Investigation on the Superconducting Properties of YGBCO/STO/YGBCO Trilayer
Superconductor/insulator/superconductor trilayer structure can be used to increase the superconducting properties in self-field of thick REBa<sub>2</sub>Cu<sub>3</sub>O<sub>7-δ</sub> (RE = rare metal) films by inhibiting the thickness effect, as well as improving in-field properties through the interlayer, which acts as a flux pinning interface. The conventional trilayer structure was always prepared symmetrically, namely, the bottom superconducting layer has the same thickness with the top superconducting layer. In this paper, Y<sub>0.5</sub>Gd<sub> 0.5</sub>Ba<sub>2</sub>Cu<sub>3</sub>O<sub>7-δ</sub>/SrTiO<sub>3</sub>/Y<sub>0.5</sub>Gd<sub>0.5</sub>Ba <sub>2</sub>Cu<sub>3</sub>O<sub>7-δ</sub> (YGBCO/STO/Y-GBCO) trilayer films were prepared asymmetrically by pulsed laser deposition on CeO<sub>2</sub> buffered IBAD-MgO tapes, which means the bottom superconducting layer has a different thickness than the top superconducting layer. YGBCO/STO/YGBCO trilayer structure had the same total YGBCO layer thickness of 720 nm and STO interlayer thickness of 80 nm, but a bottom YGBCO superconducting layer of different thickness. Microstructure, surface morphology, and self-field and in-field superconducting properties were systematically investigated. It was found that thicker bottom-layer had almost no internal residual stress, better crystalline quality, and surface morphology, which contributed to better superconducting properties of the YGBCO/STO/YGBCO trilayer sample both under self-field and magnetic field. The phenomenon was explained by the growth model. These results can provide useful information for fabricating trilayer structure with high in-field performance.