Classifications

• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
  • C03C3/00—Glass compositions
  • C03C3/04—Glass compositions containing silica
  • C03C3/076—Glass compositions containing silica with 40% to 90% silica, by weight
  • C03C3/089—Glass compositions containing silica with 40% to 90% silica, by weight containing boron
  • C03C3/091—Glass compositions containing silica with 40% to 90% silica, by weight containing boron containing aluminium
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
  • C03C3/00—Glass compositions
  • C03C3/04—Glass compositions containing silica
  • C03C3/076—Glass compositions containing silica with 40% to 90% silica, by weight
  • C03C3/083—Glass compositions containing silica with 40% to 90% silica, by weight containing aluminium oxide or an iron compound
  • C03C3/085—Glass compositions containing silica with 40% to 90% silica, by weight containing aluminium oxide or an iron compound containing an oxide of a divalent metal
  • C03C3/087—Glass compositions containing silica with 40% to 90% silica, by weight containing aluminium oxide or an iron compound containing an oxide of a divalent metal containing calcium oxide, e.g. common sheet or container glass
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
  • C03C3/00—Glass compositions
  • C03C3/04—Glass compositions containing silica
  • C03C3/076—Glass compositions containing silica with 40% to 90% silica, by weight
  • C03C3/089—Glass compositions containing silica with 40% to 90% silica, by weight containing boron
  • C03C3/091—Glass compositions containing silica with 40% to 90% silica, by weight containing boron containing aluminium
  • C03C3/093—Glass compositions containing silica with 40% to 90% silica, by weight containing boron containing aluminium containing zinc or zirconium

Definitions

• the present invention relates to glass materials in the CaO-Al 2 ⁇ 3 -B ⁇ 3-Si ⁇ 2 system, glass articles comprised of such glass, and processes for making such glass materials and such glass articles.
• the present invention relates to CaO-Al 2 O 3 -B 2 ⁇ 3-Si ⁇ 2 glass materials exhibiting desirable physical and chemical properties for substrates of flat panel displays, flat glass sheets comprised of such glass materials, as well as processes for making the glass materials and glass sheets of the present invention.
• Display devices may be broadly classified into two categories: emissive displays such as cathode ray tubes (CRTs) and plasma display panels (PDPs), and non- emissive displays.
• the latter category to which liquid crystal displays (LCD) belong, relying on an external light source, with the display serving only as a light modulator.
• this external light source may be ambient light (used in refractive displays) or a dedicated light source (such as the backlighting units of direct view displays).
• a LCD relies upon three inherent features of the liquid crystal (LC) material to modulate light. The first is the ability of the LC to cause the optical rotation of polarized light. The second is the ability of the LC to establish this rotation by mechanical orientation of the liquid crystal. The third feature is the ability of the liquid crystal to establish this orientation by the application of an external electric field.
• TN liquid crystal display In the production of a simple, twisted nematic (TN) liquid crystal display, two substrates surround a layer of liquid crystal material. In a display type known as Normally White, the application of alignment layers on the inner surface of the substrates creates a 90° spiral of the liquid crystal director. This means that the polarization of linearly polarized light entering one face of the liquid crystal will be rotated by 90° by the liquid crystal material. Polarization films, oriented 90° to each other, are placed on the outer surfaces of the substrates.
• the polarization of this light is rotated 90" and is allowed to exit through the second polarization film.
• Application of an electric field across the liquid crystal layer aligns the liquid crystal directors with the field, interrupting its ability to rotate light.
• Linearly polarized light passing through this cell does not have its polarization rotated and hence is blocked by the second polarization film.
• the liquid crystal material becomes a light valve, whose ability to allow or block light transmission is controlled by the application of an electric field.
• the two substrates that comprise the display are manufactured separately.
• the color filter plate has a series of red, blue, green, and black organic dyes deposited on it.
• Each of these primary colors must correspond precisely with the pixel electrode areas of the companion active plate.
• glass substrates whose dimensions are independent of thermal condition (i.e., glasses with lower coefficient of thermal expansion).
• this property needs to be balanced by the generation of stresses between deposited films and the substrates that arise due to expansion mismatch.
• the active plate so called because it contains the active, thin film transistors, is manufactured using typical semiconductor type processes. These include sputtering, CVD, photolithography, and etching. It is highly desirable that the glass be unchanged during these processes. Thus, the glass needs to demonstrate both thermal and chemical stability.
