红外探测器内的像元数目

非制冷红外探测器内的铁电薄膜微桥是多层的结构体系。中间一层为智能材料,上下覆盖着金属电极,还有保护层等。如今的红外探测器内的像元数目越来越多,微桥结构也越来越小,对器件的响应灵敏度要求也越来越高,其中所涉及的热学,电学,力学等等方面的问题值得深入研究。先前的研究者对结构内热传播问题的研究只是单纯研究结构内的瞬态或者是稳态的热扩散问题,所分析的结构体系为层状复合结构或者是梯度的非均匀结构,例如热防护结构内的梯度涂层。而将结构内热的传播与智能器件的信号输出相结合起来进行分析还很少。除一些研究者使用有限元软件对结构进行建模分析,或者在实验中测定实际薄膜器件的信号响应之外,还很少见到用相对简化的、解析的方法去分析薄膜的热传导和微桥器件电信号的输出问题。在结构脱层的屈曲分析方面,文献大多都是集中于层状复合材料界面脱层问题,有一些文献分析了结构材料界面裂纹上脱层的屈曲问题。所使用的方法主要是有限元法和结构力学中的梁理论。而用各向同性弹性体的有限变形理论研究脱层的屈曲问题的就比较少,所看到的文献中主要有Wang Wen-Xue[26,27],Loboda和Mityukova[29],Chiu和Erdogan[32]等。这些问题均属于平面应变问题。Madenci和Westmann[46]分析了存在于有限厚度板中面上的圆形脱层在均匀压缩和非均匀压缩载荷情况下的局部屈曲问题。文中考虑到结构的对称性,使得问题变得简单些。Madenci和Westmann分析了层状体系内局部脱层在压缩载荷作用下扩展问题。Madenci et.al分析了基底表面薄层在双轴压缩作用下的圆形脱层问题。Balkan和Madenci分析了热载荷作用下基底表面薄层的圆形脱层问题。Sburlati,Madenci和Guven分析了有限厚度基底与表层间圆形界面脱层的屈曲问题。上面所分析的均为各向同性材料问题的脱层。而对于智能材料与结构内的脱层屈曲,考虑智能材料的耦合效应对临界载荷的影响等问题还没有看到相关的文献。但是这类问题的分析是很有意义的。对于结构内脱层在弯曲作用下发生屈曲的问题,基本上是用有限元法进行分析。在所看到的文献中只有Kardomateas使用了结构力学梁理论,借助于椭圆积分公式对复合材料脱层在纯弯曲作用时的屈曲行为进行了研究,并且和实验进行了对比。而使用有限变形理论和电弹性体的偏场理论去分析智能结构体系内脱层在弯曲载荷作用下发生的屈曲行为还没有查到相关的文献。因此对这方面进行研究,对于智能器件内出现的结构损伤问题也是有借鉴意义的。基于以上的简单综述,对于智能材料结构内的信号响应,以及相关的脱层问题都很值得研究。本文的主要内容分为以下几部分:在第一章中对相关的文献进行了综述,扼要的介绍了结构内热传播问题,以及结构内脱层的屈曲问题。第二章分析红外探测器内铁电薄膜在红外辐射作用下的响应,用级数形式求解了薄膜内热传播,薄膜在热辐射作用下的电压信号响应输出,并且与有关实验结果进行了对比分析。分析结果与实验吻合很好。第三章中对半无限压电体表面金属电极的穿透性脱层的屈曲问题进行了分析。基于有限变形理论和电弹性体的偏场理论,使用Fourier积分变换和相应的边界条件,将问题归结为一组奇异积分方程,应用Muskhelishvili理论和Gauss-Chebyshev多项式将奇异积分方程组离散为齐次线性代数方程组进行求解。用Mathematica编程进行算例分析,给出了不同电极脱层长厚比的临界应变载荷和脱层的屈曲形状,研究了压电体的机电耦合效应对临界载荷的影响。第四章分析有限厚度压电层及其上下表面金属电极的层状结构在电极发生脱层时的屈曲问题。采用第三章的方法分析了电极脱层的临界载荷和相应的脱层屈曲形状。分析了当上、下电极间存在的强电场对脱层屈曲时临界载荷的影响。为了验证屈曲载荷分析结果的正确性,用Patran和Nastran软件对结构进行有限元建模,分析了脱层的临界载荷。通过对比,解析方法和有限元分析的结果十分相近。说明了解析方法和计算过程是正确的。第五章分析了有限厚度压电层及上下电极的层状结构内电极脱层在弯曲载荷作用下的屈曲问题。采用分层法,分析了在不同脱层长厚比时脱层屈曲的临界弯矩、临界曲率。将所得结果与有限元结果进行了比较。两者吻合得很好。第六章对本文作了总结,并展望了本领域的研究方向。
工业羊毛毡
The ferroelectric-thin-film pixel is an essential element in uncooled infrared focal plane array (UIRFPA) of an infrared detector. It is a multilayered structure. Its middle ply is a ferroelectric thin film, and the upper and lower surfaces are covered with metallic electrodes. In addition, some protective coatings are probably fabricated. Nowadays "the smaller the better" is becoming a principle for the design of the ferroelectric pixel. The requirements of photonic sensitivity to the infrared radiation are also increasing rapidly for military and civil uses. Therefore, the thermo-electro-mechanical problems involved in the UIRFPA design are worth studying. The works of pioneer researchers on the thermal conduction in multilayered structures or functionally graded materials are only confined in the transient or stable thermal conduction problems, such as the functionally graded coating in the heat-resistant structures. Some authors stimulated or measured the output responses of ferroelectric-thin-film elements using finite element codes or experimental methods. But there are only few works for analyzing the relationship between the thermal conduction and the output signals of the intelligent devices.Some authors studied the buckling problems of delaminates of laminated structures or laminated composite materials using finite element analysis and traditional beam/plate theories. In these works, the delaminating model might be oversimplified. Some authors studied the buckling problems in isotropic materials under the plane strain mode using finite deformation theory, such as Wang Wen-Xue , Loboda and Mityukova , Chiu and Erdogan etc. Madenci and Westmann analyzed the local buckling problems of penny-shaped delaminate in the mid-surface of the thin plate subjected to symmetric or anti-symmetric remote compression. Madenci and Westmann analyzed the propagation problem of local delaminate in the laminated structure