Ultra Thin Flexible Glass Substrates
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Ultra Thin Flexible Glass Substrates Armin Plichta, Andreas Weber and Andreas Habeck1 SCHOTT Flat Panel Display, A Business Segment of SCHOTT Spezialglas GmbH Hattenbergstr.10, D-55014 Mainz, Germany 1
Schott Glas
Hattenbergstr.10, D-55014 Mainz, Germany
Abstract New applications in the electronics market ranging from foldable displays in mobile phones to wearable displays in clothes generate a high demand for flexible materials especially for substrates. The upcoming OLED technology shows some advantages in comparison with conventional LCDs and enables real flexible or shaped displays. Moreover, the wearable displays have a barely need for flexible electronic circuits. At a first glance polymer foils are the materials of choice for flexible substrates and for electronic circuits but in general they suffer from thermal instability as well as from high permeation rates for gases and water and hence chemical stability of critical materials such as LC’s or low work function materials. In contrast, even ultra thin glass sheets have excellent barrier properties and show sufficient bending properties if they are thinner than 100µm.
Flexible glass substrates down to a thickness of 50µm have been developed. The deposition of an organic coating helps to overcome significantly the lack of mechanical stability. Therefore, our flexible glass substrates can be used in conventional display manufacturing processes which include several thin film process steps. Moreover, they are suited for production of flexible PCB’s.
Introduction In general glass is the material of choice when transmission of light is needed for a certain application. Nevertheless, plastic became the competitive material in a broad range of products. The main reason that glasses are replaced by plastics only in a small amount of applications is due to the fact that plastic suffers from lifetime problems in a lot of typical environments like
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humidity, sunlight, chemical attack, mechanical abrasion or higher temperature. Moreover, the thermal coefficient of expansion (CTE) of plastic is very high in contrast to glass and plastic is a thermally unstable material which means heating and cooling cycles lead to small deformations. This is mostly not acceptable for applications that need processes or working tolerances in the µm-region over a temperature range of some hundred °C. Therefore, the traditional usage of glass sheets today ranges still from typical window glasses to special developed glasses for optical and electronic applications.
We distinguish between soda lime glasses used for more or less cheap production of mass products (window glass, bottles,.) and so called special glasses like borosilicate glasses. These special glasses guarantee well defined physical or chemical specifications due to the very high requirements for base materials as well as very fine tuned and controlled production and process parameters. For instance, the refractive index of optical glasses is controlled up to five digits. The usable base materials for thes
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