WO2016063880A1

WO2016063880A1 - Display device

Info

Publication number: WO2016063880A1
Application number: PCT/JP2015/079596
Authority: WO
Inventors: 弘幸森脇; 佐藤　英次; 加藤　浩巳
Original assignee: シャープ株式会社
Priority date: 2014-10-24
Filing date: 2015-10-20
Publication date: 2016-04-28

Abstract

A display device (100) is provided with a first substrate (10) and a second substrate (20) as well as a display medium layer (30) the optical characteristics of which changes in response to an applied electric field. When an electric field is applied to the display medium layer, pixels have an electric field distribution wherein a first region (SR) with the electric field having a first electric field intensity and a second region (WR) with the electric field having a second electric field intensity weaker than the first electric field intensity are arranged along the planar direction of the display medium layer. In any pixel, the first region and the second region arrangements in the electric field distribution are switched at least once within a period in which the same display is carried out.

Description

Display device

The present invention relates to a display device.

A display device that performs display by controlling the transmittance (or reflectance) of incident light is required to have a high contrast ratio and a high light utilization efficiency.

A liquid crystal display device is well known as a display device that controls the light transmittance by applying a voltage. The liquid crystal display device includes a pair of substrates and a liquid crystal layer provided between the substrates. In the liquid crystal display device, the orientation of the liquid crystal molecules in the liquid crystal layer changes according to the magnitude of the voltage applied to the liquid crystal layer, thereby changing the transmittance of light incident on the liquid crystal display device. Liquid crystal display devices are widely used at present because a very high contrast ratio can be obtained.

However, since many liquid crystal display devices use a polarizing plate, more than half of the light used for display is absorbed by the polarizing plate. Therefore, the light use efficiency is low. Therefore, in recent years, development of a display device that does not require a polarizing plate has been advanced.

The present applicant has proposed a display device including a light modulation layer including a shape anisotropic member in

Patent Documents

1 and 2. In the display devices disclosed in

Patent Documents

1 and 2, the shape anisotropic member dispersed in the medium is rotated (that is, the orientation direction is changed) by applying an electric field to the light modulation layer, whereby the light of the light modulation layer is changed. Change the transmittance (or light reflectance).

Since the display devices of

Patent Documents

1 and 2 described above do not require a polarizing plate, the light use efficiency can be increased as compared with a liquid crystal panel.

Further, the applicant of the present application has proposed a display device that can apply not only a vertical electric field but also a horizontal electric field to a display medium layer (optical layer) containing shape anisotropic particles in Patent Document 3. In the display device of Patent Literature 3, display is performed by switching between a state in which a vertical electric field is generated in the display medium layer and a state in which a horizontal electric field is generated in the display medium layer. Therefore, the display device of Patent Document 3 has a faster response speed than the display devices of

Patent Documents

1 and 2.

International Publication No. 2013/129373 International Publication No. 2013/172374 International Publication No. 2014/061492 International Publication No. 2013/0665529

The applicant of the present application has made various studies in order to further improve the light utilization efficiency of a display device having a display medium layer containing shape anisotropic particles, such as the display device of Patent Document 3. Hereinafter, the knowledge obtained by the examination will be described.

As a display mode of a liquid crystal display device, a VA (Vertical Alignment) mode and an FFS (Fringe Field Switching) mode are known. In the VA mode, display is performed by applying a vertical electric field to the vertically aligned liquid crystal layer. On the other hand, in the FFS mode, display is performed by applying a fringe electric field to the horizontally aligned liquid crystal layer.

FIG. 29 shows a general structure of an FFS mode liquid crystal display device. A liquid crystal display device 800 illustrated in FIG. 29 includes a TFT substrate 810 and a counter substrate 820, and a liquid crystal layer 830 provided therebetween.

The TFT substrate 810 is provided on the transparent substrate 810a, the common electrode (lower layer electrode) 812 provided on the transparent substrate 810a, the insulating layer 813 provided to cover the common electrode 812, and the insulating layer 813. A pixel electrode (upper layer electrode) 811.

The pixel electrode 811 has a comb shape. The pixel electrode 811 has a plurality of comb teeth 811a extending in a predetermined direction and slits 811b formed between adjacent comb teeth 811a.

The counter substrate 820 includes a transparent substrate 820a and a color filter layer (not shown) provided on the transparent substrate 820a.

The liquid crystal layer 830 is a horizontal alignment type liquid crystal layer. A horizontal alignment film (not shown) is provided on the surface of the TFT substrate 810 and the counter substrate 820 on the liquid crystal layer 830 side, and the liquid crystal molecules contained in the liquid crystal layer 830 are horizontally aligned in a state where no voltage is applied (that is, Oriented substantially parallel to the surfaces of the TFT substrate 810 and the counter substrate 820).

In the FFS mode liquid crystal display device 800, when a predetermined potential difference is applied between the pixel electrode 811 and the common electrode 812, a fringe electric field (represented by an electric force line Ef) is generated in the liquid crystal layer 830. When potentials of 14 V and 7 V, for example, are applied to the pixel electrode 811 and the common electrode 812, respectively, a fringe electric field corresponding to 7 V is applied to the liquid crystal layer 830. The alignment direction of the liquid crystal molecules is changed by the fringe electric field applied to the liquid crystal layer 830, and thus display is performed.

The FFS mode described above can achieve a wide viewing angle characteristic. The VA mode can also realize a wide viewing angle characteristic.

Patent Document 4 discloses an electrode structure capable of achieving high-speed response and high transmittance of a VA mode liquid crystal display device. 30A and 30B show the structure of the liquid crystal display device disclosed in Patent Document 4. FIG. A liquid crystal display device 900 shown in FIGS. 30A and 30B includes a TFT substrate 910 and a counter substrate 920, and a liquid crystal layer 930 provided therebetween.

The TFT substrate 910 includes a glass substrate 910a, a lower layer electrode 913 provided on the glass substrate 910a, an insulating layer 914 provided so as to cover the lower layer electrode 913, and a pair of upper layer electrodes provided on the insulating layer 914. (First upper layer electrode and second upper layer electrode) 911 and 912. Each of the first upper layer electrode 911 and the second upper layer electrode 912 has a comb shape.

The counter substrate 920 includes a glass substrate 920a and a counter electrode 921 provided on the glass substrate 920a.

The liquid crystal layer 930 is a vertical alignment type liquid crystal layer. A vertical alignment film (not shown) is provided on the surface of the TFT substrate 910 and the counter substrate 920 on the liquid crystal layer 930 side, and the liquid crystal molecules contained in the liquid crystal layer 930 are vertically aligned in a state where no voltage is applied (that is, Oriented substantially parallel to the surfaces of the TFT substrate 910 and the counter substrate 920).

In the liquid crystal display device 900, at the time of start-up (when the alignment state changes from the black display state to the white display state), as shown in FIG. 30A, the first upper layer electrode 911 and the second upper layer electrode 912 are arranged. A lateral electric field (represented by electric lines of force Eh) due to the potential difference is generated in the liquid crystal layer 930. At this time, a fringe electric field (represented by electric lines of force Ef) due to a potential difference between the first upper layer electrode 911 and the lower layer electrode 913 and a potential difference between the second upper layer electrode 912 and the lower layer electrode 913 is also generated in the liquid crystal layer 930. Is done. Patent Document 4 describes an example in which potentials of 7 V, 14 V, 10.5 V, and 7 V are applied to the first upper layer electrode 911, the second upper layer electrode 912, the lower layer electrode 913, and the counter electrode 921, respectively. In this example, a lateral electric field corresponding to 7V (= 14V-7V) and a fringe electric field corresponding to 3.5V (= 14V-10.5V = 10.5V-7V) are applied to the liquid crystal layer 930. .

At the time of falling (when changing from the white display state to the black display state), as shown in FIG. 30B, the first upper layer electrode 911, the second upper layer electrode 912, and the lower layer electrode 913 Then, a vertical electric field (represented by lines of electric force Ev) due to a potential difference with the counter electrode 921 is generated in the liquid crystal layer 930. Patent Document 4 describes an example in which potentials of 14 V, 14 V, 14 V, and 0 V are applied to the first upper layer electrode 911, the second upper layer electrode 912, the lower layer electrode 913, and the counter electrode 921, respectively. In this example, a vertical electric field corresponding to 14 V is applied to the liquid crystal layer 930.

The inventor of the present application examined the use of the electrode structure proposed for the liquid crystal display device as a method for further improving the light utilization efficiency of the display device including the display medium layer containing the shape anisotropic particles. As a result, it has been found that the following problems occur when the electrode structure as described above is simply adopted.

First, in the electrode structure of Patent Document 4, the potential of the lower layer electrode 913 is limited, and a sufficiently strong fringe electric field cannot be generated. Specifically, in order to maintain the symmetry of orientation, the potential of the lower layer electrode 913 needs to be set to an intermediate potential between the potential of the first upper layer electrode 911 and the potential of the second upper layer electrode 912. As in the example described in Patent Document 4, if the potentials of the first upper electrode 911 and the second upper electrode 912 are 7V and 14V, respectively, the potential of the lower electrode 913 needs to be set to 10.5V. Therefore, since the generated fringe electric field is equivalent to 3.5 V, compared to the case where the FFS mode electrode structure is adopted (a fringe electric field equivalent to 7 V is generated as shown in FIG. 29). The alignment regulating force due to the fringe electric field is weakened.

In addition, in the electrode structure of Patent Document 4, in order to generate a fringe electric field having the same strength as that of the FFS mode electrode structure, the potential of the lower layer electrode 913 is made the same as the potential of the first upper layer electrode 911 (for example, the first 1 upper layer electrode 911, second upper layer electrode 912, lower layer electrode 913 and counter electrode 921 are applied with potentials of 7V, 14V, 7V and 7V, respectively), and as shown in FIG. 31, second upper layer electrode 912 and lower layer electrode Although a strong fringe electric field (equivalent to 7 V) is generated due to a potential difference from 913, no fringe electric field is generated in the vicinity of the first upper layer electrode 911, and a weak electric field region WR having a relatively weak electric field strength is formed. Due to the presence of the weak electric field region WR, the light use efficiency (mode efficiency) is lowered.

