噴墨印製有機薄膜電晶體及其閘極之工程設計與可靠度分析研究; Gate Stack Engineering of Inkjet-Printed Organic Thin Film Transistors and Their Reliability Study

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题名:	噴墨印製有機薄膜電晶體及其閘極之工程設計與可靠度分析研究;Gate Stack Engineering of Inkjet-Printed Organic Thin Film Transistors and Their Reliability Study
作者:	駱伯遠;Po-Yuan Lo
贡献者:	電機工程研究所
关键词:	閘極工程;有機薄膜電晶體;可靠度分析;Reliability Testing;Gate Engrieering;Organic Thin Film Transistors
日期:	2010-11-04
上传时间:	2011-06-04 16:13:11 (UTC+8)
出版者:	國立中央大學
摘要:	軟性電子在十年內的發展中以有機材料為主；在多項的研究中以有機半導體材料poly-3-hexyl-thiophene (P3HT)最被重視，並被廣泛應用到有機薄膜電晶體中，其元件的載子傳輸速率為0.01 cm2/V-s，但在實際應用上仍嫌太低，因此如何改善有機電晶體特性，並提升電晶體的可靠度，已是當前最重要的課題之一。為提升單閘極有機電晶體的元件特性，元件的接觸電阻必須先改進，利用高穩定性的pentacene為有機半導體層，使用該材料來評估當源極與汲極電極位置改變後，是否可因有機半導體與電極的接觸面積增大，而降低元件的接觸電阻。利用低接觸電阻的元件結構，來分析噴墨印製單閘極P3HT有機電晶體，評估使用噴墨印製法得到圖形化的有機半導體層，是否可有效提升P3HT有機電晶體的電流開關比。為使噴印製成更具效率，溶液的成份與噴墨參數都予以調整，再將此噴墨技術用於全印製的有機電晶體。然而，使用噴墨印製法製作的有機絕緣層，會因為單顆噴頭的印製限制，使絕緣層的薄膜粗糙度上升；因此應用該薄膜於有機電晶體內，會因為絕緣層粗糙度過大，而降低閘極的控制能力，使元件的電流開關比降低2個order。為解決印製絕緣層表面均勻度不佳的問題，以整合旋轉塗佈有機絕緣層，搭配噴墨印製有機半導體於有機薄膜電晶體，進行電晶體特性分析與研究討論。　藉由此穩定的低接觸電阻的電極結構，分析單閘極與雙閘極P3HT 有機電晶體之電性。該結果顯示雙閘極P3HT 有機電晶體表現較單閘極 P3HT 有機電晶體有更突出的特性，如: 透過電場控制以改變元件的操作模式。除了變化閘極結構外，也可更改有機薄膜電晶體的絕緣層，來達到元件特性變化目的；並應用此有機絕緣層本質的概念，導入具有施體/受體缺陷互相堆疊的絕緣層於電晶體中，進一步使兩種缺陷相互補償，進而降低元件操作時所造成的不穩定。利用光等外在因素進行元件電性衰退分析，並評估使用堆疊絕緣層的方式，來改善此衰退現象。光照射之可靠度分析中，堆疊絕緣層於P3HT 有機電晶體可使元件不具有光敏感的特性。可能的抑制機制將利用電流-電壓與電容-電壓的方法分析並予以佐證。除了光的施加可造成元件的特性衰退外，品質不佳的絕緣層，亦會因閘極偏壓的施加而導致絕緣層的破壞，並影響元件電特性。為了增加元件的良率，以非破壞性分析(例如:超音波)進行絕緣層的鑑定，以利挑選缺陷較少的有機體絕緣層來製作元件。在這個研究中，單閘極P3HT有機電晶體的物理限制將會分析，並以施加電位能的方式加以突破;該突破特點，係以利用雙閘極電晶體的結構予以實現。此外，有機薄膜電晶體的特性，可利用絕緣層堆疊時所造成的施體/受體的補償效應，予以調整元件特性並增加元件於光、電與熱等因數下的穩定性。整合論文內的物理概念，提出一種改善多晶有機材料的方法，並予以增加多晶材料的晶粒成長；同時以堆疊犧牲層的方式進行多晶材料的圖形化，藉以達到元件載子傳輸率達0.1 cm2/V-s。 The development of flexible electronics has been focused on the searching of organic materials in the past decade. An organic semiconductor material, poly-3-hexyl-thiophene (P3HT) has been found as a practical semiconductor material. The P3HT used in organic thin film transistors (OTFTs) typically has a carrier mobility of 0.01 cm2/V-s. However, the reliability of P3HT OTFTs needs further improvement for practical application and also needs to be tested under light irradiation. The low contact resistance device structure was first studied with a pentacene OTFTs of single gate devices and the thermal stability of the devices was evaluated. Base on the device structure, an inkjet printing technique is introduced to print both the semiconductor and the dielectric layers. In the printed semiconductor layer, the ION/OFF of P3HT OTFTs can be increased through a restriction of the printed area. In the printed dielectric layer, the rough dielectric surface reduces the gate controllability on the channel. The poor gate modulation dose reduces the ION/OFF by 2 orders of magnitude on the P3HT OTFTs. Therefore, spin coated dielectric film is suggested to work with inkjet printed P3HT OTFTs. An interesting result of the single gate OTFTs still shows a limitation on modulated device performance of Vth, ION, and operation power. Therefore, a double gate modulation scheme is proposed to control the Vth, ION, and operation power. Other improvements on OTFTs include an organic dielectric modification and a stacked gate dielectric layer. Either the dielectric modification or the stacked dielectric layers show the change of dielectric bulk property, which influences the carrier transportation in the P3HT. To explain a possible mechanism on this improvement, compensation between acceptor-like traps with donor-like traps in the dielectric layers is proposed. The postulate is proven by the I-V characteristics and C-V. For the reliability study, the influence of the photo generated extract electron-holes in the semiconductor are analyzed on the stacked gate dielectrics of the P3HT OTFTs. The influence of the photo generation electron-holes and the traps compensation are discussed systematically. The other reliability issue on single gate dielectric P3HT OTFTs is the introduction of electric stress that causes a defect formation in the poor quality dielectric layer. The defect can be investigated with a non-destructive scanning acoustic microscope (SAM). In order to improve the yield of OTFTs, the gate dielectric film can be inspected by SAM before integrating with the OTFTs. To reach a high performance OTFTs, the knowledge of stacked gate organic layer applied on the interface treatment. The treatment further enhances the grain growth of the polycrystalline thiophene from the electrode and improves the mobility to as high as 0.1 cm2/V-s.
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