Display device and manufacturing method thereof

• US 20050134189A1
• Filed: 12/14/2004
• Published: 06/23/2005
• Est. Priority Date: 12/18/2003
• Status: Active Grant

• Current Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Original Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Inventors: Osame, Mitsuaki, Yamazaki, Yu
• Granted Patent: US 7,460,095 B2
• Time in Patent Office: Days
• US Class Current: 315/169.100
• CPC Class Codes: G09G 2300/0417 Special arrangements specific to the use of low carrier mobility technology
• CPC Class Codes: G09G 2300/0842 forming a memory circuit, e.g. a dynamic memory with one capacitor
• CPC Class Codes: G09G 2310/0256 with the purpose of reversing the voltage across a light emitting or modulating element within a pixel
• CPC Class Codes: G09G 2320/043 Preventing or counteracting the effects of ageing
• CPC Class Codes: G09G 2360/18 Use of a frame buffer in a display terminal, inclusive of the display panel
• CPC Class Codes: G09G 3/2022 using sub-frames
• CPC Class Codes: G09G 3/3233 with pixel circuitry controlling the current through the light-emitting element
• CPC Class Codes: G09G 3/3266 Details of drivers for scan electrodes
• CPC Class Codes: G09G 3/3291 in which the data driver supplies a variable data voltage for setting the current through, or the voltage across, the light-emitting elements
• CPC Class Codes: G09G 5/399 using two or more bit-mapped memories, the operations of which are switched in time, e.g. ping-pong buffers
• CPC Class Codes: H10K 2102/3026 Top emission
• CPC Class Codes: H10K 59/12 Active-matrix OLED [AMOLED] displays
• CPC Class Codes: H10K 59/122 Pixel-defining structures or layers, e.g. banks
• CPC Class Codes: H10K 71/841 Applying alternating current [AC] during manufacturing or treatment
• CPC Class Codes: H10K 71/861 Repairing

Abstract

A display device capable of applying reverse driving voltage for a light emitting element to a light emitting element every certain period for prolonging light emitting element'"'"'s life and burning out a shorted portion. Besides a path for supplying forward current to the light emitting element, a path for supplying reverse current is provided. A driving transistor is provided in the former path while a transistor (AC transistor) is provided in the latter path, thereby a switching between the two paths is controlled. The AC transistor has a rate L/W of a channel length L to a channel width W smaller than that of the driving transistor. Accordingly, current flowing into the light emitting element can be flowed into the AC transistor in the case of reverse driving voltage being applied to the light emitting element.

Claims

1. A display device comprising:

a light emitting element;

a first path for supplying forward current to the light emitting element;

a second path for supplying reverse current to the light emitting element;

a driving transistor provided in the first path; and

an AC transistor provided in the second path,

wherein a switching between the first path and the second path is controlled by using the driving transistor and the AC transistor.

5. The display device according to claim 1,

wherein current flowing into the light emitting element when forward voltage is applied to the light emitting element is flown between a source electrode and a drain electrode of the driving transistor;

and

wherein current flowing into the light emitting element when reverse voltage is applied to the light emitting element is flown between a source electrode and a drain electrode of the AC transistor.

7. The display device according to claim 1,

wherein the ratio of a channel length of the driving transistor to a channel width thereof is 5 or more to 1.

8. The display device according to claim 1,

wherein a channel length of the AC transistor is equal to or less than a channel width thereof.

9. An electronic apparatus employing the display device, according to claim 1.

35. An electronic apparatus according to claim 9, wherein the electronic apparatus is one selected from the group consisting of a camera, a head mounted display, a navigation system, an audio reproducing device, a personal computer, a game player, a portable data terminal, and an image reproducing device.

2. A display device having a pixel, the pixel comprising:

a light emitting element;

a driving transistor for controlling the amount of forward current flowing into the light emitting element;

a switching transistor for controlling input of a video signal; and

an AC transistor for controlling reverse current flowing into the light emitting element.