On the other hand, when the FFS mode electrode structure is adopted, the plurality of comb-tooth portions 811a of the pixel electrode 811 are at the same potential, so that no horizontal electric field is generated between the adjacent comb-tooth portions 811a. Therefore, as shown in FIG. 32, a weak electric field region WR is generated near the center of the slit 811b, and the light utilization efficiency is lowered.

The present invention has been made in view of the above-described problems, and an object of the present invention is to use light efficiency due to a weak electric field region in a display device including a display medium layer whose optical characteristics change according to an applied electric field. It is in suppressing the fall of the.

A display device according to an embodiment of the present invention is a display device having pixels, and is provided between a first substrate and a second substrate provided to face each other, and the first substrate and the second substrate. A display medium layer having an optical characteristic that changes according to the applied electric field, and when the electric field is applied to the display medium layer, the pixel has a first electric field strength. And a second region having a second electric field strength whose electric field is weaker than the first electric field strength have an electric field distribution arranged along an in-plane direction of the display medium layer, The arrangement of the first region and the second region in the electric field distribution is switched one or more times within a period in which the same display is performed.

In one embodiment, the period at which the arrangement of the first area and the second area is switched is an integral multiple of a time corresponding to one frame.

In one embodiment, the first substrate includes a first electrode and a second electrode that are provided in the pixel and can be applied with different potentials, and each of the first electrode and the second electrode includes a comb tooth. Has a shape.

In one embodiment, a lateral electric field is generated in the display medium layer by the first electrode and the second electrode.

In an embodiment, when the arrangement of the first region and the second region is switched, the potential of the first electrode and the potential of the second electrode are switched.

In one embodiment, the first substrate further includes a third electrode provided below the first electrode and the second electrode via an insulating layer.

In one embodiment, a fringe electric field is generated in the display medium layer by the first electrode or the second electrode and the third electrode.

In one embodiment, the pixel has a predetermined potential difference between the first electrode and the third electrode, and the second electrode and the third electrode have substantially the same potential. And a second state in which a predetermined potential difference is given between the second electrode and the third electrode, and the first electrode and the third electrode have substantially the same potential. The first state and the second state are switched when the arrangement of the first region and the second region is switched.

In one embodiment, the second substrate has a fourth electrode facing the first electrode, the second electrode, and the third electrode.

In one embodiment, a vertical electric field is generated in the display medium layer by the first electrode, the second electrode, the third electrode, and the fourth electrode.

In one embodiment, the first substrate further includes a first thin film transistor electrically connected to the first electrode and a second thin film transistor electrically connected to the second electrode.

In one embodiment, the response time of the display medium layer is longer than a cycle in which the arrangement of the first region and the second region is switched.

In one embodiment, the display medium layer includes a medium and shape anisotropic particles dispersed in the medium and having shape anisotropy.

In one embodiment, the medium includes a liquid crystal material.

In one embodiment, at least one of the first substrate and the second substrate has a vertical alignment film that is provided on the display medium layer side and vertically aligns liquid crystal molecules contained in the liquid crystal material.

According to the embodiment of the present invention, it is possible to suppress a decrease in light utilization efficiency due to a weak electric field region in a display device including a display medium layer whose optical characteristics change according to an applied electric field.

FIG. 3 is a cross-sectional view schematically showing a display device 100 according to an embodiment of the present invention, showing a cross section taken along line 1A-1A ′ in FIG. 2. 3 is a plan view schematically showing the display device 100. FIG. (A) is a figure which shows typically the display apparatus 100 when the electric field is not applied to the display medium layer 30, (b) is a horizontal electric field and a fringe electric field being applied to the display medium layer 30. It is a figure which shows the display apparatus 100 of time. 3 is a diagram schematically showing the display device 100 when a vertical electric field is applied to the display medium layer 30. FIG. (A) is a figure which shows the mode of the display medium layer 30 immediately after changing the electric field applied to the display medium layer 30 from a horizontal electric field and a fringe electric field to a vertical electric field, (b) is enough after that It is a figure which shows the mode of the display medium layer 30 after time passes. (A) And (b) is a figure which shows the state in which the horizontal electric field and a fringe electric field are applied to the display medium layer 30, (a) is in the case where the same display is performed over several frames Corresponding to a certain frame, (b) corresponds to another certain frame. It is a figure which shows the state in which the application of a horizontal electric field and a fringe electric field is performed in the liquid crystal display device 900 of patent document 4. FIG. FIG. 11 is a diagram illustrating a state in which a fringe electric field is applied in the FFS mode liquid crystal display device 800. (A) And (b) is a figure which shows the other electrode structure of the display apparatus 100. FIG. (A) And (b) is a figure which shows the further another electrode structure of the display apparatus 100. FIG. It is a top view which shows the example of the specific wiring structure in the back substrate 10 in the case of performing active matrix drive. It is a top view which shows the electrode structure in a test cell. (A), the potential V ₁ of the first electrode 11 in the embodiment, the potential V ₂ of the second electrode 12 is a timing chart showing the potential V ₄ in the potential V ₃ and the fourth electrode 21 of the third electrode 13, (b) the voltage between the first electrode 11 and the third electrode 13 in the embodiment | and the voltage between the second electrode 12 and the third electrode 13 | | V ₁ -V ₃ and, | V ₂ -V ₃ 6 is a timing chart showing a voltage | V ₁ −V ₂ | between the first electrode 11 and the second electrode 12. (A) And (b) is a figure which shows the state of a pixel when the electric potential shown to Fig.13 (a) is given to the 1st electrode 11, the 2nd electrode 12, the 3rd electrode 13, and the 4th electrode 21. FIG. It is. (A), (b), and (c) are the optical microscope images of the display medium layer 30 in an Example, (a) shows the state (initial state) in which the electric field is not applied to the display medium layer 30. , (B) and (c) show a state after a lateral electric field and a fringe electric field are applied to the display medium layer 30 for a predetermined time. (D) is a figure which shows the state of (a) typically, (e) is a figure which shows the state of (b) and (c) typically. Optical microscope images and the like in the first to ninth frames (specifically, at

time points

0, 17, 50, 67, 83, 100, and 133 msec) after applying a lateral electric field and a fringe electric field to the display medium layer 30 in the embodiment. FIG. The potential V ₁ of the first electrode 11 of Comparative Example 1, the potential V ₂ of the second electrode 12 is a timing chart showing the potential V ₄ in the potential V ₃ and the fourth electrode 21 of the third electrode 13. FIG. 18 is a diagram illustrating a state of a pixel when the potential illustrated in FIG. 17 is applied to a first electrode 11, a second electrode 12, a third electrode 13, and a fourth electrode 21. (A), (b), and (c) are the optical microscope images of the display medium layer 30 in the comparative example 1, (a) is the state (initial state) in which the electric field is not applied to the display medium layer 30. (B) and (c) show a state after a lateral electric field and a fringe electric field are applied to the display medium layer 30 for a predetermined time. (D) is a figure which shows the state of (a) typically, (e) is a figure which shows the state of (b) and (c) typically. The potential V ₁ of the first electrode 11 of Comparative Example 2, the potential V ₂ of the second electrode 12 is a timing chart showing the potential V ₄ in the potential V ₃ and the fourth electrode 21 of the third electrode 13. FIG. 21 is a diagram illustrating a state of a pixel when the potential illustrated in FIG. 20 is applied to a first electrode 11, a second electrode 12, a third electrode 13, and a fourth electrode 21. (A), (b), and (c) are the optical microscope images of the display medium layer 30 in the comparative example 2, (a) is the state (initial state) in which the electric field is not applied to the display medium layer 30. (B) and (c) show a state after a lateral electric field and a fringe electric field are applied to the display medium layer 30 for a predetermined time. (D) is a figure which shows the state of (a) typically, (e) is a figure which shows the state of (b) and (c) typically. The potential V ₁ of the first electrode 11 of Comparative Example 3, the potential V ₂ of the second electrode 12 is a timing chart showing the potential V ₄ in the potential V ₃ and the fourth electrode 21 of the third electrode 13. FIG. 24 is a diagram illustrating a state of a pixel when the potential illustrated in FIG. 23 is applied to a first electrode 11, a second electrode 12, a third electrode 13, and a fourth electrode 21. (A), (b), and (c) are the optical microscope images of the display medium layer 30 in the comparative example 3, (a) is the state (initial state) in which the electric field is not applied to the display medium layer 30. (B) and (c) show a state after a lateral electric field and a fringe electric field are applied to the display medium layer 30 for a predetermined time. (D) is a figure which shows the state of (a) typically, (e) is a figure which shows the state of (b) and (c) typically. The potential V ₁ of the first electrode 11 of Comparative Example 4, the potential V ₂ of the second electrode 12 is a timing chart showing the potential V ₄ in the potential V ₃ and the fourth electrode 21 of the third electrode 13. FIG. 27 is a diagram illustrating a state of a pixel when the potential illustrated in FIG. 26 is applied to a first electrode 11, a second electrode 12, a third electrode 13, and a fourth electrode 21. (A), (b), and (c) are the optical microscope images of the display medium layer 30 in the comparative example 4, (a) is the state (initial state) in which the electric field is not applied to the display medium layer 30. (B) and (c) show a state after a lateral electric field and a fringe electric field are applied to the display medium layer 30 for a predetermined time. (D) is a figure which shows the state of (a) typically, (e) is a figure which shows the state of (b) and (c) typically. FIG. 6 is a cross-sectional view schematically showing an FFS mode liquid crystal display device 800. (A) And (b) is sectional drawing which shows the liquid crystal display device 900 of patent document 4 typically. It is a figure which shows typically a mode that the weak electric field area | region WR generate | occur | produces in the liquid crystal display device 900 of patent document 4. FIG. FIG. 11 is a diagram schematically showing how a weak electric field region WR is generated in an FFS mode liquid crystal display device 800.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In addition, this invention is not limited to the following embodiment.

FIG. 1 shows a display device 100 according to this embodiment. FIG. 1 is a cross-sectional view schematically showing the display device 100, and FIG. 2 is a plan view schematically showing the display device 100. FIG. 1 shows a cross section taken along line 1A-1A 'in FIG.

