本論文研究五苯 (pentacene) 有機半導體為主動層之薄膜電晶體元件特性。研究分成兩部份，第一部份，將元件置於外加磁場下操作，探討主動層與介電層交界面中，束縛電荷與缺陷對有機薄膜電晶體 (OTFTs) 的影響；第二部份，探討五苯分子振動特性與五苯複晶薄膜的表面形態的關連性。
第一部分:將五苯OTFTs元件置於磁場的環境下操作，使載子產生的偏折，探討載子受到有機半導體薄膜與介電層界面中的束縛電荷與缺陷的影響。結果指出，外加磁場會明顯影響五苯元件的輸出電流、場效遷移率、與起始電壓。外加向上磁力可使載子電洞漂移遠離五苯/介電層界面與脫離束縛態，導致較大的電流輸出與起始電壓往正向位移，因此影響到載子遷移率。磁場導致的元件電性變化與閘極誘導應力和光誘導應力導致的電性改變明顯不同，我們建議這些來自無預期的雜質摻雜的額外載子，於有機薄膜電晶體的電特性可能扮演一重要角色。
第二部份: 利用原子力顯微鏡與拉曼一維與二維掃瞄技術研究五苯複晶薄膜的表面晶粒形能與微觀分子振動特性的相關性。我們使用微拉曼光譜學去研究複晶薄膜內的分子微結構，探討C-H 共平面彎折模式與C-C 苯環內伸縮模式於1100-1400 cm-1能量區間。吾人可利用光譜的強度定義出晶粒與晶界的相關位置，結果指出五苯薄膜上的晶粒中心擁有較佳的排列秩序，且由中心向晶界遞減，而晶界上排列的秩序較差且不連續。我們建議晶粒的大小可能不是決定電性好壞的主要因素，主要因素應該是晶粒與晶界上分子的排列秩序與整體分子間偶合的能量大小。

In this study, device characteristics of polycrystalline pentacene-based organic thin-film transistors (OTFTs) were investigated. In part 1, we studied the traps and fixed charges at the interface between gate dielectric and pentacene by using an external magnetic field during device operations. In the second part, we studied the correlation between surface morphology and molecular vibrational characterizations of polycrystalline pentacene thin-films.
Part 1: External magnetic field effects in pentacene-based organic thin-film transistors (OTFTs) during device operations were studied. Herein, we showed that the output drain current (IDS), field-effect mobility, and threshold voltage (Vth) of pentacene devices were affected by the presence of a magnetic field. The upward magnetic force made the holes drift away from the pentacene/dielectric interface and/or detrapping from the immobile states, contributing to a larger IDS and a positive shift in Vth and thus, carrier mobility. The magnetic field-induced variations in electrical characteristics of pentacene-based OTFTs were different from that of gate-induced and light-induced bias-stress effects, suggesting that extra carriers from unintentional doping may play an important role in organic TFTs’ electrical characteristics.
Part 2: We studied the molecular vibrational characterizations of pentacene molecules in polycrystalline films with grain morphology using atomic force microscopy and Raman mapping measurements. We applied the micro-Raman spectroscopy to identify the molecular microstructures within the polycrystalline pentacene films, including C-H in-plane bending and C-C aromatic stretching modes in the energy range of 1140-1200 and 1300-1400 cm-1, respectively. We observed that the grain had stronger Raman intensities for all bands in the grain boundaries. At the same time, the relative intensity of 1155 (v1) and 1158 (v0) cm-1 bands was higher in those associated with a larger v0-v1 splitting in the grains than those in the grain boundaries. For polycrystalline films, the microstructures were more ordered (crystalline) in the grain and more disordered (amorphous) in the grain boundary. Consequently, we deduced that the relative intensity of v1 band and the v0-v1 splitting was proportional to the fraction of the ordered area or density of the well-defined crystal unit cell.

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