Physical vapor deposition (PVD) is a thin-film coating process that produces coatings of pure metal, metal alloys and ceramics with thicknesses typically in the range of 1 to 10 µm. As the name suggests, physical vapor deposition is the physical deposition of atoms, ions or molecules of a coating substance onto a substrate.
PVD coatings – types
There are three main types of PVD, all performed in a chamber with a controlled atmosphere under reduced pressure (0.1 to 1 N/m2):
– thermal evaporation,
– ion plating.
Thermal evaporation is the heating of a solid material to produce a vapor that condenses on the substrate to form a coating. Heating is achieved by various methods, including hot fiber, electrical resistance, electron beam or laser and arc. Sputtering involves creating a plasma between the coating layer and the substrate. Ion plating is essentially a combination of thermal evaporation and sputtering.
All three techniques can be used for target material deposition or „reactive” applications, where chemical reactions occur in the vapor/plasma phase between the coating material atoms and the „reactive” gas. The temperature of the coated substrate is typically 200-400°C, well below the temperatures associated with CVD (chemical vapor deposition, another thin-film process). PVD is an in-line process that requires easy access to the substrate surface. Rotate some parts to get an even coating.
PVD is a batch coating process with typical cycle times of 1 to 3 hours, depending on the type of material applied and the desired coating thickness. Typical application rates range from 50 to 500 µm/hr, depending on the technology. Coated parts do not require additional mechanical or heat treatment.
Coatings made with PVD have many applications including:
- aluminum tracks and ceramic resistors for electronic circuits,
- anti-reflective ceramic coatings for optics,
- decorative coatings on plastics,
- corrosion-resistant coatings on gas turbine blades,
- anti-wear coatings for stamping machinery and tools.
Because the process in question works with the coating material as a single atom or at the molecular level, it can provide extremely clean and high-performance coatings that can be preferred over other methods used in many applications. At the heart of every microprocessor and semiconductor device durable protective films, optical lenses, solar panels and many medical devices, PVD coatings provide key performance attributes for the final product. Whether the coating needs to be extremely thin, clear, durable or clean, PVD has the solution.
PVD is used in a wide range of industries, such as optical applications, from eyeglasses to tinted self-cleaning glass. In addition, it is also used for solar photovoltaics or in devices such as computer chips, displays and communication devices, as well as functional or decorative finishes.
The two most common PVD coating processes are sputtering and thermal evaporation. Sputtering is the bombardment of a coating material called a target with high-energy charges, causing atoms or particles to be deposited on substrates such as silicon wafers or solar panels. Thermal evaporation is the process of raising the coating material to boiling point in a high vacuum environment, resulting in increased vapor flow in a vacuum chamber, which then condenses on the substrate.
What makes PVD coatings highly durable, corrosion- and scratch-resistant?
PVD’s ability to apply coatings at the atomic level allows us to control the structure, density and stoichiometry of thin films. Using specific materials and processes, we can develop specific properties of the PVD coating, such as hardness, lubricity, adhesion and others.
PVD coating equipment
PVD coatings reduce friction and act as a barrier against damage. The applications of these coatings are constantly expanding. In aerospace, automotive, defense, manufacturing and more, long-term durability is crucial.
This type of PVD coating is also highly resistant to tarnishing and corrosion, making it suitable for many durable decorative finishes. Gold or platinum PVD coating provides an excellent finish, making the watch highly resistant to scratches and dings, which are less resistant to abrasion.
Titanium nitride and similar coatings provide an aesthetically pleasing finish while providing high resistance to corrosion and wear. As a result, they are widely used in household items such as door handles, water and marine accessories, as well as machining tools, knives, drills and more.
What is sputtering?
Physical vapor phase deposition is an environmentally friendly „plating” technique that significantly reduces the amount of toxic substances that must be used, managed and disposed of, compared to other „wet” processes that involve liquid precursors and chemical reactions to produce the same amount of results. Physical vapor deposition provides exceptionally clean, pure and durable coatings and is the technology of choice for the surgical and medical implant industry.
How are PVD coatings applied?
Whether the specific application process is sputtering or thermal evaporation, both physical vapor deposition processes are essentially high-vacuum techniques that evaporate the source material into a plasma of atoms or molecules and deposit them onto various substrates. The process takes place in a high vacuum chamber with a pressure close to the space of 10-2 to 10-6 Torr (102 to 104 mbar), and the process is typically carried out at 50 to 500 degrees Celsius.
The coated object is clamped in a holder and placed in a vacuum chamber. Depending on the coating material used, the substrate requirements and the process, the chamber is pumped to the optimal pressure, and the coated object is often heated and plasma cleaned.
What are the typical target materials for PVD coating?
The coating material to be sprayed or vaporized is referred to as the „target” or „source material.” There are hundreds of materials commonly used in PVD. Depending on the end product, these materials include metals, alloys, ceramics, composites and almost anything from the periodic table of elements.
Some processes require unique coatings such as carbides, nitrides, suicides and borides for special applications. Each has special properties tailored to specific performance requirements. For example, graphite and titanium are commonly used in high-performance aerospace and automotive components, where friction and temperature are key success factors.
To produce a uniform thin coating of a few atoms or particles, coated components are typically rotated around multiple axes at the same speed or placed on a conveyor belt that passes through a plasma stream of deposited material. Single or multilayer coatings can be applied in the same deposition cycle.
Why is argon used for PVD?
Argon is an inert gas, which means it cannot chemically bond with other atoms or compounds. As a result, the coating material enters the gas phase in the vacuum chamber before being applied to the substrate.
In addition, reactive gases such as nitrogen, oxygen or acetylene can be introduced into the vacuum chamber to form compounds that form very strong bonds between the coating and the substrate during deposition. Although the deposited thin films can vary in thickness from a few angstroms to a few microns, they form very viscous coatings that work well in many applications, including decorative, electrical and other functional coatings. The applications are endless!
From microprocessors to solar panels, the PVD coating process produces some of the toughest, brightest and most advanced technology of our time, the most important of which is that PVD coatings can be applied without toxic residues that damage our planet’s environment.