Multilayer Ceramic Capacitor with Reducing Atmosphere Firing
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Solution Overview
Problem
Multilayer ceramic capacitors face challenges with capacitance and temperature stability, particularly when miniaturized or subjected to direct-current voltage, leading to reduced reliability and unsatisfactory X8R characteristics, especially in extreme temperature environments like those found in automotive electronics.
Innovation Solution
A multilayer ceramic capacitor design utilizing a dielectric porcelain composite with specific accessory constituents and particle size control, including barium titanate, magnesium oxide, silicon oxide, vanadium oxide, and calcium zirconate, to maintain stable capacitance-temperature characteristics and resist changes under direct electric fields, allowing firing in a reducing atmosphere without Pb, Bi, or Zn.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If base metals such as Ni or Ni-alloys are used as conductive material for internal electrode layers to reduce cost, then manufacturing cost is reduced, but oxidization of internal electrode layers occurs during firing in atmosphere
Solution Approach 1:
The patent specifies firing in a reducing atmosphere (nitrogen or hydrogen atmosphere) to prevent oxidization of the base metal internal electrode layers. This creates an inert environment that protects the reactive base metals from oxidizing during the high-temperature firing process, resolving the contradiction between using inexpensive base metals and preventing their oxidization.
2Reliability
If firing is conducted in a reducing atmosphere to prevent internal electrode layer oxidization, then oxidization is prevented, but reduction of dielectric layers occurs and specific resistance decreases
Solution Approach 1:
The patent carefully controls the reducing atmosphere parameters (using nitrogen or hydrogen with specific purity levels) and firing temperature ranges (1200-1400°C) to achieve a balance where internal electrode layers are protected from oxidization while dielectric layer reduction is minimized. This parameter optimization resolves the contradiction between preventing oxidization and maintaining specific resistance.
Solution Approach 2:
The patent uses composite dielectric materials containing barium titanate as the primary constituent combined with accessory constituents (calcium zirconate, magnesium oxide, silicon oxide, vanadium oxide, and rare earth oxides) that are resistant to reduction in reducing atmospheres. This composite formulation protects against specific resistance degradation while allowing the use of reducing atmosphere for firing.
3Productivity
If dielectric layer thickness is decreased to reduce capacitor size and increase capacitance, then miniaturization and capacitance increase are achieved, but insulating resistance is significantly deteriorated by electric field application
Solution Approach 1:
The patent employs composite dielectric materials with barium titanate as the primary constituent combined with accessory constituents including calcium zirconate, magnesium oxide, silicon oxide, vanadium oxide, and rare earth oxides (Sc, Er, Tm, Yb, Lu, Y, Dy, Ho, Tb, Gd, or Eu). This composite formulation maintains high insulating resistance even when dielectric layers are thin, resolving the contradiction between miniaturization and insulating resistance.
Solution Approach 2:
The patent optimizes the thickness of dielectric layers and internal electrode layers within specific ranges, and controls the firing temperature and atmosphere parameters to achieve a balance where thin dielectric layers maintain sufficient insulating resistance while achieving high capacitance density and miniaturization.
4Quantity of substance
If conventional dielectric materials are used to achieve high capacitance, then capacitance is increased, but capacitance-temperature characteristics and DC bias characteristics deteriorate under direct-current voltage application
Solution Approach 1:
The patent uses composite dielectric materials with barium titanate as the primary constituent combined with accessory constituents (calcium zirconate, magnesium oxide, silicon oxide, vanadium oxide, and rare earth oxides) that improve both capacitance and stability. This composite formulation resolves the contradiction between achieving high capacitance and maintaining stable capacitance-temperature and DC bias characteristics.
Solution Approach 2:
The patent optimizes the composition parameters including the ratio of barium titanate to accessory constituents, the specific types and amounts of rare earth oxides, and the firing conditions to achieve a balance where high capacitance is obtained while capacitance-temperature characteristics and DC bias characteristics remain stable under direct-current voltage application.
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 solution ensures that the capacitors exhibit excellent X8R characteristics, minimal capacitance change over time, and improved Tc bias characteristics, making them suitable for use in harsh automotive environments with stable temperature and voltage conditions.
Implementation Method 1
the dielectric layers and internal electrode layers are simultaneously fired at a high temperature in a reducing atmosphere; however, when the firing is conducted in a reducing atmosphere, reduction of the dielectric layers occurs and thereby the specific resistance is decreased
Implementation Method 2
the relative dielectric constant ∈r decreases with time under the application of a direct electric field; which is also a problem
Data Source
AI summary
A multilayer ceramic capacitor having a laminate including alternately stacked dielectric layers of a sintered compact composed of crystal particles of a dielectric porcelain composite and internal-electrode layers. The dielectric porcelain composite comprises a primary constituent containing barium titanate; a first accessory constituent composed of at least one of MgO, CaO, BaO, and SrO; a second accessory constituent containing silicon oxide as a major constituent; a third accessory constituent composed of at least one of V2O5, MoO3, and WO3; a fourth accessory constituent composed of an oxide of R1 (wherein R1 is at least one of Sc, Er, Tm, Yb, and Lu); a fifth accessory constituent composed of CaZrO3 or a combination of CaO and ZrO2; and a sixth accessory constituent composed of an oxide of R2 (wherein R2 is at least one of Y, Dy, Ho, Tb, Gd, and Eu).