April 14, 1998Management


Asahi Glass Company, Limited (AGC), of Tokyo, Japan (President & CEO: Hiromichi Seya) has developed new alkali-free glass substrates (trademark : AN100) for TFT (thin film transistor)-LCDs and will start manufacturing them at its Keihin Factory in Yokohama city from this July.

AGC has been supplying alkali-free glass substrates (trademark : AN635) for TFT-LCDs since 1994, and has gained a good reputation for its quality level and suppliability from TFT-LCD manufacturers.
TFT-LCDs are increasingly finding various applications, from small panels to large panels, particularly in notebook personal computers with panel sizes of more than 12 inches, but also in consumer applications such as digital still cameras, mobile applications such as PDA (personal data assistance) and monitors for desk top personal computers.
Such new applications require higher and severer level of property and quality in glass substrates because of the trend towards higher resolution as well as larger and thinner panels. Particularly, the next generation substrates require certain high performance in mechanical properties such as higher Young's modulus to minimize the warpage and gravitational sag of glass substrates, and mechanical strength to reduce cracks and chips. Other properties specifically requested are thermal characteristics, i.e. lower thermal expansion and lower thermal shrinkage, and lighter weight. In addition, no content of hazardous materials such as arsenic oxide (As2O3) is important in consideration of environmental protection.

Based upon its accumulated glass-related technologies, AGC succeeded in developing new alkali-free glass substrates to fulfill the above-mentioned requirements, and decided to proceed to commercial production.
The production method used for these new alkali-free glass substrates is the float process which has been long used for glass production as the most suitable process for mass production. The product manufactured by the float process has relatively smaller warpage, better flatness and smaller thickness deviation. Moreover, it can have better thermal stability because a sufficient annealing treatment can be applied online. All of our glass-based substrates, i.e. soda lime glass substrates for TN (twisted nematic) and STN (super twisted nematic) and current alkali-free glass substrates "AN635"have been produced by the float process.

Thermal shrinkage of new alkali-free glass substrates "AN100" is successfully reduced to a level of less than half of thermal shrinkage of "AN635" by maximizing the advantages of the float process. Moreover, in comparison with "AN635" ,it achieved strain point as high as about 670°C which is more than 35°C higher than that of " AN635", 20% lower thermal expansion coefficient and 5% higher Young's modulus. Particularly, in terms of Young's modulus which should be higher to reduce the gravitational sag for larger and thinner panels, "AN100" has Young's modulus about 10% higher than that of other companies' glass substrates. As a result, for instance, the gravitational sag of a 0.7 millimeter-thick glass substrate with 1 meter width has been reduced by about 10 millimeters (calculated by AGC).

It is given as a conclusion that "AN100" cannot only contribute to higher yield in the process of amorphous-silicon TFT-LCDs but also can be used in the process of low temperature poly-silicon TFT-LCDs in which higher process temperature is required.
AGC has set 2 float furnaces in production since 1996 to manufacture alkali-free glass substrates. At present, AGC has about 30% share with "AN635"in the alkali-free glass market (estimated by AGC). By promoting this "AN100",in addition to "AN635", AGC expects that its sales will reach 50% in the market share and 20 billion Japanese Yen in amount in 2000.



The advantages of the new alkali glass substrate
(in comparison with the existing product)

new product
existing product
1) Density (lighter weight) 2.51 g/cm3 2.77g/cm3
2) Thermal shrinkage 8 ppm 18 ppm
(1 hour heat treatment at 450°C)
3) Strain point about 670°C about 635°C
4) Young's modulus 7900 kgf/mm2 7450kgf/mm2
Asahi Glass Co., Ltd.
Marketing And Sales Group
Fine Glass Div.
Electronic Products General Div.
TEL: 81-3-3218-5341