Display Grade Corning® EAGLE XG, an aluminosilicate glass used as the substrate of choice for active matrix liquid crystal displays, has a strain point of 669°C, anneal point of 722°C, softening point of 971°C, CTE of 31.7 x 107 / °C, and a refractive index of 1.5198 - 1.5078 (435.8 nm - 643.8 nm). EAGLE XG is produced by the "fusion draw process" first developed by Corning in the 1960s to produce very thin, exceptionally flat and smooth glass. Typical composition of aluminosilicate glass is 55.0% SiO2, 7.0% B2O3, 10.4% Al
2O3, 21.0% CaO, and 1.0% Na2O. No passivation layer is present - ITO is directly applied to the substrate.
Float ( Soda-Lime ) Glass
Glass which is produced using the "float" process, developed by Pilkington (UK), in which the molten glass is floated on a pool of liquid tin under a nitrogen/hydrogen atmosphere. This high volume process results in glass which does not require grinding or polishing to achieve a high-quality finish. Float glass will typically have a strain point of 523°C, an anneal point of 546°C, a softening point of 726°C, a CTE of 77 - 85 x 107 / °C, and a refractive index of 1.517. Typical composition of float glass is 72.6% SiO2, 0.8% B2O3, 1.7% Al2O3, 4.6% CaO, 3.6% MgO, and 15.2% Na
2O. ITO coated float glass is only offered with a SiO2 passivation layer applied directly on the glass prior to ITO coating. It is available in two grades of glass - unpolished float glass and polished float glass.
Fused Quartz, GE Type 124 or equivalent, has a strain point of 1,120 °C, CTE of 5.5 x 107 / °C, and a refractive index of 1.4585. Fused quartz substrates are made by machine methods, cutting raw sheets from a large fused quartz boule cast from the melt, followed by grinding and polishing to desired smoothness. No passivation layer is present - ITO is directly applied to the substrate.
Voltage necessary to achieve a given power level can be calculated by the following formula:
V = √ [ R * P * A ]
R = Resistance in Ohms
For each 1°C rise in temperature required, about 13.5 watts/meter2 will be required. The resistance of a given surface may be visualized as the sum of squares in a parallel or series circuit, but the bus locations must be defined. For example: A 40 x 60 mm rectangle having a 20 ohms coating, with bus bars on each of the 60 mm edges has one and one-half squares in parallel, or 20 ohms/1.5 squares = 13.33 ohms. If the bus bars are applied to the 40 mm edges, there are one and one-half squares in series, or 20 x 1.5 squares = 30 ohms. Either example has an area of 2,400mm2, or .0024 meter2. If we assume that we need 100 watt / meter2, the two cases become:
P = Power in Watts/meter2
A = Area in meters2
V = √ [ 13.33 * 100 * 0.0024 ] = 1.8 volts
V = √ [ 30 * 100 * 0.0024 ] = 2.7 volts
A barrier coating of 200 - 300 Ångstroms of SiO2 is applied directly to the surface of float glass, over which is coated ITO. This barrier layer is intended to minimize the leaching of alkali oxides into liquid crystals, which can have detrimental effect on the volume resistivity of the liquid crystal. This is standard for all float glass we sell. Glass can be directly coated with ITO, but will only be available as a special request, and will require a minimum volume to be made.
Corning® EAGLE XG has a typical surface roughness of
<0.02 micrometer/5 mm, peak-to-peak
Polished float glass has a typical surface roughness of
<0.05 micrometer/20 mm, peak-to-peak, for 1.1 mm substrates, and <0.075 micrometer/20 mm, peak-to-peak, for 0.7 mm substrates.
Unpolished float glass has a typical surface roughness of
<0.15 micrometer/20 mm, peak-to-peak, for 1.1 mm substrates, and <0.20 micrometer/20 mm, peak-to-peak, for 0.7 mm substrates..