A new deposition method improves the thermal and chemical stability of transition-metal nitride (TMN) thin-film layers. These thin films could be used in electronic applications ranging from cutting tools to the aerospace sector.

TMNs have previously been alloyed with aluminum to enhance the stress and high-temperature oxidation resistance that make the materials ideal for wear protection in high-temperature machining. However, the aluminum often precipitates as a wurtzite-aluminum nitride complex that lacks the hardness characteristics necessary for mechanical applications.

The innovative deposition technique uses two simultaneous plasma sources to overcome this limitation. A continuous flux of vanadium atoms to the metal substrate is achieved by DC-magnetron sputtering as periodic fluxes of ionized aluminum are delivered by high-power impulse magnetron sputtering (HIPIMS).

The nitrogen in the carrier gas, consisting of a mixture of nitrogen and argon, combines with the aluminum Source: AVSions and vanadium neutrals, forming the thin film on the metal substrate. Application of the substrate bias, which is synchronized to the aluminum ion flux, is the key to the deposition method. Separation of the vanadium from aluminum serves to improve mechanical properties of the films.

The depth of aluminum penetration in the film is controlled by adjusting the amplitude of the synchronous bias voltage pulse. By increasing their incident energy, the aluminum ions were driven deeper into the film, below the high-mobility surface layer, while creating supersaturated alloy films.

Aluminum ionization remains the limiting step in this approach, since the HIPIMS method only ionizes about 70% of the aluminum flux. The remaining 30% arrives to the metal substrate as neutrals that do not separate from the vanadium in the film.

Despite the incomplete ionization of aluminum ions, the deposition process method enables unprecedented control over the phase formation and properties of the thin films.

Researchers from Sweden’s Linköping University and Germany’s RWTH Aachen presented their research at the AVS 65th International Symposium and Exhibition, held Oct. 21-26, 2018, in Long Beach, California.