Light emitting device and electronic device

• US 7,061,451 B2
• Filed: 02/20/2002
• Issued: 06/13/2006
• Est. Priority Date: 02/21/2001
• Status: Active Grant

• Current Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Original Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Inventors: Kimura, Hajime
• Primary Examiner(s): Tran, Henry N.
• Application Number:
  US10/079,072
• Publication Number:
  US 20020113760A1
• Time in Patent Office: 1,574 Days
• Field of Search: 345/55, 345/76, 345/82, 345/84, 345/90, 345/92, 345/98, 345/204, 345/211, 3151691-169, 315/291
• US Class Current: 345/76
• CPC Class Codes: G09G 2300/0426 Layout of electrodes and connections
• 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 2310/0251 Precharge or discharge of pixel before applying new pixel voltage
• 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 2320/0238 Improving the black level
• CPC Class Codes: G09G 2320/043 Preventing or counteracting the effects of ageing
• CPC Class Codes: G09G 2330/021 Power management, e.g. power saving
• 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 3/3258 with pixel circuitry controlling the voltage across the light-emitting element

Abstract

There is provided a light emitting device capable of preventing light emission of an OLED caused due to an off current of a driver TFT and suppressing a reduction in a contrast, to thereby display a beautiful image. A wiring which is kept at a predetermined potential (hereinafter referred to as a discharge line) is provided to make the off current flow into the discharge line rather than into the OLED. A TFT such as is turned on when the driver TFT is tuned off (hereinafter referred to as a discharging TFT) is provided in each pixel. With respect to the source region and the drain region of the discharging TFT, one is connected with a pixel electrode and the other is connected with the discharge line. According to the above structure, when the driver TFT is turned off, the discharging TFT is turned on. Thus, the off current in the driver TFT actively flows into the discharge line rather than into the OLED.

Claims

1. A light emitting device including an OLED, a power source line, a discharge line, a first TFT, and a second TFT, wherein:

an anode of the OLED is connected with the power source line through the first TFT;

the anode is connected with the discharge line through the second TFT;

a source region of the second TFT is connected to the discharge line; and

when one of the first TFT and the second TFT is in an on state, the other is in an off state.

2. A light emitting device according to claim 1, wherein switchings of the first TFT and the second TFT are controlled by a digital video signal.

3. A light emitting device according to claim 1, wherein the light emitting device is incorporated into an electronic appliance selected from the group consisting of a video camera, a digital camera, a goggle type display, a navigation system, an audio reproducing device, a lap-top computer, a game machine, a portable information terminals and an image reproducing device.

4. A light emitting device including an OLED, a power source line, a discharge line, a first TFT, and a second TFT, wherein:

an anode of the OLED is connected with the power source line through the first TFT;

the anode is connected with the discharge line through the second TFT;

one of the first TFT and the second TFT is a p-channel TFT and the other is an n-channel TFT; and

a gate electrode of the first TFT and a gate electrode of the second TFT are connected with each other.

5. A light emitting device according to claim 4, wherein switchings of the first TFT and the second TFT are controlled by a digital video signal.

6. A light emitting device according to claim 4, wherein the light emitting device is incorporated into an electronic appliance selected from the group consisting of a video camera, a digital camera, a goggle type display, a navigation system, an audio reproducing device, a lap-top computer, a game machine, a portable information terminals and an image reproducing device.

7. A light emitting device including an OLED, a power source line, a discharge line, a first TFT, and a second TFT, wherein:

a pixel electrode of the OLED is connected with the power source line through the first TFT;

the pixel electrode is connected with the discharge line through the second TFT;

one of source and drain regions of the second TFT is connected to the discharge line; and

when one of the first TFT and the second TFT is in an on state, the other is in an off state.

8. A light emitting device according to claim 7, wherein switchings of the first TFT and the second TFT are controlled by a digital video signal.

9. A light emitting device according to claim 7, wherein the light emitting device is incorporated into an electronic appliance selected from the group consisting of a video camera, a digital camera, a goggle type display, a navigation system, an audio reproducing device, a lap-top computer, a game machine, a portable information terminals and an image reproducing device.

10. A light emitting device including an OLED, a power source line, a discharge line, a first TFT, and a second TFT, wherein:

a pixel electrode of the OLED is connected with the power source line through the first TFT;

the pixel electrode is connected with the discharge line through the second TFT;

one of the first TFT and the second TFT is a p-channel TFT and the other is an n-channel TFT; and

a gate electrode of the first TFT and a gate electrode of the second TFT are connected with each other.

