Glass Substrates for Flat Panel Displays
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Flat Panel Displays Dawne M. Moffatt
Introduction One material exists in most types of flat panel displays that are used in high information content applications, from liquid crystal displays to electroluminescent displays. This material is glass, something we all use daily. As a substrate, glass plays a significant role in the manufacture and function of flat panel displays (FPDs). In the case of active-matrix liquid crystal displays (AMLCDs), the semiconductor-based thin-film transistors (TFTs) or diodes are fabricated on the active glass substrate. In addition, AMLCDs require color-filter structures consisting of dyed or pigmented resins built upon the passive plate of an AMLCD cell. For plasma and electroluminescent display panels, the glass provides the surface upon which are deposited phosphors, conductive lines, and dielectrics. The excellent properties of glass make it the substrate of choice in FPDs. It is the only material that can meet the demanding requirements of high-informationcontent FPD manufacturing processes and operation. Glass' transparency is an obvious requirement. For all types of displays, the rigidity of glass also plays a important role because it adds overall mechanical integrity and strength. One of the most important attributes of glass in terms of the display manufacturing process is its thermal stability. Glass substrates, particularly those made of "hard" or high temperature glasses, can be processed at elevated temperatures with minimal deformation. In addition, the dimensional precision required in the alignment of various display components is maintained throughout the specific manufacturing processes. Finally, the glass substrates used for FPDs are chemically durable, and are able to withstand the chemically hostile environments used in cleaning and patterning steps of display manufacturing. There are many families of glasses covering a broad range of physical, mechanical, and thermal properties. The
MRS BULLETIN/MARCH 1996
glasses typically used in FPDs are silicate-based glasses such as soda lime silicate and alkaline earth aluminoborosilicate glasses, the latter used especially for the most demanding display technologies. Some of the worldwide glass suppliers that manufacture and finish glass substrates for FPDs include Corning Incorporated, Asahi Glass Company, Nippon Sheet Glass (NSG), Glaverbel, Flachglas, Pilkington Brothers Limited, Nippon Electric Glass (NEG), Schott Glass, Hoya, and NHTechno (a joint venture between Hoya and NSG). This discussion covers the manufacturing processes used to produce precision flat glass for display applications and the substrate requirements for the different types of flat panel displays, including LCDs and various kinds of emissive displays. Flat Glass Manufacturing and Forming Processes There are numerous ways to manufacture glass substrates for flat panel displays. These range from small-scale laboratory melting for sample-making to high-volume melting for producing large-sized glass substrates formed in
the same way as traditional
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