Microwave Design and Performance of PTB 10 V Circuits for the Programmable Josephson Voltage Standard

Abstract

At Physikalisch-Technische Bundesanstalt (PTB), superconducting 10 V circuits for the programmable Josephson voltage standard (PJVS) are routinely manufactured on the basis of NbxSi1−x barrier junctions. This paper describes in detail the basic design principles for an operating frequency of 70 GHz. It starts with single junctions, discusses their insertion into microstriplines and closes with the whole microwave circuit containing 69,632 NbxSi1−x barrier junctions arranged over 128 microstriplines connected in parallel. The microwave attenuation of this junction type is a key parameter for the 10 V design and we report its experimental determination. Special attention has been devoted to subarrays with just a few Josephson junctions in one of the outermost striplines. The arrangement of these subarrays determines the optimum performance of the complete 10 V series array. The high performance of programmable 10 V circuits fabricated at PTB is characterized by measured operating margins in all subarrays of more than 1 mA centered at the same dc bias current. The observed modulation of the current margins, when changing the frequency around 70 GHz, is explained by microwave reflections caused by the rf waveguide inside the cryoprobe. We determine the current margins in dependence of the output power of a microwave synthesizer and show that 60 mW is sufficient to achieve current margins larger than 1 mA.

Intrinsically shunted Josephson junctions for electronics applications

“…It permits to tune the barrier resistivity and the characteristic voltage of the junctions [68]. The most successful example is an SNS-like Josephson trilayer based on a NbxSi1-x barrier first proposed at NIST [69] and then developed at PTB [70,71]. SNIS junctions have also proved to be suitable for the realization of a programmable voltage standard.…”

Tests of SNIS Josephson Arrays Cryocooler Operation

“…The other technologies that look promising above 4.2 K, Nb/Nb x Si 1-x /Nb (SNS) and Nb/Al-AlO x /Nb (SNIS: Superconductor-Normal metal-Insulator-Superconductor) junctions, both allow to engineer the electrical properties of the barrier over a wide range of values by a suitable control of the fabrication parameters. An outstanding 20 V output level was recently reported with Nb/Nb x Si 1-x /Nb arrays [12]. The authors also The SNIS junction technology, based on low temperature superconductors but capable of operation above liquid helium temperature, is interesting for application to a cryocooled standard, allowing to set a compromise between device and refrigerator requirements.…”

A modular and customizable open-source package for quantum voltage standards operation and control

“…As shown in Fig 3, the i th subsection counts N J ( i ) junctions, where N J = [64, 32, 16, 8, 4, 2, 1, 1, 128, 256, 512, 1024, 2048, 4096] and i is an integer number between 1 and 14. The reason of this apparently atypical arrangement is related to the optimal rf transmission along the Josephson array [24]. Fifteen AWG channels (four AT-AWG1104 modules) are required and, in order to exploit all the software potentialities, connections should be done as shown in Fig 3.…”