Liquid crystal display device and electronic device

• US 9,244,323 B2
• Filed: 06/12/2014
• Issued: 01/26/2016
• 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:
  US14/302,840
• Publication Number:
  US 20140293167A1
• Time in Patent Office: 593 Days
• Field of Search: 349 42- 46, 349/52, 345/92, 257/59, 257/72
• US Class Current: 1/1
• 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 transistor comprising an oxide semiconductor layer, wherein characteristics of the transistor comprises:

an off-current being less than or equal to 10 aA/μ

m at room temperature; and

an off-current being less than or equal to 100 aA/μ

m at a temperature of 85°

C.

2. The transistor according to claim 1, wherein the oxide semiconductor layer is made to be substantially intrinsic.

3. The transistor according to claim 1, wherein a carrier concentration of the oxide semiconductor layer is 1×

10¹⁴/cm³.

4. The transistor according to claim 1, wherein the oxide semiconductor layer comprises indium, gallium, and zinc.

5. A liquid crystal display device comprising:

a transistor comprising an oxide semiconductor layer;

a liquid crystal element electrically connected to the transistor; and

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

wherein characteristics of the transistor comprises;

an off-current being less than or equal to 10 aA/μ

m at room temperature; and

an off-current being less than or equal to 100 aA/μ

m at a temperature of 85°

C.

6. The liquid crystal display device according to claim 5, wherein the oxide semiconductor layer is made to be substantially intrinsic.

7. The liquid crystal display device according to claim 5, wherein a carrier concentration of the oxide semiconductor layer is 1×

10¹⁴/cm³.

8. The liquid crystal display device according to claim 5, wherein the oxide semiconductor layer comprises indium, gallium, and zinc.

9. The liquid crystal display device according to claim 5, wherein a specific resistivity of a liquid crystal material included in the liquid crystal element is over 1×

10¹⁴ Ω

·

cm.

10. The liquid crystal display device according to claim 5, wherein a capacitance of the capacitor is 1 pF or more.

11. The liquid crystal display device according to claim 5, wherein a leakage current through transistor in an off-state is smaller than a leakage current through the liquid crystal element.

12. The liquid crystal display device according to claim 5, further comprising a touch sensor over the liquid crystal element.