Fabrication of superconducting direct detectors in submillimeter-wave bands (original) (raw)
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Future optical detectors based on Al superconducting tunnel junctions
SPIE Proceedings, 2004
Superconducting tunnel junctions are being developed for application as photon detectors in astronomy. We present the latest results on the development of very high quality, very low critical temperature junctions, fabricated out of pure Al electrodes. The detectors are operated at 50 mK in an adiabatic demagnetisation refrigerator. The contacts to the top and base electrodes of these junctions are fabricated either out of Nb or Ta, which has strong implications on the loss time of the quasiparticles. The Nb contacted junctions show quasiparticle loss times varying between 5 and 80 µsec, depending on the device size. The bias range of the Nb-contacted junctions is limited to the range 0-100 µV, because of the set-in of strong non-equilibrium quasiparticle multiplication currents at higher bias voltages. The Ta-contacted junctions, on the other hand, show quasiparticle loss times in excess of 200 µsec. These long loss times lead to very strong quasiparticle multiplication, which prevents the stable biasing of the junctions even at very low bias voltages. Junction fabrication and characterisation are described, as well as the response of the detectors to monochromatic light with wavelengths varying from 250 to 1000 nm. The energy resolution of the detectors is discussed.
Superconducting tunnel junction x-ray detectors with ultra-low subgap current
2007 2nd International Workshop on Advances in Sensors and Interface, 2007
Superconducting tunnel junctions are promising as radiation detectors because of their larger energy resolution with respect to conventional Si-based detectors. We have developed a fabrication process for Nb-based STJ devices which allows to fabricate junctions with leakage currents well below 50 pA at 300 mK, a factor of 10 −6 less than the leakage current at 4.2 K. The junctions are diamond-shaped with areas between 20 × 20 and 100 × 100 µm 2 . We report the details of the fabrication process, together with an analysis of the structure of films by AFM, SEM and x-ray spectroscopy. We show the measured I − V curves at 300 mK, together with preliminary results on x-ray measurements at 300 mK with a 5 mC 55 Fe source.
Optical and near-infrared photon counting detector using superconducting tunnel junctions
Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment - NUCL INSTRUM METH PHYS RES A, 2000
The properties of Superconducting Tunnel Junctions (STJ) make them very suitable for low light level astronomical observations. The applications are of great importance for the future in the field of high-angular resolution astronomy where STJ surpass all other detectors. STJ detectors will be used to improve the sensitivity of such a system to be implemented on ground-based interferometer like the GI2T in France or IOTA in USA. All this instrumentation is developed in the framework of the Very Large Telescopes Interferometer built by the European Southern Observatory in Chile.We have developed a modified version of the “SNEP” fabrication process for making Nb/Al-AlOx-Al/Nb and Ta/Al-AlOx-Al/Ta/Nb STJs, showing very low sub-gap leakage current at 0.2K by using double thin aluminium trapping layers and the higher energy gap of the Ta or Nb absorber grown epitaxially on the R-plane sapphire substrate.The key points of the junction fabrication process have been studied: experimental pa...
Future optical detectors based on Al superconducting tunnel junctions
Optical and Infrared Detectors for Astronomy, 2004
Superconducting tunnel junctions are being developed for application as photon detectors in astronomy. We present the latest results on the development of very high quality, very low critical temperature junctions, fabricated out of pure Al electrodes. The detectors are operated at 50 mK in an adiabatic demagnetisation refrigerator. The contacts to the top and base electrodes of these junctions are fabricated either out of Nb or Ta, which has strong implications on the loss time of the quasiparticles. The Nb contacted junctions show quasiparticle loss times varying between 5 and 80 µsec, depending on the device size. The bias range of the Nb-contacted junctions is limited to the range 0-100 µV, because of the set-in of strong non-equilibrium quasiparticle multiplication currents at higher bias voltages. The Ta-contacted junctions, on the other hand, show quasiparticle loss times in excess of 200 µsec. These long loss times lead to very strong quasiparticle multiplication, which prevents the stable biasing of the junctions even at very low bias voltages. Junction fabrication and characterisation are described, as well as the response of the detectors to monochromatic light with wavelengths varying from 250 to 1000 nm. The energy resolution of the detectors is discussed.
Characterization of an STJ-Based Direct Detector of Submillimeter Waves
IEEE Transactions on Appiled Superconductivity, 2005
We have developed submillimeter-wave direct detectors employing niobium-based superconducting tunnel junctions (STJs), with broadband spectral response, high sensitivity and imaging capability. Spectral response peaked at 650 GHz with a fractional bandwidth of 14 percent, which fits one of the important atmospheric windows for an astronomical project. We also confirmed the linearity of the detector response in the dynamic range greater than 10 6 . The measured coupling efficiency was about 0.2, which was lower than the expected value of 0.5. The measured noise current of the detector was 10 fA Hz, which agreed with the shot noise from the residual leakage current of 100 pA at 0.3 K. Resultant noise equivalent power (NEP) is 1 6 10 16 W Hz, that is less than the background photon fluctuation limit for ground-based submillimeter-wave observations.
