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Final Report

YBCO Josephson Junction Arrays

Randy W. Simon

Published Jul 14, 1993• 0 citations
OpenAlex

Abstract

Josephson junction arrays have long been suggested as efficient, tunable sources for upper microwave and mm-wave frequencies. Based on the fundamental properties of the junction and the ability to combine the power output of many junctions using an array, the circuit concept is quite promising. The challenge is to phase lock the junctions so that power adds coherently and a number of demonstrations with Nb junction arrays have been performed doing this. This program was intended to begin using YBCO junction arrays to demonstrate source potential at 77K. Edge junctions have been used in arrays with up to 60000 junctions and the ability to couple power off-chip has been demonstrated directly for frequencies of at least 70-160 GHz. Power outputs have approached 1 micro W (in relatively narrow bands) and tunability has exceeded 20 GHz. Some novel array architectures have been built, including one with improved linewidth per unit junction, and new techniques developed for extracting junction statistics from array spectra. These techniques are used as feedback for process optimizations now in progress.

Related papers

Josephson Junctions: Oscillators and Broadband Spectrometers at Frequencies up to 1 THz

J. Edstam

This thesis is devoted to some selected applications of the Josephson junction oscillator. The initial work was performed using low-Tc Nb/PbBi tunnel junctions, while the later parts were done using the recently developed high-Tc YBa2Cu3O7 (YBCO) Josephson junctions. The latter junctions have raised the hope for Josephson oscillator applications with substantially increased operation frequencies and temperatures. In the first part of this thesis the use of inductor-resistor (LR) shunted tunnel junctions in arrays of phase locked Josephson junction oscillators was investigated. The LR shunt is designed to resonate out the intrinsic tunnel junction capacitance at the operation frequency. We show that LR shunted tunnel junctions have important advantages compared to the commonly used resistively shunted tunnel junctions; i.e. narrower linewidths, higher impedance of the junctions and that they can be optimized also at frequencies higher than about 100 GHz. Design rules for stable, non-chaotic oscillations with optimized output power were developed. Measurements on a non- optimized circuit show that oscillator arrays of LR shunted tunnel junctions can generate substantial power, ~10 nW to a 300 .OMEGA. load at 390 GHz from a 10 junction array. In the second part the phase locking of YBCO Josephson junctions was clearly demonstrated for the first time. Mutual phase locking of two junctions was observed at frequencies between 0.2 and 1 THz, and was only limited by the bandwidth of the coupling circuit. The locking was in good agreement with simulations based on the resistively shunted junction model. The interaction of a single Josephson junction with a 5 junction oscillator array was also measured at frequencies up to about 350 GHz, but was substantially reduced by the high losses of the coupling circuit. The YBCO Josephson junctions were found to be interesting candidates for microwave generation at frequencies approaching 1 THz and oscillator arrays to be mainly limited by the high losses of the coupling circuits at these frequencies. In the third part the interaction of YBCO Josephson junctions with integrated resonators were studied for the first time. Using a novel method, Josephson Broadband Spectroscopy (JOBS), the high frequency properties of the resonators were measured with a bandwidth of up to 1 THz and in the temperature range 4-77 K. The YBCO surface resistance (9 m.OMEGA. at 4 K and 100 GHz) was found to scale as f2 and had a temperature dependence in good agreement with the two-fluid model, modified with 18% non-pairing charge carriers. The YBCO London penetration depth was frequency independent (460 nm at 4 K) and had a temperature dependence in agreement with the two-fluid model.

•Jan 1, 1994•0 citations

High Temperature Superconducting Josephson Junction Array Systems Phase 1

J. Martens, A. Pance, K. Char +2 more

High temperature superconducting Josephson arrays were investigated as possible millimeter wave sources. A junction technology was selected and improved to the point where radiation, near 1 microwatt off-chip, was measured from a variety of 2-dimensional arrays in the 70-160 GHz range. The arrays were tunable and were successfully coupled to a number of antennas for broadband, tunable transmission. Antennas for a variety of specific applications were selected on the basis of bandwidth requirements, impedance levels, polarization, and the possibility of sufficient monolithic integration. The final part of the program was a study of potential subsystems that would utilize these arrays. Interchip communications transceivers were studied and interchip coupling was demonstrated using two antenna-coupled arrays. The most promising application may be a monolithic clock source, near 100 GHz, for communications and signal processing systems. Josephson arrays, mm-wave sources.

