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IEEE Transactions on Applied Superconductivity

Response properties at 2.525 terahertz using high-T/sub c/ Josephson junctions on silicon bicrystal substrates

J. Chen, E. Kobayashi, Koji Nakajima, Takashi Yamashita, S. Linzen, F. Schmidl, P. Seidel

Published Jun 1, 1999• 8 citations
Publisher

Abstract

Using high-T/sub c/ grain boundary Josephson junctions (GBJJs) made of YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// deposited across silicon bicrystal boundary, we successfully demonstrated direct response at frequency as high as 2.525 THz and the operation temperature up to 70 K. Also, the effects of response on polarization of electromagnetic waves and the harmonic mixing properties are investigated. It is found that there is no polarization dependence of the response for our high-quality GBJJs. This result is favorable to the spectroscopy application. At frequency as high as 2.525 THz, the high-order harmonic mixing at zero and finite bias voltage has been demonstrated.

DOI
10.1109/77.784020

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Using high-T/sub c/ grain boundary Josephson junctions (GBJJs) made of YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// deposited across silicon bicrystal boundary, we successfully demonstrated direct response at frequency as high as 2.525 THz and the operation temperature up to 70 K. Also, the effects of response on polarization of electromagnetic waves and the harmonic mixing properties are investigated. It is found that there is no polarization dependence of the response for our high-quality GBJJs. This result is favorable to the spectroscopy application. At frequency as high as 2.525 THz, the high-order harmonic mixing at zero and finite bias voltage has been demonstrated.
The high-frequency response of bicrystal YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// Josephson junctions for far infrared laser irradiation is presented. The junctions on silicon and MgO substrates exhibit a remarkable first order Shapiro step for the methanol line at 1.76 THz. dV/dI measurements reveal several steps corresponding to the methanol lines at 1.48, 1.76 and 2.53 THz. The line width of Josephson oscillation at these frequencies is estimated from the width of the Shapiro steps. It is suggested that the excess shot noise broadens the line width.
Abstract Josephson devices have demonstrated the capability to work as harmonic mixers at terahertz frequencies. Low temperature devices, in particular Nb–Nb point contacts have proven particularly successful. However, practical applications of these devices have been limited by the need of utilizing liquid helium. To overcome this limitation we have investigated the use of high- T c devices. In this paper, we report mixings up to the 154th harmonic at zero-bias in a series of YBa 2 Cu 3 O 7−δ (YBCO) grain boundary Josephson junctions. We have integrated a meander series of three bicrystal YBCO Josephson junctions with a log-periodic antenna. When properly operated, this configuration allows to reach a harmonic number much higher than what possible with a single junction. This shows that the mixing performance benefits from the synchronous operation which also results in an improvement of dynamic range. We believe that the integration of a higher number of phase-locked junctions may further improve the mixer’s performance. Future studies should investigate the effect of higher number of junctions on the mixer performances, as well as the effect of the meander length.
Using high-Tc Josephson junctions made of YBa2Cu3O7−δ deposited across MgO bicrystal boundary, at terahertz (THz) frequency band, we demonstrated both fundamental and harmonic mixing. Radiation from a far-infrared laser was coupled to the junction, which was integrated with a planar bow-tie antenna, via an extended hyperhemispherical silicon lens. Fundamental mixing manifested itself in the junction’s dc current–voltage (I–V) curve as a third Shapiro step in addition to those two induced by the THz laser lines from a slightly misaligned resonator. In harmonic mixing between a THz laser line and a microwave local oscillator, the highest harmonic number we could get was 490 with a signal-to-noise ratio of 9 dB at the intermediate frequency.
Using YBa 2 Cu 3 O 7 /MgO bicrystal Josephson junctions operating between 6–77 K, we have studied their responses to monochromatic electromagnetic radiation from 50 GHz to 4.25 THz. We have obtained direct detections for radiation at 70 K from 50 GHz to 760 GHz and at 40 K from 300 GHz to 3.1 THz. This indicates that fast detectors can be realized to cover the 10:1 frequency band at one operation temperature, and about 100:1 can be covered by operating only one junction at two different temperatures. Both the highest response frequency and the maximum value of the normalized response are shown to be proportional to the I C R N product of the junction, where I C and R N are the critical current and the normal resistance of the junction, respectively.
We have investigated YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// superconductor-normal-superconductor Josephson junctions as mixers of 30 THz radiation. We have directly observed (2nd order) difference frequencies from 10 MHz to 12.8 GHz between two CO/sub 2/ laser lines. Applying a third microwave signal to the junction, we have observed CO/sub 2/ laser difference frequencies up to 27 GHz. The d.c. bias dependence of the difference frequency signal, as well as other evidence, suggests two distinct mixing mechanisms: hot-electron mixing in the junction banks at high d.c. biases, and bolometric Josephson mixing at low d.c. biases. The latter is the first observation of Josephson mixing at CO/sub 2/ laser frequencies in high-T/sub c/ junctions. The Josephson mixing has generated observable mixing products up to 6th order.>
Millimeter-wave detection in the heterodyne mixing mode has been carried out using the high-T/sub c/ superconducting GBJJ (grain boundary Josephson junction). The GBJJ was fabricated from high T/sub c/ superconducting Y-Ba-Cu-O films, prepared on YSZ and SrTiO/sub 3/ substrates using an RF sputtering technique. The junction was patterned by chemical wet etching with phosphoric acid solution. The authors carried out experiments in the heterodyne mixing mode for a signal of 35 GHz with local oscillation at 34.97 GHz. The detected IF (intermediate frequency) output power was obtained at a bias voltage lying midway between the zeroth and first Shapiro steps. A mixer conversion efficiency of -15 dB was obtained with a dynamic range of about 20 dB at 35 GHz. This result strongly implies that high-T/sub c/ superconducting GBJJ works well as a detector at millimeter-wave frequencies.>