Stock material or miscellaneous articles – Structurally defined web or sheet – Continuous and nonuniform or irregular surface on layer or...
Reexamination Certificate
1998-11-12
2001-02-20
Speer, Timothy M. (Department: 1775)
Stock material or miscellaneous articles
Structurally defined web or sheet
Continuous and nonuniform or irregular surface on layer or...
C428S469000, C428S471000, C428S472000, C428S692100, C428S698000, C428S701000, C428S702000
Reexamination Certificate
active
06190752
ABSTRACT:
BRIEF DESCRIPTION OF THE INVENTION
This invention relates generally to thin films. More particularly, this invention relates to thin oxide films of the type having a rock-salt-like structure, deposited on amorphous surfaces with substantially in-plane alignment as well as substantially out-of-plane alignment.
BACKGROUND OF THE INVENTION
There are an increasing number of thin film and thick film materials which, in their application to devices of all types, depend on properties dependent on their anisotropic physical properties, or which require low-angle grain boundaries between grains. Thus, these materials must be deposited in special orientations in order to utilize their properties. The present method of achieving this is to epitaxially deposit onto carefully selected single crystal substrates with matching lattice constants and chemical compatibility.
Ion beam assisted deposition (IBAD) has shown promise as means to produce textured films on non-epitaxial substrates that can then subsequently be used as a structural template for the deposition of other films, eliminating the requirement of single crystalline substrates. The material commonly used has been (100)-oriented Yttria-Stabilized-Zirconia (YSZ). However, the texturing of (100) YSZ evolves slowly, so a thick film (>0.5 &mgr;m) is required to achieve good in-plane alignment (~13°), limiting the application of YSZ due to high processing time and cost. Other materials, characterized by rock salt and rock salt-like structures, have been considered potentially advantageous for use as templates for forming well textured layers such as superconducting films due to their simple crystal lattice which tends to naturally align with a preferred surface for subsequent growth of textured films {(001) type sheet axis}. Rock salt structures tend to have a reasonable lattice match with films such as YBCO and PZT which make them attractive for a variety of electronic and electrical applications. In addition, the simple chemistry of these structures makes them easier to process than the more complex multi-cation structures. By “rock-salt material” is meant a structure having a cF8 Pearson symbol and a B1 Sturukturbericht designation. Typical rock salt materials are described, for example, by “Metals Handbook, Ninth Edition”, volume 9, p707-711, which pages are herein incorporated in their entirety by reference , and by C. S. Barrett and T. B. Massalski, “Structure of Metals”, McGrawHill, 3rd edition, 1966, p.240-241, which pages are herein incorporated in their entirety by reference. Exemplary rock salt materials include CaO, SrO, TiN, ZrO, and BaO. By “rock-salt-like material” is meant a material with a crystalline structure with atomic arrangements identical to or similar to that in rock-salt, such as cubic structures with (100) close-packed planes or cubic structures in which a part of the lattice (some planes) has the same atomic arrangement as in rock-salt. Examples, in addition to rock salt materials, are rock-salt superstructure B1, cubic superlattice LI
2
spinel superlattice H1
1
, and perovskites & perovskite superstructures E2
1
. Exemplary compounds with rock-salt superstructure B1 are LiNiO
2
, and LiInO
2
. Typical cubic superlattice LI
2
compounds are Ni
3
Al, Au
3
Cu, AlZr
3
, etc. Typical spinet superlattice H1
1
compounds are MgAl
2
O
4
, and &ggr;-Al
2
O
3
. Typical perovskites & perovskite superstructures E2
1
compounds are SrTiO
3
, CaTiO
3
, NdGaO
3
, LaAlO
3
, SrZrO
3
, BaZrO
3
, and SrRuO
3
. However, at present, these materials are typically used either in expensive single crystal forms or as epitaxially grown films which must be produced upon substrates which themselves exhibit a biaxially textured surface.
OBJECTS AND SUMMARY OF THE INVENTION
It is a general object of the present invention to provide an improved technique for producing textured films of materials having a rock-salt structure on amorphous substrates.
It is another object of the present invention to provide a technique for producing textured films having a rock salt-like structure on amorphous substrates.
It is a further object of the present invention to provide an economical method of producing textured films on an amorphous substrate.
It is a further object of the present invention to provide an economical thin film buffer layer for the deposition of high temperature superconductor material.
The present invention provides a method of forming textured thin films having a rock-salt-like structure on an amorphous surface employing ion beam assisted deposition of the thin film material and a method of forming composite articles including multiple film layers having substantial alignment both in-plane and out-of-plane.
In one aspect, the invention is a method of forming a composite article by forming a buffer layer including a first thin film formed on a smooth amorphous surface of a substrate from a material having a rock-salt-like structure and substantial alignment both in-plane and out-of-plane, and forming a second film having substantial alignment both in-plane and out-of-plane on a surface of said buffer layer, wherein said first film provides a template for the epitaxial growth of said second film. The first thin film is formed by ion-beam assisted deposition of the rock-salt-like material under first conditions of temperature, rock-salt-like material evaporation rate, ion energy and flux selected to promote formation of in-plane aligned crystallites of the rock-salt-like material on the smooth amorphous surface at the nucleation stage of film formation and subsequent pseudo-columnar growth of columns of the crystallites, resulting in substantial alignment both in-plane and out-of-plane.
Typically, the ion beam assistance is ended after the thickness of said first film is such that said smooth amorphous surface is substantially covered with said in-plane aligned crystallites and before the thickness of said first film is about twice the thickness at which said surface is substantially covered with said in-plane aligned crystallites. In one aspect, a homo-epitaxial layer of the rock salt-like material is then formed on the surface of the first film by deposition of the same rock salt-like material under second conditions of temperature and rock salt-like material evaporation rate which are elevated in relation to the first conditions to increase the thickness of the buffer layer. The first film provides a template for the epitaxial growth of the homoepitaxial layer. In other aspects, the method may include formation of additional buffer layer films of additional materials deposited after formation of the first film, and the first film will provide a template for the epitaxial growth of the these films.
In another aspect, the invention features an article, including a substrate with at least one smooth amorphous surface, a buffer layer comprising a first thin film formed on said smooth amorphous surface of said substrate from a material having a rock-salt-like structure, and a second film formed on a surface of said buffer layer. The first film has substantial alignment both in-plane and out-of-plane; and provides a template for the epitaxial growth of the second film. The second film may be formed from a material selected from the group consisting of superconductors, semiconductors, photovoltaic materials, magnetic materials, and precursors of superconductors. Typically, the RMS of the smooth amorphous surface is less than about 100 angstroms.
In some aspects, the entire substrate is amorphous, as for example, Metglas or &agr;-Si
3
N
4
. In other aspects, the substrate is a polycrystalline non-amorphous base structure with a smooth amorphous surface layer. In some aspects, this layer may be chemically identical to the base structure. For example, polycrystalline Ni in some forms is an intrinsically an ordered structure with an amorphous surface. The desired amorphous surface may also be created, for example, by laser glazing, ion damage, or high rate mechanical deformation. In other aspects, the layer is not chemically i
Do Khiem B.
Geballe Theodore H.
Hammond Robert H.
Wang Pin-Chin Connie
Board of Trustees of the Leland Stanford Junior University
Fish & Richardson P.C.
Speer Timothy M.
Young Bryant
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