以蒽并二噻吩具液晶相有機半導體材料製作之高電荷遷移率有機場效電晶體分析與鑑定

Abstract

本研究合成鑑定了兩系列以蒽并二噻吩做為主體具液晶相有機半導體材料，並藉由不同的元件製作條件以及結構得到高效率的OFET元件電荷遷移率。第一系列液晶分子設計在蒽并二噻吩主體外兩邊或一邊延伸出辛基噻吩以及十二烷基噻吩分子，合成了三個有機半導體材料C12T-a-ADT、 Bis-C8T-a-ADT以及Bis-C12T-a-ADT；第二系列材料分子設計在蒽并二噻吩主體外一邊加入十二烷基、戊基苯以及十二烷基苯，合成了三個有機半導體材料C12-a-ADT、 C5P-a-ADT以及C12P-a-ADT。以上合成分子由微差掃描卡計以及偏光顯微鏡鑑定液晶相，化合物Bis-C8T-a-ADT具向列型及層列型A液晶相而Bis-C12T-a-ADT和C12T-a-ADT兩者都只具層列型A液晶相；化合物C12-a-ADT不具任何液晶相而C5P-a-ADT以及C12P-a-ADT兩者都只具層列型A液晶相。在OFET元件製作及結構探討上我們也分為兩個部分研究，第一部分元件結構以SAM當半導體材料修飾層，搭配上述兩系列材料製作元件，兩系列的元件製作上皆須對半導體材料成膜轉速，成膜後的退火溫度以及自組層材料的選用作最佳化，以得到最高的電荷遷移率。第一系列材料製作的元件在參數最佳化後於C12T-a-ADT得到最高的電荷遷移率0.12 cm2/Vs，；而第二系列材料製作的元件在參數最佳化後於C12P-a-ADT得到最高的電荷遷移率0.68 cm2/Vs。 在OFET元件探討的第二部分我們以Polyimide為有機半導體的修飾材料製作元件， Bis-C12T-a-ADT、C12T-a-ADT以及Pyrene-based具液晶相化合物BOBTP為半導體材料，元件電荷遷移率都可以接近1cm2/Vs，已高於目前顯示器產業成熟量產的TFT-LCD製程所使用非晶矽a-Si:H技術電荷遷移率的0.5cm2/Vs，相對於對照組無修飾元件電荷遷移率增益值最高更可達4個order。

In this study, two series of anthradithiophene-based liquid crystals were synthesized and characterized. The obtained liquid crystals were used to fabricate high efficient organic field effect transistors using different SAM layers and polyimide alignment layer. In the first series of liquid crystals, both octylthiophene and dodecylthiophene groups were introduced onto one side or both sides of angular anthradithiophene core(a-ADT) to yield C12T-a-ADT, Bis-C8T-a-ADT and Bis-C12T-a-ADT compounds. In the second series, dodecyl, pentylphenyl and dodecylphenyl groups were attached to one side of a-ADT core to yield C12-a-ADT, C5P-a-ADT and C12P-a-ADT compounds. The obtained compounds were characterized by differential scanning calorimetry and polarized optical microscope to determine their mesomorphic properties. Compound Bis-C8T-a-ADT showed nematic and smectic A phase while both compounds Bis-C12T-a-ADT and C12T-a-ADT reveal only a semectic A phase. Compound C12-a-ADT shows no liquid crystalline phase while C5P-a-ADT and C12P-a-ADT reveal only smectic A phase. Two FET device structures were fabricated and characterized in this study. The devices of first structure were modified by SAM layers that using above two series anthradithiophene -based materials as organic semiconductor layers. Various of fabrication recipes were applied such as organic semiconductor spin-coating speed, annealing temperature and SAM materials.The highest FET device mobility 0.12 cm2/Vs was obtained for C12T-a-ADT and 0.68 cm2/Vs for C12P-a-ADT. The devices of second structure were modified by polyimide layers. Both Bis-C12T-a-ADT and C12T-a-ADT and BOBTP with liquid crystal phases were applied in the devices. All the mobilities of OTFT devices modified by polyimide layers are around 1cm2/Vs , which is higher than traditional a-Si:H technology (mobility ~0.5cm2/Vs) . In comparison with the non-modified OTFT devices, the mobilities of modified OTFT devices increase about 4 orders.