Electrodeposition of FeCoNi thin films for magnetic-MEMS devices

The physical properties, including macro and microstructures, film stress, and corrosion resistances, along with the magnetic properties of electrodeposited FeCoNi thin films, which can be later integrated to magnetic-MEMS devices were systematically investigated by varying film composition. Increased Ni content affected both macro and microstructure of electrodeposits, switching from columnar structure to lamellar structure and from body centered cubic (BCC) to face centered cubic (FCC), respectively. The film stress of electrodeposits was increased with increasing deposit Ni content and it was inversely proportional to grain size. The corrosion resistance of films determined by polarization resistance and pitting potential initially improved with increasing deposit nickel content, followed by a maximum at ∼48 at.% deposit Ni content. After reaching an upper limit, the corrosion resistance slightly decreased with increasing deposit Ni content. The coercivity of FeCoNi alloy decreased when Ni content increased from 0 at.% to ∼13 at.% which might be due to decrease in grain size. However, from ∼13 at.% to ∼48 at.%, coercivity increased, which could be predominately affected by changes in film stress and microstructure. Fe-rich FeCoNi thin films (e.g. 68Fe29Co 3Ni) show good magnetic properties with minimum film stress for magnetic-MEMS actuated in the out-of-plane direction.