Light emitting device having TFT

• US 7,723,721 B2
• Filed: 11/04/2002
• Issued: 05/25/2010
• Est. Priority Date: 11/09/2001
• Status: Expired due to Fees

• Current Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Original Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Inventors: Udagawa, Makoto, Osame, Mitsuaki, Hayakawa, Masahiko, Anzai, Aya, Koyama, Jun
• Primary Examiner(s): Ha; Nathan W
• Application Number:
  US10/286,868
• Publication Number:
  US 20030089905A1
• Time in Patent Office: 2,759 Days
• Field of Search: 257/72, 257/59, 257/359, 257/40, 257/79, 257/E33.053, 438/308
• US Class Current: 257/40
• CPC Class Codes: H01L 27/12 the substrate being other than a semiconductor body, e.g. an insulating body
• CPC Class Codes: H01L 27/1222 with a particular composition, shape or crystalline structure of the active layer
• CPC Class Codes: H01L 27/124 with a particular composition, shape or layout of the wiring layers specially adapted to the circuit arrangement, e.g. scanning lines in LCD pixel circuits wiring structures per se H01L23/52
• CPC Class Codes: H01L 29/78675 with normal-type structure, e.g. with top gate
• CPC Class Codes: H01L 29/78696 characterised by the structure of the channel, e.g. multichannel, transverse or longitudinal shape, length or width, doping structure, or the overlap or alignment between the channel and the gate, the source or the drain, or the contacting structure of the channel H01L29/78612 takes precedence; transistors having a drain offset region or a lightly doped drain [LDD] H01L29/78621
• CPC Class Codes: H10K 50/80 Constructional details
• CPC Class Codes: H10K 59/1213 the pixel elements being TFTs
• CPC Class Codes: H10K 59/131 Interconnections, e.g. wiring lines or terminals

Abstract

The present invention provides a TFT that has a channel length particularly longer than that of an existing one, specifically, several tens to several hundreds times longer than that of the existing one, and thereby allowing turning to an on-state at a gate voltage particularly higher than the existing one and driving, and allowing having a low channel conductance gd. According to the present invention, not only the simple dispersion of on-current but also the normalized dispersion thereof can be reduced, and other than the reduction of the dispersion between the individual TFTs, the dispersion of the OLEDs themselves and the dispersion due to the deterioration of the OLED can be reduced.

Claims

1. A light emitting device having a light emitting element, the light emitting element comprising:

a cathode;

an organic compound layer over the cathode; and

an anode over the organic compound layer;

wherein a thin film transistor connected to the light emitting element comprised a polysilicon film including a channel forming region interposed between a least one pair of impurity regions, and

wherein a channel length L of the film transistor is 100 μ

m or more.

2. A light emitting device as set forth in claim 1, wherein a ratio of a channel width W of the thin film transistor to the channel length L thereof is from 0.1 to 0.01.

3. A light emitting device according to claim 1, wherein the thin film transistor connected to the light emitting element is a p-channel type thin film transistor or an n-channel type thin film transistor.

4. A light emitting device according to claim 1, wherein the thin film transistor connected to the light emitting element, in the range that the sum of source-drain voltage Vd and threshold voltage Vth is larger than gate voltage Vg, has a channel conductance gd from 0 to 1×

10<sup>−

8</sup> S.

5. A light emitting device according to claim 1, wherein the thin film transistor connected to the light emitting element, in the range that the sum of source-drain voltage Vd and threshold voltage Vth is larger than gate voltage Vg, has a channel conductance gd from 0 to 5×

10<sup>−

9</sup> S.

6. A light emitting device according to claim 1, wherein the light emitting device is incorporated into an electronic equipment selected from the group consisting of a personal computer, a video camera, a mobile computer, a goggle type display, a recording medium, a digital camera, a mobile phone and a display.

7. A light emitting device according to claim 1, further comprising:

a desiccant;

an organic resin over the anode;

a protective film over the organic resin; and

a cover member covering the protective film,

wherein the desiccant is set in the cover member.

