Miniaturization of Josephson Junctions for Digital Superconducting Circuits

Abstract

In this work, we briefly overview various options for Josephson junctions, which should be scalable down to nanometer range for utilization in nanoscale digital superconducting technology. Such junctions should possess high values of critical current, I c , and normal state resistance, R N . Another requirement is the high reproducibility of the junction parameters across a wafer in a fabrication process. We argue that superconductor-normal metal-superconductor (SN -N -NS) Josephson junction of "variable thickness bridge" geometry is a promising choice to meet these requirements. Theoretical analysis of the SN -N -NS junction is performed in the case where the distance between the S electrodes is comparable to the coherence length of the N material. The restriction on the junction geometrical parameters providing the existence of superconductivity in the S electrodes is derived for the current flowing through the junction of an order of I c . The junction heating, as well as available mechanisms for the heat removal, is analyzed. The obtained results show that a SN -N -NS junction with a high (submillivolt) value of I c R N product can be fabricated from a broadly utilized combination of materials like Nb/Cu using well-established technological processes. The junction area can be scaled down to that of semiconductor transistors fabricated in the frame of a 40-nm process.

Lateral Josephson Junctions as Sensors for Magnetic Microscopy at Nanoscale

“…Invented a long time ago, , lateral Josephson junctions (LJJ) are key elements of superconducting quantum electronic devices: single photon detectors, − thermometers, and RF-sensors, among many others. LJJ are also widely used in fundamental studies − as they are extremely sensitive to magnetic field that creates superconducting phase gradients, redistributes supercurrents, causes Josephson vortex entry, , thus modifying the electronic response of LJJ. − …”

Boundary conditions for the order parameter and the proximity influenced internal phase differences in double superconducting junctions

“…Here t − and t 1,2 are on the order of g 2 ℓ t + , with the higher order terms disregarded. One finds two solutions to equations (41) that are of the form…”

“…When a normal metal is placed between the superconductors, the Josephson coupling emerges as a consequence of superconducting correlations generated by proximity effects in the normal metal region [22][23][24][25][26]. A number of hybrid systems with proximity-induced Josephson coupling through normal metal electrodes, have recently been the focus of scientific scrutiny [27][28][29][30][31][32][33][34][35][36][37][38][39][40][41].…”

Superconducting Bio-Inspired Au-Nanowire-Based Neurons

“…While the superconducting neural networks of various kinds are rapidly developed currently [ 22 , 23 , 24 , 28 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 ], their complexity is severely limited by the low integration density of superconducting circuits [ 41 , 42 ]. One of the main reasons for this is a comparatively large area (an order of a micron to few tenths of a micron squared) of commonly used superconductor-insulator-superconductor tunnel Josephson junction [ 32 ].…”