Light-emitting device

• US 7,995,010 B2
• Filed: 10/26/2006
• Issued: 08/09/2011
• Est. Priority Date: 02/29/2000
• Status: Expired due to Fees

• Current Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Original Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Inventors: Koyama, Jun, Yamazaki, Shunpei, Osada, Mai
• Primary Examiner(s): Abdulselam; Abbas I
• Application Number:
  US11/553,197
• Publication Number:
  US 20070052634A1
• Time in Patent Office: 1,748 Days
• Field of Search: 345/76, 345/82, 345/92, 345/94, 345/100, 345/208, 315/169.3, 257/22, 257/66, 257/350, 257/E21.35, 257/202, 257/212, 257/224, 313/498, 313/505, 349/43, 349/44, 349/141, 438/29, 438/141
• US Class Current: 345/76
• CPC Class Codes: G09G 2300/0417 Special arrangements specific to the use of low carrier mobility technology
• CPC Class Codes: G09G 2300/0426 Layout of electrodes and connections
• CPC Class Codes: G09G 2300/0809 Several active elements per pixel in active matrix panels
• CPC Class Codes: G09G 2300/0814 used for selection purposes, e.g. logical AND for partial update
• 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 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 2320/0233 Improving the luminance or brightness uniformity across the screen
• CPC Class Codes: G09G 2320/043 Preventing or counteracting the effects of ageing
• 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 3/3275 Details of drivers for data electrodes
• CPC Class Codes: H01L 27/1214 comprising a plurality of TFTs formed on a non-semiconducting substrate, e.g. driving circuits for AMLCDs
• CPC Class Codes: H01L 27/1222 with a particular composition, shape or crystalline structure of the active layer
• CPC Class Codes: H01L 27/1251 comprising TFTs having a different architecture, e.g. top- and bottom gate TFTs
• CPC Class Codes: H01L 27/1296 adapted to increase the uniformity of device parameters
• CPC Class Codes: H01L 29/42384 for thin film field effect transistors, e.g. characterised by the thickness or the shape of the insulator or the dimensions, the shape or the lay-out of the conductor
• CPC Class Codes: H01L 29/4908 for thin film semiconductor, e.g. gate of TFT
• 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 29/78627 : with a significant overlap between the lightly doped drain and the gate electrode, e.g. GOLDD
• CPC Class Codes: H01L 29/78654 : Monocrystalline silicon transistors
• CPC Class Codes: H01L 29/7866 : Non-monocrystalline silicon transistors
• CPC Class Codes: H01L 29/78672 : Polycrystalline or microcrystalline silicon transistor
• 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 50/805 : Electrodes
• CPC Class Codes: H10K 59/00 : Integrated devices, or assemblies of multiple devices, comprising at least one organic light-emitting element covered by group H10K50/00
• CPC Class Codes: H10K 59/12 : Active-matrix OLED [AMOLED] displays
• CPC Class Codes: H10K 59/1201 : Manufacture or treatment
• CPC Class Codes: H10K 59/1213 : the pixel elements being TFTs
• CPC Class Codes: H10K 59/1216 : the pixel elements being capacitors
• CPC Class Codes: H10K 59/123 : Connection of the pixel electrodes to the thin film transistors [TFT]
• CPC Class Codes: H10K 59/124 : Insulating layers formed between TFT elements and OLED elements
• CPC Class Codes: H10K 59/35 : comprising red-green-blue [RGB] subpixels
• CPC Class Codes: H10K 59/871 : Self-supporting sealing arrangements
• CPC Class Codes: H10K 59/8722 : Peripheral sealing arrangements, e.g. adhesives, sealants

Abstract

There is provided an EL light-emitting device with less uneven brightness. When a drain current of a plurality of current controlling TFTs is Id, a mobility is μ, a gate capacitance per unit area is Co, a maximum gate voltage is Vgs_(max), a channel width is W, a channel length is L, an average value of a threshold voltage is Vth, a deviation from the average value of the threshold voltage is ΔVth, and a difference in emission brightness of a plurality of EL elements is within a range of ±n %, a semiconductor display device is characterized in that

