Semiconductor device including semiconductor substrate, silicon carbide semiconductor layer, unit cells, source, and gate

1. A semiconductor device comprising:

a semiconductor substrate of a first conductivity type, having a first principal surface and a second principal surface;

a first silicon carbide semiconductor layer of the first conductivity type, disposed on the first principal surface of the semiconductor substrate;

unit cells;

a source including a source pad and a source wiring extending from the source pad; and

a gate including a gate pad and a gate wiring extending from the gate pad, wherein:

each of the unit cells includes:

a body region of a second conductivity type, disposed in the first silicon carbide semiconductor layer;

a source region of the first conductivity type, disposed in contact with the body region;

a second silicon carbide semiconductor layer of the first conductivity type, disposed on the first silicon carbide semiconductor layer and in contact with at least part of the body region and at least part of the source region;

a gate insulating layer disposed on the second silicon carbide semiconductor layer;

a gate electrode disposed on the gate insulating layer and above the body region, the gate insulating layer and the second silicon carbide semiconductor layer being interposed between the gate electrode and the body region;

a source electrode electrically connected to the source region and electrically connected to the source; and

a drain electrode disposed on the second principal surface of the semiconductor substrate,

the unit cells include first unit cells disposed in a first element region and second unit cells disposed in a second element region, and in a plan view, the first element region and the second element region are adjacent to each other with the gate wiring interposed between the first and second element regions,

at least some of the first unit cells are disposed below one of the source pad and the source wiring,

at least some of the second unit cells are disposed below another of the source pad and the source wiring,

a first electrode including the gate electrode of each of the first unit cells is disposed in the first element region and electrically connected to the gate,

a second electrode including the gate electrode of each of the second unit cells is disposed in the second element region and not electrically connected to the gate, and

the first electrode and the second electrode are separated from each other below the gate wiring.

2. The semiconductor device according to claim 1 , wherein the first electrode is electrically connected to the gate wiring below the gate wiring.

3. The semiconductor device according to claim 1 , wherein the second electrode is electrically connected to the source.

4. The semiconductor device according to claim 1 , wherein in a plan view, the second electrode extends from the second element region so as to partially overlap the gate wiring.

5. The semiconductor device according to claim 1 , wherein:

the unit cells further include third unit cells disposed in a third element region,

in a plan view, the third element region is adjacent to the first element region with the gate wiring interposed between the first and third element regions,

a third electrode including the gate electrode of each of the third unit cells is disposed in the third element region and separated from the first electrode and the second electrode.

6. The semiconductor device according to claim 5 , wherein the third electrode is electrically connected to the source.

7. The semiconductor device according to claim 5 , wherein the third electrode is electrically connected to the gate.

8. The semiconductor device according to claim 5 , wherein in a plan view, the third electrode partially extends from the third element region so as to overlap the gate wiring.

9. The semiconductor device according to claim 1 , further comprising a second-conductivity-type region disposed below the gate wiring and disposed in the first silicon carbide semiconductor layer,

wherein in a plan view, the first electrode and the second electrode are separated from each other above the second-conductivity-type region.

10. The semiconductor device according to claim 9 , wherein:

in a plan view, the second-conductivity-type region overlaps part of the first electrode and part of the second electrode, and

the second-conductivity-type region and the source are electrically connected to each other in an opening in the first electrode and an opening in the second electrode.

11. The semiconductor device according to claim 1 , wherein:

when, in each of the first unit cells, Vds and Vgs, which are electric potentials based on the source electrode, are applied to the drain electrode and the gate electrode, respectively,

in a case where Vgs≧Vth, where Vth is a gate threshold voltage, an electric current flows from the drain electrode to the source electrode, and

in a case where Vgs<Vth, as Vds becomes smaller than 0 volt, an electric current flows from the source electrode to the drain electrode via the second silicon carbide semiconductor layer before an electric current starts to flow from the source electrode to the drain electrode via the body region.

12. The semiconductor device according to claim 11 , wherein when Vgs is 0 volt, Vds at which an electric current of 1 mA flows from the source electrode to the drain electrode via the second silicon carbide semiconductor layer is equal to or larger than −1 V at room temperature.

13. The semiconductor device according to claim 1 , wherein:

each of the first unit cells is a transistor, and

each of the second unit cells is a diode.