Active-matrix substrate and display device

An active matrix substrate having a display region defined by a plurality of pixel regions, the active matrix substrate comprising a substrate and a plurality of oxide semiconductor TFTs supported on the substrate,

• wherein each of the plurality of oxide semiconductor TFTs includes
• a lower gate electrode provided on the substrate,
• a gate insulating layer covering the lower gate electrode,
• an oxide semiconductor layer provided on the gate insulating layer, the oxide semiconductor layer overlapping the lower gate electrode with the gate insulating layer interposed therebetween, the oxide semiconductor layer including a channel region and a source contact region and a drain contact region which are present on opposite sides of the channel region,
• a source electrode which is in contact with the source contact region of the oxide semiconductor layer,
• a drain electrode which is in contact with the drain contact region of the oxide semiconductor layer,
• an insulating layer covering the oxide semiconductor layer, the source electrode and the drain electrode, and
• an upper gate electrode provided on the insulating layer, the upper gate electrode overlapping the oxide semiconductor layer with the insulating layer interposed therebetween, wherein
• when viewed in a normal direction of the substrate, the upper gate electrode does not overlap a first electrode which is one of the source electrode and the drain electrode, and a second electrode which is the other of the source electrode and the drain electrode does not overlap the lower gate electrode,
• the upper gate electrode is arranged such that a static capacitance formed between the upper gate electrode and the first electrode is not more than 80% of a static capacitance formed between the upper gate electrode and the second electrode, and
• the second electrode is arranged such that a static capacitance formed between the second electrode and the lower gate electrode is not more than 80% of a static capacitance formed between the first electrode and the lower gate electrode.

An active matrix substrate having a display region defined by a plurality of pixel regions, the active matrix substrate comprising a substrate and a plurality of oxide semiconductor TFTs supported on the substrate,

• wherein each of the plurality of oxide semiconductor TFTs includes
• a lower gate electrode provided on the substrate,
• a gate insulating layer covering the lower gate electrode,
• an oxide semiconductor layer provided on the gate insulating layer, the oxide semiconductor layer overlapping the lower gate electrode with the gate insulating layer interposed therebetween, the oxide semiconductor layer including a channel region and a source contact region and a drain contact region which are present on opposite sides of the channel region,
• a source electrode which is in contact with the source contact region of the oxide semiconductor layer,
• a drain electrode which is in contact with the drain contact region of the oxide semiconductor layer,
• an insulating layer covering the oxide semiconductor layer, the source electrode and the drain electrode, and
• an upper gate electrode provided on the insulating layer, the upper gate electrode overlapping the oxide semiconductor layer with the insulating layer interposed therebetween, wherein
• when viewed in a normal direction of the substrate, the upper gate electrode does not overlap a first electrode which is one of the source electrode and the drain electrode, and a second electrode which is the other of the source electrode and the drain electrode does not overlap the lower gate electrode,
• the active matrix substrate has a non-display region lying around the display region,
• the active matrix substrate further includes a peripheral circuit provided in the non-display region,
• the plurality of oxide semiconductor TFTs include a plurality of first TFTs provided in the non-display region and included in the peripheral circuit and a plurality of second TFTs provided in the display region or the non-display region,
• the oxide semiconductor layer of the plurality of first TFTs and the oxide semiconductor layer of the plurality of second TFTs are formed by an identical oxide semiconductor film, and
• a carrier density in the channel region of the plurality of first TFTs is higher than a carrier density in the channel region of the plurality of second TFTs.