Transistor with receded conductor, semiconductor device, and electronic device
A semiconductor device capable of retaining data for a long time is provided. A first transistor and a second transistor having different electrical characteristics from those of the first transistor are provided over the same layer without an increase in the number of manufacturing steps.
1. A transistor comprising:
a first oxide;
a second oxide which is level with the first oxide;
a first conductor over the first oxide, wherein a first side surface of the first conductor recedes from a first side surface of the first oxide;
a second conductor over the second oxide, wherein a first side surface of the second conductor recedes from a first side surface of the second oxide;
a third oxide in contact with the first side surface of the first conductor, a top surface and the first side surface of the first oxide, the first side surface of the second conductor, and a top surface and the first side surface of the second oxide; and
a gate electrode overlapping with the third oxide,
wherein a bottom surface of the third oxide is below a bottom surface of the first oxide.
2. The transistor according to claim 1 , wherein the third oxide has a step shape in a cross section of the transistor.
3. The transistor according to claim 1 ,
wherein the first conductor is over and in contact with the first oxide, and
wherein the second conductor is over and in contact with the second oxide.
4. The transistor according to claim 1 ,
wherein a second side surface of the first conductor is aligned with a second side surface of the first oxide, and
wherein a second side surface of the second conductor is aligned with a second side surface of the second oxide.
5. The transistor according to claim 1 ,
wherein the third oxide comprises a channel of the transistor, and
wherein the first conductor and the second conductor are a source electrode and a drain electrode of the transistor.
6. The transistor according to claim 1 , further comprising:
a first barrier film over and in contact with the first conductor; and
a second barrier film over and in contact with the second conductor,
wherein the first barrier film and the second barrier film each comprise aluminum and oxygen.
7. The transistor according to claim 1 , wherein the first oxide, the second oxide, and the third oxide each comprise an oxide semiconductor.
8. The transistor according to claim 1 , wherein a part of a top surface of the third oxide is below the bottom surface of the first oxide.
9. A transistor comprising:
an insulating film;
a first oxide semiconductor layer over the insulating film;
a second oxide semiconductor layer which is level with the first oxide semiconductor layer;
a first conductor over the first oxide semiconductor layer, wherein a first side surface of the first conductor recedes from a first side surface of the first oxide semiconductor layer;
a second conductor over the second oxide semiconductor layer, wherein a first side surface of the second conductor recedes from a first side surface of the second oxide semiconductor layer;
a third oxide semiconductor layer in contact with the first side surface of the first conductor, a top surface and the first side surface of the first oxide semiconductor layer, a top surface of the insulating film, the first side surface of the second conductor, and a top surface and the first side surface of the second oxide semiconductor layer; and
a gate electrode overlapping with the third oxide semiconductor layer,
wherein a bottom surface of the third oxide semiconductor layer is below a bottom surface of the first oxide semiconductor layer.
10. The transistor according to claim 9 , wherein the third oxide semiconductor layer has a step shape in a cross section of the transistor.
11. The transistor according to claim 9 ,
wherein the first conductor is over and in contact with the first oxide semiconductor layer, and
wherein the second conductor is over and in contact with the second oxide semiconductor layer.
12. The transistor according to claim 9 ,
wherein a second side surface of the first conductor is aligned with a second side surface of the first oxide semiconductor layer, and
wherein a second side surface of the second conductor is aligned with a second side surface of the second oxide semiconductor layer.
13. The transistor according to claim 9 ,
wherein the third oxide semiconductor layer comprises a channel of the transistor, and
wherein the first conductor and the second conductor are a source electrode and a drain electrode of the transistor.
14. The transistor according to claim 9 , further comprising:
a first barrier film over and in contact with the first conductor; and
a second barrier film over and in contact with the second conductor,
wherein the first barrier film and the second barrier film each comprise aluminum and oxygen.
15. The transistor according to claim 9 , wherein the first oxide semiconductor layer, the second oxide semiconductor layer, and the third oxide semiconductor layer each comprise indium, gallium, and zinc.
16. The transistor according to claim 9 , further comprising a back gate electrode, wherein the insulating film is over the back gate electrode.
17. The transistor according to claim 9 , wherein the insulating film comprises excess oxygen.
18. A semiconductor device comprising a first transistor and a second transistor,
the first transistor comprising:
a first oxide semiconductor layer on an insulating film;
a second oxide semiconductor layer which is level with the first oxide semiconductor layer;
a first conductor over the first oxide semiconductor layer, wherein a first side surface of the first conductor recedes from a first side surface of the first oxide semiconductor layer;
a second conductor over the second oxide semiconductor layer, wherein a first side surface of the second conductor recedes from a first side surface of the second oxide semiconductor layer;
a third oxide semiconductor layer in contact with the first side surface of the first conductor, a top surface and the first side surface of the first oxide semiconductor layer, a top surface of the insulating film, the first side surface of the second conductor, and a top surface and the first side surface of the second oxide semiconductor layer; and
a first gate electrode overlapping with the third oxide semiconductor layer; and
the second transistor comprising:
a fourth oxide semiconductor layer on the insulating film;
a third conductor over a first region of the fourth oxide semiconductor layer;
a fourth conductor over a second region of the fourth oxide semiconductor layer;
a fifth oxide semiconductor layer in contact with a first side surface of the third conductor, a top surface of the fourth oxide semiconductor layer, and a first side surface of the fourth conductor; and
a second gate electrode overlapping with the fifth oxide semiconductor layer,
wherein a bottom surface of the third oxide semiconductor layer is below a bottom surface of the first oxide semiconductor layer,
wherein the first oxide semiconductor layer, the second oxide semiconductor layer, and the fourth oxide semiconductor layer each comprise a material having a same composition, and
wherein the third oxide semiconductor layer and the fifth oxide semiconductor layer each comprise a material having a same composition.
19. The semiconductor device according to claim 18 , wherein a threshold voltage of the first transistor is higher than a threshold voltage of the second transistor.
20. The semiconductor device according to claim 18 , wherein the third oxide semiconductor layer has a step shape in a cross section of the first transistor.
21. The semiconductor device according to claim 18 ,
wherein the third oxide semiconductor layer comprises a channel of the first transistor,
wherein the fifth oxide semiconductor layer comprises a channel of the second transistor,
wherein the first conductor and the second conductor are a source electrode and a drain electrode of the first transistor, and
wherein the third conductor and the fourth conductor are a source electrode and a drain electrode of the second transistor.
22. The semiconductor device according to claim 18 , wherein the first oxide semiconductor layer, the second oxide semiconductor layer, the third oxide semiconductor layer, the fourth oxide semiconductor layer, and the fifth oxide semiconductor layer each comprise indium, gallium, and zinc.
23. An electronic device comprising:
the semiconductor device according to claim 18 ; and
at least one of an antenna, a battery, an operation switch, a microphone, and a speaker.