Buffer layers for superconducting YBaCuO thin films on silicon and SiO₂

By direct deposition onto hot substrates, using laser ablation, crystalline YBa₂Cu₃O_7-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.