Electrodeposition and properties of NiW films for MEMS application

The study reports basic investigations on the electroplating and properties of movable NiW microstructures with potential application in MEMS as temporary contacts for IC integration. The NiW layers have been deposited from nickel sulphamate electrolyte (MICROFAB NI-110, Enthone GmbH, Germany) with addition of citric acid stabilized tungsten complex at operating temperature of 50 °C and pH of about 3.0 using direct und pulse current plating regimes. The influence of the electroplating parameters, such as the tungsten concentration in the electrolyte and the current density on the tungsten content in the electroplated alloy, the surface structure and morphology of the deposits, as well as the mechanical properties of the alloy have been thoroughly investigated. The process allows deposition of 12 μm thick homogeneous NiW layers. An essential improvement of the mechanical properties such as micro hardness, elasticity and internal stress compared to that of the pure nickel has been achieved at comparatively low tungsten content of 3.2 wt.%.