16. The display device according to claim 2,

wherein current flowing into the light emitting element when forward voltage is applied to the light emitting element is flown between a source electrode and a drain electrode of the driving transistor;

and

wherein current flowing into the light emitting element when reverse voltage is applied to the light emitting element is flown between a source electrode and a drain electrode of the AC transistor.

17. The display device according to claim 2,

wherein the ratio of a channel length of the driving transistor to a channel width thereof is 5 or more to 1.

18. The display device according to claim 2,

wherein a channel length of the AC transistor is equal to or less than a channel width thereof.

19. An electronic apparatus employing the display device according to claim 2.

37. An electronic apparatus according to claim 19, wherein the electronic apparatus is one selected from the group consisting of a camera, a head mounted display, a navigation system, an audio reproducing device, a personal computer, a game player, a portable data terminal, and an image reproducing device.

3. A display device having a pixel, the pixel comprising:

a light emitting element;

a driving transistor for controlling the amount of forward current flowing into the light emitting element;

a switching transistor for controlling input of a video signal; and

an AC transistor for controlling reverse current flowing into the light emitting element,

wherein the light emitting element comprises a pixel electrode and an opposing electrode;

wherein a gate electrode of the switching transistor is connected to a gate signal line;

wherein one of a source electrode and a drain electrode of the switching transistor is connected to a source signal line flowing the video signal while the other is connected to a gate electrode of the driving transistor;

wherein one of a source electrode and a drain electrode of the driving transistor is connected to a power source line while the other is connected to the pixel electrode of the light emitting element;

wherein a gate electrode of the AC transistor is connected to the power source line;

wherein one of a source electrode and a drain electrode of the AC transistor is connected to the pixel electrode while the other is connected to a current lead-in line;

wherein the driving transistor and the AC transistor have the identical polarity;

wherein the driving transistor operates in the saturation region; and

wherein the AC transistor operates in the linear region.

6. The display device according to claim 3,

wherein potential of the power source line is fixed and potential of the opposing potential is varied depending on a direction of current flowing into the light emitting element.

20. The display device according to claim 3,

wherein current flowing into the light emitting element when forward voltage is applied to the light emitting element is flown between the source electrode and the drain electrode of the driving transistor;

and

wherein current flowing into the light emitting element when reverse voltage is applied to the light emitting element is flown between the source electrode and the drain electrode of the AC transistor.

21. The display device according to claim 3,

wherein the ratio of a channel length of the driving transistor to a channel width thereof is 5 or more to 1.

22. The display device according to claim 3,

wherein a channel length of the AC transistor is equal to or less than a channel width thereof.

23. An electronic apparatus employing the display device according claim 3.

38. An electronic apparatus according to claim 23, wherein the electronic apparatus is one selected from the group consisting of a camera, a head mounted display, a navigation system, an audio reproducing device, a personal computer, a game player, a portable data terminal, and an image reproducing device.

4. A display device having a pixel, the pixel comprising:

a light emitting element;

a driving transistor for controlling the amount of forward current flowing into the light emitting element;

a switching transistor for controlling input of a video signal; and

an AC transistor for controlling reverse current flowing into the light emitting element,

wherein the light emitting element comprises a pixel electrode and an opposing electrode;

wherein a gate electrode of the switching transistor is connected to a gate signal line;

wherein one of a source electrode and a drain electrode of the switching transistor is connected to a source signal line flowing the video signal while the other is connected to a gate electrode of the driving transistor;

wherein one of a source electrode and a drain electrode of the driving transistor is connected to a power source line while the other is connected to the pixel electrode of the light emitting element;

wherein a gate electrode of the AC transistor is connected to the power source line;

wherein one of a source electrode and a drain electrode of the AC transistor is connected to the pixel electrode while the other is connected to the power source line;

wherein the driving transistor and the AC transistor have the identical polarity;

wherein the driving transistor operates in the saturation region; and

wherein the AC transistor operates in the linear region.

24. The display device according to claim 4,

wherein current flowing into the light emitting element when forward voltage is applied to the light emitting element is flown between the source electrode and the drain electrode of the driving transistor;

and

wherein current flowing into the light emitting element when reverse voltage is applied to the light emitting element is flown between the source electrode and the drain electrode of the AC transistor.

