论文总字数：45602字

摘 要

热电多层膜由于能实现低维尺寸效应及超晶格效应，较热电块体材料表现出更优异的热电性质，在柔性热电器件中有着非常重要的应用。而热电多层膜性能受膜层形状、厚度、界面影响较大，因此，研究热电多层膜电输运机理对热电多层膜设计及性能测量有非常重要的意义。目前，热电多层膜的电输运性能测量及预测往往采用并联模型理论，然而该并联模型使用条件缺乏理论和实验的支持于验证。本文在Ag/Si、Cu/Si双层薄膜的电输运测试数据的基础上，借助于COMSOL Multiphysics软件采用有限元理论模拟了双层膜在施加电势差下的导电性能以及施加温度差下的热电性能，并与并联模型进行了比较。主要研究内容和结果如下：

1.建立单层硅膜模型，研究四探针法测电导率时影响测量精度的因素。①研究显示测量时若选用面电流源，测量结果准确且不会因为探针的位置改变而发生变化。②采用点电流源或线电流源测量时，电流源附近的电势沿电流方向分布不均，探针在此处测量时结果会有正的或负的偏差，而探针在远离电流源的位置测量精度会有所提高。③采用点电流源时，对称性好的模型测量精度更高。

2.建立Cu/Si双层膜模型，用四探针法研究模型的电输运性能，并验证双层膜并联电导模型。①研究显示测量电导率时若选用点电流源或线电流源，四探针放置在不同位置会产生不同的电导率测量结果：四探针放置在Cu上，测量值接近Cu材料自身电导率真实值；四探针放置在Si上，测量值介于Si和Cu两者的电导率之间。②采用面电流源测量时，Si、Cu两侧电导率测量值相同，并且会随着Cu膜的厚度的减小而减小。③经验证，只有选用面电流源测量时双层膜并联电导模型才适用。

3. 建立Cu/Si热电双层膜模型，研究赛贝克系数测量结果影响因素，并验证双层膜赛贝克系数并联模型。①对于冷热端没有金属层的模型，Si侧的电势沿温度梯度方向不均匀分布，随着探针从冷热端向中部移动，采用四线法测量得到的赛贝克系数会逐渐减小，最大最小值的偏差可达94.28%，Cu/Si膜厚比以及模型尺寸的改变不影响Si侧不均匀分布的电势。而Cu侧测量结果与Cu的赛贝克系数真实值相同且不会因为探针的位置改变而发生变化。②对于冷热端有金属层的模型，Si侧和Cu侧的电势沿温度梯度方向均匀分布，两侧赛贝克系数测量值均与Cu材料自身的赛贝克系数相同，且不会因为探针的位置改变而发生变化，③经验证，冷热端有金属层的模型才适用双层膜赛贝克系数并联模型。

4.建立具有高阻、低阻或者电绝缘等不同界面的热电双层模型，研究界面接触以及冷热端的金属层对塞贝克系数测量的影响。①在冷热端没有金属层时，高阻界面和电绝缘界面会隔离Si、Cu两侧的电势，Si和Cu两侧电势分别沿温度梯度方向均匀分布，赛贝克系数测量值分别与其自身赛贝克系数值相同；低阻界面Si侧电势不均匀分布，与没有设置界面类型的双层模型数据相近。②如果在冷热端加上金属层，对于高阻界面和低阻界面，Si和Cu两侧测量值均与Cu自身赛贝克系数值相同，金属层的存在让模型中界面和硅对赛贝克系数测量值没有影响；电绝缘界面Cu侧测量值与Cu自身赛贝克系数值相同，Si侧赛贝克系数测量值与Cu侧接近但最大有7.50%偏差，偏差表明电绝缘界面的电势隔离作用相比高阻界面更强。

