Hybrid monolithic integration of high-power DC-DC converters in a high-voltage technology

The supply of electrical energy to home, commercial, and industrial users has become ubiquitous, and it is hard to imagine a world without the facilities provided by electrical energy. Despite the ever increasing efficiency of nearly every electrical application, the worldwide demand for electrical power continues to increase, since the number of users and applications more than compensates for these technological improvements. In order to maintain the affordability and feasibility of the total production, it is essential for the distribution of the produced electrical energy to be as efficient as possible. In other words the loss in the power distribution is to be minimized. By transporting electrical energy at the maximum safe voltage, the current in the conductors, and the associated conduction loss can remain as low as possible. In order to optimize the total efficiency, the high transportation voltage needs to be converted to the appropriate lower voltage as close as possible to the end user. Obviously, this conversion also needs to be as efficient, affordable, and compact as possible. Because of the ever increasing integration of electronic systems, where more and more functionality is combined in monolithically integrated circuits, the cost, the power consumption, and the size of these electronic systems can be greatly reduced. This thorough integration is not limited to the electronic systems that are the end users of the electrical energy, but can also be applied to the power conversion itself. In most modern applications, the voltage conversion is implemented as a switching DC-DC converter, in which electrical energy is temporarily stored in reactive elements, i.e. inductors or capacitors. High switching speeds are used to allow for a compact and efficient implementation. For low power levels, typically below 1 Watt, it is possible to monolithically implement the voltage conversion on an integrated circuit. In some cases, this is even done on the same integrated circuit that is the end user of the electrical energy to minimize the system dimensions. For higher power levels, it is no longer feasible to achieve the desired efficiency with monolithically integrated components, and some external components prove indispensable. Usually, the reactive components are the main limiting factor, and are the first components to be moved away from the integrated circuit for increasing power levels. The semiconductor components, including the power transistors, remain part of the integrated circuit. Using this hybrid approach, it is possible in modern converterapplications to process around 60 Watt, albeit limited to voltages of a few Volt. For hybrid integrated converters with an output voltage of tens of Volt, the power is limited to approximately 10 Watt. For even higher power levels, the integrated power transistors also become a limiting factor, and are replaced with discrete power devices. In these discrete converters, greatly increased power levels become possible, although the system size rapidly increases. In this work, the limits of the hybrid approach are explored when using so-called smart-power technologies. Smart-power technologies are standard lowcost submicron CMOS technologies that are complemented with a number of integrated high-voltage devices. By using an appropriate combination of smart-power technologies and circuit topologies, it is possible to improve on the current state-of-the-art converters, by optimizing the size, the cost, and the efficiency. To determine the limits of smart-power DC-DC converters, we first discuss the major contributing factors for an efficient energy distribution, and take a look at the role of voltage conversion in the energy distribution. Considering the limitations of the technologies and the potential application areas, we define two test-cases in the telecommunications sector for which we want to optimize the hybrid monolithic integration in a smart-power technology. Subsequently, we explore the specifications of an ideal converter, and the relevant properties of the affordable smart-power technologies for the implementation of DC-DC converters. Taking into account the limitations of these technologies, we define a cost function that allows to systematically evaluate the different potential converter topologies, without having to perform a full design cycle for each topology. From this cost function, we notice that the de facto default topology selection in discrete converters, which is typically based on output power, is not optimal for converters with integrated power transistors. Based on the cost function and the boundary conditions of our test-cases, we determine the optimal topology for a smart-power implementation of these applications. Then, we take another step towards the real world and evaluate the influence of parasitic elements in a smart-power implementation of switching converters. It is noticed that the voltage overshoot caused by the transformer secondary side leakage inductance is a major roadblock for an efficient implementation. Since the usual approach to this voltage overshoot in discrete converters is not applicable in smart-power converters due to technological limitations, an alternative approach is shown and implemented. The energy from the voltage overshoot is absorbed and transferred to the output of the converter. This allows for a significant reduction in the voltage overshoot, while maintaining a high efficiency, leading to an efficient, compact, and low-cost implementation. The effectiveness of this approach was tested and demonstrated in both a version using a commercially available integrated circuit, and our own implementation in a smart-power integrated circuit. Finally, we also take a look at the optimization of switching converters over the load range by exploiting the capabilities of highly integrated converters. Although the maximum output power remains one of the defining characteristics of converters, it has been shown that most converters spend a majority of their lifetime delivering significantly lower output power. Therefore, it is also desirable to optimize the efficiency of the converter at reduced output current and output power. By splitting the power transistors in multiple independent segments, which are turned on or off in function of the current, the efficiency at low currents can be significantly improved, without introducing undesirable frequency components in the output voltage, and without harming the efficiency at higher currents. These properties allow a near universal application of the optimization technique in hybrid monolithic DC-DC converter applications, without significant impact on the complexity and the cost of the system. This approach for the optimization of switching converters over the load range was demonstrated using a boost converter with discrete power transistors. The demonstration of our smart-power implementation was limited to simulations due to an issue with a digital control block. On a finishing note, we formulate the general conclusions and provide an outlook on potential future work based on this research

