Active matrix display and electrooptical device

• US 6,297,518 B1
• Filed: 06/26/1998
• Issued: 10/02/2001
• Est. Priority Date: 06/02/1994
• Status: Expired due to Term

• Current Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Original Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Inventors: Zhang, Hongyong
• Primary Examiner(s): Tran, Minh Loan
• Application Number:
  US09/104,990
• Time in Patent Office: 1,194 Days
• Field of Search: 257/59, 257/72, 257/296, 257/347, 257/350, 349/42, 349/43, 349/44, 349/139, 349/140
• US Class Current: 257/59
• CPC Class Codes: G02F 1/13624 having more than one switching element per pixel
• CPC Class Codes: G02F 1/13685 Top gates
• CPC Class Codes: G09G 2300/0809 Several active elements per pixel in active matrix panels
• CPC Class Codes: G09G 2300/0819 used for counteracting undesired variations, e.g. feedback or autozeroing
• CPC Class Codes: G09G 2300/0842 forming a memory circuit, e.g. a dynamic memory with one capacitor
• CPC Class Codes: G09G 2300/0852 being a dynamic memory with more than one capacitor
• CPC Class Codes: G09G 2320/0214 with crosstalk due to leakage current of pixel switch in active matrix panels
• CPC Class Codes: G09G 3/3648 using an active matrix G09G3/367 - G09G3/3696 take precedence
• CPC Class Codes: H01L 27/12 the substrate being other than a semiconductor body, e.g. an insulating body
• 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 29/78621 with LDD structure or an extension or an offset region or characterised by the doping profile
• CPC Class Codes: H01L 29/78645 with multiple 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

Abstract

A structure for reducing the OFF current of an active matrix display. In the active matrix display, plural TFTs are connected in series with each one pixel electrode. Of these TFTs connected in series, at least one TFT excluding the TFTs located at opposite ends is maintained in conduction. Alternatively, at least one capacitor is connected between the junction of the drain and source of each TFT connected in series and an AC grounded point. Thus, the amount of electric charge released from auxiliary capacitors during cutoff of the TFTs is reduced.

Claims

1. An electrooptical device comprising:

an active matrix circuit over a substrate;

a plurality of source lines over said substrate;

a plurality of gate lines extending across said source lines wherein an array of pixels are defined by said plurality of source lines and said plurality of gate lines;

a plurality of pixel electrodes formed at said pixels, respectively;

at least first and second thin-film transistors formed at each intersection of said source lines and said gate lines for switching one of said pixel electrodes; and

wherein a channel region of said first thin film transistor is at least partially overlapped with corresponding one of said source lines while a channel region of said second thin film transistor is not overlapped with corresponding one of said source lines.

2. An electro-optical device according to claim 1 wherein said channel region of said first thin film transistor is completely overlapped with said corresponding one of said source lines.

3. An electro-optical display device comprising:

at least one source line over a substrate;

at least one gate line over said substrate extending across said source line; and

a pixel addressable by said source line and said gate line, said pixel comprising at least first and second thin film transistors and a pixel electrode wherein said first thin film transistor is connected to said source line and said second thin film transistor is connected to said pixel electrode,

wherein at least a channel region of said first thin film transistor is covered at least partially by said source line while a channel region of said second thin film transistor is not covered by said source line.

4. An electro-optical display device according to claim 3 wherein a carrier flows through the channel region of said first transistor along the source line.

5. An electro-optical display device according to claim 3 wherein each of said thin film transistors is a top-gate type in which a gate electrode is located over said channel region.

6. An electro-optical device according to claim 3 wherein said channel region of said first thin film transistor is completely covered by said source line.

7. An active matrix type electro-optical device comprising:

a substrate having an insulating surface;

a source line and a gate line over said substrate wherein said gate line extends across said source line;

a pixel electrode over said substrate;

a first thin film transistor formed over said substrate and connected to said source line;

a second thin film transistor formed over said substrate and connected to said first thin film transistor and said pixel electrode, each of said first and second thin film transistors having source, drain and channel regions;

wherein at least the channel region of said first thin film transistor is covered at least partially by said source line while the channel region of said second thin film transistor is not overlapped with said source line.

8. An active matrix type electro-optical device according to claim 7 wherein said gate line overlaps each of the channel regions of said first and second thin film transistors.

9. An active matrix type electro-optical device according to claim 7 wherein said gate line comprises a material selected from the group consisting of polysilicon, aluminum and tantalum.

