Liquid crystal display device with transistor including oxide semiconductor layer and electronic device

• US 8,823,893 B2
• Filed: 12/15/2010
• Issued: 09/02/2014
• Est. Priority Date: 12/18/2009
• Status: Active Grant

• Current Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Original Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Inventors: Yamazaki, Shunpei
• Primary Examiner(s): Nguyen, Hoan C
• Application Number:
  US12/968,336
• Publication Number:
  US 20110149185A1
• Time in Patent Office: 1,357 Days
• Field of Search: 349 42- 46, 349/52, 345/92, 257/59, 257/72
• US Class Current: 349/43
• CPC Class Codes: G02F 1/13338 Input devices, e.g. touch panels
• CPC Class Codes: G02F 1/136286 Wiring, e.g. gate line, drain line
• CPC Class Codes: G02F 1/1368 in which the switching element is a three-electrode device G02F1/136277 takes precedence
• CPC Class Codes: G06F 3/0412 Digitisers structurally integrated in a display
• CPC Class Codes: G06F 3/044 by capacitive means
• CPC Class Codes: G06F 3/045 using resistive elements, e.g. a single continuous surface or two parallel surfaces put in contact
• CPC Class Codes: G09G 2300/0426 Layout of electrodes and connections
• CPC Class Codes: G09G 2310/04 Partial updating of the display screen
• CPC Class Codes: G09G 2310/08 Details of timing specific for flat panels, other than clock recovery
• CPC Class Codes: G09G 2320/0214 with crosstalk due to leakage current of pixel switch in active matrix panels
• CPC Class Codes: G09G 2320/0247 Flicker reduction other than flicker reduction circuits used for single beam cathode-ray tubes
• CPC Class Codes: G09G 2320/043 Preventing or counteracting the effects of ageing
• CPC Class Codes: G09G 2320/103 Detection of image changes, e.g. determination of an index representative of the image change
• CPC Class Codes: G09G 2330/021 Power management, e.g. power saving
• CPC Class Codes: G09G 3/3648 using an active matrix G09G3/367 - G09G3/3696 take precedence
• CPC Class Codes: G09G 3/3677 suitable for active matrices only
• CPC Class Codes: H01L 21/02483 Oxide semiconducting materials not being Group 12/16 materials, e.g. ternary compounds
• CPC Class Codes: H01L 27/1225 with semiconductor materials not belonging to the group IV of the periodic table, e.g. InGaZnO
• CPC Class Codes: H01L 27/1255 integrated with passive devices, e.g. auxiliary capacitors
• CPC Class Codes: H01L 29/78609 for preventing leakage current H01L29/78618 takes precedence
• CPC Class Codes: H01L 29/7869 : having a semiconductor body comprising an oxide semiconductor material, e.g. zinc oxide, copper aluminium oxide, cadmium stannate

Abstract

To reduce power consumption and suppress display degradation of a liquid crystal display device. To suppress display degradation due to an external factor such as temperature. A transistor whose channel formation region is formed using an oxide semiconductor layer is used for a transistor provided in each pixel. Note that with the use of a high-purity oxide semiconductor layer, off-state current of the transistor at a room temperature can be 10 aA/μm or less and off-state current at 85° C. can be 100 aA/μm or less. Consequently, power consumption of a liquid crystal display device can be reduced and display degradation can be suppressed. Further, as described above, off-state current of the transistor at a temperature as high as 85° C. can be 100 aA/μm or less. Thus, display degradation of a liquid crystal display device due to an external factor such as temperature can be suppressed.

Claims

1. A liquid crystal display device comprising:

a plurality of pixels arranged in a matrix form, each including;

a transistor, switching of which is configured to be controlled by a scan line driver circuit;

a liquid crystal element including one terminal to which an image signal is input from a signal line driver circuit through the transistor and the other terminal to which a common potential is supplied, so that voltage corresponding to the image signal is applied; and

a capacitor configured to store voltage applied to the liquid crystal element; and

a control circuit,

wherein the control circuit is configured to control operation of the scan line driver circuit and the signal line driver circuit and is configured to select input of the image signal to each pixel,

wherein the transistor includes a channel formation region comprising an oxide semiconductor layer,

wherein an amount of leakage of the image signal through the transistor in an off state is smaller than an amount of leakage of the image signal through the liquid crystal element,

wherein an off-state current of the transistor is less than or equal to 10 aA/μ

m at room temperature, and

wherein the off-state current of the transistor is less than or equal to 100 aA/μ

m at a temperature of 85°

C.

2. The liquid crystal display device according to claim 1,

wherein the oxide semiconductor layer is made to be substantially intrinsic.

3. The liquid crystal display device according to claim 1,

wherein a specific resistivity of a liquid crystal material included in the liquid crystal element is over 1×

10¹⁴ Ω

·

cm.

4. The liquid crystal display device according to claim 1,

wherein a capacitance of the capacitor is 1 pF or more.

