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IEEE Transactions on Applied Superconductivity

Magnetic flux controlled Josephson array oscillators

Donald S. Crankshaw, Enrique Trias, Terry P. Orlando

Published Mar 1, 2001• 4 citations
Publisher

Abstract

One-dimensional parallel arrays of Josephson junctions have the ability to perform as oscillators tunable by magnetic flux. We have designed and tested an array impedance matched to a detector junction load. The amplitude and frequency of the array are controlled by the independent variables of magnetic field and current bias. We report on the array's characteristics and compare them to the results predicted by nonlinear simulations and a linear circuit model. This confirms the accuracy of the circuit model, both for impedance matching and in describing the dynamics of the array, even in a multiple-frequency regime.

DOI
10.1109/77.919570

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One-dimensional parallel arrays of Josephson junctions have the ability to perform as oscillators tunable by magnetic flux. We have designed and tested an array impedance matched to a detector junction load. The amplitude and frequency of the array are controlled by the independent variables of magnetic field and current bias. We report on the array's characteristics and compare them to the results predicted by nonlinear simulations and a linear circuit model. This confirms the accuracy of the circuit model, both for impedance matching and in describing the dynamics of the array, even in a multiple-frequency regime.
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Two-dimensional arrays of Josephson junctions have been shown to operate in a state in which the microwave oscillations of the junctions are phase-coherent. However, the performance of an array is strongly dependent on both the details of the load-coupling circuit and the characteristic parameters of the junctions. We have measured two-dimensional arrays of resistively shunted Josephson tunnel junctions which are capacitively coupled to a nearby detector junction. Changing the critical current of the junctions in our arrays, while keeping the junction parasitics and array coupling roughly the same, results in an unexpected change in device operation. We have also investigated variations of the coupling circuit. Numerical simulations of the detection circuit enable us to estimate the power output from the array and to optimize the parameters of the system.
We report on the investigation of the effects of the nonlinear inductance of huge Josephson junction arrays on high-quality RF circuits. The inductance of a single junction is far too small for use in many RF applications; however, Josephson junction stacks and especially intrinsic Josephson junctions in crystalline-layered superconductors open new opportunities. The stack inductance can be altered by changing a DC Josephson current either using an external bias current or an external magnetic field applied to a closed superconducting loop containing two stacks connected in parallel. Using stacks of Josephson junctions in the LC resonators, a tunable 4-pole, 15 MHz band-pass filter with a centre frequency at 1.1 GHz was designed. The filter was simulated in the time domain and the response was converted to the frequency domain. It was found that using an input power level of −62 dBm, corresponding to 0.5% of the junctions' critical current, a linear approximation for the stack nonlinear inductance can be used. By changing the applied magnetic field, a tuning range of 20% was demonstrated with a tuning speed of 2 µs or better. An estimate of the losses is also given. In addition, power handling up to −26 dBm is reported using increasing circuit complexity.