Interdiffusion and interfacial mixing in superconducting YBaCuO thin films

We report on the interdiffusion of substrate and superconducting thin film species after annealing at different temperatures in an oxygen atmosphere. Thin films of YBa₂Cu₃O₇ were deposited on (100) strontium titanate (100) magnesium oxide, (100) silicon, and unoriented yttria stabilized zirconia (YSZ) substrates using the pulsed-laser evaporation technique. The annealing were performed at different temperatures and times ranging from 650°C for 20 min for low temperature processing through 900°C for 2 min to 920°C for 20 min for high temperature processing of films deposited on strontium titanate and magnesium oxide substrates. For silicon substrates, low temperature processing cycles ranging from 550°C to 70 min to 650°C for 70 min were used. The diffusion profiles for the substrate (magnesium, strontium, titanium) and thin film elements (yttrium, barium, copper) were analysed for magnesium oxide and strontium titanate substrates respectively using secondary ion mass spectrometry and Rutherford backscattering spectrometry. The overall diffusion coefficients at 920°C were determined to be 1.6×10^-13 cm² s^-1 and 2.0×10^-14 cm² s^-1 for strontium and magnesium substrate species into YBa₂Cu₃O₇ thin films. The diffusion coefficients were found to be dependent on the substrate temperatures and on the concentration of the species. The thin films deposited on the silicon substrates exhibited appreciable interdiffusion for substrate temperatures above 550°C.