5. An electronic device comprising the liquid crystal display device according to claim 1.

6. A liquid crystal display device comprising:

a plurality of pixels arranged in a matrix form, each including;

a transistor;

a liquid crystal element electrically connected to the transistor, the liquid crystal element including a terminal which is configured to be supplied with an image signal through the transistor; and

a capacitor configured to store a voltage applied to the liquid crystal element;

wherein the transistor includes a channel formation region comprising an oxide semiconductor layer,

wherein an amount of leakage of the image signal through the transistor in an off state of the transistor is smaller than an amount of leakage of the image signal through the liquid crystal element,

wherein an off-state current of the transistor is less than or equal to 10 aA/μ

m at room temperature, and

wherein the off-state current of the transistor is less than or equal to 100 aA/μ

m at a temperature of 85°

C.

7. The liquid crystal display device according to claim 6,

wherein the oxide semiconductor layer is made to be substantially intrinsic.

8. The liquid crystal display device according to claim 6,

wherein a specific resistivity of a liquid crystal material included in the liquid crystal element is over 1×

10¹⁴ Ω

·

cm.

9. The liquid crystal display device according to claim 6,

wherein a capacitance of the capacitor is 1 pF or more.

10. An electronic device comprising the liquid crystal display device according to claim 6.

11. A display device comprising:

a display panel comprising a pixel and a driver circuit configured to supply the pixel with an image signal; and

a touch panel adjacent to the display panel,

wherein the pixel comprises a transistor and a display element electrically connected to the transistor,

wherein the transistor comprises an oxide semiconductor layer including a channel formation region,

wherein an amount of leakage of the image signal through the transistor in an off state is smaller than an amount of leakage of the image signal through the display element,

wherein an off-state current of the transistor is less than or equal to 10 aA/μ

m at room temperature, and

wherein the off-state current of the transistor is less than or equal to 100 aA/μ

m at a temperature of 85°

C.

12. The display device according to claim 11,

wherein the oxide semiconductor layer is made to be substantially intrinsic.

13. The display device according to claim 11,

wherein the pixel further comprises a capacitor electrically connected to the display element, and

wherein a capacitance of the capacitor is 1 pF or more.

14. The display device according to claim 11, wherein the touch panel is a surface capacitive touch sensor or a projected capacitive touch sensor.

15. The display device according to claim 11, wherein the display element is a liquid crystal element.

16. A display device comprising:

a display panel comprising a pixel and a driver circuit configured to supply the pixel with an image signal; and

a touch panel adjacent to the display panel,

wherein the pixel comprises a transistor and a display element electrically connected to the transistor,

wherein the transistor comprises an oxide semiconductor layer including a channel formation region,

wherein current flowing through the transistor in an off state is smaller than current flowing through the display element,

wherein an off-state current of the transistor is less than or equal to 10 aA/μ

m at room temperature, and

wherein the off-state current of the transistor is less than or equal to 100 aA/μ

m at a temperature of 85°

C.

17. The display device according to claim 16,

wherein the oxide semiconductor layer is made to be substantially intrinsic.

18. The display device according to claim 16,

wherein the pixel further comprises a capacitor electrically connected to the display element, and

wherein a capacitance of the capacitor is 1 pF or more.

19. The display device according to claim 16, wherein the touch panel is a surface capacitive touch sensor or a projected capacitive touch sensor.

20. The display device according to claim 16, wherein the display element is a liquid crystal element.

21. A display device comprising:

a substrate;

a transistor over the substrate;

a display element over the substrate, the display element being electrically connected to the transistor;

a driver circuit configured to supply the display element with an image signal; and

a capacitive touch sensor over the substrate,

wherein the transistor comprises an oxide semiconductor layer including a channel formation region,

wherein an amount of leakage of the image signal through the transistor in an off state is smaller than an amount of leakage of the image signal through the display element,

wherein an off-state current of the transistor is less than or equal to 10 aA/μ

m at room temperature, and

wherein the off-state current of the transistor is less than or equal to 100 aA/μ

m at a temperature of 85°

C.

22. The display device according to claim 21,

wherein the oxide semiconductor layer is made to be substantially intrinsic.

23. The display device according to claim 21, further comprising a capacitor electrically connected to the display element, and

wherein a capacitance of the capacitor is 1 pF or more.

24. The display device according to claim 21, wherein the capacitive touch sensor is comprised in a touch panel.

25. The display device according to claim 21, wherein the display element is a liquid crystal element.

26. A display device comprising:

a substrate;

a transistor over the substrate;

a display element over the substrate, the display element being electrically connected to the transistor;

a driver circuit configured to supply the display element with an image signal; and

a capacitive touch sensor over the substrate,

wherein the transistor comprises an oxide semiconductor layer including a channel formation region,

wherein current flowing through the transistor in an off state is smaller than current flowing through the display element,

wherein an off-state current of the transistor is less than or equal to 10 aA/μ

m at room temperature, and

wherein the off-state current of the transistor is less than or equal to 100 aA/μ

m at a temperature of 85°

C.

27. The display device according to claim 26,

wherein the oxide semiconductor layer is made to be substantially intrinsic.

28. The display device according to claim 26, further comprising a capacitor electrically connected to the display element, and

wherein a capacitance of the capacitor is 1 pF or more.

29. The display device according to claim 26, wherein the capacitive touch sensor is comprised in a touch panel.

30. The display device according to claim 26, wherein the display element is a liquid crystal element.