有机薄膜分子取向影响机理及其电荷传输特性

发布时间：2019-02-18 17:57

【摘要】：有机薄膜晶体管凭借其加工工艺过程简单、制造成本低廉、有望实现柔性卷到卷(roll-to-roll)大面积生产等特点,已在柔性显示、柔性存储、射频识别(RFID)标签、传感器等领域展现出巨大的应用前景。但是目前有机半导体材料的载流子迁移率普遍仍处于较低水平,还无法满足微电子器件的要求。研究表明,有机半导体材料的分子取向对材料内部的电荷传输起着决定性作用,不同器件对于分子取向的要求也不尽相同。分子取向取决于有机分子间相互作用力、有机分子与绝缘层间相互作用力二者之间的竞争关系,是可以通过改变外界条件进行调控的。因此,在原子水平上深入理解有机薄膜沉积生长过程中分子取向影响机理及电荷传输特性,是提升有机半导体器件性能的核心问题。本学位论文以典型的并五苯有机薄膜晶体管有源层的沉积制造为研究对象,通过仿真模拟-理论计算-实验验证相结合的方法,从分子间相互作用力的角度揭示了有机薄膜初始生长过程中分子取向的形成和转变机理,探讨了工艺参数对分子取向的影响规律,对不同工艺参数下有机薄膜的电荷传输性质进行了理论预测,给出了合理的工艺参数区间,并通过实验进行了验证。论文主要研究工作和创新点包括：结合理论分析和分子动力学模拟,研究了并五苯薄膜生长过程中分子由平行取向转变为直立取向的现象,得到了取向转变临界分子数,揭示了分子取向是由并五苯分子间相互作用能、并五苯分子与基底间相互作用能二者之间的强弱关系控制的,基底表面的改变可调控二者的强弱关系。基于分子动力学方法系统地探讨了基底温度和外加电场对并五苯薄膜分子取向的影响规律,确定了最优的基底温度区间,以及合理的电场方向和强度。研究发现,低温时并五苯分子聚集形成具有直立取向、有序且热稳定的团簇；高温时并五苯分子将形成具有平行取向的无序团簇。平行于并五苯分子长轴或短轴的外加电场有助于分子直立在基底表面；垂直于并五苯分子平面的外加电场将使得分子平躺在基底表面。基于Marcus电荷传输理论,结合分子动力学方法,密度泛函理论和动态蒙特卡洛模拟研究了并五苯单晶和团簇的电荷传输性质,通过计算不同基底温度下并五苯薄膜载流子迁移率的变化趋势,得到了基底温度的合理范围。通过真空蒸镀实验,测试了不同基底温度下制备的并五苯OTFT器件的载流子迁移率,建立了基底温度与器件迁移率的关系,验证了仿真模拟和理论计算的结果。
[Abstract]:Organic thin film transistors have been widely used in flexible display, flexible storage, radio frequency identification (RFID) tags, due to their simple processing process and low manufacturing cost. Sensors and other fields show great application prospects. However, the carrier mobility of organic semiconductor materials is still at a low level, which can not meet the requirements of microelectronic devices. The results show that the molecular orientation of organic semiconductor materials plays a decisive role in the charge transport within the materials, and the requirements of molecular orientation are different for different devices. Molecular orientation depends on the interaction between organic molecules. The competitive relationship between organic molecules and insulating layers can be regulated by changing the external conditions. Therefore, understanding the mechanism of molecular orientation and charge transport during the deposition and growth of organic thin films at atomic level is the core problem in improving the performance of organic semiconductor devices. In this dissertation, the deposition of active layer of typical pentaben organic thin film transistors is studied. The method of simulation, theoretical calculation and experimental verification is used. The formation and transformation mechanism of molecular orientation during the initial growth of organic thin films are revealed from the point of view of intermolecular interaction forces. The influence of process parameters on molecular orientation is discussed. The charge transport properties of organic thin films under different process parameters are predicted theoretically and the reasonable range of process parameters is given and verified by experiments. The main research work and innovations are as follows: combining with theoretical analysis and molecular dynamics simulation, the phenomenon of molecular transformation from parallel orientation to vertical orientation during the growth process of penta-benzene thin film is studied, and the critical number of orientation transition molecules is obtained. It is revealed that the molecular orientation is controlled by the interaction energy between pentabenzene and the substrate, and the change of the substrate surface can regulate the strong or weak relationship between them. The effects of substrate temperature and applied electric field on molecular orientation of penta-benzene films were systematically discussed based on molecular dynamics method. The optimum substrate temperature range and the reasonable electric field direction and intensity were determined. It was found that clusters with vertical orientation, order and thermal stability were formed at low temperature and disordered clusters with parallel orientation at high temperature. The external electric field parallel to the long axis or short axis of pentabenzene helps the molecule to stand upright on the surface of the substrate, and the applied electric field perpendicular to the plane of pentabenzene will cause the molecule to lie flat on the surface of the substrate. Based on the Marcus charge transport theory, the density functional theory and the dynamic Monte Carlo simulation, the charge transport properties of penta-benzene single crystals and clusters were studied. The reasonable range of substrate temperature is obtained by calculating the trend of carrier mobility at different substrate temperatures. The carrier mobility of pentaben OTFT devices prepared at different substrate temperatures was measured by vacuum evaporation experiments. The relationship between substrate temperature and device mobility was established, and the results of simulation and theoretical calculation were verified.
【学位授予单位】：华中科技大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TN304;TN321.5

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