By direct deposition onto hot substrates, using laser ablation, crystalline YBa2Cu3O7−δ (123) was obtained at 650°C on SiO2, but not on (100) Si substrates. The 123 film did not show a superconducting transition due to interfacial reactions. The failure temperature of insulating buffer layers, such as tantalum oxide and hafnium oxide, is around 500 °C. Although MgO and BaZrO3 show a high stability in contact with 123 at 900 °C, they fail as a diffusion barrier at much lower temperatures. Below 400 °C barium diffuses through MgO, which itself remains unaffected. Using BaZrO3 the same happens around 700 °C. BaF2 fails as a diffusion barrier below 400 °C. Using laser ablation, high quality 123 films were grown on ZrO2 buffer layers above 650 °C. For the first time we report superconducting transitions of 123 deposited at 650 °C onto an amorphous metal alloy, Ir45Ta55. The problems encountered using conducting buffer layers are either a low reaction temperature with 123 (HfB2 and HfN) or oxidation of the metal alloy (Ir45Ta55) around 400 °C. Intermediate noble metal layers silver and Ag/Au/Ag could not prevent oxygen diffusion towards the underlying buffer layer.
de Reus, R., Saris, F. W., van der Kolk, G. J., Witmer, C., Dam, B., Blank, D. H. A., ... Flokstra, J. (1990). Buffer layers for superconducting Y-Ba-Cu-O thin films on Si and SiO2. Materials science & engineering B, 7(1-2), 135-147. https://doi.org/10.1016/0921-5107(90)90018-7