MLCC Permittivity Stability via Si Oxide Grain Boundary Control
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Solution Overview
Problem
The existing multi-layer ceramic capacitors experience excessive lowering of permittivity due to the precipitation of the glass phase at the crystal grain boundary, caused by the addition of Si oxide, which exerts compressive stresses on ceramic crystal grains, leading to reduced volumic ratio and reliability.
Innovation Solution
The ceramic dielectric layer contains Si oxide converted as SiO2 at a ratio from 0.5 to 10 mol based on 100 mol of barium titanate, with a volumic ratio of Si oxide at the crystal grain boundary and grain boundary triple point kept at 0.5 or less, and the firing process is conducted with a temperature reduction rate of 100° C./hr or lower to suppress excessive permittivity lowering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Si oxide is added to the ceramic dielectric layer, then the glass phase precipitates at the crystal grain boundary, but this causes excessive lowering of permittivity due to compressive stresses on ceramic crystal grains
Solution Approach 1:
The patent changes the chemical composition parameters by limiting Si oxide content to 0.5-10 mol% and adjusting the ratio of Ba oxide (0.5-5 mol%) to Ca oxide (0.5-5 mol%). These parameter changes control the glass phase precipitation behavior, preventing excessive permittivity lowering while maintaining the beneficial effects of glass phase at grain boundaries.
Solution Approach 2:
The patent creates a composite ceramic dielectric layer containing barium titanate ceramic particles combined with a controlled glass phase matrix. The glass phase is formed from specific ratios of Ba oxide, Ca oxide, and Si oxide, creating a composite structure where the glass phase fills grain boundaries without causing excessive compressive stress that would lower permittivity.
2Volume of moving object
If the thickness of the ceramic dielectric layer is reduced, then the size is reduced and capacitance increases, but the temperature characteristic deteriorates
Solution Approach 1:
The patent changes the compositional parameters of the glass phase by controlling the Ba oxide and Ca oxide ratios (each 0.5-5 mol%). This compositional adjustment modifies the thermal expansion characteristics and dielectric properties of the glass phase, enabling thin ceramic dielectric layers to maintain stable temperature characteristics despite reduced thickness.
3Ease of manufacture
If the content of glass component is increased, then the sintering is improved and grain growth is controlled, but the permittivity is excessively lowered
Solution Approach 1:
The patent optimizes the glass component content parameter, limiting Si oxide to 0.5-10 mol% and controlling Ba oxide and Ca oxide ratios. This parameter optimization ensures sufficient glass phase for good sintering and grain boundary control, while preventing excessive glass phase that would cause compressive stresses and lower permittivity.
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
This approach stabilizes the production of multi-layer ceramic capacitors with maintained permittivity, preventing excessive lowering and ensuring reliable performance by controlling the Si oxide distribution and firing conditions.
Implementation Method 1
the glass phase is precipitated to the crystal grain boundary in the ceramic dielectric layer by the addition of the Si oxide
Implementation Method 2
fired at a programming rate of 200° C./hr, at a maintenance temperature of about 1200° C. (1180° C. to 1280° C.) for a temperature holding time of 2 hr
Implementation Method 3
external electrodes are coated and fired to obtain a multi-layer ceramic capacitor
Data Source
AI summary
A small, large-capacitance multi-layer ceramic capacitor suppressed for remarkable lowering of permittivity, having a capacitor main body formed of ceramic dielectric layers comprising barium titanate as a main component and an Si oxide at a ratio of 0.5 to 10 mol being converted as SiO2 based on 100 mol of barium titanate and internal electrode layers, and a pair of external electrodes which are formed at the end faces of the capacitor main body and connected electrically with the internal electrode layers, in which the ceramic dielectric layer has crystal grains, crystal grain boundaries each present between the crystal grains and a grain boundary triple point, and B/A is 0.5 or less assuming the amount (mol) of an Si oxide being converted as SiO2 contained based on 100 mol of barium titanate as A and the volumic rate (vol %) of the Si oxide present at the crystal grain boundary and the grain boundary triple point of the ceramic dielectric layer as B, whereby remarkable lowering of a permittivity due to precipitation of an Si oxide to the crystal grain boundary and the grain boundary triple point is suppressed.