Heating in Nb edge junctions

Heating in Josephson tunnel junctions fabricated on the edge of a Nb line, and the cooperative heating effects of edge junctions on the same line and on adjacent lines were studied. In one measurement two edge junctions on adjacent parallel lines share a common counter electrode. One junction serves as the heat source and the other as a temperature sensor. The sensor temperature was found to increase linearly with power at the first junction to near the Tc(6.8 K) of the counter electrode. In addition, by varying the distance between edge junctions in several test sites the temperature profile was measured and a thermal healing length of 5 μm was determined. In a second geometry two edge junctions share common base and counter electrodes while the width between junctions is varied in different test sites. Critical power levels were measured and again related to a temperature rise. Combining these two results it is predicted that a high current device using multiple edge junctions at a spacing of 2.5 μm and a current density of 4000 A/cm²would have a temperature rise of 150 mK when powered halfway up the current step at the gap voltage.