Capacitive HF Feed for Tubular Cathodes in Plasma Coating
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Solution Overview
Problem
Existing methods for supplying high-frequency current to rotatable tubular cathodes in plasma coating systems face issues such as thermal stress in vacuum feed-throughs, contamination from carbon brushes, inhomogeneous current distribution leading to uneven sputter removal, and limited suitability of commutator systems for HF feed.
Innovation Solution
A capacitive HF feed system using a coupling capacitor formed between the tubular cathode and a metal plate or foil, which extends over the cathode's length within the vacuum chamber, ensuring maximum capacitance and uniform current distribution, with adjustable gap to compensate for wear and reactive current reduction through insulation and shielding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a vacuum feed-through is used to supply HF current to the tubular cathode, then the cathode can be powered, but the feed-through becomes thermally stressed and leaks over time
Solution Approach 1:
The invention removes the vacuum feed-through component entirely from the system. Instead of conducting HF current through the vacuum wall, the system uses capacitive coupling where the HF power is transmitted through the vacuum boundary without direct electrical contact, eliminating the thermal stress and leakage problems associated with traditional feed-throughs
Solution Approach 2:
The invention introduces a capacitive coupling mechanism as an intermediary between the HF power source and the tubular cathode. This coupling acts as a mediator that transfers energy through the vacuum boundary without requiring direct electrical connection, thereby avoiding the thermal and mechanical stresses that cause feed-through failure
2Reliability
If carbon brushes are used to supply HF current, then the cathode can be powered, but the vacuum chamber becomes contaminated with brush abrasion
Solution Approach 1:
The invention replaces the mechanical contact system (carbon brushes physically touching the rotating cathode) with a non-contact capacitive coupling system. This substitution eliminates mechanical wear and the generation of contaminating particles while maintaining reliable power transmission to the rotating cathode
Solution Approach 2:
The capacitive coupling serves as an intermediary that transfers HF power without direct mechanical contact. This intermediary mechanism eliminates the need for sliding contacts, thereby preventing the generation of abrasive particles that would contaminate the vacuum environment
3Device complexity
If HF current is fed through a single point, then the power supply is simple, but the current distribution becomes inhomogeneous leading to uneven sputtering
Solution Approach 1:
The invention divides the power coupling into multiple segments along the length of the tubular cathode. Instead of a single point feed, the capacitive coupling is distributed along the cathode axis, creating multiple coupling points that collectively provide uniform current distribution and homogeneous sputtering across the entire cathode surface
Solution Approach 2:
The invention transitions from a zero-dimensional point feed to a one-dimensional distributed feed along the cathode length. By extending the capacitive coupling along the axial dimension, the system achieves uniform current distribution without significantly increasing structural complexity
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 capacitive HF feed system provides a uniform and low-loss supply of HF current, ensuring homogeneous sputtering and maintaining mechanical stability and capacitance over the cathode's lifespan, while preventing contamination and thermal stress.
Implementation Method 1
the high-frequency power source is coupled to the tubular cathode within the vacuum chamber via a capacitive HF feed in the form of a coupling capacitor
Implementation Method 2
the coupling capacitor of the HF feed consisting of a part of the surface of the tubular cathode and a metal plate or foil
Implementation Method 3
a stationary magnet arrangement located within the tubular cathode and extending along the same to form a magnetic field
Data Source
Figure 1
Figure 2
AI summary
The invention relates to an assembly for feeding in HF current for rotatable tubular cathodes (1) in a vacuum chamber (4) of a plasma coating system, and a high-frequency current source (14) and a magnet assembly (7) located within the tubular cathode (1) and extending along the tubular cathode for producing a magnetic field (6). The aim of the invention is to create an assembly for feeding in HF current for tubular cathodes that enables a low-loss feed-in of the HF current in such a manner that especially homogeneous sputter removal from the tubular cathode is guaranteed. Said aim is achieved in that the HF current source (14) is coupled to the tubular cathode (1) within the vacuum chamber (4) by means of a capacitive HF feed-in (9) in the form of a coupling capacitor (18). The coupling capacitor (18) of the HF feed-in (9) comprises a part of the surface of the tubular cathode (1) and a metal plate or metal film (10), which surrounds the tubular cathode (1) at least partially at a specified distance.