Light emitting device and driving method of the same

• US 20040263506A1
• Filed: 06/28/2004
• Published: 12/30/2004
• Est. Priority Date: 06/30/2003
• Status: Active Grant

• Current Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Original Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Inventors: Osame, Mitsuaki, Fukumoto, Ryota, Anzai, Aya, Koyama, Jun, Yamazaki, Yu
• Granted Patent: US 8,552,933 B2
• Time in Patent Office: Days
• US Class Current: 345/204
• CPC Class Codes: G09G 2300/0842 forming a memory circuit, e.g. a dynamic memory with one capacitor
• CPC Class Codes: G09G 2300/0861 with additional control of the display period without amending the charge stored in a pixel memory, e.g. by means of additional select electrodes
• CPC Class Codes: G09G 2300/0866 by means of changes in the pixel supply voltage
• CPC Class Codes: G09G 3/2022 using sub-frames
• CPC Class Codes: G09G 3/3225 using an active matrix
• CPC Class Codes: H10K 2102/3031 Two-side emission, e.g. transparent OLEDs [TOLED]
• CPC Class Codes: H10K 59/1213 the pixel elements being TFTs

Abstract

The invention provides a light emitting device and an element substrate in which a luminance variation of light emitting elements among pixels due to variation in characteristics of driving transistors can be suppressed even without suppressing the off-current of a switching transistor low or increasing the capacitance of a capacitor. A gate of a first transistor is connected to a first scan line, and a gate of a second transistor is connected to a second scan line. A connection between a signal line and a gate of a third transistor is controlled by the first transistor. The second transistor and the third transistor are connected in series between a pixel electrode of a light emitting element and a power supply line. The signal line, the second scan line and the power supply line are disposed in parallel, while the first scan line is crossed with the signal line, the second scan line and the power supply line.

Claims

1. A light emitting device comprising a first transistor, a second transistor, a third transistor and a light emitting element,

wherein a gate electrode of the first transistor is connected to a first scan line,

wherein a gate electrode of the second transistor is connected to a second scan line,

wherein the first transistor controls a connection between a signal line and a gate electrode of the third transistor,

wherein the second transistor and the third transistor are connected in series between a pixel electrode of the light emitting element and a power supply line,

wherein the signal line, the second scan line and the power supply line are disposed in parallel, and

wherein the first scan line crosses the signal line, the second scan line and the power supply line.

9. The light emitting device according to claim 1,

wherein the third transistor has its channel width and length in the ratio of 1:

5 or more.

10. The light emitting device according to claim 1,

wherein when it is assumed that the channel length and the channel width of the driving transistor are L1 and W1 respectively, and the channel length and the channel width of the current controlling transistor are L2 and W2 respectively, L1/W1:

L2/W2=X;

1 is satisfied and X is desirably in the range of 5 to 6000.

34. The light emitting device according to claim 9,

wherein when it is assumed that the channel length and the channel width of the driving transistor are L1 and W1 respectively, and the channel length and the channel width of the current controlling transistor are L2 and W2 respectively, L1/W1:

L2/W2=X;

1 is satisfied and X is desirably in the range of 5 to 6000.

2. A light emitting device comprising a first transistor, a second transistor, a third transistor and a light emitting element,

wherein a gate electrode of the first transistor is connected to a scan line,

wherein the first transistor controls a connection between a signal line and a gate electrode of the third transistor,

wherein the second transistor and the third transistor are connected in series between a pixel electrode of the light emitting element and a power supply line,

wherein the signal line and the power supply line are disposed in parallel,

wherein the scan line crosses the signal line and the power supply line,

wherein a first region of a gate electrode of the second transistor is connected to corresponding one of a plurality of second scan lines disposed in parallel with the signal line, and

wherein a second region of the gate electrode of the second transistor is connected to corresponding one of a plurality of second scan lines disposed in parallel with the signal line.

20. The light emitting device according to claim 2,

wherein the third transistor has its channel width and length in the ratio of 1:

5 or more.

27. The light emitting device according to claim 2,

wherein when it is assumed that the channel length and the channel width of the driving transistor are L1 and W1 respectively, and the channel length and the channel width of the current controlling transistor are L2 and W2 respectively, L1/W1:

L2/W2=X;

1 is satisfied and X is desirably in the range of 5 to 6000.

