PREPARATION AND PROPERTIES OF THIN-FILM YBA2CU3OX DEVICES

Low-noise YBa2Cu3Ox dc SQUIDs and flux transformers were fabricated by laser deposition. The Josephson junctions were of grain boundary type , formed by epitaxial thin filmes, covering Ar+ ion milled step edge s ubstrates. The 5 mum wide dc SQUIDs were patterned by a SiO inhibit te chnique. The SQUID hole was varied between 5 mum10 mum and 50 mum*50 mum, representing SQUID inductances between 20 p and 140 pH. The optim um transfer function delta V/delta PHI at the appropriate flux bias wa s greater than 100 mu V/PHI(o) at 77K for samples with 20 pH. The best value of the energy resolution for samples with 20 pH is epsilon(n,w) (f > 30 Hz) = 610(-31)J/Hz in the white noise region and dc bias modu lation. The energy sensitivity was measured as a function of the SQUID inductance. The coloured noise could be reduced by one order of magni tude applying an ac-bias to the SQUIDs obtaining an energy resolution for samples with 20 pH of 310(-30)J/Hz at 1 Hz. Noise contributions f rom conductance fluctuations or flux hopping could be seperated by mea suring the equivalent flux noise as a function of the bias current. A preparation technique for thin-film input coils has been developed, in which the three epitaxial layers were patterned either by deposition through shadow masks or by Ar+ ion milling. A 12 turn flux transformer with 25 mum wide lines carried a persistent current of about 1 mA for more than two hours. To fabricate a homogeneous multilayer sequence o f YBa2Cu3Ox-SrTiO3-YBa2Cu3Ox on a SrTiO3-substrate, an off axis laser deposition geometry was established, providing smooth films without la ser particulates.