WO2003031362A1

WO2003031362A1 - Coated glass for use in displays and other electronic devices

Info

Publication number: WO2003031362A1
Application number: PCT/US2002/031821
Authority: WO
Inventors: Scott Kisting; Paul J. O'connor
Original assignee: Dow Global Technologies Inc.
Priority date: 2001-10-05
Filing date: 2002-10-04
Publication date: 2003-04-17

Abstract

This invention is a method for preventing diffusion of small, monovalent metal ions out of a substrate which contains such ions comprising plasma enhanced chemical vapor depositing a carbon modified metal oxide layer onto the substrate at a temperature of less than about 550 °C, preferably at temperatures less than 500 °C, and more preferably less than about 400 °C wherein the carbon modified metal oxide comprises Me, O, C, and H covalently bonded to one another, where Me is selected from Silicon, Titanium, and Cerium; the mole ration of O to Me is 1:1 to 2.4:1; the mole ratio of C to Me is 0.1:1 to 4.5:1; and the mole ratio of H to Me is 0:1 to 8:1. This invention is also an electroactive display device comprising a sodium containing glass substrate with the carbon modified metal oxide layer as a protective inner coating.

Description

COATED GLASS FOR USE IN DISPLAYS AND OTHER ELECTRONIC DEVICES

This invention relates to coated glass substrates for use in electronics and to electronic devices made with such coated glass. Liquid crystal flat panel displays are commonly made by sandwiching electroactive layers - transparent electrodes and liquid crystal polymers - between two glass substrates. Other layers such as color filters and polarizers are also typically utilized in these displays. Other electronic display devices, such as electrochromic devices and organic small molecule or polymeric light emitting devices may also use an electronically active material located under a glass substrate and transparent electrode.

In making the liquid crystal displays, particularly active matrix displays, glass which is low in sodium is used because the sodium is harmful to the reliability of the display when thin film devices, such as diodes or transistors, are employed. See, for example, U.S. Patent 6,216,491B1. If soda lime glass is used an SiO₂ coating may be applied. The SiO₂ coating is most often applied by dip coating the glass with a siloxane and heating to burn off the organic part of the siloxane. However, CVD coating may also be used. See O'Mara, Liquid Crystal Flat Panel Displays, pages 58-70 and 113-114, Nan Νostrand Reinhold, 1993. While these approaches to avoiding sodium contamination to the electronic devices is helpful, some sodium migration nevertheless occurs. In U.S. Patents 4,828,880 and 4,995,893, Jenkins et al. teach the application of a barrier layer by thermal pyrolysis of a gaseous mixture of a silane, an unsaturated hydrocarbon and an oxygen containing gas on a hot glass surface at temperatures of 600 to 750°C. These barrier layers were said to prevent alkali metal ion migration and/or suppress irridescence in the end coated article. The underlayers made by this technique have a relatively high index of refraction - greater than 1.6.

Plastic substrates have also been considered as possible transparent substrates for liquid crystal displays. However, such substrates may be less than satisfactory due to insufficient resistance to abrasion and to diffusion through the substrate of chemicals to which the device may be exposed during manufacture or use. Thus, U.S. Patent 5,718,967 taught use of a plasma enhanced chemical vapor deposited (PECND) organosilicon as a protective layer. An optional SiO_x layer applied over the protective organosilicon layer was also mentioned.

Similar PECND coatings to those discussed in U.S. Patent 5,718,967 were examined for their effectiveness in preventing migration of large multi-valent ions such as lead (Pb ) and cadmium (Cd^"1-1") from leaded crystal and from ceramic articles.

Applicants have discovered that carbon modified metal oxide layers deposited from relatively low temperature PECND processes are effective barriers to small, monovalent metal ions (particularly Νa⁺) even though these layers may be less dense than the materials taught by Jenkins. Such coatings will render relatively inexpensive glass more suitable for use in applications where the presence of sodium ions may be detrimental and even improves the performance of low sodium containing glass such as aluminoborosilicate.

