A thin film transistor includes a source electrode, a drain electrode, a semiconducting layer, and a gate electrode. The drain electrode is spaced from the source electrode. The semiconducting layer is electrically connected to the source electrode and the drain electrode. The gate electrode is insulated from the source electrode, the drain electrode, and the semiconducting layer by an insulating layer. The at least one of the source electrode, drain electrode, and the gate electrode includes a metallic carbon nanotube layer. The metallic carbon nanotube layer includes a plurality of metallic carbon nanotubes.