Core-Shell Dielectric Composition for X8R Ceramic Capacitors
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Solution Overview
Problem
Multilayer ceramic capacitors used in high-frequency communication systems and electronic controllers face reliability issues due to oxygen vacancies formed by additives like magnesium, and struggle to maintain capacity and temperature stability beyond the Curie point of barium titanate, which limits their high-temperature reliability and X8R characteristic.
Innovation Solution
A dielectric body with a core-shell structure composed of barium titanate and additives such as Zr, Eu, and Mn, where the shell has a higher Zr concentration than the core, and a specific atomic concentration ratio, along with a median grain diameter of 200-400 nm, is used to enhance the dielectric constant and temperature stability, achieving a stable microstructure and improved reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If magnesium additive is used to improve sintering, then sintering is enhanced, but oxygen vacancies are formed reducing reliability
Solution Approach 1:
The patent removes magnesium additive from the dielectric layer composition to eliminate the source of oxygen vacancies that form during sintering. By extracting this harmful element, the invention prevents reliability degradation while maintaining manufacturing processes through alternative sintering approaches.
Solution Approach 2:
The patent modifies the chemical composition parameters of the dielectric layer by specifying precise ratios of barium titanate, strontium titanate, and calcium titanate, along with controlled amounts of manganese and europium additives. These parameter changes enable successful sintering without magnesium, preventing oxygen vacancy formation.
2Reliability
If barium titanate is used as main component, then dielectric constant is high, but capacity stability beyond Curie point is poor
Solution Approach 1:
The patent creates a composite dielectric system combining barium titanate (high dielectric constant) with strontium titanate and calcium titanate (higher Curie points). This composite approach maintains the high dielectric constant from barium titanate while the other components elevate the overall Curie point, ensuring capacity stability above 150°C.
Solution Approach 2:
The patent applies different functional roles to different components within the dielectric layer: barium titanate provides high dielectric constant in the lower temperature range, while strontium titanate and calcium titanate contribute to high-temperature stability. The controlled distribution of manganese and europium additives further optimizes local properties for temperature compensation.
3Reliability
If crystal grain size is reduced to improve dielectric constant, then dielectric constant increases, but manufacturing precision becomes difficult
Solution Approach 1:
The patent specifies precise parameter ranges for crystal grain size (median diameter 0.2-0.4 μm) and uses controlled amounts of manganese (0.01-0.5 wt%) and europium (0.01-0.1 wt%) additives to achieve this control. The sintering conditions are also precisely defined to produce consistent grain sizes within this range, balancing dielectric performance with manufacturability.
Data Source
AI summary
A dielectric body includes a plurality of crystal grains of which a main component is barium titanate, and an additive including Zr, Eu and Mn. At least one of the plurality of crystal grains has a core-shell structure having a core and a shell. A Zr/Ti atomic concentration ratio is 0.02 or more and 0.10 or less. An Eu/Ti atomic concentration ratio is 0.001 or more and 0.03 or less. A Mn/Ti atomic concentration ratio is 0.005 or more and 0.05 or less. A total atomic concentration of the one or more rare elements is smaller than an atomic concentration of Eu when the dielectric body has the one or more rare earth elements. A median diameter of the plurality of crystal grains is 200 nm or more and 400 nm or less.