under compressive load. Madenci et al analyzed the buckling problem of penny-shaped delaminate in the interface of coating and substrate under biaxial loading. Balkan and Madenci analyzed the same problem but under thermal loading. Sburlati, Madenci and Guven analyzed the same problem but the thickness of the substrate was finite. These analyses only considered the delaminating in isotropic materials. But hardly can be found the works analyzing the buckling problems of delaminates in intelligent structures and materials taking account of the influence of the coupling effects.In many works, buckling of delaminating in structures under bending was analyzed by using the finite element method. It was only found that Kardomateas analyzed this problem using traditional beam theory. The solution was expressed in the form of elliptic integrals, and compared with experimental data. But hardly can be found the works for analyzing the buckling of delaminates in the smart structures and materials employing finite deformation theory and bias electric field theory under bending. Analyses of these problems are important and benefit for studying the damage problems in the intelligent devices.In this work, the output responses of a smart structure and the related delaminate buckling problems will be analyzed, including the follows:In chapter 1 the summary of the related works will be given. Heat conduction and buckling of delaminates in structures are introduced briefly.In chapter 2, heat conduction and the output response of voltage of a ferroelectric thin film pixel are analyzed. The solution is compared with experimental evidence.In chapter 3, buckling of a through-the-width delaminate in the interface between the infinitely deep ferroelectric substrate and the metallic coating subjected to remote uniform compression is analyzed. The finite deformation theory and bias electric field theory are employed. Using Fourier integral transformation and the corresponding boundary conditions, a set of singular integral equations is obtained. Using Muskhelishvili theory and Gauss-Chebyshev polynomial, these singular integral equations are discretized to a set of homogeneous linear algebraic equations, and the solution can be obtained. The code of the problem is written in the Mathematica. In the example, the critical remote strain and the buckling configuration for different length-to-thickness ratios of delaminating are given. The effect of electric-mechanical coupling is included.In chapter 4, the same problem as that in chapter 3 is analyzed. But the ferroelectric substrate has a finite thickness with the lower surface covered by metallic electrode. In other words, the model is a ferroelectric thin film with its upper and lower surfaces covered by metallic electrodes. The method employed for analyzing is more or less the same as in chapter 3. The case of electric field in the ferroelectric thin film is also considered. In order to verify this analytical solution, a finite element solution is obtained in help of PATRAN and NASTRAN codes. It is found that both solutions are in a good agreement. In chapter 5, the same problem as that in chapter 3 is analyzed. But the model is subjected to a remote pure bending. In the procedure of solution, the model is divided into several layers. The continuity conditions are employed in the interfaces of these layers. The critical bending moment, curvature and the configuration of buckling for different ratios of the delaminate length and the thickness of the electrode are given. Solution of the finite element analysis in virtue of PATRAN and NASTRAN codes is obtained to verify the analytical solution.The conclusion and prediction of research in this area are given in chapter