Method of producing thin film transistor, thin film transistor, display device, image sensor, and X-ray sensor

1. A method of producing a thin film transistor, comprising:

forming a gate electrode;

forming a gate insulating film that contacts the gate electrode;

forming, by a liquid phase method, an oxide semiconductor layer arranged facing the gate electrode with the gate insulating film provided therebetween, the oxide semiconductor layer comprising a first region and a second region, the first region being represented by In (a) Ga (b) Zn (c) O (d) , wherein a≧0, b≧0, c≧0, a+b+c=1, d>0, b≦a/2−1/10, b≦−3a/2+11/10, b≧1/20, and c≧1/20 are satisfied, the second region being represented by In (e) Ga (f) Zn (g) O (h) , wherein e≧0, f≧0, g≧0, e+f>0, h>0, and f/(e+f)>0.250 are satisfied, and the second region being located farther from the gate electrode than the first region; and

forming a source electrode and a drain electrode that are arranged apart from each other and are capable of being conductively connected through the oxide semiconductor layer.

2. The method of producing a thin film transistor according to claim 1 , wherein, in the forming of the oxide semiconductor layer, a raw material solution comprising a solvent and at least one selected from the group consisting of a metal alkoxide, a β-diketone complex, and a nitrate is used to form the oxide semiconductor layer.

3. The method of producing a thin film transistor according to claim 1 , wherein, in the forming of the oxide semiconductor layer, a raw material solution comprising a solvent and at least one selected from the group consisting of a metal alkoxide and a β-diketone complex is used to form the oxide semiconductor layer.

4. The method of producing a thin film transistor according to claim 1 , wherein, in the forming of the oxide semiconductor layer, a raw material solution comprising a solvent and a metal alkoxide is used to form the oxide semiconductor layer.

5. The method of producing a thin film transistor according to claim 4 , wherein the raw material solution comprises an aminoethanol as the solvent.

6. The method of producing a thin film transistor according to claim 1 , wherein, in the forming of the oxide semiconductor layer, a raw material solution comprising a solvent and a β-diketone complex is used to form the oxide semiconductor layer.

7. The method of producing a thin film transistor according to claim 6 , wherein the raw material solution comprises a β-diketone as the solvent.

8. The method of producing a thin film transistor according to claim 1 , wherein the second region has a composition satisfying f/(e+f)<0.875.

9. The method of producing a thin film transistor according to claim 1 , wherein a film thickness of the second region is more than 10 nm but less than 70 nm.

10. The method of producing a thin film transistor according to claim 1 , wherein the oxide semiconductor layer is amorphous.

11. The method of producing a thin film transistor according to claim 1 , wherein, in the forming of the oxide semiconductor layer, an oxide precursor film including at least one metal organic compound selected from the group consisting of a metal alkoxide and a β-diketone complex is formed, and the oxide precursor film is subjected to a heat treatment at a temperature equal to or higher than a thermal decomposition temperature of the metal organic compound.

12. The method of producing a thin film transistor according claim 11 , wherein the heat treatment is carried out at 400° C. or higher.

13. A thin film transistor, produced by the method according to claim 1 .

14. A display device, comprising the thin film transistor according to claim 13 .

15. An image sensor, comprising the thin film transistor according to claim 13 .

16. An X-ray sensor, comprising the thin film transistor according to claim 13 .

17. An X-ray digital imaging device, comprising the X-ray sensor according to claim 16 .

18. The X-ray digital imaging device according to claim 17 , capable of capturing a moving image.