关键词：多层热电薄膜；电导率；赛贝克系数；多层膜并联模型；COMSOL Multiphysics

Abstract

Thermoelectric multilayer film has a very important application in flexible thermoelectric devices because of its low dimensional effect and superlattice effect. Therefore, it is very important to study the thermoelectric transport mechanismof thermoelectric multilayer films for the design and performance measurement . At present, parallel model is often used to measure and predict the performance of thermoelectric multilayer films. However, the using of the parallel model lacks theoretical and experimental support. On the basis of the electrical transport test data of the Ag/Si、Cu/Si double-layer film, the electrical conductivity under the applied potential difference and thermoelectric properties under the applied temperature difference of the double-layer film are simulated by finite element theory with the aid of comsol multiphysics software, and the results are compared with the parallel model. The main research contents and results are as follows :

1. A single-layer film model is established to study the factors that affect the measurement accuracy by four-probe method. It is found that if the surface current source is used in the measurement, the measurement results are accurate and will not change along with the probe position . In the condition of point current source or line current source, the electric potential near the current source is unevenly distributed along the current direction, and the results will deviate from the theortical one, and the accuracy will be improved.when the the probe positions are away from the current source. In the condition of point current source, the models’ accuracy increase for models with good symmetry.

2. We establish a double-layer membrane model, study the electrical transport performance by four-probe method, and the parallel conductance model of the double-layer membrane is verified. The results show that when the four-probes are placed on the Cu film and the measured value is close to the true value of the material's own conductivity. The four-probe is placed on the Si and the measured values are between the that of the Si and the Cu. When the surface current source is used to measure, the measured conductivities of both sides of the Si、Cu are the same and will decrease as the thickness of the Cu film decreases. It is proved that the parallel conductance model of double-layer film is only applicable when the surface current source is selected.

3. We establish the thermoelectric double-layer model, study the influence factors on the measurement results of Seebeck coefficient, and verify the parallel model of the Seebeck coefficient.s For models with no metal layers on the cold and hot ends, the potential on the Si side is unevenly distributed along the direction of temperature gradient. As the probe positons move from the cold and hot ends to the middle, the measured value of Seebeck coefficient will gradually decrease, the deviation of the maximum and minimum value can reach 94.28%, and the change of film thickness ratio and model size does not affect the uneven distribution of potential on the Si side. The results measured on the Cu side are the same as the true value of the Seebeck coefficient of the Cu and will not change along with probe position. With respect to the model with metal layer at the hot and cold end, the potential of the Si side and the Cu side is uniformly distributed along the direction of temperature gradient. The measured values of both sides are the same as that of the Cu material itself and will not change along with probe position.

4. Thermoelectric double-layer model with high resistance interface, low resistance interface or electrical insulation interface are established to study the influence of interface contact and metal layer at cold and hot end. When there is no metal layer at the cold and hot ends, the high resistance interface and the electrical insulation interface will isolate the potential on both sides of the Si、Cu. The potentials on both sides of the Si and Cu are uniformly distributed along the temperature gradient. The measured values of the Seebeck coefficient are the same as their own Seebeck coefficient values. With the addition of metal layers at the hot and cold ends, for both the high resistance interface and the low resistance interface modles, the measured Seebeck values of Si, Cu sides are the same as the their intrinsic values. In the condition of metal layers on both ends, the Seebeck values will not be affected by the interface, and the measured result is the same as that of Cu. The Seebeck coefficient values measured on the Si side are close to the Cu side but have a maximum deviation of 7.50%.

Key Words: Multi-layer thermoelectric film; conductivity; Seebeck coefficient; Multi-layer parallel model；COMSOL Multiphysics

目录

摘 要 I

Abstract II

第1章 绪论 1

1.1研究背景 1

1.2热电效应 1

1.2.1赛贝克效应 2

1.2.2帕尔贴效应 3

1.2.3汤姆森效应 3

1.2.4热电效应之间的关系 4

1.3热电材料的电热输运性能 4

1.3.1电导率 4

1.3.2赛贝克系数 5

1.3.3热导率 5

1.4热电薄膜的研究模型及进展 5

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