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Applied Physics Letters

Microwave coupling of frequency-locked Josephson junction arrays

Insang Song, Yongheum Eom, Gwangseo Park, E.‐H. Lee, S.-J. Park

Published Jun 16, 1997• 8 citations
Publisher

Abstract

A high temperature superconducting YBa2Cu3Oy array of five Josephson junctions designed with additional coupling lines has been developed to demonstrate the effects of frequency locking and impedance matching for applications such as oscillators, mixers, and detectors. The Josephson self-radiation power was directly detected by a superheterodyne receiver, and Shapiro steps were also measured. The Josephson self-radiation properties reveal good quality of phase locking and microwave coupling with external circuits. The maximum self-radiation power of our array is about 50 pW which is several ten times higher than that of a single Josephson junction, and its peak point exactly satisfies the Josephson current-voltage relation. The Shapiro-step measurements show that the behavior of current-voltage curve depends on the effective inductance of coupling lines which affects the total impedance of Josephson junction array and microwave coupling. The Josephson oscillation frequency was obtained up to about 880 GHz which is 73% of the maximum available frequency calculated from the characteristic voltage of the Josephson junctions. Experimental results show that this type of Josephson junction array can improve the Josephson self-radiation power and increase the maximum detectable frequency.

DOI
10.1063/1.118430

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A high temperature superconducting YBa2Cu3Oy array of five Josephson junctions designed with additional coupling lines has been developed to demonstrate the effects of frequency locking and impedance matching for applications such as oscillators, mixers, and detectors. The Josephson self-radiation power was directly detected by a superheterodyne receiver, and Shapiro steps were also measured. The Josephson self-radiation properties reveal good quality of phase locking and microwave coupling with external circuits. The maximum self-radiation power of our array is about 50 pW which is several ten times higher than that of a single Josephson junction, and its peak point exactly satisfies the Josephson current-voltage relation. The Shapiro-step measurements show that the behavior of current-voltage curve depends on the effective inductance of coupling lines which affects the total impedance of Josephson junction array and microwave coupling. The Josephson oscillation frequency was obtained up to about 880 GHz which is 73% of the maximum available frequency calculated from the characteristic voltage of the Josephson junctions. Experimental results show that this type of Josephson junction array can improve the Josephson self-radiation power and increase the maximum detectable frequency.
We have fabricated a YBa/sub 2/Cu/sub 3/O/sub y/ (YBCO) array of five Josephson junctions designed with additional inductive coupling lines (AICLs). The junctions in this array were dc-biased in parallel to oscillate coherently in-phase and integrated with AICLs to improve the impedance matching between this array and external circuits such as a waveguide. The effect of AICLs was investigated by studying its influence on the current-voltage characteristics of the Josephson junction array (JJA) under external microwave irradiations with frequency of 22 GHz. The experimental results show that the behavior of the Shapiro-steps depends upon the effective inductance of AICLs which affects the total impedance and microwave coupling. We were able to obtain an oscillation frequency of about 73% of the maximum available frequency calculated from the characteristic voltage of the Josephson junctions in the array at a temperature of 12 K. By calculating the total impedance of the array, we obtained the suitable parameters of the array for microwave coupling with waveguide for various values of inductance, ac frequencies and number of Josephson junctions.
We fabricated a Josephson junction array with an additional inductive coupling line to detect the high frequency and power of Josephson self-radiation. The YBa2Cu3O y Josephson junctions are fabricated by a pulsed laser deposition method on bicrystal MgO substrates. We measured the submillimeter wave and the Josephson self-radiation power in an external waveguide system. The Josephson junction arrays showed the resistively shunted junction (RSJ)-like current–voltage characteristics and good frequency-locking of Josephson self-radiation. As the number of Josephson junctions increased, the maximum detected power was increased. We observed the maximum frequency of above 6 THz for Josephson self-radiation in the array with 11 Josephson junctions from the Shapiro steps under 22 GHz irradiation.
Frequency-locked and microwave-coupled arrays of high- superconducting Josephson junctions have been developed. The Josephson junctions were prepared on bicrystal MgO substrates using a pulsed laser ablation method. The maximum detected power of Josephson self-radiation, which is directly detected by a superheterodyne receiver with a central frequency of 22 GHz, from the arrays was enhanced with increasing number of Josephson junctions. The Josephson self-radiation properties of the arrays revealed a good quality of frequency locking and exactly satisfied the Josephson voltage-frequency relationship. A narrower linewidth of the Josephson self-radiation was obtained by increasing the number of Josephson junctions in the array.
We have investigated the mutual phase interaction between a single detector junction and a phase-locked three-junction array of high-T/sub c/ Josephson junctions. The YBCO Josephson junctions were fabricated on a MgO bicrystal substrate. In the array junction structure, the dc bias current was fed to the junction array having parallel geometry with each pair of junctions shunted by a superconducting coplanar microstrip superconducting loop. The configuration of bias leads was a series connection of interlocking dc SQUIDs geometry which enables all junctions to oscillate at the same frequency. We measured the radiation power of a Josephson-junction array using an off-chip coupled to a radiometer and on-chip coupled to a single junction from centimeter- to millimeter-wave ranges. Clear self-induced Shapiro steps were observed in the current-voltage curves of the detector junction. The power transfered to the single detector junction was estimated from the modulation of Shapiro step height. The maximum detected power level was about 7 nW at frequency 150-250 GHz. The Josephson oscillation power excited the resonant mode coupled to the coplanar microstrip loops.
We have integrated an array of five High-T/sub c/ Josephson junction oscillators with a Josephson detector junction of high resistance, e.g. 25 /spl Omega/. High impedance detectors are suitable in integrated superconducting receivers. We find the output power to be sufficient to modulate the detector junction with large Shapiro steps in the frequency range 200-700 GHz. The oscillator junctions were dc-biased in parallel and integrated in an inductive high frequency coupling circuit to oscillate coherently in-phase. The high frequency coupling circuit is evaluated through its influence on the current-voltage characteristic of the Josephson junctions.>
Using high temperature superconducting thin films, we designed and fabricated Josephson junctions associated with a log-periodic toothed trapezoid antenna. Microwave self-radiation from the Josephson junction was measured by using both a superheterodyne receiver at the center frequency of 22 GHz and an external waveguide system. In the case of junction incorporated with an antenna structure, there was a significant increase of power by an order of magnitude with respect to a junction without antenna. Under the 22 GHz irradiation, we observed distinctive Shapiro steps in the I-V measurement, which allowed as estimating the received power of the junction. The received power of the junction with an antenna exhibited as a large increase as that of a self-radiation. Our results indicate that a Josephson junction with an antenna is very effective for the microwave coupling between Josephson junction and free space. The combined device can be used either for a high power microwave source or for a high sensitive sensor.