INTRINSIC NOISE TEMPERATURES OF YBA2CU3O7-DELTA JOSEPHSON DEVICES ON BICRYSTAL SUBSTRATES AND THE UPPER FREQUENCY LIMIT FOR THEIR OPERATION

Following a method proposed by Divin and Modovets [Sov. Tech. Phys. Le tt. 9, 108 (1983)], we have measured at millimeter waveband the intrin sic noise temperatures T-N Of YBa2Cu3O7-delta Josephson junctions or d e superconducting quantum interference devices (SQUIDs) fabricated on SrTiO3, yttria-stabilized ZrO2, or Si bicrystal substrates. Over wide ranges of physical temperatures T-p and the junction's normal resistan ce R(N), it was found that T-N follows T-p pretty well. This indicates that the intrinsic noise in the devices is dominated by Johnson noise . T-N was also measured in cases where there is external magnetic fiel d applied, or where then is another microwave radiation like the local oscillator in a mixer. The magnetic held or microwave radiation does not seem to affect T-N in any appreciable way. To estimate the high fr equency performance of the junctions on Si bicrystal substrates, direc t irradiation by a far infrared laser at 1.81 THz is carried out and t he clear first Shapiro step is observed. (C) 1996 American Institute o f Physics.