Zinc Oxide Varistor with Bismuth Sputtering
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Solution Overview
Problem
Zinc oxide varistors with low dopant levels exhibit high resistance, leading to high voltages in high-current regions, which can cause dielectric breakdown and are not effectively managed by existing voltage nonlinear resistive elements.
Innovation Solution
A voltage nonlinear resistive element is created by joining a zinc oxide ceramic layer with a bismuth oxide layer, where the zinc oxide ceramic layer has a volume resistivity of 1.0×10−1 Ωcm or less, and electrodes are formed to pass through the junction, allowing for lower clamping voltage in high-current regions, and the bismuth oxide layer is formed using sputtering to avoid increasing the resistivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the dopant level in zinc oxide porcelains is kept very low (0.0009% to 0.018% by mass Al2O3), then the voltage nonlinear resistive element maintains good voltage nonlinear characteristics, but the resistance becomes too high leading to high clamping voltage in high-current regions
Solution Approach 1:
The invention introduces a dedicated zinc oxide ceramic layer with specifically engineered low volume resistivity (1.0×10^-1 Ωcm or less) that is joined to the bismuth oxide layer. This localized low-resistance pathway allows high-current regions to be handled effectively without compromising the overall voltage nonlinear characteristics of the varistor structure.
Solution Approach 2:
The invention creates a composite structure combining a zinc oxide ceramic layer (with controlled low resistivity) and a bismuth oxide layer. This composite material approach allows the system to simultaneously achieve good voltage nonlinear characteristics from the bismuth oxide interface and low clamping voltage in high-current regions through the low-resistivity zinc oxide ceramic layer.
2Object-generated harmful factors
If the zinc oxide ceramic layer has low volume resistivity (1.0×10^-1 Ωcm or less), then the clamping voltage in high-current region is reduced, but the manufacturing process becomes more complex
Solution Approach 1:
The invention specifies that the zinc oxide ceramic layer should be prepared in advance with the appropriate low volume resistivity (1.0×10^-1 Ωcm or less) through dopant selection and controlled processing. This preliminary preparation of the ceramic layer with optimized properties simplifies the subsequent assembly process, as the low-resistivity characteristic is already built into the material before joining with the bismuth oxide layer.
3Reliability
If the bismuth oxide layer is formed by sputtering, then the zinc oxide ceramic layer is not exposed to high temperature and volume resistivity is not increased, but the manufacturing process requires vacuum equipment
Solution Approach 1:
The invention replaces traditional high-temperature thermal processing methods with sputtering technology to form the bismuth oxide layer. This substitution of the deposition method allows the zinc oxide ceramic layer to maintain its low volume resistivity by avoiding high-temperature exposure, while still achieving effective joining between the layers through the sputtering process.
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 lowers the clamping voltage in high-current regions, preventing dielectric breakdown and ensuring the voltage nonlinear resistive element can handle large currents without significant voltage rise, even due to static electricity.
Implementation Method 1
the bismuth oxide layer may be formed on the zinc oxide ceramic layer by sputtering
Data Source
AI summary
A voltage nonlinear resistive element includes a resistor containing a joined body in which a zinc oxide ceramic layer composed mainly of zinc oxide and having a volume resistivity of 1.0×10−1 Ωcm or less is joined to a bismuth oxide layer composed mainly of bismuth oxide, and a pair of electrodes disposed on the resistor such that an electrically conductive path passes through a joint surface between the zinc oxide ceramic layer and the bismuth oxide layer. In this element, the zinc oxide ceramic layer of the joined body has a lower volume resistivity than before. This can result in a lower clamping voltage in a high-current region than before.