Multilayer Varistor Cover Layer for Lower Stray Capacitance
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Solution Overview
Problem
Existing multilayer varistors face challenges in reducing capacitance while maintaining effective protection against overvoltages, as methods to minimize stray capacitance are either ineffective or costly, and often compromise the component's durability or production complexity.
Innovation Solution
A multilayer varistor design utilizing two ceramic materials with differing concentrations of monovalent elements, where the second ceramic material with higher monovalent element content forms an insulating cover layer, significantly reducing stray capacitance without affecting the active region's properties, and a manufacturing method that ensures these materials are processed together without defects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the active region (overlap area) is reduced to lower capacitance, then the capacitance decreases, but the leakage current and protective effect decrease proportionally
Solution Approach 1:
The patent applies different ceramic materials with different dielectric constants to different regions of the varistor. The first ceramic material with lower dielectric constant is used in the inactive region near the surface, while the second ceramic material with higher dielectric constant is used in the active region. This local differentiation allows the inactive region to contribute less to stray capacitance while preserving the active region's protective characteristics.
2Reliability
If a bismuth-containing top layer is applied as electroplating protection, then chemical insulation and durability are improved, but diffusion and reaction zones during sintering occur due to different chemical composition
Solution Approach 1:
The patent uses two ceramic materials that are both based on zinc oxide with similar chemical compositions, differing only in their dielectric constants. This compositional homogeneity ensures that both materials can be sintered together without forming disadvantageous diffusion and reaction zones, while still achieving the desired electrical property differentiation through controlled doping with monovalent elements.
3Quantity of substance
If lithium or sodium is diffused into the surface during additional heat treatment, then leakage current and relative permittivity of the outermost layer are reduced, but further heat treatment for glass layer application becomes extremely difficult
Solution Approach 1:
The patent incorporates the monovalent element doping directly into the ceramic materials during the initial sintering process, rather than requiring subsequent heat treatment. The first ceramic material is doped with monovalent elements during manufacturing, which reduces its dielectric constant before the component is assembled. This preliminary action eliminates the need for additional heat treatment steps and allows standard glass layer application procedures to be used.
4Quantity of substance
If two different ceramics with very different properties are used for carrier layer and varistor ceramic, then low relative permittivity is achieved, but weak bond between layers occurs
Solution Approach 1:
The patent uses two ceramic materials that are both based on zinc oxide with similar chemical compositions and sintering characteristics, differing only in their dielectric constants achieved through different doping levels. This compositional similarity ensures strong bonding between layers during sintering, eliminating the weak bond problems associated with using two completely different ceramics while still achieving the desired low relative permittivity in the inactive region.
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 effectively reduces the total capacitance of the multilayer varistor while maintaining its protective effectiveness and durability, avoiding the drawbacks of previous methods such as high production costs and mechanical instability.
Implementation Method 1
The first and the second ceramic material differ in a concentration of monovalent elements X+
Implementation Method 2
The DK of this ceramic is dominated by barrier layers between the ZnO grains
Implementation Method 3
stacking, laminating and sintering of the green films
Data Source
AI summary
In an embodiment a method for manufacturing a multilayer varistor includes providing a first ceramic powder for producing a first ceramic material and at least one second ceramic powder for producing a second ceramic material, wherein the ceramic powders differ from each other in concentration of monovalent elements X+ by 50 ppm≤Δc(X+)≤5000 ppm, wherein X+=(Li+, Na+, K+ or Ag+), and wherein Δc denotes a maximum concentration difference occurring between an active region and a near-surface region of the multilayer varistor, slicking of the ceramic powders and forming of green films, partially printing of a part of the green films with a metal paste to form inner electrodes, stacking printed and unprinted green films, laminating, decarbonizing and sintering the green films and applying outer electrodes.