Focus on protective: Coating technology makes comprehensive surface protection possible

Dr. Chi Ma, Applied Materials Inc., discusses the innovations and deposition methods that have improved the wear protection of coatings across a variety of surfaces

The tribology and wear protection of coatings has been an active and rapidly developing area for research and industries in recent years, with innovative coating materials, structures and fabrication technologies. From the view of coating composition, one of the most widely studied organic coatings for wear protection is diamond-like carbon (DLC) due to its atomic high-strength bonding ability and therefore, macroscopic wear resistance [1,2,3].

Atomic layer deposition

As the coating’s thickness scales down to nanometers, more precision coating techniques, e.g., atomic layer deposition (ALD), emerge and fit within its scope. Atomic layer deposition (ALD) is a thin-film deposition technique that allows precise control over the thickness and composition of deposited films. ALD involves the alternating exposure of the substrate to two or more precursor gases, which react with the surface to deposit a thin film of material.

In recent years, researchers have focused on developing new materials for ALD coatings, such as metal oxides, nitrides and sulphides. These new materials offer unique properties, such as high electrical conductivity, optical transparency and catalytic activity. Metal oxides are widely used as dielectric materials in microelectronic devices due to their high electrical insulation properties. ALD has been used to deposit high-quality metal oxide films onto substrates, such as silicon and metal foils. For example, Beladiya et al. [16] developed a method for depositing high-quality hafnium oxide (HfO₂) films onto flexible substrates using plasma-enhanced ALD. The HfO₂ films showed excellent electrical insulation properties, making them suitable for flexible electronic applications.

Nitrides and sulphides are promising materials for various applications, such as energy storage and catalysis. ALD has been used to deposit high-quality nitride and sulphide films onto substrates, such as silicon and metal foils. For example, Mattinen et al. [17] developed a method for depositing high-quality molybdenum disulfide (MoS₂) films onto silicon substrates using thermal ALD. The MoS₂ films showed excellent catalytic activity, making them suitable for catalysis applications. In addition to new materials, researchers have also focused on developing new deposition methods for ALD coatings. Plasma-enhanced ALD (PEALD) is a method that involves using plasma to break down the precursor gas into reactive species that can react with the substrate’s surface. PEALD can produce high-quality films with improved adhesion and uniformity. For example, Elers et al. [18] used PEALD to deposit a titanium nitride (TiN) film on a silicon substrate. The film showed excellent electrical conductivity properties, making it suitable for electronic device applications.

Spatial ALD (SALD) is a method that involves using a mask to define the deposition area, resulting in patterned films with high resolution. SALD can produce films with precise thickness and composition control, making them suitable for various applications, such as microelectronics and sensors. For example, Kannan et al. [19] used SALD to deposit patterned zirconium oxide (ZrO₂) films on a silicon substrate. The patterned ZrO₂films showed excellent electrical insulation properties, making them suitable for microelectronic applications.

Laser cladding

While existing coating techniques alleviate damage and prevent failure by tailoring the coating’s composition and microstructure, new technologies are continuously developed to improve coating performance. Laser cladding is a coating technique that is used for surface modification, repair and restoration. Similarly to additive manufacturing, laser cladding is a process where a laser beam is used to melt and fuse the coating material onto the substrate. Zhu et al. [20] reviewed the principle, practice and application of laser cladding. They reported that laser cladding is used in various applications such as aerospace, automotive and biomedical coatings. Laser cladding has the advantage of achieving coatings with high precision and low heat input, but it has limitations in achieving coatings with high productivity.

Another newly developed technique, surface severe plastic deformation (SSPD), was also used to process the substrate and sequential coating layers were found to exhibit stronger adhesion [21]. SSPD was believed to induce activated sites with higher surface energy on substrates. During deposition processes, stronger atomic bonding eventually leads to good adhesion and high-quality coatings. From the above two examples, it can be observed that cross-discipline techniques can be applied in the coating field and the techniques achieve unexpected high-quality coatings and efficient improvements. However, no matter what the coating compositions or mechanisms are, the fact is that more and more innovative technologies are incorporated to enrich the family of coating strategies, and such a topic is of significant interest.

Conclusion

In conclusion, coating technologies are a critical aspect of modern manufacturing and have many applications in various industries. It covers and involves multi-physics and many research fields. Advances in coating technology, including the development of new materials and deposition methods, will continue to drive innovation in industry and academia, leading to new products and applications. As such, further research and development in this field will be essential, and any breakthrough deserves significant attention from all research communities.