Final Report•Jan 25, 1994•0 citations

Testing of Josephson Array Antennas and Trim Current Tuning

A. A. Abdumalikov, P. Caputo, Alexey Vladimirovich Ustinov

This report results from a contract tasking University of Erlangen-Nuremberg as follows: contractor will investigate novel designs of triangular Josephson Junction arrays attempting to improve the high-frequency performance of the arrays in two ways; first, increase the operation frequencies and second, increase the output power of the millimeter-band radiation to level enabling practical application of the arrays. Three approaches will be investigated. First, trimming of currents at the array edges is expected to stabilize coherent oscillations and increase the operation margins (output power). Second, it appears promising to set up a traveling wave in a transmission line that contains an array comparable with the wavelength. Third, testing dipole-like active antennas to couple radiation out from arrays is a high priority task for emission in free space at high frequencies. The contractor will experimentally verify the above concepts by designing new circuits and performing experiments with Nb/AOx/Nb Josephson Junction arrays. For these experiments, the contractor will use a millimeter-wave band receiver as well an on-chip detection circuits up to 300 GHz. Spatially-resolved measurements using low temperature scanning laser microscopy will be performed in order to monitor array dynamics at the junction level. Furthermore, the contractor intends to design a dipole antenna and test it with an integrated receiver in 400-500 GHz frequency range. For this purpose, improvements for a flux-flow oscillator as a local oscillator may be needed. Finally, the contractor will perform experiments with shunted junction arrays in order to simulate intrinsically overdamped high-Tc junctions and explore a possibility of using high Tc layered junctions for oscillator application

•Sep 1, 2002•0 citations

High-frequency oscillators using phase-locked arrays of Josephson junctions

Samuel P. Benz, P.A.A. Booi

We present a basic description of Josephson junctions and discuss their use as GHz and THz oscillators. The resistively shunted junction model is used to calculate the available power, linewidth, and operating frequency of the oscillators. We discuss how phase-locked arrays of junctions are used to achieve higher power and narrower linewidth. Two experimental examples of phase-locked emission are shown: one from on-chip detection circuits at 150 GHz and one detected off-chip showing a 13-kHz linewidth at 88.8 GHz.>

IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control•Sep 1, 1995•6 citations

High-frequency oscillators using phase-locked arrays of Josephson junctions

Samuel P. Benz, P.A.A. Booi

We present a basic description of Josephson junctions and discuss their use as GHz and THz oscillators. The resistively shunted junction model is used to calculate the available power, linewidth and operating frequency of the oscillators. We discuss how phase-locked arrays of junctions are used to achieve higher power and narrower linewidth. Two experimental examples of phase-locked emission are shown: one from on-chip detection circuits at 150 GHz and one detected off-chip showing a 13 kHz linewidth at 88.8 GHz.>

Joint Conference of the European Frequency and Time Forum and IEEE International Frequency Control Symposium (EFTF/IFCS)•Dec 17, 2002•2 citations

Microwave coupling of frequency-locked Josephson junction arrays

Insang Song, Yongheum Eom, Gwangseo Park +2 more

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.

