Hysteresis-free deposition of niobium oxide films by HiPIMS using different pulse management strategies

We systematically investigate the reactive behaviour of two types of high-power pulsed magnetron discharges above a Nb target using either square voltage pulses (denoted as HiPIMS) or custom-shaped pulses (denoted as MPPMS), and compare it with that of a dc magnetron sputtering (DCMS) discharge. We demonstrate that the surface metal oxides can be effectively sputter-eroded from the target during both HiPIMS and MPPMS pulses operated in reactive O2/Ar gas mixtures, and that sputtering from a partially oxide-free target is possible even at high oxygen concentrations. This results in a hysteresis-free deposition process which allows one to prepare optically transparent high refractive index Nb2O5 coatings exhibiting an elevated deposition rate without the need for feedback control commonly used in reactive DCMS. The cathode voltage was identified as the principal parameter that affects the reactive discharge behaviour.