Comparison of effective noise temperatures in YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// junctions

The dc voltage response to 70 GHz radiation was measured for YBCO bicrystal junctions, step edge junctions and ramp edge junctions at temperatures from 4 K to 90 K. Employing the RSJ-model and assuming thermal noise, the Josephson radiation is about equal to the voltage difference of the voltage response to the small signal microwave irradiation. In the presence of excess noise, an effective noise temperature can be defined and is used as a figure of merit. In bicrystal grain boundary junctions with zero magnetic field the effective noise temperature was determined to be equal to the physical temperature within experimental error. Bicrystal grain boundary junctions with non-zero magnetic field, step edge junctions and ramp edge junctions showed excess noise. The scaling of the noise temperature is compared with the width of the junction in units of the Josephson penetration depth.