Overcoming the insulating materials limitation in HiPIMS: Ion-assisted deposition of DLC coatings using bipolar HiPIMS

The present study aims to demonstrate that operating the HiPIMS discharge in bipolar regime (BP-HiPIMS) enables an energy-enhanced deposition process of high-quality hydrogen-free DLC thin films (high hardness, low coefficient of friction, good wear resistance, good adherence to the substrate and very low surface roughness). The structural and mechanical properties of DLC thin films deposited using the BP-HiPIMS technique were compared to those of the films prepared using a conventional HiPIMS process, under various deposition conditions. The BP-HiPIMS technique generates an energetic ion population and a substantial increase in the ion flux as compared to the conventional (monopolar) HiPIMS. This phenomenon overcomes the limitations when working with insulating or high electrical resistivity materials (both substrates and coatings), i.e. the need to accelerate the film-forming species. Energetic enhanced deposition conditions during bipolar HiPIMS facilitate the densification (up to 2.7 g/cm3) of amorphous carbon thin films which results in an increase in the film hardness (23 GPa) when depositing on Si substrates, without using substrate bias voltage, adhesion interfacial layer or substrate pre-treatment. Besides high hardness, the BP-HiPIMS process allows growing DLC coatings with good elastic strain to failure and high resistance to plastic deformation and cracking.