Microstructure and microfabrication considerations for self-supported on-chip ultra-thinmicro-solid oxide fuel cellmembranes

La_0.6Sr_0.4Co_0.8Fe_0.2O ₃ - δ (LSCF) has been sputtered on bare Si and Si ₃N₄ and yttria-stabilised zirconia (YSZ) thin films to investigate annealing temperature- and thickness-dependent microstructure and functional properties, as well as their implications for designing failure-resistant micro-solid oxide fuel cell (lSOFC) membranes. The LSCF thin films crystallise in the 400-450 °C range; however, after annealing in the 600-700 °C range, cracks are observed. The formation of cracks is also thickness-dependent. High electrical conductivity, ̃520 Scm^-1 at 600 °C, and low activation energy, ̃0.13 eV, in the 400-600 °C range, are still maintained for LSCF films as thin as 27 nm. Based on these studies, a strong correlation between microstructure and electrical conductivity has been observed and an annealing temperature-thickness design space that is complementary to temperaturestress design space has been proposed for designing reliable membranes using sputtered LSCF thin films. Microfabrication approaches that maintain the highest possible surface and interface quality of heterostructured membranes have been carefully examined. By taking advantage of the microstructure, microfabrication and geometrical structural considerations, we were able to successfully fabricate large-area, self-supported membranes. These results are also relevant to conventional or grid-supported SOFC membranes using ultrathin nanocrystalline cathodes and lSOFCs using cathode thin films other than LSCF.