# Patent

## Title
High strain point glasses

## Abstract

A family of glasses from the rare earth alumino-silicate (RE2O3—Al2O3—SiO2) ternary system exhibiting high strain point and low liquidus temperatures; preferably the La2O3—Al2O3—SiO2 ternary system. The glasses are excellent candidates for electronics applications and have the following composition, expressed in mole percent and calculated from the glass batch on an oxide basis: 60-85% SiO2, 10-25% Al2O3, and 4-15% RE2O3.

## Background
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims the benefit of U.S. application Ser. No. 60/709,337 filed on Aug. 17, 2005 and entitled “High Strain Point Glasses” which is incorporated by reference herein in.


FIELD OF THE INVENTION
The invention relates to rare earth aluminosilicate (RE2O3—Al2O3—SiO2) glasses that are characterized by a high strain point and a relatively low liquidus temperature.
BACKGROUND OF THE INVENTION
The materials of the present invention are most importantly substrate candidates for electronic devices. Several processes in the manufacture of electronic devices such as liquid crystal displays (LCDs), solar cells, electronics, microelectronics etc. include steps that are performed at extremely high temperatures. For example, active matrix LCDs employ an active device such as a diode or thin film transistor at each pixel thereby enabling high contrast and high response speed. Although many display devices currently utilize amorphous silicon (a-Si), the processing of which may be accomplished at temperatures under 450° C., polycrystalline-silicon (poly-Si) processing is preferred. Poly-Si has a much higher drive current and electron mobility thereby increasing the response time of the pixels. Further, it is possible, using poly-Si processing, to build the display drive circuitry directly on the glass substrate. By contrast, a-Si requires discrete driver chips that must be attached to the display periphery utilizing integrated circuit packaging techniques. The most efficient poly-Si processing methods operate at temperatures of at least 730° C., such processes enable formation of poly-Si films having extremely high electron mobility (for rapid switching) and excellent TFT uniformity across large areas. This fabrication process typically consists of successive deposition and patterning of thin films using elevated temperature processes which result in the substrate being heated to temperatures in the range of 650° C. or higher. Common commercial LCD glasses (e.g. Corning 1737 and Corning Eagle) exhibit strain points of approximately 670° C. Fused silica has a sufficiently high strain point of 990-1000° C., but its coefficient of thermal expansion (C.T.E.) of 5×10−7/° C.) is significantly lower than that of silicon which has a C.T.E. of 37×10−7/° C.) which can lead to high stress and failure. Further, the cost associated with formed fused silica substrates suitable for electronic devices is a deterrent. The strain point of most LCD glasses can be increased by lowering the modifier content of the glass and increasing the silica content, but this also raises the temperature required to melt and fine the glass to a high quality melt. This temperature is often referred to as the 200 Poise temperature or T200P. Thus generally, the higher the strain point, the higher the T200P, which accelerates corrosion of the refractories, increases energy consumption, and the overall cost, so there is often a tradeoff between strain point and meltability.
For other electronic devices, common processing steps also require high temperature substrates to withstand processing. Most high level electronic fabrication requires annealing of the gate oxide and dopant activation. These processes occur at temperatures in excess of 650° C.
Even in the case of single crystal silicon (x-Si) fabrication techniques that employ a thin layer of single crystal silicon bonded to a substrate, high temperature substrates are required. Single crystal silicon allows for even greater electron mobility than that achieved with poly-Si. The bonding step often requires high temperatures as well as the gate oxide and dopant activation steps previously described.
Liquidus viscosity also plays a major role in glass selection for substrate candidates. Lower liquidus temperatures translate into higher liquidus viscosities. These high viscosities allow for a large selection of commercially relevant forming techniques such as downdraw techniques. One particular example of a downdraw technique is known as the overflow downdraw or fusion sheet manufacturing process. The overflow downdraw process is described in U.S. Pat. No. 3,338,696 and U.S. Pat. No. 3,682,609. Glasses with low liquidus temperatures, allowing for high viscosities in the forming apparatus, are therefore good candidates for downdraw manufacturing processes. Lower liquidus temperature glasses also have the advantage of causing less corrosion on the refractory materials used in the forming processes. This translates into longer life for the forming apparatus, while a glass with a low melting and fining temperature (T200P) increases tank life.
A need exists, then, for a glass that (1) has a high strain point (>650° C.), (2) does not require costly heat treatments after fabrication, (3) has a CTE close to that of silicon, and (4) can be melted in a conventional melting unit (T200P<1650° C.) and formed according to a commercially proven method. In addition, the glass will preferably be transparent to visible radiation and be chemically durable. These several qualities are needed in glasses for production of such varied products as flat panel displays, photovoltaic cells, photomasks, optomagnetic disks and tubing and fiber applications that require stability at high temperatures.
A primary purpose of the present invention is to provide an alkali-free glass that has properties suited to production of a poly-Si or x-Si coating on its surface.
Another purpose is to produce a glass having a sufficiently high strain point to permit processing at temperatures in excess of 650° C.
A further purpose is to provide a glass that can be melted and formed by conventional procedures, and that can provide a substrate for application of a high quality, poly-Si or x-Si film.
A still further purpose is to provide an electronic device, in particular, a flat panel display, and having a high-quality, poly-Si or x-Si, thin film on its surface.
Another purpose is to provide a novel glass family consisting essentially of RE2O3—Al2O3—SiO2, with RE comprising a rare earth, and optionally containing selected oxides such as alkali, alkaline earth, and transition metal oxides.
SUMMARY OF THE INVENTION
The invention resides in part in the rare earth aluminosilicate (RE2O3—Al2O3—SiO2) system of glasses exhibiting, a strain point in excess of 650° C. and preferably in excess of 730° C., a liquidus temperature of 1300° C. or less, T200P of approximately 1500° C. or less, and liquidus viscosities favorable for a variety of forming processes.
The invention further resides in an electronic device having a poly-silicon film on a transparent, glass substrate, the substrate being a rare earth-aluminosilicate glass having an RE2O3 content of 4-15 mol percent, and a strain point in excess of 730° C. The rare earth (RE) being selected from the group consisting of Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and mixtures thereof. In a preferred embodiment the rare earth comprises lanthanum.