The display device 100 is a reflective display device that can perform display in a reflection mode using light incident from the outside (ambient light). The display device 100 includes pixels. Here, the display device 100 includes a plurality of pixels arranged in a matrix.

As shown in FIG. 1, the display device 100 includes a first substrate 10 and a second substrate 20 provided so as to face each other, and a display medium layer (between the first substrate 10 and the second substrate 20). Optical layer) 30. Hereinafter, of the first substrate 10 and the second substrate 20, the first substrate 10 positioned relatively on the back side may be referred to as a “back side substrate” and may be referred to relatively on the front side (that is, on the viewer side). The second substrate 20 positioned at () may be referred to as a “front substrate”.

The first substrate (back substrate) 10 has a first electrode 11 and a second electrode 12 that can be given different potentials. The first electrode 11 and the second electrode 12 are provided in each of the plurality of pixels. Each of the 1st electrode 11 and the 2nd electrode 12 has a comb-tooth shape, as shown in FIG.

The first electrode 11 has a trunk portion 11b and a plurality of branch portions 11a extending from the trunk portion 11b. Similarly, the second electrode 12 includes a trunk portion 12b and a plurality of branch portions 12a extending from the trunk portion 12b. The first electrode 11 and the second electrode 12 are arranged so that the plurality of

branch portions

11a and 12a mesh with each other via a predetermined gap (hereinafter also referred to as “interelectrode distance”) g. Yes.

There is no restriction | limiting in particular in the distance g between electrodes. Further, the width w ₁ of the branch part 11 a of the first electrode 11 and the width w ₂ of the branch part 12 a of the second electrode 12 are not particularly limited. The inter-electrode distance g, the width w ₁ of the branch portion 11a of the first electrode 11, and the width w ₂ of the branch portion 12a of the second electrode 12 are each about several μm to several tens of μm, for example. The width w ₁ of the branch portion 11a of the first electrode 11 and the width w ₂ of the branch portion 12a of the second electrode 12 may be the same or different.

The first substrate 10 further includes a third electrode 13 provided below the first electrode 11 and the second electrode 12 with the insulating layer 14 interposed therebetween. Hereinafter, the first electrode 11, the second electrode 12, and the third electrode 13 may be referred to as “first upper layer electrode”, “second upper layer electrode”, and “lower layer electrode”, respectively. In the example shown in FIGS. 1 and 2, the third electrode 13 is a so-called solid electrode in which no slit or notch is formed.

The first substrate 10 is typically an active matrix substrate, and includes a plurality of thin film transistors (TFTs) provided in each pixel and various wirings (a gate wiring, a source wiring, etc. electrically connected to the TFT). (Both not shown here). The first electrode 11, the second electrode 12, and the third electrode 13 are electrically connected to the corresponding TFTs, respectively, and supplied with a voltage corresponding to the source signal through the TFTs.

The first substrate 10 further includes a light absorption layer 16 that absorbs light. There is no restriction | limiting in particular in the material of the light absorption layer 16. FIG. As a material of the light absorption layer 16, for example, a pigment used for a black matrix material included in a color filter of a liquid crystal display device or the like can be used. Alternatively, a low-reflection chromium film having a two-layer structure (having a structure in which a chromium layer and a chromium oxide layer are stacked) can be used as the light absorption layer 16.

The components of the first substrate 10 (such as the first electrode 11 described above) are supported by an insulating substrate (for example, a glass substrate) 10a. In FIG. 1, the light absorption layer 16 is provided on the back side of the substrate 10a. However, the light absorption layer 16 may be provided on the display medium layer 30 side of the substrate 10a.

The second substrate (front substrate) 20 has a fourth electrode (counter electrode) 21 facing the first electrode 11, the second electrode 12 and the third electrode 13. The fourth electrode 21 may be a so-called solid electrode in which no slit or notch is formed. In the example illustrated in FIG. 1, the second substrate 20 further includes a dielectric layer (overcoat layer) 22 provided on the fourth electrode 21. The fourth electrode 21 does not need to be electrically independent for each pixel, and may be a continuous single conductive film (that is, a common electrode) common to all pixels. When the fourth electrode 21 is a solid electrode common to all the pixels, patterning by a photolithography technique is not necessary, so that the manufacturing cost can be reduced. When performing color display, the second substrate 20 includes a color filter (not shown).

The components of the second substrate 20 (such as the fourth electrode 21 described above) are supported by an insulating substrate (for example, a glass substrate) 20a.

Each of the first electrode 11, the second electrode 12, the third electrode 13, and the fourth electrode 21 is made of a transparent conductive material such as ITO (indium tin oxide) or IZO (indium zinc oxide). There is no particular limitation on the method for depositing the conductive film to be these electrodes, and various known methods such as a sputtering method, a vacuum evaporation method, and a plasma CVD method can be used. Further, there is no particular limitation on the method for patterning the conductive film in order to form the first electrode 11 and the second electrode 12 having a comb-teeth shape, and a known patterning method such as photolithography can be used. The thicknesses of the first electrode 11, the second electrode 12, the third electrode 13, and the fourth electrode 21 are, for example, 100 nm.

The optical properties of the display medium layer 30 change according to the applied electric field. The display medium layer 30 includes a liquid medium 31 and particles 32 that are dispersed in the medium 31 and have shape anisotropy (hereinafter referred to as “shape anisotropic particles”). The first substrate 10 and the second substrate 20 described above are bonded together via a seal portion (not shown here) formed so as to surround the display region, and the medium 31 and the shape anisotropic particles 32 are: It is enclosed in a region (that is, a display region) surrounded by the seal portion. There is no particular limitation on the thickness (cell gap) of the display medium layer 30. The thickness of the display medium layer 30 is, for example, 5 μm to 30 μm.

The shape anisotropic particle 32 has light reflectivity. The shape anisotropic particle 32 has, for example, a flake shape (flaky shape).

The orientation direction of the shape anisotropic particles 32 changes according to the electric field (voltage) applied to the display medium layer 30. Since the shape anisotropic particles 32 have shape anisotropy, when the orientation direction of the shape anisotropic particles 32 changes, the substrate surface of the shape anisotropic particles 32 (the substrate surface of the first substrate 10). The projected area on the screen also changes, and accordingly, the optical characteristics (in this case, reflectance) of the display medium layer 30 change. In the display device 100 of the present embodiment, display is performed using this fact. The reason why the orientation direction of the shape anisotropic particles 32 changes according to the applied electric field will be described in detail later.

In the display device 100 of this embodiment, the medium 31 is a liquid crystal material and includes liquid crystal molecules. Here, the liquid crystal material has positive dielectric anisotropy. That is, the medium 31 is a so-called positive liquid crystal material, and the dielectric constant ε _{// in} the major axis direction of the liquid crystal molecules is larger than the dielectric constant ε _{の in the} minor axis direction.

Each of the first substrate 10 and the second substrate 20 has

vertical alignment films

15 and 25 provided on the display medium layer 30 side. The

vertical alignment films

15 and 25 have an alignment regulating force for vertically aligning liquid crystal molecules contained in the medium (liquid crystal material) 31 (aligned substantially perpendicularly to the substrate surface of the first substrate 10 or the second substrate 20). Further, the

vertical alignment films

15 and 25, as will be described in detail later, are alignment restrictions that cause the shape anisotropic particles 32 to be vertically aligned (aligned substantially perpendicularly to the substrate surface of the first substrate 10 or the second substrate 20). Also has power. Note that the vertical alignment film is not necessarily provided on both the first substrate 10 and the second substrate 20, and the vertical alignment film may be provided on only one (for example, only the first substrate 10).

In the display device 100 according to the embodiment of the present invention, a lateral electric field is generated in the display medium layer 30 by the first electrode (first upper layer electrode) 11 and the second electrode (second upper layer electrode) 12. Further, a fringe electric field is generated in the display medium layer 30 by the first electrode 11 or the second electrode 12 and the third electrode (lower layer electrode) 13. In this specification, an electric field generated by a potential difference between two electrodes provided on the same substrate on the same level is called a “lateral electric field”, and is generated by a potential difference between two electrodes provided on different levels on the same substrate. The electric field is called a “fringe electric field”. In the display device 100 according to the embodiment of the present invention, a vertical electric field is generated in the display medium layer 30 by the first electrode 11, the second electrode 12, the third electrode 13, and the fourth electrode (counter electrode) 21. .

Hereinafter, the reason why the orientation direction of the shape anisotropic particles 32 changes according to the applied electric field (applied voltage) will be described in more detail with reference to FIGS. 3 (a) and 3 (b). FIG. 3A is a diagram schematically showing the display device 100 when no electric field is applied to the display medium layer 30, and FIG. 3B shows a horizontal electric field and a fringe electric field in the display medium layer 30. It is a figure which shows typically the display apparatus 100 when being applied.

When no electric field is applied to the display medium layer 30, as shown in FIG. 3A, the shape anisotropic particles 32 are arranged in the first direction (longitudinal direction) by the alignment regulating force of the

vertical alignment films

15 and 25. The one substrate 10 is oriented so as to be substantially perpendicular to the substrate surface (that is, in a vertically oriented state). In addition, the alignment of the liquid crystal molecules substantially perpendicular to the substrate surface by the alignment regulating force of the

vertical alignment films

15 and 25 serves to support the shape anisotropic particles 32 taking a vertical alignment state. In this state, most of the incident ambient light L is transmitted through the display medium layer 30. That is, the display medium layer 30 is in a transparent state. Since the ambient light transmitted through the display medium layer 30 is absorbed by the light absorption layer 16, black display can be performed in this state. In the present specification, “the shape anisotropic particles 32 are oriented substantially perpendicular to the substrate surface” means that the shape anisotropic particles 32 are oriented strictly perpendicular to the substrate surface. Refers to a state of being oriented at an angle exhibiting substantially the same optical characteristics as the state of being, specifically, the shape anisotropic particles 32 are oriented at an angle of 75 ° or more with respect to the substrate surface. Refers to the state.

