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 current leads, interconnects, current limiters and cryotron-type switches. As the film thickness of HTSC films is increased using the conventional method of pulsed laser deposition, the surface morphology is degraded 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 is used to prepare Y-Ba-Cu-O thick films. The high-quality Y-Ba-Cu-O superconducting 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 repetition rate of 1 Hz at laser fluence 3 J cm-2. Then, various repetition rates at the fluence 2 J cm-2 were chosen for deposition of the intermediate layer and the surface layer, both with thicknesses of about 1 μm. It is shown that surface morphology and vertical growth are significantly dominated by the initial layer structure and the following deposition conditions. The thick films with high Tc(zero) 89 K were obtained when the surface layer was prepared at a lower repetition rate under lower process temperature. The three step procedure prepared the superconducting thick films with the critical current density of 1.2 x 106 A cm-2 (at 5 K). (orig.)