Display device, display module including the display device, and electronic device including the display device or the display module

Patent metadata

Field	Value
Publication number	US-10706790-B2
Application number	US-201515529363-A
Country	US
Kind code	B2
Filing date	Nov 26, 2015
Priority date	Dec 1, 2014
Publication date	Jul 7, 2020
Grant date	Jul 7, 2020

Abstract

Provided is a novel display device without deterioration of display quality or a novel display device in which flickering due to a reduced refresh rate is suppressed. The display device includes a pixel for displaying a still image at a frame frequency of less than or equal to 1 Hz. The pixel includes a liquid crystal layer. The liquid crystal layer includes a molecule whose dipole moment is greater than or equal to 0 debye and less than or equal to 3 debye. Thus, flickering due to a reduced refresh rate can be suppressed, which leads to an improvement in display quality.

First claim

The invention claimed is:

1. A display device comprising:
a pixel comprising:
a transistor comprising an oxide semiconductor in a channel thereof;
a pixel electrode electrically connected to the transistor; and
a liquid crystal layer over the pixel electrode; and

a driver circuit for outputting a signal to the pixel,
wherein:
the liquid crystal layer comprises a liquid crystal mixture formed only of materials having a dipole moment of 3 debye or less,
the liquid crystal layer has a resistivity of 1.0×10 14 (Ω·cm) or more,
the driver circuit is configured to switch a first mode in which the signal for a moving image is output to the pixel at a frequency of 30 Hz or more, and a second mode in which the signal for a still image is output to the pixel at a frequency of 1 Hz or less, and
the pixel is configured to display the still image at a frame frequency of 1/30 Hz to 1 Hz.

2. The display device according to claim 1 , wherein the oxide semiconductor contains In, Ga, and Zn.

3. The display device according to claim 1 , wherein a voltage holding ratio of the pixel is in a range of 98.8% or more and 100% or less.

4. A display module comprising:
the display device according to claim 1 ; and
a touch sensor.

5. An electronic device comprising:
the display device according to claim 1 , and
an operation key or a battery.

6. A display device comprising:
a pixel comprising:
a transistor comprising an oxide semiconductor in a channel thereof;
a reflective electrode electrically connected to the transistor; and
a liquid crystal layer over the reflective electrode; and

a driver circuit for outputting a signal to the pixel,
wherein:
the reflective electrode has a projection and a depression,
the liquid crystal layer comprises a liquid crystal mixture formed only of materials having a dipole moment of 3 debye or less,
the liquid crystal layer has a resistivity of 1.0×10 14 (Ω·cm) or more,
the driver circuit is configured to switch a first mode in which the signal for a moving image is output to the pixel at a frequency of 30 Hz or more, and a second mode in which the signal for a still image is output to the pixel at a frequency of 1 Hz or less, and
the pixel is configured to display the still image at a frame frequency of 1/30 Hz to 1 Hz.

7. The display device according to claim 6 , wherein the oxide semiconductor contains In, Ga, and Zn.

8. The display device according to claim 6 , wherein a voltage holding ratio of the pixel is in a range of 98.8% or more and 100% or less.

9. A display module comprising:
the display device according to claim 6 , and
a touch sensor.

10. An electronic device comprising:
the display device according to claim 6 , and
an operation key or a battery.

Assignees

• Semiconductor Energy Lab

Inventors

• Niikura Yasuhiro
• Ikenaga Makoto
• Kubota Daisuke
• Hatsumi Ryo

Classifications

• C09K19/02 Primary

  characterised by optical, electrical or physical properties of the components, in general · CPC title

• G02F1/139

  based on orientation effects in which the liquid crystal remains transparent · CPC title

• G02F1/1396

  the liquid crystal being selectively controlled between a twisted state and a non-twisted state, e.g. TN-LC cell (G02F1/141 takes precedence) · CPC title

• G09G3/34 Primary

  by control of light from an independent source · CPC title