A work module includes a substrate and a transistor unit disposed on the substrate. The transistor unit includes an active layer, a source electrode, and a drain electrode. The active layer has a thickness, a first surface, and a second surface. The first surface is parallel with the second surface. The source electrode and the drain electrode at least partially overlap the active layer. The second surface contacts the source electrode and the drain electrode. A first zinc concentration exists within a first range from the second surface to a site located away from the second surface by a tenth of the thickness. A second zinc concentration exists within a second range from a site located away from the second surface by nine tenths of the thickness to the first surface. The first zinc concentration is higher than the second zinc concentration.