Pulse-reverse electrodeposited nanograinsized CoNiP thin films and microarrays for MEMS actuators

This paper reports on a low residual stress hard magnetic CoNiP alloy electrodeposition technique for microelectromechanical systems (MEMS) applications based on techniques previously developed for CoNiP thin films for perpendicular magnetic recording. Besides electrolyte chemicals, various processing parameters including applied current density, film thickness, electrolyte agitation, electrolyte pH, and temperature are optimized to provide thick films with low residual stress. The resulting hard magnetic CoNiP alloy exhibits a relatively high perpendicular coercivity (H-c) of around 700-1200 Oe and a high saturation magnetization (M-s) of 0.41-0.52 kG. Thick films up to 52 mm with a low residual stress have been realized using this CoNiP electrodeposition technique. In addition, CoNiP microarrays 22.5 mu m thick are surface micromachined for the integrations with magnetic MEMS devices. Experimental results confirm that these microarray configurations have a higher coercivity and maximum magnetic energy density, (BH)(max), than thin films in the perpendicular direction. (c) 2005 The Electrochemical Society. All rights reserved.