Display device

Abstract

To provide a display device with high response speed and brightness.SOLUTION: A display device includes a plurality of scanning lines, a plurality of signal lines, a plurality of pixels, and a common electrode. The plurality of pixels has a shape of a square of which length in a first direction is the same as length in a second direction. A trunk portion extends along the first direction, each of the plurality of branch portions extends from the trunk portion along the second direction, a part of the signal lines extends along the first direction, the branch portions close to the signal lines among the plurality of branch portions are shielded by a light shielding region, which is the part of the signal lines, and the plurality of pixels are driven by a field sequential method.SELECTED DRAWING: Figure 9

Description

[Technical Field]

[0001] FIELD An embodiment of the present invention relates to a display device. [Background technology]

[0002] One example of a display device is an in-plane switching (IPS) mode liquid crystal display device. In an IPS mode liquid crystal display device, a pixel electrode and a common electrode are provided on one of a pair of substrates facing each other with a liquid crystal layer interposed therebetween, and the orientation of the liquid crystal molecules in the liquid crystal layer is controlled by utilizing a transverse electric field generated between these electrodes. Furthermore, among IPS mode liquid crystal display devices, an FFS (Fringe Field Switching) mode liquid crystal display device, in which the pixel electrode and the common electrode are arranged on different layers, has been put to practical use. In this liquid crystal display device, the orientation of the liquid crystal molecules is controlled by utilizing a fringe electric field generated between the pair of electrodes. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2023-139968 Summary of the Invention [Problem to be solved by the invention]

[0004] This embodiment provides a display device with high response speed and brightness. [Means for solving the problem]

[0005] A display device according to an embodiment includes: a plurality of scan lines extending along a first direction; a plurality of signal lines extending along a second direction intersecting the first direction; a plurality of pixels provided at intersections of the plurality of signal lines and the plurality of scanning lines; a common electrode having a slit including a trunk and a plurality of branches; Equipped with The shape of the plurality of pixels is a square shape having the same length in the first direction and the same length in the second direction, The stem extends along the first direction, Each of the plurality of branch portions extends from the trunk portion along the second direction, a portion of the signal line extends along the first direction; Among the plurality of branch portions, a branch portion close to the signal line is shielded from light by a light-shielding region that is a part of the signal line; The pixels are driven in a field sequential manner. [Brief explanation of the drawings]

[0006] [Figure 1] FIG. 1 is a diagram showing an example of an equivalent circuit of a display device. [Figure 2] FIG. 2 is a cross-sectional view showing an example of the structure of a display device. [Figure 3] FIG. 3 is a plan view showing the arrangement of pixels in a display device of a comparative example. [Figure 4] FIG. 4 is a plan view showing the configuration of a pixel of a comparative example. [Figure 5] FIG. 5 is a plan view showing the relationship between the slits and the liquid crystal molecules of the positive liquid crystal. [Figure 6] FIG. 6 is a plan view showing the relationship between the slits and the liquid crystal molecules of the negative liquid crystal. [Figure 7] FIG. 7 is a diagram showing the relationship between the branches of the slit and light transmission in the comparative example. [Figure 8] FIG. 8 is a diagram showing the relationship between the branches of the slit and light transmission in the comparative example. [Figure 9] FIG. 9 is a plan view showing the configuration of a pixel according to the embodiment. [Figure 10] FIG. 10 is a plan view showing the pixel electrode and the common electrode of the pixel. [Figure 11] FIG. 11 is a cross-sectional view showing the cross-sectional configuration of the pixel shown in FIG. 10 taken along line A1-A2. [Figure 12] FIG. 12 is a diagram showing the response speed of a pixel with respect to an applied voltage. DETAILED DESCRIPTION OF THE INVENTION

[0007] Hereinafter, each embodiment of the present invention will be described with reference to the drawings. The disclosure is merely an example, and appropriate modifications that a person skilled in the art can easily conceive while maintaining the gist of the invention are naturally included within the scope of the present invention. Furthermore, in order to clarify the explanation, the drawings may show the width, thickness, shape, etc. of each part schematically compared to the actual embodiment, but these are merely examples and are not intended to limit the interpretation of the present invention. Furthermore, in this specification and each drawing, elements similar to those described above with reference to the previous drawings may be designated by the same reference numerals, and detailed descriptions may be omitted as appropriate.

