METHOD FOR THE MANUFACTURE OF COPPER OXIDE SUPERCONDUCTING FILMS

Abstract: Films of superconducting material having T c > 77K can be deposited by means of evaporation from two separate binary alloys, one of Cu-Y (102) and the other Ba-Cu (104). They can be evaporated by electron beams (108, 110) in vacuum and subsequently oxidized or they can be directly evaporated in a low pressure oxygen atmosphere.

Description: The present invention relates to a method for the manufacture of superconducting films having a critical temperature, T c greater than 77 K by the utilization of two binary alloy evaporation sources. By "critical temperature" is meant the temperature at which the film becomes super-conducting. It has recently been found that ceramic materials based on Y-Ba-Cu-O exhibit superconducting properties at temperatures higher than 77 K, the temperature of boiling liquid nitrogen. Such materials having a high superconducting temperature are very economical as they do not have to be cooled to lower temperatures by means of costly liquid helium. It would be useful to be able to deposit thin films of superconducting materials as parts of integrated circuits such as conductors between various components or a part of the components themselves such as superconducting quantum interference devices (SQUIDS). However previously used techniques for deposition of the thin films such as plasma spraying have proved unsatisfactory because of the inability to sufficiently control the film thickness of the deposited film and its exact composition. Furthermore, in cathode sputtering processes it is difficult to use separate sources for each of the three metallic elements as two of these, i.e. Y and Ba, react with air and are subject to deterioration during inevitable handling procedures. For example, Physical Review Letters, Vol. 58, No. 25 22 June 1987, pages 2684-2686 describes an evaporation method for the manufacture of an epitaxial YBa₂Cu₃O 7-x film according to which Y, Ba and Cu are evaporated from three separate sources in a vacuum comprising primarily oxygen. It is therefore an objet of the present invention to provide an improved method of manufacture of a deposited film of a superconducting element having a more carefully controlled film thickness. It is another object of the present invention to provide an improved method of manufacture of a deposied film of a superconducting element having a more closely controllable composition. These and other objects of the present invention will become apparent by reference to the following description and the single figure of the drawing wherein: The drawing shows a respresentation of an evaporation chamber useful in depositing films of the present invention. According to the present invention there is provided a method for the manufacture of a deposited film of a superconducting element based on Y-Ba-Cu-O and having a critical temperature greater than 77K, comprising the steps of: I. evaporating the elements Cu and Y from a binary alloy of Cu and Y onto a substrate in an evaporation chamber; II. simultaneously evaporating the elements Ba and Cu from a binary alloy of Ba and Cu onto the substrate in the same chamber; both of said evaporation steps I and II taking place either under vacuum followed by subsequent oxidation or directly in a low pressure oxidizing atmosphere in said chamber. The drawing shows an evaporation chamber 100 containing a first binary alloy source 102 which can conveniently be an intermetallic binary alloy of Cu and Y such as Cu₁Y₁, Cu₂Y, Cu₄Y, Cu₆Y or Cu₇Y. A second binary alloy source 104 can conveniently be an intermetallic binary alloy of Ba and Cu such as Ba₁Cu₁, Ba₁Cu₃ or Ba₂Cu₃. An electron source 106 provides two electron beams 108, 110 within evacuated chamber 100 which focus onto sources 102 and 104 causing them to evaporate their component elements onto a substrate 112 held on a support 114, in the form of a film 116. The intensities of electron beams 108, 110 can be varied to suitably adjust the composition of the deposited film 116. The film 116 can then be oxidized by a suitable means or the evaporation can take place directly in a low pressure oxidizing atmosphere. Other deposition techniques such as by evaporation from the binary alloys by means of laser evaporation or cathode sputtering can be used, for instance in the presence of an argon atmosphere or other techniques well known in the manufacture of semiconductor circuits.

Claims: A method for the manufacture of a deposited film of a superconducting material based on Y-Ba-Cu-O having a critical temperature greater than 77K, characterized by comprising the steps of: I. evaporating the elements Cu and Y from a binary alloy of Cu and Y onto a substrate in an evaporation chamber; II. simultaneously evaporating the elements Ba and Cu from a binary alloy of Ba and Cu onto the substrate in the same chamber; both of said evaporation steps I and II taking place either under vacuum followed by subsequent oxidation or directly in a low pressure oxidizing atmosphere in said chamber. A method according to claim 1 in which the alloy of Cu and Y comprises one or more intermetallic compounds chosen from the group consisting of Cu₁Y₁, Cu₂Y, Cu₄Y, Cu₆Y, Cu₇Y. A method according to claim 1 in which the alloy of Cu and Ba comprises one or more intermetallic compounds chosen from the group consisting of Ba₁Cu₁, Ba₁Cu₃ and Ba₂Cu₃.

Inventors: BOFFITO, CLAUDIO
Applicants: SAES GETTERS S.P.A.
Application year: 1988
Main classification: H01L39
IPC codes: C01G1, C23C14, H01B13, C01G3, C04B35, H01B12, H01L39