Thus, according to a first embodiment, this invention is a method for preventing diffusion of small, monovalent metal ions out of a substrate which contains such ions comprising plasma enhanced chemical vapor depositing a carbon modified metal oxide layer onto the substrate at a temperature of less than about 550°C, preferably at temperatures less than 500°C, and more preferably less than about 400°C wherein the carbon modified metal oxide comprises Me, O, C, and H covalently bonded to one another, where Me is selected from ,. Silicon, Titanium, Tin, Indium, Germanium, and combinations thereof; the mole ratio of O to Me is 1:1 to 2.4:1; the mole ratio of C to Me is 0.1:1 to 4.5:1; and the mole ratio of H to Me is 0:1 to 8:1. The metal oxide may additionally comprise nitrogen at a mole ratio of N to Me of 0: 1 to 1 : 1.

According to another embodiment, this invention is an electronic optical device comprising:

(a) a sodium containing glass substrate having an interior surface and an exterior surface, wherein the interior surface is coated with a protective coating comprising Me, O,

C, and H covalently bonded to one another, where Me is selected from Silicon, Titanium, and Cerium; the mole ratio of O to Me is 1:1 to 2.4:1; the mole ratio of C to Me is 0.1:1 to 4.5:1; and the mole ratio of H to Me is 0:1 to 8:1,

(b) a first transparent electrode adjacent to the protective coating and a second electrode, (c) an electroactive material located between the electrodes. "Electroactive material" as used herein means any material which responds when a voltage is passed between the electrodes.

The substrates used in this invention may be any substrate that contain small, monovalent metal ions either by virtue of these ions inherently being present in the substrate or by virtue of the ions migrating into the substrate during manufacture or use of the substrate. Preferably, the substrate is sodium containing glass.

The carbon modified metal oxide protective coating is applied by plasma enhanced chemical vapor deposition of a starting organometallic compound, preferably an organosilicon, at a power level sufficient to create an interfacial chemical reaction for adhesion and in the presence of a sufficient amount of oxygen containing compounds to give the desired stoichiometry in the end product. The PECVD process occurs at temperatures less than 550°C, preferably less than 500°C, more preferably less than 400°C. The organosilicon starting materials may include silane, siloxane, or a silazane. Examples of silanes include methyl silane, dimethyl silane, trimethyl silane, tetramethyl silane, dimethoxydimethylsilane, methyltrimethoxysilane, tetramethoxysilane, methyltriethoxysilane, diethoxydimethylsilane, methyltriethoxysilane, triethoxyvinylsilane, tetraethoxysilane, dimethoxymethylphenylsilane, phenyltrimethoxysilane, 3- glycidyloxypropyltrimethoxysilane, 3-methacryloxypropyltrimethoxysilane, diethoxymethylphenylsilane, tris(2-methoxyethoxy)vinylsilane, phenyltriethoxysilane, tetraethylorthosilane and dimethoxydiphenylsilane. Examples of siloxanes include tetramethyldisiloxane (TMDSO), tetraethylorthosilicate (TEOS), and hexamethyldisiloxane. Examples of silazanes include hexamethylsilazane and tetramethylsilazane. The stoichiometry of the resultant PECVD applied polymer is preferably:

SiOxCyHz, where x is from about 1 to about 2.4, y is from 0.1 to about 4.5, more preferably about 0.2 to 2.4, and z is from 0 to about 8, more preferably 0 to 4.

Optionally, a multilayered system may be used in which different layers may contain metal oxides or carbon modified metal oxides of different compositions. In one preferred embodiment of such a multilayer system, the layer located closest to the substrate has the highest concentration of carbon and the top or external layer of the multilayer barrier comprises the least carbon and, may in fact contain no carbon atoms. The low carbon layer, in the preferred embodiment the external layer, of the multi-layer barrier may therefore have the preferred formula: SiO1.8-2.4C0.0-0.3H0.0-4.0- third layer, which is higher in carbon content may also be used. A suitable formula for that layer is SiO₁.o-₂.₄Co. - ₄.₅Ho.o-8.o- In one preferred embodiment this high carbon content layer is located closest to the substrate. This latter layer referred to herein as an adhesion layer may be particularly important if adhesion or cushioning of the substrate are important. Each layer may be prepared from the same or different starting materials. The adhesion layer is applied by plasma enhanced chemical vapor deposition

