臺灣博碩士論文加值系統

本論文主要內容在於研究五苯環有機薄膜電晶體搭配頂接觸式結構之元件製作以及其電特性分析與改善。首先，我們提出以 6,13-五并苯醌薄膜作為載子注入層，穿插於五苯環通道層與源/汲極之間來改善上接觸式元件結構之電性特性。其研究結果顯示，6,13-五并苯醌薄膜在五苯環通道層上呈現不連續的島嶼狀，當元件經由使用五奈米厚度之 6,13-五并苯醌載子注入層之後，其輸出電流與載子移動率的表現與未使用 6,13-五并苯醌載子注入層之元件相比，分別增加了 2.25 倍和 1.79 倍。這可以歸因於在島嶼狀之6,13-五并苯醌載子注入層的引入大幅降低了有機半導體與金屬之間的載子注入能障，並使載子能輕易地藉由穿隧效應進行傳輸，進而大幅提升載子注入效率。而載子注入效率的提升亦反映在元件之有機半導體與金屬之間的接觸電阻上，進而提升元件之電性表現。
其次，我們提出以共蒸鍍方式摻雜四氟四氰基醌二甲烷於五苯環中作為載子注入層，穿插於五苯環通道層與源/汲極之間來改善上接觸式元件結構之電性特性，並同時比較摻雜型與絕緣型(鐵氟龍)的載子注入層應用於上接觸式結構有機薄膜電晶體之製程容忍度。其研究結果顯示，藉由沉積厚度為五奈米且摻雜比例為 1:1 之四氟四氰基醌二甲烷的五苯環的載子注入層，可以得到五苯環通道層與源/汲極之間最佳載子注入效率，進而提升元件之電氣特性。其輸出電流與載子移動率的表現與未使用四氟四氰基醌二甲烷的五苯環載子注入層之元件相比，分別增加了 1.93 倍和 1.75 倍。這可以歸因於四氟 四氰基醌二甲烷的摻雜增加五苯環內的電洞濃度，進而提升了有機半導體與金屬之間的導電度，另外透過多層階能障的形成使電洞載子能輕易地進行傳輸，大幅提升載子注入效率。此外觀察發現摻雜型四氟四氰基醌二甲烷的五苯環載子注入層厚度變化對上接觸式結構有機薄膜電晶體電性影響比絕緣型鐵氟龍的厚度變化影響有著較穩定的製程容忍度。這可以歸因於當絕緣型鐵氟龍屬於高阻值材料，當厚度增加則會大幅降低載子穿隧效率，然而摻雜型四氟四氰基醌二甲烷的五苯環載子注入層具有高導電度及細分介面能障而較不受厚度增加的影響。
再者，我們探討在持續彎曲情況下以聚(4-乙基苯酚)作為閘極絕緣層之可撓式有機薄膜電晶體在真空環境及一般大氣下的電性變化機制。其研究結果顯示，當可撓式元件持續彎曲的時間越久，其汲極通道電流和載子移動率會大幅降低。這可以歸因於彎曲下的機械應力造成五苯環通道的破裂，進而阻礙電洞載子的跳躍傳輸過程。然而當一持續彎曲可撓式元件處於一般大氣下時，環境水氣分子易透過機械彎曲應力所造成元件五苯環通道的裂縫擴散至聚(4-乙基苯酚)閘極絕緣層和五苯環通道層介面形成極化水分子缺陷，進而增加汲極通道電流、關閉電流和次臨界百幅。這可以歸因於吸附在聚(4-乙基苯酚)閘極絕緣層表面的極化水分子缺陷會增加五苯環通道的導電度所致。
最後，我們提出以兩階段式 SU8/聚乙烯醇雙層舉離黃光技術製作出具短通道的有機薄膜電晶體來改善上接觸式元件結構之電性特性。其研究結果顯示，藉由此雙層舉離黃光技術五苯環通道層不僅不受聚乙烯醇緩衝層塗佈和去離子水舉離過程的傷害，且能製作出通道長度僅為五微米的上接觸式結構元件。此外觀察發現其起始電壓和載子移動率分別受到汲極誘導能障降低效應及接觸電阻在總電阻內比例的增加所影響，因此其隨著元件通道縮小而降低。

