Semiconductor device

1. A semiconductor device including a field effect transistor, the field effect transistor comprising:

(a) a nitride semiconductor layer;

(b) a first ohmic electrode including a plurality of first unit electrodes, each of the first unit electrodes coming in physical and ohmic contact with the nitride semiconductor layer, the first unit electrodes being separated from each other and extending serially in a first direction along a long axis of the first unit electrodes;

(c) a second ohmic electrode having a plurality of second unit electrodes, each of the second unit electrodes corning in physical and ohmic contact with the nitride semiconductor layer, the second unit electrodes being separated from each other and extending serially in the first direction, in which the second ohmic electrode is separated from the first ohmic electrode;

(d) a gate electrode sandwiched between the first ohmic electrode and the second ohmic electrode and running in a direction parallel to the first ohmic electrode and the second ohmic electrode;

(e) an insulating film formed to cover the first ohmic electrode and the second ohmic electrode;

(f) a plurality of first opening portions that is formed in the insulating film, and reaches the respective first unit electrodes configuring the first ohmic electrode;

(g) a plurality of second opening portions that is formed in the insulating film, and reaches the respective second unit electrodes configuring the second ohmic electrode;

(h) a source electrode that extends from an interior of the first opening portions onto the insulating film, and is electrically connected to the first ohmic electrode; and

(i) a drain electrode that extends from an interior of the second opening portions onto the insulating film, and is electrically connected to the second ohmic electrode, in which the drain electrode is electrically isolated from the source electrode.

2. The semiconductor device according to claim 1 ,

wherein the first unit electrodes and the second unit electrodes each include an aluminum film.

3. The semiconductor device according to claim 1 ,

wherein in a direction along which the electrodes are aligned, each width of the first unit electrodes is larger than each width of the first opening portions, and

wherein in a direction along which the second unit electrodes are aligned, each width of the second unit electrodes is larger than each width of the second opening portions.

4. The semiconductor device according to claim 3 ,

wherein in a plan view, the first opening portions are included in the respective first unit electrodes, and

wherein in the plan view, the second opening portions are included in the respective second unit electrodes.

5. The semiconductor device according to claim 1 ,

wherein the number of first unit electrodes is different from the number of second unit electrodes.

6. The semiconductor device according to claim 1 ,

wherein the number of first unit electrodes is equal to the number of second unit electrodes.

7. The semiconductor device according to claim 1 ,

wherein the first unit electrodes and the second unit electrodes each include a laminate film having an aluminum film sandwiched between titanium films.

8. The semiconductor device according to claim 1 ,

wherein the source electrode and the drain electrode each include an aluminum alloy film.

9. The semiconductor device according to claim 8 ,

wherein the aluminum alloy film includes one of an AlCu film and an AlSiCu film.

10. The semiconductor device according to claim 1 ,

wherein the ohmic contact is a resistive contact having no rectification.

11. A semiconductor device including a field effect transistor, the field effect transistor comprising:

(a) a nitride semiconductor layer;

(b) a first ohmic electrode including a plurality of first unit electrodes, each of the first unit electrodes coming in physical and ohmic contact with the nitride semiconductor layer, the first unit electrodes being separated from each other and extending serially in a first direction along a long axis of the first unit electrodes;

(c) a second ohmic electrode having a plurality of second unit electrodes, each of the second unit electrodes coming in physical and ohmic contact with the nitride semiconductor layer, the second unit electrodes being separated from each other and extending serially in the first direction, in which the second ohmic electrode is separated from the first ohmic electrode;

(d) a gate electrode sandwiched between the first ohmic electrode and the second ohmic electrode and running in a direction parallel to the first ohmic electrode and the second ohmic electrode;

(e) an insulating film formed to cover the first ohmic electrode and the second ohmic electrode;

(f) a plurality of first opening portions that is formed in the insulating film, and reaches the respective first unit electrodes configuring the first ohmic electrode;

(g) a plurality of second opening portions that is formed in the insulating film, and reaches the respective second unit electrodes configuring the second ohmic electrode;

(h) a plurality of first plugs embedded in each interior of the first opening portions;

(i) a source electrode which is disposed over the insulating film, and comes in contact with the first plugs;

(j) a plurality of second plugs embedded in each interior of the second opening portions; and

(k) a drain electrode which is disposed over the insulating film, and comes in contact with the second plugs, in which the drain electrode is electrically isolated from the source electrode.