25. The display device according to claim 4,

wherein potential of the power source line is fixed and potential of the opposing potential is varied depending on a direction of current flowing into the light emitting element.

26. The display device according to claim 4,

wherein the ratio of a channel length of the driving transistor to a channel width thereof is 5 or more to 1.

27. The display device according to claim 4,

wherein a channel length of the AC transistor is equal to or less than a channel width thereof.

28. An electronic apparatus employing the display device according to claim 4.

39. An electronic apparatus according to claim 28, wherein the electronic apparatus is one selected from the group consisting of a camera, a head mounted display, a navigation system, an audio reproducing device, a personal computer, a game player, a portable data terminal, and an image reproducing device.

10. A driving method of a display device comprising:

a light emitting element;

a switching transistor;

a first path for supplying forward current to the light emitting element;

a second path for supplying reverse current to the light emitting element;

a driving transistor provided in the first path;

an AC transistor provided in the second path; and

a means for controlling a switching between the first path and the second path by using the driving transistor and the AC transistor,

the driving method comprising the steps of;

setting whether a light emitting element emits light or not by the switching transistor and the driving transistor while flowing reverse current into the light emitting element by the AC transistor in a write period; and

operating the light emitting element in accordance with the setting performed in the write period in a display period,

wherein a total period of light emission of the light emitting element is controlled to perform a gray scale display;

wherein one frame period is comprises a plurality of subframe periods; and

wherein each subframe period comprises the write period and the display period.

14. The driving method of a display device, according to claim 10,

wherein the light emitting element comprises a pixel electrode and an opposing electrode;

wherein a gate electrode of the switching transistor is connected to a gate signal line;

wherein one of a source electrode and a drain electrode of the switching transistor is connected to a source signal line flowing video signals while the other is connected to a gate electrode of the driving transistor;

wherein one of a source electrode and a drain electrode of the driving transistor is connected to a power source line while the other is connected to the pixel electrode of the light emitting element;

wherein a gate electrode of the AC transistor is connected to the power source line;

wherein one of a source electrode and a drain electrode of the AC transistor is connected to the pixel electrode while the other is connected to the power source line; and

wherein potential of the power source line is fixed and potential of the opposing potential is varied depending on a direction of current flowing into the light emitting element.

15. An electronic apparatus employing the driving method of a display device according claim 10.

36. An electronic apparatus according to claim 15, wherein the electronic apparatus is one selected from the group consisting of a camera, a head mounted display, a navigation system, an audio reproducing device, a personal computer, a game player, a portable data terminal, and an image reproducing device.

11. A driving method of a display device comprising:

a light emitting element;

a switching transistor;

a first path for supplying forward current to the light emitting element;

a second path for supplying reverse current to the light emitting element;

a driving transistor provided in the first path;

an AC transistor provided in the second path; and

a means for controlling a switching between the first path and the second path by using the driving transistor and the AC transistor,

the driving method comprising the steps of;

setting whether a light emitting element emits light or not by the switching transistor and the driving transistor in a write period;

operating the light emitting element in accordance with the setting performed in the write period in a display period; and

flowing reverse current into the light emitting element by the AC transistor in the reverse bias period,

wherein a total period of light emission of the light emitting element is controlled to perform a gray scale display;

wherein one frame period comprises a plurality of subframe periods and a plurality of reverse bias periods;

wherein each subframe period comprises the write period and the display period.

29. The driving method of a display device, according to claim 11,

wherein the light emitting element comprises a pixel electrode and an opposing electrode;

wherein a gate electrode of the switching transistor is connected to a gate signal line;

wherein one of a source electrode and a drain electrode of the switching transistor is connected to a source signal line flowing video signals while the other is connected to a gate electrode of the driving transistor;

wherein one of a source electrode and a drain electrode of the driving transistor is connected to a power source line while the other is connected to the pixel electrode of the light emitting element;

wherein a gate electrode of the AC transistor is connected to the power source line;

wherein one of a source electrode and a drain electrode of the AC transistor is connected to the pixel electrode while the other is connected to the power source line; and

wherein potential of the power source line is fixed and potential of the opposing potential is varied depending on a direction of current flowing into the light emitting element.

