Semiconductor device

1. A semiconductor device, comprising:

a first transistor including:

a first electrode;

a first insulating layer above the first electrode, the first insulating layer having a first sidewall;

a first oxide semiconductor layer on the first sidewall, the first oxide semiconductor layer being connected with a top surface of the first electrode;

a first gate electrode facing the first oxide semiconductor layer;

a first gate insulating layer between the first oxide semiconductor layer and the first gate electrode;

a second electrode above the first insulating layer, the second electrode being connected with a top surface of the first oxide semiconductor layer; and

a first assisting electrode on the first insulating layer, the first assisting electrode being connected with a bottom surface of the first oxide semiconductor layer; and

a second transistor including:

a third electrode;

a fourth electrode separated from the third electrode;

a second oxide semiconductor layer between the third electrode and the fourth electrode, the second oxide semiconductor layer being connected with a top surface of each of the third electrode and the fourth electrode;

a second gate electrode facing the second oxide semiconductor layer; and

a second gate insulating layer between the second oxide semiconductor layer and the second gate electrode.

2. The semiconductor device according to claim 1 , wherein the first oxide semiconductor layer and the second oxide semiconductor layer are formed of the same layer as each other.

3. The semiconductor device according to claim 2 , wherein the first gate insulating layer and the second gate insulating layer are formed of the same layer as each other.

4. The semiconductor device according to claim 3 , wherein the first gate electrode and the second gate electrode are formed of the same layer as each other.

5. The semiconductor device according to claim 4 , wherein the first electrode, the third electrode and the fourth electrode are formed of the same layer as each other.

6. The semiconductor device according to claim 1 , wherein a length of the second oxide semiconductor layer between the third electrode and the fourth electrode is longer than a length of the first oxide semiconductor layer between the first electrode and the second electrode.

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

the second transistor further includes:

a second insulating layer having a second sidewall;

a third oxide semiconductor layer on the second sidewall, the third oxide semiconductor layer being connected with the second oxide semiconductor layer,

a third gate electrode facing the third oxide semiconductor layer, and

a third gate insulating layer between the third oxide semiconductor layer and the third gate electrode; and

the third electrode is located above the second insulating layer.

8. The semiconductor device according to claim 7 , wherein the first oxide semiconductor layer, the second oxide semiconductor layer and the third oxide semiconductor layer are formed of the same layer as each other.

9. The semiconductor device according to claim 8 , wherein the first gate insulating layer, the second gate insulating layer and the third gate insulating layer are formed of the same layer as each other.

10. The semiconductor device according to claim 9 , wherein the first gate electrode, the second gate electrode and the third gate electrode are formed of the same layer as each other.

11. The semiconductor device according to claim 10 , wherein the second electrode and the third electrode are formed of the same layer as each other.

12. The semiconductor device according to claim 7 , wherein:

the length of the second oxide semiconductor layer between the third electrode and the fourth electrode is longer than the length of the first oxide semiconductor layer between the first electrode and the second electrode; and

a length of the third oxide semiconductor layer between the third electrode and the second oxide semiconductor layer is equal to the length of the first oxide semiconductor layer between the first electrode and the second electrode.

13. The semiconductor device according to claim 1 , further comprising a second insulating layer above the third electrode;

wherein:

the third electrode includes a protrusion portion protruding from an end of the second insulating layer; and

the second oxide semiconductor layer is connected with the protrusion portion.

14. The semiconductor device according to claim 7 , wherein:

the second transistor further includes:

a third insulating layer having a third sidewall;

a fourth oxide semiconductor layer on the third sidewall, the fourth oxide semiconductor layer being connected with the second oxide semiconductor layer,

a fourth gate electrode facing the fourth oxide semiconductor layer; and

a fourth gate insulating layer between the fourth oxide semiconductor layer and the fourth gate electrode; and

the fourth electrode is located above the third insulating layer.

15. The semiconductor device according to claim 14 , wherein the first oxide semiconductor layer, the second oxide semiconductor layer, the third oxide semiconductor layer and the fourth oxide semiconductor layer are formed of the same layer as each other.

16. The semiconductor device according to claim 15 , wherein the first gate insulating layer, the second gate insulating layer, the third gate insulating layer and the fourth gate insulating layer are formed of the same layer as each other.

17. The semiconductor device according to claim 16 , wherein the first gate electrode, the second gate electrode, the third gate electrode and the fourth gate electrode are formed of the same layer as each other.

18. The semiconductor device according to claim 17 , wherein the second electrode, the third electrode and the fourth electrode are formed of the same layer as each other.

19. The semiconductor device according to claim 14 , wherein:

the length of the second oxide semiconductor layer between the third electrode and the fourth electrode is longer than the length of the first oxide semiconductor layer between the first electrode and the second electrode; and

the length of the third oxide semiconductor layer between the third electrode and the second oxide semiconductor layer, and a length of the fourth oxide semiconductor layer between the fourth electrode and the second oxide semiconductor layer, are each equal to the length of the first oxide semiconductor layer between the first electrode and the second electrode.

20. The semiconductor device according to claim 1 , further comprising:

a second insulating layer above the third electrode; and

a third insulating layer above the fourth electrode;

wherein:

the third electrode includes a first protrusion portion protruding from an end of the second insulating layer;

the fourth electrode includes a second protrusion portion protruding from an end of the third insulating layer;

the second oxide semiconductor layer is connected with the first protrusion portion; and

the second oxide semiconductor layer is connected with the second protrusion portion.