Springer Proceedings in Physics, 2018
We present the status of the development of Superconducting Tunnel Junction (STJ) detector with the cryogenic preamplifier as far-infrared single photon detector for the COsmic BAckground Neutrino Decay search (COBAND) experiment. The photon energy spectrum from the radiative decay of the cosmic background neutrino is expected to have a sharp cutoff at high energy end in a far-infrared region ranging from 15 meV to 30 meV. The detector is required to measure an individual photon energy with a sufficient energy resolution less than 2% for identifying the cutoff structure, and to be designed for a rocket or satellite experiment. We develop an array of Nb/Al-STJ pixels which can detect a single far-infrared photon delivered by a diffractive grating according to its wavelength. To achieve high signal-to-noise ratio of the STJ, we use a preamplifier made with the Silicon-on-Insulator (SOI) technique that can be operated around 0.3K. We have developed the Nb/Al-STJ with the SOI cryogenic preamplifier and have tested the detector performance around 0.3K.
Anomaly in Fabrication Processes for Large-Scale Array Detectors of Superconducting Tunnel Junctions
Journal of Low Temperature Physics, 2008
The STJ array detectors with an effective detection area of 4 mm 2 , which consist of 100 Nb/Al-AlOx/Al/Nb junctions with a size of 200 × 200 µm, have been fabricated. In order to improve the reproducibility of the STJ array fabrication, we investigated a correlation between the junction surface structures and the leakage currents. It has been found that the junctions near the fringe of the array detectors have a step of about 5 nm at the middle of the array detector, of which leakage currents are considerably larger than 1 µA. The step structure was formed after the etching of the bottom Nb layer for complete separation of Nb/Al/AlOx/Al/Nb/Si. In case of the sputtered Nb/Al/Nb/Si multilayers without 1 nm-thick tunneling barrier, no stepped surface was observed even after the bottom Nb layer etching. Therefore, it is apparent that the 5 nm step structure is a cause of the large leakage currents. We solved the step-fringe problem by a kind of extra patterning along the fringe of the array or lift-off patterning of the Nb/Al multilayers. It is concluded that the number of the junctions with the step structure depends on a slight difference in film deposition or etching conditions.
Bandwidth and noise of submillimeter wave cuprate bicrystal Josephson junction detectors
IEEE Transactions on Applied Superconductivity, 2005
Detectors made from superconducting cuprate YBa 2 Cu 3 Ox bicrystal Josephson junctions (BJJs) on sapphire and NdGaO 3 substrates have been fabricated and characterized in the frequency band 200-900 GHz. Junctions on sapphire substrates had a normal state resistance 15 60 , and product up to 2.5 mV at = 4 2 K. Junctions on NdGaO 3 substrates had lower = 1 5 and = 0 4-0.9 mV at = 77 K. Three types of detecting devices have been investigated in both the broadband and the frequency-selective detection modes. One type was patterned with log-periodic antenna, and two others with Pt-metal double-slot antenna designed for a central frequency = 300 GHz and = 400 GHz, respectively. Measurements at = 320 GHz of the reception bandwidth 1f for a device with double-slot antenna gave a quality factor = 1 10. A low-noise cooled 1-2 GHz bandwidth amplifier enables a better sensitivity in the self-pumping frequency mixing mode, avoiding the 1/f noise. The dependence of the spectral density of noise on voltage was compared to the data for the Josephson emission linewidth obtained by the selective detector response method. Also discussed are measurements at 500 GHz of the NEP values carried out at different experimental conditions. Index Terms-High-temperature cuprate superconductors, Josephson junction, submillimeter wave devices.
Development of terahertz wave detector using superconducting tunnel junction
Physica C-superconductivity and Its Applications, 2005
We have developed a new terahertz (THz) wave detector using an Nb-based superconducting tunnel junction (STJ). The STJ consists of a Nb/Al/AlO x /Al/Nb structure on a single-crystal LiNbO 3 substrate. Using LiNbO 3 as a substrate, an irradiating THz wave is converted to phonons in LiNbO 3 , which has a relatively high absorption coefficient. The phonons propagating in the substrate reach the Nb base electrode of the STJ and break Cooper pairs. As a result, the THz wave can be detected as tunneling current signals in the STJ. THz waves from a widely tunable THz-wave parametric oscillator (TPO) were irradiated on to the STJ, which acted as a THz wave detector. The STJs were cooled to an operating temperature of 0.4 K using a 3 He cryostat. We have observed STJ signals related to THz wave irradiations. In this paper, fabrication processes and characteristics of THz wave detectors using STJs are also discussed.