| Abstract [eng] |
This dissertation is dedicated to the development and improvement of the µ-SOFC manufacturing process by applying microelectromechanical system (MEMS) technologies with respect to the properties of µ-SOFC construction elements, such as electrode (anode and cathode), as well as electrolyte materials and thin films. The co-precipitation synthesis and incipient wetness impregnation methods were tailored for the synthesis of YSZ and GDC micro- and nanostructures (ceramics), further used as a target in the electron beam evaporation technique for the deposition of µ-SOFC electrolyte thin films. A prehensive study of ceramics and thin films was performed and presented. The deviation of stoichiometry in the evaporated thin films, compared to the original target (ceramics) composition, was observed. It was shown that stoichiometry deviations in thin films may reach more than 30%. Synthesized oxygen vacancy conducting ceramics and thin films evaporated on Al2O3 and SiO2/Si substrates have been studied by impedance spectroscopy. In order to investigate electrical properties of electrolyte thin films, several configurations of the Pt electrode were applied. The photomasks were designed and produced. Also the design of geometry and technological route of µ-SOFC manufacturing process was developed and tested. The photomasks were fabricated from chromium and soda lime glass. The manufacturing process involved back-side photolithography, magnetron sputtering of platinum thin films, electron beam evaporation of YSZ or GDC electrolyte, deep reactive ion etching of silicon, and, finally, the release of free-standing membrane. The technological route of the micro-solid oxide fuel cell was modified during an investigation using direct Ar+ ion beam etching of platinum and YSZ or GDC electrolyte thin films instead of lift-off lithography technique. Test samples of the µ-SOFC three-layered structure, sometimes called PEN (Positive electrode-Electrolyte-Negative electrode) membrane structures, were fabricated. The cell diameter was about 2.4 mm with the electrolyte and total cell thickness of about 600 and 1000 nm, respectively. Suitable conditions and technological parameters for the manufacturing of μ-SOFC test sample were chosen. It was determined that the formation of positive/negative Pt electrode with appropriate properties, such as structure, morphology and porosity, is possible through controlling both deposition conditions (argon gas pressure in the chamber) during the magnetron sputtering process and by applying additional thermal treatment. It was found that Pt electrodes sputtered at 0.065 Pa argon gas pressure in the chamber and thermally treated at 600°C for 15 min reveal nanopores, which remain open after exposure at 800°C, even with increasing annealing duration. Thus, optimal conditions and additional thermal treatment were employed in order to create a PEN structure exhibiting the required mechanical, thermal stability, structural, and electrical properties. |
