Display device

• US 10,211,230 B2
• Filed: 02/10/2016
• Issued: 02/19/2019
• Est. Priority Date: 01/24/2010
• Status: Active Grant

• Current Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Original Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Inventors: Yamazaki, Shunpei
• Primary Examiner(s): Eurice, Michael J
• Application Number:
  US15/040,101
• Publication Number:
  US 20160155761A1
• Time in Patent Office: 1,105 Days
• CPC Class Codes: G02F 1/1368 in which the switching element is a three-electrode device G02F1/136277 takes precedence
• CPC Class Codes: G09G 2320/0252 Improving the response speed
• 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 2340/16 Determination of a pixel data signal depending on the signal applied in the previous frame
• CPC Class Codes: G09G 3/344 based on particles moving in a fluid or in a gas, e.g. electrophoretic devices electrophoretic devices per se G02F1/167
• CPC Class Codes: G09G 3/3629 using liquid crystals having memory effects, e.g. ferroelectric liquid crystals
• CPC Class Codes: G09G 3/3648 using an active matrix G09G3/367 - G09G3/3696 take precedence
• CPC Class Codes: G09G 3/3651 using multistable liquid crystals, e.g. ferroelectric liquid crystals
• CPC Class Codes: G09G 3/3655 Details of drivers for counter electrodes, e.g. common electrodes for pixel capacitors or supplementary storage capacitors
• CPC Class Codes: H01L 27/1225 with semiconductor materials not belonging to the group IV of the periodic table, e.g. InGaZnO

Abstract

A driver circuit portion of a display device has a function in which image signals are written to a selected pixel successively so as to display an image on a screen and a function in which writing operation of an image signal is stopped and a transistor is turned off so as to maintain one image written to the screen when the one image is continuously displayed on the screen. Such functions are achieved by a transistor whose off current per micrometer in channel width is reduced to an extremely low value that is lower than 10 zA/μm at room temperature and lower than 100 zA/μm at 85° C.

Claims

1. A display device comprising:

a display element;

a first transistor electrically connected to a first electrode of the display element; and

a second transistor electrically connected to a second electrode of the display element,

wherein each of the first transistor and the second transistor comprises an oxide semiconductor layer,

wherein an off current per micrometer in channel width of each of the first transistor and the second transistor is lower than 10 zA/μ

m at room temperature and lower than 100 zA/μ

m at 85°

C.

2. The display device according to claim 1, wherein the display element comprises a liquid crystal.

3. The display device according to claim 1, wherein the oxide semiconductor layer comprises indium, gallium, and zinc.

4. The display device according to claim 1, wherein the oxide semiconductor layer comprises indium, tin, and zinc.

5. The display device according to claim 1,

wherein the oxide semiconductor layer comprises a crystal, and

wherein a c-axis of the crystal is aligned in a direction perpendicular to a surface of the oxide semiconductor layer.

6. The display device according to claim 1, further comprising a driver circuit,

wherein the driver circuit comprises a first operation mode to display a moving image on a screen and a second operation mode to display a still image on the screen, and

wherein a frequency of the first operation mode is higher than a frequency of the second operation mode.

7. The display device according to claim 1, further comprising a driver circuit, wherein the driver circuit is configured to turn the first transistor off when a difference between successive image signals is not detected.

8. The display device according to claim 7, wherein the second transistor is turned off while the first transistor is turned off.

9. The display device according to claim 1, further comprising a driver circuit, wherein the driver circuit is configured to turn the first transistor off while one image is displayed on a screen for one second or more.

10. The display device according to claim 9, wherein the second transistor is turned off while the first transistor is turned off.

11. A display device comprising:

a display element in a pixel portion;

a first transistor electrically connected to a first electrode of the display element, the first transistor provided in the pixel portion; and

a second transistor electrically connected to a second electrode of the display element, the second transistor provided outside the pixel portion,

wherein each of the first transistor and the second transistor comprises an oxide semiconductor layer,

wherein an off current per micrometer in channel width of each of the first transistor and the second transistor is lower than 10 zA/μ

m at room temperature and lower than 100 zA/μ

m at 85°

C.

12. The display device according to claim 11, wherein the display element comprises a liquid crystal.

13. The display device according to claim 11, wherein the oxide semiconductor layer comprises indium, gallium, and zinc.

14. The display device according to claim 11, wherein the oxide semiconductor layer comprises indium, tin, and zinc.

15. The display device according to claim 11,

wherein the oxide semiconductor layer comprises a crystal, and

wherein a c-axis of the crystal is aligned in a direction perpendicular to a surface of the oxide semiconductor layer.

16. The display device according to claim 11, further comprising a driver circuit,

wherein the driver circuit comprises a first operation mode to display a moving image on a screen and a second operation mode to display a still image on the screen, and

wherein a frequency of the first operation mode is higher than a frequency of the second operation mode.

17. The display device according to claim 11, further comprising a driver circuit, wherein the driver circuit is configured to turn the first transistor off when a difference between successive image signals is not detected.

18. The display device according to claim 17, wherein the second transistor is turned off while the first transistor is turned off.

19. The display device according to claim 11, further comprising a driver circuit, wherein the driver circuit is configured to turn the first transistor off while one image is displayed on a screen for one second or more.

20. The display device according to claim 19, wherein the second transistor is turned off while the first transistor is turned off.

21. A display device comprising:

a display element;

a transistor electrically connected to an electrode of the display element,

wherein the transistor comprises an oxide semiconductor layer,

wherein an off current per micrometer in channel width of the transistor is lower than 10 zA/μ

m at room temperature and lower than 100 zA/μ

m at 85°

C.

22. The display device according to claim 21, wherein the display element comprises a liquid crystal.

23. The display device according to claim 21, wherein the oxide semiconductor layer comprises indium, gallium, and zinc.

24. The display device according to claim 21, wherein the oxide semiconductor layer comprises indium, tin, and zinc.

25. The display device according to claim 21,

wherein the oxide semiconductor layer comprises a crystal, and

wherein a c-axis of the crystal is aligned in a direction perpendicular to a surface of the oxide semiconductor layer.

26. The display device according to claim 21, further comprising a driver circuit, wherein the driver circuit is configured to turn the transistor off when a difference between successive image signals is not detected.

27. The display device according to claim 21, further comprising a driver circuit, wherein the driver circuit is configured to turn the transistor off while one image is displayed on a screen for one second or more.

28. The display device according to claim 21, further comprising a driver circuit,

wherein the driver circuit comprises a first operation mode to display a moving image on a screen and a second operation mode to display a still image on the screen, and

wherein a frequency of the first operation mode is higher than a frequency of the second operation mode.