Semiconductor device

1. A semiconductor device comprising:

a first conductivity type semiconductor substrate to be a drain area;

a drift area formed on the drain area;

a second conductivity type body area formed on an upper portion of the drift area;

a first conductivity type source area formed on an upper portion of the body area;

a trench that penetrates the source area and the body area, and reaches the drift area;

an insulation film formed on an inner wall of the trench;

a gate electrode formed inside the insulation film; and

a second conductivity type back gate electrode formed inside the body area and electrically connected with the body area,

wherein:

a current flows from the drain area to the source area in a state where a first voltage is applied to the drain area, a second voltage lower than the first voltage is applied to the source area and the body area, and a third voltage equal to or higher than a first threshold is applied between the gate electrode and the source area,

a current flows from the source area to the drain area in a state where the first voltage is applied to the source area, the second voltage is applied to the drain area and the body area, and a fourth voltage equal to or higher than a second threshold is applied between the gate electrode and the drain area,

a sheet resistance of the back gate electrode is lower than a sheet resistance of the body area, and

the source area and the back gate electrode are disposed apart from each other with a clearance sufficient for preventing a breakdown phenomenon caused between the source area and the back gate electrode when a maximum operation voltage is applied between the source area and the drain area.

2. The semiconductor device according to claim 1 , wherein an insulation film is formed between the back gate electrode and the source area.

3. The semiconductor device according to claim 1 , wherein the back gate electrode is formed of polysilicon.

4. The semiconductor device according to claim 1 , wherein the back gate electrode includes a diffusion layer.

5. The semiconductor device according to claim 1 , wherein

the back gate electrode is connected with a back gate terminal via a first contact,

the gate electrode is connected with a gate terminal via a second contact, and

a voltage driving distance of the back gate electrode driven from the first contact when a voltage is applied to the back gate terminal is shorter than a voltage driving distance of the gate electrode driven from the second contact when a voltage is applied to the gate terminal.

6. The semiconductor device according to claim 1 , wherein the gate electrode is surrounded by the back gate electrode in a plan view.

7. The semiconductor device according to claim 1 , wherein the back gate electrode extends over the body area and the drift area.

8. The semiconductor device according to claim 2 , wherein the back gate electrode is formed of polysilicon.

9. The semiconductor device according to claim 2 , wherein the back gate electrode includes a diffusion layer.

10. The semiconductor device according to claim 2 , wherein

the back gate electrode is connected with a back gate terminal via a first contact,

the gate electrode is connected with a gate terminal via a second contact, and

a voltage driving distance of the back gate electrode driven from the first contact when a voltage is applied to the back gate terminal is shorter than a voltage driving distance of the gate electrode driven from the second contact when a voltage is applied to the gate terminal.

11. The semiconductor device according to claim 2 , wherein the gate electrode is surrounded by the back gate electrode in a plan view.

12. The semiconductor device according to claim 2 , wherein the back gate electrode extends over the body area and the drift area.