MOCVD-Based YBCO-Coated Conductors
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MOCVD-Based
YBCO-Coated Conductors
V. Selvamanickam, Y. Xie, J. Reeves, and Y. Chen Abstract Metalorganic chemical vapor deposition (MOCVD) is a well-developed deposition process that shows great promise for scaling up the production of high-temperature superconductors (HTSs) to quickly fabricate useful lengths of superconducting tapes and wires. The primary advantage of MOCVD is its potential for high tape throughput, a key factor in determining the cost of second-generation HTS tapes. This article details progress in long-length HTS tape fabrication, high-throughput processing, and techniques to improve critical current levels in high magnetic fields. Keywords: metalorganic chemical vapor deposition, high-temperature superconductors, MOCVD, thin films, YBCO-coated conductors.
Introduction The widespread use of coated hightemperature superconductors (HTSs) in electric power applications depends in a great part on the achievement of a lowcost method of fabrication. Since capital equipment for coated conductor manufacturing is expensive, it is important to achieve large-volume production for a given equipment base in order to reduce the unit cost of HTSs. Large-volume production is possible only if high throughput is achievable. High-performance conductors in practical 4 mm widths will require thick-film HTS coatings on the order of few micrometers, which is about an order of magnitude thicker than the buffer films. As such, the overall throughput in processing coated conductors is dependent on the deposition of the HTS layer. Among the techniques that are being currently pursued for depositing the HTS layer of coated conductors, metalorganic chemical vapor deposition (MOCVD) has the potential for the highest throughput. In MOCVD, cationic organic molecules in the HTS layer are vaporized and transported to a reactor where they are injected onto a heated substrate. Throughput is determined by the size of the deposition area and the deposition rate. Deposition rates as high as 15 nm/s have been demonstrated by MOCVD with a performance level, in terms of critical current density
MRS BULLETIN/AUGUST 2004
(Jc), of 1 MA/cm2.1 In MOCVD, the deposition area can be as long and as wide as the showerhead, which is essentially unlimited; for our application, the deposition zone is projected to be a maximum of 10 m. In addition to high throughput, MOCVD provides a number of advantages, including simple refill of precursors (which are maintained outside the vacuum chamber), double-sided coating (non-line-of-sight coating), and the ability to modify film composition continuously during growth. Even complex multilayer structures such as YBCO/RE-BCO/YBCO/RE-BCO/YBCO (YBCO yttrium barium copper oxide, RE rare earth) can be readily deposited in a single run using a multizone showerhead. Similarly, layered structures with modulated doping can be easily processed with the multizone showerhead technique. Recognizing these advantages, SuperPower Inc. (Schenectady, N.Y.) has been pursuing an MOCVD technique to scale-up coated cond
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