The first gate electrode 213, the first source electrode 215a, and the first drain electrode 215b may include various conductive materials. For example, the first gate electrode 213 may include molybdenum or aluminum, and may have a multi-stack structure. For example, the first gate electrode 213 may have a triple-layer structure including a molybdenum layer, an aluminum layer, and a molybdenum layer. The first source electrode 215a and the first drain electrode 215b may include titanium or aluminum, and may have a multi-stack structure. For example, the first source electrode 215a and the first drain electrode 215b may each have a triple-layer structure including a titanium layer, an aluminum layer, and a titanium layer. However, the present disclosure is not limited thereto.

A buffer layer 110 including an inorganic material such as, for example, silicon oxide, silicon nitride and/or silicon oxynitride may be interposed between the first thin-film transistor 210 and the substrate 100. The buffer layer 110 may be configured to improve planarization of a top surface of the substrate 100, or to prevent or minimize penetration of impurities from the substrate 100 into the first semiconductor layer 211 of the first thin-film transistor 210.