Micro-fabrication of patterned LSCF thin-film cathodes with gold current collectors

Lanthanum strontium cobalt iron oxide (La_0.6Sr _0.4Co_0.2Fe_0.8O_{3 - δ}) thin films were deposited via pulsed laser deposition on single-crystal yttria-stabilised zirconia (YSZ) substrates and lithographically patterned to produce geometrically well-defined micro-cathodes. The films had low porosity and a mainly columnar microstructure. A minimum LSCF feature size of 20 μm was achieved and a range of designs fabricated for studies of the oxygen reduction reaction. Wet etching in dilute hydrochloric acid and dry etching via Ar⁺ sputtering were investigated in order to produce structures with near-vertical side walls and well-defined geometries. Ar ⁺ sputter-etching yielded structures with side walls inclined at approximately 75° to the substrate and was the preferential choice. Etch rates of 400 nm min^{- 1} and 3.4 nm min^{- 1} were determined for wet and dry etching, respectively. A novel gold current collector geometry was fabricated using photolithography lift-off technique in order to reduce ohmic drops due to the cathode geometry, whilst controlling the LSCF active area and TPB lengths. The deposited LSCF had an electronic conductivity of 5700 S/m in air and an activation energy, E_A of 0.14 eV. Degradation of LSCF conductivity upon heat cycling was observed for thin films that had been subjected to an etching process, in contrast to shadow mask processed structures.