The materials processing research base of the Materials Processing Center

The goals and activities of the center are discussed. The center activities encompass all engineering materials including metals, ceramics, polymers, electronic materials, composites, superconductors, and thin films. Processes include crystallization, solidification, nucleation, and polymer synthesis

Electrical surface properties of HTV silicone rubber used for high voltage insulation

This thesis presents a laboratory study on the aging mechanisms responsible for loss and recovery of hydrophobicity of high temperature vulcanized silicone rubber used as a high voltage insulator. The effects of different stresses of heat and water salinity on the hydrophobicity were determined as a function of time, by measuring intermittently the static contact angle, the weight and average surface roughness during aging as well as recovery. The SEM, EDS and ATR-FTIR spectroscopy were utilized to study the physical and chemical changes on the surface. In addition, the surface free energies γ s, γsl and W sl of the specimens were calculated from the measured data of the contact angles of &thetas;W and &thetas;MI. The loss and recovery of hydrophobicity of the specimens due to migration of the low molecular weight (LMW) fluid from bulk to the surface under different stress conditions was investigated. The contents of the extracted LMW fluid were characterized by mass spectrometry, IR and NMR spectroscopy

Synthesis and characterization of functional polymers with controlled architecture and their application as anticorrosion primers

There are over 2900 ballast tanks in the U.S. Navy inventory and their annual maintenance cost amounted to 415 million dollars in 2006, half of which was directly correlated to corrosion. Ballast tanks which form the basic skeleton of a vessel, are subjected to very corrosive conditions. Epoxy based protective coatings are used by the Navy for minimizing corrosion and they currently offer five to seven years of protection. The work described in this thesis is in line with a major program instigated by the U.S. Navy to improve the reliability of tank coatings. This thesis investigates the synthesis and use of carefully designed functional poly(methacrylate) copolymers as a primer coating addressing one of the major failure mechanisms responsible for corrosion: delamination of the coating at the steel-coating interface. Novel polymers were designed and synthesized to improve corrosion protection and adhesion of epoxy coatings to steel. They possess two types of functional groups which are incorporated in the polymer and distributed in blocks or other related structures. One block is designed to bind strongly to the metal substrate and therefore protect that surfaces from corrosion, the other block possesses the ability to interact with the bulk coating. The epoxy coating and the metal surface are therefore linked through a series of strong durable polymeric bonds. Several monomers possessing either a metal chelating group or a group allowing blending with the coating were thus prepared. Block copolymers and other polymer structures were synthesized by nitroxide mediated polymerization, a polymerization technique that allows control of the molecular weight and architecture. An AEMA-GMA block copolymer was synthesized in a two-step process and gradient copolymers were synthesized in a one-pot synthesis. Copolymer anti-corrosion properties were then evaluated through a series of tests (salt spray, hot water immersion, cathodic disbondment, electrochemical impedance spectroscopy, polarization curves and pull-off test). A deposition method was developed to generate the optimal coating system: the steel to protect was dipped in a dilute solution of the copolymer, rinsed with pure solvent to eliminate the excess material and painted by spraying the epoxy mixture. Electrochemical techniques showed a 60% corrosion inhibition for the AEMA-GMA copolymers. An improvement of the epoxy coating corrosion resistance with the addition of the AEMA-GMA gradient copolymer and the AEMA-GMA star-block copolymer was noticed when subjected to hot water immersion and salt spray tests. While the polymeric primers showed to be quite effective in improving the coating\u27s corrosion resistance, the common corrosion resistance tests were found to be inadequate to robustly characterize their full potential. Nonetheless, the functional copolymers polymer with controlled architecture, their formulation and improved testing techniques, present challenging and interesting work to continue for anticorrosion research

Numerical simulation of fluid-fluid and solid-fluid interactions: a lattice Boltzmann strategy

