Operation of a NbN-based programmable Josephson voltage standard chip with a compact refrigeration system

Abstract

A refrigeration system was designed and constructed for realizing a liquid-He-free programmable Josephson voltage standard. The system is equipped with a two-stage Gifford-McMahon cooler, a thermal-radiation shield, a magnetic-field shield and semi-rigid coaxial cables to supply microwave power to a chip. The performance of the system was examined by use of a NbN-based 8-bit digital-to-analog converter (DAC) chip designed as a 1 V programmable voltage standard. When operated at 8.5 K on the cryocooler, constant-voltage steps with amplitudes greater than 1 mA were observed for every segment of junction arrays on the chip.

A Programmable Josephson Voltage Standard Chip using Arrays of NbN/TiN/NbN/TiN/NbN Double-Junction Stacks Operated at 10K

“…NbN has a critical temperature of 16 K, and a chip consisting of NbN/TiN/NbN junctions can be operated at a temperature higher than that of liquid helium, which leads to a more compact, lower-power system. We have previously demonstrated operation of a PJVS chip with IV output [2] and are developing chips with output voltages of 5 V and 10 V. Here we report the fabrication and electrical characteristics of a PJVS chip composed of arrays of NbN/TiN/NbN/TiN/NbN double-junction stacks. Figure 1 shows the layout of metal layers in a PJVS chip designed for obtaining constant voltages of 5 V or 10 V. The edge of the square chip is 15 mm.…”

“…A Programmable Josephson Voltage Standard (PJVS) was first demonstrated by Hamilton et al in 1995 [1] and has some attractive features: (1) sub-millisecond voltage settling time, (2) large operating current range (>1 mA), and (3) inherent voltage stability against noise. We have been developing a PJVS system using NbN/TiN/NbN junction arrays that can be operated with a compact cryocooler [2].…”

“…We have been developing a PJVS system using NbN/TiN/NbN junction arrays that can be operated with a compact cryocooler [2]. NbN has a critical temperature of 16 K, and a chip consisting of NbN/TiN/NbN junctions can be operated at a temperature higher than that of liquid helium, which leads to a more compact, lower-power system.…”

Heat transfer analysis of a programmable Josephson voltage standard chip operated with a mechanical cooler

“…The output voltage of the PJVS can be programmed to have arbitrary values by controlling the ON/OFF states of the bias current applied to each segment, enabling us to realize a digital-to-analog (D/A) converter operation with a quantum-mechanical-theory-based accuracy. To realize more user-friendly and low operating-cost systems, a liquid-helium-free PJVS system using a mechanical refrigerator has been developed at the National Institute of Advanced Industrial Science and Technology (AIST) [2].…”

4 K cryocooler implementation of a DC programmable voltage standard

“…The final development phase for these systems is to install the PJVS chip in a new cryostat utilizing a cryogen-free, closed-cycle refrigerator (CCR) at 4 K. The present cryostat design is an extension of the 4 K cryocooled 10 V conventional JVS that HYPRES has previously developed and demonstrated [4]. A complementary effort into implement a NbN-based programmable voltage standard chip on a 10 K cryocooler is being pursued through a collaboration between AIST and NIST [5].…”