DESCRIPTION OF FIGURES
FIG. 1 is a viscosity curve demonstrating the viscosity of a glass of the present invention compared to a commercially available display substrate glass.
FIG. 2 is a plot that shows variation of strain point, annealing point and CTE as a function of ZrO2 content in glasses of the present invention.



DESCRIPTION OF THE INVENTION
Broadly stated, the present alkali-free glasses have compositions falling within the following ranges, expressed in mole % as calculated from the glass batch on an oxide basis:
















SiO2
60-88%



Al2O3
10-20%



RE2O3
 2-15%



RO
 1-12%










SiO2 serves as the major network-forming component of the glass. When the SiO2 content falls below 60 mole percent, chemical resistance is adversely affected and strain point is lowered and the CTE raised to unacceptable levels. When the SiO2 level surpasses 85%, the liquidus and melting temperatures are raised to levels not compatible with accepted sheet glass manufacturing methods.
Al2O3 as a glass component serves to further stabilize the glass network, especially in the presence of network-modifying components, enhancing heat and devitrification resistance of glass. When the level of Al2O3 drops below 10 mole percent, devitrification readily occurs in the glass. If the glass contains greater than 25 mole percent Al2O3, the liquidus exceeds 1300° C. and the glass becomes subject to acid degradation. In on aspect, the amount of Al2O3 ranges from 10-20 mol %. In another aspect, the amount of Al2O3ranges from10.6-20 mol %.
As demonstrated in the present invention, RE2O3 as a glass component has been shown to maintain the high strain point of the base aluminosilicate glass while reducing the liquidus and T200P temperatures. As the RE2O3 content decreases, the glass becomes too refractory for conventional melting and forming practices for high strain point compositions. Too much RE2O3 could decrease strain point and raise CTE. As a general rule, the total amount of modifying oxides (including preferably La2O3) should not exceed the amount of alumina in order to maintain the structural integrity of the glass network and, hence , the desired high strain point. The best properties (low CTE and liquidus temperature) are usually obtained when the modifier to alumina ratio given by (RO+1.5*RE2O3)/Al2O3 is close to 1 and between 0.85 and 1.2 depending on the makeup of the alkaline earth oxides, where RE (rare earth) is selected from the group defined as Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. In one aspect, the amount of RE2O3 ranges from 2-15 mol %. In another aspect, the amount of RE2O3 ranges from 2-12.49 mol %.
Any number of fluxes (e.g. modifying oxides) may be added to the batch in order to impart desired characteristics. While these fluxes may lower the strain point of the native glass, they are often necessary for any or all of the following purposes: raise the CTE, lower the liquidus temperature, obtain a preferred strain point for compaction, absorption at specific wavelengths, facilitate melting, modify density, or modify durability. The effects that certain oxides have on the physical and chemical characteristics of glass are generally known. For example, B2O3 is a component that serves to lower viscosity and facilitate melting. Addition of MgO and/or CaO is known to decrease liquidus temperature without significantly lowering strain point when balanced by an equivalent Al2O3 addition. Likewise BaO and/or SrO are also valuable for lowering the liquidus and are known to improve the chemical resistance of glass and improve resistance to devitrification but tend to increase the CTE faster than MgO or CaO. ZnO is known to enhance resistance to buffered hydrofluoric acid as well as resistance to devitrification. As2O3 , Sb2O5 , CeO2 , SO3 , SnO2 , halides and other known fining agents may be added to the batch to reduce bubbles in the glass.
Fluxes in the form of modifying oxides, represented by RO may be added in amounts up to 20% or as limited by solubility. Preferably fluxes are added in amounts less then 15 mole percent. In one aspect, RO ranges from 1 to 12 mol %. Modifying oxides may be selected from those of alkali metals, alkaline earth metals, transition metals as well as oxides of the lanthanide series. Specific examples include, ZrO2, HfO2, MgO CaO, SrO, BaO, As2O3, SnO2, GeO2, Ga2O3, Sb2O3,P2O5 and/or B2O3. In one aspect, the modifying oxide is B2O3 ranging from 0 to 9 mol %. In another aspect, the modifying oxide is SnO2 ranging from 0 to 2 mol %. For preferred embodiments, R shall be the alkaline earth elements Mg, Ca, Sr, or Ba. In this aspect, RO ranges from 1 to 12 mol %, wherein R is an alkaline earth metal selected from the group consisting of Mg, Ca, and Sr; or when R is Ba, at least one additional alkaline earth metal selected from the group consisting of Mg, Ca, and Sr is present.
It should be noted that for glasses used for flat panel display devices, modifying oxides are preferred. However, modifying with nitrides such as AlN, or modifying with halogens such as F−, alone or in combination with modifying oxides may be acceptable for particular applications. In such event, the total modifier content should still not exceed 20 mole percent and preferably be less than 15 mole percent. Likewise, although it is preferred for glasses that used as substrates for LCD displays be free alkali-free, this limitation may not be critical for other applications and the invention is therefore not to be interpreted as limited to alkali-free glasses.
Preferably, the glasses of the present invention have the following characteristic properties:
















Strain Point
>730° C.



CTE
25-50 × 10−7/° C.



Liquidus T
<1300° C.



T200P
<1600° C.



Liquidus Viscosity
>10,000 poise










Even more preferred ranges include glasses exhibiting strain points in excess of 750° C., 775° C., and 800° C.; liquidus temperatures less than 1250° C., 1200° C., and 1150° C.; 200 poise temperatures less than 1550° C., 1500° C. and 1475° C.; and, liquidus viscosities in excess of 50,000 poise, 100,000 poise, and 200,000 poise.
A preferred embodiment has compositions within the above identified ranges, again in mol % on an oxide basis, as calculated from the glass batch:
















