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Cylindrical cathodes for PVD coating

In the context of physical vapor deposition (PVD), "cylindrical cathode PVD" typically refers to a configuration used for the deposition of thin films onto a substrate for a variety of applications, including optical coatings, decorative finishes, and protective coatings.

Cylindrical cathode PVD is frequently employed in techniques such as magnetron sputtering or arc evaporation, in which the cylindrical cathode is frequently rotated or surveyed across the substrate to ensure uniform deposition and coating thickness.

Archives of Applied Science Reseach, vacuum chamber

Schematic curtesy: Archives of Applied Science Research (2009)

In cylindrical cathode PVD the target material functions as the source to be deposited in the form of thin metal or compound films, such as titanium, aluminum, or chromium, or metal oxides or nitrides.

During the PVD process, a high voltage is applied between the cylinder cathode and the substrate, which can be positioned in closer proximity than the widely used flat cathodes.

The cathode is then bombarded with ions, typically from a plasma or ion source, which causes the material to be discharged or sputtered from the cathode surface. The atoms or molecules that have been sputtered then move in a straight line and deposit on the substrate, producing a thin film.

Compared to conventional flat cathodes, cylindrical cathodes confine electrons near the target surface more effectively, resulting in a dense plasma sheath.

The cylindrical shape of the cathode enables

  • uniform erosion of the material

  • efficient utilization of the target material, and a

  • higher degree of ionization.

Using a cylindrical compressed graphitic cathode in magnetron sputtering can increase the sp3 content of the deposited carbon coatings, but I cannot guarantee that the sp3 content will exceed 70%. It also enables a larger deposition surface area, which can be advantageous for high-volume production procedures.

Proceedings of the Institution of Mechanical Engineers, Part B: Journal of Engineering Manufacture

Picture curtesy: Proceedings of the Institution of Mechanical Engineers, Part B: Journal of Engineering Manufacture (April 2013)

What are all the benefits of cylindrical cathodes, apart from process advantages?

Apart from the process advantages, other commercial overhead benefits of the cylindrically designed cathode types are:

  • Excellent thickness uniformity: The cylindrical cathode design incorporates excellent thickness uniformity. This is especially advantageous when depositing thin film coatings onto curved surfaces such as high precision optics; lenses and mirrors; a cylindrical cathode makes it possible to achieve uniform thickness across the bent or curved surface without the need for any intricate motions or uniformity shape modulations.

  • Capability to encapsulate complex or three-dimensional shapes: Uniformity is advantageous for all substrate types, but especially for those with complex surfaces, such as artificial bones, knee-cap replacements and stents. The cylindrical cathode configuration can aid in the deposition of homogeneous coatings across the entire surface, regardless of the topography or substrate shape.

  • High deposition rates: Cylindrical cathode offers inherently high deposition rates, so production volume need not be sacrificed for acceptable performance.

In other configurations, the sputtering process creates a racetrack-like furrow on the cathode, which can significantly reduce target utilization. However, a cylindrical cathode provides highly uniform erosion across the cathode target's surface, which may up to quadrupole the quantity of material that can be sputtered from a single target without being wasted or sent for recycling. This is especially essential for applications requiring expensive target materials; a cylindrical cathode may help reduce the total system's total cost of ownership by lowering net target costs.

PVD deposition system: M. Kroker et al. from Peter Vsna’s group. Surface and Coatings Technology, Volume 377

Schema curtesy: M. Kroker et al. from Peter Vsna’s group. Surface and Coatings Technology, Volume 377, 15 November 2019, 124864.

Schematic representation of deposition system a) three-dimensional representation, b) Overview of the chamber with carousel, substrate holders and magnetron sputter source with cylindrical target

When searching for a high-quality cylindrical PVD target, the following factors must be considered:

Purity: The target material must have a high level of purity to ensure that the deposited thin film has the desired properties. Impurities can alter the properties and efficacy of the film.

Homogeneity: The composition of the target should be uniform throughout its entire structure to ensure uniform film deposition and prevent differences in film properties across the substrate.

Density: The density of the target material influences its sputtering or evaporation rate, influencing the efficiency and quality of the deposition process and film.

Composition: The composition of the target should precisely mirror that of the desired film. Certain applications necessitate the use of alloys or compounds, so the target must be formulated accordingly.

Mechanical properties: The target must have the appropriate mechanical properties, such as hardness, to withstand the sputtering or evaporation process without degrading or contaminating the deposited film.

Size and shape: The target should be available in the size and shape required by the PVD apparatus being utilized.

PVD rotatable target - Avaluxe Nb rotatable

Nb rotatable

Notably, the specific requirements for a high-quality PVD target can vary depending on the application and the properties of the desired thin film. Therefore, it is crucial to consider the specific requirements of your PVD procedure and to consult with experts or reputable suppliers to choose the most appropriate target material.

PVD rotatable target - Avaluxe NbOx rotatable

NbOx rotatable

Beitrag: Blog2_Post
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