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Lattice Matched Thin Film Substrates for the Growth of Oxide Films

IP.com Disclosure Number: IPCOM000108517D
Original Publication Date: 1992-Jun-01
Included in the Prior Art Database: 2005-Mar-22
Document File: 1 page(s) / 46K

Publishing Venue

IBM

Related People

Gupta, A: AUTHOR [+2]

Abstract

The growth of high quality thin films of superconducting oxides requires high quality substrates whose lattice constants should ideally be perfectly matched to those of the film. In reality, it is difficult, if not impossible, to satisfy this criterion. For example, the "best" substrates available for the growth of YBa2Cu3O7 are SrTiO3, LaAlO3 and NdGaO3. Although these give films of reasonable quality, the mismatch of symmetry and lattice constants at the film/substrate interface causes strain-induced defect formation.

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Lattice Matched Thin Film Substrates for the Growth of Oxide Films

       The growth of high quality thin films of superconducting
oxides requires high quality substrates whose lattice constants
should ideally be perfectly matched to those of the film.  In
reality, it is difficult, if not impossible, to satisfy this
criterion.  For example, the "best" substrates available for the
growth of YBa2Cu3O7 are SrTiO3, LaAlO3 and NdGaO3.  Although these
give films of reasonable quality, the mismatch of symmetry and
lattice constants at the film/substrate interface causes
strain-induced defect formation.

      Disclosed is a solution in the form of thin film substrate
layers grown on top of the commonly used substrate materials. For
example, by growing SrTiO3 thin film layers with increasing
concentration of barium, the lattice parameter of the (Sr,Ba)TiO3
solid solution can be adjusted continuously between 3.905 o (SrTiO3)
and 4.01 Ao (BaTiO3). Similarly, the lattice constant can be
continuously reduced to 3.83 o by creating solid solutions of SrTiO3
and NdMnO3 . A graded composition leading to the desired lattice
parameter will prevent build up of excess strain in the layers that
can cause formation of dislocations or other defects.

      The graded composition films can be produced by controlled
growth using a variety of deposition techniques, including
sputtering, evaporation, laser ablation, etc. Many different
compositions and structure types can be deposited...