Josephson Digital and Analog Devices with Niobium Junctions

Abstract

This paper describes recent progress on digital and analog circuits using all niobium (Nb/AlQx/Nb) Josephson junctions. A niobium junction has excellent characteristics with a low leakage current, and is stable with respect to thermal cycling and long term storage. We used the niobium junctions in a variety of digital and analog circuits. This paper firstly describes the logic gate family, named the MVTL (Modified Variable Threshold Logic) gate family. The lowest experimentally obtained MVTL-OR gate delay was only 2.5 ps with a power consumption of 17 uW/gate. The gate family was applied to various circuits, such as 8-bit shift registers, 16-bit ALUs (Arithmetic Logic Unit), and 4-bit microprocessors. We confirmed the high speed operation of less than 10 ps per gate on the average for these circuits.

We also developed a new high-sensitivity magnetic sensor using the SQUID (Superconducting Quantum Interference Device). We call it a single-chip SQUID magnetometer, because the feedback circuit, which is operated at room temperature in a conventional SQUID system, has been integrated on the same chip as the SQUID sensor itself.