10. An active matrix type electro-optical device according to claim 7 wherein each of the channel regions of the first and second thin film transistors comprises polysilicon.

11. An active matrix type electro-optical device according to claim 7 wherein said pixel electrode comprises indium tin oxide.

12. An active matrix type electro-optical device according to claim 7 wherein each of said first and second thin film transistors is a bottom gate type.

13. An active matrix type electro-optical device according to claim 7 wherein said device is a liquid crystal device.

14. An active matrix type electro-optical device according to claim 7 wherein said channel region of said first thin film transistor is completely covered by said source line.

15. An active matrix type electro-optical device comprising:

a substrate having an insulating surface;

a source line and a gate line over said substrate wherein said gate line extends across said source line;

a pixel electrode over said substrate;

a first thin film transistor and a second thin film transistor formed over said substrate, said first and second thin film transistors being connected to said source line and said pixel electrode in series wherein each of said first and second thin film transistors has source, drain and channel regions;

wherein at least the channel region of said first thin film transistor is covered at least partially by said source line while the channel region of said second thin film transistor is not covered by said source line.

16. An active matrix type electro-optical device according to claim 15 wherein each of said first and second thin film transistors is a bottom gate type.

17. An active matrix type electro-optical device according to claim 15 wherein said device is a liquid crystal device.

18. An active matrix type electro-optical device according to claim 15 wherein said channel region of said first thin film transistor is completely covered by said source line.

19. An active matrix type electro-optical device comprising:

a substrate having an insulating surface;

a source line and a gate line over said substrate wherein said gate line extends across said source line;

a pixel electrode over said substrate;

a first thin film transistor formed over said substrate and connected to said source line;

a second thin film transistor formed over said substrate and connected to said first thin film transistor and said pixel electrode, each of said first and second thin film transistors having source, drain and channel regions, and a gate electrode adjacent to said channel region wherein the gate electrodes of said first and second thin film transistors are commonly connected to said gate line;

wherein at least the channel region of said first thin film transistor is overlapped at least partially with said source line while the channel region of said second thin film transistor is not overlapped with said source line.

20. An active matrix type electro-optical device according to claim 19 wherein each of said first and second thin film transistors is a bottom gate type.

21. An active matrix type electro-optical device according to claim 19 wherein said device is a liquid crystal device.

22. An active matrix type electro-optical device according to claim 19 wherein said channel region of said first thin film transistor is completely overlapped with said source line.

23. An active matrix type electro-optical device comprising:

a substrate having an insulating surface;

a source line and a gate line over said substrate wherein said gate line extends across said source line;

a pixel electrode over said substrate;

a first thin film transistor formed over said substrate and connected to said source line;

a second thin film transistor formed over said substrate and connected to said first thin film transistor and said pixel electrode, each of said first and second thin film transistors having source, drain and channel regions wherein at least the channel region of said first thin film transistor is at least partially overlapped with said source line while the channel region of said second thin film transistor is not overlapped with said source line;

a light source to irradiate said substrate with light,

wherein said source line shields at least the channel region of said first thin film transistor from the light of said light source.

24. An active matrix type electro-optical device according to claim 23 wherein each of said first and second thin film transistors is a bottom gate type.

25. An active matrix type electro-optical device according to claim 23 wherein said device is a liquid crystal device.

26. An active matrix type electro-optical device according to claim 23 wherein said channel region of said first thin film transistor is completely overlapped with said source line.

27. An active matrix type electro-optical device comprising:

a substrate having an insulating surface;

a source line and a gate line over said substrate wherein said gate line extends across said source line;

a pixel electrode over said substrate;

a first thin film transistor and a second thin film transistor formed over said substrate, said first and second thin film transistors being connected to said source line and said pixel electrode in series wherein each of said first and second thin film transistors has source, drain and channel regions;

a light source to irradiate said substrate with light,

wherein at least the channel region of said first thin film transistor is at least partially overlapped with said source line while the channel region of said second thin film transistor is not overlapped with said source line, and

wherein said source line shields at least the channel region of said first thin film transistor from said light.

28. An active matrix type electro-optical device according to claim 27 wherein each of said first and second thin film transistors is a bottom gate type.

29. An active matrix type electro-optical device according to claim 27 wherein said device is a liquid crystal device.

30. An active matrix type electro-optical device according to claim 27 wherein said channel region of said first thin film transistor is completely overlapped with said source line.

