Thin-film transistor substrate

1. A thin-film transistor substrate comprising:

an insulating substrate;

a first insulating layer provided on the insulating substrate;

a first thin-film transistor provided on the insulating substrate and including a first oxide semiconductor film;

a second insulating layer provided on the insulating substrate and being located upper than the first insulating layer; and

a second thin-film transistor provided on the insulating substrate and including a second oxide semiconductor film different in composition from the first oxide semiconductor film,

wherein at least a part of the first oxide semiconductor film is provided above and in contact with the first insulating layer,

wherein the first insulating layer is the uppermost insulating layer among insulating layers located lower than and in contact with the first oxide semiconductor film,

wherein at least a part of the second oxide semiconductor film is provided above and in contact with the second insulating layer,

wherein the second insulating layer is the uppermost insulating layer among insulating layers located lower than and in contact with the second oxide semiconductor film, and

wherein a channel region of the oxide semiconductor film of either one of the first thin-film transistor and the second thin-film transistor has a wider bandgap than a channel region of the oxide semiconductor film of the other one of the first thin-film transistor and the second thin-film transistor.

2. The thin-film transistor substrate according to claim 1 ,

wherein the channel region of the oxide semiconductor film of the one of the thin-film transistors has a lower mobility than the channel region of the oxide semiconductor film of the other of the thin-film transistors.

3. The thin-film transistor substrate according to claim 1 ,

wherein the entirety of the first oxide semiconductor film is provided above and in contact with the first insulating layer, and

wherein the entirety of the second oxide semiconductor film is provided above and in contact with the second insulating layer.

4. The thin-film transistor substrate according to claim 1 ,

wherein a part of the first insulating layer is included in a gate insulating film of the first thin-film transistor, and

wherein a part of the first insulating layer and a part of the second insulating layer are included in a gate insulating film of the second thin-film transistor.

5. The thin-film transistor substrate according to claim 1 , wherein a part of the first oxide semiconductor film, a part of the second oxide semiconductor film, and a part of the second insulating layer constitute a capacitor.

6. The thin-film transistor substrate according to claim 1 ,

wherein the thin-film transistor substrate is a component of a display device,

wherein the first thin-film transistor and the second thin-film transistor are included in a peripheral circuit outside a display region, and

wherein the channel region of the oxide semiconductor film of the first thin-film transistor has a lower mobility than the channel region of the oxide semiconductor film of the second thin-film transistor.

7. The thin-film transistor substrate according to claim 6 ,

wherein the first thin-film transistor is an electrostatic discharge protection element, and

wherein the second thin-film transistor is an output driving transistor in a shift register.

8. The thin-film transistor substrate according to claim 1 , wherein at least either one of the first oxide semiconductor film and the second oxide semiconductor film include a part of an electrode of a capacitor.

9. The thin-film transistor substrate according to claim 8 , wherein the part of the electrode of the capacitor is an extension from the first oxide semiconductor film of the first thin-film transistor.

10. The thin-film transistor substrate according to claim 8 , wherein the part of the electrode of the capacitor is an extension from the second oxide semiconductor film of the second thin-film transistor.

11. The thin-film transistor substrate according to claim 1 ,

wherein the thin-film transistor substrate is a component of a display device,

wherein either one of the first thin-film transistor and the second thin-film transistor is included in a pixel circuit in a display region, and

wherein the other one of the first thin-film transistor and the second thin-film transistor is included in a peripheral circuit outside the display region.

12. The thin-film transistor substrate according to claim 11 ,

wherein the channel region of the oxide semiconductor film of the one of the thin-film transistors has a lower mobility than the channel region of the oxide semiconductor film of the other of the thin-film transistors.

13. The thin-film transistor substrate according to claim 11 ,

wherein the one of the thin-film transistors is a switching thin-film transistor, and

wherein the other of the thin-film transistors is an output driving transistor in a shift register.

14. The thin-film transistor substrate according to claim 11 ,

wherein a channel region of the oxide semiconductor film of the one of the thin-film transistors has a higher mobility than a channel region of the oxide semiconductor film of the other of the thin-film transistors,

wherein the one of the thin-film transistors is a driving thin-film transistor configured to control electric current to a light-emitting element in the pixel circuit, and

wherein the other of the thin-film transistors is an electrostatic discharge protection element.

15. The thin-film transistor substrate according to claim 11 ,

wherein a channel region of the oxide semiconductor film of the one of the thin-film transistors has a higher mobility than a channel region of the oxide semiconductor film of the other of the thin-film transistors,

wherein the one of the thin-film transistors is a driving thin-film transistor configured to control electric current to a light-emitting element in the pixel circuit,

wherein the other of the thin-film transistors is included in a shift register,

wherein a power-supply potential is applied to a source/drain of the other of the thin-film transistors, and

wherein output of a previous stage is input to the gate of the other of the thin-film transistors.

16. A method of manufacturing a thin-film transistor substrate, the method comprising:

forming a first insulating layer on an insulating substrate;

forming a first oxide semiconductor layer including a channel region of a first thin-film transistor after forming the first insulating layer;

forming a second insulating layer to cover the first oxide semiconductor layer; and

forming a second oxide semiconductor film including a channel region of a second thin-film transistor in a state where the first oxide semiconductor layer is covered with the second insulating layer,

wherein a channel region of the oxide semiconductor film of either one of the first thin-film transistor and the second thin-film transistor has a wider bandgap than a channel region of the oxide semiconductor film of the other one of the first thin-film transistor and the second thin-film transistor.

17. The method of manufacturing a thin-film transistor substrate according to claim 16 ,

wherein the channel region of the oxide semiconductor film of the one of the thin-film transistors has a lower mobility than the channel region of the oxide semiconductor film of the other of the thin-film transistors.