On-Chip Temperature Distribution of Josephson Voltage Standard Devices

A substrate surface temperature characterization for the National Institute of Standards and Technology Josephson voltage standard has been performed by fabricating and measuring Josephson junction arrays with on-chip thermometry. Circuits were designed with a single voltage standard style array consisting of 12 810 junctions. 31 banks of thermometer junctions were placed around the array and microwave termination resistor to monitor temperature via a junction critical current measurement. Temperature rise in devices with on-chip termination resistors were compared to that of devices terminated off-chip. The thermal profiles on several different substrates were measured and compared to determine which substrate exhibited the best thermal transport. Finally, the thermal properties of junctions deposited directly on silicon were compared to those of the junctions deposited on an interface layer. We found that devices with off-chip terminations had half the temperature rise compared to the devices with on-chip termination, and the devices with remotely located terminations exhibited larger constant-voltage steps over a larger frequency/power range than the devices with termination resistors very close to array junctions. Comparing substrates, we found that sapphire was best for transporting heat from voltage standard circuits and that an interface layer did not affect heat transport in the substrate.