• Thermal stability also known as thermal compaction or shrinkage
• thermal compaction or shrinkage is dependent upon both the inherent viscous nature of a particular glass composition (as indicated by its strain point) and the thermal history of the glass sheet as determined by the manufacturing process.
• Glasses with a strain point in excess of 600°C and with the thermal history of the fusion process will have acceptable thermal stability for active plates based both on amorphous silicon (a-Si) thin film transistors (TFTs) and super low temperature polysilicon (p-Si) TFTs.
• a-Si amorphous silicon
• p-Si super low temperature polysilicon
• Higher temperature processing may require the addition of an annealing step to the glass substrate to ensure thermal stability.
• Chemical stability implies a resistance to attack of various etching solutions used in the manufacture processes. Of particular interest is the resistance to attack from the dry etching conditions used to etch the silicon layer.
• a substrate sample is exposed to an etching solution known as 110BHF. This test consists of immersing a sample of glass in a solution of 1 volume of 50% by weight HF and 10 volumes 40% by weight NH F at 30°C for 5 minutes. The sample is graded on weight loss and appearance.
• the glass it would be advantageous for the glass to have a strain point over about 600°C, preferably in the range of about 600°C to about 700°C, more preferably in the range of about 600°C to about 660°C, and for the glass to be resistant to attack from etching solutions.
• the present invention is founded in the discovery of a glass material having a density lower than 2.35 g/cm 3 , preferably in the range of 2.18-2.30 g/cm 3 , more preferably in the range of 2..19-2.30 g/cm 3 , a liquidus temperature lower than or equal to about 1200°C, and a liquidus viscosity (defined as the viscosity of the glass at the liquidus temperature) greater than about 200,000 poise, preferably greater than about 400,000 poise, more preferably greater than about 600,000 poise, and most preferably greater than about 800,000 poise.
• the glass of the present invention exhibits a linear coefficient of thermal expansion over the range of 0-300°C between about 23-35xlO "7 /°C, preferably between about 25-30xlO "7 /°C, and a strain point over about 600°C, preferably between about 600°C to 700°C, more preferably between about 600°C and about 660°C.
• the glass of the present invention has a 500 poise temperature (defined as the temperature at which the glass viscosity is about 500 poise) lower than about 1750°C.
• the glass of the present invention exhibits a durability, expressed in terms of weight loss after immersion in a solution of 1 volume of 50 wt. % HF and 10 volumes of 40 wt.
• the glass material of the present invention has a composition consisting essentially, expressed by mole on an oxide basis, of
• the glass material essentially free of BaO and alkali oxide of the present invention has a composition consisting essentially, expressed by mole on an oxide basis, of
• wwhheerree RO and XO have the same meaning as defined above.
• the liquidus viscosity of the glass is strongly influenced by the ratio of the sum of the mole percentages of alkaline earth oxides and ZnO, R'O (R'O represents, collectively, MgO, CaO, SrO and ZnO) to the mole percentage of Al 2 O 3 , viz., the R'O/Al 2 O 3 ratio.
• R'O represents, collectively, MgO, CaO, SrO and ZnO
• This ratio should be preferably held within 0.8-1.5. Most preferably, this R'O/Al 2 O 3 range should be between 0.9 and 1.3, in order to obtain the highest liquidus viscosity.
• a low density glass of the present invention is obtained when the mole percentages of the respective oxides in the glass composition meet the following provisos: (i) -0.25 ⁇ (RO-Al 2 O 3 )/B 2 O 3 ⁇ 0.25, and preferably 0 ⁇ (R'O- Al 2 O 3 )/B 2 O 3 ⁇ 0.15, and (ii) (RO+Al 2 ⁇ 3 )/B 2 ⁇ 3 ⁇ 2, where R'O represents, collectively, MgO, CaO, SrO and ZnO.
• the glass of the present invention is essentially free of BaO, which means that the glass composition preferably contains less than about 0.1 % by mole of BaO.
• the glass of the present invention is essentially free of alkali oxides, which means that it contains preferably a total of less than about 0.1 % by mole of alkali oxides.
• the glass of the present invention may contain fining agents, such as the oxides of arsenic, antimony, cerium, tin and/or chlorine/fluorine.
• the glass of the present invention is essentially free of arsenic oxide and antimony oxide for environmental concerns.
• the present invention is concerned with improved glasses for use as flat panel display substrates.
