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An Integrated Superconducting Sub-mm Measurements Wave Receiver for Linewidth of Josephson Flux-Flow Oscillators

Y. M. Zhang, D. WinMer

Published Jan 1, 1994• 0 citations
OpenAlex

Abstract

By using an integrated superconducting sub-mm wave receiver, the composite linewidth of two Josephson flux- flow oscillators (FFO) was measured to be less than 2.1 MHz in the band 280-330 GHz. The output power coupled to a 10 R microstripline was about 0.5 pW, and could be adjusted by changing the current bias of the oscillator junction. The receiver consists of two identical FFO's and an SIS (superconductor- insulator-superconductor) mixer. The composite linewidth of the oscillators was determined by mixing the two signals in the SIS mixer to a lower intermediate frequency (if). The FFO's are connected to the SIS mixer via centerfed interdigital capacitors. One FFO is well coupled to the SIS mixer by using a 3-step Chebychev microstriplie transformer and a fairly large inter- digital capacitor, while the second FFO has about 15-20 dB weaker coupling. A strip inductor, rf-terminated by a radial stub, resonates out the SIS junction capacitance at about 340 GHz. Radial stubs were also used as rf chokes for the if-line (4 GHz). The FFO's and the SIS element are made of NbNb-oxidelPbBi tunnel junctions. The receiver circuit was optimized by careful CAD modeling (HP Microwave Design System). and gives rise to the emission of a pulse of electromagnetic energy when it hits the ends of the junction. If the arrival of solitons at one end of the junction is periodic, rf radiation is emitted. The propagation mode of the fluxon in a LJJ depends on the junction quality factor QJ, which is related to the junction losses as (3) QJ = ((wo/uJ)2P -t a)-'.

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An integrated superconducting sub-mm wave receiver for linewidth measurements of Josephson flux-flow oscillators

Y.M. Zhang, Dag Winkler

By using an integrated superconducting sub-mm wave receiver, the composite linewidth of two Josephson flux-flow oscillators (FFO) was measured to be less than 2.1 MHz in the band 280-330 GHz. The output power coupled to a 10 /spl Omega/ microstripline was about 0.5 /spl mu/W, and could be adjusted by changing the current bias of the oscillator junction. The receiver consists of two identical FFO's and an SIS (superconductor-insulator-superconductor) mixer. The composite linewidth of the oscillators was determined by mixing the two signals in the SIS mixer to a lower intermediate frequency (if). The FFO's are connected to the SIS mixer via centerfed interdigital capacitors. One FFO is well coupled to the SIS mixer by using a 3-step Chebychev microstripline transformer and a fairly large interdigital capacitor, while the second FFO has about 15-20 dB weaker coupling. A strip inductor, rf-terminated by a radial stub, resonates out the SIS junction capacitance at about 340 GHz. Radial stubs were also used as rf chokes for the if-line (4 GHz). The FFO's and the SIS element are made of Nb/Nb-oxide/PbBi tunnel junctions. The receiver circuit was optimized by careful CAD modeling (HP Microwave Design System).>

IEEE Transactions on Microwave Theory and Techniques•Apr 1, 1994•8 citations

Linewidth Measurements of Flux-Flow Josephson Oscillators using a CAD Designed Integrated Sub-MM Wave Receiver

Y. M. Zhang, Dag Winkler, T. Claeson

By using a superconducting integrated sub-mm wave receiver, the linewidth of a flux-flow type Josephson oscillator (FFO) was measured to be less than 2.1 MHz in the band 280-330 GHz. The output power coupled to a 10 i2 microstripline was about 0.5 jiW, and could be adjusted by changing the current bias of the oscillator junction. The integrated receiver consists of two identical Josephson flux-flow oscillators and an SIS (superconductor-insulator-superconductor) mixer. We can determine the composite linewidth of the oscillators by mixing them down to an intermediate frequency in the 515 mixer. The FPOs are connected to the SIS mixer via centerfed interdigital capacitors. One FFO is well coupled to the SIS mixer by using a 3-step Chebychev rnicrostripline transformer and a fairly large interdigital capacitor, while the second H0 has about 15 20 dB weaker coupling. A strip inductor, rf-terminated by a radial stub resonates out the SIS junction capacitance at about 340 GHz. Radial stubs were also used as RF chokes for the if-line (4 GHz). The FFOs and the SIS element are made of Nb/Nb-oxide/PbBi tunnel junctions. The circuit was optimized by careful CAD modeling (HP Microwave Design System). Normal conductors were used with the resistivity set to zero. Microstripline widths and lengths were recalculated for the superconducting case with the London penetration depths of the electrodes (Nb and PbBi) taken into account. After adjusting the area of the SIS element and the length of the tuning strip inductor, a good response was observed from 280 to 330 GHz, with the LC resonance at 340 GHz. The power was high enough to pump the SIS mixer.

