Reactive High Power Impulse Magnetron Sputtering
Increasing the energy per pulse (peak power) in HiPIMS leads to increased metal ionization, from few to more than 50%. The discharge colour also changes
Although magnetron sputtering is widely used for thin films deposition, the deposition flux consists predominantly of neutral atoms. When ions are employed in the material synthesis, non-thermal energy may be delivered to the growing film and trigger various physical and chemical processes.
In order to significantly increase the ionization in magnetron sputtering, we use HiPIMS, a process where high power is applied in a pulsed manner. Typical peak power densities reach kW/cm2 in HiPIMS, two orders of magnitude higher than in standard sputtering. The resulting high instantaneous plasma densities lead to high metal ionization.
Because of the complex interaction between plasma and surfaces, and the dynamic nature of the HiPIMS, the process physics is rather complex. We combine experiments and modelling to understand the process physics and develop novel deposition processes.
Low temperature growth of compound thin films
VO2 thin films prepared by standard DC sputtering at 300° (blue) are not active. HiPIMS films prepared by HiPIMS at the same temperature (red) show thermochromic behaviour.
Synthesis of high quality compound thin films at low temperatures is an important challenge. When the growth temperature is reduced, thin films can then be prepared on polymer substrates or incorporated in complex systems with limited thermal budget.
For example, we have reduced the growth temperature of thermochromic VO2 films from 450 °C to 300 °C so far. This has been achieved using highly ionized deposition fluxes generated by high power impulse magnetron sputtering (HiPIMS). The advantage of employing ionized fluxes of deposition material, as compared to relying on neutral atoms in DCMS, is that ions provide means for controlling the energy input to the growing films and thus allow for the synthesis of thin films at low temperatures.
Same approach is suitable for highly textured piezoelectric AlN as well. We have demonstrated strong preferred (002) oriented AlN at room temperature without any seed layer.