High throughput continuous pulsed laser deposition process and apparatus

Abstract

The present invention relates to an apparatus and method for forming a high-temperature superconducting film on a long tape substrate at speeds suitable for large-scale production. The method includes a spooling system for use in a high-throughput, continuous pulsed laser deposition (PLD) process in which a superconducting layer, such as yttrium-barium-copper-oxide (YBCO), is deposited atop a buffered metal substrate tape that is translated through one or more deposition chambers via the action of a reel-to-reel spooling system and a conductive-radiant multi-zone substrate heater. It also optionally includes a multi-target manipulator apparatus and multiple laser beams in which multiple targets are impinged upon simultaneously.

Description

FIELD OF THE INVENTION [0001] The present invention relates to an apparatus and method for forming a high-temperature superconducting film on a long tape substrate at speeds suitable for large-scale production, includes a spooling system for use in a high-throughput, continuous pulsed laser deposition (PLD) process. BACKGROUND OF THE INVENTION [0002] In the past three decades, electricity has risen from 25% to 40% of end-use energy consumption in the United States. With this rising demand for power comes an increasingly critical requirement for highly reliable, high quality power. As power demands continue to grow, older urban electric power systems in particular are being pushed to the limit of performance, requiring new solutions. [0003] Wire forms the basic building block of the world's electric power system, including transformers, transmission and distribution systems, and motors. The discovery of revolutionary high-temperature superconductor (HTS) compounds in 1986 led to the ...

AI Technical Summary

Benefits of technology

[0036] The presence of multiple overlapping plumes arranged sequentially effectively lengthens the deposition zone wherein the substrate is exposed to the evaporant material. The thickness of the HTS film deposited onto the substrate tape is controlled by the rotational speed of a payout and take-up spool within the spooling system, thereby controlling the time that the substrate is present in the deposition zone.

[0038] Subsequent to undergoing the deposition of a superconducting layer, the tape is made to wind onto a take-up spool such that the HTS-coated side winds in an orientation toward the center of the spool rather than toward the outer perimeter of the spool, as the superconducting film is less likely to be damaged when under compressive strain rather than when under tensile strain. As an additional protective measure, a length of polymer interleaf may be wound into the take-up spool between tape layers as the tape winds onto the take-up spool, thereby protecting the superconducting layer form being scratched by the non-coated side of the substrate tape.

[0042] For use in a pulsed laser deposition (PLD) process, the multi-zone heater of the present invention includes passages that enable one or more laser beams to pass unimpeded to one or more targets, which otherwise would be obstructed by the size of such a substrate heater that is necessary to accommodate the increased deposition zone length necessary to a high throughput PLD system. The multi-zone heater also allows for accurate monitoring of the substrate temperature via thermocouples and an optical pathway disposed through its structure that enables a pyrometer to make temperature measurements to the non-coated side of the translating tape.

[0044] In operation, the multi-target manipulator apparatus, having multiple target holders upon which are placed multiple targets, respectively, allows multiple laser beams to impinge simultaneously upon the targets. As a result, multiple plumes of ablated material, to which a substrate is exposed for a predetermined time, are formed, thereby forming a film on the substrate. Furthermore, due to the appropriate spacing between the multiple target manipulators arranged in a line, the resulting plumes slightly overlap one to another and therefore ensure uniformity of film deposition over an expanded deposition zone length.

Problems solved by technology

As power demands continue to grow, older urban electric power systems in particular are being pushed to the limit of performance, requiring new solutions.

However, to date only short lengths of coated conductor wire samples have been fabricated at high performance levels with any of the conventional fabrication processes.

However, to date only short lengths of coated conductor wire samples have been fabricated at high performance levels using prior art vapor deposition processes and equipment.

While this represents a step toward the large-scale production of HTS coated tape, it is limited in its scalability.

To achieve significantly longer lengths of HTS coated tape the cylindrical substrate holder must increase in size accordingly, making it impractical to be housed within the main vapor deposition chamber.

Thus, a drawback of the vapor deposition process described in Youm is that the system is not easily scalable to produce long lengths (e.g, several kilometers) of HTS coated tape and is therefore not suited for the large-scale production of HTS coated wire.

A first challenge to the continuous deposition of HTS tapes utilizing a reel-to-reel tape transport system that is not overcome by Youm is the maintenance optimum tape tension throughout the extended deposition runs necessary to high-throughput systems.

This results in a variation in the target-to-substrate distance and a compromise of the thin film uniformity.

A second technical challenge to the continuous deposition of HTS tapes utilizing a reel-to-reel tape transport system that is not overcome by Youm is the maintenance of the tape at the optimal speed throughout extended deposition runs.

Lateral, as well as longitudinal, movement of the tape results in an inconsistent and non-uniform deposition resulting in variations in film thickness.

The importance of film uniformity cannot be an overemphasized: if there is an insufficient superconducting quality at a single point over the entire length of a few hundred meters of tape, the current carrying capacity of the entire length of tape is compromised.

Further, any elements that serve to position the tape must do so in such a way as to not induce stress or strain in the tape, which may damage the delicate thin films

Another technical challenge not overcome by Youm is how to wind the tape onto a spool subsequent to its undergoing the deposition process without damaging the delicate thin film housed thereon.

The ceramic grains of superconducting films may fracture if bent beyond a certain strain, which may result in a decrease in the critical current-carrying capacity of the finished superconductor tape.

However, in the case of a continuously translating substrate as is necessary for a continuous flow manufacturing process, it is difficult to maintain a uniform temperature profile using resistive heaters as disclosed by the prior art.

Any local loss of contact with the heating element by a rapidly moving substrate can cause large temperature variations and in turn inhomogeneities in the coating film.

Consequently, a technical challenge to overcome is how to heat a rapidly moving substrate in a continuous flow high-throughput manufacturing process for producing long lengths of HTS-coated wire.

Current substrate heaters do not provide multiple heating zones with differing temperature ranges as required for continuous flow manufacturing of HTS-coated wire and thus are not suited for use in the large-scale production of HTS-coated wire.

Conventional target manipulators are therefore of limited use in a multi-laser beam PLD application.

Although it is conceivable that multiple lasers could be focused on all targets simultaneously, it is not practical for a continuous flow application in which a substrate tape is translating in a straight line, thereby requiring the targets to be arranged in a straight line.

A further limitation is that Kim et al.

This type of multi-target manipulator is therefore not suited for use in the large-scale production of HTS-coated wire utilizing a continuously translating substrate through a deposition chamber.

However, using such an arrangement of several conventional target manipulators in a multi-laser beam PLD system is very costly and therefore not practical.

Also, conventional target manipulators occupy lot of space and as a result, there will be large gaps between targets.

This will result in large gaps between plumes from the targets when used with multiple lasers.

Consequently, this arrangement of several conventional target manipulators is not economically or practically suited for use in the large-scale production of HTS-coated wire.

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