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NOISE FIGURE MEASUREMENT OF HIGH TEMPERATURE SUPERCONDUCTING Bi-CRYSTAL JOSEPHSON JUNCTION MIXERS

Peiheng Wu

Published Jan 1, 2012• 0 citations
OpenAlex

Abstract

Noise figure(NF) is an important parameter of the superconducting mixer,which is a key indicator of the mixer's sensitivity depending on the internal noise.Using the efficient and durable small size pulse tube refrigerator for the cold source,we designed the High Temperature Superconducting(HTS) Josephson junction harmonic mixer and noise figure automatic measurement systems which operated at 60 K.YBa2Cu3O7-δ(YBCO)/MgO Josephson junctions was fabricated through argon ion band etching.Using the Y-factor measurement method,we estimated the noise figure of the HTS Josephson junction mixer with conventional hot/cold blackbodies irradiation techniques.The Josephson junction,we had successfully fabricated,had 1mV characteristic voltage,and it had good microwave response and high harmonic numbers at operating frequencies around 650 GHz.At the 30th harmonic of fS=210GHz,the double-crystal Josephson junction biased in the different voltages,IF output signal to noise ratio changed in the range of 30 dB.The noise figure had a minimum 10 dB at a bias voltage of 300 μV and at the irradiation of blackbodies at 77 K and 300 K.

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Noise figure(NF) is an important parameter of the superconducting mixer,which is a key indicator of the mixer's sensitivity depending on the internal noise.Using the efficient and durable small size pulse tube refrigerator for the cold source,we designed the High Temperature Superconducting(HTS) Josephson junction harmonic mixer and noise figure automatic measurement systems which operated at 60 K.YBa2Cu3O7-δ(YBCO)/MgO Josephson junctions was fabricated through argon ion band etching.Using the Y-factor measurement method,we estimated the noise figure of the HTS Josephson junction mixer with conventional hot/cold blackbodies irradiation techniques.The Josephson junction,we had successfully fabricated,had 1mV characteristic voltage,and it had good microwave response and high harmonic numbers at operating frequencies around 650 GHz.At the 30th harmonic of fS=210GHz,the double-crystal Josephson junction biased in the different voltages,IF output signal to noise ratio changed in the range of 30 dB.The noise figure had a minimum 10 dB at a bias voltage of 300 μV and at the irradiation of blackbodies at 77 K and 300 K.
A Josephson quasioptical detector comprising YBaCuO junction on bicrystal MgO substrate, integrated log-periodic Au antenna, MgO extended hyperhemisphere lens attached to the substrate and 1.4 GHz cold amplifier with cold circulator has been designed, fabricated and experimentally studied. We fabricated several integrated Josephson junctions 1-2 /spl mu/m wide which at 4.2 K demonstrate RSJ IV curves with critical currents 100-300 /spl mu/A and normal resistance of 10-20 /spl Omega/. The noise temperature (T/sub N/) at 4.2 K and 330 GHz measured by a hot/cold load method in fundamental mixing mode with external BWO local oscillator brings T/sub N/=1100 K for the junction shunted by low-inductance resistive shunt and T/sub N/=1400 K without shunting. At bath temperatures of 20-40 K the noise temperature was in the range 1500-3000 K, at 50 K the noise temperature was below 2000 K, and at 60-70 K increased over 3000 K in the frequency range 310-586 GHz. The noise temperatures measured in the self-pumping mode vary between 580-2300 K with dc bias in the range 0.1-0.5 mV. The linewidth of Josephson oscillations has been extracted from a selective detector response and IF noise voltage dependence. The measured excess noise can be attributed to shot noise and multiple Andreev reflection in pinholes with Ss'S structure. We observed small subharmonic steps in IV curve and noise dependencies, which are typical for SNS junctions.
Two high-Tc superconducting (HTS) YBa2Cu3O7-δ(YBCO) grain boundary (GB) Josephson junctions in series as a harmonic mixer is investigated. The research shows that the mixer consisting of two series YBCO Josephson junctions has a larger harmonic number than that with only one junction in heterodyne mixing at zero-voltage bias. One of the advantages of the series-Josephson-junction mixer is that the total critical current is improved without sacrificing the sensitivity of the junctions in the array that makes the mixer easier to get more microwave induced-steps required by larger harmonic number. Furthermore, the underdamped YBCO GB series-Josephson-junction mixer operated at zero-bias voltage, where the zero-order Shapiro step exists, achieves mutual phase locking of the junctions in the array, resulting in an excellent mixing performance. Thus, the series-underdamp-Josephson-junction mixer with zero bias is predominant and compact in terahertz (THz) application due to its excellent performance and no dc bias supply.
This letter presents both theoretical and experimental investigations on the noise and conversion performance of a high-Tc superconducting (HTS) step-edge Josephson-junction mixer at the frequency of 0.6 THz and operating temperatures of 20–40 K. Based on the Y-factor and U-factor methods, a double-sideband noise temperature of around 1000 K and a conversion gain of −3.5 dB were experimentally obtained at 20 K. At the temperature of 40 K, the measured mixer noise and conversion efficiency are around 2100 K and −10 dB, respectively. The experimental data are in good agreement with the numerical analysis results using the three-port model. A detailed performance comparison with other reported HTS terahertz mixers has confirmed the superior performance of our presented mixer device.
The authors report on the mixing properties of high-temperature superconductor bicrystal Josephson junctions at 345 GHz and high-operating temperatures. A variable backshort and E-plane tuner enabled the control of impedance matching between the junction and the RF environment. The local oscillator frequency and intermediate frequency were 345 and 1.4 GHz, respectively. The double-side band (DSB) mixer noise temperature and the conversion efficiency were determined using the hot/cold method. The authors observed that the noise temperature was strongly dependent on the matching conditions. The lowest noise temperatures were observed for tuner positions supporting the formation of a subharmonic step which appeared between the zeroth and first Shapiro step. At T = 20 K they obtained a lowest DSB mixer noise temperature of 1003 K and a conversion efficiency of -1.2 dB. They have investigated the dependence of the noise temperature on the operating temperature in detail. The impact of resonances on the device performance will be discussed.