Display device

Abstract

To provide a display device that performs voltage decrease in a polymer dispersion type liquid crystal layer, and is capable of suppressing reduction in scattering luminance.SOLUTION: A display device comprises a first display panel, a second display panel, and a first light source. The first display panel and the second display panel are arranged in contact with each other. A first polymer dispersion liquid crystal layer is provided between a first alignment layer and a second alignment layer. A second polymer dispersion liquid crystal layer is provided between a third alignment layer and a fourth alignment layer. A first thickness between the first alignment layer and the second alignment layer, and a second thickness between the third alignment layer and the fourth alignment layer are respectively 2 μm or less.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present embodiment relates to a display device. [Background technology]

[0002] 2. Description of the Related Art In recent years, display devices have been proposed that use polymer dispersed liquid crystal that is switchable between a scattering state in which incident light is scattered and a transmitting state in which incident light is transmitted. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6654014 [Patent Document 2] JP 2020-091389 A [Patent Document 3] JP 2020-086089 A Summary of the Invention [Problem to be solved by the invention]

[0004] The present embodiment provides a display device capable of lowering the voltage required for a polymer dispersed liquid crystal layer and suppressing a decrease in the brightness due to scattering. [Means for solving the problem]

[0005] A display device according to an embodiment includes: a first display panel including a first substrate, a second substrate, and a first polymer dispersed liquid crystal layer provided between the first substrate and the second substrate; a second display panel including a third substrate, a fourth substrate, and a second polymer dispersed liquid crystal layer provided between the third substrate and the fourth substrate; a first light source provided at an edge of the first display panel; Equipped with The first substrate is A plurality of first signal lines; A plurality of first scan lines; a plurality of first pixels defined by the plurality of first signal lines and the plurality of first scanning lines; a plurality of first switching elements provided in the plurality of first pixels; A first alignment film; Equipped with the second substrate includes a second alignment film facing the first alignment film, The third substrate is A plurality of second signal lines; A plurality of second scan lines; a plurality of second pixels partitioned by the plurality of second signal lines and the plurality of second scanning lines; a plurality of second switching elements provided in the plurality of second pixels; A third alignment film; Equipped with the fourth substrate includes a fourth alignment film facing the third alignment film, the first display panel and the second display panel are disposed in contact with each other, the first polymer dispersed liquid crystal layer is provided between the first alignment film and the second alignment film, the second polymer dispersed liquid crystal layer is provided between the third alignment film and the fourth alignment film, A distance between the first alignment film and the second alignment film is a first thickness; A distance between the third alignment film and the fourth alignment film is a second thickness; The first thickness and the second thickness are each 2 μm or less. [Brief description of the drawings]

[0006] [Figure 1] FIG. 1 is an exploded perspective view that illustrates a schematic configuration of a display device that includes two display panels. [Diagram 2] FIG. 2 is a cross-sectional view showing an example of a schematic configuration of a display device. [Diagram 3] FIG. 3 is a cross-sectional view showing an example of a schematic configuration of a display device. [Figure 4] FIG. 4 is a cross-sectional view showing an example of a schematic configuration of a display device. [Diagram 5]FIG. 5 is a cross-sectional view showing an example of a schematic configuration of a display device. [Figure 6] FIG. 6 is a plan view showing a configuration of pixels on a substrate. [Figure 7] FIG. 7 is an enlarged plan view showing an example of the switching element shown in FIG. [Figure 8] FIG. 8 is a cross-sectional view of the display panel shown in FIG. 7 taken along line A1-A2. [Figure 9] FIG. 9 is a diagram showing the relationship between the applied voltage and the scattering luminance with respect to the thickness of the liquid crystal layer. [Figure 10] FIG. 10 is an enlarged view of the area surrounded by the dotted line in FIG. [Figure 11] FIG. 11 is a diagram showing the relationship between the thickness of the liquid crystal layer and the threshold voltage. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0007] Hereinafter, each embodiment of the present invention will be described with reference to the drawings. Note that the disclosure is merely an example, and those who are skilled in the art can easily come up with appropriate modifications while maintaining the gist of the invention, which are naturally included in the scope of the present invention. In addition, in order to make the explanation clearer, the drawings may show the width, thickness, shape, etc. of each part in a schematic manner compared to the actual embodiment, but these are merely examples and do not limit the interpretation of the present invention. In addition, in this specification and each figure, elements similar to those described above with respect to the previous figures may be given the same reference numerals, and detailed explanations may be omitted as appropriate.

[0008] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The embodiments described in this specification are not general, but are embodiments describing the same or corresponding special technical features of the present invention.

[0009] In this embodiment, the first direction X, the second direction Y, and the third direction Z are perpendicular to each other, 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 called the X direction, the Y direction, and the Z direction, respectively.

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

[0011] Also, it is assumed that an observation position for observing the display device is located at the tip side of the arrow in the third direction Z, and a planar view refers to a view from this observation position toward the XY plane defined by the first direction X and the second direction Y. A cross-sectional view refers to a view of 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.

[0012] [Embodiment] Fig. 1 is an exploded perspective view showing a schematic configuration of a display device including two display panels. Fig. 1 shows a three-dimensional space defined by a first direction X, a second direction Y perpendicular to the first direction X, and a third direction Z perpendicular to the first direction X and the second direction Y.

[0013] As shown in FIG. 1, the display device DSP includes a first display panel PNL1 and a second display panel PNL2.