(PECND) preferably of an organosilicon compound. This layer is deposited on the surface of the substrate at a power level sufficient to create an interfacial chemical reaction for adhesion, preferably at a power level from about 5 10 J kg to about 5 x 10 J/kg, and in the substantial absence of oxygen. The thickness of the adhesion promoter layer is application dependent and is preferably not less than about 50 A, more preferably not less than about 500 A, and most preferably not less than about 1000 A, and preferably not more than about 10,000 A, more preferably not more than about 5000 A, and most preferably not more than about 2000 A. Alternatively, adhesion may be enhanced by exposing the substrate to an oxygen containing plasma according to known processes. The polymerized carbon modified metal oxide layer may then be applied to the substrate or to the adhesion layer by PECND of an organometal compound. Again the preferred organosilicon compound starting material may be applied and polymerized in presence of oxygen and preferably at a power density from about 10⁶ J/kg to about 10⁹ J/kg. The thickness of the protective coating for the substrate depends primarily on the properties of the coating as well as the substrate. Preferably, the coating thickness is not less than about 0.01 micron, more preferably not less than about 0.05 micron, and most preferably not less than about 0.1 micron, and not greater than about 10 microns, more preferably not greater than about 5 microns, and most preferably not greater than about 2 microns. The metal oxide or low carbon containing metal oxide layer optionally may be applied. Any known method may be used but preferably it is applied by PECVD of an organometal compound, preferably of an organosilicon compound, in the presence of a stoichiometric excess of oxygen, and at a power density of at least about twice, more preferably at least about four times, and most preferably at least about six times the power density used to form the protective coating layer. This layer is conveniently referred to as an MeO_X; preferably an SiO_x layer. However, the MeO_x layer may also contain hydrogen and carbon atoms (for example, Me O₁.₈-2.₄ C₀._0-o.₃ H ₀.₀-₄.₀)- The thickness of the MeO_x layer is generally less than the thickness of the protective coating layer, and is preferably not less than about 0.01 micron, more preferably not less than about 0.02 micron, and most preferably not less than about 0.05 micron, and preferably not more than about 5 microns, more preferably not more than about 2 microns, and most preferably not more than about 1 micron.

It may be desirable to coat the adhesion promoter layer with alternating layers of the protective coating layer and the MeO_x layer. The ratio of the thicknesses of the protective coating layers and the MeO_x layers are preferably not less than about 1:1, more preferably not less than about 2:1, and preferably not greater than about 10:1, more preferably not greater than about 5:1.

Additional layers may be applied as desired. The term "substantial absence of oxygen" is used herein to mean that the amount of oxygen present in the plasma polymerization process is insufficient to oxidize all the silicon and carbon in the organosilicon compound. Similarly, the term "stoichiometric excess of oxygen" is used herein to mean that the total moles of oxygen present is greater than the total moles of the silicon and carbon in the organosilicon compound. The devices of this invention include organic and polymeric electroluminescent devices, such as are described in U.S. Patent 5,247,190, photodetectors, photodiodes, and photovoltaics, but are most preferably liquid crystal display devices.

If the electroactive material is an opto-electrically active material, that is, a single layer or multi-layer structure which is capable of transporting charge and which emits light when charge is transported through the film and/or generates current when light is incident upon the film, the material may comprise inorganic or organic electroluminescent materials. Suitable organic electroluminescent materials include small organic molecules that have been taught to have electroluminescent properties include those taught by Tang and VanSlyke in U.S. Patent 4,885,221 and by Tang in Information Display, pp. 16-19, Oct. 1996. Polymeric, organic electroluminescent materials (for example, polythiophenes, polyphenylene vinylenes, and polyfluorenes) are also useful. Polymers which are solution processible are most desirable for the ease of manufacture as these can easily be coated out of solution by various known coating methods. Fluorene based polymers are especially preferred. See, for example, U.S. Patents 5,708,130 and 5,728,801; WO97/33193, and WO 00/46321. These devices may or may not have a second substrate in which case the electroactive materials and electrodes are found between the two substrates. The second substrate and the second electrode may or may not be transparent and may be any suitable material as has been taught in the art.