[0008] The embodiments described in this specification are not general but are embodiments that describe the same or corresponding special technical features of the present invention. Hereinafter, a display device according to an embodiment will be described in detail with reference to the drawings.

[0009] In this embodiment, the first direction X, the second direction Y, and the third direction Z are perpendicular to one another, but may intersect at an angle other than 90 degrees. The direction toward the tip of the arrow of the third direction Z is defined as up or upward, and the direction opposite to the direction toward the tip of the arrow of the third direction Z is defined as down or downward. The first direction X, the second direction Y, and the third direction Z may also be referred to as the X direction, the Y direction, and the Z direction, respectively.

[0010] Furthermore, when the terms "second member above the first member" and "second member below the first member" are used, the second member may be in contact with the first member or may be located apart from the first member. In the latter case, a third member may be interposed between the first and second members. On the other hand, when the terms "second member above the first member" and "second member below the first member" are used, the second member is in contact with the first member.

[0011] Furthermore, it is assumed that an observation position for observing the display device is located at the tip of the arrow in the third direction Z, and viewing from this observation position toward the XY plane defined by the first direction X and the second direction Y is called planar view. Viewing a cross section of the display device in the XZ plane defined by the first direction X and the third direction Z, or in the YZ plane defined by the second direction Y and the third direction Z, is called cross-sectional view.

[0012] [Embodiment 1] FIG. 1 is a diagram showing an example of an equivalent circuit of a display device. The display device DSP has a display area DA for displaying an image, and includes a plurality of pixels PX, a plurality of scanning lines GL, and a plurality of signal lines SL. The plurality of scanning lines GL and the plurality of signal lines SL intersect with each other. The display device DSP also has a driver DR1 and a driver DR2 outside the display area DA. The plurality of scanning lines GL are electrically connected to the driver DR1. The plurality of signal lines SL are electrically connected to the driver DR2. The drivers DR1 and DR2 are controlled by a control unit.

[0013] The pixel PX shown here is called a sub-pixel or color pixel, and corresponds to a pixel that displays, for example, red, green, blue, or white. The pixel PX is located at the intersection of a scan line GL and a signal line SL. The pixel PX is also defined by two scan lines GL and two signal lines SL.

[0014] Each pixel PX includes a switching element SW, a pixel electrode PE, and a common electrode CE facing the pixel electrode PE. The switching element SW is electrically connected to the scanning line GL and the signal line SL. The pixel electrode PE is electrically connected to the switching element SW. In other words, the pixel electrode PE is electrically connected to the signal line SL via the switching element SW. The common electrode CE is formed across multiple pixels PX. A common potential is applied to the common electrode CE.

[0015] The driver DR1 supplies a scan signal to each scan line GL. The driver DR2 supplies a video signal to each signal line SL. The switching element SW, electrically connected to the scan line GL to which the scan signal is supplied, conducts the signal line SL with the pixel electrode PE, and a voltage corresponding to the video signal supplied to the signal line SL is applied to the pixel electrode PE. The liquid crystal layer LC is driven by an electric field generated between the pixel electrode PE and the common electrode CE. More specifically, the electric field generated between the pixel electrode PE and the common electrode CE changes the orientation of the liquid crystal molecules in the liquid crystal layer LC from its initial orientation state when no voltage is applied. This operation displays an image in the display area DA.

[0016] FIG. 2 is a cross-sectional view showing an example of the structure of a display device. The display device DSP comprises a substrate SUB1, a substrate SUB2, and a liquid crystal layer LC held between the substrates SUB1 and SUB2.

[0017] The substrate SUB1 includes a base material BA1, insulating layers INS and DIE, and an alignment film AL1 in addition to the switching elements SW, pixel electrodes PE, and common electrodes CE. The substrate SUB1 also includes the scanning lines GL, signal lines SL, and drivers DR1 and DR2 shown in FIG. 1. The substrate BA1 is formed from a light-transmitting glass substrate or resin substrate. The substrate BA1 has a main surface S1A facing the substrate SUB2 and a main surface S1B opposite the main surface S1A.

