This invention relates to biaxially textured metal oxide buffer layer on metal substrates. More specifically, the invention relates to a non-vacuum process for depositing single epitaxial films of rare-earth oxides on metal substrates.
Biaxially textured metal oxide buffer layers on metal substrates are potentially useful in electronic devices where an electronically active layer is deposited on the buffer layer. The electronically active layer may be a superconductor, a semiconductor, or a ferroelectric material.
For example, the next generation of superconducting wire to be used for power transmission lines will have a multi-layer composition. Such deposited conductor systems consist of a metal substrate, buffer layer, and a superconducting layer. The metal substrate, such as Ni, Ag, or Ni alloys, provides flexibility and support for the wire. Metal oxide buffer layers, such as cerium oxide (CeO2), or yttria-stabilized zirconia (YSZ), comprise the next layer and serve as chemical barriers between the metal substrate and the top layer, the high-temperature superconductor.
For a superconducting film to carry a high current, a certain degree of alignment between grains of the superconductor is required. Most preferably, the grains should be aligned both perpendicular to the plane of the substrate (c-axis oriented) and parallel to the plane of the substrate (a-b alignment). To achieve this alignment, high Tc superconductors have generally been deposited on (100) oriented single-crystal oxide substrates. However, single-crystal substrates are generally too expensive and have poor mechanical properties. As such, single-crystal substrates are presently unsuitable as practical conductors.
A method to develop practical coated conductors is disclosed in U.S. Pat. No. 5,741,377 (""377) by Goyal et al. This method called RABiTs, short for rolling assisted biaxially textured substrates, uses roll-texturing of metal to form a metallic tape with a {100} less than 001 greater than  cubic structure. However, if the metal is nickel or a nickel alloy, a buffer layer between the metal substrate and the ceramic superconductor is necessary to prevent interdiffusion of the ceramic superconductor and the metal substrate and also to prevent the oxidation of nickel substrate during the deposition of the superconducting layer. Useful buffer layers include cerium oxide, yttrium stabilized zirconia (YSZ), strontium titanium oxide, rare-earth aluminates and various rare-earth oxides.
To achieve high critical current densities, it is important that the biaxial orientation be transferred from the substrate to the superconducting material. As stated, a biaxially textured metal substrate can be provided by the method disclosed in the ""377 patent. The conventional processes that are currently being used to grow buffer layers on metal substrates and achieve this transfer of texture are vacuum processes such as pulsed laser deposition, sputtering, and electron beam evaporation. Researchers have recently used such techniques to grow biaxially textured YBa2CU3Ox (YBCO) films on metal substrate/buffer layer samples that have yielded critical current densities (Jc) between 700,000 and 106 A/cm2 at 77xc2x0 K. (A. Goyal, et al., xe2x80x9cMaterials Research Society Spring Meeting, San Francisco, Calif., 1996; X. D. Wu, et al., Appl. Phys. Lett. 67:2397, 1995). One drawback of such vacuum processes is the difficulty of coating long or irregularly shaped substrates, and the long reaction times and relatively high temperatures required.
A further consideration during the fabrication process is the undesirable oxidation of the metal substrate (for example, when using Ni). If the Ni begins to oxidize, the resulting NiO will likely to grow in the (111) orientation regardless of the orientation of the Ni (J. V. Cathcart, et al., J. Electrochem. Soc. 116:664, 1969). This (111) NiO orientation adversely affects the growth of biaxially textured layers and will be transferred, despite the substrate""s original orientation, to the following layers.
For producing high current YBCO conductors on {100} less than 001 greater than  textured Ni substrates, high quality buffer layers are necessary. Buffer layers such as CeO2 and YSZ have previously been deposited using pulsed laser ablation, e-beam evaporation, and sputtering. In addition, solution techniques have been used to deposit films of rare-earth aluminates on biaxially textured nickel substrates. However, the rare-earth aluminates had c-axis alignment but has always given a mixture of two epitaxies (100) [001] and (100) [011]. This is a structure believed to be unsuitable for growth of high critical current YBCO films.
It is an object of the invention to provide a new and improved method for fabricating alloy and laminated structures having epitaxial texture.
It is another object of the invention to provide a method to produce epitaxial superconductors on metal alloys and laminated structures having epitaxial texture.
It is yet another object of the invention to provide a non-vacuum process to produce epitaxial buffer layers on metal substrates.
It is a further object of the invention to provide a process for growing rare-earth oxide buffer layers with single in-plane epitaxy.
Another object of the invention is to provide an epitaxial textured laminate using rare-earth oxides.
Still another object of the invention is to provide an epitaxial textured superconducting structure having a Jc of greater than 100,000 A/cm2 at 77 K, and self-field.
Yet another object of the invention is to provide a solution process for producing single cube oriented oxide buffer layers, such as cerium oxide.
These and other objects of the invention are achieved by the subject method and product.
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