BS in Materials Engineering
Materials Engineering Department
Photosensitive negative resist polymer layers of SU-8 2050 were adhered to 100 mm n-type silicon and Pyrex wafers via spin coating. These wafers were then bonded together at various temperatures of 100 ͦC, 120 ͦC, 140 ͦC, 150 ͦC, 160 ͦC, and 180 ͦC. The target thickness of each SU-8 layer was 100 µm. Photolithography was used to create microfluidic channels within the SU-8. An n-type silicon wafer and a Pyrex wafer, each with an SU-8 layer, were brought together on the “hard bake” or final step of SU-8 polymerization. A pressure of ~300 KPa was applied during the hard bake for 20 minutes. The apparatus was left under pressure to cool to room temperature. A JEOL JSM-6390 SEM and optical microscopy were used to observe effects on channels to determine if the hard bake temperature caused deterioration of channel walls or an incomplete bond. Void formation was avoided by drilling fluid input and output holes through Pyrex wafer prior to wafer bonding processes, allowing air and solvent release points while under heat and pressure treatment. Tensile testing was performed on partially overlapped wafers by pulling them apart to quantify the bond strength at stated temperatures. The bond temperature with the strongest SU-8 to SU-8 bond that withheld channel integrity will be used for electrokinetic microfluidic pumping thesis analysis of buffer solutions ranging from pH 2 to 12.