【作者】 袁广才；

【导师】 徐叙瑢；

【作者基本信息】 北京交通大学 ， 光学， 2009， 博士

【摘要】 本论文就如何改善和提高pentacene基有机薄膜晶体管的性能以及性能改善的机理进行了研究。主要针对现有pentacene基OTFT器件所存在的问题,研究了栅极绝缘层的种类、界面修饰层对器件性能影响机制、pentacene薄膜的相态变化、结晶对器件性能影响的规律、pentacene薄膜晶粒的大小对OTFT器件性能的影响、小曲率半径的弯曲对OTFT器件性能影响的机理以及室温空气环境下实现C₆₀/pentacene基OTFT器件的双极型特性及对器件性能改善等热点问题。本论文针对上述热点问题,主要研究工作如下:第一,对OTFT器件中有机半导体层与栅极绝缘层之间界面处的电荷陷阱对OTFT器件性能的影响进行了研究。利用不同种类的界面修饰材料对绝缘层表面进行修饰来改善OTFT器件的性能,找出最佳界面修饰层材料,得出OTFT器件性能改善原因。通过采用不同的界面修饰材料处理栅极绝缘层的表面,如octadecyltrichlorosilane和phenyltrimethoxysilane,得到OTFT器件的半导体有源层薄膜的晶型转变机制以及其界面处电荷载流子的陷阱态密度变化引起的OTFT器件沟道电阻的变化,以及在栅极电压作用下,OTFT器件电荷载流子在陷阱中的运动机制,进而得到改善OTFT器件性能的有效途径。第二,研究了栅极绝缘层的介电常数以及绝缘层的种类对OTFT器件性能的影响。主要针对硅基无机绝缘层、有机绝缘层、有机/无机复合栅极绝缘层的OTFT器件性能进行研究,并比较不同种类的绝缘层对pentacene有源层薄膜生长机制的影响,找出影响OTFT器件性能变化的因素,从而得出最佳的器件制备方案。在本文中,OTFT器件所使用的无机栅极绝缘层主要是通过射频磁控溅射、电子束热蒸发和热氧化等方法制备得到的,如:SiO₂、SiNx和SiOxNy等无机绝缘层材料。有机栅极绝缘层材料主要是通过溶液旋涂的方法得到的,如poly（4-vinylphenyl）（PVP）等有机绝缘材料。采用复合的PVP/SiO₂作为器件的栅极绝缘层时,器件性能得到很大改善。通过对不同修饰材料处理的复合PVP/SiO₂以及单一的SiO₂栅极绝缘层的OTFT器件性能对比研究中,很好的解释了备受广大研究学者们争议的pentacene薄膜的晶粒尺寸“大”还是“小”对OTFT器件性能更加有利的问题。第三,为了研究OTFT器件在受力作用以及弯曲的情况下器件内部载流子的传输机制,主要针对以带有ITO导电层的PET（polyethylene terephthalate）为衬底,以PVP为绝缘层的全有机柔性OTFT器件性能进行了研究。通过对柔性OTFT器件的受力研究得到,当对OTFT器件进行小曲率半径反复弯曲后,导致器件性能降低。其主要原因是,pentacene薄膜在反复的变化弯曲作用后,薄膜内部发生了微观结构的相转变过程,从而导致器件性能的降低。这对OTFT器件在柔性显示方面的应用提供了很好的理论依据。第四,为了更好的研究OTFT器件中电荷载流子输运情况对器件性能的影响以及未来OTFT在数字集成电路自补偿反相器中的应用,本文还制备了复合C₆₀/pentacene有源层的OTFT器件,并对其双极型特性进行了研究。首先,通过采用1nm的超薄LiF作为电极修饰层,来调节器件的注入特性,器件实现了很好的双极型特性;其次,为了进一步优化器件的双极型特性以及改善器件内部载流子的传输复合机制。本文在原有器件的基础上,在C₆₀和pentacene有源层之间引入一层超薄的N,N’-bis-（1-naphthyl）-N,N’-biphenyl-1,1’-biphenyl-4,4’diamine电子阻挡层,用以来调节器件内部载流子的分配以及抑制异种半导体材料对异种电荷的俘获。从而,来改善双极型OTFT器件内部电荷载流子的传输,进而改善OTFT器件的性能。更多还原

