Oxide-Resistant Grounding for AIMD Feedthrough Capacitors
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Solution Overview
Problem
Existing feedthrough capacitors in active implantable medical devices face challenges with high-frequency performance due to titanium oxide formation, which increases equivalent series resistance and degrades performance, and the use of gold braze for attachment is expensive and inefficient.
Innovation Solution
A hermetically sealed filtered feedthrough assembly with an oxide-resistant metal addition, such as platinum iridium wire, is used to provide a low impedance and oxide-resistant grounding pathway, reducing resistance to less than 5 milliohms and inductance to less than 10 nanohenries, avoiding direct contact with titanium and minimizing oxide formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the feedthrough capacitor ground plates are directly connected to the titanium ferrule, then the grounding pathway is simple and direct, but titanium oxide formation increases the equivalent series resistance and degrades high-frequency performance
Solution Approach 1:
The patent introduces an intermediate oxide-resistant metal layer (such as platinum, iridium, or other noble metals) between the titanium ferrule and the feedthrough capacitor ground plates. This intermediary layer prevents direct contact between titanium and oxygen, eliminating oxide formation that would increase ESR. The intermediate layer serves as a mediator that maintains electrical conductivity while protecting against oxidation, thus resolving the contradiction between simple grounding structure and reliable high-frequency performance.
2Reliability
If gold braze is used to form the hermetic seal between the alumina and titanium ferrule, then the hermetic seal is reliable and oxide-resistant, but the cost increases significantly
Solution Approach 1:
The patent applies local quality by using oxide-resistant metal additions specifically at critical interfaces where oxidation would harm performance (such as the ferrule surface and bonding areas), rather than using expensive precious metals throughout the entire structure. This localized application of oxide-resistant materials maintains hermetic seal reliability and prevents oxide formation at critical points while significantly reducing overall precious metal consumption and cost.
3Device complexity
If the titanium ferrule is used directly for electrical connection, then the structure is simple and cost-effective, but the oxide formation increases equivalent series resistance
Solution Approach 1:
The patent implements preliminary anti-action by pre-coating the titanium ferrule surface with an oxide-resistant metal layer before assembly and exposure to oxygen-containing environments. This preliminary protective action prevents oxide formation from occurring in the first place, rather than attempting to remove or mitigate oxides after they form. The oxide-resistant coating is applied in advance to the ferrule surface, creating a barrier that eliminates the harmful oxidation effect while maintaining structural simplicity and cost-effectiveness.
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 equivalent series resistance and inductance of the grounding pathway, enhancing the high-frequency performance of feedthrough capacitors while reducing costs by minimizing the use of precious metals.
Implementation Method 1
an oxide-resistant metal addition electrically coupling the ground conductor to the second metallization of the filter capacitor
Implementation Method 2
titanium tends to form oxides which act as either insulators or semi-conductor. Accordingly, grounding the feedthrough capacitor electrode plates directly to the titanium ferrule is contra-indicated
Data Source
AI summary
A hermetically sealed filtered feedthrough assembly for an AIMD includes an electrically conductive ferrule with an electrically conductive extension at least partially extending into the ferrule opening. An electrically non-conductive insulator hermetically seals the ferrule opening. An electrically conductive pathway is hermetically sealed and disposed through the insulator between a body fluid and device side. A filter capacitor is located on the device side. A first low impedance electrical coupling is between a first metallization of the filter capacitor and the pathway. A ground conductor is disposed through the filter capacitor in non-conductive relation with the at least one active and ground electrode plates, where the ground conductor is electrically coupled to the extension of the ferrule. An oxide-resistant metal addition is disposed on the device side and electrically couples the ground conductor to the second metallization of the filter capacitor.