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Far infrared detection with Josephson junctions. Final report

C. K. So, William O. Hamilton

Published Dec 1, 1976• 0 citations
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Abstract

The response of Josephson junctions to microwave and far infrared radiation was studied. Junctions are formed by pressing a Nb or Nb-Ti pointed wire onto a Nb thin film which in turn is pressed against the open end of a waveguide. Electromagnetic radiation is applied through the back of the film so that only the wave magnetic field is coupled to the junctions. The change of the dc Josephson current is monitored at different levels of microwave power over a frequency range from 22GHz to 105GHz. The dependence of the responsivity of these current on film thickness over a range from 50 A to 500 A was studied. The observed responsivity agrees very well with that predicted by theory. Higher responsivity is observed for thinner films and lower microwave frequencies.

Related papers

Untuned Josephson detectors of microwave and millimeter-wave radiation

C. K. So, William O. Hamilton

The intrinsic response of Josephson junctions to microwave and far-infrared radiation is studied. Junctions are formed by pressing a Nb or Nb-Ti pointed wire onto a Nb thin film which in turn is pressed against the open end of a waveguide. Electromagnetic radiation is applied through the back of the film so that only the wave magnetic field is coupled to the junction. The change of the dc Josephson current is monitored at different levels of microwave power over a frequency range from 22 to 105 GHz. The dependence of the responsivity of these currents on film thickness over a range from 50 to 500 Å is studied. The observed responsivity agrees very well with that predicted by theory. Higher responsivity is observed for thinner films and lower microwave frequencies. The observed responsivity of a 50-Å film junction at 22 GHz is (6±3) ×10−2 V/W. To facilitate comparison of our results with other experiments, a more conventional coupling configuration in which the wave electric field rather than the wave magnetic field is coupled to the junction is studied. The results are comparable with other experiments with the responsivity in the E field coupling case 106 times larger than in the B field coupling configuration. We demonstrate that for successful use of simple Josephson junction detectors in the microwave and millimeter region it seems crucial to impedance match the junctions to the radiation source, probably by making them a part of a resonant structure.

Journal of Applied Physics•May 1, 1977•1 citation

Interactions in small systems of coupled Josephson junctions at microwave frequencies

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A major factor in the practical utilization of any Josephson device for microwave and higher frequency applications (such as the generation and detection of electromagnetic radiation) is the success with which the junction device can be coupled to an external transmission line. As part of an experimental investigation of the electrodynamics of small arrays of Josephson tunnel junctions, the properties of the coherent radiation emitted both by individual junctions and by coupled junction systems have been studied at frequencies between 2 and 12 GHz. Near 9 GHz, more than 10-9 W of coherent radiation has been detected from a single Pb-Pb oxide-Pb junction coupled via waveguide. The development of thin film devices in which the tunnel junctions form part of a microstrip line have made it feasible to observe directly (in a single device) the radiation emitted both at the fundamental geometrical frequency and at the low order harmonics. The observed temperature dependence of the junction cavity Q indicate the low temperature losses are primarily due to cavity loading of the external transmission line.

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Fabrication of Niobium Nanobridge Josephson Junctions

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To realize antenna-coupled Josephson detectors for microwave and millimeter-wave radiation, planar-type Nb nanobridge Josephson junctions were fabricated. Nb thin films whose thickness, the root mean square roughness and the critical temperature were 20.0 nm, 0.109 nm and 8.4 K, respectively were deposited using a DC magnetron sputtering at a substrate temperature of 700°C. Nanobridges were obtained from the film using 80-kV electron beam lithography and reactive ion-beam etching in CF 4 (90%) + O2 (10%) gases. The minimum bridge area was 65 nm wide and 60 nm long. For the nanobridge whose width and length were less than 110 nm, an I-V characteristic showed resistively-shunted-junction behaviour near the critical temperature. Moreover, Shapiro steps were observed in the nanobridge with microwave irradiation at a frequency of 6 – 30 GHz. The Nb nanobridges can be used as detectors in the antenna-coupled devices.

Journal of Physics Conference Series•May 12, 2014•1 citation

I-V Characteristics of NbN-NbN Josephson Point Contacts

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Current-voltage characteristics of NbN-NbN Josephson point contacts have been examined. The point contacts were formed by NbN thin films deposited on Nb or W whiskers and Nb posts. The current-voltage characteristics of those contacts were investigated with and without irradiation of microwaves and far-infrared light. High values of the I c R n product and the energy gap structure were observed, which corresponded to the high-energy gap of NbN. Shapiro steps for far-infrared light up to 170 µm were observed and the possibility of replacing Nb Josephson point contacts with NbN ones is indicated.

Japanese Journal of Applied Physics•Apr 1, 1988•0 citations

Microwave detector response of the Josephson junction arrays

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Microwave detector response ( eta ) for three types of superconducting structures-single edge-type Josephson junctions, arrays of series-connected junctions, and arrays of RF-series and DC parallel-connected junctions-were investigated in the frequency range 35-120 GHz. Experimental dependence of eta versus biasing voltage is mainly determined by the interaction of junctions in the array. The selective response, which means a narrow linewidth of Josephson radiation, is observed for the third type of superconducting structure in a small magnetic field changing the phase shift between closely-spaced junctions. These arrays have the advantage in coupling with the external microwave system.

