Study of environmental factors effect on bias-temperature instability of alkyl-substituted oligothiophene organic thin film transistors

• Main Authors: Po-Han Chen, 陳柏翰
• Other Authors: Pei-Wen Li
• Format: Others
• Language: zh-TW
• Published: 2011
• Online Access: http://ndltd.ncl.edu.tw/handle/18279361477957952436

碩士 === 國立中央大學 === 電機工程研究所 === 99 === 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.