應用於有機薄膜電晶體的閘極絕緣層與透明電極之研究

Abstract

本論文針對以下兩類有機電子材料進行研究，以期應用於有機薄膜電晶體（OTFT）元件的製作。 第一類為閘極絕緣層。1-(a) 研究開發以溶膠-凝膠法製備五氧化二鉭摻雜在高分子聚亞醯胺之絕緣薄膜，1-(b) 研究常用的高分子PI和PVP絕緣薄膜，驗證它們在OTFT製程中的匹配特性。 第二類為在導電高分子中摻雜奈米銀線當作有機薄膜電晶體的透明電極，導電高分子為poly-(3,4-ethylenedioxythiophene /polystyrene sulphonate) (PEDOT: PSS)。 上述材料皆與可溶性有機半導體5,11-bistriethylsilylethynyl anthradithiophene ( TES-ADT)進行整合，製成OTFT。並對該元件的物理與電性做一系列研究與探討。 1-(a)子項的研究發現聚亞醯胺中五氧化二鉭添加量增加時複合薄膜的熱性質會變差而介電常數增加。製成的OTFT載子遷移率會隨薄膜介電常數升高而增加。此外，五氧化二鉭添加量也會影響亞醯胺化程度並影響薄膜之漏電流。 第一類(b)子項的研究發現PI和PVP薄膜不同的表面能會影響 TES-ADT的成膜品質以及所製成的OTFT電性穩定性。並且確認圖案化製程可以提升OTFT電流的開關比，其側向漏電也可以大幅的降低。以表面能較低的PI為絕緣材料，所製成的元件開關比可由102提升至106，並使得TES-ADT薄膜成長結晶較佳，其載子移動率可達0.43 cm2/Vs。

第二類的研究將奈米銀線與導電高分子複合材料發展為可塗佈式，所得透明薄膜電極在可見光區域的穿透度可達70 %。片電阻可小於140 Ω/sq。以0.1 wt銀線比例混合的電極功函數為5.0 eV。其與OTFT元件的接觸阻值為2.7x 104 Ω•cm。以TES-ADT薄膜匹配此電極，可製得元件載子移動率0.21 cm2/Vs。

In this study, two kinds of organic electronic materials have been studied for the application in organic thin film transistors (OTFT). The first kind is the thin-film materials for gate insulator. 1-(a) To develop the insulating films made of Ta2O5-doped polyimide utilizing sol-gel processes. 1-(b) To study the insulating thin films of polyimide (PI) and poly vinyl phenol (PVP), aimed at their match with the OTFT processing. The second kind is the conducting films for transparent electrodes of OTFT, which is made of conducting polymer, poly-(3,4-ethylenedioxythiophene /polystyrene sulphonate) (PEDOT: PSS), mixing with nano-sized silver wires. The above mentioned thin-film materials are integrated with a solution processed organic semiconductor 5,11-bis(triethylsilylethynyl) anthradithiophene (TES-ADT) to fabricate OTFT devices. Their physical and electronic properties are characterized and investigated. The study of 1-(a) showed that the composite insulating films have thermal properties degrading and dielectric constant increasing with the content of Ta2O5 in the polyimide. The OTFT incorporating the films showed that the carrier mobility increased with the dielectric constant of the films. Furthermore, the degree of imidization of the composite films is affected by the amount of Ta2O5 added, and consequently, influences the leakage current densities of the films. In the study of 1-(b), the surface energies of PI and PVP films are found critical to the qualities of TES-ADT films formed on them as well as the electronic stability of the fabricated OTFT. Furthermore, it was verified that the thithography applied on organic semiconductor layer could reduce parasitic leakage current and increase current on/off ratio. The OTFT based on spin-cast TES-ADT films grown on the low-surface-energy PI dielectric exhibited enhanced electrical performance with a carrier mobility as high as 0.43 cm2/Vs and a current on/off ratio of 106. At last, the study of the silver wires/PEDOT: PSS composite film shows that the transparent conductive electrodes have a low sheet resistance less than 140 Ω/sq and a transmittance as high as 70 % in the visible region. For the composite film with 0.1 wt% of AgNWs, the work function is 5.0 eV and the corresponding contact resistance is as low as 2.7 × 104 Ω•cm. The resulting OTFT device utilizing TES-ADT as active layer showed a high electrical performance with carrier mobility 0.21 cm2/Vs.