Variable Power Capacitor for RF Plasma Systems
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Solution Overview
Problem
Existing RF power capacitors face limitations in dynamically matching rapidly changing load impedance in plasma systems due to slow tuning times and bulkiness, and previous solutions like vacuum variable capacitors or switched-based adjustments suffer from inefficiencies and reliability issues.
Innovation Solution
The use of a paraelectric dielectric material with variable relative permittivity, controlled by a DC bias voltage, allows for extremely fast and continuous capacitance adjustment in RF power applications, reducing the size and complexity of capacitors while maintaining high power handling capabilities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If vacuum variable capacitors with mechanical drive mechanisms are used, then high power handling capability is achieved, but tuning time becomes slow (100 ms to several seconds)
Solution Approach 1:
The patent replaces the mechanical drive mechanism with an electric field-based tuning system. A DC control voltage is applied to the dielectric layer to change its permittivity, thereby adjusting capacitance values. This eliminates the mechanical motor and drive components, achieving instantaneous or near-instantaneous capacitance adjustment without the 100 ms to several seconds delay inherent in mechanical systems, while maintaining high power handling capability through the solid-state dielectric structure.
Solution Approach 2:
The patent changes the physical parameter of the dielectric material by applying a DC control voltage that modifies the permittivity of the dielectric layer. This allows continuous adjustment of capacitance values without mechanical movement, resolving the contradiction between fast tuning and high power handling by using an electric field effect rather than mechanical displacement.
2Power
If vacuum variable capacitors with mechanical drive mechanisms are used, then high power handling capability is achieved, but device size and manufacturing complexity increase
Solution Approach 1:
The patent eliminates the mechanical motor, drive shafts, and precision-machined electrode components by using a solid-state dielectric structure with DC voltage control. This substitution dramatically simplifies manufacturing, removes the need for long-lasting vacuum seals and precisely-machined parts, while maintaining high power handling through the robust dielectric-electrode configuration.
Solution Approach 2:
The patent uses a composite structure consisting of conductive electrodes and a dielectric layer (which may be a functional coating or deposited layer). This composite approach simplifies manufacturing compared to traditional vacuum capacitor construction, allowing the dielectric to be applied as a coating or layer rather than requiring precision-machined components, thereby reducing manufacturing complexity while maintaining high power handling capability.
3Loss of time
If switched-based capacitance adjustment (PIN diodes, BJTs, IGBTs) is used, then tuning speed is improved, but capacitance variation becomes stepped rather than continuous
Solution Approach 1:
The patent applies a continuously variable DC control voltage to the dielectric layer, which produces a corresponding continuous variation in the dielectric's permittivity and thus continuous capacitance adjustment. This eliminates the stepped capacitance changes inherent in switched-based systems while maintaining fast tuning speed, as the capacitance can be adjusted to any value within the operating range by varying the DC control voltage continuously.
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 solution enables rapid and continuous impedance matching in RF power systems, reducing the size and manufacturing complexity of capacitors, and achieving high power handling with improved reliability and efficiency.
Implementation Method 1
a non-linear (e.g. ceramic) dielectric material in its paraelectric phase whose relative permittivity varies with applied electric field
Data Source
AI summary
A power capacitor (7) is described for use in an RF power delivery system. The power capacitor comprises at least two RF electrodes (18, 19) separated by a capacitor dielectric (17) comprising a solid paraelectric dielectric material whose relative permittivity is controllable by varying a DC bias voltage applied across the dielectric (17) at DC bias electrodes (10, 26, 28). Composite capacitor configurations, an RF power system and a method of controlling the power capacitor are also described.