Sputtering technique forms transition-metal interstitial compounds into superconducting thin films having transition temperatures similar to those of the bulk materials. Since the magnetic-field and current-carrying properties of the films exceed those of the bulk materials, they may have applications other than in tunneling devices

Gavaler, J. R.

English

NASA Technical Reports Server

October 1969	 Brief 69-10470 
•	
•NASA TECH BRIEF 
NASA Tech Briefs are issued to summarize specific innovations derived from the U.S. space program, 
to encourage their commercial application. Copies are available to the public at 15 cents each 
from the Clearinghouse for Federal Scientific and Technical Information-,Springfield, Virginia 22151. 
Preparation of Superconducting Thin Films of Transition-Metal
Interstitial Compounds 
.
The problem: 
Preparation of thin films of NbN, or of similar com-
pounds, having transition temperatures similar to that 
of the bulk material. Hitherto no superconducting 
compounds having transition temperatures extending 
into the liquid-hydrogen range ( 13.6°K) have been 
successfully made into thin films for use in tunneling 
devices. 
The solution: 
By a new technique such transition-metal intersti-
tial compounds can be formed into thin films having 
transition temperatures similar to those of the bulk 
materials. Since the films' magnetic-field and current-
carrying properties exceed those of the bulk materials, 
they may have applications
.
 other than in tunneling 
devices. 
How it's done: 
An all-glass-and-metal sputtering system was con-
structed, capable of evacuation down to the low 
10_ 10
 Torr range. The disposition chamber proper 
consists of two glass portions sealed together over 
copper gaskets. Multiple electrodes entering the 
chamber, through glass presses, permit the use of a 
quartz-crystal microbalance, temperature-monitoring 
thermocouples, bias sputtering, or substrate-heating 
—in addition to the sputtering. The system is 
evacuated with an oil-diffusion pump trapped with 
liquid nitrogen. After a 16-hour bake-out at about 
400°C or its equivalent, the system normally reaches 
a pressure of less than about 5 x 10-10Torr. 
Simple cold-cathode dc sputtering is used, but a 
unique cathode configuration can be employed. Instead 
of the usual flat configuration the cathodes are shaped 
like a square box open at one end, the substrate-holder 
being positioned inside the box. As well as removing
the substrate from the line of sight of the residual 
gas impurities in the system, this system provides a 
gettering action from the material sputtered from the 
back and sides of the cathode. 
After evacuation and the baking-out, and with the 
pumps still operating, nitrogen is leaked into the 
system until the pressure reaches 6 x 10-5Torr. 
Argon is then introduced until the desired current-
voltage conditions are established: 80 mA and 1700V. 
At this current the cathode is bombarded at about 
1 mA/cm 2 ; the pressure of argon required for this 
power is about 50 x 10 Torr. The rate of sputter-
ing under these conditions is about 5 A/sec at a sub-
strate-target distance of 0.375 inch. No external 
heating of the substrate need be employed since, 
under the conditions described, the substrates 
reach a temperature of about 500°C within about 30 
seconds and remain there throughout. 
The conditions described are for NbN; related com-
pounds can be sputtered as easily by variation of the 
compositions of the cathode target and the reactant 
gas—of either or both. Thin films of NbN can be 
grown having transition temperatures between 15° 
and 16°K; they have upper critical fields at least 
50-kgauss higher than do bulk samples, and at 4.2°K 
they are still superconducting at 180 kgauss. 
Note: 
No further documentation is available. Inquiries 
may be directed to: 
Technology Utilization Officer 
Headquarters 
National Aeronautics 
and Space Administration 
Washington, D.C. 20546 
Reference: B69-10470
(continued overleal) 
This document was prepared under the sponsorship of the National 
Aeronautics and Space Administration. Neither the United States 
Government nor any person acting on behalf of the United States
Government assumes any liability resulting from the use of the 
information contained in this document, or warrants that such use 
will be free from privately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19690000458 2020-03-16T18:03:49+00:00Z
Patent status: 
Title to this invention has been waived, under the 
provisions of the National Aeronautics and Space Act 
[42 U.S.C. 2457 (f)], to the Westinghouse Electric 
Corporation, Pittsburgh, Pennsylvania 15235. 
Source: J. R. Gavaler et al. of 
Westinghouse Electric Corporation 
under contract to 
NASA Headquarters 
(HQN- 10445) 
Brief 69-10470	 Category 01


Preparation of superconducting thin films of transition-metal interstitial compounds

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