If the device is the preferred liquid crystal display device, the device will comprise two transparent substrates each having an interior and exterior surface; two transparent electrodes of the interior side of the substrates; a color filter array also found on the interior side of one of the substrates which substrate is known as the color filter array substrate; and a liquid crystal material located between the transparent electrodes. Other layers, such as polarizers and compensation films, are typically laminated on the extrerior surface of the color filter array substrate. The device structure may be any structure as known in the art. See, for example, O'Mara, Liquid Crystal Flat Panel Displays, Van Nostrand Reinhold, 1993 for componentry and methods of manufacture of LCD devices. The substrates may be the same or different. As the second substrate may be a substantially sodium free glass, plastic, or a sodium containing glass. On the interior surface of the sodium containing glass substrate the coatings discussed above are added prior to addition of any of the internal layers - that is, color filters, electrodes, etc.

The electrodes for liquid crystal display devices are preferably a transparent conductive material such as indium tin oxide (ITO). When the electrode is made of ITO, the ITO can be vapor deposited onto the protective layer according to normal procedures for depositing ITO onto substrates.

Other applications where coatings such as taught herein would be useful are other areas where alkali ion migration has been identified as a problem including: data storage memory cells (see EP 281140); sodium high pressure discharge lamps (see EP 464083); photochromic cells (see U.S. 5830,252); seals for sodium-sulfur cells (see U.S. 4,341,849); content contamination in containers (see U.S. 5,431,707); loss of mechanical strength of glass (see Kruger in NATO ASI Ser. E 173 (Surf. Interfaces Ceram. Mater.) 725-35, 1989); inorganic coating adhesion loss (see Baird and Haeberle, J. Vac. Sci. Tech. A 4(3, Part 1), 532-535, 1986); and crystal growth modification (Janke et al., in Glass Sci. Technol. (Frankfor/Main) 73(5), 143-155, 2000).

Examples Example 1 The deposition of a highly crosslinked high carbon content silicon-oxide coating of the general formula

was done in a plasma enhanced chemical vapor deposition (PECVD) stainless steel box equipped with a shower head coplanar magnetron electrodes spaced at 25 cm. The soda lime substrate was suspended approximately midway between the electrodes. The substrates were then coated with a 100 to 1000 A thick adhesion layer of plasma polymerized tetramethyldisiloxane (TMDSO). TMDSO was fed into the chamber through the shower head electrode at 16.5 seem. The gas inlet holes of the shower head were evenly distributed on the plasma oval of the magnetron electrode. This configuration of the gas inlet maximizes the decomposition probability of the TMDSO by assuring that the molecules flow through the most intense plasma region. The TMDSO vapor flow was controlled by a Model 1152 MKS Inc. vapor flow controller and the plasma power was supplied by a Advanced Energy power supply (Model PE II). The power loaded to the plasma during deposition of the adhesion promoter was 800 watts (W) at 40 kHz. The chamber base pressure was less than 1 mTorr, the process pressure was approximately 6 mTorr. A second carbon modified silicon-oxide layer was deposited on the adhesion layer by feeding the chamber 40 seem of oxygen (using a Model 1160 MKS gas flow controller) and 50 seem of TMDSO, and was plasma polymerized using 800 W at 40 kHz. The thickness of this layer range between 0.5 and 3 microns. The chamber pressure for this process was approximately 9 mTorr. The empirical formula for this layer was about SΪOUCUHLO. .0 • A third layer, nominally the SiO_x layer, which was plasma polymerized organosilicon compound was deposited on the protective layer using 16.5 seem of TMDSO, 195 seem of oxygen, and loading the plasma with between 1200 and 1800 W at 40 kHz. The thickness of this layer was approximately 300 A . The chamber pressure for this process was approximately 13 mTorr. The empirical formula for this layer was about SiOo.₉Co.₂Ho.₂-₁.o.

