Nitride semiconductor device

1. A nitride semiconductor device comprising:

a substrate;

a semiconductor multilayer structure including a first nitride semiconductor layer and a second nitride semiconductor layer, the first nitride semiconductor layer being above the substrate, and the second nitride semiconductor layer being on the first nitride semiconductor layer and having a greater band gap than a band gap of the first nitride semiconductor layer;

a source electrode and a drain electrode arranged at a distance from each other on the semiconductor multilayer structure;

a gate electrode disposed between the source electrode and the drain electrode, at a distance from the source electrode and the drain electrode; and

a gate wiring line that transmits a gate driving signal to one or more gate electrodes including the gate electrode,

wherein the nitride semiconductor device includes in planar view of the substrate:

a channel region in which an actual current path from the drain electrode to the source electrode is formed in the semiconductor multilayer structure when a voltage equal to or higher than a threshold voltage is applied between the gate electrode and the source electrode; and

a non-channel region in which the actual current path from the drain electrode to the source electrode is not formed in the semiconductor multilayer structure, and

the nitride semiconductor device further comprises

a first shield structure on the semiconductor multilayer structure between the drain electrode and the gate electrode in the non-channel region or between the drain electrode and the gate wiring line in the non-channel region,

wherein the first shield structure causes the semiconductor multilayer structure under the first shield structure to have normally-off properties, suppresses a current flowing from the semiconductor multilayer structure, and is set to have a substantially same potential as a potential of the source electrode.

2. The nitride semiconductor device according to claim 1 ,

wherein the first shield structure has a rectification structure for blocking the current flowing from the semiconductor multilayer structure.

3. The nitride semiconductor device according to claim 2 ,

wherein the first shield structure is disposed in and above a recess in the second nitride semiconductor layer.

4. The nitride semiconductor device according to claim 2 ,

wherein the first shield structure includes:

a first electrode disposed on the second nitride semiconductor layer; and

a p-type semiconductor layer disposed on the second nitride semiconductor layer and being Schottky-connected to a side of the first electrode.

5. The nitride semiconductor device according to claim 2 ,

wherein the first shield structure includes:

a p-type semiconductor layer disposed in and above a recess in the second nitride semiconductor layer; and

a first electrode disposed on the p-type semiconductor layer.

6. The nitride semiconductor device according to claim 1 ,

wherein the first shield structure includes:

an insulating film disposed in and above a recess in the second nitride semiconductor layer; and

a first electrode disposed on the insulating film.

7. The nitride semiconductor device according to any one of claims 1 , 2 , and 6 , further comprising

a second shield structure on the semiconductor multilayer structure between the drain electrode and the gate electrode in the channel region,

wherein the second shield structure causes the semiconductor multilayer structure under the second shield structure to have normally-on properties, suppresses the current flowing from the semiconductor multilayer structure, and is set to have a substantially same potential as a potential of the source electrode.

8. The nitride semiconductor device according to claim 7 ,

wherein the second shield structure has a discontinuous shape.

9. The nitride semiconductor device according to claim 7 ,

wherein the second shield structure includes

one of three structures: (1) a first structure in which a second electrode is disposed on the second nitride semiconductor layer, (2) a second structure in which a p-type semiconductor layer is disposed on the second nitride semiconductor layer and a third electrode is disposed on the p-type semiconductor layer, and (3) a third structure in which an insulating film is disposed on the second nitride semiconductor layer and a fourth electrode is disposed on the insulating film.

10. The nitride semiconductor device according to claim 7 , further comprising

a third shield structure disposed on the semiconductor multilayer structure between the second shield structure and the drain electrode,

wherein the third shield structure causes the semiconductor multilayer structure under the third shield structure to have normally-on properties, suppresses the current flowing from the semiconductor multilayer structure, and is set to have a substantially same potential as a potential of the source electrode, and

the third shield structure is one of the first structure, the second structure, and the third structure, and is different from the structure of the second shield structure.

11. The nitride semiconductor device according to claim 10 ,

wherein the third shield structure has a discontinuous shape.