Dielectric properties of colossal permittivity materials: An update

During the last 10 years, a lot of interests have been devoted to the so-called CDC (colossal dielectric constant) materials. The first materials exhibiting this behavior were the perovskite-based ceramics on the CCTO (CaCu3Ti4O12) composition. Relative dielectric permittivity can attain values up to (or even larger than) 105. Nevertheless, their dielectric losses are too high, the lower values ranging 10%, in a narrow frequency range, thus limiting their applications. The underlying physical mechanisms at the origin of the CDC are still under study. The analysis of broadband impedance spectroscopy measurements leads most of the authors to propose an interfacial polarization mechanism (at the electrodes or at internal barriers), there is a limited number of complementary electrical characterization techniques, which, up to now, comfort the proposed interfacial polarization mechanisms. In the present work, I-V and time-domain polarization are used to characterize these materials. One of the main results is the observation of a non-symmetrical response of these materials related to the direction of the polarization. These results are observed for both macroscopic level on bulk polycrystalline material and within individual grains of the same samples. These results do not fit current accepted models for polarization for CDC materials

Caracterización de las propiedades eléctricas locales del CaCu3 Ti4 O12.

CaCu3Ti4O12 (CCTO) is a material that presents a colossal dielectric constant (>105). In this work, CCTO was synthesized by chemical coprecipitation and sintered at 1050°C. Electrical properties were studied in bulk ceramic materials, as well as on individual grains and trough grain boundaries in alternative regime and continuous current. In AC regime, grains and grain boundaries show a resistive-like behavior. In DC regime local grain and grain boundary measurements do not allow determining the origin of the non-symmetric response in the bulk samples. It is finally found that non-ohmic contact between the heterogeneous ceramic and the electrodes could explain both the bulk and local electrical behaviors

Caracterización de las Propiedades eléctricas locales del CaCu3Ti4O12

El CaCu3Ti4O12 (CCTO) es un material que presenta permitividad dieléctrica colosal (>105). En este trabajo, el CCTO fue sintetizado mediante coprecipitación química y sinterizado a 1050°C. Las propiedades eléctricas fueron estudiadas de manera macroscópica y localmente en granos y a través de fronteras de grano, tanto en corriente continua como en régimen alternativo. En este régimen, los granos y fronteras de granos presentan un comportamiento resistivo, no capacitivo. En corriente continua, las medidas locales no permiten distinguir el origen de la respuesta asimétrica macroscópica del material. Finalmente se encuentra que un contacto no-óhmico entre el cerámico heterogéneo y los electrodos podría explicar el comportamiento macroscópico y de las mediciones locales. ABSTRACT CaCu3Ti4O12 (CCTO) is a material that presents a colossal dielectric constant (>105). In this work, CCTO was synthesized by chemical coprecipitation and sintered at 1050°C. Electrical properties were studied in bulk ceramic materials, as well as on individual grains and trough grain boundaries in alternative regime and continuous current. In AC regime, grains and grain boundaries show a resistive-like behavior. In DC regime local grain and grain boundary measurements do not allow determining the origin of the non-symmetric response in the bulk samples. It is finally found that non-ohmic contact between the heterogeneous ceramic and the electrodes could explain both the bulk and local electrical behaviors

Metallized ceramic substrate with mesa structure for voltage ramp-up of power modules

International audienceAs the available wide bandgap semiconductors continuingly increase their operating voltages, the electrical insulation used in their packaging is increasingly constrained. More precisely the ceramic substrate, used in demanding applications, represents a key multi-functional element is being in charge of the mechanical support of the metallic track that interconnects the semiconductor chips with the rest of the power system, as well as of electrical insulation and of thermal conduction. In this complex assembly, the electric field enhancement at the triple junction between the ceramic, the metallic track borders and the insulating environment is usually a critical point. When the electrical field at the triple point exceeds the critical value allowed by the insulation system, this hampers the device performance and limits the voltage rating for future systems. The solution proposed here is based on the shape modification of the ceramic substrate by creating a mesa structure (plateau) that holds the metallic tracks in the assembly. A numerical simulation approach is used to optimize the structure. After the elaboration of the structures by ultrasonic machining we observed a significant increase (30%) in the partial discharge detection voltages, at 10 pC sensitivity, in a substrate with a mesa structure when comparing to a conventional metallized ceramic substrate

Modélisation et identification sous représentation diffusive de comportements dynamiques non rationnels en génie électrique

TOULOUSE3-BU Sciences (315552104) / SudocSudocFranceF

Identification of dielectric relaxations: a suitable infinite-dimensional state-space approach

International audienceThe concept of Diffusive Representation is used in this paper for modeling purposes in the field of electrical engineering, namely when some non-rational dynamics are involved [2]. Diffusive formulations are convenient for analysis and cheap numerical approximations. We study the problem of time-domain identification of the so-called diffusive symbol η(ξ) associated to the permittivity ε(p) of dielectric material. The so-obtained state-space models allow simple and precise time-domain simulation of such dynamical components

Modeling and Optimal Identification of Pseudodifferential Electrical Dynamics by Means of Diffusive Representation—Part I: Modeling

International audienc

Étude des mécanismes physiques à l'origine de la permittivité colossale observée dans certaines céramiques

TOULOUSE3-BU Sciences (315552104) / SudocSudocFranceF

Modélisation des phénomènes de relaxation diélectrique par Réalisation Diffusive

International audienceLe concept de représentation diffusive permet d'obtenir un modèle numérique pour la simulation temporelle de phénomènes de relaxation étudiés usuellement dans un cadre fréquentiel. L'identification temporelle de ce modèle permet de montrer les différents avantages de cette représentation

Design of packaging structures for high voltage power electronics devices: Electric field stress on insulation

International audienceThe use of very high voltage power modules (> 10 kV) requires the implementation of appropriate structures for the device packaging. Particularly the triple point between the insulating substrate, the metallization and the encapsulation is subjected to strong electric field stress. A novel architecture is proposed for the metallized ceramic substrate. Its interest is validated by using finite element method simulations to analyze the electric field distribution inside the module. It is shown that creating a gap between the top electrodes thus forming mesa structures, enables a significant spreading of the equipotential lines. The resulting maximum electric field decreases exponentially versus the height of the mesa structure, with better results than when simply increasing the thickness of the ceramic in a conventional module structure