Preparation and characterization of submicron
stacked Josephson junctions
on Tl-2212 epitaxial films
Y.
Koval, A.
Franz, P.
Müller
Physikalisches Institut III, Universitaet
Erlangen-Nuernberg, D-91058 Erlangen, Germany
H.Schneidewind
Institut fuer Physikalische Hochtechnologie,
D-07702 Jena, Germany
There are two tasks of great interest
which demand a preparation of stacked Josephson junctions of submicron
dimensions.
1. Experimental investigation of
charge soliton influence on electron transport and observation of Coulomb
blockade effect at elevated temperature.
2. High frequency application as
a mixers and possibly as a powerful radiation sources in the THz range.
Up to the moment stacked junctions
were prepared on single crystals. We present a technology in order to realize
sub-micron sized mesas on top of Tl2212 epitaxial films on sapphire substrates.
A new method for mesa insulation was used. It is based on the properties
of the electron resist poly methyl methacrylate (PMMA):
1) PMMA can be used both as a positive
and as a negative resist just by variation of exposure dose.
2) PMMA in cross linked state (negative
mode) can be effectively used as an insulator [1].
Minimum dimensions of mesa areas
were - 0.3x0.3 µm2.
We present transport measurements
of these devices.
It was found that a very high critical
current density of 2000-10000 A/cm2 is typical for junctions
of 0.7x0.7 µm2. Sub-gap structures were observed similar
to the ones reported in [2]. Hysteric IV characteristics can be observed
up to 110K which is rather unusual for such kind of junctions. Decrease
of junction areas to 0.3x0.3 µm2 leads to a strong suppression
of critical current density which never exceeds 1000 A/cm2.
These results are in agreement with results published in [3].
1. Y.Koval, A. Wallraff, M. Fistul,
N. Thyssen, H. Kohlstedt, A.V. Ustinov, IEEE Trans. Appl. Supercond.
, 9, 1999, 3957.
2. K. Schlenga, G. Hechtfischer,
R. Kleiner, W. Walkenhorst, P. Müller, H. L. Johnson, M. Veith, W.
Brodkorb, and E.Steinbeiß, Phys.Rev. Lett. 76, 4943 (1996)
3. Yu. I. Latishev, S.-J. Kim,
T. Yamashita, JETP lett. 69, 84 (1999).
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"This
publication is based (partly) on the presentations made at the European
Research Conference (EURESCO) on "Future Perspectives of
Superconducting Josephson Devices: Euroconference on Physics and
Application of Multi-Junction Superconducting Josephson Devices,
Acquafredda di Maratea, Italy, 1-6 July 2000, organised by the European
Science Foundation and supported by the European Commission, Research
DG, Human Potential Programme, High-Level Scientific Conferences, Contract
HPCFCT-1999-00135. This information is the sole responsibility of the
author(s) and does not reflect the ESF or Community's opinion. The ESF
and
the Community are not responsible for any use that might be made of data
appearing in this publication."
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