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IEEE Transactions on Magnetics

Refractory submillimeter Josephson effect sources

K. Wan, Baokang Bi, A. K. Jain, Linus A. Fetter, Siyuan Han, W. H. Mallison, James E. Lukens

Published Mar 1, 1991• 25 citations
Publisher

Abstract

Niobium Josephson effect array oscillators have been fabricated and tested. These devices deliver about 1 mu W of power in the submillimeter-wave range to 20-60 Omega load resistors. The present upper frequency limit of about 500 GHz appears to be set by losses in the superconducting microstrip. Data on the submillimeter-wave surface impedance of the niobium microstrip and details of the trilayer junction processing, which gives value of V/sub m/ at 2 K up to 800 mV, are presented.

DOI
10.1109/20.133927

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IEEE Transactions on Applied Superconductivity•Mar 1, 1993•67 citations
Niobium Josephson effect array oscillators have been fabricated and tested. These devices deliver about 1 mu W of power in the submillimeter-wave range to 20-60 Omega load resistors. The present upper frequency limit of about 500 GHz appears to be set by losses in the superconducting microstrip. Data on the submillimeter-wave surface impedance of the niobium microstrip and details of the trilayer junction processing, which gives value of V/sub m/ at 2 K up to 800 mV, are presented.
We have developed resistively shunted tunnel junctions with a small parasitic inductance (/spl equiv/100 fH) to improve the high-frequency performance of Josephson array oscillators. Josephson array oscillators with 11 such junctions and Nb microstrip resonators were designed and fabricated to operate at 690 GHz. Shapiro steps induced by Josephson oscillation were clearly observed at the submillimeter frequency region. By comparing the step height with the numerical simulation, we estimated the power of the Josephson oscillator delivered to the load resistor to be about 10 /spl mu/W at 625 GHz. The linewidth of the Josephson array oscillator was also measured using an integrated receiver consisting of two Josephson array oscillators and an SIS mixer. The designed frequency of the receiver was set at 550 GHz. IF output power spectrum was observed when both the oscillators were biased at about 1.17 mV which corresponds to 566 GHz. The composite linewidth of Josephson oscillation was measured about 8 MHz at 4.2 K.
A submillimeter wave source based on a new design using Josephson junction arrays has been developed and tested. The maximum rf power, delivered to a 68Ω load and detected on chip, was 47 μW at 394 GHz. Significant power was detected at a number of frequencies from 300 to 500 GHz where the power was 10 μW. The observed power at the designed operating frequency near 400 GHz is consistent with all 500 junctions in the series biased array delivering current in phase to the loads. This is in agreement with simulations of smaller arrays of the same design. The linewidth, inferred from the measured resistance at the point of maximum power, with T=4.2 K, is less than 1 MHz. The minimum inferred linewidth near 400 GHz, at somewhat lower power, is about 100 kHz.
A submillimeter-wave oscillator using a phase-locked array of Josephson junctions is demonstrated. With an array of 40 shunted tunnel junctions, the oscillator delivers 1 mu W of power at 350 GHz into a 60- Omega load on the chip. The operating frequency of the oscillator is tunable over a range of about 10%. Experiments on two coupled lead alloy tunnel junctions show that Josephson oscillations exist to about 1 THz. Using a similar design and a higher gap superconductor such as NbN for the transmission lines, arrays operating at 1 THz with power outputs of 1 mW should be feasible.>
All-refractory material superconducting millimeter-wave oscillators have been designed and investigated experimentally with different superconductor-insulator-superconductor (SIS) mixers integrated on the same chip. Tested structures include a flux-flow oscillator (FFO) based on a long Josephson junction, a coupling section, and an SIS detector with tuned out junction capacitance. Coupling sections were designed as multistep microstrip quarter-wave impedance transformers. All junctions have been fabricated on the basis of a high-quality trilayer Nb-AlO/sub x/-Nb process. Microwave oscillations in the frequency range 75-500 GHz have been detected experimentally. The level of delivered power was estimated from the pumped I-V curve of the strongly coupled single junction detector. Coupled power levels higher than 0.1 mu W at 256 GHz were achieved. A spectral linewidth of the FFO of less than 1 MHz has been estimated experimentally. The first attempt to create an integrated receiver based on an FFO and an SIS array mixer integrated on the same chip was made in the 2-mm wavelength band.>