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arXiv:1809.01642 · Journal of Low Temperature Physics

Microscopic Tunneling Model of Nb–AlN–NbN Josephson Flux-Flow Oscillator

D. R. Gulevich, Lyudmila V. Filippenko, V. P. Koshelets

Published Dec 5, 2018• 10 citations
arXivHTMLPDF
DOI
10.1007/s10909-018-2106-x

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This chapter presents an overview of the Nb-based tunnel junction's technology at Kotelnikov IREE in Moscow. By improving on the fully Nb-based SIR, the chapter develops and studies Nb-AlN-NbN circuits that exhibit an extended operation frequency range. Continuous frequency tuning for the phase-locked superconducting local oscillators (LO) has been experimentally demonstrated in the range of 350-750 GHz. As a result of Nb-AlO x -Nb technology optimization and extensive analysis of the SIS receiver designs, a number of low-noise receivers have been designed and tested. The Josephson flux flow oscillators based on Nb-AlO x -Nb and Nb-AlN-NbN junctions have proven to be the most developed superconducting local oscillator for integration with an SIS mixer in a single-chip submicrometer-wave superconducting integrated receiver. The implementation of an AlN tunnel barrier in combination with a NbN top superconducting electrode is expected to give a significant improvement in SIS THz mixer performance. High-quality Nb-AlN-NbN tunnel junctions were used for development of the superconducting LO and fully integrated superconducting receivers.
The superconducting integrated receiver (SIR) comprising in one chip a superconductor-insulator-superconductor (SIS) mixer and a phase-locked superconducting flux flow oscillator (FFO) is under development for the international project TELIS. To overcome temperature constraints and extend operation frequency of the SIR we have developed and studied Nb-AlN-NbN-Nb circuits with a gap voltage Vg up to 3.7 mV and extremely low leakage currents . Based on these junctions integrated microcircuits comprising FFO and harmonic mixer have been designed, fabricated and tested; the radiation from such circuits has been measured at frequencies up to 700 GHz. Employment of NbN electrode does not result in the appearance of additional noise. For example, FFO linewidth as low as 1 MHz was measured at 600 GHz, that allows us to phase lock up to 92% of the emitted by FFO power and realize very low phase noise about 90 dBc. Preliminary results demonstrated uncorrected DSB noise temperature of the Nb-AlN-NbN SIR below 250 K at frequencies around 600 GHz.
To develop an efficient local oscillator (LO) integrated with a SIS mixer operating above the gap frequency of Nb, we have investigated the radiation power P of NbN-based flux-flow-type Josephson oscillators (FFO's). The designed and fabricated chip incorporates FFO's, SIS power detectors (DET's), and their coupling circuits. Both FFO's and DET's consist of epitaxial NbN/AlN/NbN junctions with high critical current density J/sub C/ (15200 nW, enough for the optimum pumping of a SIS mixer with rf-resistance of 50 /spl Omega/, is coupled to DET's for 0.5-0.9 THz. The coupling bandwidth is larger than 20% of its central frequency. In the band, the radiation frequency is tuned by the control current through the FFO of 10-100 mA. The maximum coupling frequency of the present experiment is quantitatively agreed with the theoretical one. The peak power of 1.3 /spl mu/W is detected at 0.76 THz. The dissipated power in a FFO is smaller than 500 /spl mu/W, which is 10/sup -4/ times less than that of semiconductor sources. These results indicate the feasibility of NbN-based FFO's for a practical on-chip LO.