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IEEE Transactions on Applied Superconductivity

MM and sub-MM properties of ramp-type Josephson junctions on MgO with STO buffer layers

Hiroaki Myoren, J. Chen, Takashi Yamashita, L. É. Amatuni, A.H. Sonnenberg, G.J. Gerritsma, Horst Rogalla

Published Jun 1, 1999• 2 citations
Publisher

Abstract

We have successfully fabricated ramp-type junctions on MgO substrates using an SrTiO/sub 3/ (STO) buffer layer. The observed I/sub c/R/sub n/ product for the junctions on MgO with STO buffer layer were about 2 mV at 4.2 K and 0.1 mV at 60 K. The junctions clearly showed Shapiro steps under irradiation of MM-waves and sub-MM-waves. We observed Josephson emission at 50 GHz from a junction on a MgO substrate with STO buffer layer at 17 K. We have also confirmed mixing in the self-oscillating mode using MM-wave and sub-MM-wave signals.

DOI
10.1109/77.783868

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We have successfully fabricated ramp-type junctions on MgO substrates using an SrTiO/sub 3/ (STO) buffer layer. The observed I/sub c/R/sub n/ product for the junctions on MgO with STO buffer layer were about 2 mV at 4.2 K and 0.1 mV at 60 K. The junctions clearly showed Shapiro steps under irradiation of MM-waves and sub-MM-waves. We observed Josephson emission at 50 GHz from a junction on a MgO substrate with STO buffer layer at 17 K. We have also confirmed mixing in the self-oscillating mode using MM-wave and sub-MM-wave signals.
We report on the characterization at high frequencies of DyBa/sub 2/Cu/sub 3/O/sub 7-x/ thin film ramp-type junctions with a PrBa/sub 2/Cu/sub 3/O/sub 7-x/ barrier fabricated on MgO substrates using a thin SrTiO/sub 3/ buffer layer. Josephson emission has been detected over a wide temperature range from 4.2 K to 85 K at millimeter wavelengths using a sensitive receiver. Measured spectrum characteristics, emitted power and linewidth are well described by theoretical models. Signal frequency down conversion has been carried out in two different modes using external and internal local oscillators. Wide band electronically tunable Josephson emission allowed us to achieve the frequency down conversion in a very sensitive self-oscillator-mixing mode up to 2.5 THz. For the first time, for any type of Josephson junction, self-oscillator mixing has been achieved at ambient temperatures as high as 80 K.
Superconducting step-edge junctions were fabricated on step-edges in (100) LaAlO/sub 3/ substrates by sputter-deposited epitaxial YBaCuO and TlBaCaCuO thin films. The substrate steps were patterned by ion beam etching using metal film as a mask. The transport properties of the junctions were characterized by four-probe electrical measurements. The critical current-normal resistance product (I/sub c/R/sub N/) was larger than 0.2 mV (77 K) for most of the junctions. Clear Shapiro steps were observed in the current-voltage characteristics of the junctions with 36 GHz or 95 GHz millimeter-wave irradiation. The high frequency properties of these high T/sub c/ Josephson junctions showed that they were quite suitable for the Josephson harmonic mixer used in the digital phase locked millimeter and sub-millimeter wave sources.>
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