Method of producing bismuth layered compound

Details Method of producing bismuth layered compound Method of producing bismuth layered compound

1999-08-09

2001-06-26

Bos, Steven (Department: 1754)

Chemistry of inorganic compounds

Oxygen or compound thereof

Metal containing

C423S126000, C423S255000

Reexamination Certificate

active

06251360

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of producing a bismuth layered compound for use in an electronic device such as a ferroelectric memory, for example.
2. Description of the Related Art
Bismuth layered compounds including bismuth superconducting oxides having a critical temperature of 110 K and ferroelectric memory materials play a very important role in industrial applications. For applying such bismuth layered compounds to electronic devices, it is necessary to develop a thin-film fabrication process for those bismuth layered compounds.
The structure of a bismuth layered compound, e.g., Bi
2
PbNb
2
O
9
, is of a pseudo tetragonal system having a columnar shape extending in the direction of a c-axis. It has a repetitive structure comprising layers of a bismuth oxide and oxides of other elements which are laminated in a certain sequence (see G. A. SMOLENSKII et al., SOVIET PHYSICS—SOLID STATE, p. 651-655 (1961) and E. C. SUBBARAO, J. Phys. Chem. Solids Pergamon Press. Vol. 23, p. 665-676 (1972)).
In the repetitive structure, the number of bismuth oxide layers in one unit structure and the length of the unit structure vary from bismuth layered compound to bismuth layered compound.
Attempts to apply such bismuth layered compounds to electronic devices have been made in the art. According to one of the efforts, a thin film of a bismuth layered compound which exhibits good ferroelectric properties is produced by a spin coating process such as a MOD (Metal Organic Deposition) process.
However, the spin coating process fails to meet requirements for clean environments that are to be established in the actual semiconductor fabrication process.
For the above reasons, there has been a need for a new thin-film fabrication process for manufacturing a thin film of a bismuth layered compound. To make a thin film of an oxide, however, it is difficult to rely on oxidization carried out by an ultrahigh vacuum process such as molecular beam epitaxy or laser ablation. The application of the MOCVD (Metal Organic Chemical Vapor Deposition) process which is widely used for semiconductor fabrication has encountered obstacles because a hydrogen gas cannot be used as a carrier and a good source material is not available.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a method of producing a bismuth layered compound which has good crystalline properties and good electric properties.
According to the present invention, there is provided a method of producing a bismuth layered compound comprising the step of heating a compound of fluorite structure as a precursor into a bismuth layered compound.
The bismuth layered compound thus produced has good crystalline properties and good electric properties.
Specifically, a compound of fluorite structure as a precursor is produced by a deposition process, and the precursor is heated by a oxidizing and crystallizing process, i.e., a hot annealing process, in an oxidizing atmosphere.


REFERENCES:
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patent: 5935549 (1999-08-01), Ami et al.
patent: 5976624 (1999-11-01), Ami et al.
Atsuki, et al., “Preparation of Bi-Based Ferroelectric Thin Films by Sol-Gel Method” Jpn. J. Appl. Phys. vol. 34, pp.5096-9, Sep. 1995.

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