Carbonization of SU-8 Based Electrode for MEMS Supercapacitors
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Supercapacitors are more sustainable and environmentally friendly energy sources than traditional ones. To achieve the supercapacitors with both energy density and power density that mainly depend on the effective surface area of theelectrodes, SU-8 can be used for electrode material to fabricate 3D microstructures as the electrodes that increase the effective surface area significantly. The objective of this project is to fabricate the reliable electrodes of large surface area for supercapacitors by SU-8 process, in which the SU-8 films are carbonized in an inert atmosphere in high temperaturefurnace. To improve the adhesion between the developed electrodes and the substrate is the key task in my thesis work. The micromechanical interlocking is proposed and designed for improving the adhesion which can also be optimized by controlling the heating and cooling rate in carbonization process.According to the force analysis, the inverted-trapezoid pits are the most reliable structures in the substrate as the root for SU-8 films. Inverted-trapezoid pits are obtained by combining both dry etching and wet etching technologies. The dry etching is very important to influence the depth of inverted-trapezoidstructures. Based on the characteristics of pyrolysis process for SU-8, in our experiments the highest carbonization temperature is chosen at such as 700℃, 900℃ or 1000℃, respectively. We have found that after finishing the carbonization process, the carbon film is locked firmly on the substrate by the inverted-trapezoid pits, but the warping phenomenon appears in the thick films and cracks occur in the thin films. These problems can be solved by modifying the process parameters in fabricating the inverted-trapezoid pits and the SU-8 structure films. In addition, the weight loss and vertical shrink increase with increasing the carbonization temperature during this process.