Sd. Leith et Dt. Schwartz, High-rate through-mold electrodeposition of thick (> 200 mu m) NiFe MEMS components with uniform composition, J MICROEL S, 8(4), 1999, pp. 384-392
An electrodeposition process for achieving good uniformity, growth rate, an
d yield in NiFe microgears is described. Microgears are electrodeposited fr
om a mixed nickel sulfamate/iron chloride electrolyte through a 230-mu m-th
ick polymethylmethacrylate mold patterned using synchrotron X-ray radiation
. Despite the use of a plating cell with nearly ideal wafer-scale electroly
te mixing characteristics [the uniform injection cell (UIC)], a degree of c
ompositional variation in the microgears can arise. The composition variati
on is shown to be due primarily to nonuniformities in microscopic electroly
te mixing patterns within the mold. To a lesser extent, nonuniformity in th
e local current distribution also contributes to feature-scale composition
variation. Improved composition uniformity is achieved when the plating bat
h is formulated to reduce the sensitivity to electrolyte agitation. Electro
deposition of MEMS components from a low-flow sensitivity electrolyte using
the UIC results in NiFe growth rates greater than 60 mu m/h, yields in exc
ess of 90% and good compositional uniformity. Analysis of mechanical proper
ties illustrates that NiFe parts made using this technique compare favorabl
y to typical electrodeposited MEMS components made from nickel and copper.
[386].