LCD-Based Flexible Displays Could Offer Cost Benefit Over AMOLED if Backlight Issues Resolved, DisplaySearch Says

Extending the attributes of flexible AMOLED-based display technology -- used in the Galaxy S6 Edge and Apple Watch -- to lower-cost LCD screens is possible but with challenges, said DisplaySearch analyst Charles Annis in a blog post. Plastic thin-film transistor (TFT) LCDs offer many of the advantages of flexible AMOLEDs in being unbreakable, thin, light and conformable, Annis said, but illumination is an obstacle for LCDs that require either a backlight or front light for illumination compared with self-emitting AMOLED displays. AMOLED is also superior in motion response, color reproduction and contrast ratio, he said. LCDs have the potential for color shifting from nonalignment of the TFT and corresponding color filter subpixel, viewing angle dependence and light leakage after curving or flexing, said Annis. Merck affiliate EMD and FlexEnable are attempting to overcome the obstacles to flexible LCDs and have demonstrated functioning plastic IPS (in-plane switching)-type TFT LCD, he said. EMD and FlexEnable see LCDs as a lower cost and faster road to widescale flexible display adoption than AMOLEDs and maintain that challenges to flexible LCD commercialization can be overcome by incremental improvements that don't require major technology breakthroughs. They propose using organic TFTs (OTFTs) to drive the active matrix because they’re intrinsically flexible and can be fabricated at very low temperatures. That enables the use of low-cost conventional plastic substrates and involves a simple and high-yielding bond/de-bond process, he said. EMD is also developing a new type of cell architecture/spacer technology to overcome cell gap variation problems in flexible LCDs, said Annis. The technology polymerizes walls between the front and back planes to maintain the gap and contain liquid crystal (LC) material within a defined area, he said. The backlight remains a sticking point for flexible displays. They can be curved, but making them flexible is more difficult, said Annis. “Reflective LCDs and front-lights are a potential way to side-step this concern, but color reproduction and contrast are typically compromised in reflective displays,” he said. Plastic TFT LCDs made on low-cost flexible substrates for curved applications may be feasible -- and could theoretically be produced more cost effectively than AMOLEDs -- but there’s “a long road to travel” before flexible LCDs can move from prototyping to commercial production, said Annis.