A maskless exposure device includes an exposure head including a digital micro-mirror device, the digital micro-mirror device being configured to scan an exposure beam to a substrate by reflecting a source beam from an exposure source; and a system control part configured to control the digital micro-mirror device by utilizing a graphic data system file. The graphic data system file includes data for a source electrode, a drain electrode and a channel portion between the source electrode and the drain electrode in a plan view. The channel portion includes a first portion extending in a direction perpendicular to a scan direction of the exposure head. A width of the first portion of the channel portion is defined to be a multiple of a pulse event generation of the exposure beam.