Semiconductor device and method for manufacturing the same
It is an object to provide a highly reliable semiconductor device including a thin film transistor with stable electric characteristics. In a semiconductor device including an inverted staggered thin film transistor whose semiconductor layer is an oxide semiconductor layer, a buffer layer is provided over the oxide semiconductor layer. The buffer layer is in contact with a channel formation region of the semiconductor layer and source and drain electrode layers. A film of the buffer layer has resistance distribution. A region provided over the channel formation region of the semiconductor layer has lower electrical conductivity than the channel formation region of the semiconductor layer, and a region in contact with the source and drain electrode layers has higher electrical conductivity than the channel formation region of the semiconductor layer.
1. A semiconductor device comprising:
an oxide semiconductor layer including a channel formation region, a first region, and a second region;
a layer including a metal oxide over and in contact with the oxide semiconductor layer;
a source electrode over and in contact with the first region including a first top surface of the oxide semiconductor layer; and
a drain electrode over and in contact with the second region including a second top surface of the oxide semiconductor layer,
wherein an electrical conductivity of the first region is higher than an electrical conductivity of the channel formation region, and
wherein an electrical conductivity of the second region is higher than an electrical conductivity of the channel formation region.
2. The semiconductor device according to claim 1 ,
wherein a concentration of oxygen contained in the first region is lower than a concentration of oxygen contained in the channel formation region, and
wherein a concentration of oxygen contained in the second region is lower than a concentration of oxygen contained in the channel formation region.
3. The semiconductor device according to claim 1 , wherein a thickness of the oxide semiconductor layer is larger than a thickness of the layer including the metal oxide.
4. The semiconductor device according to claim 1 , wherein the layer including the metal oxide is in contact with the source electrode and the drain electrode.
5. The semiconductor device according to claim 1 , wherein a side surface of the oxide semiconductor layer is in contact with the source electrode and the drain electrode.
6. The semiconductor device according to claim 1 , further comprising an insulating film over and in contact with the layer including the metal oxide.
7. The semiconductor device according to claim 1 , wherein the oxide semiconductor layer comprises indium, gallium, and zinc.
8. The semiconductor device according to claim 1 , wherein the source electrode and the drain electrode each comprises at least one of titanium, aluminum, manganese, magnesium, zirconium, beryllium, thorium, and copper.
9. A display module comprising the semiconductor device according to claim 1 , wherein the display module comprises an FPC.
10. An electronic apparatus comprising the semiconductor device according to claim 1 , wherein the electronic apparatus comprises at least one of a speaker, a battery, and an operation key.
11. A semiconductor device comprising:
a gate electrode;
a gate insulating layer over the gate electrode;
an oxide semiconductor layer over the gate insulating layer, wherein the oxide semiconductor layer includes a channel formation region, a first region, and a second region;
a layer including a metal oxide over and in contact with the oxide semiconductor layer;
a source electrode over and in contact with the first region including a first top surface of the oxide semiconductor layer; and
a drain electrode over and in contact with the second region including a second top surface of the oxide semiconductor layer,
wherein an electrical conductivity of the first region is higher than an electrical conductivity of the channel formation region, and
wherein an electrical conductivity of the second region is higher than an electrical conductivity of the channel formation region.
12. The semiconductor device according to claim 11 ,
wherein a concentration of oxygen contained in the first region is lower than a concentration of oxygen contained in the channel formation region, and
wherein a concentration of oxygen contained in the second region is lower than a concentration of oxygen contained in the channel formation region.
13. The semiconductor device according to claim 11 , wherein a thickness of the oxide semiconductor layer is larger than a thickness of the layer including the metal oxide.
14. The semiconductor device according to claim 11 , wherein the layer including the metal oxide is in contact with the source electrode and the drain electrode.
15. The semiconductor device according to claim 11 , wherein a side surface of the oxide semiconductor layer is in contact with the source electrode and the drain electrode.
16. The semiconductor device according to claim 11 , further comprising an insulating film over and in contact with the layer including the metal oxide.
17. The semiconductor device according to claim 11 , wherein the oxide semiconductor layer comprises indium, gallium, and zinc.
18. The semiconductor device according to claim 11 , wherein the source electrode and the drain electrode each comprises at least one of titanium, aluminum, manganese, magnesium, zirconium, beryllium, thorium, and copper.
19. A display module comprising the semiconductor device according to claim 11 , wherein the display module comprises an FPC.
20. An electronic apparatus comprising the semiconductor device according to claim 11 , wherein the electronic apparatus comprises at least one of a speaker, a battery, and an operation key.