The present invention concerns thin diffusion barriers in metal and metal alloy layer sequences of contact area/barrier layer/first bonding layer type for metal wire bonding applications. The diffusion barrier is selected from Co-M-P. Co-M-B and Co-M-B—P alloys wherein M is selected from Mn, Zr, Re, Mo, Ta and W having a thickness in the range 0.03 to 0.3 μm. The first bonding layer is selected from palladium and palladium alloys.