Fabrication of high current coated high temperature superconducting tapes

Abstract

The fabrication of high current coated high temperature superconducting tapes utilizing vaporized rare earth, barium and copper tetramethyl heptanedionates is disclosed.

Description

[0001] 1. Field of the Invention[0002] This invention relates generally to an apparatus and method for the production of high temperature superconducting materials. More specifically, the invention relates to the preparation of high current and high current density HTS materials prepared by MOCVD deposition of dissimilar precursor materials.[0003] 2. Description of the Related Art[0004] High temperature superconducting (HTS) materials have immense potential for use in electric power, electronics, and medical industries. Presently, the HTS material that is manufactured in considerable quantities by industry is based on (Bi,Pb)SrCaCuO (BSCCO) superconductor. This material and the process used to manufacture it have proven to be expensive. Furthermore, the properties of this material degrade quickly in the presence of magnetic fields that are generated in a number of electric power devices.[0005] ReBaCuO (Re=rare earth) superconductor is being developed as a potential alternative to th...

AI Technical Summary

Benefits of technology

[0023] The present invention relates to the use of a metal organic chemical vapor deposition (MOCVD) process for fabrication of coated HTS conductors. In a MOCVD process, chemical precursors of the constituent elements are vaporized at a low temperature and the vapors are deposited on a heated substrate to form the HTS film. The equipment can be designed for the vapors to flow over a large area i.e. a long-length of tape can be coated instantaneously or a number of tapes can be coated in parallel, both of which result in high throughput. The precursors of individual elements of the HTS material can be mixed in an infinite number of combinations. Therefore, the composition of the HTS film can be tailored to that preferred to achieve specific performance parameters. The precursors are maintained outside the deposition chamber under ambient conditions. Therefore, refill of precursors is very simple which is important for long length manufacturing. The precursors need not be formed into any shape, which does not add extra cost. MOCVD is performed at a pressure much higher than that used for PVD techniques and so, cost of capital equipment is relatively low.

Problems solved by technology

This material and the process used to manufacture it have proven to be expensive.

Furthermore, the properties of this material degrade quickly in the presence of magnetic fields that are generated in a number of electric power devices.

However, these techniques are limited in several ways.

First, they are all limited by line of sight i.e. the vapors can coat the substrate only where they can `see` the substrate, which means that the coated area is small.

This limits the throughput of coated tape.

Second, the composition of the coated film is limited to the composition of the material being vaporized.

Third, the source material has to be maintained under vacuum causing refill to be difficult and in turns poses a problem for long-length manufacturing.

Fourth, the source material has to be formed into a monolith, which adds cost to the process.

Fifth, a high vacuum is needed which increases cost of capital equipment.

The limitations of wet chemical processes are thickness control, multiple steps for film formation (deposition, bakeout, & heat treatment as a minimum), need for repeat these multiple steps multiple times to build thick films, carbon residue incorporation in the films, difficulties in epitaxial growth in thick films, and evolution of harmful byproducts such as HF if fluorinated precursors are used.

Desirable CVD reagents therefore are fairly reactive and volatile.

Unfortunately, for many of the materials described above, volatile reagents do not exist.

In many cases, the source reagents are solids whose sublimation temperature may be very close to the decomposition temperature, in which case the reagent may begin to decompose in the lines before reaching the reactor, and it therefore is very difficult to control the stoichiometry of the deposited films from such decomposition-susceptible reagents.

In other cases, the CVD, reagents are liquids, but their delivery into the CVD reactor in the vapor phase has proven difficult because of problems of premature decomposition or stoichiometry control.

However, MOCVD has yet to be shown to be a viable approach to achieve high current and high current density with HTS Coated conductors because suitable MOCVD apparatus and process has not been developed.

MOCVD is performed at a pressure much higher than that used for PVD techniques and so, cost of capital equipment is relatively low.

If it is introduced non-uniformly, the film growth will be non-uniform when depositing on large areas.

However, after the shutter is opened the showerhead may overheat due to exposure to the heat from the substrate heater.

If it is placed too close, the showerhead will overheat due to the heat from the heater.

Also, the precursor may decompose and result in deposition of particles on the substrate.

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