Post-buckling design of thin-film electrolytes in micro-solid oxide fuel cells

The buckling behavior of a thin-film electrolyte of a micro-solid oxide fuel cell is investigated based on experimental measurements, analytical estimations and numerical simulations. An energy minimization procedure is applied in combination with the Rayleigh-Ritz method to represent the buckling modes, evaluate the buckling amplitude and determine the threshold values for instability transitions in the system. The residual stresses in the film deposited on a silicon substrate are evaluated based on wafer curvature whereby nanoindentations tests are applied to estimate the Young's modulus of the deposited film. The partial release of residual stresses in the film during free etching of the substrate is estimated by a new method combining pre-etching optical measurements with posteriori stress analysis. The energy interpretation of the obtained deflection shape is discussed. Comparisons between simulation results and experimental data show the efficiency of this method to predict various buckling stages of free-standing thin films. A post-buckling design space for thin-film electrolyte fabrication is presented by applying a stress-based failure criterion.