• the glass of the present invention meets the various requirements of such substrates.
• the glass in accordance with the present invention exhibits a density in the range of 2.18-2.35 g/cm 3 , preferably 2.19-2.30 g/cm 3 , a coefficient of thermal expansion in the temperature range of 0-300°C of 23-35xl0 "7 /°C, preferably 25-30xl0 "7 /°C, a strain point over about 600°C, preferably between about 600-700°C, more preferably between about 600- 660°C. High strain point and low coefficient of thermal expansion are desirable to help prevent panel distortion due to compaction shrinkage during subsequent thermal processing. [0042] For more demanding manufacturing conditions such as the fusion process, described in U.S. Pat. Nos.
• the glass should exhibit a density less than 2.35 g/cm and a liquidus viscosity greater than about 200,000 poise, preferably greater than about 400,000 poise, more preferably greater than about 600,000 poise, and most preferably greater than about 800,000 poise.
• substrates made from glass of the present invention can be made using other manufacturing processes such as the float process, the fusion process is preferred for several reasons. First, glass substrates made from the fusion process do not require polishing.
• Current glass substrate polishing is capable of producing glass substrates having an average surface roughness greater than about 0.5 nm (Ra), as measured by atomic force microscopy. Glass substrates produced according to the present invention and using the fusion process have an average surface roughness as measured by atomic force microscopy of less than 0.5 nm.
• Chemical durability involves resistance of the glass to attack of the various etchant solutions used in the manufacture process.
• the resistance to attack from dry etching conditions used to etch the silicon layer of the LCD is of particular interest.
• One benchmark of the dry etching conditions is exposure to an etchant solution known as 110BHF. This test consists of immersing a sample of glass in a solution of 1 volume of 50 wt. % HF and 10 volumes of 40 wt. % NH 4 F at 30°C for 5 minutes.
• the chemical resistance is determined by measuring the weight loss in terms of mg/cm 2 during the process.
• the glasses of the present invention include 70-80%, and preferably 72-77% by mole of SiO 2 as the primary glass former. Increasing SiO 2 content improves the liquidus viscosity and reduces the density and CTE of the glass, but excessive SiO 2 is detrimental to the melting temperatures.
• the glasses also comprise 3-9%, preferably 4-7% by mole of AI 2 O 3 . Higher AI 2 O 3 percentage increases glass durability and decrease CTE, but liquidus temperature increases correspondingly. At least 3 mol % of Al 2 O 3 is required in the glass composition in order to have the desired strain point; however, more than 9 mol % results in a less than desired liquidus temperature.
• the glasses of the present invention further contain 8-18 mol %, preferably
• B 2 O 3 10-16 mol % B 2 O 3 .
• Increasing B 2 O 3 content lowers the liquidus temperature and density and thus it is preferably present at least 8 mol %. More than 18 mol % B 2 O 3 will lead to less than desired glass strain point.
• CaO is useful in lowering both the melting and liquidus temperatures of the glass; however, more than 10 mol % will result in a less than desired CTE. Therefore, CaO is present in the glass composition of the present invention at 3-10 mol %, preferably 3-8 mol %.
• alkaline earth oxides including MgO and SrO, as well as ZnO, collectively referred to as RO in the present application, can be included in the glass composition of the present invention in the amount of 0-4 mol %, preferably 0-3 mol %.
• MgO is beneficial in reducing glass density, but high MgO content lowers liquidus viscosity and raises the liquidus temperature as well.
• An important aspect of the glass of the present invention is its low density.
• the present inventor has discovered that, in order to achieve the low density range of 2.18- 2.35 g/cm 3 , the compositional range specified above is necessary. In order to achieve a desirable liquidus viscosity, it is desired that the mole percentages of the respective oxides in the glass composition meet the following proviso: 0.8 ⁇ RO/AI2O 3 ⁇ 1.5, preferably 0.9 ⁇ R'O/Al 2 O 3 ⁇ 1.3, where R'O represents, collectively, MgO, CaO, SrO and ZnO.
• the respective mole percentages of the oxides meet the following provisos: (i) -0.25 ⁇ (R'O-Al2 ⁇ 3 )/B 2 ⁇ 3 ⁇ 0.25, preferably 0 ⁇ (RO-Al 2 O 3 )/B 2 O 3 ⁇ 0.15, and (ii) (Al 2 ⁇ 3 +R'O)/B 2 ⁇ 3 ⁇ 2, where R'O has the same meaning as defined above.