[0018] The switching element SW is formed on the main surface S1A side of the base material BA1 and is covered with an insulating layer INS. In the example shown in FIG. 2, for the convenience of explaining the embodiment, the switching element SW is shown in a simplified form, and the scanning lines GL and signal lines SL are not shown. In practice, the insulating layer INS may include multiple insulating layers. The switching element SW includes semiconductor layers and various electrodes formed on these layers.

[0019] The pixel electrodes PE are formed on an insulating layer INS and are arranged for each of the pixels PX. The pixel electrodes PE are covered with an insulating layer DIE. The common electrode CE is provided across the pixels PX. The common electrode CE is formed on the insulating layer DIE and faces the pixel electrodes PE via the insulating layer DIE.

[0020] The pixel electrodes PE are electrically connected to the switching elements SW through contact holes CH that penetrate the insulating layer INS. The pixel electrodes PE and the common electrode CE are transparent electrodes made of a transparent conductive material such as indium tin oxide (ITO) or indium zinc oxide (IZO).

[0021] The alignment film AL1 covers the common electrode and is in contact with the liquid crystal layer LC. The alignment film AL1 is, for example, a photo-alignment film that has been subjected to a photo-alignment treatment.

[0022] The substrate SUB2 includes a base material BA2 and an alignment film AL2. The base material BA2 is formed from a light-transmitting glass base material, a resin base material, or the like. The base material BA2 has a main surface S2A facing the substrate SUB1 and a main surface S2B opposite to the main surface S2A.

[0023] The alignment film AL2 is provided in contact with the base material BA2 and is in contact with the liquid crystal layer LC. The alignment film AL2 is a photo-alignment film that has been subjected to a photo-alignment treatment, similar to the alignment film AL2. An insulating layer, a light-shielding layer facing the switching element SW, or the like may be provided between the alignment film AL2 and the base material BA2.

[0024] A polarizing plate PL1 is adhered to the main surface S1B of the base material BA1, and a polarizing plate PL2 is adhered to the main surface S2B of the base material BA2.

[0025] The display device DSP is driven by a field sequential method, which controls pixels so that multiple colors of light are transmitted from the same pixel at different times. For example, one frame period has multiple subframe (field) periods, and red, green, and blue pixels are selectively displayed in each subframe period. The pixels of each color displayed in this time-division manner are combined to form a multi-color display image that is visually recognized by the user.

[0026] In a display device DSP that operates using the field sequential method, it is necessary to drive the pixels at high speed, because if the pixels are not driven at high speed, flickering and other problems will occur in the displayed image, resulting in a deterioration in display quality.

[0027] Fig. 3 is a plan view showing the arrangement of pixels in a display device of the comparative example, which shows only the scanning lines GL and signal lines SL provided in the display area DA of the display device DSPr of the comparative example.

[0028] The multiple scanning lines GL extend along the first direction X and are arranged side by side along the second direction Y. The multiple signal lines SL extend along the second direction Y and are arranged side by side along the first direction X. The length (width) of each scanning line GL along the second direction Y is defined as width WG. The length (width) of each signal line SL along the first direction X is defined as width WS.

[0029] Each of the multiple pixels PX is provided in an area surrounded by two scanning lines GL and two signal lines SL. In Fig. 3, the pixels PX are indicated by dotted lines. The length of each of the multiple pixels PX along the first direction X is defined as length LX, and the length along the second direction Y is defined as length LY. The lengths LX and LY correspond to the pitches of the signal lines SL and scanning lines GL, respectively.

[0030] The width WG of the scanning line GL is longer than the width WS of the signal line SL. The length LX and the length LY of the pixel PX are approximately equal. Therefore, the pixel PX has a square shape.

[0031] The length LX and the length LY are, for example, 12.7 μm. The width WG of the scanning line GL is, for example, 8.0 μm. The width WS of the signal line SL may be, for example, 2.0 μm or more and 2.5 μm or less.