30. An electronic apparatus employing the driving method of a display device according claim 11.

40. An electronic apparatus according to claim 30, wherein the electronic apparatus is one selected from the group consisting of a camera, a head mounted display, a navigation system, an audio reproducing device, a personal computer, a game player, a portable data terminal, and an image reproducing device.

12. A driving method of a display device comprising:

a light emitting element;

a switching transistor;

a first path for supplying forward current to the light emitting element;

a second path for supplying reverse current to the light emitting element;

a driving transistor provided in the first path;

an AC transistor provided in the second path; and

a means for controlling a switching between the first path and the second path by using the driving transistor and the AC transistor,

the driving method comprising the steps of;

setting whether a light emitting element emits light or not by the switching transistor and the driving transistor in a write period;

operating the light emitting element in accordance with the setting performed in the write period in a display period; and

flowing reverse current into the light emitting element by the AC transistor in the reverse bias period,

wherein a total period of light emission of the light emitting element is controlled to perform a gray scale display;

wherein one frame period comprises a plurality of subframe periods and a reverse bias period; and

wherein each subframe period comprises the write period and the display period.

31. The driving method of a display device, according to claim 12,

wherein the light emitting element comprises a pixel electrode and an opposing electrode;

wherein a gate electrode of the switching transistor is connected to a gate signal line;

wherein one of a source electrode and a drain electrode of the switching transistor is connected to a source signal line flowing video signals while the other is connected to a gate electrode of the driving transistor;

wherein one of a source electrode and a drain electrode of the driving transistor is connected to a power source line while the other is connected to the pixel electrode of the light emitting element;

wherein a gate electrode of the AC transistor is connected to the power source line;

wherein one of a source electrode and a drain electrode of the AC transistor is connected to the pixel electrode while the other is connected to the power source line; and

wherein potential of the power source line is fixed and potential of the opposing potential is varied depending on a direction of current flowing into the light emitting element.

32. An electronic apparatus employing the driving method of a display device according claim 12.

41. An electronic apparatus according to claim 32, wherein the electronic apparatus is one selected from the group consisting of a camera, a head mounted display, a navigation system, an audio reproducing device, a personal computer, a game player, a portable data terminal, and an image reproducing device.

13. A driving method of a display device comprising:

a light emitting element;

a switching transistor;

a first path for supplying forward current to the light emitting element;

a second path for supplying reverse current to the light emitting element;

a driving transistor provided in the first path;

an AC transistor provided in the second path; and

a means for controlling a switching between the first path and the second path by using the driving transistor and the AC transistor,

the driving method comprising the steps of;

flowing forward current into the light emitting element and making the light emitting element emit light at luminance in accordance with the amount of current flowing into the light emitting element by the switching transistor and the driving transistor in a forward bias period; and

flowing reverse current into the light emitting element by the AC transistor in a reverse bias period,

wherein one frame period comprises the forward bias period and the reverse bias period;

33. The driving method of a display device, according to claim 13,

wherein the light emitting element comprises a pixel electrode and an opposing electrode;

wherein a gate electrode of the switching transistor is connected to a gate signal line;

wherein one of a source electrode and a drain electrode of the switching transistor is connected to a source signal line flowing video signals while the other is connected to a gate electrode of the driving transistor;

wherein one of a source electrode and a drain electrode of the driving transistor is connected to a power source line while the other is connected to the pixel electrode of the light emitting element;

wherein a gate electrode of the AC transistor is connected to the power source line;

wherein one of a source electrode and a drain electrode of the AC transistor is connected to the pixel electrode while the other is connected to the power source line; and

wherein potential of the power source line is fixed and potential of the opposing potential is varied depending on a direction of current flowing into the light emitting element.

34. An electronic apparatus employing the driving method of a display device according claim 13.

42. An electronic apparatus according to claim 34, wherein the electronic apparatus is one selected from the group consisting of a camera, a head mounted display, a navigation system, an audio reproducing device, a personal computer, a game player, a portable data terminal, and an image reproducing device.