3. A light emitting device comprising a first transistor, a second transistor, a third transistor and a light emitting element,

wherein a gate electrode of the first transistor is connected to a first scan line;

wherein a gate electrode of the second transistor is connected to a second scan line;

wherein the first transistor controls a connection between a signal line and a gate electrode of the third transistor;

wherein the second transistor and the third transistor are connected in series between a pixel electrode of the light emitting element and a power supply line;

wherein the signal line and the second scan line are disposed in parallel;

wherein the first scan line and the power supply line are disposed in parallel; and

wherein the first scan line and the power supply line cross the signal line and the second scan line.

21. The light emitting device according to claim 3,

wherein the third transistor has its channel width and length in the ratio of 1:

5 or more.

28. The light emitting device according to claim 3,

wherein when it is assumed that the channel length and the channel width of the driving transistor are L1 and W1 respectively, and the channel length and the channel width of the current controlling transistor are L2 and W2 respectively, L1/W1:

L2/W2=X;

1 is satisfied and X is desirably in the range of 5 to 6000.

4. A light emitting device comprising a first transistor, a second transistor, a third transistor, a fourth transistor and a light emitting element,

wherein the first transistor controls an input of a video signal to the pixel;

wherein the third transistor controls a switching according to a potential of the video signal; and

wherein the second to fourth transistors are connected in series between a pixel electrode of the light emitting element and a power supply line.

22. The light emitting device according to claim 4,

wherein the third transistor has its channel width and length in the ratio of 1:

5 or more.

29. The light emitting device according to claim 4,

wherein when it is assumed that the channel length and the channel width of the driving transistor are L1 and W1 respectively, and the channel length and the channel width of the current controlling transistor are L2 and W2 respectively, L1/W1:

L2/W2=X;

1 is satisfied and X is desirably in the range of 5 to 6000.

5. A light emitting device comprising a first transistor, a second transistor, a third transistor, a fourth transistor and a light emitting element,

wherein the first transistor controls an input of a video signal to the pixel;

wherein the third transistor controls a switching according to a potential of the video signal;

wherein the second transistor controls a current value supplied to the light emitting element when the third and the fourth transistors are ON;

wherein the fourth transistor can stop the current supply to the light emitting element when the first transistor is ON; and

wherein the second to fourth transistors are connected in series between a pixel electrode of the light emitting element and a power supply line.

23. The light emitting device according to claim 5,

wherein the third transistor has its channel width and length in the ratio of 1:

5 or more.

30. The light emitting device according to claim 5,

wherein when it is assumed that the channel length and the channel width of the driving transistor are L1 and W1 respectively, and the channel length and the channel width of the current controlling transistor are L2 and W2 respectively, L1/W1:

L2/W2=X;

1 is satisfied and X is desirably in the range of 5 to 6000.

6. A light emitting device comprising a first transistor, a second transistor, a third transistor, a fourth transistor and a light emitting element,

wherein a gate electrode of the first transistor is connected to a first scan line;

wherein the first transistor controls a connection between a signal line and a gate electrode of the third transistor;

wherein the second to fourth transistors are connected in series between a pixel electrode of the light emitting element and a first power supply line;

wherein a gate electrode of the second transistor is connected to a second power supply line; and

wherein a gate electrode of the fourth transistor is connected to a second scan line.

24. The light emitting device according to claim 6,

wherein the third transistor has its channel width and length in the ratio of 1:

5 or more.

31. The light emitting device according to claim 6,

wherein when it is assumed that the channel length and the channel width of the driving transistor are L1 and W1 respectively, and the channel length and the channel width of the current controlling transistor are L2 and W2 respectively, L1/W1:

L2/W2=X;

1 is satisfied and X is desirably in the range of 5 to 6000.

7. A light emitting device comprising a first transistor, a second transistor, a third transistor and a light emitting element,

wherein a gate electrode of the first transistor is connected to a scan line;

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

wherein the first transistor controls a connection between the signal line and a gate electrode of the third transistor;

wherein the second and third transistors are connected in series between a pixel electrode of the light emitting element and a power supply line; and

wherein a circuit element such as a single or a plurality of switching element can change a potential supplied to the signal line.

