Dielectric Ceramic with Graded Rare-Earth Distribution for X5R Capacitors
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Solution Overview
Problem
The existing dielectric ceramic materials used in monolithic ceramic capacitors have a low dielectric constant and inadequate temperature stability, failing to meet the requirements for high capacitance and reliable performance in miniaturized devices.
Innovation Solution
A dielectric ceramic composition with a primary component of ABO3 (where A is Ba or Ba and Ca, and B is Ti, Zr, or Hf) and additional components including rare-earth elements, Cu, Mg, Mn, and Si, with a specific distribution of rare-earth elements in crystal grains and grain boundaries, forming a solid solution to enhance dielectric constant and temperature stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a dielectric ceramic material with high dielectric constant is used to increase capacitance, then the capacitance increases, but the temperature stability deteriorates
Solution Approach 1:
The patent applies local quality by creating distinct regions within the ceramic material: crystal grains with specific rare-earth element concentrations and grain boundaries with different compositions. The crystal grains contain rare-earth elements at concentrations that provide high dielectric constant, while the grain boundaries have controlled rare-earth element distribution that ensures temperature stability. This spatial differentiation of composition allows simultaneous achievement of high capacitance and temperature stability.
Solution Approach 2:
The patent uses composite materials by combining multiple components: ABO3 perovskite structure as the base dielectric material, rare-earth elements (such as Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, or Y) as dopants to enhance dielectric constant, and Cu as an additional component. The composite structure consists of crystal grains containing these components in specific proportions, creating a material that achieves both high dielectric constant and good temperature characteristics.
2Volume of moving object
If the dielectric ceramic is miniaturized to reduce device size, then the device size decreases, but the reliability deteriorates
Solution Approach 1:
The patent applies parameter changes by precisely controlling the chemical composition parameters of the dielectric ceramic. The formula specifies exact ranges: 95-105 parts by mole of ABO3, 0.1-5 parts by mole of rare-earth elements, and 0.1-5 parts by mole of Cu. By optimizing these compositional parameters, the material achieves high dielectric constant and good temperature stability even in miniaturized form, thereby maintaining reliability while reducing device size.
3Quantity of substance
If the rare-earth element concentration is increased to improve dielectric constant, then the dielectric constant increases, but the manufacturing precision deteriorates
Solution Approach 1:
The patent applies preliminary action by pre-establishing the rare-earth element distribution pattern during the manufacturing process. The method specifies that rare-earth elements should be present in 90% or more of the region of each crystal grain in 55%-85% of the crystal grains, and in less than 10% of the region in 15%-45% of the crystal grains. This predetermined distribution pattern is achieved through controlled sintering processes, ensuring both high dielectric constant and manufacturability.
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 proposed solution achieves a high dielectric constant of 5,500 or more, satisfying the X5R characteristic and ensuring reliable performance under high-temperature and high-voltage conditions, with improved capacitance and reduced defectives in long-term load life tests.
Implementation Method 1
having a structure composed of crystal grains containing the above-described ABO3 as a primary component and grain boundaries between the crystal grains, wherein when a cross section of the above-described dielectric ceramic is observed, the condition that in 55% to 85% by number of the above-described crystal grains, the above-described rare-earth element is present in 90% or more of the region of each crystal grain
Data Source
AI summary
Dielectric ceramic having a high dielectric constant of 5,500 or more and exhibiting good dielectric constant temperature characteristic, and a small, high-capacitance monolithic ceramic capacitor having an electrostatic capacitance temperature characteristic satisfying the X5R characteristic are provided. The dielectric ceramic includes a BaTiO3 based or (Ba,Ca)TiO3 based primary component, a rare-earth element and Cu, and has a structure composed of crystal grains and grain boundaries between the crystal grains. The ratio of the average concentration of the rare-earth element in the grain boundaries to the average concentration of the rare-earth element in the inside of the crystal grains is less than 2, and in a cross section of the dielectric ceramic, the rare-earth element is present in 90% or more of the region of first crystal grains, the number of which is 55% to 85% of the crystal grains, and the rare-earth element is present in less than 10% of the region of second crystal grains, the number of which is 15% to 45% of the crystal grains.