As shown in FIG. 3B, when a lateral electric field (represented by an electric force line Eh) and a fringe electric field (represented by an electric force line Ef) are applied to the display medium layer 30, the shape anisotropic particles 32. Is oriented so that its longitudinal direction is substantially parallel to the substrate surface of the first substrate 10 (that is, it takes a horizontal orientation state). The liquid crystal molecules are also aligned substantially parallel to the substrate surface of the first substrate 10. In this state, most of the incident ambient light L is reflected by the shape anisotropic particles 32 in the display medium layer 30. That is, the display medium layer 30 is in a reflective state, and white display can be performed in this state. Further, halftone display can be performed by applying a voltage lower than that during white display.

In the example shown in FIG. 3B, a fringe electric field due to the potential difference between the first electrode 11 and the third electrode 13 is generated, but the fringe electric field due to the potential difference between the second electrode 12 and the third electrode 13 is Not generated. That is, FIG. 3B shows an example in which the same potential is applied to the second electrode 12 and the third electrode 13. However, as will be described later, the potential setting for performing white display or halftone display is not limited to the example shown in FIG.

Further, in the display device 100, the second substrate 20 includes the fourth electrode 21 that faces the first electrode 11, the second electrode 12, and the third electrode 13, so that a vertical electric field is generated in the display medium layer 30. You can also

As shown in FIG. 4, when a vertical electric field (represented by an electric force line Ev) is applied to the display medium layer 30, the shape anisotropic particles 32 (the longitudinal direction thereof) is the substrate surface of the first substrate 10. Is aligned so as to be substantially perpendicular to (i.e., assume a vertical alignment state). The liquid crystal molecules are also aligned substantially perpendicular to the substrate surface of the first substrate 10. In this state, most of the incident ambient light L is transmitted through the display medium layer 30. That is, the display medium layer 30 is in a transparent state. Since the ambient light transmitted through the display medium layer 30 is absorbed by the light absorption layer 16, black display can be performed in this state.

The orientation change of the shape anisotropic particles 32 as described above is caused by the dielectrophoretic force due to the interaction between the electric field and the electric dipole moment induced thereby. Hereinafter, a more specific description will be given with reference to FIGS. 5 (a) and 5 (b). FIGS. 5A and 5B show the display medium layer immediately after the electric field applied to the display medium layer 30 is changed from the horizontal electric field and the fringe electric field to the vertical electric field, and after a sufficient time has elapsed thereafter. It is a figure which shows the mode 30 (electric charge distribution and an electric force line).

When the dielectric constant of the shape anisotropic particles 32 and the dielectric constant of the medium 31 are different, if the direction of the electric field applied to the display medium layer 30 is changed, as shown in FIG. A large distortion occurs. Therefore, as shown in FIG. 5B, the shape anisotropic particles 32 rotate so that the energy is minimized.

In general, the dielectrophoretic force F _dep acting on particles dispersed in a medium is expressed as follows, where the dielectric constant of the particles is ε _p , the dielectric constant of the medium is ε _m , the radius of the particles is a, and the strength of the electric field is E. It is represented by Formula (1). Re in the expression (1) is an operator that extracts a real part. In the present embodiment, the medium 31 is a liquid crystal material and has dielectric anisotropy. That is, the dielectric constant epsilon _⊥ the long axis direction of the dielectric constant epsilon _// and the minor axis direction of liquid crystal molecules is different, is considered to correspond to _{_{_{ε m = ε // -ε ⊥ =}}} Δε.

Further, as can be seen from the above description, in addition to the above-described dielectrophoretic force, the shape anisotropic particles 32 are allowed to develop a vertical alignment state by the alignment regulating force of the

vertical alignment films

15 and 25 and the support of liquid crystal molecules. Thus, the vertical alignment operation and the horizontal alignment operation of the shape anisotropic particles 32 can be suitably switched.

As described above, in the display device 100 according to the present embodiment, the orientation direction of the shape anisotropic particles 32 can be changed by applying a voltage to the display medium layer 30, and display is performed using this. be able to. Since the display device 100 does not require a polarizing plate, high light utilization efficiency can be realized.

Further, in the display device 100 according to the present embodiment, it is possible to suppress a decrease in light utilization efficiency due to a weak electric field region formed when a lateral electric field and a fringe electric field are applied. Hereinafter, this will be specifically described with reference to FIGS.

6A and 6B are views showing a state in which a lateral electric field and a fringe electric field are applied to the display medium layer 30, and FIG. 6A shows the same display over a plurality of frames. 6B corresponds to a certain frame, and FIG. 6B corresponds to another certain frame.

In the display device 100, when an electric field is applied to the display medium layer 30, each pixel includes a first region SR in which the electric field has a first electric field strength and an electric field, as shown in FIGS. 6 (a) and 6 (b). And a second region WR having a second electric field strength weaker than the first electric field strength has an electric field distribution arranged along the in-plane direction of the display medium layer 30. Hereinafter, the first region SR having a relatively strong electric field strength is referred to as a “strong electric field region”, and the second region WR having a relatively weak electric field strength is referred to as a “weak electric field region”.

In FIG. 6A, a fringe electric field (hereinafter referred to as “first fringe electric field” for convenience) generated by the potential difference between the first electrode 11 and the third electrode 13 is generated. In the example, a fringe electric field (hereinafter referred to as “second fringe electric field” for convenience) is not generated due to a potential difference with the third electrode 13. In this example, the region where the fringe electric field is not generated in the vicinity of the branch portion 12a of the second electrode 12 is the weak electric field region WR, and the other region including the vicinity of the branch portion 11a of the first electrode 11 is the strong electric field region SR. Become.

FIG. 6B shows an example in which the second fringe electric field is generated but the first fringe electric field is not generated. In this example, the region where the fringe electric field is not generated near the branch portion 11a of the first electrode 11 is the weak electric field region WR, and the other region including the vicinity of the branch portion 12a of the second electrode 12 is the strong electric field region SR. Become.

In the display device 100, as shown in FIGS. 6A and 6B, a period during which the same display is performed in any pixel among the plurality of pixels (that is, a certain pixel has the same gradation). Within the period of level display), the arrangement of the strong electric field region SR and the weak electric field region WR in the electric field distribution is switched one or more times. That is, the position of the weak electric field region WR is not fixed, and the region that has been the weak electric field region WR in one frame becomes the strong electric field region SR in another certain frame. Therefore, the orientation direction of the shape anisotropic particles 32 can be changed over almost the entire pixel, and a decrease in light use efficiency (mode efficiency) due to the weak electric field region WR can be suppressed.

6A and 6B, the potentials of the first electrode 11, the second electrode 12, and the third electrode 13 are set so that only one of the first fringe electric field and the second fringe electric field is generated. However, the potential setting of the first electrode 11, the second electrode 12, and the third electrode 13 is not limited to this example. As long as the strengths of the first fringe field and the second fringe field are different from each other, both the first fringe field and the second fringe field may be generated simultaneously. In that case, the region in which the fringe electric field having the relatively strong electric field strength of the first fringe electric field and the second fringe electric field is generated becomes the strong electric field region SR, and the fringe electric field having the relatively weak electric field strength. The region in which is generated becomes the weak electric field region WR.

Further, in the display device 100, there is no restriction that the potential of the third electrode 13 must be set to an intermediate potential between the potential of the first electrode 11 and the potential of the second electrode 12. By making the potential of one of the first electrode 11 and the second electrode 12 the same as the potential of the third electrode 13, the fringe due to the potential difference between the other of the first electrode 11 and the second electrode 12 and the third electrode 13. The electric field can be strongest. For example, when the potential of the first electrode 11 is B [V], the potential of the second electrode 12 is A [V], and the potential of the third electrode 13 is C [V], the first electrode 11 and the second electrode 12 The horizontal electric field due to the potential difference is equivalent to | AB | [V], and the fringe electric field due to the potential difference between the first electrode 11 and the third electrode 13 is equivalent to | BC | V (FIG. 6A). reference). Here, if the potential C [V] of the third electrode 13 is made the same as the potential A [V] of the second electrode 12 (C = A), a fringe electric field due to the potential difference between the first electrode 11 and the third electrode 13. Is equivalent to | BC | = | BA | = | AB | [V]. Further, when the potential of the first electrode 11 is A [V], the potential of the second electrode 12 is B [V], and the potential of the third electrode 13 is C [V], the first electrode 11, the second electrode 12, The horizontal electric field due to the potential difference is equivalent to | AB | [V], and the fringe electric field due to the potential difference between the second electrode 12 and the third electrode 13 is equivalent to | BC | V (FIG. 6B). reference). Here, if the potential C [V] of the third electrode 13 is made the same as the potential A [V] of the first electrode 11 (C = A), a fringe electric field due to the potential difference between the second electrode 12 and the third electrode 13. Is equivalent to | BC | = | BA | = | AB | [V]. As described above, in the display device 100, since the potential of the third electrode 13 is not limited, a fringe electric field having the same strength as that when the FFS mode electrode structure is employed can be applied to the display medium layer 30. Further, as shown in FIGS. 6A and 6B, the arrangement of the strong electric field region SR and the weak electric field region WR can be changed by switching the potential of the first electrode 11 and the potential of the second electrode 12, for example. Can be replaced.

On the other hand, in the electrode structure of Patent Document 4, when the potential of the first upper electrode 911 is A [V] and the potential of the second upper electrode 912 is B [V], as shown in FIG. Is required to be Min (A, B) + | (AB) | / 2 [V]. Therefore, the lateral electric field due to the potential difference between the first upper electrode 911 and the second upper electrode 912 is equivalent to | AB | [V], whereas the fringe electric field due to the potential difference between the first upper electrode 911 and the lower electrode 913 is used. The fringe electric field due to the potential difference between the second upper layer electrode 912 and the lower layer electrode 913 is equivalent to | AB | / 2 [V]. For this reason, the fringe electric field becomes weaker than when the FFS mode electrode structure is adopted.

