A liquid crystal display device and an EL (electroluminescence) display device which respectively have a liquid crystal element and a light-emitting element in each pixel are represented as a typical example of a display device.  These display devices have display elements such as a liquid crystal element or an organic light-emitting element (hereinafter, referred to as a light-emitting element) in each of the plurality of pixels formed over a substrate.  A liquid crystal element and a light-emitting element have a liquid crystal and a layer including an organic compound (hereinafter, referred to an organic layer), respectively, between a pair of electrodes and are operated by applying a voltage or supplying current between the pair of electrodes. 
A light-emitting element is formed as a fully solid display element.  Therefore, apart from a liquid crystal element, quality of display is not generally influenced even if a light-emitting element is provided with flexibility and folded or bent because a change in gap between the substrates does not cause any influence to an organic layer.  This feature has been utilized to fabricate a so-called flexible display (sheet display) in which a light-emitting element is formed over a flexible substrate.  For example, Japanese patent application publication No.  2013-15835 discloses a flexible organic EL display device which can be folded.