The core technologies for the foldable display device are a flexible OLED panel, a flexible cover window and a folding hinge. Among them a hinge controls folding motion trajectory of an OLED panel. It is very important for an OLED panel not to apply any additional stress during folding motion. We developed the stress‐free folding (SFF) hinge with a virtual axis structure (VAS). Using SFF hinge we can achieved that the stress on OLED panel during folding is almost same as the free folding stress. As a result, there is no issue on an OLED panel in 200k folding reliability test with SFF hinge. Its torque reduction is less than 20% after 200k folding test.

After a foldable mobile phone's success, a rollable device has received a great attention in the market. Several makers have demonstrated its prototypes and trying to commercializing it. We have reviewed its mechanism and technical issues and suggest a novel rolling hinge for a rollable mobile device. We have developed a new back‐plate for stable and durable motion. Using our back‐plate and rolling hinge we have made a mock‐up of a rollable device and confirmed its performance and durability. Our mock‐up has the thickness of ~12.0 mm which is very slimmer than a foldable device. It can drive by manual, semi‐auto or auto ways. We designed motor force or spring force considering its moving resistance.