SiO2
60-75%



Al2O3
15-20%



RE2O3
 4-15%



RO
<10%










TABLES I and II, below, set forth several compositions, in mol % on an oxide basis, illustrative of compositional ranges of the invention. 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.
The batch ingredients were compounded, tumble mixed together thoroughly to aid in producing a homogeneous melt, and charged into platinum crucibles. After placing lids thereon, the crucibles were moved into furnaces operating at temperatures of between 1450 and 1650° C. The crucibles were then removed after approximately 4 to 16 hours and poured onto a steel mold. The glass patty was then removed from the mold and placed into an annealing furnace at a temperature slightly above the annealing point of the glass. The glasses were then cooled in the annealing furnace and removed.
Several relevant observations are noted from the numerous glasses listed in Table 1, for example, the first 7 glasses (Examples 1-7) show that replacing Y2O3 with La2O3 lowers the liquidus temperature by approximately 150° C., which increases liquidus viscosity by a factor of 100. In turn, the strain point is only decreased by about 45° C. The increased liquidus viscosity makes the glasses easier to form and allows for greater options in manufacturing including slot drawn and fusion forming techniques. The CTE and density also increase with La2O3 for Y2O3 as expected from the lower field strength and larger mass of La relative to Y. The lowest observed liquidus temperature was obtained near 70 SiO2-18 Al2O3-12 La2O3 (7) at 1210° C., which is the eutectic between cristobalite, mullite and lanthanum pyrosilicate (La2Si2O7).
The next 29 glasses in sequence (7-36) show the effect of varying the SiO2, Al2O3 and La2O3 contents at 3 different levels of Y2O3 (0, 1 and 3 mole %). The results show that the 70 SiO2-18 Al2O3-12 La2O3 (7) composition remains optimal in that Y2O3 increases the liquidus temperature in all composition tested, indicating that La2O3 is more effective in suppressing the crystallization of mullite and/or cristobalite than Y2O3.
The next 44 composition examine the effects of various additional oxides to the “eutectic glass” (7). Most additions had little to no effect on lowering the liquidus temperature. However, B2O3, MgO and F additions all lowered the liquidus temperature. As shown, the addition of 3 mole % MgO (74) appears to provide an optimal effect on depressing liquidus temperature (1180° C.), resulting in a corresponding increased liquidus viscosity of 24,000 poise. This glass is easy to melt, exhibiting a 1425° C. 200 poise temperature. The strain point, although lowered by the addition of MgO, is still 784° C.
Table II further displays the effects of varying amounts of oxides have on glass properties. The first 36 glasses in Table II show mixtures of the 70 SiO2-18 Al2O3-12 La2O3 “eutectic glass” with 2 eutectic compositions in each of the alkaline earth aluminosilicate systems. The high silica cristobalite-mullite-feldspar eutectic composition was chosen as a first end member since it offers the highest strain point and viscosity and lowest CTE for a glass-forming composition in the RO—Al2O3—SiO2 system. The more alkaline earth rich cristobalite-feldspar-alkaline earth silicate eutectic composition was chosen as a second end member since it may provide a lower liquidus temperature at the possible expense of lower strain point and higher CTE. The first 5 glasses in each alkaline earth series are mixes of the 70 SiO2-18 Al2O3-12 La2O3 “eutectic glass” with the cristobalite-mullite-feldspar (first) eutectic composition and the last 4 glasses of each set are mixtures of the 70 SiO2-18 Al2O3-12 La2O3 “eutectic glass” with the cristobalite-feldspar-alkaline earth silicate (second) eutectic composition. The data show that small additions of the first eutectic composition can lower the liquidus temperature from about 1215° C. (90) to 1200° C. or less, with BaO being the most effective and lowering the liquidus temperature to 1195° C. It is also surprising that the heavier alkaline earth ions do not degrade the strain point at all, while lighter MgO and CaO do. Unfortunately the heavier alkaline earths such as BaO also cause the largest increase in CTE as shown in Table II. Thus a mixture of alkaline earths provide the best combination of decreased liquidus temperature and improved properties.
The next 2 glasses (117) and (118) show how nitriding the glass can increase its strain point from 805 to 826° C. with additions of AlN which has the added benefit of decreasing CTE as well, but could be problematic for Pt lined melters which can be susceptible to melting if the Pt has ever been exposed to polyvalent and reducible ions.
122-124 show how higher levels of B2O3 quickly degrade the strain point without any beneficial impact on liquidus temperature for the 70 SiO2-18 Al2O3-12 La2O3 “eutectic glass”.
Since high CTE and density are the biggest drawbacks to the use of the 70 SiO2-18 Al2O3-12 La2O3 “eutectic glass” for flat panel display substrates, it was then mixed with several conventional RO—B2O3—Al2O3—SiO2 glasses that have lower CTE and density and higher viscosity at 1600° C. to get the best of both and achieve a high strain point glass that is easier to melt than conventional RO—B2O3—Al2O3—SiO2 glasses and similar physical properties. This resulted in a particularly preferred glass demonstrating an extremely low liquidus temperature of 1120° C. a high liquidus viscosity of 265,000 Poise with a 754° C. strain point. It is very unusual for a glass with such a high strain point to have a 200 Poise temperature of only 1474° C., which is almost 200° C. cooler than that of commercially available LCD substrate glass such as Eagle 2000 (Corning Incorporated) that exhibits a strain point of only 667° C. Thus the inventive glass has a higher strain point and is easier to melt because of the steeper viscosity curve enabled by the presence of La2O3 as illustrated in FIG. 1.
Glasses 146-189 are more variants on this mixture of oxides to improve properties, but there are many tradeoffs, so one of skill in the art will readily appreciate that the particular application and desired glass characteristics will determine the selection of the optimal composition. For example glasses 191 and 192 show how strain point of 137 increases by partially substituting Y2O3 for La2O3, which also lowers the density and CTE, but at the expense of liquidus temperature.
Table III demonstrates that high strain point glasses may also be achieved in the SiO2—Al2O3—La2O3 system by addition of ZrO2.
The use of ZrO2 as a component to improve melting characteristics of lanthanum, yttrium or other high strain point rare earth aluminosilicate glasses avoids redox problems sometimes associated with the addition of TiO2 and density/cost penalties associated with the use of Ta2O5. The use of ZrO2 as a modifier also has the advantageous effect of increasing strain point. Further such glasses are effectively pre-saturated with Zr and as such will be much less corrosive to zircon based refractory materials that contact the glass during manufacture.
Due to chemical similarity of Hf and Zr, the use of HfO2 or a mixture of HfO2 and ZrO2 would also result in colorless, high strain point glasses.
FIG. 2 shows the variation in strain point (Tstr), anneal point (Tann) and CTE as a function of ZrO2 content in LaZr aluminosilicate glasses containing 14 mole % Al2O3 and 80% SiO2.
Table III demonstrates that additions of MgO, SrO, SnO2 as well as ZrO2 and lanthanum aluminosilicate glasses provide materials with high strain point and, in some cases, CTE that are comparable to that of silicon. The high silica content of these glasses assures a relatively high liquidus temperature, but use of a lower liquidus temperature base glass, such as the “eutectic” glasses previously described (7) would bring the liquidus temperatures more into line with those of commercial LCD substrate glasses such as Corning 1737 and Corning Eagle.
Table IV illustrates two glasses, 227 and 228, which comprise a rare earth (RE2O3) combination comprising lanthanum and yttrium.
As can be observed from the Tables, not all tests were performed for all compositions.






















