Solid Electrolytic Capacitor Leakage Current Reduction
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Solution Overview
Problem
Conventional solid electrolytic capacitors with in situ-polymerized polymers exhibit high leakage current and failure at high voltages due to poor adhesion of the polymer layer to the dielectric coating, especially when using valve metal powders with high specific charge, which results in poor electrical performance.
Innovation Solution
A capacitor design that includes a sintered porous anode body from a high specific charge powder, a dielectric layer formed by anodically oxidizing the anode, and a solid electrolyte with an in situ-polymerized conductive polymer layer, where the polymerization process involves a thiophene monomer reaction and subsequent washing and drying to ensure good adhesion and low leakage current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If in situ-polymerized conductive polymer is used as solid electrolyte, then equivalent series resistance is reduced, but leakage current increases
Solution Approach 1:
The patent applies parameter changes by optimizing the polymerization time (1 minute or more), washing time (25 minutes or more), and drying conditions to achieve the desired balance between low ESR and low leakage current. By controlling these process parameters, the polymer layer achieves proper adhesion and coverage without excessive polymerization that would increase leakage.
Solution Approach 2:
The patent employs preliminary action through the anodization step that creates a dielectric coating on the anode body before polymerization. This pre-formed dielectric layer provides a foundation that improves polymer adhesion and reduces leakage current, allowing the subsequent polymer layer to achieve low ESR without the harmful side effect of high leakage.
2Quantity of substance
If high specific charge powder is used to form anode, then capacitance is increased, but polymer layer adhesion to dielectric coating deteriorates
Solution Approach 1:
The anodization process is performed as a preliminary action to create a dielectric coating with optimized surface properties before polymerization. This pre-treatment ensures that even with high specific charge powder having small particles and large surface area, the subsequent polymer layer can adhere properly to the dielectric coating.
Solution Approach 2:
The patent changes the polymerization parameters by extending the reaction time to 1 minute or more, which allows sufficient time for the monomer to penetrate and adhere to the dielectric coating surface. This parameter adjustment compensates for the challenging surface conditions created by high specific charge powder, achieving both high capacitance and good adhesion.
3Strength
If polymerization time is extended to improve adhesion, then manufacturing time increases
Solution Approach 1:
The anodization step is performed as a preliminary action that prepares the dielectric coating surface to be more receptive to polymer adhesion. This pre-treatment reduces the polymerization time required to achieve adequate adhesion, as the surface is already optimized for polymer attachment before the monomer is applied.
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 capacitor achieves a leakage current of 110 microamps or less and low equivalent series resistance, maintaining stability and capacitance recovery even at high temperatures and humidity levels, with improved electrical properties and reduced capacitance loss.
Implementation Method 1
anodically oxidizing the sintered porous anode body to form a dielectric that overlies the anode body
Implementation Method 2
the monomer is allowed to react for a time period of about 1 minute or more to form a conductive polymer layer on the anode
Data Source
AI summary
A capacitor that is capable of exhibiting good electrical properties even under a variety of conditions is provided. More particularly, the capacitor contains a capacitor element that comprises a sintered porous anode body formed from a powder having a specific charge of about 100,000 μF*V/g or more; a dielectric that overlies the anode body; and a solid electrolyte that overlies the dielectric. The solid electrolyte contains an in situ-polymerized conductive polymer. Further, the capacitor exhibits a leakage current of about 110 microamps or less at a temperature of about 23° C. after being subjected to an applied rated voltage.