Influence of argon gas pressure and target power on magnetron plasma parameters

The use of thin film sensors for measuring pressure and temperature distribution in tribological contacts was limited to hydrodynamic and elasto-hydrodynic contacts. Under mixed lubrication conditions the sensors regularly failed in the past. Therefore a new sensor generation is to be developed, which withstands the conditions of boundary friction within certain limits. These are based on electrically isolating DLC thin films (diamond-like carbon) as protecting and insulating coatings, between which the sensors are embedded. DLC thin films were deposited by r.f. magnetron sputtering of a graphite target (75 mm in diameter) in a pure argon discharge at low substrate temperatures (60–150 °C). For optimization of film constitution and properties, the target power was changed in the range of 50 W and 500 W and the argon gas pressure between 0.4 Pa and 0.7 Pa. The film characteristics were studied and related to plasma parameters and particle fluxes onto substrate and target during deposition, including ion saturation current density, electron saturation current density, plasma density, electron temperature und plasma potential. These plasma parameters were systematically analyzed in dependence of target power and gas pressure by using electrical double probes.