Nb-based A15 compound Josephson tunnel junctions fabricated using a CF/sub 4/ cleaning process: II. Properties of magnetron-sputtered Nb/sub 3/X(X = Al,Ge) films

Journal Article · Thu Jan 15 04:00:00 EST 1987 · J. Appl. Phys.; (United States)

DOI:https://doi.org/10.1063/1.338218· OSTI ID:6868850

Tanabe, K; Asano, H; Michikami, O

Josephson tunnel junctions with Pb counterelectrodes have been fabricated using a CF/sub 4/ plasma cleaning process on A15 Nb/sub 3/X(X = Al,Ge) thin films prepared by magnetron sputtering. The effects of deposition conditions on junction quality as well as superconducting parameters (gap, dc Josephson current, and magnetic penetration depth) of the films have been investigated. The junction quality is largely influenced by film deposition conditions, especially by substrate temperature. Junctions with base electrodes which are deposited on oxidized silicon (for Nb/sub 3/Al) or sapphire (for Nb/sub 3/Ge) radiatively heated above approximately 700 /sup 0/C show high-quality I--V curves, while lower temperatures lead to increases in the excess conductance and the width of the sum-gap structure. High-quality junctions with large sum gaps (up to 4.05 mV at 4.2 K for Nb/sub 3/Al/Pb and 5.05 mV for Nb/sub 3/Ge/Pb) can be prepared on such films. Furthermore, systematic relationships between the superconducting parameters and the energy gaps are observed, which indicate a good homogeneity of the films. In contrast, all junctions on higher-T/sub c/ films prepared by means of self-epitaxial deposition or using a molybdenum substrate holder exhibit apparent current rise at lower voltages, indicating the coexistence of low-T/sub c/ materials. Systematic correlation between the junction quality and the residual resistivity ratio shows that such an inhomogeneity extends to the bulk of the films. Radiatively heated samples with the A15 phase composition near the boundary of the film homogeneity range exhibit favorable properties for electric applications such as large energy gaps and small magnetic penetration depths (--150 nm).

• Research Organization: NTT Electrical Communications Laboratories, Nippon Telegraph and Telephone Corporation, Tokai, Ibaraki 319-11, Japan
• OSTI ID: 6868850
• Journal Information: J. Appl. Phys.; (United States), Journal Name: J. Appl. Phys.; (United States) Vol. 61:2; ISSN JAPIA
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360104 -- Metals & Alloys-- Physical Properties
420201* -- Engineering-- Cryogenic Equipment & Devices
656100 -- Condensed Matter Physics-- Superconductivity
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
ALLOYS
ALUMINIUM ALLOYS
ELECTRIC CONDUCTIVITY
ELECTRICAL PROPERTIES
ELECTRON TUBES
ELECTRONIC EQUIPMENT
EQUIPMENT
FABRICATION
FILMS
JOSEPHSON JUNCTIONS
JUNCTIONS
MAGNETRONS
MICROWAVE EQUIPMENT
MICROWAVE TUBES
NIOBIUM ALLOYS
NIOBIUM BASE ALLOYS
PERFORMANCE
PHYSICAL PROPERTIES
SPUTTERING
SUPERCONDUCTING FILMS
SUPERCONDUCTING JUNCTIONS
SUPERCONDUCTIVITY
TUNNEL EFFECT