基于表面势的非晶铟镓氧化锌薄膜晶体管紧凑模型的研究
发布时间：2018-09-17 13:50
【摘要】：以非晶铟镓氧化锌(a-IGZO)为代表的非晶金属氧化物半导体被视为下一代薄膜晶体管(TFTs)技术的有力候选者。在多个产业领域,特别是有源矩阵有机发光二极面板(AMOLED)与柔性电路,a-IGZO TFTs有着广阔的应用前景。a-IGZO TFTs工作的物理机制不同于早期的硅基器件。基于其独特的物理机制,建立紧凑模型以理解材料创新对TFTs电学性能的影响,并最终用于辅助集成电路的设计,对促进和发展AMOLED和集成电路产业有着深远意义。本文的主要内容是分析a-IGZO TFTs的物理机制,考虑载流子简并的情况,建立基于表面势的a-IGZO TFTs直流(DC)和电容紧凑模型,并使模型具备嵌入电路仿真器的条件。分析材料的能带结构与带隙缺陷,为建立数学模型提供了清晰的理论依据。由于电负性的差异,a-IGZO的导带由铟离子的s轨道相互交叠构成,价带由氧离子的2p轨道构成,导致a-IGZO导带附近的带尾局域态密度要远小于氢化非晶硅(a-Si:H)等共价半导体。同时,a-IGZO的价带顶附近存在高密度深缺陷态,易使费米能级钉扎而难以移动至价带附近,因而a-IGZO TFTs多见于n型器件。结合这两点可以说明,在a-IGZO TFTs中,施加足够正的栅压就可使费米能级进入导带。因此,提出的模型必须考虑简并传导机制。基于理论分析,本文指明了玻尔兹曼统计的局限性,给出适用于非简并和简并状态的自由电荷和陷阱电荷浓度公式。结合泊松方程和高斯定理,运用数学变换和Lambert W函数,非迭代地求解出亚阈值区和积累区的表面势。利用光滑函数与施罗德级数修正,得到了一个完整的、高精度的表面势解析模型。模型结果与数值迭代解进行了比较,绝对误差可控制在10-8V范围内。利用表面势计算结果,基于Pao-Sah双重积分公式,建立了a-IGZO TFTs的直流紧凑模型,包括亚阈值电流与积累区电流。迁移率模型基于实际的载流子传输机制,主要包括陷阱限制传导(TLC)机制和渗流导电(PM)机制两种,其遵循幂律函数关系,并且考虑了声子散射与表面粗糙散射对迁移率的退化。在核心电流模型的基础上,融入了载流子速度饱和与沟道长度调制两个高阶效应。基于薄层电荷模型(CSM)与对称正交方法(SQM),求解出各个端电荷的表达式,建立了考虑简并机制的a-IGZO TFTs的电容紧凑模型。该模型满足电荷守恒与电容非互易性的条件,能够很好地描述器件的动态行为。综上所述,提出的a-IGZO TFTs直流模型与电容模型都是以器件内部物理机制为基础的。通过与数值迭代解或实验数据多方面的比较,模型有效性得到了有力的支持。该模型物理概念清晰,算法简单明了,易于嵌入电路仿真器。
[Abstract]:Amorphous metal-oxide semiconductors, represented by amorphous indium gallium oxide (a-IGZO), are considered as potential candidates for the next generation of thin film transistor (TFTs) technology. In many industrial fields, especially active matrix organic light-emitting bipolar panel (AMOLED) and flexible circuit (a-IGZO TFTs) have broad application prospects. The physical mechanism of a-IGZO TFTs is different from that of silicon based devices. Based on its unique physical mechanism, a compact model is established to understand the impact of material innovation on the electrical properties of TFTs, which is ultimately used to assist the design of integrated circuits. It is of great significance to promote and develop the AMOLED and IC industry. The main content of this paper is to analyze the physical mechanism of a-IGZO TFTs, consider the degeneracy of carriers, establish a compact model of a-IGZO TFTs DC (DC) and capacitance based on surface potential, and make the model have the condition of embedded circuit simulator. The energy band structure and band gap defects of the materials are analyzed, which provides a clear theoretical basis for the establishment of mathematical models. Because of the difference in electronegativity, the conduction band of a-IGZO is composed of the S-orbitals of indium ions and the valence band is composed of the 2p orbitals of oxygen ions. The local density of states near the a-IGZO conduction band is much smaller than that of covalent semiconductors such as hydrogenated amorphous silicon (a-Si:H). At the same time, there are high density and deep defect states near the top of valence band of a-IGZO, which makes it difficult to move to the valence band due to the pinning of Fermi level, so a-IGZO TFTs is more common in n-type devices. Combined with these two points, it can be concluded that in a-IGZO TFTs, Fermi level can enter the conduction band by applying enough positive gate voltage. Therefore, the proposed model must consider the degenerate conduction mechanism. Based on theoretical analysis, this paper points out the limitation of Boltzmann statistics, and gives the free charge and trap charge concentration formulas suitable for nondegenerate and degenerate states. Combined with Poisson's equation and Gao Si's theorem, the surface potentials of sub-threshold region and accumulation region are solved without iteration by means of mathematical transformation and Lambert W function. By using smooth function and Schroeder series correction, a complete and high precision analytical model of surface potential is obtained. The results of the model are compared with the numerical iterative solution. The absolute error can be controlled in the range of 10 ~ (-8) V. Based on the results of surface potential calculation and Pao-Sah 's double integral formula, a direct current compact model of a-IGZO TFTs is established, including subthreshold current and accumulative current. The mobility model is based on the actual carrier transport mechanism, including trapping restricted conduction (TLC) mechanism and percolation conductive (PM) mechanism. The mobility model follows the power law function and considers the degradation of phonon scattering and surface rough scattering to mobility. Based on the core current model, two higher order effects, carrier velocity saturation and channel length modulation, are incorporated. Based on the thin layer charge model (CSM) and symmetric orthogonal method (SQM), the expressions of each end charge are solved, and a compact capacitance model of a-IGZO TFTs with degenerative mechanism is established. The model satisfies the condition of non-reciprocity between charge conservation and capacitance, and can describe the dynamic behavior of the device well. In conclusion, the proposed a-IGZO TFTs DC model and capacitance model are based on the internal physical mechanism of the device. Compared with numerical iterative solution or experimental data, the validity of the model is strongly supported. The physical concept of the model is clear, the algorithm is simple and clear, and it is easy to embed the circuit simulator.