$A=\frac{2\mathrm{Id}}{\mu *C_0}$ $\frac{A}{{\left({\mathrm{Vgs}}_{\left(\max \right)}-\mathrm{Vth}\right)}^2}\leqq \frac{W}{L}\leqq {\left(\sqrt{1+\frac{n}{100}}-1\right)}^2*\frac{A}{\Delta {\mathrm{Vth}}^2}$ $\Delta \mathrm{Vth}\leqq \left(\sqrt{1+\frac{n}{100}}-1\right)*\sqrt{A*L/W}$

Claims

1. A light-emitting device comprising:

a first pixel comprising;

a first thin film transistor comprising a first channel forming region, the first channel forming region having a first channel width and a first channel length; and

a first EL element connected to the first thin film transistor; and

a second pixel comprising;

a second thin film transistor comprising a second channel forming region, the second channel forming region having a second channel width and a second channel length; and

a second EL element connected to the second thin film transistor,

wherein a ratio of the first channel width to the first channel length is different from a ratio of the second channel width to the second channel length,

wherein the first EL element and the second EL element comprise a first EL material and a second EL material, respectively, and

wherein the first EL material is different from the second EL material.

2. A light-emitting device according to claim 1, wherein each of the first thin film transistor and the second thin film transistor is a current controlling thin film transistor.

3. A light-emitting device according to claim 1, wherein each of the first thin film transistor and the second thin film transistor comprises a crystalline semiconductor film.

4. A light-emitting device according to claim 1, wherein emission color of the first pixel is different from that of the second pixel.

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

a first switching thin film transistor having a double gate structure, the first switching thin film transistor being connected to the first thin film transistor; and

a second switching thin film transistor having a double gate structure, the second switching thin film transistor being connected to the second thin film transistor.

6. A light-emitting device according to claim 1, wherein the ratio of the first channel width to the first channel length is equal to or larger than 2.26×

10<sup>−

3</sup> and equal to or smaller than 0.214.

7. An electronic apparatus having a light-emitting device according to claim 1, wherein the electronic apparatus is one selected from the group consisting of a video camera, a digital camera, a goggle type display, a car navigation system, an audio reproduction device, a notebook personal computer, a game equipment, a mobile computer, a mobile telephone, a mobile game equipment, an electronic book, and an image reproduction device provided with a recording medium.

8. A light-emitting device according to claim 1, wherein each of the first thin film transistor and the second thin film transistor is a p-channel thin film transistor.

9. A light-emitting device according to claim 1, wherein each of the first thin film transistor and the second thin film transistor includes an LDD region.

10. A light-emitting device comprising:

a first pixel comprising;

a first thin film transistor comprising a first channel forming region, the first channel forming region having a first channel width and a first channel length; and

a first EL element connected to the first thin film transistor; and

a second pixel comprising;

a second thin film transistor comprising a second channel forming region, the second channel forming region having a second channel width and a second channel length; and

a second EL element connected to the second thin film transistor,

wherein a ratio of the first channel width to the first channel length is different from a ratio of the second channel width to the second channel length, and

wherein the first channel length is larger than the first channel width.

11. A light-emitting device according to claim 10, wherein each of the first thin film transistor and the second thin film transistor is a current controlling thin film transistor.

12. A light-emitting device according to claim 10, wherein each of the first thin film transistor and the second thin film transistor comprises a crystalline semiconductor film.

13. A light-emitting device according to claim 10,

wherein the first EL element and the second EL element comprise a first EL material and a second EL material, respectively, and

wherein the first EL material is different from the second EL material.

14. A light-emitting device according to claim 10, wherein emission color of the first pixel is different from that of the second pixel.

15. A light-emitting device according to claim 10, further comprising:

a first switching thin film transistor having a double gate structure, the first switching thin film transistor being electrically connected to the first thin film transistor; and

a second switching thin film transistor having a double gate structure, the second switching thin film transistor being electrically connected to the second thin film transistor.

16. A light-emitting device according to claim 10, wherein the ratio of the first channel width to the first channel length is equal to or larger than 2.26×

10<sup>−

3</sup> and equal to or smaller than 0.214.

17. An electronic apparatus having a light-emitting device according to claim 10, wherein the electronic apparatus is one selected from the group consisting of a video camera, a digital camera, a goggle type display, a car navigation system, an audio reproduction device, a notebook personal computer, a game equipment, a mobile computer, a mobile telephone, a mobile game equipment, an electronic book, and an image reproduction device provided with a recording medium.