Softwaretechnik-Trends•Apr 1, 1993•1 citation

Linewidth measurements of Josephson flux-flow oscillators in the band 280–330 GHz

Y. M. Zhang, Dag Winkler, T. Claeson

An integrated receiver consisting of two Josephson flux-flow oscillators and a superconductor-insulator-superconductor (SIS) mixer has been used to measure the linewidth of the oscillators. The oscillators are coupled to the SIS mixer using two centerfed interdigital capacitors, one of which with a fairly weak (−20 dB) coupling. By biasing the two oscillators (a few microvolt apart) on their velocity matching steps, the two resulting oscillations (280–330 GHz) were mixed in the SIS mixer. The difference frequency was amplified and detected on a spectrum analyzer. The combined linewidth of the two oscillators was 2.1 MHz throughout the band. The calculated available power incident on the SIS mixer was 430 nW at 320 GHz. The rf power from the oscillators, which could be tuned by changing the current bias, is high enough to pump the SIS mixer optimally.

Applied Physics Letters•Jun 14, 1993•94 citations

Dynamics and Applications of Long Josephson Junctions

Yongming Zhang

The first object of this work is to theoretically study the effects of tunnel junction parameters on flux-flow Josephson oscillators (FFOs) by numerical simulation and to experimentally study the rf properties of FFOs by integrating them together with an SIS (superconductor-insulator-superconductor) mixer/detector on a chip. By using a CAD modeled integrated sub-mm wave receiver, the composite linewidth of two FFOs was measured to be less than 2.1 MHz in the band 280-330 GHz. The receiver consists of two identical FFOs and an SIS mixer. The linewidth was determined by mixing the two signals in the SIS mixer and analyzing the intermediate frequency. The output power coupled to a 10 .OMEGA. microstripline was about 0.5 µW, and could be adjusted by changing the current bias of the oscillator. The FFOs are connected to the SIS mixer via interdigital capacitors. The FFOs and the SIS element are made of Nb/NbOx/PbBi junctions by the "reactive ion beam oxidation" technique with the critical current density jc controlled by the oxidation time. Lift-off stencils for defining the junction sizes and the top-electrodes were made by using electron-beam writing on PMMA/Copolymer double layer resist. The jc of a long Josephson junction (LJJ) determines the fluxon motion. For LJJs which had jc > 1 kA/cm2, velocity-matching (VM, where the phase velocity of propagating fluxons equals that of the electromagnetic wave in the LJJ) steps could be tuned linearly from about 0.2 to 1.4 mV by an applied magnetic field. Coupled radiation at around 100 GHz (about 3 nW), 261 GHz (4.6 nW), and 330 GHz (0.43 µW), from flux-flow oscillations, was observed. From the step's steepness, the junction quality factor QJ is determined. QJ is between 4 to 7 in the voltage range of 0.4 to 1 mV. Coupled radiation (> 3 nW) at around 100 GHz corresponding to resonant soliton oscillation in low jc samples (250 to 1000 A/cm2) was detected. Simulations show that, for a uniform bias feed, the height of the VM step .gammam increases almost linearly with the external magnetic field .beta.e and the quasiparticle loss .alpha., but is less dependent on the surface loss .beta.. An approximate expression .gammam = a + .alpha(1+b).beta.e agrees with simulations. The maximum ac output voltage decreases with increasing dampings .alpha. and .beta.. It is important to include the .beta.-term in the mathematical model. The second part of this work is devoted to rf properties of long YBa2Cu3O7-.delta. (YBCO) grain boundary junctions made on 0- 32 °. [001]-tilt YSZ bicrystals. Josephson flux-flow resonances and Fiske resonances were observed. The first resonances could be tuned from about 0.5 to 2.0 mV in a 30 µm long junction at 16 K, and we determined the ratio between barrier thickness and relative dielectric constant td/.epsilon.r=2.9 Å and the loss .alpha.= 1.3 at 16 K. Simulations support the experimental observation that Josephson vortices can propagate unidirectionally in an overdamped, homogeneous junction up to .alpha.Ã? 2. From the Fiske resonances at 256-638 GHz, their Q-values, and the Steward-McCumber parameter, we find td/.epsilon.r=4 Å, the London penetration depth .gamma.L=145±5 nm and the surface resistance RS ~20 m.OMEGA. at 280 GHz. We conclude that the boundary is dielectric and the YBCO grains are well superconducting within 5-20 nm from the boundary. The dielectric between the grains could be part of a tunnel barrier and/or a matrix for filamentary conduction. Josephson flux-flow transitors based on long bicrystal junctions were made with an Au loop used as the control line. The line modulated the critical current Ic. Current gain larger than unity was obtained below 70 K. The gain increased with the junction length and varied roughly like the square root Ic when adjusting the temperature. A transresistance larger than 5 .OMEGA. was obtained at 15 K. Better performance is expected from junctions with high current densities.