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Far Infrared Response of Point-Contact Josephson Junctions

C. C. Grimes, P. L. Richards, S. M. Shapiro

We have measured spectral-response curves of superconducting point contacts suggesting the existence of frequency-dependent Josephson current amplitudes peaking in the vicinity of the energy gap. These point-contact Josephson junctions respond sensitively and with high speed to millimeter and submillimeter radiation. Radiation emitted to free space by one such junction was detected by another junction.

Physical Review Letters•Aug 22, 1966•60 citations
The response of Josephson junctions to microwave and far infrared radiation was studied. Junctions are formed by pressing a Nb or Nb-Ti pointed wire onto a Nb thin film which in turn is pressed against the open end of a waveguide. Electromagnetic radiation is applied through the back of the film so that only the wave magnetic field is coupled to the junctions. The change of the dc Josephson current is monitored at different levels of microwave power over a frequency range from 22GHz to 105GHz. The dependence of the responsivity of these current on film thickness over a range from 50 A to 500 A was studied. The observed responsivity agrees very well with that predicted by theory. Higher responsivity is observed for thinner films and lower microwave frequencies.
The intrinsic response of Josephson junctions to microwave and far-infrared radiation is studied. Junctions are formed by pressing a Nb or Nb-Ti pointed wire onto a Nb thin film which in turn is pressed against the open end of a waveguide. Electromagnetic radiation is applied through the back of the film so that only the wave magnetic field is coupled to the junction. The change of the dc Josephson current is monitored at different levels of microwave power over a frequency range from 22 to 105 GHz. The dependence of the responsivity of these currents on film thickness over a range from 50 to 500 Å is studied. The observed responsivity agrees very well with that predicted by theory. Higher responsivity is observed for thinner films and lower microwave frequencies. The observed responsivity of a 50-Å film junction at 22 GHz is (6±3) ×10−2 V/W. To facilitate comparison of our results with other experiments, a more conventional coupling configuration in which the wave electric field rather than the wave magnetic field is coupled to the junction is studied. The results are comparable with other experiments with the responsivity in the E field coupling case 106 times larger than in the B field coupling configuration. We demonstrate that for successful use of simple Josephson junction detectors in the microwave and millimeter region it seems crucial to impedance match the junctions to the radiation source, probably by making them a part of a resonant structure.
A major factor in the practical utilization of any Josephson device for microwave and higher frequency applications (such as the generation and detection of electromagnetic radiation) is the success with which the junction device can be coupled to an external transmission line. As part of an experimental investigation of the electrodynamics of small arrays of Josephson tunnel junctions, the properties of the coherent radiation emitted both by individual junctions and by coupled junction systems have been studied at frequencies between 2 and 12 GHz. Near 9 GHz, more than 10-9 W of coherent radiation has been detected from a single Pb-Pb oxide-Pb junction coupled via waveguide. The development of thin film devices in which the tunnel junctions form part of a microstrip line have made it feasible to observe directly (in a single device) the radiation emitted both at the fundamental geometrical frequency and at the low order harmonics. The observed temperature dependence of the junction cavity Q indicate the low temperature losses are primarily due to cavity loading of the external transmission line.
To realize antenna-coupled Josephson detectors for microwave and millimeter-wave radiation, planar-type Nb nanobridge Josephson junctions were fabricated. Nb thin films whose thickness, the root mean square roughness and the critical temperature were 20.0 nm, 0.109 nm and 8.4 K, respectively were deposited using a DC magnetron sputtering at a substrate temperature of 700°C. Nanobridges were obtained from the film using 80-kV electron beam lithography and reactive ion-beam etching in CF 4 (90%) + O2 (10%) gases. The minimum bridge area was 65 nm wide and 60 nm long. For the nanobridge whose width and length were less than 110 nm, an I-V characteristic showed resistively-shunted-junction behaviour near the critical temperature. Moreover, Shapiro steps were observed in the nanobridge with microwave irradiation at a frequency of 6 – 30 GHz. The Nb nanobridges can be used as detectors in the antenna-coupled devices.
Current-voltage characteristics of NbN-NbN Josephson point contacts have been examined. The point contacts were formed by NbN thin films deposited on Nb or W whiskers and Nb posts. The current-voltage characteristics of those contacts were investigated with and without irradiation of microwaves and far-infrared light. High values of the I c R n product and the energy gap structure were observed, which corresponded to the high-energy gap of NbN. Shapiro steps for far-infrared light up to 170 µm were observed and the possibility of replacing Nb Josephson point contacts with NbN ones is indicated.
Microwave detector response ( eta ) for three types of superconducting structures-single edge-type Josephson junctions, arrays of series-connected junctions, and arrays of RF-series and DC parallel-connected junctions-were investigated in the frequency range 35-120 GHz. Experimental dependence of eta versus biasing voltage is mainly determined by the interaction of junctions in the array. The selective response, which means a narrow linewidth of Josephson radiation, is observed for the third type of superconducting structure in a small magnetic field changing the phase shift between closely-spaced junctions. These arrays have the advantage in coupling with the external microwave system.