Andreas Habeck

Ultra Thin Flexible Glass Substrates

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 LCs 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 PCBs.

6.3: Thin Glass-Polymer Systems as Flexible Substrates for Displays

Thin and flexible substrates are urgently needed to realize new applications for LCD- and OLED displays. The use of polymer foils is limited due to high permeation rates for oxygen and water and complicated coatings are needed to reduce the permeation rate. On the other hand even ultra thin glass has excellent barrier properties but limitations regarding mechanical stability. The developed thin glass-polymer systems with a thickness range from 100-50 μm show excellent barrier properties combined with sufficient bending property to shape displays for various applications. An organic polymer coating on the ultra thin glass by means of dipping or spin coating improves significantly the mechanical stability of the thin glass. Thus, the thin glass-polymer substrates can be used in conventional cleaning and ITO process lines. The influence of various coatings on the mechanical properties is shown.