Electrodeposited metal matrix nanocomposites as thin films and high aspect ratio microstructures for MEMS

The electrodeposition of metal-matrix nanocomposites as thin film and high aspect ratio microstructures (HARM’s) for MicroElectroMechanical Systems (MEMS) components is examined. The effect of -Al2O3 nanopowder on copper reduction from acidic and basic electrolytes is examined with rotating disk electrodes (RDE’s). At pH 0.2, regions of copper inhibition and enhancement are identified in the kinetic regime. Low particle loading (12.5 g/L) results in an inhibited copper rate, while, high particle concentration (60 g/L) does both, inhibits the rate at low overpotentials and accelerates it at higher overpotentials, depending on the electrode rotation rate. At pH 8 the presence of particles resulted in an enhancement of the Cu reaction rate, while at pH 10 the reaction rate appeared inhibited. The change of the Cu partial current density was attributed to the change of copper complexed species. A mathematical model that couples particle mass transport with metal kinetics during Cu--Al2O3 electrodeposition from acidic electrolytes was developed. The model, based on convective-diffusion transport and Tafel reaction kinetics, is solved numerically, and the calculated species concentrations at the solution-electrode interface are used to describe the electrode processes. The simulation was in agreement with experimental observations, predicting the influence of experimental variables. A comparison of Cu-particle nanocomposites electrodeposition into deep recesses from sulfuric acid and ammonia-citrate electrolytes is presented, to provide better understanding of how complexing agents affect the copper-alumina codeposition rate and establish the best operating conditions for useful nanocomposites for HARM’s. Recessed electrodes were prepared using X-ray lithography. Partial current density, current efficiency and deposited particle concentration were determined with RDE’s. Cu--Al2O3, Cu-CeO2 and Cu-TiO2 micropost nanocomposites were successfully performed into 500 m deep recesses. Particle concentration and uniformity was dependent upon particle and electrolyte type. The electrodeposition of NiCu composites using nanometric diameter alumina and ceria was examined using the Rotating Cylinder Hull Cell (RCHC). A variation in rotation rate was studied with and without particles. The amount of alumina particles in the alloy composite was much higher than the content of ceria with the same electrolyte loading. Particles altered the deposition rate of Cu and Ni affecting the deposit composition