• alkalis such as Li 2 O, Na 2 O, K 2 O, and the like, are controlled and excluded from the compositions of the present invention glass. It is an important feature of the glass composition of the present invention that it is essentially free of alkali oxides. BaO as a heavy oxide tends to negatively increase the glass density, and thus is controlled to be essentially free in the glass compositions of the present invention.
• Fining agents such as SnO 2 , CeO 2 , sulfates, F, Cl, As 2 O 3 , Sb 2 O , and the like, may also be present in the compositions of the glasses of the present invention to aid in removing seeds in the final glass during the glass melting and fining process.
• the glasses of the present invention may contain contaminants as typically found in commercially prepared glasses.
• the following materials may be added to the glass compositions in the amount of 0-1 mol % without pushing the properties of the glass out of the limits specified above: TiO 2 , ZrO , Y 2 O 3 and/or La 2 O 3 .
• Flat glass sheet having the glass composition and the properties of the glasses of the present invention suitable for LCD glass substrates is another aspect of the present invention.
• Such glass sheet should advantageously have a surface smoothness (Ra) of less than 0.50 nm as measured by atomic force microscopy (AFM), and an internal stress less than about 150 psi.
• Ra surface smoothness
• Such substrates can be produced using conventional glass making processes, such as float process, fusion draw process and slot draw process, to name a few. Other processes may be employed as well.
• One of skill in the art can calculate the batch compositions of the glass using various starting materials. To meet the requirements of LCD manufacturing, some glass sheets produced from these processes may need to be polished before using. Fusion draw process, as disclosed in U.S. Pat. Nos.
• 3,338,696 Dockerty
• 3,682,609 Dockerty
• a high liquidus viscosity is required for the fusion draw process.
• the glass of the present invention due to its high liquidus viscosity, is compatible with the fusion draw process.
• TABLE I sets forth exemplary glass compositions, where the amounts of the oxides are expressed in terms of parts by mole on an oxide basis.
• TABLE II sets forth the same glass compositions as in TABLE I in terms of weight percentage of the oxides, calculated from the mole percentages. The following discussion of the examples are based on the data in TABLE I.
• Example 8 both Ai 2 Cl 6 together with other source materials were used as the source of AI 2 O 3 .
• the actual mole percentage of AI2O3 in the final glass should be the sum total of the mole percentage of AI 2 O 3 and the mole percentage of "AI2O3 as as reported in TABLE I.
• CaCl2 and/or CaBr 2 were used in the batch materials.
• the actual mole percentage of CaO in the final glass should be the sum total of the mole percentage of CaO and the mole percentage of "CaO as CaBr 2 " and/or "CaO as CaCl 2 " in TABLE I.
• the actual batch ingredients may comprise any materials, either oxides, or other compounds, which, when melted together with the other batch components, will be converted into the desired oxide in the proper proportions.
• SrCO 3 and CaCO 3 can provide the source of SrO and CaO, respectively.
• These exemplary glasses were prepared by melting 1 ,000-5,000 gram batches of each glass composition at a temperature and for a time to result in a relatively homogeneous glass composition, e.g., at a temperature of about 1650°C for a period of about 4-16 hours in platinum crucibles.
• a relatively homogeneous glass composition e.g., at a temperature of about 1650°C for a period of about 4-16 hours in platinum crucibles.
• TABLE I are the relevant glass properties for each glass composition, determined on the glasses in accordance with techniques conventional in the glass art.
• the linear coefficient of thermal expansion (CTE) over the temperature range 0-300°C is expressed in terms of xlO "7 /°C, the softening point (Soft. Pt.) and the annealing point (Ann. Pt.) and strain point (Str.
• Pt. are expressed in terms of °C. These were determined from fiber elongation techniques (ASTM references E228-85, C338 and C336, respectively).
• the density (Den.), in terms of g/cm was measured via the Archimedes method (ASTM C693).
• the durability in BHF was measured by immersing a glass sample in a solution of 1 volume of 50 wt. % HF and 10 volumes of 40 wt. % NH 4 F at 30°C for 5 minutes, and reported as weigh loss in terms of mg/cm 2 .
• the liquidus temperature (Liq. Temp.) of the glass was measured using the standard liquidus method.

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• 2002
  • 2002-08-29 US US10/232,500 patent/US6992030B2/en not_active Expired - Lifetime
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