Multilayer Varistor with Silver Electrodes and Doped ZnO Ceramic
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Solution Overview
Problem
Multilayer varistors using silver-palladium internal electrodes face issues with high costs due to expensive palladium and increased delamination risks from thick electrode layers, which are problematic for small components.
Innovation Solution
A multilayer component with a ceramic main element doped with a chemical compound of the metal structure, allowing cosintering at controlled temperatures with reduced diffusion, enabling thin internal electrodes and external metallizations, and eliminating the need for palladium by using silver or palladium alloys, along with a passivating layer doped to prevent material loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If silver-palladium alloy is used for internal electrodes, then diffusion of electrode material into ceramic is reduced, but production cost increases significantly
Solution Approach 1:
The patent replaces expensive palladium-containing alloys with pure silver electrodes, which are cheaper and more readily available. The ceramic body is doped with silver to prevent diffusion, eliminating the need for costly palladium while maintaining electrode stability during sintering.
Solution Approach 2:
The patent changes the chemical composition parameters by doping the zinc oxide ceramic with silver (0.1-5 mol%) and adjusting the sintering temperature (900-1100°C). This parameter optimization allows pure silver electrodes to maintain their shape and prevent diffusion without requiring expensive palladium additives.
2Reliability
If greater layer thicknesses (up to 10 μm) are used for electrode layers, then reduction of electrode layer during sintering is countered, but delamination occurs to increased extent
Solution Approach 1:
The patent optimizes the electrode layer thickness to a specific range (0.5-5 μm, preferably 1-3 μm) and adjusts the sintering temperature (900-1100°C) to achieve proper bonding. The zinc oxide ceramic body is doped with silver (0.1-5 mol%) to match the thermal expansion coefficients, preventing delamination while maintaining electrode stability during sintering.
Solution Approach 2:
The patent addresses thermal expansion mismatch by doping the zinc oxide ceramic with silver, which adjusts the thermal expansion properties of the ceramic body to match the silver electrodes. This prevents delamination caused by differential thermal expansion during heating and cooling cycles.
3Reliability
If greater layer thicknesses (up to 10 μm) are used for electrode layers, then reduction of electrode layer during sintering is countered, but volume requirement increases
Solution Approach 1:
The patent reduces electrode layer thickness to an optimized range (0.5-5 μm, preferably 1-3 μm) and adjusts the sintering temperature (900-1100°C) to compensate for material loss. The zinc oxide ceramic body is doped with silver (0.1-5 mol%) to minimize diffusion and maintain electrode dimensions, achieving stable electrodes with minimal thickness and volume.
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 reduces material loss, minimizes delamination, and allows for precise, cost-effective production of small, high-performance multilayer components with consistent thermal and electrical properties.
Implementation Method 1
The main element comprises, for example, about 95 mol per cent of ZnO... The component can further comprise Co3O4, Mn2O3, SiO2, Cr2O3... The main element and the metal structure are preferably cosintered.
Implementation Method 2
Costly internal electrodes composed of silver and palladium (Ag, Pd) are generally used for electrical contacting of multilayer varistors... The addition of palladium increases the melting point of the electrode layers in a suitable way, so that the electrode layer can be sintered together with the ceramic and diffusion of silver during sintering is reduced.
Data Source
AI summary
A multilayer component and a mathod for producing a multilayer component are disclosed. In an embodiment a multilayer component includes a ceramic main element and at least one metal structure, wherein the metal structure is cosintered and wherein main element is a varistor ceramic having ≥90 mol % of ZnO, from 0.5 to 5 mol % of Sb2O3, from 0.05 to 2 mol % of Co3O4, Mn2O3, SiO2 and/or Cr2O3, and <0.1 mol % of B2O3, Al2O3 and/or NiO.