In this thesis, we study on the device fabrication and electrical performance analysis and improvement of pentacene-based organic thin-film transistors (OTFTs) with top-contact (TC) structure. First, we demonstrate top-contact pentacene-based OTFTs fabricated by inserting a PQ carrier injection layer between the pentacene channel layer and S/D electrodes to improve electrical performance of the OTFTs. The PQ film surface presumed to be discrete with
discontinuous islands on pentacene channel layer, this results in the formation of two different junctions at Au/pentacene and Au/PQ/pentacene interface. Compared to device without a PQ layer, the inserted 5-nm-thick PQ layer can enhance the IDS and μFE by 225% and 179%, respectively. The improvements are attributed to the reduction of hole injection barrier and tunneling process at the Au/pentacene interface, which can be confirmed by the reduced contact resistance measured at linear region.
Second, we demonstrated the co-evaporation scheme is used for evaporating
tetrafluorotetracyanoquinodimethane (F4TCNQ) and pentacene simultaneously to form an F4TCNQ-doped pentacene interlayer between the Au S/D electrodes and the pentacene channel layer of TC pentacene-based OTFTs and, thus, improve the OTFT performance. Compared with a pentacene-based OTFT without an F4TCNQ-doped pentacene interlayer, OTFTs with an 5 nm thick and F4TCNQ:pentacene ratio of 1:1 showed considerably improved electrical characteristics. The improvements are attributed to the formation of a subdivided barrier and high local conductivity at the Au electrode/pentacene channel interface, which effectively reduced the hole injection barrier. In addition, the dependence of the OTFT performance on the thickness of the F4TCNQ-doped pentacene interlayer is weaker
than that on a Teflon interlayer. A molecular doping-type F4TCNQ-doped pentacene interlayer is a suitable carrier injection layer that can improve the TC-OTFT performance and facilitate obtaining a stable process window. The results are attributed to Teflon is an insulating material with an extremely high resistivity (1018 Ω·cm). When the Teflon interlayer thickness exceeds a critical value, the insulating properties of the interlayer become dominant
and reduce the carrier tunneling probability.
Third, we investigated how continuous bending stress affected the electrical
characteristics of pentacene-based OTFTs with the poly-4-vinylphenol (PVP) gate insulator in a vacuum and ambient air. The OTFT device bent in a vacuum exhibited a decreased on current because the pentacene channel layer was cracked, which obstruct the transport of charge carriers, deteriorating the on current of OTFTs. However, the OTFTs device bent in ambient air exhibited a slightly decreased on current and the greatly increased off current and
subthreshold swing. We presume that the moisture in the air can pass through the pentacene cracks into the interface between the PVP and pentacene layer, yielding the increase in polar moisture traps, and leading to an increase in the conductivity of pentacene.
Finally, we propose a two-step SU8/poly(vinyl alcohol) (PVA) lift-off photolithography scheme for fabricating top-contact pentacene-based OTFTs with small channels. The bilayer of PVA and SU8 will not damage the pentacene channel layer in the lift-off photolithography process used in forming the patterned pentacene channel layer and source/drain metal electrodes. The proposed scheme produces pentacene-based OTFTs with a patterned pentacene channel layer and S/D metal electrodes that prevent fringe current and obtain a
minimum channel length of 5µm. In addition, the μFE and VTH of the pentacene-based OTFTs decrease with the channel length, resulting from the increased proportion of RC in total resistance and drain-induced barrier lowering, respectively.

Abstract (in Chinese)
Abstract
Acknowledgement (in Chinese)
Contents
List of Tables
List of Figures
Chapter 1 Introduction
1.1 Overview of Organic Thin-Film Transistors
1.2 Organic Semiconductor Materials
1.2.1 Polymers
1.2.2 Small Molecules
1.3 Charge Carrier Transport in Organic Semiconductors
1.4 Device Structures and Operation of OTFTs
1.4.1 Device Structures of OTFTs
1.4.2 Operation of OTFTs
1.5 Motivation
1.6 Thesis Organization
Chapter 2 Device Fabrication and Electrical Parameters Extraction
2.1 Materials Selection
2.1.1 Substrate and Gate Electrode
2.1.2 Gate dielectric
2.1.3 Organic Semiconductor Layer
2.1.4 Carrier injection buffer
2.1.5 Source and Drain Electrodes
2.2 Device Fabrication Process
2.3 Measurement and Characterization for OTFTs
2.3.1 Electrical Measurement
2.3.2 Electrical Characterization
2.3.3 Material Characterization
Chapter 3 Performance enhancement of pentacene-based organic thin-film transistors using 6,13-pentacenequinone as a carrier injection interlayer
3.1 Introduction
3.2 Experiments
3.3 Results and Discussion
3.4 Conclusion
Chapter 4 Effects of the F4TCNQ-Doped Pentacene Interlayers on Performance Improvement of Top-Contact Pentacene-Based Organic Thin-Film Transistors
4.1 Introduction
4.2 Experiments
4.3 Results and Discussion
4.4 Conclusion
Chapter 5 Correlation between ambient air and continuous bending stress for the electrical reliability of flexible pentacene-based thin-film transistors
5.1 Introduction
5.2 Experiments
5.3 Results and Discussion
5.4 Conclusion
Chapter 6 The top-contact pentacene-based organic thin-film transistors with short-channel length using two-step SU8/PVA lift-off photolithography process
6.1 Introduction
6.2 Experiments
6.3 Results and Discussion
6.4 Conclusion
Chapter 7 Conclusions and Future Works
7.1 Conclusions
7.2 Future Works
References
Resume (個人簡歷)

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