Organic compounds -- part of the class 532-570 series – Organic compounds – Heavy metal containing
Reexamination Certificate
1999-09-13
2001-11-13
Nazario-Gonzalez, Porfirio (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Heavy metal containing
C556S001000, C556S044000, C556S055000, C427S126300, C423S608000, C423S617000, C423S618000
Reexamination Certificate
active
06316651
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an improved process for fabricating Group II and Group IV or V ceramic materials, such as barium strontium titanate, and devices made therefrom via metallo-organic decomposition methods.
BACKGROUND ART
Barium strontium titanate (BST), which is an oxide ceramic, has a high dielectric constant and excellent ferroelectric and paraelectric properties. As a result, BST is extensively used in the electronics industry for dynamic random access memory (DRAM), ferroelectric, and paraelectric devices and in other applications where a high dielectric constant material is useful.
Applicant Ser. No. 09/300,962, filed Apr. 28, 1999, entitled “Voltage Variable Capacitor (Varactor) for High Frequency Power” describes a BST varactor and its application. The BST varactor was made using 2-ethylhexanoate acid salts.
Thin films of barium strontium titanate have been extensively studied for application in high density dynamic random access memories, monolithic microwave integrated circuit capacitors, tunable microwave filters, and phased array antennae.
Thin films of BST from 2-ethylhexanoate acid salts are also described in U.S. Pat. No. 5,514,822.
The synthesis of thin film ceramic from metal organic acid salts (most usually aliphatic acids such as neodeacanoic or 2-ethylhexanoic) is described in the above-referenced application Ser. No. 09/300,962; application Ser. No. 08/863,117, filed May 27, 1997, entitled “Process for Making Stoichiometric Mixed Metal Oxide Films”; Mantese, Micheli, Hamdi and West in MRS Bulletin, 1989, pp. 48-53; PCT Publication WO 93/12538 (Applicant: Symetrix Corporation); U.S. Pat. Nos. 5,434,102 and 5,439,845, issued to H. Watanabe et al; and C. M. Vest et al,
Materials Research Society Symposium,
Vol. 60 pp. 35-42 (1986).
The use of anhydride of 2-ethylhexanoic acid to better control the reaction of metal alkoxides to metal salts is disclosed and claimed in U.S. Pat. No. 5,721,009, issued Feb. 24, 1998.
Many of the foregoing references, while providing improved synthetic routes for preparing barium strontium titanate, nevertheless use solvents, such as xylenes and n-butyl acetate, that are toxic or not environmentally friendly.
A review of the need for environmentally benign ceramic precursors and the alumina precursor made from 3,6-dioxaheptanoic acid and an alumina mineral (Group III precursor) is described in “Aqueous Synthesis of Water-Soluble Alumoxanes: Environmentally Benign Precursors to Alumina and Alumina Based Ceramics”,
Chemical Materials,
Vol. 9, No. 11, pp. 2418-2433 (1997).
A paper by A. M. Bahl et al, “Heavy Alkaline Earth Polyether Carboxylates”,
Inorganic Chemistry,
Vol. 36, pp. 5413-5415 (1997) describes the synthesis of barium and strontium oxyacid complexes from the metal hydroxides. The reaction is long and produces water as a by-product, which may not be desired for some applications. The present invention provides for an anhydrous method to produce these compounds.
In a related patent application, “Polyether Acid Anhydride Useful for Improved Non-Toxic Solvent Soluble Group IV and V Metal Acid Salt Complexes”, the titanium salt of 3,6-dioxaheptanoic acid is described; see, application Ser. No. 09/307,589, filed on May 7, 1999.
Thus, there is a need for providing improved quality Group II and Group IV or Group V metal oxide films, such as BST films, with less toxic solvents.
DISCLOSURE OF INVENTION
The present invention is directed to the synthesis, processing and test of improved Group II and Group IV or Group V metal spin-on precursor materials, such as barium strontium titanate (BST), useful for making thin films of oxides of these metals. BST is an oxide ceramic extensively used for DRAM, ferroelectric, paraelectric and in applications where a high dielectric constant material is useful. The present invention provides for a soluble spin-on precursor which is compatible and soluble in non-toxic and environmentally benign solvents. In addition, this spin-on precursor material has been shown to give much improved electrical performance properties of the BST thin films produced.
In accordance with the present invention, metal acid salt complexes are provided comprising (1) a first metal comprising at least one Group II ion and at least one second metal selected from the group consisting of Group IV and Group V ions and (2) a polyether acid. The metal acid salt complexes are prepared by combining (1) at least one first metal and at least one second metal ion and (2) at least one of a polyether acid and a polyether acid anhydride. Solutions of these metal acid salt complexes in water and/or an alchol and/or other polar solvents are also provided, useful in the preparation of the metal oxide films.
Specifically, in accordance with the present invention, a method is provided for fabricating electronic devices employing Group II-Group IV (or Group V) oxide as the active device. The method comprises:
(a) providing a substrate;
(b) forming a bottom electrode on the substrate;
(c) depositing a solution comprising polyether acid salts of the Group II-Group IV (or Group V) metal ion on the bottom electrode;
(d) forming an oxide film from the solution; and
(e) forming a top electrode on the oxide film.
The present invention is directed to the formation of improved electronic devices from less toxic and easier handled precursors and solvents.
REFERENCES:
patent: 5434102 (1995-07-01), Watanabe et al.
patent: 5439845 (1995-08-01), Watanabe et al.
patent: 5514822 (1996-05-01), Scott et al.
patent: 5721009 (1998-02-01), Dougherty et al.
patent: 6054600 (2000-04-01), Dougherty et al.
patent: WO93/12538 (1993-06-01), None
J.V. Mantese et al, “Metalorganic Deposition (MOD): A Nonvacuum, Spin-on, Liquid-Based, Thin Film Method”,MRS Bulletin, pp. 48-53 (Oct. 1989).
C.M. Vest et al, “Synthesis of Metallo-Organic Compounds for MOD Powders and Films”,Materials Research Society Symposium, vol. 60, pp. 35-42 (1986).
Callender et al, “Aqueous Synthesis of Water-Soluble Alumoxanes: Environmentally Benign Precursors to Alumina and Alumina Based Ceramics”,Chemical Materials, vol. 9, No. 11, pp. 2418-2433 (1997).
A.M. Bahl et al, “Heavy Alkaline Earth Polyether Carboxylates”,Inorganic Chemistry, vol. 36, pp. 5413-5415 (1997).
Dougherty T. Kirk
Drab John J.
Alkov Leonard A.
Lenzen, Jr. Glenn H.
Nazario-Gonzalez Porfirio
Raufer Colin M.
Raytheon Company
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