8. A light emitting device having a light emitting element, the light emitting element comprising:

a cathode;

an organic compound layer over the cathode; and

an anode over the organic compound layer;

wherein a thin film transistor connected to the light emitting element comprises a polysilicon film including a channel forming region interposed between at least one pair of impurity regions, and

wherein a ratio of a channel width W of the thin film transistor to the channel length L thereof is from 0.1 to 0.01.

9. A light emitting device according to claim 8, wherein the thin film transistor connected to the light emitting element is a p-channel type thin film transistor or an n-channel type thin film transistor.

10. A light emitting device according to claim 8, wherein the thin film transistor connected to the light emitting element, in the range that the sum of source-drain voltage Vd and threshold voltage Vth is larger than gate voltage Vg, has a channel conductance gd from 0 to 1×

10<sup>−

8</sup> S.

11. A light emitting device according to claim 8, wherein the thin film transistor connected to the light emitting element, in the range that the sum of source-drain voltage Vd and threshold voltage Vth is larger than gate voltage Vg, has a channel conductance gd from 0 to 5×

10<sup>−

9</sup> S.

12. A light emitting device according to claim 8, wherein the light emitting device is incorporated into an electronic equipment selected from the group consisting of a personal computer, a video camera, a mobile computer, a goggle type display, a recording medium, a digital camera, a mobile phone and a display.

13. A light emitting device according to claim 8, further comprising:

a desiccant;

an organic resin over the anode;

a protective film over the organic resin; and

a cover member covering the protective film,

wherein the desiccant is set in the cover member.

14. A light emitting device having a light emitting element, the light emitting element comprising:

a cathode;

an organic compound layer over the cathode; and

an anode over the organic compound layer;

wherein a thin film transistor connected to the light emitting element comprises a polysilicon film including a channel forming region interposed between a source region and a drain region, and

wherein a thin film transistor, in the range that the sum of source-drain voltage Vd and threshold voltage Vth is larger than gate voltage Vg, has a channel conductance gd from 0 to 2×

10<sup>−

9</sup> S.

15. A light emitting device according to claim 14, wherein the thin film transistor connected to the light emitting element is a p-channel type thin film transistor or an n-channel type thin film transistor.

16. A light emitting device according to claim 14, wherein the thin film transistor connected to the light emitting element, in the range that the sum of source-drain voltage Vd and threshold voltage Vth is larger than gate voltage Vg, has a channel conductance gd from 0 to 1×

10<sup>−

8</sup> S.

17. A light emitting device according to claim 14, wherein the thin film transistor connected to the light emitting element, in the range that the sum of source-drain voltage Vd and threshold voltage Vth is larger than gate voltage Vg, has a channel conductance gd from 0 to 5×

10<sup>−

9</sup> S.

18. A light emitting device according to claim 14, wherein the light emitting device is incorporated into an electronic equipment selected from the group consisting of a personal computer, a video camera, a mobile computer, a goggle type display, a recording medium, a digital camera, a mobile phone and a display.

19. A light emitting device according to claim 14, further comprising:

a desiccant;

an organic resin over the anode;

a protective film over the organic resin; and

a cover member covering the protective film,

wherein the desiccant is set in the cover member.

20. A light emitting device comprising:

a light emitting element having a cathode, an organic compound layer over the cathode and an anode over the organic compound layer; and

a thin film transistor connected to the light emitting element,

wherein the thin film transistor comprises;

a polysilicon film including a rectangular-shaped channel forming region interposed between at least one pair of impurity regions;

a gate insulating film formed over the rectangular-shaped channel region; and

a gate electrode formed over the gate insulating film,

wherein a channel length L of the rectangle-shaped channel region is 100 μ

m or more.

21. A light emitting device according to claim 20, wherein the thin film transistor connected to the light emitting element is a p-channel type thin film transistor or an n-channel type thin film transistor.

22. A light emitting device according to claim 20, wherein the thin film transistor connected to the light emitting element, in the range that the sum of source-drain voltage Vd and threshold voltage Vth is larger than gate voltage Vg, has a channel conductance gd from 0 to 1×

10<sup>−

8</sup> S.

