用于薄、轻、柔性OLED照明的超薄玻璃基板

Over the last decade, OLED materials, fabrication methods, and device technologies have made significant progress as the demand for OLED TVs grew within the display industry. Around the same time, manufacturers OSRAM and Philips began to consider the use of OLED materials for lighting applications. Indeed, although LED technology has advanced significantly with decreasing costs, in the past five years there has been steady progress in OLED lighting technology, led by LGD (which was within LG Chemical until 2017), OSRAM, and OLEDWorks.

Flexible surface lighting is the key differential advantage of OLED lighting technology. Table 1 shows the substrate material attributes for possible flexible substrate options that enable this and how flexible glass compares against the alternatives. In this case Corning® Willow® Glass,2  is used as the example. Flexible glass provides advanced attributes in areas of optical and surface quality, dimensional and thermal stability, chemical compatibility, and hermeticity. In addition, flexible glass is compatible with high-throughput manufacturing methods such as roll-to-roll (R2R) processing.

Previous work extensively covered flexible glass properties such as mechanical reliability, as well as device fabrication methods (including R2R processing) and example applications.3-5 Willow Glass is produced in a continuous fusion-forming process, similar to OLED and LCD display glass substrates, at thickness ≤ 200 µm and widths > 1 meter (m). During manufacturing, the glass is wound onto spools in lengths up to 300 m. The flexible glass can be cut into sheets and temporarily bonded to a rigid carrier to enable sheet processing, or be used as a flexible web in R2R manufacturing.

With these demonstrated process capabilities, we see that electronic devices fabricated routinely on thicker rigid glass substrates also can be manufactured on flexible glass. The key difference is that ultrathin glass opens up new opportunities for thin, lightweight, and flexible form factor applications or applications dependent on high-throughput scaling of R2R processing not accessible to rigid substrates.

OLED lighting and OLED TV manufacturing share similar challenges, but with one significant difference—lighting applications do not need thin-film transistor backplanes, which simplifies the manufacturing process for OLED lighting considerably. However, they both need high-moisture-barrier sealing performance (~10-6 g/m² /day WVTR) and high-power efficacy (lm/W), along with low manufacturing costs—these continue to be industry concerns. Significant progress has occurred on these fronts over the past four years. Use of bottomemission OLED structures on glass-substrate, thin-film encapsulation with metal foil on the back side, and new internal and external lightextraction technology has allowed manufacturers to commercialize OLED lighting panels with 100,000 hours of lifetime (LT70) and an efficacy of 85 lm/W.

Fig6

Considering flexible OLED lighting applications, we had to resolve two technical challenges to enable flexible glass use. First, processing flexible substrates in existing tools designed for rigid substrates needed a glass-on-carrier solution that can handle flexible glass as a rigid substrate for device processing. The bonding between flexible glass and the carrier must be strong enough to survive all device-processing conditions, but also weak enough so that after processing, the glass can be lifted easily from the carrier for subsequent cutting and finishing the lighting panels.

The second challenge had to do with the device panels’ mechanical reliability after singulation from the large sheet. The standard cutting process renders edges with defects (microcracks) and reduces tolerance for stress induced by bending. Here also, Corning developed a proprietary edge-finishing process that let us render a nearly defect-free edge after singulation, and enabled highly reliable panels that simultaneously are flexible and present a strong barrier, resulting in a lifetime of 50,000 hours.7  OLEDWorks released the first flexible panel—LumiCurve Wave—in November 2018, which used the aforementioned groundbreaking carrier and singulation technologies. Fig. 6 offers more detail of the bonding and debonding and edge-healing technology used for LumiCurve Wave panels. Fig. 7 shows an example of an OLED lighting panel fabricated in a carrier process with processed edges for improved bend strength.