兰州大学机构库 >物理科学与技术学院
Alternative TitleStudies and Fabrication of Organic Field Effect Transistor
Thesis Advisor张福甲
Degree Grantor兰州大学
Place of Conferral兰州
Degree Name博士
Keyword有机场效应 晶体管 有机电子学

有机场效应晶体管(OFET)也称有机薄膜场效应晶体管(OTFT),它是有机电子学的重要研究课题之一。由于它具有良好的发展前景和商用价值,因而具有重要的研究意义,为此,本文从理论上、实验上、模拟上分别对 OFET进行了相关的研究。

文中首先回顾了 OFET 的发展历史,评述了OFET发展过程中所存在的问题及 各阶段的研究重点。除此之外,对现阶段 OFET 存在的问题、研究热点及未来的发展方向作了总结。这些热点研究内容中的一部分也是本文的重要研究对象,如 绝缘层和半导体间的相互作用对 OFET 性能的影响等。 其次,概述了各种 OFET 中常用的材料,包括有机场效应半导体材料、电极材料和绝缘层材料等。其中着重对有机场效应材料进行了分析,并根据有机分子的大小将之分为有机小分子、有机低聚物、有机高聚物,根据有机分子对电子和 空穴传输能力的不同将之分为 p 型、n 型、双极型分别进行了论述。此外,对各 种电极材料和绝缘材料也作了综述。 阐释了 OFET 的工作机理,这分别是从 OFET 结构、有机半导体中的载流子 传输机理、OFET 的 I-V 公式推导等方面进行阐述的。由于不同的载流子传输方式 是有机、无机半导体器件的重要差别所在,而目前关于 OFET 的载流子传输模 型有多种,为此本文对此作了分析与归纳。另一方面,OFET 是工作在增强模式 下,这也区别于常见的无机单晶 FET,文中对此也进行了论述,并推导了相关的 电流电压特性方程。 制备了几种不同结构的 OFET(包含顶部电极结构、底部电极结构等),确定了相关的工艺条件。对OFET 中常用的源漏电极材料 Au 进行了替代,并采用ITO作为OFET的源漏电极,所制器件性能良好,文中对相关机理进行了分析。为充分利用 ITO 材料的优点,本文还在采用 ITO 载玻片为衬底的基础上制备了一种新的器件结构――“倒置的顶电极结构”。其中,在 ITO 载玻片形成源漏电极是其关 键步骤,为此本文研究了其光刻条件。由于该结构 OFET 具有一些明显区别于顶 电极结构和底电极结构 OFET 的特征,使得它在某些特定场合下,如发光(双极 型)OFET 等领域,具有一定的优势。 研究了绝缘层对 OFET 性能有影响的一些因素,如绝缘层厚度、绝缘层/有机半导体层间的相互作用等。实验表明,绝缘层厚度不但影响沟道载流子浓度,而 且还通过感应出的载流子对半导体层中定域态的填充机制和 Poole-Frenkel 机制影响了载流子迁移率的大小;对绝缘层/半导体层表面界面电子状态的研究则表明, 从绝缘层扩散至半导体层中的O元素对表面界面处的各元素电子状态影响非常重 要,它很可能是导致 OFET 性能劣化的因素之一。 后对OFET 进行了模拟,分析了一些参数对 OFET 性能的影响,其中着重对源漏电极处的接触电阻进行了分析,得出了一些有意义的结果。分析表明,当 器件载流子迁移率升到 10-1cm2/V.s 数量级时,源漏区的接触电阻对 OFET 的影响 已不可忽略,它对 OFET 的“有效漏压”,沟道电流等均可造成较大影响。为此,制作过程中,必须严格控制源漏区接触电阻的大小。分析表明,只有当接触电阻 低于本底电阻(正偏时施加的高栅压、漏压为零时的沟道电阻)的 1/15 时,这种影响才可忽略不计。另一方面,若接触电阻无可避免,为保证 OFET 的特性曲 线,可酌情考虑降低器件的工作电压,但这是以牺牲 OFET 部分性能为代价的。

Other Abstract

Organic Filed Effect Transistor (OFET), namely Organic Thin-film Filed-effect Transistor (OTFT), is one of the most important research subjects in organic electronics. Considerable improvements have been achieved since it was invented, and it is hopefully to be applied to many fields in commercial scale. Concerning about this, the study on OFET is quite significant. In this thesis, it was performed in theory, by experiment and simulation, respectively.  Firstly, the evolution history of OFET was reviewed. The different problems appeared at different stages of OFET were summarized. The existing questions and hot topics for the future study were also discussed. In fact, some of them, e.g., the influence of interaction of semiconductor/insulator on OFET performance, became the important subjects investigated in the thesis. Then, the materials widely used in OFET, including organic field-effect material, electrode material and insulator material, were summarized in detail, in which the organic field-effect material was classified into n-type, p-type and bipolar-type to be carefully analyzed, respectively.  The operation principle of OFET was demonstrated mainly from the following two aspects. First, the transport mechanism of carrier in organic semiconductor was discussed. It is commonsense that the different transport mechanism of carrier is the primary factor which differentiates organic semiconductor from inorganic semiconductor. Thus there were many transport mechanisms for organic semiconductor had been proposed and they are carefully generalized and analyzed. Second, the I-V equations of OFET were deduced. As we know, OFET is operated under enhancement mode, distinguished from the inversion mode of other Si-based Field-effect transistors, resulting in the different I-V equations. In this article, the principle of OFET and I-V equations were analyzed and deduced. Several kinds of OFETs with different configurations were fabricated. During the process, ITO was employed as the substitute of Au to act as the Source/Drain materials. It didn’t deteriorate OFET performances and the principle was demonstrated. Moreover, in order to farthest utilize the ITO performance, the photolithography process of ITO thin film was studied, which is one crucial step to fabricate one new configuration, namely “reversed top-contact” OFET. This kind of OFET has some advantages than “top-contact” and “bottom-contact” OFET,it is potentially to be used in light-emitting OFET (bipolar), etc.  The influence of insulator on OFET was also studied, which aimed to analyze the influence of insulator layer thickness, and of insulator/semiconductor interaction on the OFET’s performances. Experimental results showed that, when insulator thickness decreased, both carrier density and electric filed in semiconductor would be enhanced greatly, which further changed the carrier mobility via traps-filled mechanism and Poole-Frenkel mechanism, respectively. Besides this, the surface and interface electron states of insulator/semiconductor were characterized. The O element diffused from insulator layer was proved to have great bearing on the chemical shift of other elements, which may degrade the performance of OFET.  Finally, the numerical simulation of OFET was also performed, focusing its analysis on the influence of “contact resistance (RC)” on OFET performances. Analyzed results showed that when carrier mobility exceed 10-1 cm2/V.s, great negative effect will be brought about by RC. To avoid this effect, RC should be reduced to one fifteen of the intrinsic resistance (the Channel Resistance when the maximum Gate voltage, zero Drain voltage were applied). In addition, if the contact resistance is inevasible, it seems a good measure to reduce the operating voltage to guarantee the basic I-V characteristic of OFET, while this will degrade the performance of OFET. 

Document Type学位论文
Recommended Citation
GB/T 7714
陈金伙. 有机场效应晶体管的研究与试制[D]. 兰州. 兰州大学,2006.
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