18. A light-emitting device according to claim 10, wherein each of the first thin film transistor and the second thin film transistor is a p-channel thin film transistor.

19. A light-emitting device according to claim 10, wherein the second channel length is larger than the second channel width.

20. A light-emitting device according to claim 10, wherein each of the first thin film transistor and the second thin film transistor includes an LDD region.

21. A light-emitting device comprising:

a first pixel comprising;

a first source signal line;

a first switching thin film transistor connected to the first source signal line;

a first power supply line;

a first EL element; and

a first current controlling thin film transistor connected to the first power supply line and the first EL element; and

a second pixel comprising;

a second source signal line;

a second switching thin film transistor connected to the second source signal line;

a second power supply line;

a second EL element; and

a second current controlling thin film transistor connected to the second power supply line and the second EL element,

wherein a gate electrode of the first current controlling thin film transistor is connected to the first switching thin film transistor,

wherein a gate electrode of the second current controlling thin film transistor is connected to the second switching thin film transistor,

wherein the first current controlling thin film transistor comprises a first channel forming region having a first channel width and a first channel length,

wherein the second current controlling thin film transistor comprises a second channel forming region having a second channel width and a second channel length, and

wherein a ratio of the first channel width to the first channel length is different from a ratio of the second channel width to the second channel length.

22. A light-emitting device according to claim 21, wherein each of the first current controlling thin film transistor and the second current controlling thin film transistor comprises a crystalline semiconductor film.

23. A light-emitting device according to claim 21,

wherein the first EL element and the second EL element comprise a first EL material and a second EL material, respectively, and

wherein the first EL material is different from the second EL material.

24. A light-emitting device according to claim 21, wherein emission color of the first pixel is different from that of the second pixel.

25. A light-emitting device according to claim 21, wherein the ratio of the first channel width to the first channel length is equal to or larger than 2.26×

10<sup>−

3</sup> and equal to or smaller than 0.214.

26. An electronic apparatus having a light-emitting device according to claim 21, wherein the electronic apparatus is one selected from the group consisting of a video camera, a digital camera, a goggle type display, a car navigation system, an audio reproduction device, a notebook personal computer, a game equipment, a mobile computer, a mobile telephone, a mobile game equipment, an electronic book, and an image reproduction device provided with a recording medium.

27. A light-emitting device according to claim 21, wherein each of the first current controlling thin film transistor and the second current controlling thin film transistor is a p-channel thin film transistor.

28. A light-emitting device according to claim 21, wherein each of the first switching thin film transistor and the second switching thin film transistor comprises a double gate structure.

29. A light-emitting device according to claim 21, wherein each of the first current controlling thin film transistor and the second current controlling thin film transistor includes an LDD region.

30. A light-emitting device comprising:

a first pixel comprising;

a first source signal line;

a first switching thin film transistor connected to the first source signal line;

a first power supply line;

a first EL element; and

a first current controlling thin film transistor connected to the first power supply line and the first EL element; and

a second pixel comprising;

a second source signal line;

a second switching thin film transistor connected to the second source signal line;

a second power supply line;

a second EL element; and

a second current controlling thin film transistor connected to the second power supply line and the second EL element,

wherein a gate electrode of the first current controlling thin film transistor is connected to the first switching thin film transistor,

wherein a gate electrode of the second current controlling thin film transistor is connected to the second switching thin film transistor,

wherein the first current controlling thin film transistor comprises a first channel forming region having a first channel width and a first channel length,

wherein the second current controlling thin film transistor comprises a second channel forming region having a second channel width and a second channel length,

wherein a ratio of the first channel width to the first channel length is different from a ratio of the second channel width to the second channel length, and

wherein the first channel length is larger than the first channel width.

31. A light-emitting device according to claim 30, wherein each of the first current controlling thin film transistor and the second current controlling thin film transistor comprises a crystalline semiconductor film.

32. A light-emitting device according to claim 30,

wherein the first EL element and the second EL element comprise a first EL material and a second EL material, respectively, and

wherein the first EL material is different from the second EL material.