[0032] The area of ​​the pixel PX that does not overlap with the scanning line GL and the signal line SL is defined as the opening area OP. The lengths of the opening area OP along the first direction X and the second direction Y are defined as the length LOX and the length LOY, respectively. The length LOX may be, for example, 10.2 μm or more and 10.7 μm or less. The length LOY may be 4.7 μm or less.

[0033] Fig. 4 is a plan view showing the configuration of a pixel of a comparative example. The pixel PX of the display device DSPr shown in Fig. 4 includes half of each of two adjacent signal lines SL, one scanning line GL, and a common electrode CE. Note that Fig. 4 omits the illustration of switching elements and pixel electrodes.

[0034] The common electrode CE is provided with a slit CST. The slit CST includes a trunk portion CMK extending along the first direction X, a protrusion portion CPR protruding from the trunk portion CMK in the direction opposite to the second direction Y, and a branch portion CBR extending from the trunk portion CMK along the second direction Y. In other words, the extension direction of the protrusion portion CPR and the extension direction of the branch portion CBR are opposite directions. Each of the multiple protrusion portions CPR is arranged between adjacent branch portions CBR along the first direction X.

[0035] The protrusion CPR has a trapezoidal shape with an upper side shorter than a lower side. The lower side of the protrusion CPR is the side that is the boundary with the trunk CMK. The upper side of the protrusion CPR is the side that is spaced apart from the trunk CMK.

[0036] The branch CBR has a trapezoidal shape with its upper side longer than its lower side. The upper side of the branch CBR is the side that borders the trunk CMK. The lower side of the trunk CMK is the side that separates from the trunk CMK. The branch CBR can also be said to have a shape that tapers toward the lower tip, or a wedge shape.

[0037] The length (width) of the trunk portion CMK along the second direction Y is defined as length LMK. The length of the protrusion portion CPR along the second direction Y is defined as length LPR. The length LMK may be, for example, 0.5 μm or more and 1.5 μm or less, more specifically, 1.5 μm. The length LPR may be, for example, 0 μm or more and 0.5 μm or less, more specifically, 0.5 μm.

[0038] The length of the branch portion CBR along the second direction Y is defined as the length LBR. The pitch at which the branch portions CBR are arranged along the first direction X is defined as the pitch PBR. The length LBR may be, for example, 4.0 μm or more and 5.0 μm or less, more specifically, 4.7 μm. The pitch PBR may be, for example, 3.5 μm or more and 4.0 μm or less, more specifically, 4.0 μm.

[0039] Fig. 5 is a plan view showing the relationship between the slits and the liquid crystal molecules of the positive liquid crystal. Fig. 6 is a plan view showing the relationship between the slits and the liquid crystal molecules of the negative liquid crystal. In Figs. 5 and 6, the alignment direction of the alignment films AL1 and AL2 is defined as the alignment direction ORI. In Figs. 5 and 6, the alignment direction ORI is a direction parallel to the second direction Y.

[0040] Positive liquid crystal is a liquid crystal with positive dielectric anisotropy. Negative liquid crystal is a liquid crystal with negative dielectric anisotropy. The initial alignment direction of the liquid crystal molecules of positive liquid crystal is parallel to the alignment direction ORI, while the initial alignment direction of the liquid crystal molecules of negative liquid crystal is perpendicular to the alignment direction ORI.

[0041] 5 and 6, the left side of the slit CST on the paper surface is designated as side ED1, and the right side of the slit CST on the paper surface is designated as side ED2. In Fig. 5, when a voltage is applied to the common electrode CE, the liquid crystal molecules LCM near side ED1 rotate clockwise. The liquid crystal molecules near side ED2 rotate counterclockwise.

[0042] The upper side of the trunk CMK of the slit CST is called side MKU, and the lower side is called side MKD. The liquid crystal molecules LCM near side MKU that are aligned along the second direction Y with the liquid crystal molecules LCM near side ED1 rotate clockwise. The liquid crystal molecules LCM near side MKU that are aligned along the second direction Y with the liquid crystal molecules LCM near side ED2 rotate counterclockwise.