•Jan 1, 1993•7 citations

Superconducting millimeter wave oscillators and SIS mixers integrated on a chip

V. P. Koshelets, А. В. Щукин, S. V. Shitov +1 more

All-refractory material superconducting millimeter-wave oscillators have been designed and investigated experimentally with different superconductor-insulator-superconductor (SIS) mixers integrated on the same chip. Tested structures include a flux-flow oscillator (FFO) based on a long Josephson junction, a coupling section, and an SIS detector with tuned out junction capacitance. Coupling sections were designed as multistep microstrip quarter-wave impedance transformers. All junctions have been fabricated on the basis of a high-quality trilayer Nb-AlO/sub x/-Nb process. Microwave oscillations in the frequency range 75-500 GHz have been detected experimentally. The level of delivered power was estimated from the pumped I-V curve of the strongly coupled single junction detector. Coupled power levels higher than 0.1 mu W at 256 GHz were achieved. A spectral linewidth of the FFO of less than 1 MHz has been estimated experimentally. The first attempt to create an integrated receiver based on an FFO and an SIS array mixer integrated on the same chip was made in the 2-mm wavelength band.>

IEEE Transactions on Applied Superconductivity•Mar 1, 1993•67 citations

Linewidth of frequency locked flux flow oscillators for sub-mm wave receivers

V. P. Koshelets, S. V. Shitov, А. В. Щукин +2 more

Presently Flux Flow Oscillators (FFOs) are being developed for integration with superconductor-insulator-superconductor (SIS) mixers intended for submillimeter wave integrated receivers. Here we report on a detailed study of the dc and microwave properties of Nb-AlO/sub x/-Nb FFOs. A model based on the Josephson self-pumping effect is proposed for explanation of the experimentally measured dc I-V curves (IVC). Extensive measurements of the spectral linewidth of the radiation emitted from a FFO have been performed up to 600 GHz using a new reliable technique based on harmonic mixing. The results are compared to recent theoretical predictions.