In the FFS mode electrode structure, as shown in FIG. 8, when the potential of the common electrode 812 is A [V] and the potential of the pixel electrode 811 is B [V], a potential difference between the pixel electrode 811 and the common electrode 812 is obtained. The fringe electric field due to is equivalent to | AB | [V]. The FFS mode electrode structure can generate a sufficiently strong fringe electric field, but a horizontal electric field is not generated between adjacent comb-tooth portions 811a, so that a weak electric field region WR is generated near the center of the slit 811b. . On the other hand, in the display device 100 according to the embodiment of the present invention, a lateral electric field can be generated between the first electrode 11 and the second electrode 12, so that the branch portion 11 a of the first electrode 11 and the second electrode 12 electrode 12 A decrease in light utilization efficiency due to the formation of the weak electric field region WR near the middle of the branch portion 12a can be suppressed.

When performing active matrix driving, the period in which the arrangement of the strong electric field region SR and the weak electric field region WR is switched (hereinafter also simply referred to as “switching cycle”) is typically an integer multiple of the time corresponding to one frame. . From the viewpoint of improving the light utilization efficiency, the replacement period is preferably short, and most preferably a time corresponding to one frame. Since the replacement cycle is short, the number of fluctuations in the electric field distribution per unit time can be increased, and the light utilization efficiency can be further improved. Further, the switching period may not be constant within the period during which the same display is performed, but the total time during which the positive voltage is applied to the display medium layer 30 and the negative voltage are applied. It is preferable that the total amount of time is substantially equal.

As already described, the arrangement of the strong electric field region SR and the weak electric field region WR can be replaced by, for example, switching the potential of the first electrode 11 and the potential of the second electrode 12. In other words, the arrangement of the strong electric field region SR and the weak electric field region WR can be exchanged by the first substrate 10 having two comb electrodes (electrodes having a comb shape) that can be given different potentials. it can.

Further, as described above, the first substrate 10 has the third electrode 13 provided below the first electrode 11 and the second electrode 12 with the insulating layer 14 interposed therebetween, so that the display medium layer 30 has a fringe. An electric field can be generated.

In addition, the structure of the 1st electrode 11, the 2nd electrode 12, and the 3rd electrode 13 is not limited to what was illustrated in FIG. 9A and 9B show other electrode configurations of the display device 100. FIG.

In the example shown in FIGS. 9A and 9B, a further insulating layer 17 is provided so as to cover the first electrode 11, and the second electrode 12 is provided on the further insulating layer 17. That is, the second electrode 12 is provided above the first electrode 11 via the further insulating layer 17. In the configuration shown in FIGS. 9A and 9B, since the first electrode 11 and the second electrode 12 are provided at different levels, a potential difference between the first electrode 11 and the second electrode 12 causes a lateral electric field. Instead, a fringe electric field (represented by electric field lines Ef ′) is generated. In the configuration shown in FIGS. 9A and 9B, since the further insulating layer 17 is located between the first electrode 11 and the second electrode 12, the distance between the first electrode 11 and the second electrode 12. Even if the width is narrowed, there is an advantage that there is no short circuit.

10 (a) and 10 (b) show still another electrode configuration of the display device 100. FIG. In the example shown in FIGS. 10A and 10B, the third electrode 13 has a plurality of slits 13 s formed at positions overlapping the first electrode 11 and the second electrode 12. In the configuration shown in FIGS. 10A and 10B, the fringe electric field distribution is concentrated from the end of the first electrode 11 or the second electrode 12 to between the first electrode 11 and the second electrode 12 (adjacent to each other). (Between the

branch portions

11a and 12a) can be made closer to the center. On the other hand, as shown in FIG. 1 and the like, in the configuration in which the third electrode 13 is a solid electrode, the first electrode 11 and the second electrode 12, the third electrode 13, and the insulating layer 14 positioned between them. The advantage that an auxiliary capacity can be configured is obtained.

Here, an example of a specific wiring structure in the rear substrate 10 when active matrix driving is performed will be described with reference to FIG.

In the example shown in FIG. 11, three TFTs (first TFT, second TFT, and third TFT) t1, t2, and t3 are provided for each pixel. The first electrode 11, the second electrode 12, and the third electrode 13 are electrically connected to the first TFT t1, the second TFT t2, and the third TFT t3, respectively. In the example shown in FIG. 11, a gate line GL extending in the row direction and a first source line SL1, a second source line SL2, and a third source line SL3 extending in the column direction are provided. The first TFT t1 is supplied with a gate signal and a first source signal from the gate line GL and the first source line SL1. The second TFT t2 is supplied with a gate signal and a second source signal from the gate line GL and the second source line SL2. The third TFT t3 is supplied with the gate signal and the third source signal from the gate line GL and the third source line SL3. With the wiring structure shown in FIG. 11, active matrix driving can be performed. Of course, the wiring structure of the back substrate 10 is not limited to the example shown in FIG.

The effect of improving the light utilization efficiency due to the exchange of the strong electric field region SR and the weak electric field region WR within the period during which the same display is performed is more remarkable in the configuration in which the response time of the display medium layer 30 is switched and longer than the period. Is obtained. Here, “the response time of the display medium layer 30 is longer than the switching period” means that at least the rising time of the rising time and the falling time is longer than the switching period. In the case of 60 Hz driving, the time corresponding to one frame is 16.6 msec. When the display device 100 including the display medium layer 30 including the shape anisotropic particles 32 as exemplified in the present embodiment was prototyped with the specifications described later, the response time (rise time) was about 133 msec. It was. Therefore, it can be said that the embodiment of the present invention is suitably used for a display device including a display medium layer containing shape anisotropic particles.

In the present embodiment, the fourth electrode 21 is provided on the second substrate 20 side, but the fourth electrode 21 may be omitted. This is because when the display medium layer 30 is in a state where no electric field is applied, the shape anisotropic particles 32 are in a vertically aligned state. However, from the viewpoint of response speed, it is preferable to adopt a configuration in which the fourth electrode 21 is provided on the second substrate 20 side (that is, a configuration in which a vertical electric field can be applied to the display medium layer 30). That is, the display is switched by switching between a state in which a vertical electric field is generated in the display medium layer 30 and a state in which a horizontal electric field and a fringe electric field (or only a fringe electric field as shown in FIG. 9) are generated in the display medium layer 30. Preferably, it is done. Since the change from the former state to the latter state and the change from the latter state to the former state are both performed by changing the direction of the applied electric field, a sufficient response speed can be realized. .

In this embodiment, a liquid crystal material is used as the medium 31, but the medium 31 may be other than the liquid crystal material (for example, propylene carbonate). The medium 31 is preferably a material that is highly transparent to visible light. The viscosity of the medium 31 is preferably 200 mPa · s or less from the viewpoint of response characteristics.

As in this embodiment, when the medium 31 is a liquid crystal material, the orientation direction of the shape anisotropic particles 32 can be efficiently changed by utilizing the change of the director of the liquid crystal molecules. In addition, the liquid crystal molecules that are aligned in a desired direction can be obtained by switching the arrangement of the strong electric field region SR and the weak electric field region WR within the period in which the same display is performed (that is, reducing the region that always becomes the weak electric field region WR). The number of can be increased. Therefore, when the medium 31 is a liquid crystal material, the effect of improving the light utilization efficiency is further increased.

In addition, since the specific resistance of the liquid crystal material is generally several orders of magnitude higher than that of propylene carbonate or the like, if the medium 31 is a liquid crystal material, the off-leakage via the medium 31 occurs when the TFT after writing to the pixel is off. Is prevented from occurring. Therefore, a high voltage holding ratio can be obtained, and active matrix driving can be suitably performed. Further, since the leakage current is small, power consumption can be reduced. The power consumption P of the display device 100 is expressed by the following formula (2), where C is the panel capacitance, V is the voltage applied to the display medium layer 30, f is the drive frequency, and I is the leakage current.
P = C · V · f + I · V (2)

The first term on the right side of Equation (2) should be called the pixel capacitance term, and the second term should be called the leakage current term. That is, the power consumption P can be considered separately for the pixel capacitance component and the leakage current component. When the specific resistance of the medium 31 is high, the leakage current I decreases, so that the power consumption P can be reduced as is apparent from the equation (2).

If the liquid crystal material is positive as in the present embodiment, the behavior of the shape anisotropic particles 32 and the behavior of the liquid crystal molecules when an electric field is applied to the display medium layer 30 match. For example, when the electric field applied to the display medium layer 30 is switched from a horizontal electric field and a fringe electric field to a vertical electric field, the shape anisotropic molecules 32 try to change from the horizontal alignment state to the vertical alignment state, and the liquid crystal molecules are also in the horizontal alignment state. Try to change from vertical alignment to vertical alignment. Therefore, since the number (existence probability) of the shape anisotropic particles 32 that are properly vertically aligned can be increased, a higher contrast ratio can be realized.

As the positive liquid crystal material, a liquid crystal material for a liquid crystal display device can be used widely and suitably. For example, a fluorine-based liquid crystal material in which fluorine is introduced into the side chain can be suitably used. Fluorine-based liquid crystal materials are often used for passive matrix drive liquid crystal display devices, and have large dielectric anisotropy and high specific resistance. Specifically, for example, a dielectric constant in the major axis direction epsilon _// 24.7, the short axial permittivity epsilon _⊥ 4.3, the specific resistance ρ is a liquid crystal material 6 × 10 ¹³ Ω · cm be able to. Of course, the dielectric constant and specific resistance of the liquid crystal material are not limited to those exemplified here. From the viewpoint of sufficiently suppressing the occurrence of off-leakage through the medium 31, the specific resistance of the liquid crystal material is preferably 1 × 10 ¹¹ to ¹² Ω · cm or more. The dielectric anisotropy Δε of the liquid crystal material preferably exceeds 10 (Δε> 10).

Note that a liquid crystal material having negative dielectric anisotropy (that is, a negative liquid crystal material) may be used as the medium 31.

Further, when the first substrate 10 and the second substrate 20 have the

vertical alignment films

15 and 25 as in the present embodiment, the shape anisotropic particles 32 are caused by the alignment regulating force of the

vertical alignment films

15 and 25. Is prevented from sticking to the substrate surface in a horizontal state. As the

vertical alignment films

15 and 25, a vertical alignment film for a liquid crystal display device in a VA (Vertical Alignment) mode (for example, a polyimide-based or polyamic acid-based vertical alignment film manufactured by JSR or Nissan Chemical) is preferably used. be able to. In order to vertically align a high dielectric constant positive liquid crystal material, it is preferable to use a vertical alignment film in which a relatively large number of hydrophobic structures such as alkyl groups and fluorine-containing groups are introduced into the side chain. The thickness of each of the

vertical alignment films

15 and 25 is, for example, 100 nm. Of course, it is not limited to this.

