A new family of dielectric materials has been studied, individually as thick-film capacitors and as buried components incorporated in second-order lowpass and bandpass RC active filter circuits. The materials were electrically characterized in terms of the variation of dielectric constant and dissipation factor with frequency. The performance of the filter circuit is related to the characteristics of the dielectric materials. An analysis of the circuit is developed which accounts for the capacitor losses. / Master of Science

This thesis develops a method for obtaining the complex resonant frequency of a post dielectric resonator in the presence of a lossy conductor. A full field analysis is performed on an infinite dielectric rod from which the complex propagation constant and modal solutions are found. Using a single dominant mode (HEM_ll), the boundary conditions at the end of the resonator are enforced, to obtain a complex reflection coefficient. Using the propagation constant from the infinite dielectric rod and the reflection coefficient derived from considering the dielectric-air interface at the resonator ends, a two dimensional search is performed to find the complex frequency for which the gain/phase criterion of the resonator is satisfied. In the final step, boundary conditions are enforced for a lossy conductor at a distance Az from the dielectric which yields the objective -- the complex resonate frequency of a post dielectric in close proximity of a lossy conductor / Master of Science

Oxide dielectric breakdown is an old problem that has been studied over decades. It causes power dissipations and irreversible damage to the electronic devices. The aggressive downscaling of the device size exponentially increases the leakage current density, which also raises the risk of dielectric breakdown. It has been proposed that point defects, current leakages, impurity diffusions, etc. all contribute to the change of oxide chemical composition and ultimately lead to the dielectric breakdown. However, the conclusive cause and a clear understanding of the entire process of dielectric breakdown are still under debate. In this research, the electronic structure at metal/oxide interfaces is studied using first-principle calculations within the framework of Density Functional Theory (DFT) to investigate any possible key signature that would trigger the dielectric breakdown. A classical band alignment method, the Van de Walle method, is applied to the case study of the Al/crystal-SiO2 (Al/c-SiO2) interface. Point defects, such as oxygen vacancy (VO) and hydrogen impurity (IH), are introduced into the Al/c-SiO2 interface to study the effects on band offset and electronic structure caused by point defects at metal/oxide interfaces. It is shown that the bonding chemistry at metal/oxide interfaces, which is mainly ionic bond, polarizes the interface. It results in many interface effects such as the interface dipole, built-in voltage, band bending, etc. Charge density analysis also indicates that the interface can localize charge due to such ionic bonding. It is also found that VO at the interface traps metal electrons which closes the open -sp3 orbital. The analysis on local potential shows that the metal potential penetrates through a few layers of oxide starting from the interface, which metalizes the interfacial region and induces unoccupied states in the oxide band gap. In addition, it is shown that higher oxygen content at metal/oxide interfaces minimizes such metal potential invasion. In addition, an oxygen vacancy is created at multiple sites through the Al/c-SiO2 and Al/a-SiO2 interface systems, separately. The oxygen local pressure is also calculated before its removal using Quantum Stress Density theory. Correlations among electronic structure, stress density, and vacancy formation energy are found, which provide informative insights into the defect generation controlling and dielectric breakdown analysis. A new band alignment approach based on the projection of plane-waves (PWs) into the space-dependent atomic orbital (LCAO) basis is presented and tested against classical band offset methods -- the Van de Walle method. It is found that the new band alignment approach can provide a quantitative and reliable band alignment and can be applied to the heterojunctions consisting of amorphous materials. The new band alignment approach reveals the real-space dependency of the electronic structure at interfaces. In addition, it includes all interface effects, such as the interface dipole, built-in voltage, virtual oxide thinning, and band deformation, which cannot be derived using classical band offset methods. This new band alignment approach is applied to the case study of both the Al/amorphous-SiO2 (Al/a-SiO2) interface and the Al/c-SiO2. We have found that at extremely low dimensions, the reduction of the insulator character due to the virtual oxide thinning is a pure quantum effect. I highlight that the quantum tunneling current leakage is more critical than the decrease of the potential barrier height on the failure of the devices. / PHD

This work combines many characterization techniques in an effort to enhance understanding of molecular motions of polymers and. how they are influenced by' structure. The primary characterization method was dielectric spectroscopy which utilizes an AC electric field as the stress field. A variety of new, well controlled polymeric systems were studied. The first series included a number of radial starblock copolymers, styrene/isoprene, t-butyl- styrene/isoprene, and t-butyl-styrene/butadiene. These ABA copolymers consisted of hard and soft blocks, with the soft block comprising 75% by weight. The effect of microstructure of the soft block, casting solvent, hydrogenation, and chemical composition of the hard block were some of the variables studied. The amount of phase separation and the molecular motions occurring will be influenced by these parameters. Hydrogenation of the soft block increased the phase separation. Another system investigated included some stereospecific poly(alkyl methacrylates) which were synthesized anionically. In this series the alkyl group was systematically changed in order to study the effects of the bulkiness of the substituent and the tacticity on the a and ß transitions. The ß transition associated with side chain rotations was only observed in the case of the methyl and ethyl substituents. The Havriliak-Negami data analysis was used to evaluate the breadth and the skewness of the distribution of relaxation times. Finally, some high temperature thermoplastic polymers were evaluated with dielectric spectroscopy. The effect of the backbone composition, moisture, and fillers on the β transition was looked at. These studies showed that moisture and fillers play an important role on the magnitude and temperature of the observed β transition. / Ph. D.