33. A light-emitting device according to claim 30, wherein emission color of the first pixel is different from that of the second pixel.

34. A light-emitting device according to claim 30, wherein the ratio of the first channel width to the first channel length is equal to or larger than 2.26×

10<sup>−

3</sup> and equal to or smaller than 0.214.

35. An electronic apparatus having a light-emitting device according to claim 30, wherein the electronic apparatus is one selected from the group consisting of a video camera, a digital camera, a goggle type display, a car navigation system, an audio reproduction device, a notebook personal computer, a game equipment, a mobile computer, a mobile telephone, a mobile game equipment, an electronic book, and an image reproduction device provided with a recording medium.

36. A light-emitting device according to claim 30, wherein each of the first current controlling thin film transistor and the second current controlling thin film transistor is a p-channel thin film transistor.

37. A light-emitting device according to claim 30, wherein the second channel length is larger than the second channel width.

38. A light-emitting device according to claim 30, wherein each of the first switching thin film transistor and the second switching thin film transistor comprises a double gate structure.

39. A light-emitting device according to claim 30, wherein each of the first current controlling thin film transistor and the second current controlling thin film transistor includes an LDD region.

40. A light-emitting device comprising:

a first pixel over a substrate, the first pixel comprising;

a first thin film transistor comprising a first channel forming region, the first channel forming region having a first channel width and a first channel length;

a first pixel electrode electrically connected to the first thin film transistor; and

a first EL layer formed over the first pixel electrode; and

a second pixel over the substrate, the second pixel comprising;

a second thin film transistor comprising a second channel forming region, the second channel forming region having a second channel width and a second channel length;

a second pixel electrode electrically connected to the second thin film transistor; and

a second EL layer formed over the second pixel electrode,

wherein a ratio of the first channel width to the first channel length is different from a ratio of the second channel width to the second channel length.

41. A light-emitting device according to claim 40, wherein each of the first thin film transistor and the second thin film transistor is a current controlling thin film transistor.

42. A light-emitting device according to claim 40, wherein each of the first thin film transistor and the second thin film transistor comprises a crystalline semiconductor film.

43. A light-emitting device according to claim 40,

wherein the first EL layer and the second EL layer comprise a first EL material and a second EL material, respectively, and

wherein the first EL material is different from the second EL material.

44. A light-emitting device according to claim 40, wherein emission color of the first pixel is different from that of the second pixel.

45. A light-emitting device according to claim 40, further comprising:

a first switching thin film transistor having a double gate structure, the first switching thin film transistor being electrically connected to the first thin film transistor; and

a second switching thin film transistor having a double gate structure, the second switching thin film transistor being electrically connected to the second thin film transistor.

46. A light-emitting device according to claim 40, wherein the ratio of the first channel width to the first channel length is equal to or larger than 2.26×

10<sup>−

3</sup> and equal to or smaller than 0.214.

47. An electronic apparatus having a light-emitting device according to claim 40, wherein the electronic apparatus is one selected from the group consisting of a video camera, a digital camera, a goggle type display, a car navigation system, an audio reproduction device, a notebook personal computer, a game equipment, a mobile computer, a mobile telephone, a mobile game equipment, an electronic book, and an image reproduction device provided with a recording medium.

48. A light-emitting device according to claim 40, wherein the substrate is a glass substrate.

49. A light-emitting device according to claim 40, wherein each of the first pixel electrode and the second pixel electrode is an indium-tin oxide film.

50. A light-emitting device according to claim 40, wherein each of the first thin film transistor and the second thin film transistor is a p-channel thin film transistor.

51. A light-emitting device according to claim 40, wherein each of the first thin film transistor and the second thin film transistor includes an LDD region.

52. A light-emitting device comprising:

a first pixel over a substrate, the first pixel comprising;

a first thin film transistor comprising a first channel forming region, the first channel forming region having a first channel width and a first channel length;

a first pixel electrode electrically connected to the first thin film transistor; and

a first EL layer formed over the first pixel electrode; and

a second pixel over the substrate, the second pixel comprising;

a second thin film transistor comprising a second channel forming region, the second channel forming region having a second channel width and a second channel length;

a second pixel electrode electrically connected to the second thin film transistor; and

a second EL layer formed over the second pixel electrode,

wherein a ratio of the first channel width to the first channel length is different from a ratio of the second channel width to the second channel length, and

wherein the first channel length is larger than the first channel width.