12. The semiconductor device according to claim 11 ,

wherein the first unit electrodes and the second unit electrodes each include an aluminum film.

13. The semiconductor device according to claim 11 ,

wherein the insulating film includes a first insulating film, and a second insulating film formed over the first insulating film.

14. The semiconductor device according to claim 13 ,

wherein the first insulating film is a silicon oxide film, and

wherein the second insulating film is a silicon nitride film.

15. The semiconductor device according to claim 11 ,

wherein a material of the first plugs is different from a material of the source electrode, and

wherein a material of the second plugs is different from a material of the drain electrode.

16. A semiconductor device, comprising:

(a) a source electrode having a source pad and a plurality of source comb shaped electrodes protruded from the source pad in a first direction;

(b) a drain electrode having a drain pad, and a plurality of drain comb shaped electrodes protruded from the drain pad in the first direction, in which the source comb shaped electrodes and the drain comb shaped electrodes are alternately arranged along a second direction orthogonal to the first direction;

(c) a plurality of gate electrodes sandwiched between the respective source comb shaped electrodes and the respective drain comb shaped electrodes;

(d) an insulating film disposed over lower layers of the respective source comb shaped electrodes so as to provide a plurality of first opening portions along the first direction, and disposed over lower layers of the respective drain comb shaped electrodes so as to provide a plurality of second opening portions along the first direction;

(e) a plurality of first plugs embedded in respective interiors of the first opening portions, and electrically connected to the respective source comb shaped electrodes;

(f) a plurality of second plugs embedded in respective interiors of the second opening portions, and electrically connected to the respective drain comb shaped electrodes;

(g) a plurality of first unit electrodes disposed over lower layers of the respective first plugs arranged along the first direction, electrically connected to the respective first plugs arranged along the first direction, and separated from each other in the first direction and extending serially in the first direction along a long axis of the first unit electrodes, for each of the source comb shaped electrodes;

(h) a plurality of second unit electrodes disposed over lower layers of the respective second plugs arranged along the first direction, electrically connected to the respective second plugs arranged along the first direction and extending serially in the first direction, and separated from each other in the first direction, for each of the drain comb shaped electrodes; and

(i) a nitride semiconductor layer disposed over lower layers of first unit electrodes and the second unit electrodes, and coming in physical and ohmic contact with the first unit electrodes and the second unit electrodes.

17. The semiconductor device according to claim 16 ,

wherein the first unit electrodes and the second unit electrodes each include an aluminum film,

wherein a width of the respective source comb shaped electrodes in the second direction is equal to a width of the respective drain comb shaped electrodes in the second direction, and

wherein the number of first unit electrodes is equal to the number of second unit electrodes.

18. The semiconductor device according to claim 16 ,

wherein the first unit electrodes and the second unit electrodes each include an aluminum film,

wherein a width of the respective source comb shaped electrodes in the second direction is smaller than a width of the respective drain comb shaped electrodes in the second direction, and

wherein the number of first unit electrodes is larger than the number of second unit electrodes.

19. The semiconductor device according to claim 16 ,

wherein the first unit electrodes and the second unit electrodes each include an aluminum film,

wherein a width of the respective source comb shaped electrodes in the second direction is larger than a width of the respective drain comb shaped electrodes in the second direction, and

wherein the number of first unit electrodes is smaller than the number of second unit electrodes.

20. The semiconductor device according to claim 1 , where the number of the plurality of first unit electrodes is four, and the number of the plurality of second unit electrodes is four.