聚合物介质材料电荷捕获输运特性和机理的研究

发布时间：2018-08-12 17:29

【摘要】：聚合物介质材料的电荷输运特性决定介质的空间电荷积聚特性。空间电荷积聚会造成介质中电场畸变,当介质中的局部电场达到一定阈值,电-机械应力、或电荷脱陷过程中释放的能量会造成材料的老化或劣化、甚至击穿,影响电力设备、航天器的安全运行和寿命。介质的电荷输运特性决定着材料的空间电荷积聚水平,然而一些高阻聚合物介质材料的电导机制、空间电荷形成与传导等电荷输运特性和机理尚不完全清楚。因此,有必要深入系统地研究聚合物介质材料电荷输运特性和机理。本文研究了聚合物介质材料中存在单一分立能级陷阱、多重分立能级陷阱和指数能级分布陷阱时,介质中的电荷入陷/脱陷动力学响应特性,稳态载流子有效迁移率及其随陷阱分布、电荷密度、温度和电场的变化关系,及空间电荷限制电流(SCLC)特性。测试了电子束辐射后聚酰亚胺(PI)材料的二维表面电位衰减(SPD)特性,建立了SPD模型,计算了材料的表面和体电荷输运参数。采用双极性电荷输运模型(BCT)仿真计算了SPD过程中的表面电荷衰减、体内电荷和电场分布时空演变特性。研究了高温强场下PI薄膜的SCLC电流特性、及不同SCLC电流区的电荷输运特性和机理。首先,研究了陷阱捕获效应对介质电荷入陷/脱陷动力学响应特性、电荷输运特性和SCLC电流的影响规律。提出了库仑势垒电荷捕获修正模型,得到了陷阱捕获截面和捕获概率解析表达式。推导了载流子有效迁移率和SCLC电流随陷阱能级、载流子迁移率边缘、温度、电荷密度和电场变化的解析表达式。其次,研究了温度在298-338K、电场强度小于5.4×107Vm-1时,厚度为27μm PI材料的SPD特性和电荷输运特性。考虑材料的表面传导和体传导过程,建立了结合遗传算法的二维SPD模型,计算得到了不同温度下PI材料的视在表面电阻率、体欧姆电阻率和载流子有效迁移率,及视在表面电阻率和体欧姆电阻率的活化能和材料的深陷阱能级。再次,采用BCT模型仿真研究了PI材料在室温不同初始表面电位时的SPD特性和空间电荷时空演变特性,提取了材料的电荷输运参数。BCT模型结合遗传算法计算得到了不同初始表面电位时材料的SPD曲线,得到了经过优化的松弛极化和电荷输运参数。将优化过的参数带入BCT模型中,计算得到了SPD过程中材料的表面沉积电荷、体内自由电荷分布、陷阱电荷分布和电场分布随时间的变化特性。接着,研究了多重分立能级陷阱和指数能级分布陷阱中电荷动力学响应特性,及稳态载流子有效迁移率随陷阱分布、电荷密度和温度等的变化特性。通过理论推导和数值仿真研究了电荷入陷/脱陷动力学响应特性,得到了等效电路模型。推导得出了稳态时陷阱电荷密度与自由电荷密度的关系式,得到了指数能级分布陷阱中载流子有效迁移率的解析表达式。最后,研究了在高温(593-673K)、强场(107-3×108Vm-1)条件下,厚度为1.4μm PI薄膜的电荷输运特性和空间电荷分布特性。研究PI薄膜的单一分立能级陷阱和指数能级分布陷阱SCLC电流特性,计算得到了PI材料的陷阱分布参数。然后,计算得到了介质的准费米能级和载流子有效迁移率随电荷密度和温度的变化关系,以及不同SCLC电流区介质中的电荷密度和电场随位置的分布特性。
[Abstract]:Charge transport characteristics of polymer dielectric materials determine the space charge accumulation characteristics of the medium.Space charge accumulation will cause electric field distortion in the medium.When the local electric field in the medium reaches a certain threshold,the electrical-mechanical stress or the energy released during the process of charge collapse will cause aging or deterioration of the material,even breakdown,and affect the power equipment. Safe operation and lifetime of spacecraft. Charge transport properties of dielectric determine the level of space charge accumulation of materials. However, the conductivity mechanism, space charge formation and conduction characteristics and mechanism of some high-resistivity polymer dielectric materials are not completely clear. Therefore, it is necessary to study the charge of polymer dielectric materials thoroughly and systematically. Transport properties and mechanisms. The dynamic response of charge trapping/detachment, the effective mobility of steady-state carriers and its dependence on trap distribution, charge density, temperature and electric field are investigated in polymer media with single discrete level traps, multiple discrete level traps and exponential level distribution traps. Space Charge Limited Current (SCLC) Characteristic. The two-dimensional surface potential attenuation (SPD) characteristics of polyimide (PI) materials irradiated by electron beam were measured. The SPD model was established and the surface and bulk charge transport parameters were calculated. The surface charge attenuation, internal charge and electrical properties were simulated by bipolar charge transport model (BCT). The characteristics of SCLC current and charge transport in different SCLC current regions are studied. Firstly, the effects of trap trapping on the dynamic response of dielectric charge entrapment/detachment, charge transport and SCLC current are studied. The analytical expressions of trap capture cross section and trap probability are obtained by modifying the model. The analytical expressions of carrier effective mobility and SCLC current with trap energy level, carrier mobility edge, temperature, charge density and electric field are derived. Secondly, the thickness of 27 micron PI material is studied when the temperature is 298-338K and the electric field intensity is less than 5.4 *107Vm-1. SPD characteristics and charge transport properties of PI materials are studied. Considering the surface conduction and bulk conduction process of PI materials, a two-dimensional SPD model based on genetic algorithm is established. The apparent surface resistivity, bulk ohmic resistivity and carrier effective mobility of PI materials at different temperatures, and the activation energies of apparent surface resistivity and bulk ohmic resistivity are calculated. Thirdly, the SPD characteristics and space-time charge evolution of PI materials at different initial surface potentials at room temperature are simulated by BCT model. The charge transport parameters are extracted. The SPD curves of PI materials at different initial surface potentials are obtained by BCT model and genetic algorithm. The relaxation polarization and charge transport parameters are obtained. The surface deposition charge, the free charge distribution, the trap charge distribution and the electric field distribution in the SPD process are calculated by introducing the optimized parameters into the BCT model. The dynamic response characteristics of charge trapping/detachment are studied by theoretical derivation and numerical simulation, and the equivalent circuit model is obtained. The relationship between trap charge density and free charge density is deduced. Finally, the charge transport and space charge distribution characteristics of PI thin films with thickness of 1.4 micron at high temperature (593-673K) and high field (107-3 *108Vm-1) are studied. The current characteristics of single discrete level trap and exponential level distribution trap SCLC of PI thin films are studied. The trap distribution parameters of PI material are calculated. Then, the relationship between the quasi-Fermi level and carrier effective mobility with charge density and temperature, and the distribution characteristics of charge density and electric field with position in different SCLC current regions are obtained.
【学位授予单位】：西安交通大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TM21

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