25. The light emitting device according to claim 7,

wherein the third transistor has its channel width and length in the ratio of 1:

5 or more.

32. The light emitting device according to claim 7,

wherein when it is assumed that the channel length and the channel width of the driving transistor are L1 and W1 respectively, and the channel length and the channel width of the current controlling transistor are L2 and W2 respectively, L1/W1:

L2/W2=X;

1 is satisfied and X is desirably in the range of 5 to 6000.

8. A light emitting device comprising a first transistor, a second transistor, a third transistor and a light emitting element,

wherein a gate electrode of the first transistor is connected to a first scan line;

wherein a gate electrode of the second transistor is connected to a second scan line;

wherein the first transistor controls a connection between the signal line and a gate electrode of the third transistor;

wherein the second and third transistors are connected in series between a pixel electrode of the light emitting element and a power supply line; and

wherein a circuit element such as a single or a plurality of switching element can change a potential supplied to the signal line.

26. The light emitting device according to claim 8,

wherein the third transistor has its channel width and length in the ratio of 1:

5 or more.

33. The light emitting device according to claim 8,

wherein when it is assumed that the channel length and the channel width of the driving transistor are L1 and W1 respectively, and the channel length and the channel width of the current controlling transistor are L2 and W2 respectively, L1/W1:

L2/W2=X;

1 is satisfied and X is desirably in the range of 5 to 6000.

11. A driving method of a light emitting device comprising a first transistor, a second transistor, a third transistor and a light emitting element,

wherein the light emitting element comprises a pixel electrode, a counter electrode, and an electroluminescent layer formed between the pixel electrode and the counter electrode;

wherein the second transistor and the third transistor are connected in series between a power supply line and the pixel electrode;

wherein in a first period, a potential of a video signal is supplied to a gate electrode of the third transistor by turning ON the first transistor and a first potential is supplied to the power supply line and the counter electrode;

wherein in a second period, a potential of the video signal is held at a gate electrode of the third transistor by turning OFF the first transistor and the first potential is supplied to the power supply line and a second potential is supplied to the counter electrode;

wherein in the first and second periods, a potential which is high enough to turn ON the second transistor when the third transistor is ON is applied to a gate electrode of the second transistor; and

wherein the first and second potentials are high enough to supply a forward bias current to the light emitting element when the third transistor is ON in the second period.

17. The driving method of a light emitting device according to claim 11,

wherein the first transistor operates in a linear region.

18. The driving method of a light emitting device according to claim 11,

wherein the second transistor operates in a saturation region.

19. The driving method of a light emitting element according to claim 11,

wherein the third transistor operates in a linear region.

45. The driving method of a light emitting device according to claim 17,

wherein the second transistor operates in a saturation region.

51. The driving method of a light emitting element according to claim 17,

wherein the third transistor operates in a linear region.

52. The driving method of a light emitting element according to claim 18,

wherein the third transistor operates in a linear region.

12. A driving method of a light emitting device comprising a first transistor, a second transistor, a third transistor and a light emitting element,

wherein the light emitting element comprises a pixel electrode, a counter electrode, and an electroluminescent layer formed between the pixel electrode and the counter electrode;

wherein the second and third transistors are connected in series between a power supply line and the pixel electrode;

wherein in a first period, a potential of a video signal is supplied to a gate electrode of the third transistor by turning ON the first transistor, and the second transistor is turned OFF;

wherein in a second period, a potential of the video signal is held at a gate electrode of the third transistor by turning OFF the first transistor and a potential which is high enough to turn ON the second transistor when the third transistor is ON is applied to a gate electrode of the second transistor;

wherein a first potential is supplied to the power supply line and a second potential is supplied to the counter electrode at least in the second period; and

wherein the first and second potentials are high enough to supply a forward bias current to the light emitting element when the third transistor is ON in the second period.

35. The driving method of a light emitting device according to claim 12,

wherein the first transistor operates in a linear region.

40. The driving method of a light emitting device according to claim 12,

wherein the second transistor operates in a saturation region.

46. The driving method of a light emitting element according to claim 12,

wherein the third transistor operates in a linear region.

