Recent light-emitting devices and display devices are expected to be applied to a variety of uses and become diversified.
For example, light-emitting devices and display devices for mobile devices and the like are required to be thin, lightweight, and less likely to be broken.
Light-emitting elements utilizing EL (also referred to as EL elements) have features such as ease of thinning and lightening, high-speed response to an input signal, and driving with a direct-current low voltage source; therefore, application of the light-emitting elements to light-emitting devices and display devices has been proposed.
For example, Patent Document 1 discloses a flexible active matrix light-emitting device in which an organic EL element or a transistor serving as a switching element is provided over a film substrate.
An organic EL element has a problem in that entry of impurities such as moisture or oxygen from the outside erodes the reliability.
When impurities such as moisture or oxygen enter an organic compound or a metal material contained in an organic EL element from the outside of the organic EL element, the lifetime of the organic EL element is significantly shortened in some cases. This is because an organic compound or a metal material contained in the organic EL element reacts with the impurities such as moisture or oxygen and thus deteriorates.
Thus, a technique to seal an organic EL element for preventing entry of impurities has been researched and developed.