IEEE Transactions on Applied Superconductivity•Jun 1, 1997•8 citations
By using an integrated superconducting sub-mm wave receiver, the composite linewidth of two Josephson flux- flow oscillators (FFO) was measured to be less than 2.1 MHz in the band 280-330 GHz. The output power coupled to a 10 R microstripline was about 0.5 pW, and could be adjusted by changing the current bias of the oscillator junction. The receiver consists of two identical FFO's and an SIS (superconductor- insulator-superconductor) mixer. The composite linewidth of the oscillators was determined by mixing the two signals in the SIS mixer to a lower intermediate frequency (if). The FFO's are connected to the SIS mixer via centerfed interdigital capacitors. One FFO is well coupled to the SIS mixer by using a 3-step Chebychev microstriplie transformer and a fairly large inter- digital capacitor, while the second FFO has about 15-20 dB weaker coupling. A strip inductor, rf-terminated by a radial stub, resonates out the SIS junction capacitance at about 340 GHz. Radial stubs were also used as rf chokes for the if-line (4 GHz). The FFO's and the SIS element are made of NbNb-oxidelPbBi tunnel junctions. The receiver circuit was optimized by careful CAD modeling (HP Microwave Design System). and gives rise to the emission of a pulse of electromagnetic energy when it hits the ends of the junction. If the arrival of solitons at one end of the junction is periodic, rf radiation is emitted. The propagation mode of the fluxon in a LJJ depends on the junction quality factor QJ, which is related to the junction losses as (3) QJ = ((wo/uJ)2P -t a)-'.
By using an integrated superconducting sub-mm wave receiver, the composite linewidth of two Josephson flux-flow oscillators (FFO) was measured to be less than 2.1 MHz in the band 280-330 GHz. The output power coupled to a 10 /spl Omega/ microstripline was about 0.5 /spl mu/W, and could be adjusted by changing the current bias of the oscillator junction. The receiver consists of two identical FFO's and an SIS (superconductor-insulator-superconductor) mixer. The composite linewidth of the oscillators was determined by mixing the two signals in the SIS mixer to a lower intermediate frequency (if). The FFO's are connected to the SIS mixer via centerfed interdigital capacitors. One FFO is well coupled to the SIS mixer by using a 3-step Chebychev microstripline transformer and a fairly large interdigital capacitor, while the second FFO has about 15-20 dB weaker coupling. A strip inductor, rf-terminated by a radial stub, resonates out the SIS junction capacitance at about 340 GHz. Radial stubs were also used as rf chokes for the if-line (4 GHz). The FFO's and the SIS element are made of Nb/Nb-oxide/PbBi tunnel junctions. The receiver circuit was optimized by careful CAD modeling (HP Microwave Design System).>
By using a superconducting integrated sub-mm wave receiver, the linewidth of a flux-flow type Josephson oscillator (FFO) was measured to be less than 2.1 MHz in the band 280-330 GHz. The output power coupled to a 10 i2 microstripline was about 0.5 jiW, and could be adjusted by changing the current bias of the oscillator junction. The integrated receiver consists of two identical Josephson flux-flow oscillators and an SIS (superconductor-insulator-superconductor) mixer. We can determine the composite linewidth of the oscillators by mixing them down to an intermediate frequency in the 515 mixer. The FPOs are connected to the SIS mixer via centerfed interdigital capacitors. One FFO is well coupled to the SIS mixer by using a 3-step Chebychev rnicrostripline transformer and a fairly large interdigital capacitor, while the second H0 has about 15 20 dB weaker coupling. A strip inductor, rf-terminated by a radial stub resonates out the SIS junction capacitance at about 340 GHz. Radial stubs were also used as RF chokes for the if-line (4 GHz). The FFOs and the SIS element are made of Nb/Nb-oxide/PbBi tunnel junctions. The circuit was optimized by careful CAD modeling (HP Microwave Design System). Normal conductors were used with the resistivity set to zero. Microstripline widths and lengths were recalculated for the superconducting case with the London penetration depths of the electrodes (Nb and PbBi) taken into account. After adjusting the area of the SIS element and the length of the tuning strip inductor, a good response was observed from 280 to 330 GHz, with the LC resonance at 340 GHz. The power was high enough to pump the SIS mixer.
An integrated receiver consisting of two Josephson flux-flow oscillators and a superconductor-insulator-superconductor (SIS) mixer has been used to measure the linewidth of the oscillators. The oscillators are coupled to the SIS mixer using two centerfed interdigital capacitors, one of which with a fairly weak (−20 dB) coupling. By biasing the two oscillators (a few microvolt apart) on their velocity matching steps, the two resulting oscillations (280–330 GHz) were mixed in the SIS mixer. The difference frequency was amplified and detected on a spectrum analyzer. The combined linewidth of the two oscillators was 2.1 MHz throughout the band. The calculated available power incident on the SIS mixer was 430 nW at 320 GHz. The rf power from the oscillators, which could be tuned by changing the current bias, is high enough to pump the SIS mixer optimally.
