Organic compounds -- part of the class 532-570 series – Organic compounds – Heavy metal containing
Reexamination Certificate
2001-11-09
2004-02-03
Nazario-Gonzalez, Porfirio (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Heavy metal containing
C556S001000, C556S042000, C556S044000, C556S051000, C556S054000, C556S055000, C556S077000, C556S078000, C556S105000, C556S106000, C556S442000, C556S482000, C534S016000, C423S593100, C252S182300
Reexamination Certificate
active
06686489
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to metal oxides useful in making transparent electrodes and conductive layers, protective layers for such conductive layers and dielectric layers in flat panel displays, fluorescent lamps and other electrooptical devices, and more particularly to liquid precursors for making such transparent metal oxides and methods for making such precursors.
2. Statement of the Problem
A typical fluorescent lamp comprises a cylindrical glass tube or envelope containing mercury vapor and a phosphor layer covering the inside of the tube wall. Many fluorescent lamps, in particular rapid-start fluorescent lamps, usually comprise one or more transparent metal oxide layers; for example, an electrically conductive metal oxide layer on the inner surface of the glass tube, and a metal oxide protective layer between the conductive layer and the phosphor layer of the lamp.
A conventional technique of the art of forming transparent metal oxide layers in fluorescent lamps involves: dispersing a solid powder of the desired oxide in a liquid medium to make a colloidal suspension of the oxide; applying a coating of the suspension onto a surface of the lamp; and drying the coating to form the oxide layer. Generally, it is difficult to achieve a uniform, continuous thin film by applying a colloidal suspension of powdered particles. Another technique involves dissolving a precursor compound in a solvent and spraying the precursor solution onto a hot surface having a temperature above the crystallization temperature of the desired oxide, whereby the precursor compound is immediately pyrolyzed. A typical conventional precursor for a conductive layer contains tin tetrachloride, SnCl
4
, and hydrogen fluoride, HF, in butanol. The chlorine and fluorine are highly electronegative, salt-forming atoms that may lead to lamp defects called “measles”, as described below. Further, highly reactive precursor compounds such as SnCl
4
and HF are toxic and difficult to handle, and do not store well.
It is known in the flourescent lamp art to employ a protective layer of aluminum oxide, often called alumina, or certain other metal oxides, such as oxides of cerium, yttrium, titanium, and zirconium to inhibit or delay discoloration and other appearance defects in the phosphor layer or the conductive oxide layer. Silicon oxide, often referred to as silica, may also be included in a protective layer. These barrier layers of the prior art are located between the conductive oxide layer and the phosphor layer. The advantages of the protective coating are probably a result of the relatively nonporous metal oxide coating that protects the conductive oxide layer from ion bombardment resulting from arc discharge. The protective layer is generally formed utilizing an aqueous colloidal suspension or a dispersion of the metal oxide in a liquid. As indicated above, it is difficult to deposit a continuous solid layer using a colloidal suspension or dispersion. Another typical conventional precursor for a protective layer is a metal alkyl compound in a solvent, which is pyrolyzed. It is generally difficult to form a uniform, continuous metal oxide thin film by the conventional pyrolysis method of the prior art because pyrolysis of the sprayed precursor compound on the hot substrate results in a broken, uneven surface on the microscopic level.
Flat panel displays typically comprise one or more layers of transparent metal oxide thin films. Transparent conductive metal oxide thin films commonly serve as electrodes between the light source and the viewing surface to assist in establishing electric fields for operating the display. It is usual for thousands of metal oxide electrodes to be formed. The electrodes must necessarily be transparent so that they do not interfere with the intensity and quality of the light images produced for display. A flat panel display often also comprises one or more transparent nonconductive metal oxide thin films that serve as insulators or protective coatings in the display. These metal oxide thin films are typically deposited using sputtering techniques that are complex and unreliable. Conventional deposition techniques often result in problems, such as poor adherence of the thin films to their substrate and “pinhole” defects in the deposited thin film.
SOLUTION
The present invention provides novel precursors for forming transparent metal oxide thin film layers in a fluorescent lamp, a flat panel display or other electrooptical device. In particular, the invention provides novel nonaqueous metal organic liquid precursor solutions (“liquid precursors”) and methods of making such precursors.
In one embodiment, the invention provides a novel liquid precursor for forming a transparent, electrically conductive metal oxide thin film layer (“conductive layer”), which may be used, for example, in a fluorescent lamp.
The invention further provides a novel liquid precursor for forming an electrically nonconductive metal oxide protective layer (“protective layer”), which may be used, for example, between the phosphor layer and the conductive layer of a fluorescent lamp. The inventive metal organic precursors may be used to fabricate a wide variety of metal oxide thin film layers.
The invention further provides a novel liquid precursor for forming an electrically conductive metal oxide thin film as a transparent electrode in a flat panel display.
A nonaqueous metal organic liquid precursor solution (“liquid precursor”) of the invention is usually applied to a substrate surface using a liquid source deposition technique. The liquid precursor contains one or more metal organic precursor compounds that lead to formation of the desired metal oxide thin film layer upon reaction and crystallization on the substrate surface. Usually, the desired oxide is a metal oxide; therefore, the liquid precursor usually contains a metal organic precursor compound. The oxide formed by the inventive liquid precursor may also be a nonmetallic oxide, such as silicon oxide, in which case the organic precursor compound of the liquid precursor is also nonmetallic. An inventive liquid precursor is a solution of one or more organic compounds dissolved in a nonaqueous solvent. The precursor is applied to the substrate surface and treated, usually by one or more heating techniques. As a result, the organic precursor compound or compounds react to form a solid thin film having the desired composition on the substrate surface. In the fabrication of a fluorescent lamp, the lamp envelope may be dipped or rolled in liquid precursor to form a liquid coating of precursor, which is then treated; the liquid precursor solution may also be applied using a conventional liquid spraying method, as known in the fluorescent lamp art. In the fabrication of flat panel displays, fluorescent lamps and other electrooptical devices, the liquid precursor is often applied by a liquid misted deposition method, in which a very fine mist of liquid particles is formed in a carrier gas and deposited on the substrate surface.
A nonaqueous metal organic liquid precursor solution of the invention comprises an organic precursor compound containing a first metal selected from the group including tin, antimony, indium, niobium, tantalum, bismuth, cerium, yttrium, titanium, zirconium, hafnium, and silicon. In one embodiment, the first metal is selected from the group consisting of tin, antimony, indium to make a conductive metal oxide material that may include SnO
2
, Sb
2
O
3
, and In
2
O
3
. In this embodiment, the liquid precursor preferably further comprises an organic dopant precursor compound containing a metal selected from the group including niobium, tantalum, bismuth, cerium, yttrium, titanium, zirconium, hafnium, silicon, zinc and magnesium. In another embodiment of the invention, the liquid precursor comprises an organic precursor compound containing a metal selected from the group including cerium, yttrium, titanium, zirconium, hafnium, silicon, niobium, tantalum, and bismuth. Thus, the liquid precurso
Bacon Jeffrey W.
Celinska Jolanta
Cuchiaro Joseph D.
McMillan Larry D.
Paz de Araujo Carlos A.
Nazario-Gonzalez Porfirio
Patton & Boggs LLP
Symetrix Corporation
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