【学位授予单位】：暨南大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TN321.5
本文编号：2246120
[Abstract]:Amorphous metal-oxide semiconductors, represented by amorphous indium gallium oxide (a-IGZO), are considered as potential candidates for the next generation of thin film transistor (TFTs) technology. In many industrial fields, especially active matrix organic light-emitting bipolar panel (AMOLED) and flexible circuit (a-IGZO TFTs) have broad application prospects. The physical mechanism of a-IGZO TFTs is different from that of silicon based devices. Based on its unique physical mechanism, a compact model is established to understand the impact of material innovation on the electrical properties of TFTs, which is ultimately used to assist the design of integrated circuits. It is of great significance to promote and develop the AMOLED and IC industry. The main content of this paper is to analyze the physical mechanism of a-IGZO TFTs, consider the degeneracy of carriers, establish a compact model of a-IGZO TFTs DC (DC) and capacitance based on surface potential, and make the model have the condition of embedded circuit simulator. The energy band structure and band gap defects of the materials are analyzed, which provides a clear theoretical basis for the establishment of mathematical models. Because of the difference in electronegativity, the conduction band of a-IGZO is composed of the S-orbitals of indium ions and the valence band is composed of the 2p orbitals of oxygen ions. The local density of states near the a-IGZO conduction band is much smaller than that of covalent semiconductors such as hydrogenated amorphous silicon (a-Si:H). At the same time, there are high density and deep defect states near the top of valence band of a-IGZO, which makes it difficult to move to the valence band due to the pinning of Fermi level, so a-IGZO TFTs is more common in n-type devices. Combined with these two points, it can be concluded that in a-IGZO TFTs, Fermi level can enter the conduction band by applying enough positive gate voltage. Therefore, the proposed model must consider the degenerate conduction mechanism. Based on theoretical analysis, this paper points out the limitation of Boltzmann statistics, and gives the free charge and trap charge concentration formulas suitable for nondegenerate and degenerate states. Combined with Poisson's equation and Gao Si's theorem, the surface potentials of sub-threshold region and accumulation region are solved without iteration by means of mathematical transformation and Lambert W function. By using smooth function and Schroeder series correction, a complete and high precision analytical model of surface potential is obtained. The results of the model are compared with the numerical iterative solution. The absolute error can be controlled in the range of 10 ~ (-8) V. Based on the results of surface potential calculation and Pao-Sah 's double integral formula, a direct current compact model of a-IGZO TFTs is established, including subthreshold current and accumulative current. The mobility model is based on the actual carrier transport mechanism, including trapping restricted conduction (TLC) mechanism and percolation conductive (PM) mechanism. The mobility model follows the power law function and considers the degradation of phonon scattering and surface rough scattering to mobility. Based on the core current model, two higher order effects, carrier velocity saturation and channel length modulation, are incorporated. Based on the thin layer charge model (CSM) and symmetric orthogonal method (SQM), the expressions of each end charge are solved, and a compact capacitance model of a-IGZO TFTs with degenerative mechanism is established. The model satisfies the condition of non-reciprocity between charge conservation and capacitance, and can describe the dynamic behavior of the device well. In conclusion, the proposed a-IGZO TFTs DC model and capacitance model are based on the internal physical mechanism of the device. Compared with numerical iterative solution or experimental data, the validity of the model is strongly supported. The physical concept of the model is clear, the algorithm is simple and clear, and it is easy to embed the circuit simulator.
【学位授予单位】：暨南大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TN321.5
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