Here, a preferred driving method of the display device 100 according to the embodiment of the present invention will be described.

Each pixel of the display device 100 has a first potential in which a predetermined potential difference is given between the first electrode 11 and the third electrode 13, and the second electrode 12 and the third electrode 13 have substantially the same potential. A predetermined potential difference is applied between the second electrode 12 and the third electrode 13 and the first electrode 11 and the third electrode 13 are substantially the same (the state of FIG. 6A). It is preferable that the second state (the state of FIG. 6B) which is a potential can be switched and exhibited, and when the arrangement of the strong electric field region SR and the weak electric field region WR is switched, the first state and the first state are changed. It is preferable that the state 2 is switched. By performing such driving, the fringe electric field due to the potential difference between the first electrode 11 and the third electrode 13 and the fringe electric field due to the potential difference between the second electrode 12 and the third electrode 13 are alternately (complementarily). Since it is turned on and off (that is, when one fringe electric field is generated, the other fringe electric field is not generated), it is possible to drive efficiently. Moreover, the following effects can also be acquired by performing such a drive.

The applicant of the present application proposes a technique for realizing brighter display in a display device (optical device) including an optical layer containing shape anisotropic particles in International Publication No. 2015/098184. The entire disclosure of WO 2015/098184 is incorporated herein by reference.

In International Publication No. 2015/098184, in order to increase the ratio (existence probability) of shape anisotropic particles whose orientation direction changes according to the application of voltage, the voltage applied to the optical layer is relatively It has been proposed to use an oscillating voltage that alternately has a first period having a large absolute value and a second period having a relatively small absolute value. By making the voltage applied to the optical layer an oscillating voltage, the medium can be perturbed, thereby increasing the proportion of shape-anisotropic particles that change the desired orientation. Further, the smaller the absolute value of the oscillating voltage in the second period is relative to the absolute value of the oscillating voltage in the first period, the stronger the medium can be shaken, and the oscillating voltage in the second period is approximately 0 V. If so, the medium can be moved most strongly.

In the display device 100 according to the embodiment of the present invention, the fringe electric field due to the potential difference between the first electrode 11 and the third electrode 13 and the fringe electric field due to the potential difference between the second electrode 12 and the third electrode 13 are complementarily turned on / off. Since the medium 31 can be vibrated strongly by turning it off, the same effect as the method proposed in International Publication No. 2015/098184 can be obtained.

(Example)
Next, a description will be given of results (examples) of trial production of the display device 100 according to the embodiment of the present invention (that is, production of a test cell) and verification of the effect.

The test cell adopts an electrode structure as shown in FIG. 12 instead of active matrix driving. In the electrode structure shown in FIG. 12,

terminals

11t, 12t, and 13t are provided at the respective ends of the first electrode 11, the second electrode 12, and the third electrode 13. A voltage having a desired waveform was input from the arbitrary waveform generator to the first electrode 11, the second electrode 12, and the third electrode 13 via the

terminals

11t, 12t, and 13t.

In the test cell, the thickness (cell gap) of the display medium layer 30 is 15 μm. The medium 31 is a positive liquid crystal material (manufactured by Merck & Co., Inc.) having a dielectric anisotropy Δε of 20.4. The average particle diameter of the shape anisotropic particles 32 is 7 μm, and the content of the shape anisotropic particles 32 in the display medium layer 30 is 6% by weight. The

substrates

10a and 20a are glass substrates, respectively. Each of the first electrode (first upper layer electrode) 11 and the second electrode (second upper layer electrode) 12 has a comb-tooth shape. The third electrode (lower layer electrode) 13 has a plurality of slits 13s. The fourth electrode (counter electrode) 21 is a solid electrode. Each of the first electrode 11, the second electrode 12, the third electrode 13, and the fourth electrode 21 is made of IZO and has a thickness of 100 nm. The width w ₁ of the branch portion 11a of the first electrode 11 and the width w ₂ of the branch portion 12a of the second electrode 12 are each 3 μm, and the inter-electrode distance g is 10 μm. The insulating layer 14 is made of SiNx and has a thickness of 350 nm. The overcoat layer 22 is formed of a photoresist (manufactured by Toppan Printing Co., Ltd.) having a relative dielectric constant εr = 3.4, and has a thickness of 3 μm. The

vertical alignment films

15 and 25 are polyamic acid-based vertical alignment films (manufactured by Nissan Chemical Industries) having a surface energy of 35 mJ / m ² .

13 (a) shows, the potential V ₁ of the first electrode 11 in the present embodiment, the potential V ₂ of the second electrode 12, a timing chart showing the potential V ₄ in the potential V ₃ and the fourth electrode 21 of the third electrode 13 It is. As shown in FIG. 13 (a), the potential V ₂ of the potentials V ₁ and second electrode 12 of the first electrode 11 is a rectangular wave having a period of four frames, 0V for each frame within one period, Varies with 10V, 0V, and -10V. However, the potential V ₁ of the first electrode 11 and the potential V ₂ of the second electrode 12, are out of one frame phase. The potential V ₃ and the potential V ₄ of the fourth electrode 21 of the third electrode 13 is much 0V (ground potential).

FIG. 13B shows the voltage (potential difference) | V ₁ −V ₃ | between the first electrode 11 and the third electrode 13 and the voltage (potential difference) between the second electrode 12 and the third electrode 13 in this embodiment. 12 is a timing chart showing | V ₂ −V ₃ | and a voltage (potential difference) | V ₁ −V ₂ | between the first electrode 11 and the second electrode 12. As shown in FIG. 13 (b), between the first electrode 11 and the third electrode 13 voltage | V ₁ -V ₃ | and between the second electrode 12 and the third electrode 13 voltage | V ₂ -V ₃ | of When one is 10V, the other is 0V. Therefore, when a fringe electric field (corresponding to 10 V) is generated due to the potential difference between the first electrode 11 and the third electrode 13, no fringe electric field is generated due to the potential difference between the second electrode 12 and the third electrode 13. In addition, when a fringe electric field (corresponding to 10 V) is generated due to a potential difference between the second electrode 12 and the third electrode 13, no fringe electric field is generated due to a potential difference between the first electrode 11 and the third electrode 13. . As shown in FIG. 13B, the voltage | V ₁ −V ₂ | between the first electrode 11 and the second electrode 12 is always 10V. Therefore, a lateral electric field (equivalent to 10 V) due to a potential difference between the first electrode 11 and the second electrode 12 is always generated.

When the potential shown in FIG. 13A is applied to the first electrode 11, the second electrode 12, the third electrode 13, and the fourth electrode 21 (that is, the voltage shown in FIG. When applied between the third electrodes 13, between the second electrode 12 and the third electrode 13, and between the first electrode 11 and the second electrode 12, each pixel is shown on the left side of FIG. The state shown on the right side and the state shown on the right side are switched for each frame. Therefore, when time averaged over a plurality of frames, the fringe electric field affects both the vicinity of the first electrode 11 and the vicinity of the second electrode 12 as virtually shown in FIG. Can be covered with the shape anisotropic particles 32 whose orientation has been changed.

15A, 15B, and 15C are optical microscope images of the display medium layer 30 in the example. 15A shows a state (initial state) where no electric field is applied to the display medium layer 30, and FIGS. 15B and 15C show a horizontal electric field and a fringe electric field (FIG. 13) on the display medium layer 30, respectively. (According to the potential shown in (a)) shows a state after application for a predetermined time. FIGS. 15A and 15B are images when focusing on the first substrate 10 side, and FIG. 15C is an image when focusing on the second substrate 20 side. FIG. 15 (d) is a diagram schematically showing the state of FIG. 15 (a), and FIG. 15 (e) is a diagram schematically showing the states of FIGS. 15 (b) and (c). is there.

15A shows that many shape anisotropic particles 32 are vertically aligned in the initial state (see also FIG. 15D). Further, FIG. 15B shows that many shape anisotropic particles 32 are horizontally oriented after the lateral electric field and the fringe electric field are applied for a predetermined time (see also FIG. 15E). Further, from FIG. 15C, there are almost no shape anisotropic particles 32 whose orientation direction has not changed on the counter substrate 20 side (there are almost no shape anisotropic particles 32 in focus). It can be seen that the orientation direction of many shape anisotropic particles 32 changes. In the state shown in FIGS. 15B and 15C, the reflectance (Y value) of the SCE method was measured and found to be 41.5%.

As described above, the arrangement of the strong electric field region SR and the weak electric field region WR in the electric field distribution is exchanged one or more times within the period in which the same display is performed, so that the light use efficiency can be increased and a brighter display can be achieved. Can be realized.

FIG. 16 shows the first to ninth frames (specifically, at

time points

0, 17, 50, 67, 83, 100, and 133 msec) after applying the horizontal electric field and the fringe electric field to the display medium layer 30 in the embodiment. An optical microscope image is shown. FIG. 16 also schematically shows cross sections A and B (cross sections corresponding to lines 16A-16A ′ and 16B-16B ′ in the optical microscope image, respectively) at each time point. Further, in FIG. 16, the potential V ₁ of the first electrode 11, the potential V ₂ of the second electrode 12 also shows a timing chart of the potential V ₄ in the potential V ₃ and the fourth electrode 21 of the third electrode 13.

As can be seen from FIG. 16, in the test cell, the shape anisotropic particles 32 are gradually horizontally oriented over about nine frames after application of the electric field. The response time (rise time) was about 133 msec.

(Verification of comparative example)
Subsequently, using the above-described test cell, driving different from that of the display device 100 according to the embodiment of the present invention (the arrangement of the strong electric field region SR and the weak electric field region WR in the electric field distribution in the period during which the same display is performed is performed). The result of verifying an example (Comparative Examples 1 to 4) in which driving without replacement is performed will be described.

