Influence of a degraded SrTiO3 layer at the YBa2Cu3O7−δSrTiO3 interface on the dielectric behavior at cryogenic temperature

In an YBa₂Cu₃O_7−δ/SrTiO₃/YBa₂Cu₃O_7−δ parallel capacitor fabricated by a chemical mechanical planarization method, the dielectric constant and loss in the presence of electric fields at 2.2 K were more than 26,000 and less than 0.027, respectively. We propose a multilayer model that explains this behavior. The model assumes that the SrTiO₃ film is composed of single-crystal-like SrTiO₃ layers with a dielectric constant ε_r = 30,000 and degraded SrTiO₃ layers with dielectric constants that vary continuously from 25, the dielectric constant of YBa₂Cu₃O_7−δ, to 30,000. Results of a numerical calculation revealed that the thickness of the single-crystal-like SrTiO₃ layer was more than 92% of a 600-nm-thick SrTiO₃ film.