53. A light-emitting device according to claim 52, wherein each of the first thin film transistor and the second thin film transistor is a current controlling thin film transistor.

54. A light-emitting device according to claim 52, wherein each of the first thin film transistor and the second thin film transistor comprises a crystalline semiconductor film.

55. A light-emitting device according to claim 52,

wherein the first EL layer and the second EL layer comprise a first EL material and a second EL material, respectively, and

wherein the first EL material is different from the second EL material.

56. A light-emitting device according to claim 52, wherein emission color of the first pixel is different from that of the second pixel.

57. A light-emitting device according to claim 52, further comprising:

a first switching thin film transistor having a double gate structure, the first switching thin film transistor being electrically connected to the first thin film transistor; and

a second switching thin film transistor having a double gate structure, the second switching thin film transistor being electrically connected to the second thin film transistor.

58. A light-emitting device according to claim 52,

wherein the ratio of the first channel width to the first channel length is equal to or larger than 2.26×

10<sup>−

3</sup> and equal to or smaller than 0.214.

59. An electronic apparatus having a light-emitting device according to claim 52, wherein the electronic apparatus is one selected from the group consisting of a video camera, a digital camera, a goggle type display, a car navigation system, an audio reproduction device, a notebook personal computer, a game equipment, a mobile computer, a mobile telephone, a mobile game equipment, an electronic book, and an image reproduction device provided with a recording medium.

60. A light-emitting device according to claim 52, wherein the substrate is a glass substrate.

61. A light-emitting device according to claim 52, wherein each of the first pixel electrode and the second pixel electrode is an indium-tin oxide film.

62. A light-emitting device according to claim 52, wherein each of the first thin film transistor and the second thin film transistor is a p-channel thin film transistor.

63. A light-emitting device according to claim 52, wherein the second channel length is larger than the second channel width.

64. A light-emitting device according to claim 52, wherein each of the first thin film transistor and the second thin film transistor includes an LDD region.

65. A light-emitting device comprising:

a first pixel over a substrate, the first pixel comprising;

a first switching thin film transistor;

a first current controlling thin film transistor comprising a first channel forming region, the first channel forming region having a first channel width and a first channel length;

a first pixel electrode electrically connected to the first current controlling thin film transistor; and

a first EL layer formed over the first pixel electrode; and

a second pixel over the substrate, the second pixel comprising;

a second switching thin film transistor;

a second current controlling thin film transistor comprising a second channel forming region, the second channel forming region having a second channel width and a second channel length;

a second pixel electrode electrically connected to the second current controlling thin film transistor; and

a second EL layer formed over the second pixel electrode,

wherein a ratio of the first channel width to the first channel length is different from a ratio of the second channel width to the second channel length.

66. A light-emitting device according to claim 65, wherein each of the first current controlling thin film transistor and the second current controlling thin film transistor comprises a crystalline semiconductor film.

67. A light-emitting device according to claim 65,

wherein the first EL layer and the second EL layer comprise a first EL material and a second EL material, respectively, and

wherein the first EL material is different from the second EL material.

68. A light-emitting device according to claim 65, wherein emission color of the first pixel is different from that of the second pixel.

69. A light-emitting device according to claim 65, wherein the ratio of the first channel width to the first channel length is equal to or larger than 2.26×

10<sup>−

3</sup> and equal to or smaller than 0.214.

70. An electronic apparatus having a light-emitting device according to claim 65, wherein the electronic apparatus is one selected from the group consisting of a video camera, a digital camera, a goggle type display, a car navigation system, an audio reproduction device, a notebook personal computer, a game equipment, a mobile computer, a mobile telephone, a mobile game equipment, an electronic book, and an image reproduction device provided with a recording medium.

71. A light-emitting device according to claim 65, wherein the substrate is a glass substrate.

72. A light-emitting device according to claim 65, wherein each of the first pixel electrode and the second pixel electrode is an indium-tin oxide film.

73. A light-emitting device according to claim 65, wherein each of the first current controlling thin film transistor and the second current controlling thin film transistor is a p-channel thin film transistor.