Microwaves heat food rapidly and foods are prepared in less time. However, due to non-uniform heating nature of microwave cooking, there exists a serious concern over complete elimination of pathogens in the food. There has been an increase in interest to accurately understand the behavior of different food materials in a microwave field and microbial inactivation during microwave cooking. Recent research showed that fat content in muscle food plays an important role in microbial inactivation by increasing the inactivation level with an increase in the fat level. It was also demonstrated that muscle food heats up differently than a vegetable food product. Cooking food in a microwave oven either by covering the food container or not results in significantly different temperature profiles. The current research attempts to use modeling techniques to analyze impact of these factors on microwave heating. Mathematical modeling is faster, easier and economically better than actual experiments in determining heating behavior of a microwave-cooked food. Though modeling cannot completely replace actual experiments, it can be used as a tool to understand the effects of various factors influencing the microwave cooking. A factor that is highly important during microwave processing is dielectric properties of the material. The interaction of microwave with the food is mainly based on its dielectric properties, which can change with temperature. Therefore, determination of dielectric properties of food with respect to temperature becomes critical. The current research project has two parts. One to determine the dielectric properties of food being tested and another is to employ mathematical modeling techniques to analyze the effect of fat content, food type and the effect of cooking food by covering the bowl using the lid and not covering bowl. Dielectric properties of ground beef patties at 4%, 9%, 20% fat levels and frozen broccoli were determined using an open-ended, 3.6 mm diameter, semi-rigid coaxial line with copper conductors, connected to a network analyzer. The properties were determined at various temperatures. Foods were measured in triplicate. Results showed that dielectric constant and dielectric loss factor of low fat ground beef were higher than that of high fat level ground beef. In addition, the dielectric properties of florets were lower than that of stem parts for frozen broccoli. A 1,200W, household type microwave oven was used in this study to heat the food. Food was placed in a microwave-safe glass bowl and cooked for 120 seconds. One headspace and three internal temperature measurements were recorded for every 0.6 seconds. Five replications were performed. Finite element method was used as modeling technique and temperatures were predicted. Experimental and predicted temperature values were compared. Results showed that the model used in the study was more suitable for modeling the uncovered cooking than covered cooking process. Modeling results also revealed that high fat ground beef patties reached higher temperature than low fat patties. In high fat meat products, fat content also contributed to increase in temperature during microwave heating. In vegetable products and low fat meat food, moisture content is mainly responsible for microwave heating. A more extensive study on critical fat level above which fat content helps in increasing temperature is needed. In addition, inclusion of steam properties in the headspace for modeling the covered cooking is recommended. / Master of Science

A new approach is presented that relies upon 3D electromagnetic simulation results to characterize the complex permittivity of homogeneous dielectric materials. By modeling the test fixture and obtaining a set of simulated S-parameters through an iterative solution process, the dielectric constant and loss tangent can be found. With further development, the 3D simulation results may be used to replace the need for complex theoretical analysis of the measurement geometry. The method is applied to an X-band rectangular waveguide setup, for which the theoretical S-parameters can be readily calculated. A Teflon sample, for which the dielectric properties are well-known, is used for all measurements and calculations. After presenting a detailed derivation to obtain the theoretical S-parameters, the Teflon sample is measured and compared to the theoretical results, from which the comparison shows great promise. An inverse solution algorithm is used to solve for the material properties from the experimental S-parameters. Low-frequency measurement of the Teflon sheet was performed by using a dielectric capacitor test fixture. The results show the effect of an air gap between the electrode and sample, producing serious errors. / Master of Science