It is crucial to obtain a better understanding of fluid-fluid and solid-fluid interactions with several applications in science and engineering disciplines. Associating fluids such as water, alcohols, asphaltene might exist in many processes. Modeling associating fluids to explore phase equilibrium behaviors is required for proper design, operation, and optimization of various chemical and energy processes. Pseudopotential lattice Boltzmann method (LBM) can be a promising and capable mesoscopic approach to study phase transition and thermodynamic behaviors of complex fluid systems. Results of integrating the cubic equations of state (EOSs) with LBM showed a considerable deviation from experimental data for associating fluids. Cubic-plus-association (CPA) EOS is utilized in the LBM to increase the accuracy of modeling associating fluids. A global optimization approach is applied to determine the optimum association parameters of CPA EOS for water and primary alcohols in the lattice units. Maxwell equal area construction is used to verify the thermodynamic consistency. By increasing the isotropy order of gradient operator, the spurious velocities are decreased, and an extended form of CPA EOS is introduced to find proper initial densities, which increase the stabilities at low reduced temperatures. Simulating fluid flow at high Reynolds number is another aspect of an LBM study that needs further improvement. In fluid flow in porous media, specifically at tight gas reservoirs, a high flow rate might happen at pore throat. Therefore, to increase the stability of the model at high Reynolds number, the central moments collision operator is implemented in the LBM. The advantages of central moments collision operator are shown by comparing with multi relaxation time (MRT) collision operator in the double shear layers test. It is found that using a higher order of isotropy in the gradient operator can lead to a 34% reduction in spurious velocities. From the thermodynamic consistency point of view, it is concluded that collision operators can also have an impact on the consistency of the model. Furthermore, the model validation is performed by observing a straight line in the Laplace law test. Surface wettability is known as an important concept to achieve a better understanding of fluid flow and distribution in both porous and non-porous systems. Improving the solid-fluid interaction can help to have a better understanding of thermodynamics of curved interfaces. The contact angle is an important parameter to study the multiphase fluid flow in various systems such as porous media and membranes. It helps to design better production, separation, treatment, and reaction processes in different applications. In order to increase the accuracy and reliability of the model for simulation of the surface wettability and absorption, a new solid-fluid interaction in the pseudopotential approach is introduced. Usually, the surface wettability is reported by the contact angle, which is measured by fitting a circle on the drop. Because the circle is a constant curvature shape, it is not suitable to consider the disjoining pressure. A new strategy is presented based on the Smoothing Splines to measure the contact angle without considering a constant curvature shape of the interface profile. The new solid-fluid interaction exhibits the capability of simulating extreme non-wetting surfaces without detaching the drop. The probability histogram of the density domain appears to be a reliable tool to measure the phase density in the presence of a surface. The results of the current research have a wide range of applications in energy and environment, such as simulation of fluid flow in porous systems (e.g., shale reservoirs and membranes). Pores and fractures are large in conventional permeable media and pressure-drive convective flow is applicable in the framework of continuum flow. Shale reservoir have fine grains and pores in the range on nanometer where fluid molecular distribution is inhomogeneous and surface adsorption may be significant. Coupling the introduced method with nucleation theory provide a powerful tool to simulate asphaltene precipitation in the porous media. The presence of water component as an associating fluid in some biological processes such as blood coagulation makes the presented model an effective tool to simulate those processes

Engineering and built environment project conference 2014: book of abstracts - Toowoomba, Australia, 22-26 September 2014

Book of Abstracts of the USQ Engineering and Built Environment Conference 2014, held Toowoomba, Australia, 22-26 September 2014. These proceedings include extended abstracts of the verbal presentations that are delivered at the project conference. The work reported at the conference is the research undertaken by students in meeting the requirements of courses ENG4111/ENG4112 Research Project for undergraduate or ENG8411/ENG8412 Research Project and Dissertation for postgraduate students

MIMC reliability and electrical behavior defined by a physical layer property of the dielectric

Metal-insulator-metal capacitor (MIMC) reliability and electrical properties are defined by the TDDB lifetime. breakdown voltage and leakage current. In this article, the correlation is determined between these electrical properties and the physical and chemical properties of the SiN dielectric layer. It is demonstrated how a SiN dielectrics with a high refractive index have high Si content and show an increased initial leakage Current. However, contradictory to the high leakage current, these dielectrics also show high lifetimes. It is shown that SiN dielectrics with a high Si content contain high numbers of charge trapping centers. Over time, a high concentration of trapped charges is build up to such an extend that the local electric field over the dielectric is significantly decreased. This results in the observed reliability improvement of the dielectric. The final intrinsic quality and reliability of MIMC capacitors can therefore be determined by Measurable physical properties of the MIMC dielectric at the time of the deposition of this layer. (C) 2008 Elsevier Ltd. All rights reserved