【Abstract】 In this doctoral dissertation,the ways to enhance and improve the performance of pentacene-based OTFTs（organic thin film transistors） are investigated by using different kinds of gate insulators and different interface modified-layers,and by controlling the phase-transformation and crystallization of pentacene polymorphic film and the particle size of pentacene grains.The mechanism of enhancements is explained. In addition,the effect of bending-strain on structure and electrical characteritics of the flexible devices,and the operation and improvement of ambipolar OTFTs with C₆₀/pentacene active layer at room temperature and atmosphere are studied too.The details as follows:Firstly,in order to investigate the effect of defect trapping at the interface between the semiconductor active layer and the gate insulator layer of OTFTs,the surface of gate insulator is treated by using different interface modified-layers,such as octadecyltrichlorosilane（OTS） and phenyltrimethoxysilane（PhTMS）.The microstructure phase-transformation mechanism of the pentacene polymorphic film induced by modified-layers is investigated,and then the carrier transport mechanism in trap states under gate-source voltage is explained.It is the good way to improve the performance of OTFTs.Secondly,in order to study further the characteristics of OTFTs,we also investigate the effect of dielectric constant and kinds of gate insulator layers on the performance of OTFTs.The works mainly focus on OTFTs with different gate insulators including inorganic,organic and organic/inorganic complex insulator.The effect of different insulators on the growth mechanism of pentacene thin film is compared.Inorganic gate insulator layers,such as SiO₂、SiNx and SiOxNy,of OTFTs are fabricated by ratio frequency（rf） magnetron sputtering,electron beam evaporation and thermal oxidation methods,respectively.The organic gate insulator layers such as poly（4-vinylphenyl） （PVP） are fabricated by spin coating method.It is found that the performance of OTFTs with PVP/SiO₂ complex gate insulator is improved greatly.The hot dispute about the effect of pentacene particle size on the performance of OTFTs is explained through the comparation of OTFTs with treated PVP/SiO₂ gate insulator and with single SiO₂gate insulator.Thirdly,in order to investigate the effect of bending-strain on the performance of flexible OTFT devices and the carrier transport mechanism in bending-strained devices, the flexible pentacene-based OTFTs with bottom gate top conduct structure are fabricated on the flexible ITO-PET substrate.PVP,pentacene and Au are used as the gate insulator,the active layer and the source-drain（S-D） electrode,respectively.When OTFT devices are repeatedly bended with small radius of curvature about 0.9-1.1 cm, the device performance has been reduced.The main reason is that bending-strain induces the microstructure phase-transformation of the pentacene polymorphic film from "thin-film phase" to "triclinic bulk phase",which results in the performance degradation of OTFTs.These results for the application of OTFT device at the flexible display field provide a good theoretical and experimental basis.Finally,in order to study the carrier transport mechanism of OTFTs and the application of OTFTs at digital integrated circuit complementary inverter,the ambipolar characteristics of complex C₆₀/pentacene-based OTFTs are investigated.A good am-bipolar performance of OTFTs is achieved at room temperature and atmosphere by using an ultra-thin electrode modified-layer（LiF） between pentacene and S-D electrodes to adjust the injection characteristics of charge carriers.Then in order to further optimize the ambipolar characteristics of devices and improve the carrier transport of OTFT devices,an ultra-thin electron blocking-layer N, N’-bis-（1-naphthyl）-N,N’-biphenyl-1,1’-biphenyl-4,4’diamine（NPB） is inserted between C₆₀ and pentacene at the basis of the above mentioned devices to adjust the distribution of charge carriers and to limit charge carriers captured by different type semiconductor materials.Therefore,the carrier transport in the am-bipolar devices is improved and results in the good performance of OTFT device.更多还原