Another of the topics that attracted several papers at the recent SVC Conference was that of HiPIMS. This has been a regular topic for research for a number of years and more recently has seen an interest in evaluating it for roll-to-roll processing. I must confess that I have been left with the impression that it is an interesting technology that is still desperately seeking an application that will make the best use of the different characteristics of the process.
Magnetron sputtering deposits coatings with some energy and so is able to improve the adhesion over simple evaporated coatings because of the removal of any loosely bound deposited material. Arc evaporated coatings have the advantage that the ionisation of the depositing material is very high but the disadvantage is that the arc source is generally a point source and does not easily convert to a roll-to-roll coating process. Also the arc is able to spit out large droplets of material and so often the ionised flux is bent around using electromagnets to ensure that the momentum of these droplets carry them onto shields and so protect the substrates from the droplets damaging the coating quality. The need to collect these droplets reduces the material efficiency too.
The HiPIMS process looks to combine the best of these two deposition processes. The system gains the uniformity available form a conventional magnetron sputtering source but by using the very high energy short duration pulse is able to ionise a significantly greater amount of the depositing material than in conventional magnetron sputtering. This further improves the coating adhesion and coating density. However, there is a higher heat load with the process and the stress in the compacted coating needs to be controlled. This often results in the process needing to be run even slower than conventional magnetron sputtering.
Alternatives to the process such as using a hollow cathode or some other additional plasma source situated between the source (either evaporation or sputtering) and substrate would appear to be capable of achieving the same final coating but at a faster deposition rate, especially if starting from an evaporation source. I can see the argument where it might be justified for some very dense hard coatings for engineering or tribological applications but ever here I am not sure it is not just a me-too process.
Hence, I enjoy seeing a new process being developed and evaluated but am still waiting for its unique advantage that will make it the compelling source to choose for some coatings. I am also yet to be convinced that it is really suitable for a roll-to-roll process. As yet I think it remains an interesting development in search of a use. What do you think?