Thin-film transistor and thin-film diode having amorphous-oxide semiconductor layer

• US 20070063211A1
• Filed: 09/01/2006
• Published: 03/22/2007
• Est. Priority Date: 09/06/2005
• Status: Active Grant

• Current Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Original Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Inventors: Iwasaki, Tatsuya
• Granted Patent: US 7,453,087 B2
• Time in Patent Office: Days
• US Class Current: 257/98
• CPC Class Codes: H01L 29/7869 having a semiconductor body comprising an oxide semiconductor material, e.g. zinc oxide, copper aluminium oxide, cadmium stannate

Abstract

A thin-film transistor including a channel layer being formed of an oxide semiconductor transparent to visible light and having a refractive index of nx, a gate-insulating layer disposed on one face of the channel layer, and a transparent layer disposed on the other face of the channel layer and having a refractive index of nt, where there is a relationship of nx>nt. A thin-film transistor including a substrate having a refractive index of no, a transparent layer disposed on the substrate and having a refractive index of nt, and a channel layer disposed on the transparent layer and having a refractive index of nx, where there is a relationship of nx>nt>no.

Claims

1. A thin-film transistor comprising:

a channel layer being formed of an oxide semiconductor transparent to visible light, the channel layer having a refractive index of nx;

a gate-insulating layer disposed on one face of the channel layer; and

a transparent layer disposed on the other face of the channel layer and having a refractive index of nt,

wherein there is a relationship of nx>

nt.

2. The thin-film transistor according to claim 1, further comprising:

a substrate disposed on the transparent layer on the side opposite the channel layer and having a refractive index of no,

wherein there is a relationship of nx>

nt>

no.

3. The thin-film transistor according to claim 1, wherein the refractive index nx of the channel layer or the refractive index nt of the transparent layer changes continuously or stepwise in the film thickness direction.

4. The thin-film transistor according to claim 1, wherein the film thickness d of the transparent layer having a refractive index of nt is defined by the following equation:

d=γ

λ

/(4×

nt)

wherein λ

is the wavelength of light.

5. The thin-film transistor according to claim 1, wherein the transparent layer is formed of an amorphous oxide having a composition represented by the following formula:

[(Sn₁−

xM4_x)O₂]a.[(In₁−

yM3_y)₂O₃]b.[(Zn₁-zM2_zO)]c
wherein 0≦

x≦

1, 0≦

y≦

1, 0≦

z≦

1, 0≦

a≦

1, 0
≦

b≦

1, 0≦

c≦

1, and a+b+c=1;

M4 is a Group 4 element having an atomic number less than that of Sn selected from the group consisting of Si, Ge, and Zr;

M3 is Lu or a Group 3 element having an atomic number less than that of In selected from the group consisting of B, Al, Ga, and Y; and

M2 is a Group 2 element having an atomic number less than that of Zn selected from the group consisting of Mg and Ca.

6. The thin-film transistor according to claim 1, wherein the channel layer is formed of an amorphous oxide having a composition represented by the following formula:

[(Sn₁−

xM4_x)O₂]a.[(In₁−

yM3_y)₂O₃]b.[(Zn₁−

zM2_zO)]c
wherein 0≦

x≦

1, 0≦

y≦

1, 0≦

z≦

1, 0≦

a≦

1, 0
≦

b≦

1, 0≦

c≦

1, and a+b+c=1;

M4 is a Group 4 element having an atomic number less than that of Sn selected from the group consisting of Si, Ge, and Zr;

M3 is Lu or a Group 3 element having an atomic number less than that of In selected from the group consisting of B, Al, Ga, and Y; and

M2 is a Group 2 element having an atomic number less than that of Zn selected from the group consisting of Mg and Ca.

7. The thin-film transistor according to claim 6, wherein M3 is Ga.

8. The thin-film transistor according to claim 7, wherein the amorphous oxide has a composition represented by the following formula:

[(In₁-yGa_y)₂O₃]b.[(ZnO)]c

9. The thin-film transistor according to claim 6, wherein the amorphous oxide has a composition represented by the following formula:

[SnO₂]a.[InO₃]b.[ZnO]c

10. The thin-film transistor according to claim 1, wherein the channel layer and the transparent layer are each formed of an amorphous oxide having a composition represented by the following formula:

[(Sn₁−

xM4_x)O₂]a.[(In₁−

yM3_y)₂O₃]b.[(Zn₁−

zM2_zO)]c
wherein 0≦

x≦

1, 0≦

y≦

1, 0≦

z≦

1, 0≦

a≦

1, 0
≦

b≦

1, 0≦

c≦

1, and a+b+c=1;

M4 is a Group 4 element having an atomic number less than that of Sn selected from the group consisting of Si, Ge, and Zr;

M3 is Lu or a Group 3 element having an atomic number less than that of In selected from the group consisting of B, Al, Ga, and Y; and

M2 is a Group 2 element having an atomic number less than that of Zn selected from the group consisting of Mg and Ca.

11. A thin-film transistor comprising:

a substrate having a refractive index of no;

a channel layer disposed on the substrate, the channel layer being formed of an oxide semiconductor transparent to visible light, and the channel layer having a refractive index of nx; and

a gate-insulating layer disposed on the channel layer and having a refractive index of ni,

wherein the refractive index nx of the channel layer changes continuously or stepwise from no to ni in the film thickness direction.

12. The thin-film transistor according to claim 11, wherein the amorphous oxide has a composition represented by the following formula:

[(In₁−

yGa_y)₂O₃]b.[(ZnO)]c

13. A thin-film diode comprising:

a substrate having a refractive index of no;

a transparent layer disposed on the substrate and having a refractive index of nt; and

an oxide semiconductor layer disposed on the transparent layer, the oxide semiconductor layer being transparent to visible light and having a refractive index of nx,

wherein there is a relationship of nx>

nt>

no.

14. The thin-film diode according to claim 13, wherein the transparent layer or the oxide semiconductor layer is formed of an amorphous oxide having a composition represented by the following formula:

[(Sn₁−

xM4_x)O₂]a.[(In₁−

yM3_y)₂O₃]b.[(Zn₁−

zM2_zO)]c
wherein 0≦

x≦

1, 0≦

y≦

1, 0≦

z≦

1, 0≦

a≦

1, 0
≦

b≦

1, 0≦

c≦

1, and a+b+c=1;

M4 is a Group 4 element having an atomic number less than that of Sn selected from the group consisting of Si, Ge, and Zr;

M3 is Lu or a Group 3 element having an atomic number less than that of In selected from the group consisting of B, Al, Ga, and Y; and

M2 is a Group 2 element having an atomic number less than that of Zn selected from the group consisting of Mg and Ca.

15. The thin-film diode according to claim 13, wherein the transparent layer and the oxide semiconductor layer are each formed of an amorphous oxide having a composition represented by the following formula:

[(Sn₁−

xM4_x)O₂]a.[(In₁−

yM3_y)₂O₃]b.[(Zn₁−

zM2_zO)]c
wherein 0≦

x≦

1, 0≦

y≦

1, 0≦

z≦

1, 0≦

a≦

1, 0
≦

b≦

1, 0≦

c≦

1, and a+b+c=1;

M4 is a Group 4 element having an atomic number less than that of Sn selected from the group consisting of Si, Ge, and Zr;

M3 is Lu or a Group 3 element having an atomic number less than that of In selected from the group consisting of B, Al, Ga, and Y; and

M2 is a Group 2 element having an atomic number less than that of Zn selected from the group consisting of Mg and Ca.