Nb-based A15 compound Josephson tunnel junctions fabricated using a CF/sub 4/ cleaning process: Fabrication conditions and barrier properties
Josephson tunnel junctions with Pb counterelectrodes have been fabricated on magnetron-sputtered Al5 Nb/sub 3/X(X = Al,Ge) thin films using a CF/sub 4/ plasma cleaning process (CFCP) in conjuction with standard photolithographic processing. The fabrication conditions necessary to produce optimized junctions and their tunneling properties have been investigated. The junction quality rapidly decreases with the increase in the discharge cathode self-bias voltage (V/sub CSB/) during the plasma oxidation as well as the CF/sub 4/ cleaning. The optimum voltage for the cleaning necessary to obtain high-quality junctions with a uniform current distribution is common to both compounds and exists in the narrower range of 120--140 V than for Nb/Pb junctions. Nevertheless, high-quality Nb/sub 3/X/Pb junctions with V/sub m/ >20 mV can be highly reproducibly fabricated for a wide range of the critical current density (1--10/sup 3/ A/cm/sup 2/). Such junctions show high barrier height values of 0.8--1.0 eV and good aging stability, which is also the case for the Nb/Pb junctions fabricated using CFCP. X-ray photoelectron spectroscopy (XPS) and ellipsometric measurements on the CF/sub 4/-cleaned base electrode surface indicate the presence of an ultrathin fluoride overlayer which is composed of Nb-F and X-fluorides. The former also show that the tunnel barrier is a mixture of Nb/sub 2/O/sub 5/, Nb-F-O, and X-F-O. These results, in addition to those for barrier height measurements, suggest that F atoms prevent the defect creation in the barrier and the selective Nb oxidation. They, thus, play an important role in the formation of the highly insulating barriers as well as a nearly ideal barrier-electrode interface without a substantial proximity layer.
- Research Organization:
- NTT Ibaraki Electrical Communication Laboratories, Nippon Telegraph and Telephone Corporation, Tokai, Ibaraki 319-11, Japan
- OSTI ID:
- 5272068
- Journal Information:
- J. Appl. Phys.; (United States), Vol. 58:9
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
GENERAL PHYSICS
JOSEPHSON JUNCTIONS
FABRICATION
TUNNEL EFFECT
ALUMINIUM ALLOYS
CARBON FLUORIDES
CATHODES
CURRENT DENSITY
ELECTRIC POTENTIAL
ELECTRICAL PROPERTIES
ELECTRODES
GERMANIUM ALLOYS
LEAD ALLOYS
MAGNETRONS
NIOBIUM ALLOYS
OPTIMIZATION
POTENTIALS
SPUTTERING
SURFACE CLEANING
ALLOYS
CARBON COMPOUNDS
CLEANING
ELECTRON TUBES
ELECTRONIC EQUIPMENT
EQUIPMENT
FLUORIDES
FLUORINE COMPOUNDS
HALIDES
HALOGEN COMPOUNDS
JUNCTIONS
MICROWAVE EQUIPMENT
MICROWAVE TUBES
PHYSICAL PROPERTIES
SUPERCONDUCTING JUNCTIONS
SURFACE FINISHING
420201* - Engineering- Cryogenic Equipment & Devices