Liquid crystal display device and electronic device including the same

• US 10,714,622 B2
• Filed: 01/26/2017
• Issued: 07/14/2020
• Est. Priority Date: 10/21/2009
• Status: Active Grant

• Current Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Original Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Inventors: Arasawa, Ryo, Shishido, Hideaki, Yamazaki, Shunpei
• Primary Examiner(s): Kim, Richard H
• Application Number:
  US15/416,164
• Publication Number:
  US 20170133511A1
• Time in Patent Office: 1,265 Days
• Field of Search: None
• CPC Class Codes: G02F 1/133345 Insulating layers G02F1/1335, G02F1/1337, G02F1/135, G02F1/136 take precedence
• CPC Class Codes: G02F 1/134336 Matrix
• CPC Class Codes: G02F 1/134345 Subdivided pixels, e.g. for grey scale or redundancy
• CPC Class Codes: G02F 1/13439 characterised by their electrical, optical, physical properties; materials therefor; method of making
• CPC Class Codes: G02F 1/136213 Storage capacitors associated with the pixel electrode
• CPC Class Codes: G02F 1/13624 having more than one switching element per pixel
• 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: G02F 2201/123 pixel
• CPC Class Codes: G02F 2201/40 Arrangements for improving the aperture ratio
• CPC Class Codes: G09G 2300/0426 Layout of electrodes and connections
• CPC Class Codes: G09G 2300/0439 Pixel structures
• CPC Class Codes: G09G 2300/0465 Improved aperture ratio, e.g. by size reduction of the pixel circuit, e.g. for improving the pixel density or the maximum displayable luminance or brightness
• CPC Class Codes: G09G 3/3614 Control of polarity reversal in general
• 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 27/1225 with semiconductor materials not belonging to the group IV of the periodic table, e.g. InGaZnO
• CPC Class Codes: H01L 27/124 with a particular composition, shape or layout of the wiring layers specially adapted to the circuit arrangement, e.g. scanning lines in LCD pixel circuits wiring structures per se H01L23/52
• CPC Class Codes: H01L 27/1255 integrated with passive devices, e.g. auxiliary capacitors
• CPC Class Codes: H01L 27/127 with a particular formation, treatment or patterning of the active layer specially adapted to the circuit arrangement
• CPC Class Codes: H01L 29/24 : including, apart from doping materials or other impurities, only semiconductor materials not provided for in groups H01L29/16, H01L29/18, H01L29/20, H01L29/22 including organic materials H10K99/00
• CPC Class Codes: H01L 29/4908 : for thin film semiconductor, e.g. gate of TFT
• 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
• 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

Abstract

A liquid crystal display device is provided in which the aperture ratio can be increased in a pixel including a thin film transistor in which an oxide semiconductor is used. In the liquid crystal display device, the thin film transistor including a gate electrode, a gate insulating layer and an oxide semiconductor layer which are provided so as to overlap with the gate electrode, and a source electrode and a drain electrode which overlap part of the oxide semiconductor layer is provided between a signal line and a pixel electrode which are provided in a pixel portion. The off-current of the thin film transistor is 1×10⁻¹³ A or less. A potential can be held only by a liquid crystal capacitor, without a capacitor which is parallel to a liquid crystal element, and a capacitor connected to the pixel electrode is not formed in the pixel portion.

Claims

1. A liquid crystal display device comprising:

a first pixel comprising a first transistor;

a second pixel comprising a second transistor;

a first signal line electrically connected to the first transistor;

a second signal line electrically connected to the second transistor; and

a liquid crystal layer over the first transistor and the second transistor,

wherein a channel formation region of each of the first transistor and the second transistor comprises an oxide semiconductor,

wherein an auxiliary capacitor is not formed in each of the first pixel and the second pixel,

wherein the first pixel is adjacent to the second pixel,

wherein a polarity of a first signal voltage applied to the first signal line is opposite to a polarity of a second signal voltage applied to the second signal line in each frame period,

wherein each of the first transistor and the second transistor has electric characteristics such that an off-current flowing through a region serving as the channel formation region is 1×

10<sup>−

12</sup> A or less under a condition at which a temperature is 120°

C.,

wherein a voltage between a source and a drain of the first transistor is 6 V at the condition, and

wherein a voltage between a source and a drain of the second transistor is 6 V at the condition.

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

wherein the first signal line is electrically connected to one of a source and a drain of the first transistor, and

wherein the second signal line is electrically connected to one of a source and a drain of the second transistor.

3. A liquid crystal display device according to claim 1, further comprising a third signal line,

wherein the third signal line is electrically connected to a gate of the first transistor and a gate of the second transistor.

4. A liquid crystal display device according to claim 1, wherein a hydrogen concentration in the oxide semiconductor is 5×

10¹⁹/cm³ or less.

5. A liquid crystal display device according to claim 1, wherein the polarity of each of the first signal voltage and the second signal voltage is alternately reversed in a frame period.

6. A liquid crystal display device according to claim 1, further comprising a third pixel and a fourth pixel,

wherein the liquid crystal display device comprises a plurality of pixels arranged in a matrix of rows and columns,

wherein the first pixel and the second pixel are arranged in a first row,

wherein the third pixel and the fourth pixel are arranged in a second row,

wherein the first row is adjacent to the second row,

wherein the first signal line is electrically connected to the first pixel and the third pixel,

wherein the second signal line is electrically connected to the second pixel and the fourth pixel,

wherein a third signal voltage is applied to the first signal line after the first signal voltage is applied to the first signal line,

wherein a fourth signal voltage is applied to the second signal line after the second signal voltage is applied to the second signal line,

wherein the polarity of the first signal voltage is opposite to a polarity of the third signal voltage, and

wherein the polarity of the second signal voltage is opposite to a polarity of the fourth signal voltage.

7. A liquid crystal display device according to claim 1,

wherein each of the first transistor and the second transistor further comprises a gate electrode, and

wherein the gate electrode comprises copper.

8. A liquid crystal display device according to claim 1, wherein the oxide semiconductor comprises indium and zinc.

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