A capacitor is a passive electrical component that is capable of storing electrical charges. A capacitor consists of two conductive surfaces called electrodes, which are usually placed very close to each other. There is an electrical insulating medium between the electrodes—in the simplest case air. The capacitor is characterised by its capacitance, which indicates how much electrical charge can be stored at a certain applied voltage. The maximum voltage that can be applied to the electrodes and the maximum radio frequency (RF) current the capacitor can handle are also of interest.

Some applications, such as the generation of radio waves in shortwave transmitters, require capacitors with very high dielectric strength and the ability to withstand very high currents. In addition, it is necessary for the capacitance of the capacitors used in these transmitters to be adjustable. In principle, only vacuum capacitors can fulfill these properties. Because of the much better insulating properties of vacuum compared to air, vacuum capacitors are very often used. The electrodes of vacuum capacitors are typically concentric rings or spirals that are immersed in each other. The capacitance can be varied by changing the depth of immersion.

Both the areas of application and the corresponding designs of capacitors are very diverse. They are used in high power broadcast stations to tune resonant circuits and antennas, or in medical and scientific RF applications, such as MRI or accelerators. Comet mainly uses them in RF Matching Networks for plasma applications in the semiconductor industry where they are well known for their quality and longevity.

Vacuum Capacitors in the semiconductor industry

In many coating and etching processes within the semiconductor industry, a plasma is used which is ignited and maintained by high-frequency energy. Because the system impedance of the RF generator and the plasma are not equal, it is necessary to match the different impedances in order to transfer as much of the generator's energy to the plasma as possible. To achieve this, RF Matching Networks (also known as “Match boxes”) adjust the dynamic RF impedance of a plasma chamber to match the impedance of the RF system. This way we can ensure that the process power, yielded by the RF generator, can be supplied to the plasma process.

Over the past decades, Comet has established a very strong market position in the field of vacuum capacitors through superior quality, exceptional customer orientation and the most reliable delivery service. The most cutting-edge equipment in the semiconductor industry utilises Comet capacitors. This is thanks to Comet’s proven expertise in high-frequency engineering and manufacturing technology.

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