TABLE I







Example
Al2O3
B2O3
CaO
F−
Gd2O3
La2O3
MgO
Nb2O5
P2O5
Sc2O3
SiO2
SnO2
SrO
Ta2O5
TiO2





 1
17.99









69.98


 2
18.00




1.00




69.98


 3
18.00




3.00




69.98


 4
18.08




6.00




69.98


 5
17.99




9.00




69.98


 6
17.99




11.00




69.98


 7
17.99




12.00




69.98


 8
13.50




4.50




81.97


 9
17.50




12.49




69.98


10
17.99




10.99




70.98


11
16.99




12.00




70.98


12
17.99




10.00




71.98


13
16.99




11.00




71.98


14
16.00




12.00




71.97


15
17.00




10.00




72.98


16
15.99




11.00




72.98


17
15.00




11.99




72.97


18
17.99




10.00




70.97


19
16.99




11.00




70.98


20
18.00




8.99




71.98


21
16.99




10.00




71.98


22
16.00




10.99




71.98


23
16.98




12.00




69.98


24
18.99




11.00




68.98


25
17.99




12.00




68.98


26
17.00




13.00




68.97


27
17.99




8.00




70.98


28
16.99




9.00




70.98



































Liq
200 P







Strain
Anneal
Soft

Density
Liquidus

Visc
Temp


Example
Y2O3
ZnO
ZrO2
Na2O
Pt
Pt
Point
CTE
(g/cc)
Temp
Phase
(P)
(° C.)





 1
12.00



839
883
1061
38.2
3.048
1460
Cristobalite
240
1472


 2
11.00



836
880
1054
38.6
3.073
1430
Cristobalite


 3
9.00



822
868
1052
39.5
3.123
1340
Cristobalite


 4
6.00



815
861
1042
39.4
3.196
1270
Mullite
6420
1455


 5
3.00



803
851
1032
40.4
3.269
1275
Mullite


 6
1.00



800
846
1028
41.8
3.329
1290
Mullite


 7




796
843
1021
43.6
3.359
1210
Mullite
22000
1436


 8




835
887
1121
24.8
2.710
1475
Mullite


 9




788
835
1016
44.6
3.329
1230
Cristobalite


10




794
841
1027
42.2
3.282
1285
Mullite


11




792
838
1022
45.1
3.355
1235
Cristobalite


12




797
845
1030
39.5
3.201
1290
Mullite


13




795
841
1036
42.1
3.273
1290
Cristobolite


14




791
837
1018
45.0
3.346
1265
Cristobolite


15




795
843
1030
40.1
3.193
1305
Cristobolite


16




792
840
1035
42.7
3.272
1305
Cristobolite


17




790
837
1020
44.5
3.345
1320
Cristobolite


18
1.00



795
843

41.2
3.251
1290
Mullite


19
1.00



791
838

43.3
3.322
1335
Cristobalite


20
1.00



797
845

39.1
3.165
1335
Mullite


21
1.00



795
842

39.5
3.243
1355
Cristobolite


22
1.00



791
838

42.4
3.316
1300
Cristobolite


23
1.00



802
845

42.9
3.407
1250
LaSi


24
1.00



806
849

43.8
3.335
1265
Mullite


25
1.00



807
849

44.5
3.411
1240
LaSi


26
1.00



803
845

46.3
3.481
1255
LaSi


27
3.00



817
861
1045
39.3
3.199
1330
Mullite


28
3.00



815
858
1039
40.4
3.273
1300
Cristobalite
























Example
Al2O3
B2O3
CaO
F−
Gd2O3
La2O3
MgO
Nb2O5
P2O5
Sc2O3
SiO2
SnO2
SrO
Ta2O5





29
17.99




7.00




71.98


30
16.99




8.00




71.98


31
16.00




9.00




71.98


32
17.00




9.99




69.97


33
18.99




9.00




68.98


34
17.99




10.00




68.97


35
17.00




11.00




68.97


36
17.99




12.00




69.98


37
17.72

1.48


11.82




68.94


38
17.47

2.91


11.65




67.93


39
17.90

15.0


10.94




69.63


40
17.81

2.98


9.90




69.28


41
16.91

1.48


9.95




71.62


42
16.82

2.98


8.91




71.26


43
17.00




12.99




69.97


44
17.99




13.00




68.98


45
17.82
0.98



11.88




69.29


46
17.64
1.96



11.76




68.60


47
17.46
2.92



11.65




67.94


48
17.81




11.88




69.28

0.99


49
17.64




11.76




68.59

1.96


50
17.46




11.64




67.92

2.91


51
16.98


5.65

11.32




66.03


52
16.06


10.72

10.71




62.48


53
15.25


15.25

10.17




59.31


54
18.00




12.00




69.99


55
18.00




11.00



1.00
69.98


56
17.99




10.00



2.00
69.99


57
17.82




11.88




69.29


58
17.64




11.76




68.60


59
17.47




11.65




67.94


60
17.82




11.88




69.29


61
17.64




11.76




68.61


62
17.48




11.65




67.94


63
17.82



0.99
11.88




69.28


64
17.82



1.98
10.89




69.28


65
17.82



2.97
9.90




69.28


66
17.81




11.88

0.99


69.29


67
17.64




11.76

1.96


68.60


68
17.46




11.65

2.91


67.94


69
17.81




11.88




69.29


0.99


70
17.64




11.76




68.60


1.96


71
17.47




11.64




67.94


2.91


72
17.81




11.88
0.98



69.29


73
17.64




11.76
1.95



68.61


74
17.46




11.65
2.91



67.94


75
17.81




11.88




69.29
0.99


76
17.64




11.76




68.60
1.96


77
17.81




11.88


0.99

69.29


78
17.64




11.76


1.96

68.60


79
17.82




11.88




69.28


80
17.64




11.76




68.60



































Liq
200 P







Strain
Anneal
Soft

Density
Liquidus

Visc
Temp


Example
TiO2
Y2O3
ZnO
ZrO2
Pt
Pt
Point
CTE
(g/cc)
Temp
Phase
(P)
(° C.)