13. A driving method of a light emitting element comprising a first transistor, a second 1110 transistor, a third transistor and a light emitting element,

wherein the light emitting element comprises a pixel electrode, a counter electrode, and an electroluminescent layer formed between the pixel electrode and the counter electrode;

wherein the second and third transistors are connected in series between a power supply line and the pixel electrode;

wherein a gate electrode of the second transistor is connected to the power supply line;

wherein in a first period, a potential of a video signal is supplied to a gate electrode of the third transistor by turning ON the first transistor, and a first potential is supplied to the power supply line and the counter electrode;

wherein in a second period, a potential of the video signal is held at a gate electrode of the third transistor by turning OFF the first transistor, and the first potential is supplied to the power supply line and a second potential is supplied to the counter electrode;

wherein a potential which is high enough to turn ON the second transistor when the third transistor is ON is applied to a gate electrode of the second transistor in the first and second periods; and

wherein the first and second potentials are high enough to supply a forward bias current to the light emitting element when the third transistor is ON in the second period.

36. The driving method of a light emitting device according to claim 13,

wherein the first transistor operates in a linear region.

41. The driving method of a light emitting device according to claim 13,

wherein the second transistor operates in a saturation region.

47. The driving method of a light emitting element according to claim 13,

wherein the third transistor operates in a linear region.

14. A driving method of a light emitting element comprising a first transistor, a second transistor, a third transistor and a light emitting element,

wherein the light emitting element comprises a pixel electrode, a counter electrode, and an electroluminescent layer formed between the pixel electrode and the counter electrode;

wherein the second and third transistors are connected in series between a power supply line and the pixel electrode;

wherein a gate electrode of the second transistor is connected to the power supply line;

wherein in a first period, a potential of a video signal is supplied to a gate electrode of the third transistor by turning ON the first transistor;

wherein in a second period, a potential of the video signal is held at a gate electrode of the third transistor by turning OFF the first transistor;

wherein a potential which is high enough to turn ON the second transistor when the third transistor ON is applied to a gate electrode of the second transistor in the first and second periods;

wherein a first potential is supplied to the power supply line and a second potential is supplied to the counter electrode through a switching element at least in the second period;

wherein the switching element is OFF in the first period; and

wherein the first and second potentials are high enough to supply a forward bias current to the light emitting element when the third transistor is ON in the second period.

37. The driving method of a light emitting device according to claim 14,

wherein the first transistor operates in a linear region.

42. The driving method of a light emitting device according to claim 14,

wherein the second transistor operates in a saturation region.

48. The driving method of a light emitting element according to claim 14,

wherein the third transistor operates in a linear region.

15. A driving method of a light emitting element comprising a first transistor, a second transistor, a third transistor, fourth transistor and a light emitting element,

wherein the light emitting element comprises a pixel electrode, a counter electrode, and

an electroluminescent layer provided between the pixel electrode and the counter electrode;

wherein the second to fourth transistors are connected in series between a power supply line and the pixel electrode;

wherein in a first period, a potential of a video signal is supplied to a gate electrode of the third transistor by turning ON the first transistor, and the fourth transistor is OFF;

wherein in a second period, a potential of the video signal is held at a gate electrode of the third transistor by turning OFF the first transistor, and the fourth transistor is ON;

wherein a potential which is high enough to turn ON the second transistor when the third and fourth transistors are ON is applied to a gate electrode of the second transistor in the first and second periods;

wherein a first potential is supplied to the power supply line and a second potential is supplied to the counter electrode at least in the second period; and

wherein the first and second potentials are high enough to supply a forward bias current to the light emitting element when the third transistor is ON in the second period.

16. The driving method of a light emitting device according to claim 15,

wherein the fourth transistor operates in a linear region.

38. The driving method of a light emitting device according to claim 15,

wherein the first transistor operates in a linear region.

39. The driving method of a light emitting device according to claim 16,

wherein the first transistor operates in a linear region.

43. The driving method of a light emitting device according to claim 15,

wherein the second transistor operates in a saturation region.

44. The driving method of a light emitting device according to claim 16,

wherein the second transistor operates in a saturation region.

49. The driving method of a light emitting element according to claim 15,

wherein the third transistor operates in a linear region.

50. The driving method of a light emitting element according to claim 16,

wherein the third transistor operates in a linear region.