Y-BA-CU-O THICK-FILM PREPARATION USING MULTISTEP KRF EXCIMER-LASER DEPOSITION

Thick films of high-temperature superconductors (HTSC) have attracted much attention to a number of current-carrying applications such as cu rrent leads, interconnects, current limiters and cryotron-type switche s. As the film thickness of HTSC films is increased using the conventi onal method of pulsed laser deposition, the surface morphology is degr aded during the film deposition. This structural transition results in decreasing the critical current density with the film thickness. Here , a multistep deposition technique in the KrF excimer laser ablation i s used to prepare Y-Ba-Cu-O thick films. The high-quality Y-Ba-Cu-O su perconducting films of thickness of a few mm were formed by optimizing the processing conditions from the bottom to the surface of the film. The initial ultrathin layer of a few nm was prepared at the low repet ition rate of 1 Hz at laser fluence 3 J cm(-2). Then, various repetiti on rates at the fluence 2 J cm(-2) were chosen for deposition of the i ntermediate layer and the surface layer, both with thicknesses of abou t 1 mu m. It is shown that surface morphology and vertical growth are significantly dominated by the initial layer structure and the followi ng deposition conditions. The thick films with high T-c (zero) 89 K we re obtained when the surface layer was prepared at a lower repetition rate under lower process temperature, The three step procedure prepare d the superconducting thick films with the critical current density of 1.2 x 10(6) A cm(-2) (at 5 K). (C) 1997 Elsevier Science S.A.