The major goal of this study was to gain a better understanding of the effects that grain boundaries have on conduction in multilayer ceramic (MLC) capacitors. Electrical measurements were made so that current-voltage curves and impedance plots could be constructed. It was found that the current-voltage curves of new COG and X7R multilayer ceramic capacitors are both ohmic at low voltages and super-ohmic at intermediate voltages. Ohmic behavior prevails at high voltages for both types. Such behavior can be attributed to grain boundaries. Grain boundary resistance was clearly exhibited by X7R-type density blanks and one commercially manufactured type of X7R MLC capacitor, while the NPO density blank and two different values of Z5U multilayer ceramic capacitors, each from a different manufacturer, indicated the possibility of grain boundary resistance. All of the samples that were tested showed possible, if not probable, evidence of grain resistance. Only the Z5U-type density blank showed a resistance contribution from the bulk-electrode interfaces. A model for the grain boundary potential barrier height was developed. It was found that barrier height reduction occurs for small grain sizes due to depletion of the grain, and for increased grain curvature. Dopant effects are also responsible for barrier height reduction. These results, and the related modelling, indicate that grain boundary contributions to titanate-based ceramic resistance can vary widely from sample to sample, since there are so many material dependent variables involved. Such measurements as those described here can help clarify how grain boundaries and other factors contribute to ceramic resistance. / M.S.

A study was conducted into the intrinsic degradation behavior of X7R and Z5U capacitors. The major goals of this research were: 1) to determine current-voltage, activation energy and leakage current characteristics for such capacitors. 2) to investigate how these characteristics change with degradation; 3) to investigate possible correlations between observed behavior and capacitor microstructure or composition. Examination of capacitor microstructures revealed large differences in grain morphology and electrode spacings. The development of a color gradient between positive and negative electrodes with. degradation was observed in one type of capacitor. Compositional studies using EDAX, AUGER, and microprobe analyses failed to detect gradients in dielectric composition in degraded capacitors indicating that gradients are less than 0.1 atomic percent. Current-voltage studies showed a 3/2 power dependance, at voltages above one volt for X7R capacitors indicating space charge limited current. This dependance was attributed to point emission from electrode protuberances. The 3/2 dependance was observed to shift to a square law behavior with degradation. This change was attributed to a increase in conductivity of the dielectric near the cathode, blunting the effect of electrode protuberances. Z5U capacitors were found to have ohmic behavior. No Schottky or Poole Frenkel currents were observed. Degradation studies were carried out on capacitors at 2 to 8 times the rated voltage, and at temperatures from 100 to 1500℃. Leakage currents in actively degrading capacitors were observed to rise exponentially with time. This rise was accompanied by a gradual decrease in activation energy. A model is proposed to explain the observed current vs degradation behavior. / Master of Science

Call number: LD2668 .T4 1964 M15 / Master of Science

published_or_final_version / abstract / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy

by Leung Tin Chi. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2003. / Includes bibliographical references (leaves 106-108). / Abstracts in English and Chinese. / Abstract / Acknowledgements / Table of Contents / Chapter Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Balun Structures --- p.2 / Chapter 1.2 --- Balun Parameters --- p.4 / Chapter 1.3 --- LTCC Multi-layer Balun --- p.5 / Chapter 1.4 --- Original Contributions of The Thesis --- p.7 / Chapter Chapter 2 --- Background --- p.8 / Chapter 2.1 --- Lumped Elements Baluns --- p.8 / Chapter 2.1.1 --- λ/4 Transmission Line Equivalent Circuit Model --- p.10 / Chapter 2.1.2 --- 3λ/4 Transmission Line Equivalent Circuit Model --- p.14 / Chapter 2.1.3 --- Design Procedure of Lumped Element Balun --- p.18 / Chapter 2.2 --- Distributed Baluns --- p.29 / Chapter 2.2.1 --- Coupled Line --- p.29 / Chapter 2.2.2 --- Marchand Balun --- p.34 / Chapter 2.2.3 --- Stepped Impedance Balun --- p.38 / Chapter 2.2.4 --- New Structure Coupled-Line Balun --- p.53 / Chapter 2.3 --- Planar Balun --- p.63 / Chapter 2.4 --- Advantage and Disadvantage of Existed Balun Design --- p.69 / Chapter Chapter 3 --- Size Reduction Method of Coupled Lines --- p.71 / Chapter 3.1 --- New Proposed Method of Coupled Line Size Reduction --- p.71 / Chapter 3.2 --- Simulation Result of Capacitor Loaded Coupled Line --- p.77 / Chapter Chapter 4 --- Capacitor Loaded Coupled Line Balun --- p.82 / Chapter 4.1 --- Simulation Result of Capacitor Loaded Coupled-Line Balun --- p.82 / Chapter Chapter 5 --- Design of New Coupled Line Balun Using Capacitor Loaded Coupled Lines --- p.88 / Chapter 5.1 --- Design Specifications of Reduced Coupled-Line Balun --- p.89 / Chapter 5.2 --- Design of Capacitors --- p.90 / Chapter 5.3 --- Layout and Simulation Result of 2.4GHZ LTCC Capacitor Loaded Coupled-Line Balun --- p.96 / Chapter Chapter 6 --- Conclusion and Future Work --- p.104 / References --- p.106 / Author's Publication --- p.109 / Appendix A Marchand Balun --- p.110 / Appendix B Reconstruction of S-Matrix for a 3-Port Measurement at Only Two-Ports --- p.117 / Appendix C Renormalization of Balun S-Matrix with Load Termination Z1 from S-Matrix with Load Termination Z0 --- p.120 / Appendix D Sensitivity analysis for capacitor loaded coupled line balun --- p.122

Polychlorinated Biphenyls (PCBs) were seen as a significant engineering advance when first commercially produced in 1929. They were used as insulators and cooling fluids in electrical transformers and capacitors. There are 209 PCB congenors that are chemically and thermally stable with low inflammability and reactivity. However,they are also highly toxic, suspected carcinogens and bioaccumulate in the food chain. Due to these characteristics they are listed by the United Nations as one of the sixteen worlds persistent organic pollutants POPs). By international agreement, undertaken by the UN, the production of PCBs has been banned and gradually their use will be phased out. Several tests and procedures are discussed in some detail in this research. / Master of Science (Hons)

Thesis (Ph. D.)--West Virginia University, 2001. / Title from document title page. Document formatted into pages; contains x, 121 p. : ill. (some col.). Vita. Includes abstract. Includes bibliographical references (p. 99-103).

Thesis (M.S.)--University of Minnesota, 2001. / "Accompanying CD-ROM contains Excel spreadsheets and Mathematica notebooks that contain data and templates" for further investigation.--P. 68. Includes bibliographical references (leaves 70-71). Also available on the World Wide Web as a PDF file.

Thesis (M.Eng.)--Memorial University of Newfoundland, 2001. / Bibliography: leaves 158-161.

Thesis (M. Phil.)--Hong Kong University of Science and Technology, 2003. / Includes bibliographical references. Also available in electronic version. Access restricted to campus users.