Thermal analysis

The Heterojunction Bipolar Transistor (HBT) is capable of delivering high current density at microwave frequencies and are now being implemented in microwave circuitry as high power amplifiers. The heat generated during device operation is dissipated through the Gallium Arsenide substrate. Because of its poor thermal conductivity the junction temperature rise can be large enough to degrade and thermally limit the performance of the device. The power HBT with multiple emitter fingers are susceptible to the thermal effect due to non-uniform temperature distribution. This results in a thermal effect called thermal runaway causing thermal-induced current instability and hot spot formation thus destroying the device. Thermal shunt technique which has been developed to suppress this non-uniform temperature involves fabrication of a thick metal thermal shunt connecting all the fingers thus forming a strong thermal coupling between the emitter fingers. In this thesis 2 and 3-dimensional thermal simulations were carried out using Finite Element techniques to study the thermal behavior of the HBT's as a function of thermal shunt and other device design configurations such as the number of emitter fingers, thickness of thermal shunt, emitter spacing, Silicon as a substrate material, power variation etc. The results are projected as a design guideline for HBT device.

The evolution of the carbon-oxygen cores of intermediate mass stars
immediately prior to and following carbon ignition is described. The
thermal consequences of the convectively driven URCA process are considered
in detail and applied to these cores following carbon ignition
to determine their thermal. We found, as did Paczynski and Ergma, and
Couch and Arnett, that a global thermal balance and stability is possible for some models. Unlike the previous investigators, however, we found that some models were possibly unstable due to local heating at
the edge of the convective region. The implications for intermediate mass stars burning carbon are potentially serious, as these stars naturally evolve into the region occupied by these unstable models.

The objective of this work is to perform the current induce thermal stress analysis of heterojunction bipolar transistor and to determine the implications of the variation of the thermal shunt thickness. A thesis presented on multi-physics using finite element analysis, covering fluid, thermal and stress with fatigue life analysis of a microelectronic heterojunction bipolar transistor.

This thesis is an approach of numerical optimization of thermal design of the ocean turbine developed by the Centre of Ocean Energy and Technology (COET). The technique used here is the integrated method of finite element analysis (FEA) of heat transfer, artificial neural network (ANN) and genetic algorithm (GA) for optimization purposes.