High-rate through-mold electrodeposition of thick (<200 μm) NiFe MEMS components with uniform composition

Abstract

An electrodeposition process for achieving good uniformity, growth rate, and yield in NiFe microgears is described. Microgears are electrodeposited from a mixed nickel sulfanate/iron chloride electrolyte through a 230-/spl mu/m-thick poly methylmethacrylate mold patterned using synchrotron X-ray radiation. Despite the use of a plating cell with nearly ideal wafer-scale electrolyte mixing characteristics [the uniform injection cell (UIC)], a degree of compositional variation in the microgears can arise. The composition variation is shown to be due primarily to nonuniformities in microscopic electrolyte mixing patterns within the mold. To a lesser extent, nonuniformity in the local current distribution also contributes to feature-scale composition variation. Improved composition uniformity is achieved when the plating bath is formulated to reduce the sensitivity to electrolyte agitation. Electrodeposition of MEMS components from a low-flow sensitivity electrolyte using the UIC results in NiFe growth rates greater than 60 /spl mu/m/h, yields in excess of 90% and good compositional uniformity. Analysis of mechanical properties illustrates that NiFe parts made using this technique compare favorably to typical electrodeposited MEMS components made from nickel and copper.