Electroplating for lab-on-a-chip electrodes and three-dimensional MEMS microstructures

The process methodology for fabricating high-aspect ratio structures for MEMS microstructures using nickel electroplating has been developed. High-aspect ratio in this thesis refers to structures with aspect ratios greater than 4. Electroplating is carried out selectively on photolithographically patterned substrates with a seed layer. A seed layer of gold (100 nm) with an adhesion layer of chromium (10 nm) was found to give the best results for nickel electroplating on silicon wafers. The molds for creating the high-aspect ratio structures were made using Shipley's SPR220 positive resist. SPR220 resist was characterized and molds having smallest feature sizes of 1 μm and heights >10 μm were fabricated. Two types of solutions, namely Technic “S” Nickel Sulfamate solution and a homemade solution of nickel sulfate, were investigated. Various factors such as addition of a wetting agent (Kodak Photoflo), change in current densities, and stirring using a magnetic stir bar were studied. These studies have helped in developing process parameters to obtain uniformly electroplated features.; Electroplating was used to fabricate three dimensional nickel electrodes on a platinum working electrode appropriate for new lab-on-a-chip designs. Thereby, the geometry, material and sensitivity of the current lab-on-a-chip systems have been altered. Sugars such as glucose and galactose can now be detected using these analytical systems.