23. A light emitting device according to claim 20, wherein the thin film transistor connected to the light emitting element, in the range that the sum of source-drain voltage Vd and threshold voltage Vth is larger than gate voltage Vg, has a channel conductance gd from 0 to 5×

10<sup>−

9</sup> S.

24. A light emitting device according to claim 20, wherein the light emitting device is incorporated into an electronic equipment selected from the group consisting of a personal computer, a video camera, a mobile computer, a goggle type display, a recording medium, a digital camera, a mobile phone and a display.

25. A light emitting device according to claim 20, further comprising:

a desiccant;

an organic resin over the anode;

a protective film over the organic resin; and

a cover member covering the protective film,

wherein the desiccant is set in the cover member.

26. A light emitting device comprising:

a light emitting element including a cathode, an organic compound layer over the cathode and an anode over the organic compound layer;

a thin film transistor connected to the light emitting element,

wherein the thin film transistor comprises;

a polysilicon film including a rectangle-shaped channel forming region interposed between at least one pair of impurity regions;

a gate insulating film formed over the rectangular-shaped channel region; and

a gate electrode formed over the gate insulating film,

wherein a ratio of a channel width W of the rectangular-shaped channel region to a channel length L of the rectangular-shaped channel region is from 0.1 to 0.01.

27. A light emitting device according to claim 26, wherein the thin film transistor connected to the light emitting element is a p-channel type thin film transistor or an n-channel type thin film transistor.

28. A light emitting device according to claim 26, wherein the thin film transistor connected to the light emitting element, in the range that the sum or source-drain voltage Vd and threshold voltage Vth is larger than gate voltage Vg, has a channel conductance gd from 0 to 1×

10<sup>−

8</sup> S.

29. A light emitting device according to claim 26, wherein the thin film transistor connected to the light emitting element, in the range that the sum of source-drain voltage Vd and threshold voltage Vth is larger than gate voltage Vg, has a channel conductance gd from 0 to 5×

10<sup>−

9</sup> S.

30. A light emitting device according to claim 26, wherein the light emitting device is incorporated into an electronic equipment selected from the group consisting of a personal computer, a video camera, a mobile computer, a goggle type display, a recording medium, a digital camera, a mobile phone and a display.

31. A light emitting device according to claim 26, further comprising:

a desiccant;

an organic resin over the anode;

a protective film over the organic resin; and

a cover member covering the protective film,

wherein the desiccant is set in the cover member.

32. A light emitting device comprising:

a light emitting element including a cathode, an organic compound layer over the cathode and an anode over the organic compound layer;

a thin film transistor connected to the light emitting element,

wherein the thin film transistor comprises;

a polysilicon film including a rectangular-shaped channel forming region interposed between at least one pair of impurity regions;

a gate insulating film formed over the rectangular-shaped channel region; and

a gate electrode formed over the gate insulating film,

wherein the thin film transistor has a channel conductance gd from 0 to 2×

10<sup>−

9</sup> S in the range that the sum of source-drain voltage Vd and threshold voltage Vth is larger than gate voltage Vg.

33. A light emitting device according to claim 32, wherein the thin film transistor connected to the light emitting element is a p-channel type thin film transistor or an n-channel type thin film transistor.

34. A light emitting device according to claim 32, wherein the thin film transistor connected to the light emitting element, in the range that the sum of source-drain voltage Vd and threshold voltage Vth is larger than gate voltage Vg, has a channel conductance gd from 0 to 1×

10 <sup>−

8</sup> S.

35. A light emitting device according to claim 32, wherein the thin film transistor connected to the light emitting element, in the range that the sum of source-drain voltage Vd and threshold voltage Vth is larger than gate voltage Vg, has a channel conductance gd from 0 to 5×

10<sup>−

9</sup> S.

36. A light emitting device according to claim 32, wherein the light emitting device is incorporated into an electronic equipment selected from the group consisting of a personal computer, a video camera, a mobile computer, a goggle type display, a recording medium, a digital camera, a mobile phone and a display.

37. A light emitting device according to claim 32, further comprising:

a desiccant;

an organic resin over the anode;

a protective film over the organic resin; and

a cover member covering the protective film,

wherein the desiccant is set in the cover member.