Browsing by Subject "Thermal stress"
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Item Nonlinear thermoelastic stress analysis of spherically curved solar panels(Texas Tech University, 1985-05) Vungutur, Krishna V S RSpherically curved glass panels are used to concentrate solar energy onto a line focus in fixed mirror distributed focus type solar collectors. These solar panels consist of thin flat glass plates bent to form a spherical surface, glued onto a paper honeycomb backing, and covered with steel plate at the back and with plastic strips on the sides. Stresses are produced in the glass plates as they are formed into spherical surfaces. In addition, when the solar receiver is not in focus relative to the bowl and the sun, a mirror hot spot condition is developed, resulting in large thermally induced stresses within glass plates. The curved glass panel is modeled as a plate on elastic foundation in order to represent the behavior of the plate in relation to other panel components. Since lateral deflections of these plates are large compared to their thickness, nonlinear von Karman plate equations are used in the analysis, A computer model has been prepared to assist in the nonlinear analysis of stresses using finite difference method. The model has flexibility to analyze a variety of rectangular plate geometries subjected to thermal and other applied loads.Item Thermo-mechanical reliability of 3-D interconnects containing through-silicon-vias (TSVs)(2010-12) Lu, Kuan Hsun; Ho, P. S.; Huang, Rui; Kovar, Desiderio; Ferreira, Paulo J.; Im, Jang-Hi; Zhao, JiehuaThis dissertation focuses on one of the most active research areas in the microelectronics industry: Thermo-mechanical reliability of 3-D interconnects containing through-silicon-vias (TSVs). This study constitutes two parts: 1. Thermal stress measurement on TSVs; 2. Analyses on thermo-mechanical reliability of TSVs. In the first part, a metrology for stress measurement of through-silicon-via (TSV) structures was developed using a bending beam technique. The bending curvature induced by the thermal expansion of a periodic array of Cu TSVs was measured during thermal cycles. The stress components in TSV structures were deduced combining the curvature measurement with a finite-element-analysis (FEA). Temperature-dependent thermal stresses in Cu TSVs and in Si matrix were derived. In the second part, the reliability issues induced by the thermal stresses of TSVs were analyzed from several aspects, including the carrier mobility change in transistors, the interfacial delamination of TSVs, and thermal stress interactions between TSVs. Among them, the mobility change in transistors was found to be sensitive to the normal stresses near the Si wafer surface. The surface area of a high mobility change was defined as the keep-out zone (KOZ) for transistors. FEA simulations were carried out to calculate the area of KOZ surrounding TSVs. The area of KOZ was found to be mainly determined by the channel direction of the transistor as a result of anisotropic piezoresistivity effects. FEA simulations also showed that the KOZ can be controlled by TSV geometry, material selection, etc. Interfacial delamination of TSVs was found to be mainly driven by a shear stress concentration at the TSV/Si interface. Crack driving force for TSV delamination was calculated using FEA simulations, which take into account the magnitude of thermal load, TSV geometry, TSV materials, etc. The results provided a design guideline to improve the TSV delamination problem. In the last, the stress interaction among TSV arrays was examined using a bi-TSV model. In the Cartesian coordinate system, thermal stresses can be intensified or suppressed between TSVs, depending on how TSVs are located. Further analyses suggested that the area of KOZ and the TSV-induced Si cracking can both be improved by optimizing the arrangement of the TSV arrays.Item Transmission electron microscopy and thermal residual stress analysis of AlN crystal(Texas Tech University, 2007-05) Lee, Rac G.; Chaudhuri, Jharna; Idesman, Alexander V.; Ma, YanzhangPresented in this thesis is an investigation into the residual thermal stress distribution in AlN single crystal (film), grown using W (substrate) as a crucible material, and appropriate crucibles, sapphire, tantalum carbide, niobium carbide and silicon carbide, are also investigated. An optimal choice of crystal growth conditions results in the formation of coalesced boundaries known as island structures. A finite element model has been used that accounts for different arrangements of these island structures. The model is based on the dimensionless coordinates that significantly reduces the number of variables to be computed. Experimentally grown aluminum nitride crystal with rough and smooth surface was examined by Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy (SEM). The special technique, Convergent Beam Electron Diffraction (CBED), was used to determine the polarity of the rough and smooth surface, and High Resolution Transmission Electron Microscopy (HRTEM) image was used to investigate the dislocation in aluminum nitride crystal.