The gate electrode G may be formed above the gate insulating film 210. The gate electrode G is connected to a gate line for applying an on/off signal of the thin film transistor TFT. The gate electrode G may include at least one metal selected from molybdenum (Mo), aluminum (Al), platinum (Pt), palladium (Pd), silver (Ag), magnesium (Mg), gold (Au), nickel (Ni), neodymium (Nd), iridium (Ir), chromium (Cr), lithium (Li), calcium (Ca), titanium (Ti), tungsten (W), and/or copper (Cu). However, the gate electrode G is not limited thereto, and may be formed of various materials in consideration of design conditions.

After the forming of the gate electrode G, an interlayer insulating film 230 may be formed over the substrate 100 to insulate the gate electrode G from the source electrode S and the drain electrode D. The interlayer insulating film 230 may be formed of an inorganic material. For example, the interlayer insulating film 230 may be formed of metal oxide and/or metal nitride, and the inorganic material may include silicon oxide (SiO₂), silicon nitride (SiN_x), silicon oxynitride (SiON), aluminum oxide (Al₂O₃), titanium oxide (TiO₂), tantalum oxide (Ta₂O₅), hafnium oxide (HfO₂), and/or zirconium oxide (ZrO₂). The interlayer insulating film 230 may include a single layer or multiple layers formed of an inorganic material, such as silicon oxide (SiO_x) and/or silicon nitride (SiN_x). In some embodiments, the interlayer insulating film 230 may include a dual structure of SiO_x/SiN_y and/or SiN_x/SiO_y.