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IEEE Transactions on Instrumentation and Measurement

High-Tc harmonic mixer applied to Josephson junction array voltage standard at NIM

S.Q. Xue, H.H. Li, X.C. Shen, H.B. Wang, Weiwei Xu, Qilin Cheng, Pan Wu

Published Apr 1, 1997• 0 citations
Publisher

Abstract

A high-Tc superconducting (YBCO) Josephson-junction harmonic mixer has been used to improve the spectrum purity of the microwave source in the JJAVS at the National Institute of Metrology (NIM). Compared with the microwave source using source-locking counter EIP 578B, the spectrum purity of the microwave source has been improved significantly from -25 dBc/Hz (offset /spl plusmn/50 kHz) to -58 dBc/Hz (offset /spl plusmn/10 kHz). Therefore, the random uncertainty of the JJAVS was reduced.

DOI
10.1109/19.571824

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A high-Tc superconducting (YBCO) Josephson-junction harmonic mixer has been used to improve the spectrum purity of the microwave source in the JJAVS at the National Institute of Metrology (NIM). Compared with the microwave source using source-locking counter EIP 578B, the spectrum purity of the microwave source has been improved significantly from -25 dBc/Hz (offset /spl plusmn/50 kHz) to -58 dBc/Hz (offset /spl plusmn/10 kHz). Therefore, the random uncertainty of the JJAVS was reduced.
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.
The design, fabrication, and the characterization of a 0.5-V Josephson junction array device are presented for the quantum voltage standards in the National Institute of Metrology (NIM) of China. The device consists of four junction arrays, each of which has 1200 3-stacked Nb/Nb x Si1−x /Nb junctions and an on-chip superconducting microwave circuit which is mainly a power divider enabling each Josephson array being loaded with an equal amount of microwave power. A direct current (dc) quantum voltage of about 0.5 V with a ∼1-mA current margin of the 1st quantum voltage step is obtained. To further prove the quality of NIM device, a comparison between the NIM device with the National Institute of Standards and Technology (NIST) programmable Josephson voltage standard (PJVS) system device is conducted. The difference of the reproduced 0.5-V quantum voltage between the two devices is about 0.55 nV, which indicates good agreement between the two devices. With the homemade device, we have realized a precise and applicable 0.5-V applicable-level quantum voltage.
Using a high Tc superconducting grain boundary Josephson junction, harmonic mixing experiments in the mm waveband were carried out, aiming at as large a harmonic number and as high a signal frequency as possible. The dependencies of intermediate frequency output on dc bias, harmonic number, frequency of local oscillator (LO), and other parameters were carefully studied. Until now, our best result was the mixing between the signal at 95 GHz and the 105th harmonic of LO at about 900 MHz. Preliminary experiments using a high Tc harmonic mixer and phase-locking loop were tried to stabilize the frequency of a mm wave source.
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 high temperature superconducting YBa2Cu3Oy array of five Josephson junctions designed with additional coupling lines has been developed to demonstrate the effects of frequency locking and impedance matching for applications such as oscillators, mixers, and detectors. The Josephson self-radiation power was directly detected by a superheterodyne receiver, and Shapiro steps were also measured. The Josephson self-radiation properties reveal good quality of phase locking and microwave coupling with external circuits. The maximum self-radiation power of our array is about 50 pW which is several ten times higher than that of a single Josephson junction, and its peak point exactly satisfies the Josephson current-voltage relation. The Shapiro-step measurements show that the behavior of current-voltage curve depends on the effective inductance of coupling lines which affects the total impedance of Josephson junction array and microwave coupling. The Josephson oscillation frequency was obtained up to about 880 GHz which is 73% of the maximum available frequency calculated from the characteristic voltage of the Josephson junctions. Experimental results show that this type of Josephson junction array can improve the Josephson self-radiation power and increase the maximum detectable frequency.