11. A light emitting device according to claim 10, wherein switchings of the first TFT and the second TFT are controlled by a digital video signal.

12. A light emitting device according to claim 10, wherein the light emitting device is incorporated into an electronic appliance selected from the group consisting of a video camera, a digital camera, a goggle type display, a navigation system, an audio reproducing device, a lap-top computer, a game machine, a portable information terminals and an image reproducing device.

13. A light emitting device including a signal line, a scan line, an OLED, a power source line, a discharge line, a first TFT, a second TFT, and a third TFT, wherein:

switching of the third TFT is controlled by a potential of the scan line;

when the third TFT is in an on state, a digital video signal inputted to the signal line is inputted to a gate electrode of the first TFT and a gate electrode of the second TFT;

a pixel electrode of the OLED is connected with the power source line through the first TFT;

the pixel electrode is connected with the discharge line through the second TFT;

switchings of the first TFT and the second TFT are controlled by the digital video signal; and

when one of the first TFT and the second TFT is in an on state, the other is in an off state.

14. A light emitting device according to claim 13, wherein the light emitting device is incorporated into an electronic appliance selected from the group consisting of a video camera, a digital camera, a goggle type display, a navigation system, an audio reproducing device, a lap-top computer, a game machine, a portable information terminals and an image reproducing device.

15. A light emitting device including a signal line, a scan line, an OLED, a power source line, a discharge line, a first TFT, a second TFT, and a third TFT, wherein:

switching of the third TFT is controlled by a potential of the scan line;

when the third TFT is in an on state, a digital video signal inputted to the signal line is inputted to a gate electrode of the first TFT and a gate electrode of the second TFT;

the pixel electrode of the OLED is connected with the power source line through the first TFT;

the pixel electrode is connected with the discharge line through the second TFT;

switchings of the first TFT and the second TFT are controlled by the digital video signal;

one of the first TFT and the second TFT is a p-channel TFT and the other is an n-channel TFT; and

the gate electrode of the first TFT and the gate electrode of the second TFT are connected with each other.

16. A light emitting device according to claim 15, wherein the light emitting device is incorporated into an electronic appliance selected from the group consisting of a video camera, a digital camera, a goggle type display, a navigation system, an audio reproducing device, a lap-top computer, a game machine, a portable information terminals and an image reproducing device.

17. A light emitting device including a signal line, a first scan line, a second scan line, an OLED, a power source line, a discharge line, a first TFT, a second TFT, a third TFT, and a fourth TFT, wherein:

switching of the third TFT is controlled by a potential of the first scan line;

switching of the fourth TFT is controlled by a potential of the second scan line;

when the third TFT is in an on state, a digital video signal inputted to the signal line is inputted to a gate electrode of the first TFT and a gate electrode of the second TFT;

when the fourth TFT is in an on state, a potential of the power source line is applied to the gate electrode of the first TFT and the gate electrode of the second TFT;

a pixel electrode of the OLED is connected with the power source line through the first TFT;

the pixel electrode is connected with the discharge line through the second TFT;

switchings of the first TFT and the second TFT are controlled by the digital video signal; and

when one of the first TFT and the second TFT is in an on state, the other is in an off state.

18. A light emitting device according to claim 17, wherein the light emitting device is incorporated into an electronic appliance selected from the group consisting of a video camera, a digital camera, a goggle type display, a navigation system, an audio reproducing device, a lap-top computer, a game machine, a portable information terminals and an image reproducing device.

19. A light emitting device including a signal line, a first scan line, a second scan line, an OLED, a power source line, a discharge line, a first TFT, a second TFT, a third TFT, and a fourth TFT, wherein:

switching of the third TFT is controlled by a potential of the first scan line;

switching of the fourth TFT is controlled by a potential of the second scan line;

when the third TFT is in an on state, a digital video signal inputted to the signal line is inputted to a gate electrode of the first TFT and a gate electrode of the second TFT;

when the fourth TFT is in an on state, a potential of the power source line is applied to the gate electrode of the first TFT and the gate electrode of the second TFT;

a pixel electrode of the OLED is connected with the power source line through the first TFT;

the pixel electrode is connected with the discharge line through the second TFT;

switchings of the first TFT and the second TFT are controlled by the digital video signal;

one of the first TFT and the second TFT is a p-channel TFT and the other is an n-channel TFT; and

the gate electrode of the first TFT and the gate electrode of the second TFT are connected with each other.

20. A light emitting device according to claim 19, wherein the light emitting device is incorporated into an electronic appliance selected from the group consisting of a video camera, a digital camera, a goggle type display, a navigation system, an audio reproducing device, a lap-top computer, a game machine, a portable information terminals and an image reproducing device.

