Layered Structures HTSC/Ferroelectric, Prepared by Sputtering

Abstract
We have investigated some formation features of thin film structures PZT / YBCO and YBCO / BSTO. PZT films have been synthesized by reactive ion beam sputtering of a multi-elemental metal target at room temperature and "ex-situ" annealing at 700-750°C. BSTO and YBCO films have been deposited "in-situ" by magnetron sputtering of stoichiometric ceramic targets in an Ar + 50% O₂ gas mixture (pure oxygen for BSTO) at temperature of 700°C. Si (100) buffered with TiN to prevent the diffusion in YBCO has been used as a substrate in the case PZT / YBCO. The layers YBCO / BSTO have been deposited on MgO (100). The substrates have been chosen according to prospective applications of PZT / YBCO as non-volatile memory cells integrated with existing CMOS transistor circuitry, and of YBCO / BSTO as voltage-tunable microwave devices. Films with composition Pb(Zr_0.44Ti_0.56)O₃ have been obtained by sputtering of a target with a ratio of 13:36:51 for Pb, Sr and Ti, respectively. The measured dielectric constant at 1 MHz in the structures Au / PZT / YBCO / TiN / Si has been 540 and the remnant polarization and coercive field values have been 5.4 µC/cm² and 25 kV/cm, respectively. Planar capacitors with a dielectric of BSTO thin film and YBCO electrodes have been produced and investigated as voltage-controlled devices at 1 MHz. A controllability of ε(0V)/ε(50V)=1.6 has been demonstrated at 77 K. The dielectric hysteresis has been compared in capacitors with YBCO electrodes and with metal ones. It has been shown that the boundary phenomena at the interface of the epitaxially grown layers differ from that in the ferroelectric / metal structures and the hysteresis effect diminishes significantly.