The first object of this work is to theoretically study the effects of tunnel junction parameters on flux-flow Josephson oscillators (FFOs) by numerical simulation and to experimentally study the rf properties of FFOs by integrating them together with an SIS (superconductor-insulator-superconductor) mixer/detector on a chip. By using a CAD modeled integrated sub-mm wave receiver, the composite linewidth of two FFOs was measured to be less than 2.1 MHz in the band 280-330 GHz. The receiver consists of two identical FFOs and an SIS mixer. The linewidth was determined by mixing the two signals in the SIS mixer and analyzing the intermediate frequency. The output power coupled to a 10 .OMEGA. microstripline was about 0.5 µW, and could be adjusted by changing the current bias of the oscillator. The FFOs are connected to the SIS mixer via interdigital capacitors. The FFOs and the SIS element are made of Nb/NbOx/PbBi junctions by the "reactive ion beam oxidation" technique with the critical current density jc controlled by the oxidation time. Lift-off stencils for defining the junction sizes and the top-electrodes were made by using electron-beam writing on PMMA/Copolymer double layer resist. The jc of a long Josephson junction (LJJ) determines the fluxon motion. For LJJs which had jc > 1 kA/cm2, velocity-matching (VM, where the phase velocity of propagating fluxons equals that of the electromagnetic wave in the LJJ) steps could be tuned linearly from about 0.2 to 1.4 mV by an applied magnetic field. Coupled radiation at around 100 GHz (about 3 nW), 261 GHz (4.6 nW), and 330 GHz (0.43 µW), from flux-flow oscillations, was observed. From the step's steepness, the junction quality factor QJ is determined. QJ is between 4 to 7 in the voltage range of 0.4 to 1 mV. Coupled radiation (> 3 nW) at around 100 GHz corresponding to resonant soliton oscillation in low jc samples (250 to 1000 A/cm2) was detected. Simulations show that, for a uniform bias feed, the height of the VM step .gammam increases almost linearly with the external magnetic field .beta.e and the quasiparticle loss .alpha., but is less dependent on the surface loss .beta.. An approximate expression .gammam = a + .alpha(1+b).beta.e agrees with simulations. The maximum ac output voltage decreases with increasing dampings .alpha. and .beta.. It is important to include the .beta.-term in the mathematical model. The second part of this work is devoted to rf properties of long YBa2Cu3O7-.delta. (YBCO) grain boundary junctions made on 0- 32 °. [001]-tilt YSZ bicrystals. Josephson flux-flow resonances and Fiske resonances were observed. The first resonances could be tuned from about 0.5 to 2.0 mV in a 30 µm long junction at 16 K, and we determined the ratio between barrier thickness and relative dielectric constant td/.epsilon.r=2.9 Å and the loss .alpha.= 1.3 at 16 K. Simulations support the experimental observation that Josephson vortices can propagate unidirectionally in an overdamped, homogeneous junction up to .alpha.Ã? 2. From the Fiske resonances at 256-638 GHz, their Q-values, and the Steward-McCumber parameter, we find td/.epsilon.r=4 Å, the London penetration depth .gamma.L=145±5 nm and the surface resistance RS ~20 m.OMEGA. at 280 GHz. We conclude that the boundary is dielectric and the YBCO grains are well superconducting within 5-20 nm from the boundary. The dielectric between the grains could be part of a tunnel barrier and/or a matrix for filamentary conduction. Josephson flux-flow transitors based on long bicrystal junctions were made with an Au loop used as the control line. The line modulated the critical current Ic. Current gain larger than unity was obtained below 70 K. The gain increased with the junction length and varied roughly like the square root Ic when adjusting the temperature. A transresistance larger than 5 .OMEGA. was obtained at 15 K. Better performance is expected from junctions with high current densities.
All-refractory material superconducting millimeter-wave oscillators have been designed and investigated experimentally with different superconductor-insulator-superconductor (SIS) mixers integrated on the same chip. Tested structures include a flux-flow oscillator (FFO) based on a long Josephson junction, a coupling section, and an SIS detector with tuned out junction capacitance. Coupling sections were designed as multistep microstrip quarter-wave impedance transformers. All junctions have been fabricated on the basis of a high-quality trilayer Nb-AlO/sub x/-Nb process. Microwave oscillations in the frequency range 75-500 GHz have been detected experimentally. The level of delivered power was estimated from the pumped I-V curve of the strongly coupled single junction detector. Coupled power levels higher than 0.1 mu W at 256 GHz were achieved. A spectral linewidth of the FFO of less than 1 MHz has been estimated experimentally. The first attempt to create an integrated receiver based on an FFO and an SIS array mixer integrated on the same chip was made in the 2-mm wavelength band.>
Presently Flux Flow Oscillators (FFOs) are being developed for integration with superconductor-insulator-superconductor (SIS) mixers intended for submillimeter wave integrated receivers. Here we report on a detailed study of the dc and microwave properties of Nb-AlO/sub x/-Nb FFOs. A model based on the Josephson self-pumping effect is proposed for explanation of the experimentally measured dc I-V curves (IVC). Extensive measurements of the spectral linewidth of the radiation emitted from a FFO have been performed up to 600 GHz using a new reliable technique based on harmonic mixing. The results are compared to recent theoretical predictions.