The TFT 130 may include a semiconductor layer 134 and a gate electrode 136. The semiconductor layer 134 may include, for example, polysilicon. The semiconductor layer 134 may include a channel region 131 overlapping the gate electrode 136 and a source region 132 and a drain region 133 located at both sides of the channel region 131 and having a higher impurity concentration than the channel region 131. Impurities may include N-type impurities or P-type impurities. The source region 132 and the drain region 133 may be understood respectively as a source electrode and a drain electrode of the TFT 130.

The semiconductor layer 134 may include polysilicon. In some implementations, the semiconductor layer 134 may include amorphous silicon or an organic semiconductor material. In another implementations, the semiconductor layer 134 may include an oxide semiconductor.

The pixel circuit PC may include the driving TFT Td and the switching TFT Ts of FIG. 2. A semiconductor layer of the driving TFT Td and a semiconductor layer of the switching TFT Ts may include different materials. For example, one of the semiconductor layers of the TFT Td and the switching TFT Ts may include an oxide semiconductor, and the remaining one may include polysilicon.

A gate insulating layer 103 may be located between the semiconductor layer 134 and the gate electrode 136. The gate insulating layer 103 may be an inorganic insulating layer formed of SiON, SiOx, and/or SiNx. The inorganic insulating layer may have a single layer structure or a multi-layer structure.