21. light emitting device in which a plurality of pixels are provided, each of the pixels including a signal line, a scan line, an OLED, a power source line, a first TFT, a second TFT, and a third TFT, wherein:

in each pixels,

switching of the third TFT is controlled by a potential of the scan line;

when the third TFT is in an on state, a digital video signal inputted to the signal line is inputted to a gate electrode of the first TFT and a gate electrode of the second TFT;

a pixel electrode of the OLED is connected with the power source line through the first TFT;

the pixel electrode is connected with the scan line of another pixel through the second TFT;

switchings of the first TFT and the second TFT are controlled by the digital video signal;

when one of the first TFT and the second TFT is in an on state, the other is in an off state; and

the third TFT and the second TFT has the same polarity.

22. A light emitting device according to claim 21, wherein the light emitting device is incorporated into an electronic appliance selected from the group consisting of a video camera, a digital camera, a goggle type display, a navigation system, an audio reproducing device, a lap-top computer, a game machine, a portable information terminals and an image reproducing device.

23. A light emitting device in which a plurality of pixels are provided, each of the pixels including a signal line, a scan line, an OLED, a power source line, a first TFT, a second TFT, and a third TFT, wherein:

in each pixel,

switching of the third TFT is controlled by a potential of the scan line;

when the third TFT is in an on state, a digital video signal inputted to the signal line is inputted to a gate electrode of the first TFT and a gate electrode of the second TFT;

a pixel electrode of the OLED is connected with the power source line through the first TFT;

the pixel electrode is connected with the scan line of another pixel through the second TFT;

switchings of the first TFT and the second TFT are controlled by the digital video signal;

one of the first TFT and the second TFT is a p-channel TFT and the other is an n-channel TFT;

the third TFT and the second TFT have the same polarity; and

the gate electrode of the first TFT and the gate electrode of the second TFT are connected with each other.

24. A light emitting device according to claim 23, wherein the light emitting device is incorporated into an electronic appliance selected from the group consisting of a video camera, a digital camera, a goggle type display, a navigation system, an audio reproducing device, a lap-top computer, a game machine, a portable information terminals and an image reproducing device.

25. A light emitting device including an OLED, a power source line, a discharge line, a first TFT, and a second TFT, wherein:

the OLED has a pixel electrode, a counter electrode, and an organic light emitting layer formed between the pixel electrode and the counter electrode;

when a potential of the counter electrode is lower than that of the power source line, a potential of the discharge line is lower than that of the power source line;

when a potential of the counter electrode is higher than that of the power source line, a potential of the discharge line is higher than that of the power source line;

the pixel electrode is connected with the power source line through the first TFT;

the pixel electrode is connected with the discharge line through the second TFT; and

when one of the first TFT and the second TFT is in an on state, the other is in an off state.

26. A light emitting device according to claim 25, wherein the organic light emitting layer contains an organic light emitting material in which phosphorescence is generated from a triplet exciton.

27. A light emitting device according to claim 25, wherein switchings of the first TFT and the second TFT are controlled by a digital video signal.

28. A light emitting device according to claim 25, wherein the light emitting device is incorporated into an electronic appliance selected from the group consisting of a video camera, a digital camera, a goggle type display, a navigation system, an audio reproducing device, a lap-top computer, a game machine, a portable information terminals and an image reproducing device.

29. A light emitting device including an OLED, a power source line, a discharge line, a first TFT, and a second TFT, wherein:

the OLED has a pixel electrode, a counter electrode, and an organic light emitting layer formed between the pixel electrode and the counter electrode;

a potential of the counter electrode is lower than that of the power source line;

a potential of the discharge line is lower than that of the power source line;

the pixel electrode of the OLED is connected with the power source line through the first TFT;

the pixel electrode is connected with the discharge line through the second TFT;

the first TFT is a p-channel TFT and the second TFT is an n-channel TFT; and

a gate electrode of the first TFT and a gate electrode of the second TFT are connected with each other.

30. A light emitting device according to claim 29, wherein the organic light emitting layer contains an organic light emitting material in which phosphorescence is generated from a triplet exciton.

31. A light emitting device according to claim 29, wherein switchings of the first TFT and the second TFT are controlled by a digital video signal.

32. A light emitting device according to claim 29, wherein the light emitting device is incorporated into an electronic appliance selected from the group consisting of a video camera, a digital camera, a goggle type display, a navigation system, an audio reproducing device, a lap-top computer, a game machine, a portable information terminals and an image reproducing device.

