Boroalumino silicate glasses

Abstract

Disclosed are alkali-free glasses having a liquidus viscosity of greater than or equal to about 90,000 poises, said glass comprising SiO 2 , Al 2 O 3 , B 2 O 3 , MgO, CaO, and SrO such that, in mole percent on an oxide basis: 64≦SiO 2 ≦68.2; 11≦Al 2 O 3 ≦13.5; 5≦B 2 O 3 ≦9; 2≦MgO≦9; 3≦CaO≦9; and 1≦SrO≦5. The glasses can be used to make a display glass substrates, such as thin film transistor (TFT) display glass substrates for use in active matrix liquid crystal display devices (AMLCDs) and other flat panel display devices.

The invention claimed is: 
     
       1. An alkali-free glass having a liquidus viscosity of greater than or equal to about 90,000 poises, a melting temperature less than or equal to about 1620° C.. and an anneal point greater than or equal to about 725° C., said glass comprising SiO 2 , Al 2 O 3 , B 2 O 3 , MgO, CaO, SrO, SnO 2 , and Fe 2 O 3 , such that, in mole percent on an oxide basis: 64≦SiO 2 ≦68.2; 11≦Al 2 O 3 ≦13.5; 5≦B 2 O 3 ≦9; 2≦MgO≦9; 3≦CaO≦9; 1≦SrO≦5; 0.02≦SnO 2 ≦0.3; and 0.005≦Fe 2 O 3 ≦0.08;
 wherein:
 (i) the glass comprises less than 0.05% by weight of Sb 2 O 3 , As 2 O 3 , or combinations thereof; 
 (ii) the BaO content of the glass on an oxide basis is less than 1000 ppm by weight; and 
 (iii) the glass is in the form of a plate produced by a fusion draw process. 
 
 
     
     
       2. An alkali-free glass according to  claim 1  wherein said glass has a liquidus viscosity of greater than or equal to about 100,000 poises and a liquidus temperature of lower than or equal to about 1200° C. 
     
     
       3. An alkali-free glass according to  claim 1  wherein said glass has a linear coefficient of thermal expansion over the temperature range of 0° C. to 300° C. of less than or equal to about 40×10 −7 /° C. 
     
     
       4. An alkali-free glass according to  claim 1 , wherein, in mole percent on an oxide basis:
   11.3≦Al 2 O 3 ≦13.5.
 
 
     
     
       5. An alkali-free glass according to  claim 1 , wherein, in mole percent on an oxide basis:
   1.05≦(MgO+CaO+SrO)/Al 2 O 3 ≦1.45;
 
   0.67≦(SrO+CaO)/Al 2 O 3 ≦0.92; and
 
   0.45≦CaO/(CaO+SrO)≦0.9;
 
 
       and the glass has a liquidus temperature of lower than or equal to about 1200° C. 
     
     
       6. An alkali-free glass according to  claim 1 , wherein, in mole percent on an oxide basis:
   1.05≦(MgO+CaO+SrO)/Al 2 O 3 ≦1.3;
 
   0.72≦(SrO+CaO)/Al 2 O 3 ≦0.9; and
 
   0.55≦CaO/(CaO+SrO)≦0.9.
 
 
     
     
       7. An alkali-free glass according to  claim 1 , wherein, in mole percent on an oxide basis:
   1.05≦(MgO+CaO+SrO)/Al 2 O 3 ≦1.3;
 
   0.72≦(SrO+CaO)/Al 2 O 3 ≦0.9; and
 
   0.8≦CaO/(CaO+SrO)≦0.9.
 
 
     
     
       8. An alkali-free glass according to  claim 1  wherein the glass contains one or more of CeO 2 , and Br. 
     
     
       9. An alkali-free glass according to  claim 1 , wherein in mole percent:
   F+Cl+Br≦0.4.
 
 
     
     
       10. An alkali-free glass according to  claim 1 , wherein said glass has a liquidus viscosity of greater than or equal to about 100,000 poises. 
     
     
       11. An alkali-free glass according to  claim 1 , wherein said glass has a liquidus viscosity of greater than or equal to about 130,000 poises. 
     
     
       12. An alkali-free glass according to  claim 1 , wherein said glass has a liquidus temperature of lower than or equal to about 1200° C. 
     
     
       13. A glass substrate, such as a display glass substrate, comprising an alkali-free glass according to  claim 1 . 
     
     
       14. A glass substrate according to  claim 13 , wherein the alkali-free glass is substantially defect-free glass substrate is a display glass substrate. 
     
     
       15. A flat panel display device comprising a flat, transparent glass substrate carrying polycrystalline silicon thin film transistors, wherein said glass substrate comprises an alkali-free glass according to  claim 1 . 
     
     
       16. A method of making a glass plate comprising melting, fining, and forming batch materials so that the glass of the glass plate is alkali-free and comprises SiO 2 , Al 2 O 3 , B 2 O 3 , MgO, CaO, and SrO, wherein the method comprises using the following relationships to select the batch materials:
   1.05≦R o ≦1.45;
     0.67≦S o ≦0.92; and
     0.45≦C o ≦0.95;
   
       where R o , S o , and C o  are given by:
   R o =(MgO+CaO+SrO)/Al 2 O 3 ; 
   S o =(CaO+SrO)/Al 2 O 3 ; and 
   C o =CaO/(CaO+SrO); 
 
       where Al 2 O 3 , MgO, CaO, and SrO are in mole percent on an oxide basis. 
     
     
       17. The method of claim 16 wherein the glass plate is formed by a downdraw process. 
     
     
       18. The method of claim 17 wherein the downdraw process is a fusion downdraw process. 
     
     
       19. The method of claim 16 further comprising using the glass plate as a substrate for a silicon semiconductor. 
     
     
       20. The method of claim 16 further comprising using the glass plate as a substrate for a flat panel display device. 
     
     
       21. A method of making a glass plate comprising melting, fining, and forming batch materials so that the glass of the glass plate is alkali-free and comprises SiO 2 , Al 2 O 3 , B 2 O 3 , MgO, CaO, and SrO;
 where, in mole percent on an oxide basis:
   64≦SiO 2 ≦68.2;
 
   11≦Al 2 O 3 ≦13.5;
 
   5≦B 2 O 3 ≦9;
 
   2≦MgO≦9;
 
   3≦CaO≦9; and
 
   1≦SrO≦4.5;
 
   and where:
 (i) the glass of the glass plate has a liquidus viscosity greater than or equal to about 90,000 poises; 
 (ii) the glass of the glass plate has an anneal point greater than or equal to about 725° C.; and 
 (iii) the BaO content of the glass of the glass plate on an oxide basis is less than 1000 ppm by weight. 
   
     
     
       22. The method of claim 21 wherein the glass plate is formed by a downdraw process. 
     
     
       23. The method of claim 22 wherein the downdraw process is a fusion downdraw process. 
     
     
       24. The method of claim 21 further comprising using the glass plate as a substrate for a silicon semiconductor. 
     
     
       25. The method of claim 21 further comprising using the glass plate as a substrate for a flat panel display device.