29

3.00


822
866
1055
38.5
3.120
1360
Mullite


30

3.00


815
859
1047
38.4
3.193
1325
Cristobalite


31

3.00


811
854
996
43.2
3.268
1330
Cristobalite


32

3.00


810
852
1033
42.7
3.355
1265
LaSi


33

3.00


812
856
1034
41.0
3.288
1285
Mullite


34

3.00


812
854
1031
43.9
3.361
1255
LaSi


35

3.00


809
851
1025
47.2
3.435
1255
LaSi


36




794
842
1018.5
43.0
3.357
1245
Mullite


37




788
835
1012.5
44.4
3.364
1225
LaSi


38




785
832
1006
46.2
3.372
1235
LaSi


39




791
839
1017.5
43.4
3.296
1240
Mullite


40




789
837
1020.5
42.7
3.233
1240
Mullite


41




789
839
1030
42.6
3.210
1265
Cristobalite


42




788
837
1028
41.4
3.149
1270
Cristobalite


43




793
839
1016
46.7
3.438
1260
LaSi


44




795
841
1013.5
46.2
3.441
1265
LaSi


45







42.1
3.316
1250
Mullite


46







43.2
3.321
1210
Mullite
11725
1433


47







45.9
3.321
1195
Mullite
14000
1430


48






1010
45.4
3.379
1280
?


49






1007
45.6
3.390
1250
?
5300
1434


50






1005
47.0
3.411
1210
?
13300
1433


51






979
41.8
3.355
1270
Mullite


52






958
43.0
3.348
1190
Mullite


53






940
43.0
3.342
1255
Mullite


54









1245
Mullite


55




807
850

42.1

1270
Mullite


56




807
850

41.6

1300
Mullite


57



0.99
806
848

44.5

1245
Mullite


58



1.96
808
850

44.7

1360
mu + zr


59



2.91
808
849

43.8

1430
Zr


60
0.99



801
843

44.5

1240
Mullite


61
1.96



798
839

42.9

1250
Mullite


62
2.91



791
833

43.6

1250
Mullite


63




805
847
1021
44.8
3.446
1255
LaSi


64




808
850
1026
44.9
3.467
1235
LaSi


65




808
850
1029
44.8
3.489
1240
LaSi


66




801
842
1017
43.6
3.385
1245
Mullite


67




793
834
1004
44.6
3.410
1235
Mullite


68




807
849
998
44.6
3.432
1250
Cristobalite


69




806
848
1029
44.5
3.452
1230
Mullite


70




806
848
1026
44.3
3.531
1250
cr + mu


71




805
847
1023
44.0
3.616
1245
Cristobalite


72




796
839

43.6

1220
Mullite


73




789
832

45.5
3.363
1200
Mullite
17800
1434


74




784
827

44.7
3.364
1180
mu + LaSi
24000
1425


75




808
850

43.8
3.373
1340
Cassiterite


76




807
849

44.1
3.387
1410
Cassiterite


77




805
847

43.3
3.413
1535
?


78




805
848

43.3


79


0.99

789
833

44.0
3.339
1220
Mullite


80


1.96

783
825

44.3
3.377
1225
Mullite





































TABLE II



















Young's
Shear




Liq
200 P













Strain
Anneal

Modulus
Modulus
Poisson's
Density
Liquidus

Visc
Temp


Example
Al2O3
Al2N2
B2O3
BaO
CaO
La2O3
MgO
SiO2
SrO
Y2O3
Pt
Pt
CTE
(Mpsi)
(Mpsi)
Ratio
(g/cm3)
Temperature
Phase
(P)
(° C.)




































