Development and characterization of Co-Ni alloys for microsystems applications

A chloride plating bath, containing boric acid and saccharin has been optimized to obtain homogeneous Co-Ni deposits over Si/SiO2/Ti/Ni substrate. The goal is to explore the synergy of these layers in microsystems applications. Anomalous codeposition occurs and both electrochemical and structural results indicate that obtained Co-Ni layers correspond to solid solutions of face-centered cubic (fcc) structure, whose composition may be varied as a function of the electrodeposition parameters. Results of the electrochemical and magnetic characterization carried out are presented, showing the trends of a soft magnetic material, i.e., high saturation magnetization (1.2 T) and low coercivity. Smooth surfaces and a steady deposition rate were observed in the Co-Ni deposits on silicon-based unpatterned substrates. In order to check the versatility and the compatibility of this Co-Ni electrodeposition with the standard microsystems fabrication technology, two processes, surface-and bulk-technology based, have been carried out. Due to the high selectivity and homogeneity of the Co-Ni layer, it has been possible to pattern the deposits with a definition down to 10 mum, as well as to fabricate 3D structures. Methods to liberate the Co-Ni films from the silicon-based substrate have been developed; as a result, low-stressed freestanding structures are presented. (C) 2002 The Electrochemical Society.