基于半解析法的全耗尽SOI MOSFET亚阈值表面势分析

发布时间：2018-04-03 04:36

本文选题：半解析法　切入点：电势　出处：《安徽大学》2017年硕士论文

【摘要】：随着集成电路的发展,MOS器件已进入深亚微米的时代,传统的MOS器件在结构和尺寸上将会达到物理极限,这时基于物理的问题会对MOS器件产生很大的影响,如短沟道效应(SCE)、漏致势垒降低效应(DIBL)等。为了克服这些影响,研究者努力寻找新的材料,开发新的器件结构,试图制作出理想的半导体器件。SOI器件与传统的体硅器件相比不仅能有效地抑制短沟道效应,还拥有更多的优点:如低功耗、无闩锁效应、寄生电容小、集成度高、抗辐射能力强、速度快、制作工艺简单等。为了对SOI MOSFET器件进行更加深入的研究,我们需要建立一个精确而又简单的电势模型,本文具体开展的工作如下。第1章介绍了传统MOS器件的发展及存在的问题,针对这些问题引入SOI MOSFET器件,并分析了 SOI MOSFET器件的研究意义,研究现状和应用。第2章综述了 SOI MOSFET模型的研究方法,讨论了已有的抛物线近似模型和准二维模型的解法和优缺点,并在此基础上着重分析了基于半解析法的SOI MOSFET亚阈值表面势模型。该模型先通过矩形等效源的方法将器件结构划分三个区域,确立各个区域的电势方程,边界条件。然后根据各个区域的电势相等和电位移相等确立衔接条件。第3章介绍了半解析法SOI MOSFET器件亚阈值表面势模型的解法。该解法的主要过程如下:首先根据分离变量法和特征函数展开法对各个区域进行求解,得到含有待定系数的电势表达式。其次根据交界面处的电势相等,设氧化层和硅膜交界面处的上表面势为φ1(x),硅膜和埋氧化层交界面处的下表面势为φ2(x),将电势方程中的待定系数用上下表面势代替,避免了由于方程中sinh和cosh的存在导致方程不收敛。然后根据交界面处的电位移相等,得到两个含有上下表面势的方程。根据相关区域的边界条件和三角函数的特性,将上下表面势设成广义傅里叶级数形式进行计算,避免由于傅里叶级数同时存在正弦和余弦函数所带来的大量计算。最后对方程进行正交函数化简,得到含有待定系数的矩阵方程。通过数学计算工具MATLAB进行求解,得到要求的系数,再将系数带入上下表面势和电势方程中,可以得到很直观的电势和表面势的解析式。半解析模型不同于数值模型和解析模型,它是在两者的基础上提出的,不仅具有很好的精确度,还具有明确的解析表达式,具有很强的实用性和价值性。第4章对全耗尽SOIMOSFET模型的验证分析。首先,利用PDE工具对模型进行数值验证,对比了各个区域的等值线图。其次,在相同尺寸下将模型计算得到的表面势和SILVACO仿真得到的表面势进行了比较,验证了模型的精确性。从比较结果可知,在不同的沟道长度、氧化层厚度、掺杂浓度、硅膜厚度下模型的计算结果和SILVACO仿真结果都能够较好的吻合,因此建立的模型能够很好的反映表面势随着器件参数的变化。
[Abstract]:With the development of integrated circuits, MOS devices have entered the age of deep submicron, and the traditional MOS devices will reach the physical limit in structure and size. At this time, the physical-based problems will have a great impact on the MOS devices.For example, short channel effect (SCE), leakage barrier reduction effect (DIBL) and so on.In order to overcome these effects, researchers try to find new materials, develop new device structures and make ideal semiconductor devices. Compared with traditional bulk silicon devices, SOI devices can not only effectively suppress the short channel effect.It also has many advantages, such as low power consumption, no latch effect, small parasitic capacitance, high integration, strong radiation resistance, high speed, simple fabrication process and so on.In order to study the SOI MOSFET devices more deeply, we need to establish an accurate and simple EMF model. The work of this paper is as follows.Chapter 1 introduces the development and existing problems of traditional MOS devices, introduces SOI MOSFET devices to these problems, and analyzes the research significance, research status and application of SOI MOSFET devices.In chapter 2, the research methods of SOI MOSFET model are summarized, and the methods of solving parabola approximate model and quasi two-dimensional model are discussed. Based on this, the sub-threshold surface potential model of SOI MOSFET based on semi-analytical method is emphatically analyzed.In this model, the structure of the device is divided into three regions by the method of rectangular equivalent source, and the potential equations and boundary conditions of each region are established.Then the connection condition is established according to the equal potential and the equal electric displacement of each region.In chapter 3, the semi-analytical method for solving the subthreshold surface potential model of SOI MOSFET devices is introduced.The main process of the solution is as follows: firstly, the potential expressions with undetermined coefficients are obtained by solving each region according to the method of separating variables and the expansion method of characteristic function.Secondly, according to the equal electric potential at the interface, let the upper surface potential of the interface between the oxide layer and the silicon film be 蠁 1kW, and the lower surface potential at the interface between the silicon film and the buried oxide layer be 蠁 2 x, so the undetermined coefficient in the potential equation is replaced by the upper and lower surface potential.It is avoided that the equation does not converge due to the existence of sinh and cosh in the equation.Then, according to the equal electric displacement at the interface, two equations with upper and lower surface potentials are obtained.According to the boundary conditions of the related regions and the characteristics of trigonometric functions, the upper and lower surface potentials are calculated in the form of generalized Fourier series, which avoids the large amount of calculation caused by the existence of both sine and cosine functions in Fourier series.Finally, the equation is simplified by orthogonal function, and the matrix equation with undetermined coefficients is obtained.The required coefficients are obtained by means of the mathematical calculation tool MATLAB, and then the coefficients are brought into the upper and lower surface potential and potential equations. The analytical expressions of the surface potential and the surface potential can be obtained directly.The semi-analytical model is different from the numerical model and the analytical model. It is based on the two models. It not only has good accuracy, but also has a clear analytical expression, which has strong practicability and value.Chapter 4 verifies the fully depleted SOIMOSFET model.First, the PDE tool is used to verify the model, and the isoline maps of each region are compared.Secondly, the accuracy of the model is verified by comparing the surface potential calculated by the model with that obtained by SILVACO simulation at the same size.From the comparison results, it can be seen that the calculation results of the model under different channel length, oxide layer thickness, doping concentration and silicon film thickness are in good agreement with the SILVACO simulation results.Therefore, the model can well reflect the change of surface potential with the device parameters.
【学位授予单位】：安徽大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TN386

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