factors effect on bias-temperature instability of alkyl-substituted oligothiophene organic thin film transistors

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Title:	儲存環境因子對於含烷基的低聚?吩有機薄膜電晶體偏壓應力的可靠度測試與評估探討;Study of environmental factors effect on bias-temperature instability of alkyl-substituted oligothiophene organic thin film transistors
Authors:	陳柏翰;Po-Han Chen
Contributors:	電機工程研究所
Keywords:	偏壓溫度不穩定;儲存環境因子;有機薄膜電晶體;organic thin film transistors;environmental factors effect;bias-temperature instability
Date:	2011-07-21
Issue Date:	2012-01-05 14:55:38 (UTC+8)
Abstract:	雖然有機薄膜元件的技術日益成熟，但是有機薄膜材料對於環境因子，如 : 溫度、濕度及儲存環境，非常的敏感。為了瞭解有機薄膜電晶體未來在可撓式顯示器、電子書或感測器等應用的可能性，本論文特別探討儲存環境因子對於該元件的可靠度及熱穩定度的影響。本文針對含烷基的低聚噻吩的裸晶有機薄膜電晶體進行了溫度相依與時間相依的電性量測。發現隨著溫度的上升，元件臨限電壓會一直往負偏壓方向移動，但奇特的是次臨限斜率及開啟電流卻隨著溫度的上升而獲得改善。此外，在閘極負偏壓應力測試中當溫度由300 K提升到330 K時，元件的臨限電壓會持續地往負偏壓方向移動。但是，當測試溫度為340 K時，發現臨限電壓向負偏壓方向移動的行為會出現逆轉的現象，並且隨著溫度的上升此逆轉現象逐漸減緩。藉由熱差分析儀的探討發現含烷基的低聚噻吩在加熱或冷卻的過程中，分別會於313 K或309 K出現相轉變。推測上述奇特的電特性可能與材料的相轉變相關。量測結果顯示該材料的相轉變有助於改善有機薄膜電晶體在高溫操作環境下，閘極負偏壓應力測試所導致臨限電壓不穩定的現象。此外，利用高溫( 370 K )退火不僅可以減緩閘極負偏壓應力導致臨限電壓不穩的現象，還可以回復水氣所引起的元件衰退。本論文也發現到當含烷基的低聚噻吩有機薄膜電晶體經護層覆蓋後，水氣所引起的元件衰退較難利用高溫( 370 K )退火回復。經護層保護的元件對於負閘極偏壓應力有較佳的抵抗能力，並且在高溫( 370 K )進行的偏壓應力測試也不會出現反向的臨限電壓移動，但是經過濕度儲存後將會導致電晶體在偏壓應力的作用下臨限電壓嚴重地被影響。 Environmental factors such as temperature, humidity, and storage ambience have profound impact on organic thin film transistors (OTFTs). Thus it is important to verify the reliability and thermal stability of OTFTs for future applications in flexible large-area display, electric paper, and sensors. This thesis investigates temperature-dependent and time-dependent current-voltage characteristics of alkyl-substituted oligothiophene OTFTs. The investigations indicate that, as temperature increases, a negative threshold voltage shift ( ?Vth ) with a surprising subthreshold slope and drive current improvement. In addition, a negative gate bias stress makes a monotonic ?Vth with stress time in the direction of stressed gate bias at T = 300-330 K. Notably as the stress temperature reaches 340 K, a reverse ?Vth motion with stress time emerges, and as the temperature increases this reverse ?Vth slows down. We performed successive differential scanning calorimetry, to study the intrinsic thermal property of the alkyl-substituted oligothiophene semiconductor in heating and cooling runs with results exhibiting a peak near 313 K and 309 K, respectively. The phase transition of the alkyl-substituted oligothiophene improves the gate-bias stress induced threshold voltage instability at high temperatures. Furthermore, the bias stress induced threshold voltage instability and humidity effect could be easily recovered by a post-stress thermal anneal at 370 K in vacuum. The study also shows that humidity effect in the passivated alkyl-substituted oligothiophene OTFTs couldn’t be easily recovered by a thermal anneal at 370 K in vacuum. The passivated alkyl-substituted oligothiophene OTFTs have performed better on the bias stress induced threshold voltage instability, and don’t have a reverse ?Vth motion with stress time emerging in high temperatures, but the bias stress induce threshold voltage instability will deteriorate after pre-storage of high humidity ambience.
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