81
17.74




12.24

69.98


799
842
42.1
13.712
5.449
0.258

1230
Mullite




82
17.55




11.64
0.76
70.02


795
838
42.5
13.668
5.403
0.265

1230
Mullite


83
17.37




11.02
1.51
70.06


791
835

13.649
5.437
0.255

1230
Mullite


84
16.99




9.80
3.01
70.17


785
829
41.1
13.597
5.424
0.253

1250
Cristobalite


85
16.62




8.58
4.50
70.27


781
826

13.589
5.445
0.248

1275
Cristobalite


86
17.34




11.63
1.51
69.48


790
833
42.9
13.838
5.495
0.259

1200
Mullite


87
16.97




11.03
3.00
68.97


782
826
43.5
13.745
5.468
0.257

1210
Cristobalite


88
16.19




9.80
6.01
67.97


771
814
42.9
14.019
5.575
0.257

1215
Cristobalite


89
15.42



0.02
8.58
8.99
66.96


761
805
43.0
13.889
5.522
0.258

1240
La2Si2O7


90
17.74




12.24

69.98


805
847
44.0
13.779
5.455
0.263

1215
La2Si2O7
15600
1436


91
17.48



0.58
11.63

70.27


802
844
43.6
13.686
5.42
0.262

1200
Cristobalite


92
17.24



1.14
11.02

70.57


800
843
43.3
13.651
5.406
0.263

1215
Cristobalite
19500
1455


93
16.71



2.27
9.80

71.19


800
843
42.2
13.399
5.314
0.261

1235
Cristobalite


94
16.20



3.42
8.57

71.77


796
841
41.8
13.141
5.291
0.242

1240
Mullite
21000
1502


95
17.30



1.30
11.64

69.73


799
841
43.9
13.648
5.432
0.256

1210
La2Si2O7


96
16.87



2.59
11.03

69.48


798
840
45.2
13.632
5.4
0.262

1240
La2Si2O7


97
15.98



5.20
9.79
0.02
68.94


791
834
46.3
13.495
5.352
0.261

1245
La2Si2O7


98
15.12



7.80
8.57
0.02
68.43


785
827
47.3
13.328
5.303
0.257

1255
La2Si2O7


99
17.35


0.01

11.64

70.47
0.50

806
848
42.7
13.695
5.398
0.268

1235
Cristobalite


100
16.97


0.01

11.02

70.96
1.00

805
847
41.7
13.462
5.355
0.257

1230
Cristobalite


101
16.19


0.01

9.80

71.97
2.00

804
847

13.261
5.294
0.252

1270
Cristobalite


102
15.42


0.02

8.58

72.94
3.00

804
849
41.3
12.997
5.21
0.247

1290
Cristobalite


103
13.86


0.04

6.12

74.93
4.99

805
852

12.509
5.076
0.232

1335
Cristobalite


104
17.25


0.01

11.64

69.92
1.15

802
845

13.644
5.43
0.263

1235
La2Si2O7


105
16.77


0.02

11.02

69.85
2.30

801
843

13.482
5.368
0.256

1260
La2Si2O7


106
15.78


0.03

9.79

69.75
4.60

798
841

13.211
5.258
0.256

1280
La2Si2O7


107
14.82


0.05

8.57

69.62
6.89

795
838

12.974
5.192
0.249

1335
SrAlSi2O8


108
18.99




12.00

68.97




42.9
13.778
5.472
0.259

1265
Mullite


109
17.36


0.45

11.64

70.51
0.01



44.8
13.481
5.379
0.253

1195
Cristobalite


110
16.98


0.90

11.03

71.03
0.02



43.4
13.385
5.329
0.256

1210
Cristobalite


111
16.22


1.80

9.81

72.09
0.04



43.0
13.095
5.25
0.247

1245
Cristobalite


112
15.46


2.70

8.59

73.13
0.05



42.3
12.865
5.153
0.248

1250
Cristobalite


113
17.18


0.96

11.63

70.17
0.02



45.8
12.824
5.1
0.257

1245
La2Si2O7


114
16.64


1.92

11.02

70.35
0.04



45.9
13.251
5.295
0.251

1245
La2Si2O7


115
15.52


3.83

9.78

70.72
0.08



45.3
12.92
5.163
0.251

1300
La2Si2O7


116
14.41


5.75

8.56

71.08
0.12



46.3
12.637
5.036
0.255

1355
La2Si2O7


117
18.00
0.00



11.00

70.00
3.00

810
850
49.5


118
14.00
2.60



11.00

70.00
3.00

826
868
45.0


119
17.31




11.53
3.84
67.29


782
824
43.6



3.378
1210
La2Si2O7


120
17.14




11.42
4.77
66.64


776
819
45.3



3.381
1205
La2Si2O7


121
16.98




11.32
5.65
66.02


754
802
44.5



3.383
1205
La2Si2O7


122
17.30

3.84


11.53

67.29


756
802
43.0



3.294
1295
Cristobalite


123
17.13

4.76


11.42

66.65


747
792
42.3



3.273
1225
Cristobalite


124
16.97

5.66


11.32

66.01


739
784
42.8



3.26
1255
Cristobalite


125
17.30




11.54
2.88
68.25


784
827
43.8



3.363
1190
La2Si2O7


126
17.14




11.42
2.87
68.54


783
827
43.8



3.353
1200
Cristobalite


127
16.97




11.32
2.83
68.85









1200
Cristobalite


128
16.97

2.83


11.32
2.84
66.01


756
801
44.0



3.326
1240
Cristobalite


129
16.66

2.78


11.11
2.77
66.65


755
799
43.5



3.302
1220
Cristobalite


130
16.35

2.73


10.90
2.73
67.25


756
801
43.7




1270
Cristobalite


131
16.06

2.67


10.71
2.69
67.83


756
801
42.8



3.267
1250
Cristobalite


132
17.39




11.60

70.98


804
847
43.3



3.326
1245
Cristobalite


133
17.14

3.81


11.42

67.59


758
803
42.7



3.287
1230
Cristobalite


134
16.97

3.77


11.32

67.91


757
802
42.9



3.284
1285
Cristobalite


135
16.81

3.75


11.21

68.20


759
804
42.4



3.268
1270
Cristobalite


136
16.50

3.66


11.01

68.79


761
806




3.258
1270
Cristobalite


137
15.66

3.10
1.72
2.05
7.21
0.98
68.74
0.50

754
802
39.6



3.071
1120
Cristobalite
265000
1474


138
14.49

4.63
2.58
3.07
4.80
1.48
68.11
0.76

730
779
38.6



2.914
1185
Cristobalite


139
13.32

6.19
3.45
4.11
2.40
1.97
67.48
1.01

707
757
37.3



2.742
1165
Cristobalite


140
12.14

7.73
4.31
5.14

2.46
66.87
1.27

685
738
37.0



2.551
1115
Cristobalite


141
16.45

2.39
0.41
0.92
9.54
0.09
