Design and Evaluation of Magnetic Field Tolerant Single Flux Quantum Circuits for Superconductive Sensing Systems

Abstract

A promising application of a single-flux quantum (SFQ) circuit is read-out circuitry for a multi-channel superconductive sensor array. In such applications, the SFQ read-out circuit is expected to operate outside a magnetic shield. We investigated an SFQ circuit structure, which is tolerant to an external magnetic field, using the AIST 2.5 kA/cm 2 Nb standard 2 process, which has four Nb wiring layers including the ground plane. By covering the entire circuit using an upper Nb wiring layer called the control (CTL) layer, the influences of the external magnetic field on the SFQ circuit operation can be avoided. We experimentally evaluated the sheet inductance of the wiring layer underneath the CTL shielding layer to design a magnetic-field-tolerant SFQ circuit. We implemented and measured test circuits comprising toggle flip-flops (TFFs) to evaluate their magnetic field tolerances. The operating margin and maximum operating frequency of the designed TFF did not deteriorate with increases in the magnetic field applied to the test circuit, whereas the operating margin of the conventional TFF was reduced by applying the magnetic field. We have also demonstrated the high-speed operation of the designed TFF operated in an unshielded environment at a frequency of up to 120 GHz with a wide operating margin.

30GHz Operation of Single-Flux-Quantum Arithmetic Logic Unit Implemented by Using Dynamically Reconfigurable Gates

“…In this study, we improved the operating margin of the dynamically reconfigurable SFQ AND/OR gate by employing a new circuit structure where the circuit is partially surrounded by under-and over-ground layers [13], [14] to reduce the parasitic inductance of the signal lines. We designed and tested an arithmetic logic unit (ALU), which is one of the most important circuit components of computation systems, using the dynamically reconfigurable AND/OR gate to evaluate the effectiveness of introducing dynamically reconfigurable logic gates in superconducting logic circuit design.…”