LIQUID CRYSTAL DISPLAY DEVICE AND ELECTRONIC DEVICE

• US 20110149185A1
• Filed: 12/15/2010
• Published: 06/23/2011
• 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
• Granted Patent: US 8,823,893 B2
• Time in Patent Office: Days
• US Class Current: 349/39
• 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 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 which stores voltage applied to the liquid crystal element,

wherein a control circuit which controls operation of the scan line driver circuit and the signal line driver circuit and selects input of the image signal to each pixel is included,

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

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.

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

wherein the transistor includes a channel formation region comprising an oxide semiconductor layer which is made to be substantially intrinsic.

7. 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×

10¹⁴Ω

·

cm.

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

wherein an off-state current of the transistor is 10 aA/μ

m or less.

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

wherein a switch which controls supply of the common potential to the liquid crystal element is included.

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

wherein a switch which controls supply of the common potential to the liquid crystal element is included, and

wherein the switch is a transistor whose channel formation region comprises an oxide semiconductor layer.

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

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

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

2. A liquid crystal display device comprising:

a pixel portion including a plurality of pixels arranged in a matrix form, each including

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

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

a capacitor which stores the image signal inputted to the first electrode,

wherein the pixel portion comprises

a memory circuit which stores an image signal for forming a first image to an image signal for forming an n-th image (n is a natural number greater than or equal to

     2);

a comparison circuit which compares an image signal for forming a k-th image (k is a natural number less than n) and an image signal for forming a (k+1)-th image and detects a difference between the image signals;

a selection circuit which selects output of the image signal for forming the (k+1)-th image to the pixel portion based on the difference; and

a display control circuit which can perform supply of a control signal to the scan line driver circuit and the signal line driver circuit when the difference is detected, and stop supply of the control signal to the scan line driver circuit and the signal line driver circuit when the difference is not detected,

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

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.

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

wherein the transistor includes a channel formation region comprising an oxide semiconductor layer which is made to be substantially intrinsic.

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

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

10¹⁴Ω

·

cm.

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

wherein an off-state current of the transistor is 10 aA/μ

m or less.

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

wherein a switch which controls supply of the common potential to the liquid crystal element is included.

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

wherein a switch which controls supply of the common potential to the liquid crystal element is included, and

wherein the switch is a transistor whose channel formation region comprises an oxide semiconductor layer.

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

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

23. An electronic device comprising the liquid crystal display device according to claim 2.

3. 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, and

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.

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

wherein the transistor includes a channel formation region comprising an oxide semiconductor layer which is made to be substantially intrinsic.

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

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

10¹⁴Ω

·

cm.

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

wherein an off-state current of the transistor is 10 aA/μ

m or less.

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

wherein a switch which controls supply of the common potential to the liquid crystal element is included.

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

wherein a switch which controls supply of the common potential to the liquid crystal element is included, and

wherein the switch is a transistor whose channel formation region comprises an oxide semiconductor layer.

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

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

24. An electronic device comprising the liquid crystal display device according to claim 3.