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Joint Conference of the European Frequency and Time Forum and IEEE International Frequency Control Symposium (EFTF/IFCS)

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

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

Published Dec 17, 2002• 2 citations
Publisher

Abstract

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.>

DOI
10.1109/freq.1994.398263

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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.>

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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.

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A submillimeter-wave oscillator using a phase-locked array of Josephson junctions is demonstrated. With an array of 40 shunted tunnel junctions, the oscillator delivers 1 mu W of power at 350 GHz into a 60- Omega load on the chip. The operating frequency of the oscillator is tunable over a range of about 10%. Experiments on two coupled lead alloy tunnel junctions show that Josephson oscillations exist to about 1 THz. Using a similar design and a higher gap superconductor such as NbN for the transmission lines, arrays operating at 1 THz with power outputs of 1 mW should be feasible.>

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We present experimental results on the emission from phase-locked twodimensional arrays of Josephson junctions. We have coupled the emission from 10 x 10 arrays to a room-temperature mixer throu h a tin-line antenna and WR-12 waveguide. A single voltagetunable peak was detected up to 230 GHz. A stripline resonance in the antenna reduced the array's dynamic resistance and thereby the emission linewidth to as low as 10 kHz. We extract an effective noise temperature of 14 K from the linewidth data. When the array's emission was coupled to an on-chip detector junction through a dc blocking capacitor, we detected voltagetunable emission from 75 GHz up to 300 GHz, and in some circuits emission above 400 GHz. The coherent power spectrum depends primarily on internal resonances.

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It is shown that inductively resistively shunted junctions are good candidates for Josephson-junction oscillator arrays. The shunt resonates out the junction intrinsic capacitance, allowing a much higher effective impedance at the resonance frequence, but still with a small shunt resistance giving a narrow linewidth. Compared to resistively shunted junctions they are advantageous for frequencies greater than about 100 GHz, when fewer junctions and lumped arrays can be used, giving larger bandwidths. Design rules that avoid chaotic solutions and optimize output power are given. A design example of an integrated circuit consisting of an SIS-mixer pumped by an array of as few as four junctions at 350 GHz is given. A bandwidth of 160 GHz and a linewidth of 400 kHz should be feasible in a practical situation.>

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Josephson array oscillators with microstrip resonators

Akira Kawakami, Yoshinori Uzawa, Z. Wang

Interaction between two Josephson junctions and a microstrip resonator is investigated using a resonator shunted junction (RLCSJ) model. A sharp current step resulting from coupling with the resonator is observed in simulated I-V characteristics. There is strong phase-locking and decreasing of dynamic resistance at the current step. We design and fabricate two types of Josephson array oscillators using these effects to obtain stable phase locking and narrow linewidth for the oscillation. The fabricated oscillators are formed with nine shunted Nb/AlOx/Nb tunnel junctions and Nb microstrip resonators. The power of the oscillator delivered to the load resistor was estimated to be about 3.6 /spl mu/W at 330 GHz. A composite linewidth of the oscillators is also measured at about 19 MHz at 4.2 K using two oscillators with a log-periodic antenna and a SIS detector.

IEEE Transactions on Applied Superconductivity•Jun 1, 1997•14 citations
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.>
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.
A submillimeter-wave oscillator using a phase-locked array of Josephson junctions is demonstrated. With an array of 40 shunted tunnel junctions, the oscillator delivers 1 mu W of power at 350 GHz into a 60- Omega load on the chip. The operating frequency of the oscillator is tunable over a range of about 10%. Experiments on two coupled lead alloy tunnel junctions show that Josephson oscillations exist to about 1 THz. Using a similar design and a higher gap superconductor such as NbN for the transmission lines, arrays operating at 1 THz with power outputs of 1 mW should be feasible.>
We present experimental results on the emission from phase-locked twodimensional arrays of Josephson junctions. We have coupled the emission from 10 x 10 arrays to a room-temperature mixer throu h a tin-line antenna and WR-12 waveguide. A single voltagetunable peak was detected up to 230 GHz. A stripline resonance in the antenna reduced the array's dynamic resistance and thereby the emission linewidth to as low as 10 kHz. We extract an effective noise temperature of 14 K from the linewidth data. When the array's emission was coupled to an on-chip detector junction through a dc blocking capacitor, we detected voltagetunable emission from 75 GHz up to 300 GHz, and in some circuits emission above 400 GHz. The coherent power spectrum depends primarily on internal resonances.
It is shown that inductively resistively shunted junctions are good candidates for Josephson-junction oscillator arrays. The shunt resonates out the junction intrinsic capacitance, allowing a much higher effective impedance at the resonance frequence, but still with a small shunt resistance giving a narrow linewidth. Compared to resistively shunted junctions they are advantageous for frequencies greater than about 100 GHz, when fewer junctions and lumped arrays can be used, giving larger bandwidths. Design rules that avoid chaotic solutions and optimize output power are given. A design example of an integrated circuit consisting of an SIS-mixer pumped by an array of as few as four junctions at 350 GHz is given. A bandwidth of 160 GHz and a linewidth of 400 kHz should be feasible in a practical situation.>
Interaction between two Josephson junctions and a microstrip resonator is investigated using a resonator shunted junction (RLCSJ) model. A sharp current step resulting from coupling with the resonator is observed in simulated I-V characteristics. There is strong phase-locking and decreasing of dynamic resistance at the current step. We design and fabricate two types of Josephson array oscillators using these effects to obtain stable phase locking and narrow linewidth for the oscillation. The fabricated oscillators are formed with nine shunted Nb/AlOx/Nb tunnel junctions and Nb microstrip resonators. The power of the oscillator delivered to the load resistor was estimated to be about 3.6 /spl mu/W at 330 GHz. A composite linewidth of the oscillators is also measured at about 19 MHz at 4.2 K using two oscillators with a log-periodic antenna and a SIS detector.