33. A light emitting device including an OLED, a power source line, a discharge line, a first TFT, and a second TFT, wherein:

the OLED has a pixel electrode, a counter electrode, and an organic light emitting layer formed between the pixel electrode and the counter electrode;

a potential of the counter electrode is higher than that of the power source line;

a potential of the discharge line is higher than that of the power source line;

the pixel electrode of the OLED is connected with the power source line through the first TFT;

the pixel electrode is connected with the discharge line through the second TFT;

the first TFT is a p-channel TFT and the second TFT is an n-channel TFT; and

a gate electrode of the first TFT and a gate electrode of the second TFT are connected with each other.

34. A light emitting device according to claim 33, wherein the organic light emitting layer contains an organic light emitting material in which phosphorescence is generated from a triplet exciton.

35. A light emitting device according to claim 33, wherein switchings of the first TFT and the second TFT are controlled by a digital video signal.

36. A light emitting device according to claim 33, wherein the light emitting device is incorporated into an electronic appliance selected from the group consisting of a video camera, a digital camera, a goggle type display, a navigation system, an audio reproducing device, a lap-top computer, a game machine, a portable information terminals and an image reproducing device.

37. A light emitting device including an OLED, a power source line, a discharge line, a first TFT, and a second TFT, wherein:

the OLED has a pixel electrode, a counter electrode, and an organic light emitting layer formed between the pixel electrode and the counter electrode;

the counter electrode and the discharge line are kept at the same potential;

the pixel electrode is connected with the power source line through the first TFT;

the pixel electrode is connected with the discharge line through the second TFT; and

when one of the first TFT and the second TFT is in an on state, the other is in an off state.

38. A light emitting device according to claim 37, wherein the organic light emitting layer contains an organic light emitting material in which phosphorescence is generated from a triplet exciton.

39. A light emitting device according to claim 37, wherein switchings of the first TFT and the second TFT are controlled by a digital video signal.

40. A light emitting device according to claim 37, wherein the light emitting device is incorporated into an electronic appliance selected from the group consisting of a video camera, a digital camera, a goggle type display, a navigation system, an audio reproducing device, a lap-top computer, a game machine, a portable information terminals and an image reproducing device.

41. A light emitting device including an OLED, a power source line, a discharge line, a first TFT, and a second TFT, wherein:

the OLED has a pixel electrode, a counter electrode, and an organic light emitting layer formed between the pixel electrode and the counter electrode;

the counter electrode and the discharge line are kept at the same potential;

a potential of the counter electrode and a potential of the discharge line are lower than that of the power source line;

the pixel electrode of the OLED is connected with the power source line through the first TFT;

the pixel electrode is connected with the discharge line through the second TFT;

the first TFT is a p-channel TFT and the second TFT is an n-channel TFT; and

a gate electrode of the first TFT and a gate electrode of the second TFT are connected with each other.

42. A light emitting device according to claim 41, wherein switchings of the first TFT and the second TFT are controlled by a digital video signal.

43. A light emitting device according to claim 41, wherein the organic light emitting layer contains an organic light emitting material in which phosphorescence is generated from a triplet exciton.

44. A light emitting device according to claim 41, wherein the light emitting device is incorporated into an electronic appliance selected from the group consisting of a video camera, a digital camera, a goggle type display, a navigation system, an audio reproducing device, a lap-top computer, a game machine, a portable information terminals and an image reproducing device.

45. A light emitting device including an OLED, a power source line, a discharge line, a first TFT, and a second TFT, wherein:

the OLED has a pixel electrode, a counter electrode, and an organic light emitting layer formed between the pixel electrode and the counter electrode;

the counter electrode and the discharge line are kept at the same potential;

a potential of the counter electrode and a potential of the discharge line are higher than that of the power source line;

the pixel electrode of the OLED is connected with the power source line through the first TFT;

the pixel electrode is connected with the discharge line through the second TFT;

the first TFT is a p-channel TFT and the second TFT is an n-channel TFT; and

a gate electrode of the first TFT and a gate electrode of the second TFT are connected with each other.

46. A light emitting device according to claim 45, wherein the organic light emitting layer contains an organic light emitting material in which phosphorescence is generated from a triplet exciton.

47. A light emitting device according to claim 45, wherein switchings of the first TFT and the second TFT are controlled by a digital video signal.

48. A light emitting device according to claim 45, wherein the light emitting device is incorporated into an electronic appliance selected from the group consisting of a video camera, a digital camera, a goggle type display, a navigation system, an audio reproducing device, a lap-top computer, a game machine, a portable information terminals and an image reproducing device.