10 V programmable Josephson voltage standard circuits using NbN∕TiNx∕NbN∕TiNx∕NbN double-junction stacks

Abstract

Using NbN / TiN x / NbN / TiN x / NbN double-junction stack technology we have demonstrated a programmable Josephson voltage standard chip that operates up to 10.16 V output voltage cooled with a two-stage Gifford-McMahon cryocooler. The circuit uses double-junction stacks, where two junctions are fabricated in each stack, in order to integrate 327 680 junctions into a 15.3 mm ϫ 15.3 mm chip. A 1-to-32 microwave distribution circuit is also integrated on the chip. The chip is divided into 22 cells, which perform as an 11-bit digital-to-analog converter. The 21 working cells include 307 200 junctions biased with 16 GHz microwaves at 10.2 K that generated flat voltage steps with current margins greater than 1 mA, which indicates good uniformity of the stacked junctions.

Compact tunable sub-terahertz oscillators based on Josephson junctions

“…While the operation frequency of niobium junctions is limited by the energy gap to around 0.7 THz, this restriction may be overcome by using niobium nitride junctions to cover the frequency range up to 1.4 THz. 16,17 FIG. 3.…”

Josephson Junctions for Present and Next Generation Voltage Metrology

“…Nb/PdAu/Nb junctions have been the first developed type of SNS junctions for this application by NIST group, and have produced stable voltage outputs at 1 V as binary arrays for programmable potentiometers, being also used in circuits for pulse driven AC synthesis [14], [15]. They feature values in the range of 100 kA/cm 2 Impressive results have been obtained with NbN/TiN/NbN junctions, developed by the Tsukuba group, since very large arrays, with more than 300.000 series connected junctions have been succesfully tested in a 8 and 11 bit DAC circuits with quantized steps at 10 V at 10 K [36], [37]. Features of these junctions are J c about 10 to 10 A/cm and V c 10-20 V at 10 K with areas of few square micrometer.…”

Fabrication and characterization of single Nb/Nb<inf>x</inf>Si<inf>1&#x2212;x</inf>/Nb Josephson junction for voltage standard

“…The non-hysteretic SNS type Josephson junction arrays consisting of hundreds of thousand junctions are the basis of the Programmable Josephson voltage standard (PJVS) [1][2][3][4]. With non-hysteretic I-V curve and large critical current, the SNS junction devices are capable of realizing stable voltage steps and good noise immunity.…”

“…With non-hysteretic I-V curve and large critical current, the SNS junction devices are capable of realizing stable voltage steps and good noise immunity. Nb and NbN are the most mature and commonly used superconductor materials for the SNS junction devices, while PdAu [5], MoSi2 [6], Nb x Si 1-x [2], TiN x [3], and etc are usually chosen as the barrier materials. It has been successful with the Nb/Nb x Si 1-x /Nb junctions.…”