Formation and Analysis of High Resistivity Electroless NiReB Films Deposited from a Sodium Citrate Bath

An electroless NiB plating bath including ammonium perrhenate was used to investigate the effect of Re and B on the resistivity and the structure of NiReB film. The Re content in the film increased rapidly while the B content decreased with increasing ammonium perrhenate concentration of the electrolyte. The films exhibit an increasing specific resistance (ρ) and decreasing temperature coefficient of resistance (TCR) as the Re content increased. For films with less than 14 wt % Re content, the value of TCR is stable until a 300°C heat-treatment; its stability is maintained until 500°C for the higher Re content films. According to X-ray diffraction measurement, the as-deposited films were amorphous for the low Re content films, while a fine devitrified structure of hexagonal close-packed ReNi was observed for films with a high Re content. After heat-treating the low Re content film at 500°C crystallized the forming face-centered cubic NiRe and Ni ₃B phases. On the other hand, the crystalline structure of the high Re content films was not altered by annealing to 500°C.