(Comparative Example 1)
17, the potential V ₁ of the first electrode 11 of Comparative Example 1, the potential V ₂ of the second electrode 12 is a timing chart showing the potential V ₄ in the potential V ₃ and the fourth electrode 21 of the third electrode 13. As shown in FIG. 17, the potential V ₂ of the potentials V ₁ and second electrode 12 of the first electrode 11 is a rectangular wave having a period of 2 frames, 5V every frame in one cycle, and -5V Change. However, the potential V ₁ of the first electrode 11 and the potential V ₂ of the second electrode 12, are out of one frame phase. The potential V ₃ and the potential V ₄ of the fourth electrode 21 of the third electrode 13 is much 0V (ground potential). That is, the potential V ₃ of the third electrode 13 is always an intermediate potential between the potential V ₂ of the potentials V ₁ and the second electrode 12 of the first electrode 11. Therefore, it can be said that Comparative Example 1 is the same drive as that of the liquid crystal display device 900 of Patent Document 4.

When the potential shown in FIG. 17 is applied to the first electrode 11, the second electrode 12, the third electrode 13, and the fourth electrode 21, a lateral electric field corresponding to 10 V is applied to the display medium layer 30 as shown in FIG. And a fringe electric field equivalent to 5V is generated.

Thus, in Comparative Example 1, the fringe electric field is weaker than in the Example. For this reason, the entire substrate surface cannot be covered with the shape-anisotropic particles 32 whose orientation has been changed, and the light utilization efficiency is reduced.

19A, 19B, and 19C are optical microscope images of the display medium layer 30 in Comparative Example 1. FIG. FIG. 19A shows a state (initial state) where no electric field is applied to the display medium layer 30, and FIGS. 19B and 19C show a horizontal electric field and a fringe electric field (FIG. 17) on the display medium layer 30, respectively. Shows the state after application for a predetermined time. FIGS. 19A and 19B are images when the first substrate 10 is focused, and FIG. 19C is an image when the second substrate 20 is focused. FIG. 19 (d) is a diagram schematically showing the state of FIG. 19 (a), and FIG. 19 (e) is a diagram schematically showing the states of FIGS. 19 (b) and (c). is there.

FIG. 19A shows that many shape anisotropic particles 32 are vertically aligned in the initial state (see also FIG. 19D). Further, from FIG. 19B, after the lateral electric field and the fringe electric field are applied for a predetermined time, although there are horizontally-oriented anisotropic particles 32, as compared with the embodiment (see FIG. 15B). And the number thereof is small (see also FIG. 19 (e)). Further, from FIG. 19C, there are a large number of shape anisotropic particles 32 whose orientation direction has not changed on the counter substrate 20 side (there are many shape anisotropic particles 32 in focus). I understand.

(Comparative Example 2)
20, the potential V ₁ of the first electrode 11 of Comparative Example 2, the potential V ₂ of the second electrode 12 is a timing chart showing the potential V ₄ in the potential V ₃ and the fourth electrode 21 of the third electrode 13. As shown in FIG. 20, the potential V ₂ of the potentials V ₁ and second electrode 12 of the first electrode 11 is a rectangular wave having a period of 2 frames, 10V for each frame within one period, and -10V Change. However, the potential V ₁ of the first electrode 11 and the potential V ₂ of the second electrode 12, are out of one frame phase. The potential V ₃ and the potential V ₄ of the fourth electrode 21 of the third electrode 13 is much 0V (ground potential). That is, the potential V ₃ of the third electrode 13 is always an intermediate potential between the potential V ₂ of the potentials V ₁ and the second electrode 12 of the first electrode 11. Therefore, it can be said that the comparative example 2 is also the same drive as the drive of the liquid crystal display device 900 of Patent Document 4.

When the potential shown in FIG. 20 is applied to the first electrode 11, the second electrode 12, the third electrode 13, and the fourth electrode 21, a lateral electric field equivalent to 20 V is applied to the display medium layer 30 as shown in FIG. 21. And a fringe electric field equivalent to 10V is generated.

Thus, in Comparative Example 2, the lateral electric field and the fringe electric field are stronger than in Comparative Example 1. However, the entire substrate surface could not be covered with the shape-anisotropic particles 32 whose orientation was changed, and the light utilization efficiency could not be sufficiently improved.

22A, 22B, and 22C are optical microscope images of the display medium layer 30 in Comparative Example 2. FIG. 22A shows a state (initial state) where no electric field is applied to the display medium layer 30, and FIGS. 22B and 22C show a lateral electric field and a fringe electric field (FIG. 20) on the display medium layer 30. Shows the state after application for a predetermined time. 22A and 22B are images when focusing on the first substrate 10 side, and FIG. 22C is an image when focusing on the second substrate 20 side. FIG. 22 (d) is a diagram schematically showing the state of FIG. 22 (a), and FIG. 22 (e) is a diagram schematically showing the states of FIGS. 22 (b) and (c). is there.

22A shows that many shape anisotropic particles 32 are vertically aligned in the initial state (see also FIG. 22D). Further, from FIG. 22B, after the lateral electric field and the fringe electric field are applied for a predetermined time, although there are the shape anisotropic particles 32 that are horizontally oriented, as compared with the embodiment (see FIG. 15B). And the number is small (see also FIG. 22E). Furthermore, from FIG. 22C, there are a large number of shape anisotropic particles 32 whose orientation direction has not changed on the counter substrate 20 side (there are many shape anisotropic particles 32 in focus). I understand.

(Comparative Example 3)
23, the potential V ₁ of the first electrode 11 of Comparative Example 3, the potential V ₂ of the second electrode 12 is a timing chart showing the potential V ₄ in the potential V ₃ and the fourth electrode 21 of the third electrode 13. As shown in FIG. 23, the potential V ₁ of the first electrode 11 is a rectangular wave with a period of 4 frames, and changes to 10 V, 0 V, −10 V, and 0 V for each frame within one period. The potential V ₂ of the second electrode 12, the potential V ₃ and the potential V ₄ of the fourth electrode 21 of the third electrode 13 is much 0V (ground potential).

When the potential shown in FIG. 23 is applied to the first electrode 11, the second electrode 12, the third electrode 13, and the fourth electrode 21, each pixel has a horizontal equivalent to 10 V on the display medium layer 30 as shown in FIG. 24. A state in which an electric field and a fringe electric field equivalent to 10 V are generated and a state in which no electric field is generated in the display medium layer 30 (not shown) are switched for each frame.

Also in Comparative Example 3, since the arrangement of the strong electric field region SR and the weak electric field region WR is not interchanged within the period during which the same display is performed, the shape anisotropic particles 32 gather in the region where the electric field strength is high. To parallel orientation. Therefore, the entire substrate surface cannot be covered with the shape anisotropic particles 32 whose orientation has been changed.

25A, 25B, and 25C are optical microscope images of the display medium layer 30 in Comparative Example 3. FIG. 25A shows a state (initial state) where no electric field is applied to the display medium layer 30, and FIGS. 25B and 25C show a lateral electric field and a fringe electric field (FIG. 23) in the display medium layer 30. Shows the state after application for a predetermined time. FIGS. 25A and 25B are images when focusing on the first substrate 10 side, and FIG. 25C is an image when focusing on the second substrate 20 side. FIG. 25 (d) is a diagram schematically showing the state of FIG. 25 (a), and FIG. 25 (e) is a diagram schematically showing the states of FIGS. 25 (b) and (c). is there.

FIG. 25 (a) shows that many shape anisotropic particles 32 are vertically aligned in the initial state (see also FIG. 25 (d)). Further, from FIG. 25B, after the lateral electric field and the fringe electric field are applied for a predetermined time, there are the shape anisotropic particles 32 that are horizontally oriented, but compared with the example (see FIG. 15B). And the number is small (see also FIG. 25 (e)). Furthermore, from FIG. 25C, there are a large number of shape anisotropic particles 32 whose orientation direction has not changed on the counter substrate 20 side (there are many shape anisotropic particles 32 in focus). I understand. When the reflectance (Y value) of the SCE method was measured in the state shown in FIGS. 25B and 25C, it was 28.9%, which was lower than the reflectance (41.5%) of the example. .

(Comparative Example 4)
26, the potential V ₁ of the first electrode 11 of Comparative Example 4, the potential V ₂ of the second electrode 12 is a timing chart showing the potential V ₄ in the potential V ₃ and the fourth electrode 21 of the third electrode 13. As shown in FIG. 26, the potential V ₂ of the potentials V ₁ and second electrode 12 of the first electrode 11 is a rectangular wave having a period of four frames, 10V for each frame within one period, 0V, - Varies with 10V and 0V. The potential V ₁ of the first electrode 11 and the potential V ₂ of the second electrode 12, the phase is the same. The potential V ₃ and the potential V ₄ of the fourth electrode 21 of the third electrode 13 is much 0V (ground potential).

When the potential shown in FIG. 26 is applied to the first electrode 11, the second electrode 12, the third electrode 13, and the fourth electrode 21, each pixel has a fringe equivalent to 10V on the display medium layer 30 as shown in FIG. A state in which an electric field is generated and a state in which no electric field is generated in the display medium layer 30 (not shown) are switched for each frame.

Also in Comparative Example 4, since the arrangement of the strong electric field region SR and the weak electric field region WR is not interchanged within the period during which the same display is performed, the shape anisotropic particles 32 are only in the region where the electric field strength is strong. The alignment does not change in a region that is parallel and has a low electric field strength (the center between the first electrode 11 and the second electrode 12). Therefore, the entire substrate surface cannot be covered with the shape anisotropic particles 32 whose orientation has been changed.

28A, 28B, and 28C are optical microscope images of the display medium layer 30 in Comparative Example 4. FIG. FIG. 28A shows a state (initial state) where no electric field is applied to the display medium layer 30, and FIGS. 28B and 28C show a lateral electric field and a fringe electric field (FIG. 26) on the display medium layer 30, respectively. Shows the state after application for a predetermined time. FIGS. 28A and 28B are images when focusing on the first substrate 10 side, and FIG. 28C is an image when focusing on the second substrate 20 side. FIG. 28 (d) is a diagram schematically showing the state of FIG. 28 (a), and FIG. 28 (e) is a diagram schematically showing the states of FIGS. 28 (b) and (c). is there.