Applied Physics Letters•Jun 16, 1997•8 citations
Josephson junction arrays have long been suggested as efficient, tunable sources for upper microwave and mm-wave frequencies. Based on the fundamental properties of the junction and the ability to combine the power output of many junctions using an array, the circuit concept is quite promising. The challenge is to phase lock the junctions so that power adds coherently and a number of demonstrations with Nb junction arrays have been performed doing this. This program was intended to begin using YBCO junction arrays to demonstrate source potential at 77K. Edge junctions have been used in arrays with up to 60000 junctions and the ability to couple power off-chip has been demonstrated directly for frequencies of at least 70-160 GHz. Power outputs have approached 1 micro W (in relatively narrow bands) and tunability has exceeded 20 GHz. Some novel array architectures have been built, including one with improved linewidth per unit junction, and new techniques developed for extracting junction statistics from array spectra. These techniques are used as feedback for process optimizations now in progress.
This thesis is devoted to some selected applications of the Josephson junction oscillator. The initial work was performed using low-Tc Nb/PbBi tunnel junctions, while the later parts were done using the recently developed high-Tc YBa2Cu3O7 (YBCO) Josephson junctions. The latter junctions have raised the hope for Josephson oscillator applications with substantially increased operation frequencies and temperatures. In the first part of this thesis the use of inductor-resistor (LR) shunted tunnel junctions in arrays of phase locked Josephson junction oscillators was investigated. The LR shunt is designed to resonate out the intrinsic tunnel junction capacitance at the operation frequency. We show that LR shunted tunnel junctions have important advantages compared to the commonly used resistively shunted tunnel junctions; i.e. narrower linewidths, higher impedance of the junctions and that they can be optimized also at frequencies higher than about 100 GHz. Design rules for stable, non-chaotic oscillations with optimized output power were developed. Measurements on a non- optimized circuit show that oscillator arrays of LR shunted tunnel junctions can generate substantial power, ~10 nW to a 300 .OMEGA. load at 390 GHz from a 10 junction array. In the second part the phase locking of YBCO Josephson junctions was clearly demonstrated for the first time. Mutual phase locking of two junctions was observed at frequencies between 0.2 and 1 THz, and was only limited by the bandwidth of the coupling circuit. The locking was in good agreement with simulations based on the resistively shunted junction model. The interaction of a single Josephson junction with a 5 junction oscillator array was also measured at frequencies up to about 350 GHz, but was substantially reduced by the high losses of the coupling circuit. The YBCO Josephson junctions were found to be interesting candidates for microwave generation at frequencies approaching 1 THz and oscillator arrays to be mainly limited by the high losses of the coupling circuits at these frequencies. In the third part the interaction of YBCO Josephson junctions with integrated resonators were studied for the first time. Using a novel method, Josephson Broadband Spectroscopy (JOBS), the high frequency properties of the resonators were measured with a bandwidth of up to 1 THz and in the temperature range 4-77 K. The YBCO surface resistance (9 m.OMEGA. at 4 K and 100 GHz) was found to scale as f2 and had a temperature dependence in good agreement with the two-fluid model, modified with 18% non-pairing charge carriers. The YBCO London penetration depth was frequency independent (460 nm at 4 K) and had a temperature dependence in agreement with the two-fluid model.
High temperature superconducting Josephson arrays were investigated as possible millimeter wave sources. A junction technology was selected and improved to the point where radiation, near 1 microwatt off-chip, was measured from a variety of 2-dimensional arrays in the 70-160 GHz range. The arrays were tunable and were successfully coupled to a number of antennas for broadband, tunable transmission. Antennas for a variety of specific applications were selected on the basis of bandwidth requirements, impedance levels, polarization, and the possibility of sufficient monolithic integration. The final part of the program was a study of potential subsystems that would utilize these arrays. Interchip communications transceivers were studied and interchip coupling was demonstrated using two antenna-coupled arrays. The most promising application may be a monolithic clock source, near 100 GHz, for communications and signal processing systems. Josephson arrays, mm-wave sources.
This report results from a contract tasking University of Erlangen-Nuremberg as follows: contractor will investigate novel designs of triangular Josephson Junction arrays attempting to improve the high-frequency performance of the arrays in two ways; first, increase the operation frequencies and second, increase the output power of the millimeter-band radiation to level enabling practical application of the arrays. Three approaches will be investigated. First, trimming of currents at the array edges is expected to stabilize coherent oscillations and increase the operation margins (output power). Second, it appears promising to set up a traveling wave in a transmission line that contains an array comparable with the wavelength. Third, testing dipole-like active antennas to couple radiation out from arrays is a high priority task for emission in free space at high frequencies. The contractor will experimentally verify the above concepts by designing new circuits and performing experiments with Nb/AOx/Nb Josephson Junction arrays. For these experiments, the contractor will use a millimeter-wave band receiver as well an on-chip detection circuits up to 300 GHz. Spatially-resolved measurements using low temperature scanning laser microscopy will be performed in order to monitor array dynamics at the junction level. Furthermore, the contractor intends to design a dipole antenna and test it with an integrated receiver in 400-500 GHz frequency range. For this purpose, improvements for a flux-flow oscillator as a local oscillator may be needed. Finally, the contractor will perform experiments with shunted junction arrays in order to simulate intrinsically overdamped high-Tc junctions and explore a possibility of using high Tc layered junctions for oscillator application
We present a basic description of Josephson junctions and discuss their use as GHz and THz oscillators. The resistively shunted junction model is used to calculate the available power, linewidth, and operating frequency of the oscillators. We discuss how phase-locked arrays of junctions are used to achieve higher power and narrower linewidth. Two experimental examples of phase-locked emission are shown: one from on-chip detection circuits at 150 GHz and one detected off-chip showing a 13-kHz linewidth at 88.8 GHz.>
We present a basic description of Josephson junctions and discuss their use as GHz and THz oscillators. The resistively shunted junction model is used to calculate the available power, linewidth and operating frequency of the oscillators. We discuss how phase-locked arrays of junctions are used to achieve higher power and narrower linewidth. Two experimental examples of phase-locked emission are shown: one from on-chip detection circuits at 150 GHz and one detected off-chip showing a 13 kHz linewidth at 88.8 GHz.>
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.