74. A light-emitting device according to claim 65, wherein each of the first switching thin film transistor and the second switching thin film transistor comprises a double gate structure.

75. A light-emitting device according to claim 65, wherein each of the first current controlling thin film transistor and the second current controlling thin film transistor includes an LDD region.

76. A light-emitting device comprising:

a first pixel over a substrate, the first pixel comprising;

a first switching thin film transistor;

a first current controlling thin film transistor comprising a first channel forming region, the first channel forming region having a first channel width and a first channel length;

a first pixel electrode electrically connected to the first current controlling thin film transistor; and

a first EL layer formed over the first pixel electrode; and

a second pixel over the substrate, the second pixel comprising;

a second switching thin film transistor;

a second current controlling thin film transistor comprising a second channel forming region, the second channel forming region having a second channel width and a second channel length;

a second pixel electrode electrically connected to the second current controlling thin film transistor; and

a second EL layer formed over the second pixel electrode,

wherein a ratio of the first channel width to the first channel length is different from a ratio of the second channel width to the second channel length, and

wherein the first channel length is larger than the first channel width.

77. A light-emitting device according to claim 76, wherein each of the first current controlling thin film transistor and the second current controlling thin film transistor comprises a crystalline semiconductor film.

78. A light-emitting device according to claim 76,

wherein the first EL layer and the second EL layer comprise a first EL material and a second EL material, respectively, and

wherein the first EL material is different from the second EL material.

79. A light-emitting device according to claim 76, wherein emission color of the first pixel is different from that of the second pixel.

80. A light-emitting device according to claim 76, wherein the ratio of the first channel width to the first channel length is equal to or larger than 2.26×

10<sup>−

3</sup> and equal to or smaller than 0.214.

81. An electronic apparatus having a light-emitting device according to claim 76, wherein the electronic apparatus is one selected from the group consisting of a video camera, a digital camera, a goggle type display, a car navigation system, an audio reproduction device, a notebook personal computer, a game equipment, a mobile computer, a mobile telephone, a mobile game equipment, an electronic book, and an image reproduction device provided with a recording medium.

82. A light-emitting device according to claim 76, wherein the substrate is a glass substrate.

83. A light-emitting device according to claim 76, wherein each of the first pixel electrode and the second pixel electrode is an indium-tin oxide film.

84. A light-emitting device according to claim 76, wherein each of the first current controlling thin film transistor and the second current controlling thin film transistor is a p-channel thin film transistor.

85. A light-emitting device according to claim 76, wherein each of the first switching thin film transistor and the second switching thin film transistor comprises a double gate structure.

86. A light-emitting device according to claim 76, wherein the second channel length is larger than the second channel width.

87. A light-emitting device according to claim 76, wherein each of the first current controlling thin film transistor and the second current controlling thin film transistor includes an LDD region.

88. A light-emitting device comprising:

a first pixel over a substrate, the first pixel comprising;

a first semiconductor film formed over the substrate;

a first gate electrode formed over the first semiconductor film; and

a first pixel electrode electrically connected to the first semiconductor film; and

a second pixel over the substrate, the second pixel comprising;

a second semiconductor film formed over the substrate;

a second gate electrode formed over the second semiconductor film; and

a second pixel electrode electrically connected to the second semiconductor film,

wherein a first region in which the first gate electrode is overlapped with the first semiconductor film has a first length in a first direction in which a first career flows and a first width in a second direction vertical to the first direction,

wherein a second region in which the second gate electrode is overlapped with the second semiconductor film has a second length in a third direction in which a second career flows and a second width in a fourth direction vertical to the third direction, and

wherein a ratio of the first width to the first length is different from a ratio of the second width to the second length.

89. A light-emitting device according to claim 88, wherein each of the first region and the second region is a channel forming region.

90. A light-emitting device according to claim 88, wherein each of the first semiconductor film and the second semiconductor film comprises a crystalline semiconductor.

91. A light-emitting device according to claim 88, wherein each of the first semiconductor film and the second semiconductor film does not include an LDD region.

92. A light-emitting device according to claim 88, wherein emission color of the first pixel is different from that of the second pixel.

93. A light-emitting device according to claim 88, further comprising:

a first switching thin film transistor having a double gate structure in the first pixel; and

a second switching thin film transistor having a double gate structure in the second pixel.

