Metal oxides as WO3, SnO2 and TiO2 are widely used as active layers in gas sensor applications. The sensor performances (sensitivity, selectivity, and ageing) are strongly dependent grain size, phase constitution, and material microstructure. It is accepted that in magnetron sputtering, these properties can be modified by controlling the energy and the flux of ions impinging the growing films. The ion bombardment allows modifying the nucleation process, increasing the film density, and changing texture, stress and microstructure of the coating, and ultimately improving its performances . Compared to other techniques used for thin films deposition, HiPIMS (High Power Impulse Magnetron Sputtering) enables the sputtered material to be strongly ionized. Therefore, using HiPIMS, the film properties can be altered to a larger extend as compared to conventional DC magnetron.

 

In this study, WO3filmshave been synthesized using reactive HiPIMS of a metallic tungsten target in Ar/O2 mixtures. A comparison is made between results obtained in HiPIMS with those obtained with a conventional DC reactive magnetron discharge (RDCMS) at identical mean power (PD). We discuss the influence of the pulse duration (t)and the target voltage (VD) on both the film deposition rate (RD)and the hysteresis behaviour. During the HiPIMS experiments, t is varied between 10 and 50 µs and VD between 800 and 1500 V. PD is kept constant by adjusting the frequency. In reactive mode, for a given value of PD, RD increases as t and VD are increased. Comparing the HiPIMS data with those recorded during the RDCMS process, it is found that for t = 50 µs and VD = 1500 V, RD in HiPIMS is larger than for the RDCMS discharge. In order to understand this behaviour, the target current waveforms associated with these working conditions have been studied. For this particular condition (t = 50 µs, VD = 1500 V), the discharge current waveforms in metallic and reactive mode are similar. This observation wouldreveal that the target surface chemistry is identical, although the discharge is ignited either in a pure Ar or a in an Ar/O2 mixture.

 

The ion flux composition was also studied with a mass spectrometer located in front of the magnetron target. Time-resolved and time-averaged measurements were carried out.