FIG. 28 (a) shows that many shape anisotropic particles 32 are vertically aligned in the initial state (see also FIG. 28 (d)). Further, from FIG. 28 (b), after the fringe electric field is applied for a predetermined time, there are the horizontally oriented shape anisotropic particles 32, but the number thereof compared to the example (see FIG. 15 (b)). (See also FIG. 28 (e)). Further, from FIG. 28C, there are a large number of shape anisotropic particles 32 whose orientation direction has not changed on the counter substrate 20 side (there are many shape anisotropic particles 32 in focus). I understand. When the SCE reflectivity (Y value) was measured in the state shown in FIGS. 28B and 28C, it was 31.0%, which was lower than the reflectivity (41.5%) of the example. .

As described above, if the arrangement of the strong electric field region SR and the weak electric field region WR in the electric field distribution is not interchanged within the same display period, the light use efficiency cannot be increased.

(About shape anisotropic particles)
As described above, the shape anisotropic particle 32 is not particularly limited in its specific shape and material as long as the projected area onto the substrate surface changes according to the applied voltage (direction of the applied electric field). The shape anisotropic particles 32 may have a flake shape (flaky shape), a cylindrical shape, an oval shape, or the like. From the viewpoint of realizing a high contrast ratio, the shape anisotropic particle 32 preferably has a shape such that the ratio of the maximum projected area to the minimum projected area is 2: 1 or more.

As a material of the shape anisotropic particle 32, a metal material, a semiconductor material, a dielectric material, and a composite material thereof can be used. The shape anisotropic particles 32 may be a dielectric multilayer film or may be formed from a cholesteric resin material. When a metal material is used as the material for the shape anisotropic particles 32, an insulating layer (dielectric layer) is preferably formed on the surface of the shape anisotropic particles 32. Although the dielectric constant of a single metal is an imaginary number, by forming an insulating layer (for example, a resin layer or a metal oxide layer) on the surface, the shape anisotropic particles 32 formed of a metal material can be handled as a dielectric. it can. In addition, since the insulating layer is formed on the surface, an effect of preventing conduction due to contact between the shape anisotropic particles 32 formed of a metal material, aggregation due to physical interaction, and the like can be obtained. As such shape anisotropic particles 32, for example, aluminum flakes whose surfaces are coated with a resin material (for example, acrylic resin) can be used. The aluminum flake content of the display medium layer 30 is, for example, 3% by weight. Alternatively, aluminum flakes having an SiO ₂ layer formed on the surface, aluminum flakes having an aluminum oxide layer formed on the surface, or the like can also be used. Of course, a metal material other than aluminum may be used as the metal material. Further, the shape anisotropic particles 32 may be colored.

The length of the shape anisotropic particles 32 is not particularly limited, but is preferably 4 μm or more and 10 μm or less. If the length of the shape anisotropic particles 32 exceeds 10 μm, the shape anisotropic particles 32 may be difficult to move. On the other hand, when the length of the shape anisotropic particles 32 is less than 4 μm, it may be difficult to produce the shape anisotropic particles 32 or the reflective performance of the shape anisotropic particles 32 may be insufficient. Further, in the reflective display device as in the present embodiment, when it is desired to cover the substrate surface with the shape anisotropic particles 32 in the horizontal alignment state in order to obtain a high reflectance, the length of the shape anisotropic particles 32 is increased. It is preferable that the pitch be equal to or greater than the electrode pitch p (see FIG. 2). The thickness of the shape anisotropic particle 32 is not particularly limited. However, since the transmittance of the display medium layer 30 in the transparent state can be increased as the thickness of the shape anisotropic particles 32 is smaller, the thickness of the shape anisotropic particles 32 is larger than the inter-electrode distance g. It is preferably small (for example, 4 μm or less), and more preferably light wavelength or less (for example, 0.5 μm or less).

The specific gravity of the shape anisotropic particles 32 is preferably 11g / cm ³ or less, more preferably 3 g / cm ³ or less, further preferably the specific gravity substantially equal to that of the medium 31. This is because if the specific gravity of the shape anisotropic particles 32 is significantly different from the specific gravity of the medium 31, there may be a problem that the shape anisotropic particles 32 settle or float. From the viewpoint of increasing the effect of moving the shape anisotropic particles 32 by the peristaltic motion of the medium 31, the shape anisotropic particles 32 are preferably light.

(Other configurations)
In the above description, the configuration in which the first substrate 10 that is an active matrix substrate is arranged on the back side is illustrated, but the arrangement of the first substrate 10 is not limited to this. The first substrate 10 may be disposed on the front side. Since the first substrate 10 that is an active matrix substrate includes components formed from a light-shielding material, if the configuration in which the first substrate 10 is disposed on the back side is adopted, the shape anisotropic particles 32 The reflection effect can be used to the maximum.

In the above description, the reflective display device 100 has been described as an example. However, the embodiment of the present invention is also suitably used for a transmissive display device. In the transmissive display device, a light absorption layer (the light absorption layer 16 illustrated in FIG. 1 and the like) is not provided on the back substrate. In a transmissive display device, an illumination element (backlight) that irradiates light to the display panel is provided.

Furthermore, in the above description, the display device 100 in which the display medium layer 30 includes the shape anisotropic particles 32 has been exemplified. However, in the embodiment of the present invention, the display medium layer whose optical characteristics change according to the applied electric field. In particular, the display medium layer can be suitably used for a display device in which the response time of the display medium layer is longer than the switching period of the arrangement of the strong electric field region and the weak electric field region. For example, in the embodiment of the present invention, similarly to a display device including shape anisotropic particles in a display medium layer, a substance for changing optical characteristics is mixed in a liquid or gas, and the movement of the substance is controlled by an electric field. The electrophoretic display device to be controlled, the electronic powder fluid (toner) display device, and the electrowetting display device are also preferably used. Alternatively, in the embodiment of the present invention, even in a liquid crystal display device or the like in which the medium itself of the display medium layer can change the optical characteristics, the liquid crystal orientation switching speed (response speed) is sufficiently slower than the electric field distribution arrangement switching period. For example, it is suitably used.

According to the embodiment of the present invention, it is possible to suppress a decrease in light utilization efficiency due to a weak electric field region in a display device including a display medium layer whose optical characteristics change according to an applied electric field. The embodiment of the present invention is preferably used for, for example, a display device including a display medium layer including shape anisotropic particles.

DESCRIPTION OF SYMBOLS 10 1st board | substrate 10a board | substrate 11 1st electrode (1st upper layer electrode)
11a Branch portion of the first electrode 11b Trunk portion of the first electrode 12 Second electrode (second upper layer electrode)
12a Branch portion of second electrode 12b Trunk portion of second electrode 13 Third electrode (lower layer electrode)
13s Slit of third electrode 14 Insulating

layer

15, 25 Vertical alignment film 16 Light absorbing layer 17 Further insulating layer 20 Second substrate 20a Substrate 21 Fourth electrode (counter electrode)
22 Dielectric layer (overcoat layer)
30 Display medium layer (optical layer)
31 Medium (Liquid Crystal Material)
32 shape anisotropic particle 100 display device GL gate wiring SL1 first source wiring SL2 second source wiring SL3 third source wiring SR strong electric field region t1 first thin film transistor t2 second thin film transistor t3 third thin film transistor WR weak electric field region

Claims

A display device having pixels,
A first substrate and a second substrate provided to face each other;
A display medium layer provided between the first substrate and the second substrate, the display medium layer having optical characteristics that change in accordance with an applied electric field,
When an electric field is applied to the display medium layer, the pixel includes a first region in which the electric field has a first electric field strength and a second region in which the electric field has a second electric field strength that is weaker than the first electric field strength. An electric field distribution arranged along the in-plane direction of the display medium layer;
The display device in which the arrangement of the first region and the second region in the electric field distribution is switched one or more times within a period in which the same display is performed in the pixel.
The display device according to claim 1, wherein a period in which the arrangement of the first region and the second region is switched is an integral multiple of a time corresponding to one frame.
The first substrate includes a first electrode and a second electrode which are provided in the pixel and can be given different potentials;
The display device according to claim 1, wherein each of the first electrode and the second electrode has a comb shape.
4. The display device according to claim 3, wherein a lateral electric field is generated in the display medium layer by the first electrode and the second electrode.
The display device according to claim 3 or 4, wherein when the arrangement of the first region and the second region is switched, the potential of the first electrode and the potential of the second electrode are switched.
6. The display device according to claim 3, wherein the first substrate further includes a third electrode provided below the first electrode and the second electrode via an insulating layer.
The display device according to claim 6, wherein a fringe electric field is generated in the display medium layer by the first electrode or the second electrode and the third electrode.
The pixel has a first state in which a predetermined potential difference is given between the first electrode and the third electrode, and the second electrode and the third electrode have substantially the same potential, A predetermined potential difference is given between the second electrode and the third electrode, and the first electrode and the third electrode are switched between a second state in which the potential is substantially the same. Can
The display device according to claim 6 or 7, wherein the first state and the second state are switched when the arrangement of the first region and the second region is switched.
The display device according to claim 6, wherein the second substrate has a fourth electrode facing the first electrode, the second electrode, and the third electrode.
The display device according to claim 8, wherein a vertical electric field is generated in the display medium layer by the first electrode, the second electrode, the third electrode, and the fourth electrode.
The first substrate further includes a first thin film transistor electrically connected to the first electrode and a second thin film transistor electrically connected to the second electrode. The display device described.
12. The display device according to claim 1, wherein a response time of the display medium layer is longer than a cycle in which the arrangement of the first region and the second region is switched.
The display device according to claim 1, wherein the display medium layer includes a medium and shape anisotropic particles dispersed in the medium and having shape anisotropy.
14. The display device according to claim 13, wherein the medium includes a liquid crystal material.
15. The display device according to claim 14, wherein at least one of the first substrate and the second substrate has a vertical alignment film that is provided on the display medium layer side and vertically aligns liquid crystal molecules contained in the liquid crystal material.