94. A light-emitting device according to claim 88, wherein the ratio of the first width to the first length is equal to or larger than 2.26×

10<sup>−

3</sup> and equal to or smaller than 0.214.

95. An electronic apparatus having a light-emitting device according to claim 88, wherein the electronic apparatus is one selected from the group consisting of a video camera, a digital camera, a goggle type display, a car navigation system, an audio reproduction device, a notebook personal computer, a game equipment, a mobile computer, a mobile telephone, a mobile game equipment, an electronic book, and an image reproduction device provided with a recording medium.

96. A light-emitting device according to claim 88, wherein the substrate is a glass substrate.

97. A light-emitting device according to claim 88, wherein each of the first pixel electrode and the second pixel electrode is an indium-tin oxide film.

98. A light-emitting device comprising:

a first pixel over a substrate, the first pixel comprising;

a first semiconductor film formed over the substrate;

a first gate electrode formed over the first semiconductor film; and

a first pixel electrode electrically connected to the first semiconductor film; and

a second pixel over the substrate, the second pixel comprising;

a second semiconductor film formed over the substrate;

a second gate electrode formed over the second semiconductor film; and

a second pixel electrode electrically connected to the second semiconductor film,

wherein a first region in which the first gate electrode is overlapped with the first semiconductor film has a first length in a first direction in which a first career flows and a first width in a second direction vertical to the first direction,

wherein a second region in which the second gate electrode is overlapped with the second semiconductor film has a second length in a third direction in which a second career flows and a second width in a fourth direction vertical to the third direction,

wherein a ratio of the first width to the first length is different from a ratio of the second width to the second length, and

wherein the first length is larger than the first width.

99. A light-emitting device according to claim 98, wherein each of the first region and the second region is a channel forming region.

100. A light-emitting device according to claim 98, wherein each of the first semiconductor film and the second semiconductor film comprises a crystalline semiconductor.

101. A light-emitting device according to claim 98, wherein each of the first semiconductor film and the second semiconductor film does not include an LDD region.

102. A light-emitting device according to claim 98, wherein emission color of the first pixel is different from that of the second pixel.

103. A light-emitting device according to claim 98, further comprising:

a first switching thin film transistor having a double gate structure in the first pixel; and

a second switching thin film transistor having a double gate structure in the second pixel.

104. A light-emitting device according to claim 98, wherein the ratio of the first width to the first length is equal to or larger than 2.26×

10<sup>−

3</sup> and equal to or smaller than 0.214.

105. An electronic apparatus having a light-emitting device according to claim 98, wherein the electronic apparatus is one selected from the group consisting of a video camera, a digital camera, a goggle type display, a car navigation system, an audio reproduction device, a notebook personal computer, a game equipment, a mobile computer, a mobile telephone, a mobile game equipment, an electronic book, and an image reproduction device provided with a recording medium.

106. A light-emitting device according to claim 98, wherein the substrate is a glass substrate.

107. A light-emitting device according to claim 98, wherein each of the first pixel electrode and the second pixel electrode is an indium-tin oxide film.

108. A light-emitting device according to claim 98, wherein the second length is larger than the second width.

109. A light-emitting device comprising:

a first pixel over a substrate, the first pixel comprising;

a first switching thin film transistor formed over the substrate;

a first current controlling thin film transistor formed over the substrate, the first current controlling thin film transistor comprising a first semiconductor film and a first gate electrode; and

a first pixel electrode electrically connected to the first current controlling thin film transistor; and

a second pixel over the substrate, the second pixel comprising;

a second switching thin film transistor formed over the substrate;

a second current controlling thin film transistor formed over the substrate, the second current controlling thin film transistor comprising a second semiconductor film and a second gate electrode; and

a second pixel electrode electrically connected to the second current controlling thin film transistor,

wherein a first region in which the first gate electrode is overlapped with the first semiconductor film has a first length in a first direction in which a first career flows and a first width in a second direction vertical to the first direction,

wherein a second region in which the second gate electrode is overlapped with the second semiconductor film has a second length in a third direction in which a second career flows and a second width in a fourth direction vertical to the third direction, and

wherein a ratio of the first width to the first length is different from a ratio of the second width to the second length.

