Low-temperature preparation of superconducting YBa₂Cu ₃O_7-δ films on Si, MgO, and SrTiO₃ by thermal coevaporation

We used simple thermal coevaporation of yttrium, barium, and copper in an oxygen atmosphere to produce thin films of the 90 K superconductor, YBa ₂Cu₃O_7-δ, on silicon, magnesium oxide, and strontium titanate. The films were deposited on 650 °C substrates and were superconducting when removed from the evaporator. A short post-anneal at 480 °C produced films on bare Si with transition temperatures (R=0) of 85 K. Films as thin as 0.13 μm, superconducting at 91 K (on MgO) and 89 K (on SrTiO₃), were obtained with no post-anneal.