Multilayer Ceramic Capacitor Core-Shell Grain Structure
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Solution Overview
Problem
Multilayer ceramic capacitors with dielectric layers composed of barium titanate crystal grains having different Ca concentrations face issues with decreasing insulation resistance over time in high temperature environments and require a reoxidation treatment to achieve practical insulation resistance and relative dielectric constant, which adds cost and complexity to production.
Innovation Solution
A multilayer ceramic capacitor design incorporating dielectric layers with a core-shell structure of barium titanate crystal grains having Ca concentrations of 0.2 atomic % or less and 0.4 atomic % or more, along with magnesium, vanadium, manganese, and rare-earth elements, where the ratios of these elements in the center and surface layers are optimized to enhance insulation resistance and relative dielectric constant without the need for reoxidation treatment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If dielectric layers are reduced in thickness to achieve smaller size and higher capacitance, then capacitance increases, but insulation resistance gradually decreases in high temperature environments
Solution Approach 1:
The patent applies local quality by creating a core-shell structure where the crystal grain center and surface have different compositions. The center contains barium titanate with low Ca concentration (0.2 atomic % or less) for high dielectric constant, while the surface shell contains barium titanate with high Ca concentration (0.4 atomic % or more) for high insulation resistance. This local differentiation allows simultaneous achievement of high capacitance and high insulation resistance in thinned dielectric layers.
Solution Approach 2:
The patent uses composite materials by combining two types of barium titanate crystal grains with different Ca concentrations within the same dielectric layer. This composite structure of low-Ca and high-Ca crystal grains enables the dielectric layer to exhibit both high dielectric constant (from low-Ca grains) and high insulation resistance (from high-Ca grains), resolving the contradiction between capacitance and insulation resistance in thinned structures.
2Reliability
If reoxidation treatment is added to achieve practical insulation resistance and relative dielectric constant, then insulation property improves, but production cost and complexity increase
Solution Approach 1:
The patent applies preliminary action by pre-forming the core-shell structure with appropriate Mg and rare-earth element concentration ratios during the initial firing process. This preliminary structuring ensures that the crystal grains have optimal composition distribution before final sintering, eliminating the need for subsequent reoxidation treatment and reducing production complexity while maintaining high insulation resistance.
Solution Approach 2:
The patent enables self-service by designing a firing process that automatically forms the desired core-shell structure and achieves appropriate oxidation state without requiring separate reoxidation treatment. The composition control during firing allows the material to self-organize into the optimal structure, making the production process more efficient and cost-effective.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The capacitor exhibits improved insulation resistance and relative dielectric constant, reducing the need for reoxidation treatment and enhancing reliability in high temperature loading tests while maintaining high capacitance and stability.
Implementation Method 1
a multilayer ceramic capacitor which provides high insulation resistance and a high relative dielectric constant without reoxidation treatment and has high reliability and a high capacitance value
Implementation Method 2
such a fired capacitor body generally needs to be subjected to a reoxidation treatment at a lower temperature than the temperature of the firing and in an atmosphere having a higher oxygen concentration than the oxygen concentration of the atmosphere used in the firing
Data Source
AI summary
The invention relates to a multilayer ceramic capacitor having dielectric layers and internal electrode layers disposed alternately. The dielectric layers include a dielectric ceramic containing barium titanate as a main component, and also calcium, magnesium, vanadium, manganese, and a rare-earth element. Crystals constituting the dielectric ceramic are constituted by grains containing barium titanate as their main component and containing calcium in a concentration of 0.2 atomic % or less or containing the calcium in a concentration of 0.4 atomic % or more. The crystals grains are also distinct in their relative distributions of magnesium and rare-earth elements between the center of the grain and the surface of the grain. Finally, the relative areas of the two kinds of crystals observed in the plane of a polished surface of the dielectric ceramic are described by a ratio b/(a+b), which is 0.5 to 0.8.