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IEEE Transactions on Applied Superconductivity

Analysis of a high-temperature superconductor quantum flux parametron operating at 77 K

Mark Jeffery

Published Jan 1, 1995• 4 citations
Publisher

Abstract

A Quantum Flux Parametron (QFP) circuit designed for implementation with high-temperature superconductors is analyzed with thermal noise at 77 K. Experimental considerations are discussed and design parameters given for fabrication of the device using a YBa/sub 2/Cu/sub 3/O/sub 7/ thin film on a SrTiO/sub 3/ bicrystal substrate. An application of the high T/sub c/ QFP for the detection of single flux quantum pulses is also described.

DOI
10.1109/77.482144

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IEEE Transactions on Applied Superconductivity•Jan 1, 1992•28 citations
A Quantum Flux Parametron (QFP) circuit designed for implementation with high-temperature superconductors is analyzed with thermal noise at 77 K. Experimental considerations are discussed and design parameters given for fabrication of the device using a YBa/sub 2/Cu/sub 3/O/sub 7/ thin film on a SrTiO/sub 3/ bicrystal substrate. An application of the high T/sub c/ QFP for the detection of single flux quantum pulses is also described.
Quantum Flux Parametron (QFP) logic gates were designed and fabricated from a single layer of YBa/sub 2/Cu/sub 3/O/sub 7/ thin film based on step-edge Josephson junctions. Self-inductance (L) of the QFP loop, an important circuit parameter, as is critical current (J/sub c/) of the Josephson junction, was determined by using directly coupled dc superconducting quantum interference devices (SQUIDs). Magnetically coupled dc SQUIDs were used to detect the output signal from the QFP. Simulated waveforms were used to identify the operation modes of the QFP as a function of the circuit parameters. From examination of the output waveforms of the QFP, operation in agreement with simulations was confirmed.
As we rapidly advance through the information age, the power consumed by computers, data centers, and networks grows exponentially. This has inspired a race to develop alternative low-power computational technologies. A new adiabatic configuration of a decades-old superconducting digital logic device has darted into the lead called quantum flux parametrons (QFP). QFP operate with dissipation so low that they seemingly violate the laws of thermodynamics. In just a short span of time, they have gone from simple single NOT gates to complex processors containing thousands of gates. They are fabricated from elemental niobium superconductors cooled to just a few degrees above absolute zero. However, their efficiency is so great that for large high-performance computers with several gates, the energy savings are immense. For smaller computational platforms QFPs from high-temperature superconductors (high-Tc) are highly desirable. In this work, we take the first steps towards this goal with the demonstration of a high-T C QFP shift register. Our device is fabricated using focused helium ion beam lithography where the material is modified with an ion beam at the nanoscale to directly pattern these circuits into a high-T C thin film. We validate the correct logical operation at 25 K, over 6 times higher than niobium devices with an estimated bit energy of 0.1 attoJoule at 10 GHz.
We report the fabrication and measurement of quantum flux parametron logic from high-transition-temperature Josephson junctions operating at 25 K, above the temperature of liquid helium. The circuits are written directly into the plane of a single-layer thin film of YBa2Cu3O7 using a focused helium ion beam. A single-cell quantum flux parametron was constructed and correct logic operation was verified by using an on-chip superconducting quantum interference device for readout. A three-cell shift register was also fabricated and tested using a three-phase clock cycle. We estimate the average bit energy to be about 1×10−20 J at 1 GHz.
A quantum flux parametron (QFP), a single quantum flux superconductive device that has a potential of up to 100-GHz switching with nW-order power dissipation, is considered. The potential of the QFP and key technologies when QFPs are applied to a Josephson supercomputer are described. Switching speed, stability, and power dissipation of a QFP are discussed. QFP gates, circuits, and systems are next described. Then, ultra-fast clock distribution using a standing wave is explained. High-speed operation at more than 10 GHz and 10/sup 14/ error-free operations per QFP have been demonstrated. Finally described is a high-density packaging scheme by three-dimensional integration, which is very important for ultra-high speed circuits because the propagation delay becomes dominant in such circuits.>
Abstruct-Quantum Flux Parametron (QFP) logic gates were designed and fabricated from a single layer of YJ3a2Cu307 thin film based on step-edge Josephson junctions. Self-inductance (L) of the QFP loop, an important circuit parameter, as is critical current (I,) of the Josephson junction, was determined by using directly coupled dc superconducting quantum interference devices (SQUIDS). Magnetically coupled dc SQUIDs were used to detect the output signal from the QFP. Simulated waveforms were used to identify the operation modes of the QFP as a function of the circuit parameters. From examination of the output waveforms of the QFP, operation in agreement with simulations was confirmed.
An analysis of the limitations imposed by thermal noise on the application of the quantum flux parametrons (QFPs) as current comparators and timing discriminators is presented. At low operational frequencies, a thermal activation approach is used, while at high frequencies a circuit simulation method is required. At frequencies greater than the Josephson junction plasma frequency, an approximate expression for the noise is given. The calculations are in good agreement with the approximations and the experimental results.>