[0043] That is, the liquid crystal molecules LCM aligned along the second direction Y with the liquid crystal molecules LCM near the side ED1 rotate clockwise even when they are away from the side ED1. The liquid crystal molecules LCM aligned along the second direction Y with the liquid crystal molecules LCM near the side ED2 rotate counterclockwise even when they are away from the side ED2.

[0044] Even when a voltage is applied to the common electrode CE to generate an electric field, the liquid crystal molecules LCM arranged in the central regions of the branch portions CBR and the protrusion portions CPR do not rotate. Such regions where the liquid crystal molecules LCM do not rotate are referred to as regions NMV. In regions NMV, the liquid crystal molecules LCM do not rotate, so light does not pass through and the region becomes dark.

[0045] 7 and 8 are diagrams showing the relationship between the branches of the slits and light transmission in a comparative example. FIG. 7 is a plan view and a light transmission diagram when no branches are provided near the signal line SL. FIG. 8 is a plan view and a light transmission diagram when branches are provided near the signal line SL. In FIG. 8, the region of the branch CBR provided near the signal line SL in one pixel PX is referred to as region CBRea. The region of the branch CBR arranged in the adjacent pixel PX, facing region CBRea across the signal line SL, is referred to as region CBReb. The sum of the areas of region CBRea and region CBReb is equal to the area of ​​one branch CBR.

[0046] 7 and 8, more light is transmitted when no branch CBR is provided near the signal line SL (FIG. 7) than when a branch CBR is provided near the signal line SL (FIG. 8). In other words, the pixel PX shown in FIG. 7 is brighter than the pixel PX shown in FIG. 8. This is thought to be because the pitch of the branch CBR changes in the slit CST shown in FIG. 8, which affects the liquid crystal alignment in the slit CST.

[0047] However, if the branch portions CBR are not provided, it is difficult to control the liquid crystal molecules LCM near the signal lines SL, and the liquid crystal molecules LCM tend to rotate. Furthermore, at the boundaries between adjacent pixels PX, the branch portions CBR are not provided across the signal lines SL. Therefore, the pitch of the areas where the liquid crystal molecules LCM do not rotate becomes longer, and the rotation speed of the liquid crystal molecules LCM becomes slower.

[0048] If the rotation speed of the liquid crystal molecules LCM in the vicinity of the signal line SL slows down, a difference in rotation speed occurs between the liquid crystal molecules LCM rotating in the vicinity of the sides ED1 and ED2 of the branch portion CBR, which results in a difference in brightness between the region in the vicinity of the signal line SL and the region in the vicinity of the sides ED1 and ED2.

[0049] In this embodiment, a portion of the signal line SL is extended to shield the area where the rotation speed of the liquid crystal molecules LCM slows down, thereby making the brightness uniform within the pixel PX and the response speed high and uniform.

[0050] Fig. 9 is a plan view showing the configuration of a pixel according to the embodiment. The display device DSP shown in Fig. 9 differs from the display device DSPr shown in Fig. 4 in that part of the signal line SL functions as a light-shielding layer.

[0051] In Figure 9, for example, a portion of the signal line SL on the right side of the paper surface extends in the direction opposite to the first direction X, covering half of the branch CBR closest to the signal line SL. The region covering half of the branch CBR is defined as region SLS. Region SLS is formed in a rectangular shape. The length (width) of region SLS in the direction parallel to the first direction X is defined as width WLS.

[0052] As described above, for example, the region SLS, which is a part of the signal line SL on the left side of the paper, extends along the first direction X and covers half of the branch CBR closest to the signal line SL.

[0053] By not locating the branch CBR of the slit CST near the signal line SL, a pixel PX with high brightness can be realized. Furthermore, by providing a light-shielding region SLS near the signal line SL, the region where the liquid crystal molecules LCM rotate slowly can be shielded from light, thereby suppressing differences in brightness and the rotation speed of the liquid crystal molecules LCM within the pixel PX. As a result, it is possible to obtain a pixel PX with high brightness, uniform brightness within the pixel PX, and a high response speed.

[0054] Fig. 10 is a plan view showing a pixel electrode and a common electrode of a pixel. Fig. 11 is a cross-sectional view showing the cross-sectional configuration of the pixel shown in Fig. 10 taken along line A1-A2. Fig. 12 is a diagram showing the response speed of a pixel with respect to an applied voltage. That is, Fig. 12 is a plot of the response speed of the pixel PX shown in Figs. 10 and 11.

