Semiconductor device including a stack of oxide semiconductor layers
View Patent ↗High field-effect mobility is provided for a semiconductor device including an oxide semiconductor. Further, a highly reliable semiconductor device including the transistor is provided. In a transistor in which a stack of oxide semiconductor layers is provided over a gate electrode layer with a gate insulating layer provided therebetween, an oxide semiconductor layer functioning as a current path (channel) of the transistor and containing an n-type impurity is sandwiched between oxide semiconductor layers having lower conductivity than the oxide semiconductor layer. In the oxide semiconductor layer functioning as the channel, a region on the gate insulating layer side contains the n-type impurity at a higher concentration than a region on the back channel side. With such a structure, the channel can be separated from the interface between the oxide semiconductor stack and the insulating layer in contact with the oxide semiconductor stack, so that a buried channel can be formed.
1. A semiconductor device comprising:
a gate electrode layer;
a gate insulating layer over the gate electrode layer;
a first oxide semiconductor layer over the gate insulating layer;
a second oxide semiconductor layer over and in direct contact with the first oxide semiconductor layer, the second oxide semiconductor layer comprising:
a first region; and
a second region;
a third oxide semiconductor layer over and in direct contact with the second oxide semiconductor layer; and
a source electrode layer and a drain electrode layer electrically connected to the third oxide semiconductor layer,
wherein the second oxide semiconductor layer contains an n-type impurity,
wherein the first region is closer to the first oxide semiconductor layer than the second region, and
wherein the first region contains the n-type impurity at a higher concentration than the second region.
2. The semiconductor device according to claim 1 ,
wherein the semiconductor device further comprises an insulating layer in contact with the source electrode layer and the drain electrode layer.
3. The semiconductor device according to claim 1 ,
wherein each of the first oxide semiconductor layer, the second oxide semiconductor layer, and the third oxide semiconductor layer comprises indium.
4. The semiconductor device according to claim 1 ,
wherein the first oxide semiconductor layer and the third oxide semiconductor layer are i-type oxide semiconductor layers.
5. The semiconductor device according to claim 1 ,
wherein metal elements included in the first oxide semiconductor layer are included in the second oxide semiconductor layer and the third oxide semiconductor layer.
6. A semiconductor device comprising:
a gate electrode layer;
a gate insulating layer over the gate electrode layer;
a first oxide semiconductor layer over the gate insulating layer;
a second oxide semiconductor layer over the first oxide semiconductor layer, the second oxide semiconductor layer comprising:
a first region; and
a second region;
a third oxide semiconductor layer over the second oxide semiconductor layer; and
a source electrode layer and a drain electrode layer electrically connected to the third oxide semiconductor layer,
wherein the second oxide semiconductor layer contains an n-type impurity,
wherein the first region is closer to the first oxide semiconductor layer than the second region, and
wherein the first region contains the n-type impurity at a higher concentration than the second region.
7. The semiconductor device according to claim 6 ,
wherein the source electrode layer and the drain electrode layer are over the third oxide semiconductor layer.
8. The semiconductor device according to claim 6 ,
wherein the semiconductor device further comprises an insulating layer over the third oxide semiconductor layer.
9. The semiconductor device according to claim 6 ,
wherein each of the first oxide semiconductor layer, the second oxide semiconductor layer, and the third oxide semiconductor layer comprises indium.
10. The semiconductor device according to claim 6 ,
wherein the third oxide semiconductor layer covers the first oxide semiconductor layer and the second oxide semiconductor layer.
11. The semiconductor device according to claim 6 ,
wherein the first oxide semiconductor layer and the third oxide semiconductor layer are i-type oxide semiconductor layers.
12. The semiconductor device according to claim 6 ,
wherein metal elements included in the first oxide semiconductor layer are included in the second oxide semiconductor layer and the third oxide semiconductor layer.
13. A semiconductor device comprising:
a gate electrode layer;
a gate insulating layer over the gate electrode layer;
a source electrode layer and a drain electrode layer over the gate insulating layer;
a first oxide semiconductor layer over the source electrode layer and the drain electrode layer;
a second oxide semiconductor layer over the first oxide semiconductor layer, the second oxide semiconductor layer comprising:
a first region; and
a second region; and
a third oxide semiconductor layer over the second oxide semiconductor layer,
wherein the second oxide semiconductor layer contains an n-type impurity,
wherein the first region is closer to the first oxide semiconductor layer than the second region, and
wherein the first region contains the n-type impurity at a higher concentration than the second region.
14. The semiconductor device according to claim 13 ,
wherein the semiconductor device further comprises an insulating layer over the source electrode layer and the drain electrode layer.
15. The semiconductor device according to claim 13 ,
wherein each of the first oxide semiconductor layer, the second oxide semiconductor layer, and the third oxide semiconductor layer comprises indium.
16. The semiconductor device according to claim 13 ,
wherein the first oxide semiconductor layer and the third oxide semiconductor layer are i-type oxide semiconductor layers.
17. The semiconductor device according to claim 13 ,
wherein metal elements included in the first oxide semiconductor layer are included in the second oxide semiconductor layer and the third oxide semiconductor layer.