Cure time is often the bottleneck of composite manufacturing processes, therefore it is important to understand the cure of today's thermosetting adhesives. This research attempts to characterize the cure rate of two commercial phenol-formaldehyde adhesives. Two methods are used, parallel-plate rheometry and dielectric spectroscopy. Viscosity data from a parallel-plate rheometer may be used to track the advance of polymerization as a function of temperature. This data can then be used to optimize press conditions and reduce production times and costs. The research will further examine resin cure through dielectric analysis; such a technique could monitor resin cure directly and in real-time press situations. Hot-pressing processes could conceivably no longer require a set press schedule; instead they would be individually set based on dielectric data for every press batch. Such a system may lead to a more efficient and uniform product because press times could be based on individual press cycles instead of entire product lines. A more likely scenario, however, is the use of in situ adhesive cure monitoring for troubleshooting or press schedule development. This research characterized the cure of two phenol-formaldehyde resins using parallel-plate rheometry, fringe-field dielectric analysis, and parallel-plate dielectric analysis. The general shape of the storage modulus vs. time curve and the gel and vitrification points in a temperature ramp were found. Both dielectric analysis techniques were able to characterize trends in the resin cure and detect points such as vitrification. The two techniques were also found to be comparable when the cure profiles of similar conditions were examined. / Master of Science

Electrical conduction mechanisms in BaTiO₃-based ferroelectric capacitor ceramics with an emphasis on the X7R type were studied. Dominant charge carriers in this material were identified as conduction band electrons below a temperature of 850°C. This was substantiated by the following results: negative Seebeck coefficients, zero galvanic cell voltage, and evidence of space charge-limited currents in MLC capacitors and related ceramic. Effects of chip thickness on the electrical parameters, as well as the I-V characteristics, were studied. Chip electrical parameters such as resistivity, dielectric constant, and activation energy were found to be independent of chip thickness. Effects of ambient were also studied and differences in current-voltage behavior were attributed to surface effects. Complex impedance spectroscopy proved to be a useful technique in separating grain, grain boundary, and contact contributions to the total impedance. Impedance plots for X7R ceramic revealed negligible contact impedance. The most probable electrical transport mechanism in X7R ceramic is small polaron hopping, although the possibility of combining small polaron hopping and grain boundary transmission cannot be excluded. / Ph. D.

This dissertation summarizes the research performed towards the development, analysis, and testing of two new sample configurations used for characterizing dielectric materials over a wide band of frequencies. In the two configurations, a cylindrical cavity completely filled with a sample of the dielectric material of interest is used. The two configurations are the following: 1. The cylindrical cavity is adapted to the end of a transmission line and the reflection coefficient is measured. The complex permittivity of the dielectric sample is then derived from the measured reflection coefficient information. 2. The cylindrical cavity is placed between two transmission lines. The complex permittivity of the dielectric material can be computed from either the measured reflection coefficient or the measured transmission coefficient. The full field analysis of these configurations is carried out and the solution is obtained using the method of moments. Computer simulation experiments are performed to test the sensitivity of these techniques and predict their performance. Actual experiments on some dielectric materials with known dielectric properties are performed for verification. The first configuration is also used to characterize two thick film dielectric materials. These configurations proved to provide solutions to the many problems with the conventional configurations found in the literature. / Ph. D.

The importance of Poly(3-hydroxybutyrate) (PHB) as a biodegradable material is well known. Due to ever increasing environmental awareness, significant efforts have been made to utilize PHB or its derivatives in producing disposable products. However, brittle mechanical properties of PHB hinder the direct application of this material in useful commodity items. In order to achieve toughened PHB, blending with other polymers which possess high relaxation behavior at room temperature seems attractive. Prior to such development, the fundamental characterization of the relaxation behavior of PHB itself is extremely important in order to assess the effect of any attempt to improve the situation in a quantitative manner. Dielectric thermal analysis was used in the study of the relaxation behavior of melt processed PHB. The approach was largely phenomenological, that was, based on the macroscopic theory of dielectric relaxation. The mean relaxation time of melt processed PHB was evaluated while PHB was undergoing crystallization at room temperature. The experimental conditions were kept as close as possible to actual shelf-life conditions. Dynamic temperature sweep experiments revealed multiple relaxation peaks at the glass transition region. Temperature plane curve resolution revealed, in the early stage of crystallization, two dynamically changing peaks whose behaviors, as the extent of crystallization progressed, were quite opposite in terms of the magnitude of the loss property. By analyzing the temperature dependence of loss property and mean relaxation time, it was concluded that the peak located at the lower temperature is related to pure amorphous chain movement, and the peak located at the higher temperature is related to the movement of amorphous chains which are confined in-between crystalline phases, such as lamellae and spherulites. For the evaluation of the mean relaxation time of binary blends or multiple relaxations arising from homopolymers and copolymers, an empirical model has been developed which is grounded in the theory of linear viscoelasticity with the aim of quantitatively assessing the effect of attempts to improve the toughness of PHB. In the course of data reduction and model development, the majority of empirical dielectric relaxation functions has been reviewed including the Havriliak-Negami model and the Kohlrausch-Williams-Watts stretched exponential function. It was found that the center of relaxation time in the Havriliak-Negami model was skewed toward short time scale of relaxation, while mean relaxation time reflected the relaxation behavior of PHB chains on average, including movement of chains which relax with difficulty as the extent of crystallization progresses. / Ph. D.