[0055] 10, the pixel electrode PE has a trunk portion PMK extending along a direction parallel to the first direction X, a protrusion portion PPR protruding from the trunk portion PMK in a direction opposite to the second direction Y, and a branch portion PED extending from the trunk portion PMK along the second direction Y. The protrusion portion PPR and the branch portion PED have a rectangular shape.

[0056] The length (width) of the trunk portion PMK along the second direction Y is defined as length LPMK. The length of the protrusion portion PPR along the second direction Y is defined as length LPPR. The length of the branch portion PED along the second direction Y is defined as length LPED. The length (width) of one branch portion PED along the first direction X is defined as width WPED. The pitch at which multiple branch portions PED are arranged along the first direction X is defined as pitch PPED.

[0057] In the example shown in FIG. 10, the length LPMK is, for example, 1.0 μm. The length LPPR is, for example, 1.0 μm. The length LPED is, for example, 4.5 μm. The width WPED is, for example, 1.5 μm. The pitch PPED is, for example, 4.0 μm.

[0058] 11, a pixel electrode PE is provided on a common electrode CE with an insulating layer DIE sandwiched therebetween. The common electrode CE and pixel electrode PE are formed of a transparent conductive material, more specifically, indium tin oxide. The insulating layer DIE is formed of, for example, an inorganic insulating material, more specifically, silicon nitride.

[0059] Fig. 12 is a diagram showing the relationship between the applied voltage and the response speed of the pixel PX shown in Fig. 10 and Fig. 11. In Fig. 12, the horizontal axis represents the applied voltage APV [V], and the vertical axis represents the response speed RPT [ms]. In the pixel PX shown in Fig. 12, when the temperature of the pixel PX is 25°C, the response speed RPT is 0.9 [ms] or more.

[0060] 9 is formed based on the pixels PX shown in Figures 10 to 12, the response speed of the pixels PX shown in Figure 9 will also be 0.9 ms or more. As described above, this embodiment makes it possible to obtain a display device DSP having pixels PX with uniform and high brightness and a high response speed.

[0061] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as defined in the claims.

[0062] For example, the light-shielding region SLS is not limited to the present embodiment in which the signal line SL is used, but may be formed so that the scanning line GL extends along the branch portion CBR of the slit CST, or may use another metal layer formed in a layer different from that of the scanning line GL and the signal line SL. Although not described in further detail, it is also possible to form a black matrix on the substrate SUB2, and to form the light-shielding layer SLS on the substrate SUB1 side or the substrate SUB2 side using a black resin like the black matrix. [Explanation of symbols]

[0063] CBR...branch, CE...common electrode, CMK...trunk, CPR...protrusion, CST...slit, DSP...display device, LCM...liquid crystal molecule, PE...pixel electrode, PX...pixel, SL...signal line, SLS...region.

Claims

1. a plurality of scan lines extending along a first direction; a plurality of signal lines extending along a second direction intersecting the first direction; a plurality of pixels provided at intersections of the plurality of signal lines and the plurality of scanning lines; a common electrode having a slit including a trunk and a plurality of branches; Equipped with the plurality of pixels have a square shape with the same length in the first direction and the same length in the second direction; The stem extends along the first direction, Each of the plurality of branch portions extends from the trunk portion along the second direction, a portion of the signal line extending along the first direction; Among the plurality of branch portions, a branch portion close to the signal line is shielded from light by a light-shielding region that is a part of the signal line; The display device, wherein the plurality of pixels are driven by a field sequential method.

2. The display device according to claim 1 , further comprising a plurality of protrusions extending from the trunk in a direction opposite to the direction in which the branch portions extend.

3. The display device according to claim 1 , wherein each of the plurality of branch portions has a trapezoidal shape with an upper side longer than a lower side.

4. The display device according to claim 2 , wherein each of the plurality of protrusions has a trapezoidal shape with a bottom side longer than an top side.

5. The display device according to claim 1 , wherein the light-shielding area has a rectangular shape.

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