The first active layer 121 may include low temperature poly-silicon (LTPS). Since a polysilicon material has low energy consumption and excellent reliability due to has high mobility (100 cm²/Vs or more), it can be applied to a multiplexer (MUX) and/or a gate driver for a driving element that drives thin film transistors for a display element and can also be applied as the active layer 121 of the driving thin film transistor in the display device according to the embodiment. However, the present disclosure is not limited thereto. For example, it may be applied as an active layer 131 of the switching thin film transistor according to characteristics of the display device. Polysilicon is formed by depositing an amorphous silicon (a-Si) material on the first buffer layer 111 and performing a dehydrogenation process and a crystallization process, and the first active layer 121 may be formed by patterning the polysilicon. The first active layer 121 may include a first channel region 121a in which a channel is formed when the first thin film transistor 120 is driven, and a first source region 121b and a drain region 121c on both sides of the first channel region 121a. The first source region 121b means a portion of the first active layer 121 that is connected to the first source electrode 122, and the first drain region 121c means a portion of the first active layer 121 that is connected to the first drain electrode 123. The first source region 121b and the first drain region 121c may be formed by ion doping (impurity doping) of the first active layer 121. The first source region 121b and the first drain region 121c may be formed by performing ion-doping on the polysilicon material, and the first channel region 121a may refer to a portion that is not ion-doped and is left as the polysilicon material.