110. A light-emitting device according to claim 109, wherein each of the first region and the second region is a channel forming region.

111. A light-emitting device according to claim 109, wherein each of the first semiconductor film and the second semiconductor film comprises a crystalline semiconductor.

112. A light-emitting device according to claim 109, wherein each of the first semiconductor film and the second semiconductor film does not include an LDD region.

113. A light-emitting device according to claim 109, wherein emission color of the first pixel is different from that of the second pixel.

114. A light-emitting device according to claim 109, wherein the ratio of the first width to the first length is equal to or larger than 2.26×

10<sup>−

3</sup> and equal to or smaller than 0.214.

115. An electronic apparatus having a light-emitting device according to claim 109, wherein the electronic apparatus is one selected from the group consisting of a video camera, a digital camera, a goggle type display, a car navigation system, an audio reproduction device, a notebook personal computer, a game equipment, a mobile computer, a mobile telephone, a mobile game equipment, an electronic book, and an image reproduction device provided with a recording medium.

116. A light-emitting device according to claim 109, wherein the substrate is a glass substrate.

117. A light-emitting device according to claim 109, wherein each of the first pixel electrode and the second pixel electrode is an indium-tin oxide film.

118. A light-emitting device according to claim 109, wherein each of the first current controlling thin film transistor and the second current controlling thin film transistor is a p-channel thin film transistor.

119. A light-emitting device according to claim 109, wherein each of the first switching thin film transistor and the second switching thin film transistor comprises a double gate structure.

120. A light-emitting device comprising:

a first pixel over a substrate, the first pixel comprising;

a first switching thin film transistor formed over the substrate;

a first current controlling thin film transistor formed over the substrate, the first current controlling thin film transistor comprising a first semiconductor film and a first gate electrode; and

a first pixel electrode electrically connected to the first current controlling thin film transistor; and

a second pixel over the substrate, the second pixel comprising;

a second switching thin film transistor formed over the substrate;

a second current controlling thin film transistor formed over the substrate, the second current controlling thin film transistor comprising a second semiconductor film and a second gate electrode; and

a second pixel electrode electrically connected to the second current controlling thin film transistor,

wherein a first region in which the first gate electrode is overlapped with the first semiconductor film has a first length in a first direction in which a first career flows and a first width in a second direction vertical to the first direction,

wherein a second region in which the second gate electrode is overlapped with the second semiconductor film has a second length in a third direction in which a second career flows and a second width in a fourth direction vertical to the third direction, and

wherein a ratio of the first width to the first length is different from a ratio of the second width to the second length, and

wherein the first length is larger than the first width.

121. A light-emitting device according to claim 120, wherein each of the first region and the second region is a channel forming region.

122. A 1 light-emitting device according to claim 120, wherein each of the first semiconductor film and the second semiconductor film comprises a crystalline semiconductor.

123. A light-emitting device according to claim 120, wherein each of the first semiconductor film and the second semiconductor film does not include an LDD region.

124. A light-emitting device according to claim 120, wherein emission color of the first pixel is different from that of the second pixel.

125. A light-emitting device according to claim 120, wherein the ratio of the first width to the first length is equal to or larger than 2.26×

10<sup>−

3</sup> and equal to or smaller than 0.214.

126. An electronic apparatus having a light-emitting device according to claim 120, wherein the electronic apparatus is one selected from the group consisting of a video camera, a digital camera, a goggle type display, a car navigation system, an audio reproduction device, a notebook personal computer, a game equipment, a mobile computer, a mobile telephone, a mobile game equipment, an electronic book, and an image reproduction device provided with a recording medium.

127. A light-emitting device according to claim 120, wherein the substrate is a glass substrate.

128. A light-emitting device according to claim 120, wherein each of the first pixel electrode and the second pixel electrode is an indium-tin oxide film.

129. A light-emitting device according to claim 120, wherein each of the first current controlling thin film transistor and the second current controlling thin film transistor is a p-channel thin film transistor.

130. A light-emitting device according to claim 120, wherein the second length is larger than the second width.

131. A light-emitting device according to claim 120, wherein each of the first switching thin film transistor and the second switching thin film transistor comprises a double gate structure.