Example 2 Sample Preparation All of the glass substrates in this analysis were cut into 11 mm squares for the purpose of analysis. The secondary ion mass spectrometer used to quantitate surface sodium concentration has a sample chuck which accommodates such a sample geometry. Soda lime samples were placed into the plasma enhanced chemical vapor deposition (PECVD) chamber, and the chamber was evacuated to a base pressure not exceeding 1 mTorr. The protective layer was then deposited on the glass as follows. A tetramethyldisiloxane (TMDSO) flow rate of 16.5 standard cubic centimeters per minutes (seem) was established and power was applied to establish the plasma by ramping the power from 0 to 800 Watts over the span of 45 seconds, and maintaining 800 W for an additional 45 seconds. This chemistry was used to establish an adhesion layer for subsequently deposited layers on the substrate. At that point in the process, a flow rate of 40 seem of oxygen (O₂) gas was established, and the TMDSO flow rate was ramped from 16.5 seem to 50 seem over the span of 180 seconds while maintaining an applied power of 800 Watts. This condition was maintained for a total of 60 minutes, establishing an organosilicone layer over the adhesion layer. At this point in the process, the SiO_x layer was deposited by reducing the TMDSO flow rate to 16.5 seem, increasing the O₂ flow rate to 195 seem, and ramping the power to 1500 Watts over the span of approximately 10 seconds. This chemistry was maintained for a total of 3 minutes. At this point, the plasma power was discontinued, gas flows are stopped, the chamber pressure was brought up to atmospheric pressure, and the samples are unloaded for analytical analysis.

Analytical Analysis

In addition to the coated soda lime samples, samples of uncoated soda lime glass and uncoated aluminoborosilicate glass, which is used to manufacture active matrix liquid crystal displays were analyzed Secondary ion mass spectrometry (SIMS) analysis an ions in-ions out technique, which essentially produces a mass spectrum of the top about 15 A of a material surface, was performed. This extreme surface sensitivity and material specificity makes it well-suited to this study. SIMS spectra were acquired using an Ion- ToF IV time of flight secondary ion mass spectrometer under the following analysis conditions (TABLE 1):

TABLE 1 : Instrument analysis conditions

Samples of the soda lime glass coated with the protective coating and the aluminoborosilicate glass were first analyzed at ambient temperature, then removed to the load lock and heated to 100°C for 20 or 40 minutes. Then the samples were reintroduced into the analytical chamber and a different area on the sample surface was analyzed. Approximately 20 minutes later, another spectrum was taken, then the temperature was raised to 200°C and spectra were taken at similar time intervals. The temperature was then raised to 300°C and spectra were taken. The maximum time at 300°C for the first soda lime / protective coating sample was 45 minutes. The maximum time at 300°C for the aluminoborosilicate glass was 2 hours. A second soda lime/protective coating sample was held at 300°C for 4 hours, with spectra taken periodically. As stated in the above table, each signal was an integrated signal count over the span of 5 minutes of data collection. The SIMS data is summarized below (TABLE 2)

Data Analysis

There was an obvious difference in the sodium ion signals detected from the various samples analyzed. In the SIMS technique, the sputtering yield for any particular chemical element is a function of the matrix in which it is contained, so even if the sodium ion concentration was identical on the surface of these two different samples, the detected sodium signal would be different. The effect of the matrix for these samples is likely relatively small since all are glassy materials with similar chemical and mechanical properties. In the opinion of the analyst, the sodium ion sensitivity factor for these surfaces would vary by less than a factor of 10. Thus, for the samples of the soda lime glass with protective coating, sodium levels are statistically significantly lower than the aluminoborosilicate glass, and very significantly lower than for the uncoated soda lime glass.