31. An active matrix type electro-optical device comprising:

a substrate having an insulating surface;

a source line and a gate line over said substrate wherein said gate line extends across said source line;

a pixel electrode over said substrate;

a first thin film transistor formed over said substrate and connected to said source line;

a second thin film transistor formed over said substrate and connected to said first thin film transistor and said pixel electrode, each of said first and second thin film transistors having source, drain and channel regions, and a gate electrode adjacent to said channel region wherein the gate electrodes of said first and second thin film transistors are commonly connected to said gate line;

a light source to irradiate said substrate;

wherein at least the channel region of said first thin film transistor is at least partially overlapped with said source line while the channel region of said second thin film transistor is not overlapped with said source line, and

wherein said source line shields at least the channel region of said first thin film transistor from said light.

32. An active matrix type electro-optical device according to claim 31 wherein each of said first and second thin film transistors is a bottom gate type.

33. An active matrix type electro-optical device according to claim 31 wherein said device is a liquid crystal device.

34. An active matrix type electro-optical device according to claim 31 wherein said channel region of said first thin film transistor is completely overlapped with said source line.

35. An active matrix type electro-optical device comprising:

a substrate having an insulating surface;

a semiconductor layer formed on said insulating surface, said semiconductor layer comprising at least first and second channel regions, a first impurity doped region between said first and second channel regions, and a pair of second impurity doped regions wherein said first and second channel regions are disposed between said pair of second impurity regions;

a first insulating layer formed on said semiconductor layer;

a gate line formed over said first insulating layer wherein said gate line extends over said first and second channel regions;

a second insulating layer formed over said gate line;

a source line formed over said second insulating layer wherein said source line is electrically connected to one of said second impurity regions;

a third insulating layer formed over said source line; and

a pixel electrode formed over said third insulating layer wherein said pixel electrode is electrically connected to the other one of said second impurity doped regions,

wherein one of the first and second channel regions is at least partially overlapped by said source line while the other one is not overlapped by said source line.

36. An active matrix type electro-optical device according to claim 35 wherein said semiconductor layer comprises polysilicon.

37. An active matrix type electro-optical device according to claim 35 wherein said semiconductor layer has a U shape.

38. An active matrix type electro-optical device according to claim 35 wherein said source line is in direct contact with said one of the second impurity doped regions.

39. An active matrix type electro-optical device according to claim 35 wherein said pixel electrode is in direct contact with said other one of the second impurity doped regions.

40. An active matrix type electro-optical device according to claim 35 wherein said device is a liquid crystal device.

41. An active matrix type electro-optical device according to claim 35 wherein said channel region of said first thin film transistor is completely overlapped with said source line.

42. An active matrix type electro-optical device comprising:

a substrate having an insulating surface;

a semiconductor layer formed over said insulating surface, said semiconductor layer comprising at least first and second channel regions, a first impurity doped region between said first and second channel regions, and a pair of second impurity doped regions wherein said first and second channel regions are disposed between said pair of second impurity regions;

a gate line formed over said substrate adjacent to said first and second channel regions;

an insulating layer formed over said semiconductor layer;

a source line formed over said insulating layer wherein said source line is electrically connected to one of said second impurity regions;

an interlayer insulating film formed over said source line; and

a pixel electrode formed over said interlayer insulating film wherein said pixel electrode is electrically connected to the other one of said second impurity doped regions,

wherein one of the first and second channel regions is at least partially overlapped by said source line while the other one is not overlapped by said source line.

43. An active matrix type electro-optical device according to claim 42 wherein said semiconductor layer comprises polysilicon.

44. An active matrix type electro-optical device according to claim 42 wherein said semiconductor layer has a U shape.

45. An active matrix type electro-optical device according to claim 42 wherein said source line is in direct contact with said one of the second impurity doped regions.

46. An active matrix type electro-optical device according to claim 42 wherein said pixel electrode is in direct contact with said other one of the second impurity doped regions.

47. An active matrix type electro-optical device according to claim 42 wherein said device is a liquid crystal device.

48. An active matrix type electro-optical device according to claim 42 wherein said gate line extends over said semiconductor layer with a gate insulating film interposed therebetween.

49. An active matrix type electro-optical device according to claim 42 wherein said one of the first and second channel regions is completely overlapped by said source line.