In situ grown Y–Ba–Cu–O barriers for high-temperature superconductor planar quasiparticles injection devices

High-quality planar Y Ba2Cu3O7−δ/barrier/Au (YBCO/I/Au) structures with cc-axis oriented YBCO layers were fabricated in situ by dc inverted-cylindrical magnetron sputtering on (001) SrTiO3 oriented substrates. Non-superconducting Y–Ba–Cu–O layers were used as barrier material in the structures. The sandwich-type structures were patterned to transistor dimension by standard UV-photolithography and Ar etching. Electrical measurements on Y Ba2Cu3O7−δ stripes and Y–Ba–Cu–O native barrier layers at different temperatures and zero magnetic field, corroborated the excellent superconducting and insulating properties of the two constituents after the intensive patterning process. The analysis of experimental data in the frame of the Glazman and Matveev theory pointed out to a predominant hopping mechanism through localized state in the barrier at high temperatures. Nevertheless, at low temperatures, the inelastic hopping transport mechanism seemed to pass into indirect elastic tunneling (resonant), as evidenced by its current–voltage characteristic. Quasiparticles, injected through such a barrier into the superconducting YBCO layer, provoked a strong suppression of its critical current ICIC. A current amplification factor, K=ΔIC/ΔIg as high as 11 at 77 K was achieved for this device.