69.57
0.41
0.20
771
817
40.1



3.194
1340
Cristobalite


142
14.93

4.74
0.81
1.82
7.11
0.19
69.13
0.81
0.39
745
792
38.8



3.031
1230
Cristobalite


143
13.43

7.07
1.20
2.71
4.71
0.30
68.72
1.21
0.59
719
768
37.2



2.856
1220
Cristobalite


144
11.95

9.37
1.59
3.59
2.34
0.39
68.32
1.60
0.78
692
742
35.5



2.665
1215
Cristobalite


145
10.48

11.64
1.98
4.47

0.50
67.90
1.99
0.97
663
715
33.5



2.474
1100
Cristobalite


146
11.48


5.98
5.49

0.02
76.82
0.12

816
872
37.4



2.538
1460
Cristobalite


147
11.37


5.93
5.43
0.99
0.02
76.07
0.11

791
845
39.5



2.698
1355
Cristobalite


148
11.25


5.87
5.38
1.96
0.02
75.31
0.12

781
833
42.0



2.789
1395
Cristobalite


149
11.14


5.81
5.32
2.91
0.02
74.60
0.11

776
826
44.1



2.866
1405
Cristobalite


150
11.31


4.42
5.41
2.95
0.02
75.72
0.09

785
836
41.3



2.819
1350
Cristobalite


151
16.69


1.20
1.10
9.59

71.35
0.03

801
846
42.5



3.223
1255
Cristobalite


152
15.38


2.40
2.19
7.19

72.73
0.05

799
846
41.3



3.079
1285
Cristobalite


153
14.08


3.59
3.30
4.79

74.09
0.07

798
847
41.1



2.927
1335
Cristobalite


154
12.77


4.79
4.39
2.40
0.02
75.46
0.10

800
852
38.5



2.780
1400
Cristobalite


155
18.29




12.19

69.48


804
847
44.8



3.361
1275
Mullite
3600
1436


156
17.24



1.14
11.02

70.57


801
845
43.7



3.298
1235
Cristobalite
1600
1455


157
16.20



3.42
8.57

71.77


799
844
40.9



3.122
1305
Cristobalite

1502


158
15.68



4.55
7.34
0.02
72.35


797
844
39.5



3.039
1290
Cristobalite

1531


159
16.97


1.00

11.02

70.95
0.02

802
847
43.4



3.314
1270
Cristobalite

1466


160
16.99


0.50
0.50
11.00

70.97
0.01

802
846
43.1



3.301
1245
Cristobalite
10100
1461


161
17.91




10.94
1.48
69.63


794
838
42.7
13.74
5.496
0.256
3.294
1270
Mullite


162
17.81




9.90
2.96
69.30


786
831
42.3
13.83
5.498
0.257
3.235
1295
Mullite


163
17.73




8.87
4.43
68.94


781
826
40.5
13.79
5.494
0.255
3.171
1300
Mullite


164
17.90



1.50
10.94

69.63


800
844
44.3
13.64
5.423
0.257
3.229
1250
Mullite


165
17.81



2.98
9.90

69.28


797
841
43.4
13.54
5.398
0.254
3.235
1235
Mullite


166
17.72



4.44
8.86

68.92


795
840
43.1
13.52
5.384
0.256
3.170
1235
Mullite


167
17.90


0.01

10.94

69.62
1.49

800
844
43.6
13.64
5.39
0.265
3.318
1220
Mullite


168
17.82


0.02

9.90

69.26
2.97

801
845
44.4
13.49
5.352
0.261
3.275
1250
SrAlSi2O8


169
17.72


0.03

8.86

68.90
4.43

800
845
45.1
13.35
5.305
0.258
3.224
1290
SrAlSi2O8


170
17.30




11.54

68.24
2.88

800
843
46.8
13.58
5.381
0.262
3.406
1260
La2Si2O7


171
17.14




11.43

68.54
2.85

800
843
47.4
13.53
5.362
0.262
3.395
1265
La2Si2O7


172
16.98




11.32

68.83
2.83

800
844
47.1
13.52
5.356
0.262
3.379
1270
La2Si2O7


173
17.82


0.99

11.88

69.28


803
846
45.5
13.59
5.397
0.259
3.389
1225
La2Si2O7


174
17.64


1.96

11.76

68.60


802
846
46.1
13.61
5.346
0.273
3.412
1310
La2Si2O7


175
17.46


2.91

11.64

67.92


802
845
47.8
13.5
5.326
0.268
3.441
1270
La2Si2O7


176
17.90


1.49

10.94

69.63


805
849
44.4
13.55
5.35
0.266
3.334
1235
La2Si2O7


177
17.81


2.97

9.89

69.26


806
850
43.4
13.23
5.271
0.255
3.304
1215
La2Si2O7


178
17.72


4.43

8.86

68.92


806
851
45.6
13.1
5.198
0.26
3.287
1325
BaAlSi2O8


179
16.57

1.96

1.82
9.96
0.04
69.53
0.11

776
882
42.6



3.210
1255
Cristobalite


180
15.09

3.91

3.65
7.48
0.08
69.57
0.22

754
801
37.7



3.014
1260
Cristobalite


181
13.60

5.88

5.48
4.99
0.13
69.60
0.32

732
779
37.4



2.814
1260
Cristobalite


182
12.11

7.84

7.31
2.49
0.17
69.64
0.43

714
763
35.7



2.598
1205
Cristobalite


183
11.37

8.82

8.23
1.25
0.19
69.65
0.49

701
751
33.2



2.486
1205
Cristobalite


184
10.63

9.80

9.14

0.21
69.67
0.54

688
742
32.9



2.369
1210
Cristobalite


185
18.05




12.45

69.50


806
848
44.0



3.402
1225
La2Si2O7


186
15.42

3.41
1.73
2.09
7.48
0.52
68.83
0.52

750
798
42.2



3.078
1205
Cristobalite


187
14.10

5.13
2.59
3.14
4.99
0.78
68.49
0.78

726
777
39.1



2.911
1200
Cristobalite


188
12.78

6.84
3.46
4.19
2.50
1.04
68.16
1.04

704
754
39.5



2.727
1200
Cristobalite


189
12.12

7.70
3.90
4.72
1.25
1.17
67.99
1.17

688
741
38.1



2.639
1160
Cristobalite


190
11.45

8.56
4.33
5.24

1.30
67.82
1.30

676
730
38.2



2.549
1120
Cristobalite


191
15.65

3.09
1.72
2.05
6.20
0.98
68.70
0.50
1.00
760
808
40.7



3.129
1355
Mullite


192
15.65

3.09
1.72
2.05
5.20
0.98
68.70
0.50
2.00
773
819
39.9



2.772
1245
Cristobalite


193
16.62

3.16
1.81
2.16
7.53
1.07
67.13
0.52

752
799
41.3



3.076
1160
Mullite
77500
1474


194
17.65


2.94

9.80

69.61


803
848
44.5



3.286
1185
La2Si2O7
62700
1473






























TABLE III















Tstr
Tann
α

Liq.


Example
La2O3
Al2O3
SiO2
MgO
ZrO2
SnO2
SrO
HfO2
Yb2O3
(° C.)
(° C.)
(ppm/° C.)
CTE
Temp.





























