Large area deposition of YBCO thick films for applications in resistive fault current limiting devices

The preparation of the switching element of a resistive superconducting fault current limiter requires the up-scaling of deposition techniques for thin YBa2Cu3O7-x (YBCO) films to large areas and high film thickness. For a projected 100 kVA limiter model an area of about 400 cm(2) and a him thickness of up to 5 mu m will be necessary, depending on the material properties like critical current density j(c) and normal state resistivity rho(n). Within a joint project various deposition methods including pulsed laser deposition (PLD), magnetron sputtering(MS), thermal evaporation (TE) and plasma Flash evaporation (PFE) are evaluated as possible candidates for the operation of deposition systems capable of coating 20x20 cm(2) substrates., Both single crystalline wafers and polycrystalline ceramic plates an considered as substrates. To achieve high j(c) on polycrystalline substrate materials an additional zirconia buffer layer consisting of biaxially orientated crystallites has to be prepared by ion beam assisted deposition (IBAD), In small samples with IBAD buffer critical currents above 10(5) A cm(-2) with a maximum of 1x10(6) A cm(-2) have been achieved. The presently available sample sizes depend on the installed systems for YBCO and buffer deposition. respectively and on the commercial availability of the substrate material. The largest samples which have been prepared and characterised have sizes of 1x25 cm(2) and 5x5 cm(2) for PLD, 10x10 cm(2) for TE and IBAD, 2 in. (1 in.=2.54 cm) diameter for MS, and 3x7 cm(2) for PFE. The corresponding highest film thicknesses are 4.5 mu m for PLD, 1.4 mu m for TE, 1.6 mu m for IBAD and 0.4 mu m for MS.