As the displays of, for example, televisions, personal computers, smartphones, tablet computers, etc., display devices which employ an organic EL device have been developed. The organic EL device emits light when voltage is applied to an organic material disposed between a positive electrode and a negative electrode.
Organic EL devices are driven, for example, by thin-film transistors. The organic EL devices and the thin-film transistors including, for example, an oxide semiconductor layer deteriorate by contact with moisture, hydrogen, or the like.