195
5
13
80

2


—
—
846
895
2.82




196
5
14
80

1


—
—
836
882
2.88


197
4
14
80

2


—
—
849
893
2.66


198
3
14
80

3


—
—
880
945
2.36


199
3
13
80

4


—
—
872
938
2.21


200
4
12
82

2


—
—
855
898
2.57


201
3
13
82

2


—
—
883
953
2.27


202
3
12
82

3


—
—
882
954
2.39


203
4.19
13.3
80

—


2.2
0.25
852
898
2.61


204
6
13
80
1





811


29.6


205
5
13
80
2





815


25.4


206
4
13
80
3





823


27.1


207
5
14
80
1





819


26.8


208
4
14
80
2





823


25.7


209
3
14
80
3





831


22.1


210
3
14
80
1.5
1.5




837


24.9


211
6
13
80


1



838


29.9


212
5
14
80


1



828


28.1


213
6
13
80



1


814


30.8


214
5
13
80



2


811


29.6


215
4
13
80



3


809


29.3


216
5
14
80



1


820


27.6


217
4
14
80



2


815


27.3


218
3
14
80



3


818


26.0


219
5.9
13.9
79.2
1





828


29.2
1460


220
5.9
13.7
78.4
2





808


33.4
1435


221
5.8
13.6
77.7
2.9





791


33.2
1430


222
5.9
13.9
79.2
0.5
0.5




833


32.4
1440


223
5.9
13.7
78.4
1
1




838


31.5
1440


224
5.8
13.6
77.7
1.45
1.45




823


32.6
1460


225
5.9
13.9
79.2

1




827


33.1
1460


226
5.8
13.6
77.7

2.9




833


31.7
1510























TABLE IV





Example
La2O3
Al2O3
SiO2
Na2O
Y2O3
SrO
Tstr (° C.)






















227
3.0
14
80
0.5
3.0
—
840


228
2.75
14
80
—
2.75
1.0
836









While the invention has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of the invention disclosed herein. The scope of the invention is defined by the attached claims.

## Claims

1. A substrate for a flat panel display device comprising a rare earth aluminosilicate glass exhibiting a strain point greater than approximately 650° C., a liquidus temperature less than approximately 1300° C., the glass comprising the following composition when calculated in mole percent and calculated from the batch on an oxide basis:


60-75%SiO2 



10.6-20% Al2O3 



2-15%RE2O3 

the RE being a rare earth selected from group consisting of Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and mixtures thereof; and
1-12% of one or more RO, wherein R is an alkaline earth metal selected from the group consisting of Mg, Ca, Sr, or any combination thereof; or when R is Ba, at least one additional alkaline earth metal selected from the group consisting of Mg, Ca, and Sr is present;
0-9% B2O3; and
0-2% SnO2,

wherein the composition does not contain TiO2 and Ta2O5 either individually or in any combination thereof.

2. The substrate of claim 1 wherein said substrate comprises the following composition when calculated in mole percent and calculated from the batch on an oxide basis:


65-75% SiO2 



10.6-20% Al2O3 



4-15% RE2O3.

3. The substrate of claim 1 having a strain point of at least 650° C.

4. The substrate of claim 1 wherein the substrate comprises, in mole percent and calculated from the batch on an oxide basis, 2-15% La2O3.

5. The substrate of claim 1 having a liquidus temperature of no greater than 1300° C.

6. The substrate of claim 1 having a liquidus viscosity greater than 10,000 poise.

7. A rare earth aluminosilicate glass exhibiting a strain point greater than approximately 650° C., a liquidus temperature less than approximately 1300° C., the glass comprising the following composition as calculated in a mole percent on an oxide basis:


65-75% SiO2 



10.6-20% Al2O3 



2-15% RE2O3 

the RE being a rare earth selected from the group consisting of Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and mixtures thereof; and
1-12% of one or more RO, wherein R is an alkaline earth metal selected from the group consisting of Mg, Ca, r, or any combination thereof; or when R is Ba, at least one additional alkaline earth metal selected from the group consisting of Mg, Ca, and Sr is presented;
0-9% B2O3; and
0-2% SnO2,

wherein the composition does not contain TiO2 and Ta2O5 either individually or in any combination thereof.

8. The glass of claim 7 further exhibiting a liquidus viscosity of greater than 10,000 poise.

9. The glass of claim 7 further exhibiting a 200 Poise temperature that is less than 1550° C.

10. The glass of claim 7, wherein the glass is a substrate present in an electronic device.

11. The glass of claim 10 wherein the electronic device is an LCD display.

12. The glass of claim 7, wherein Re is La.

13. The glass of claim 7, wherein RE is La, and the amount of La2O3 is from 2-12.49% in mole percent as calculated from the batch on an oxide basis.

14. The glass of claim 7, wherein the amount of RO is about 7-12% mole percent as calculated from the batch on an oxide basis.

15. The glass of claim 7, wherein the amount of RO is about 10-12% mole percent as calculated from the batch on an oxide basis.

16. The glass of claim 7, wherein the amount of B2O3 is about 0-3% mole percent as calculated from the batch on an oxide basis.

17. The glass of claim 7, wherein the glass has a coefficient of thermal expansion (0-300° C.) of 25-50×10−7/° C.

18. The glass of claim 7, wherein the glass has liquidus temperature less than 1250° C.

19. The glass of claim 7, further comprising a ratio (RO+1.5*RE2O3)/Al2O3 wherein the ratio is between 0.85 and 1.2.

20. A rare earth aluminosilicate glass exhibiting a strain point greater than approximately 650° C., a liquidus temperature less than approximately 1300° C., the glass consisting of the following composition as calculated in a mole percent on an oxide basis:


60-75% SiO2 



10-20% Al2O3 



2-12.49% RE2O3 

the RE being a rare earth selected from the group consisting of Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and mixtures thereof; and
1-12% of one or more RO, wherein R is an alkaline earth metal selected from the group consisting of Mg, Ca, and Sr; or when R is Ba, at least one additional alkaline earth metal, selected from the group consisting of Mg, Ca, and Sr is present;
0-9% B2O3; and
0-2% SnO2.

21. The glass of claim 20, wherein the glass is a substrate present in an electronic device.

22. The glass of claim 21, wherein the electronic device is an LCD display.

23. The lass of claim 20, further comprising a 200 Poise temperature that is less than 1550° C.