Liquid crystal display device wherein a deviation in gray level for displaying a still image in one frame period is less than or equal to 1.2% of a maximum gray level

• US 9,129,568 B2
• Filed: 11/13/2013
• Issued: 09/08/2015
• Est. Priority Date: 11/15/2012
• Status: Active Grant

• Current Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Original Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Inventors: Kubota, Daisuke, Hirakata, Yoshiharu, Hatsumi, Ryo
• Primary Examiner(s): Lee, Paul
• Application Number:
  US14/078,693
• Publication Number:
  US 20140132870A1
• Time in Patent Office: 664 Days
• Field of Search: 349/42, 349/140, 349/167, 349/36
• US Class Current: 1/1
• CPC Class Codes: G02F 1/13454 Drivers integrated on the active matrix substrate G02F1/136277 takes precedence
• CPC Class Codes: G02F 1/136213 Storage capacitors associated with the pixel electrode
• CPC Class Codes: G02F 1/13706 the liquid crystal having positive dielectric anisotropy
• CPC Class Codes: G02F 1/1396 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 Class Codes: G02F 2202/42 Materials having a particular dielectric constant
• CPC Class Codes: G09G 2330/025 Reduction of instantaneous peaks of current
• CPC Class Codes: G09G 3/36 using liquid crystals
• CPC Class Codes: G09G 3/3607 for displaying colours or for displaying grey scales with a specific pixel layout, e.g. using sub-pixels display of colours in flat matrix panels other than liquid crystal displays G09G3/2003; grey scales specific for television H04N3/127
• CPC Class Codes: G09G 3/3648 using an active matrix G09G3/367 - G09G3/3696 take precedence

Abstract

A novel liquid crystal display device without a decrease in display quality. The liquid crystal display device includes a pixel for displaying a still image at a frame frequency of less than or equal to 1 Hz, and a liquid crystal layer in the pixel has a dielectric constant anisotropy of greater than or equal to 2 and less than or equal to 5. With the above structure, a change in voltage applied to a pixel can be kept within an acceptable range of a deviation in gray level for displaying the same still image. Thus, flickers due to a low refresh rate can be reduced, which leads to an increase in display quality.

Claims

1. A liquid crystal display device comprising a pixel for displaying a still image at a frame frequency of less than or equal to 1 Hz, wherein the pixel comprises a liquid crystal layer having a dielectric constant anisotropy of greater than or equal to 2 and less than or equal to 5 and wherein a deviation in gray level for displaying the still image in one frame period is less than or equal to 1.2% of the maximum gray level.

2. The liquid crystal display device according to claim 1, wherein the pixel comprises:

a transistor; and

a liquid crystal element electrically connected to the transistor, and wherein the liquid crystal element comprises the liquid crystal layer.

3. The liquid crystal display device according to claim 2, wherein the transistor comprises a semiconductor layer, and wherein the semiconductor layer comprises an oxide semiconductor.

4. The liquid crystal display device according to claim 1, wherein the liquid crystal layer has a dielectric constant anisotropy of greater than or equal to 2.6 and less than or equal to 4.4.

5. The liquid crystal display device according to claim 1, wherein the liquid crystal layer has a dielectric constant anisotropy of greater than or equal to 3 and less than or equal to 3.8.

6. The liquid crystal display device according to claim 1, wherein the frame frequency is less than or equal to 0.2 Hz.

7. A liquid crystal display device comprising:

a pixel comprising;

a pixel electrode; and

a liquid crystal layer comprising a liquid crystal over the pixel electrode; and

a driver circuit capable of outputting a signal to the pixel with a frame frequency of 1 Hz or less, wherein the liquid crystal has a dielectric constant anisotropy of greater than or equal to 2 and less than or equal to 5 and wherein a deviation in gray level for displaying a still image in one frame period is less than or equal to 1.2% of the maximum gray level.

8. The liquid crystal display device according to claim 7, wherein the pixel comprises a transistor electrically connected to the pixel electrode.

9. The liquid crystal display device according to claim 8, wherein the transistor comprises a semiconductor layer, and wherein the semiconductor layer comprises an oxide semiconductor.

10. The liquid crystal display device according to claim 7, wherein the liquid crystal layer has a dielectric constant anisotropy of greater than or equal to 2.6 and less than or equal to 4.4.

11. The liquid crystal display device according to claim 7, wherein the liquid crystal layer has a dielectric constant anisotropy of greater than or equal to 3 and less than or equal to 3.8.

12. The liquid crystal display device according to claim 7, wherein the frame frequency is less than or equal to 0.2 Hz.