Conclusion

The protective coatings of this invention on the sodium containing glass significantly reduces the migration of sodium ions from the bulk of the glass. In these samples, the sodium ion levels detected were less than the detection limit for sodium which is estimated to be around 400 counts per 5 minutes sample segment.

Claims

WHAT IS CLAIMED IS:

1. A method for preventing diffusion of small, monovalent metal ions out of a substrate, which substrate contains such ions, comprising plasma enhanced chemical vapor depositing, at a temperature of less than 550°C, an organometallic compound to form a first carbon modified metal oxide layer onto the substrate.

2. The method of claim 1 wherein the small, monovalent metal ions are sodium ions.

3. The method of claim 1 wherein the substrate is soda lime glass.

4. The method of claim 1 wherein the carbon modified metal oxide layer comprises Me, O, C, and H covalently bonded to one another, where Me is selected from Silicon, Titanium, Indium, Tin, Germanium, and combinations thereof; the mole ratio of O to Me is 1:1 to 2.4:1; the mole ratio of C to Me is 0.1:1 to 4.5:1; and the mole ratio of H to Me is 0:1 to 8:1.

5. The method of claim 4 wherein Me is Silicon.

6. The method of claim 4 wherein organometallic compound is an organosilicon compound starting material which is applied and polymerized in presence of excess oxygen and preferably at a power density from 10 J/kg to 10 J/kg to form a carbon modified silicon oxide.

7. The method of claim 6 wherein the organosilicon compound is selected from silanes, siloxanes, and silazanes.

8. The method of claim 6 wherein the organosilicon compound is selected from methyl silane, dimethyl silane, frimethyl silane, tetramethyl silane, dimethoxydimethylsilane, methyltrimethoxysilane, tetramethoxysilane, methyltriethoxysilane, diethoxydimethylsilane, methyltriethoxysilane, triethoxyvinylsilane, tefraethoxysilane, dimethoxymethylphenylsilane, phenyltrimethoxysilane, 3- glycidyloxypropyltrimethoxysilane, 3-methacryloxypropyltrimethoxysilane, diethoxymethylphenylsilane, tris(2-methoxyethoxy)vinylsilane, phenyltriethoxysilane, tetraethylorthosilane, dimethoxydiphenylsilane, tetramethyldisiloxane, tefraethylorthosilicate, hexamethyldisiloxane, hexamethylsilazane and teframethylsilazane.

9. The method of claim 4 wherein at least one additional layer is applied which additional layer is selected from (a) carbon modified metal oxide layers containing more carbon and less cross-linking than is found in the first layer and (b) metal oxide layers containing less carbon than is found in the first layer.

10. The method of claim 9 wherein a layer (a) is applied to the substrate prior to application of the first carbon modified metal oxide layer.

11. The method of claim 9 wherein a layer (b) is applied after application of the first carbon modified metal oxide layer.

12. The method of claim 4 wherein the metal oxide layer further comprises N in a N to Me ratio of 0:1 to 1:1.

13. An electronic optical device comprising:

(a) a sodium containing glass substrate having an interior surface and an exterior surface, wherein the interior surface is coated with a protective coating comprising a carbon modified metal oxide layer which layer comprises Me, O, C, and H covalently bonded to one another, where Me is selected from Silicon, Titanium, Indium, Tin,

Germanium and combinations thereof; the mole ratio of O to Me is 1:1 to 2.4:1; the mole ratio of C to Me is 0.1:1 to 4.5:1; and the mole ratio of H to Me is 0:1 to 8:1,

(b) a first transparent electrode adjacent to the protective coating and a second electrode, and (c) an electroactive material located between the electrodes.

14. The device of claim 13 wherein Me is Si and the carbon modified metal oxide layer is applied to the glass substrate by plasma enhanced chemical vapor deposition at temperatures of less than 550°C.

15. The device of claim 14 wherein the electroactive material is a liquid crystal polymer, the device further comprises a second transparent substrate adjacent to the second electrode and the second electrode is transparent.