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IEEE Transactions on Applied Superconductivity

Noise temperature measurement of YBCO Josephson mixers in millimeter and submillimeter waves

Hisashi Shimakage, Yoshinori Uzawa, Masayoshi Tonouchi, Z. Wang

Published Jun 1, 1997• 26 citations
Publisher

Abstract

We have investigated YBCO step-edge Josephson junctions as millimeter and submillimeter wave mixers. These mixers were integrated with an Au thin-film log-periodic antenna designed for broadband coupling of the radiation. We estimated the noise temperature of the mixer using conventional hot/cold blackbody irradiation techniques in the 100- and 300-GHz bands. We found that the Au thin-film antenna yielded about 5 dB higher coupling efficiency than that of YBCO thin film antenna, and the noise temperature decreased from 2,800 K to 1,800 K. The best receiver noise temperature, 1,200 K, was achieved in the 300-GHz band through improvement in impedance matching.

DOI
10.1109/77.621770

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We have investigated YBCO step-edge Josephson junctions as millimeter and submillimeter wave mixers. These mixers were integrated with an Au thin-film log-periodic antenna designed for broadband coupling of the radiation. We estimated the noise temperature of the mixer using conventional hot/cold blackbody irradiation techniques in the 100- and 300-GHz bands. We found that the Au thin-film antenna yielded about 5 dB higher coupling efficiency than that of YBCO thin film antenna, and the noise temperature decreased from 2,800 K to 1,800 K. The best receiver noise temperature, 1,200 K, was achieved in the 300-GHz band through improvement in impedance matching.
We have fabricated YBCO step-edge Josephson junctions and measured the responses to millimeter and submillimeter irradiation. In the substrate milling process for the purpose of fabricating the step, the step angle was controlled using a Nb metal mask. At a step angle of 20 degrees, we obtained Josephson junctions, the characteristics of which are consistent with the RSJ model. We estimated the capacitance to be 4.4 fF using the RSJ model, but such a value for an 8 /spl mu/m wide and 300 nm thick junction seems too small. When the junctions were irradiated by 300 GHz radiation, Shapiro steps up to the 4th were observed. The junctions were used as mixers in the 100 GHz band, and as harmonic mixers in the 100 GHz LO and 700 GHz RF bands. Beat signals were observed in both cases. We also estimated the quasi-optical conversion losses of the step-edge junctions as mixers.>
We have fabricated YBCO step-edge Josephson junctions and measured the responses to the millimeter and submillimeter irradiation. In the substrate milling process for the purpose of fabricat- ing the step, the step angle was controlled using a Nb metal mask. At a step angle of 20 degrees, we obtained Josephson junctions, the characteristics of which are consistent with the RSJ model. We estimated the ca- pacitance to be 4.4 fF using the RSJ model, but such a value for an 8 pm wide and 300 nm thick junction seems too small. When the junctions were irradiated by 300 GHz, Shapiro steps up to the 4th were ob- served. The junctions were used as mixers in the 100 GHz band, and as harmonic mixers in the 100 GHz LO and 700 GHz RF bands. Beat signals were observed in both cases. We also estimated the quasi-optical con- version losses of the stepedge junctions as mixers.
Submillimeter wave detectors and mixers based on YBa/sub 2/Cu/sub 3/O/sub 7/ (YBCO) step-edge Josephson junctions incorporated into planar antennas were designed and tested up to 670 GHz at temperatures from 12 to 65 K. A quasi-optic coupling system with a LaAlO/sub 3/ lens was used. In some samples the noise intrinsic in the detection process does not follow the Johnson noise law but has a minimum, which for a given sample may occur in the temperature range between 35 to 50 K. Harmonic mixing recorded at 670 GHz proves that the system equilibrium is established in a time shorter than 500 fs.>
This thesis investigates the prospects of some different superconducting mixers integrated with planar antennas for the millimeter and submillimeter regime. Two kinds of Superconductor/Insulator/Superconductor (SIS) tunnel junctions for use in mixers have been fabricated; Nb/PbBi edge junctions and Nb trilayer junctions. One of the very high quality trilayer mixers is currently operating in a 350 GHz radio-telescope heterodyne-receiver. The reduced sensitivity of SIS mixers for frequencies above the gap frequency (?700 GHz) of the superconductors has directed the interest towards another type of superconducting mixer device, the superconducting Hot Electron Bolometer (HEB). Various types of this device have been studied; Nb devices for scale-measurements at 20 GHz to more easily verify some of the theoretical background of the HEB, NbN waveguide devices for 100 GHz, and NbN devices integrated with planar antennas for a quasi-optical mixer at 350 GHz. Two types of planar antennas have been used; the endfire "Broken" Linearly Tapered Slotline Antenna (BLTSA) on a thin dielectric membrane, and the double dipole antenna on a quartz substrate lens. The beam pattern of the BLTSA has been examined theoretically and measured at 40 GHz with antennas supported by Kapton foil, and at 350 and 800 GHz with antennas on thin dielectric SiOxNy membranes. Measurements of the 20 GHz Nb HEB show a mixer conversion loss close to 0 dB for IF frequencies below 40 MHz. The maximum IF bandwidth given by the electron temperature relaxation time corresponds to a frequency of about 80 MHz. A DSB mixer noise temperature of only a few hundred Kelvin has been measured. Corresponding measurements of NbN devices at 100 and 350 GHz give a mixer conversion loss of about 6-10 dB and an IF bandwidth of about 700 to 1000 MHz. The output noise is found to be dominated by electron temperature fluctuations with an equivalent noise temperature of about 100 K, and a frequency dependence equal to that of the IF signal. Phenomenological expressions for conversion loss, noise, and IF impedance have been compared measurements and shows good agreement. The quasioptical NbN HEB mixers are still under development with respect to film quality and coupling to radiation, why the mixer performance of these is expected to improve.
A high-temperature superconducting (HTS) terahertz (THz) frequency down-converter or mixer based on a thin-film ring-slot antenna coupled YBa 2 Cu 3 O 7– x (YBCO)/MgO step-edge Josephson junction is reported. The frequency down-conversion was achieved using higher order harmonics of an applied lower frequency (19–40 GHz) local oscillator signal in the Josephson junction mixing with a THz signal of over 600 GHz, producing a 1–3 GHz intermediate frequency signal. Up to 31st order of harmonic mixing was obtained and the mixer operated stably at temperatures up to 77 K. The design details of the antenna, HTS Josephson junction mixer, the matching and isolation circuits, and the DC and RF performance evaluation are described in this paper.