[0014] In one example, the first display panel PNL1 is rectangular. In the illustrated example, the short side EX of the first display panel PNL1 is parallel to the first direction X, and the long side EY of the first display panel PNL1 is parallel to the second direction Y. The third direction Z corresponds to the thickness direction of the first display panel PNL1. The main surface of the first display panel PNL1 is parallel to the XY plane defined by the first direction X and the second direction Y. The first display panel PNL1 has an effective area AA1 (display area) and a non-display area NDA1 located outside the effective area AA1. The non-display area NDA1 has a terminal area MT1 on which a driver IC and a flexible wiring board are mounted. In FIG. 1, the terminal area MT1 is indicated by diagonal lines.

[0015] The effective area AA1 is an area for displaying an image, and includes, for example, a plurality of pixels PX1 arranged in a matrix along a first direction X and a second direction Y. As shown enlarged in Fig. 1, each pixel PX1 is arranged in an area defined by scanning lines GL and signal lines SL, and includes a switching element SW, a pixel electrode PE, a common electrode CE, a liquid crystal layer LC, etc.

[0016] The switching elements SW are formed of, for example, thin film transistors (TFTs) and are electrically connected to the scanning lines GL and the signal lines SL. The scanning lines GL are electrically connected to the switching elements SW in each of the pixels PX1 aligned in the first direction X. The signal lines SL are electrically connected to the switching elements SW in each of the pixels PX1 aligned in the second direction Y. The pixel electrodes PE are electrically connected to the switching elements SW. Each of the pixel electrodes PE faces a common electrode CE, and the liquid crystal layer LC is driven by an electric field generated between the pixel electrodes PE and the common electrode CE. The capacitance CS is formed, for example, between an electrode having the same potential as the common electrode CE and an electrode having the same potential as the pixel electrode PE.

[0017] The liquid crystal layer LC includes a polymer dispersed liquid crystal (PDLC) including a polymer and liquid crystal molecules. In one example, the polymer is a liquid crystal polymer. The polymer is formed in stripes extending in one direction. The liquid crystal molecules are dispersed in the gaps between the polymer and are oriented such that their major axes are aligned along the direction in which the stripes extend. The polymer and the liquid crystal molecules each have optical anisotropy or refractive index anisotropy. The response of the polymer to an electric field is lower than the response of the liquid crystal molecules to an electric field.

[0018] In one example, the orientation direction of the polymer hardly changes regardless of the presence or absence of an electric field. On the other hand, the orientation direction of the liquid crystal molecules changes in response to an electric field when a high voltage equal to or greater than a threshold value is applied to the liquid crystal layer LC. When no voltage is applied to the liquid crystal layer LC, the optical axes of the polymer and the liquid crystal molecules are parallel to each other, and light incident on the liquid crystal layer LC is transmitted through the liquid crystal layer LC with almost no scattering within the liquid crystal layer LC (transparent state). When a voltage is applied to the liquid crystal layer LC, the optical axes of the polymer and the liquid crystal molecules cross each other, and light incident on the liquid crystal layer LC is scattered within the liquid crystal layer LC (scattered state).

[0019] The terminal region MT1 extends along the short side EX of the first display panel PNL1. A terminal portion is formed in the terminal region MT1, and the first display panel PNL1 is electrically connected to an external device such as a flexible wiring board via the terminal portion.

[0020] The second display panel PNL2 has basically the same configuration as the first display panel PNL1. The second display panel PNL2 includes a plurality of pixels PX2 arranged in a matrix along the first direction X and the second direction Y in an effective area AA2 (display area). The configuration of the pixels PX2 is the same as that of the pixels PX1, and therefore the detailed description thereof will be omitted by citing the above. In this embodiment, the pixels PX1 and PX2 have the same configuration and are also the same size. More specifically, the pixels PX1 and PX2 have the same layer configuration. Furthermore, the pixels PX1 and PX2 have the same length in each of the first direction X and the second direction Y.

[0021] The liquid crystal layer of the second display panel PNL2 also includes a polymer dispersed liquid crystal (PDLC) containing a polymer and liquid crystal molecules. Although not shown, the liquid crystal layer of the second display panel PNL2 is also referred to as a liquid crystal layer LC2. In this case, the liquid crystal layer LC of the first display panel PNL1 is also referred to as a liquid crystal layer LC1. When there is no need to distinguish between the liquid crystal layers LC1 and LC2, they are simply referred to as the liquid crystal layer LC.

[0022] The second display panel PNL2, like the first display panel PNL1, has a non-display area NDA2 located outside the effective area AA2. The non-display area NDA2 has a terminal area MT2 in which a driver IC and a flexible wiring board are mounted. The non-display area NDA2 and the terminal area MT2 are similar to the non-display area NDA1 and the terminal area MT1, respectively. The flexible wiring boards of the first display panel PNL1 and the second display panel PNL2 are electrically connected and further connected to a control element. The pixels PX1 and PX2 are driven in synchronization with each other by a signal from the control element. The same video signal is input to the pixels PX1 and PX2, which overlap in a planar view.

[0023] The threshold voltage of a polymer dispersed liquid crystal layer is higher than that of a TN (Twisted Nematic) liquid crystal layer, for example. Therefore, the polymer dispersed liquid crystal layer needs to be driven at a high voltage. In order to drive the polymer dispersed liquid crystal layer, it is necessary to use a high voltage driver.

[0024] The threshold voltage of the polymer dispersed liquid crystal layer is proportional to the electric field strength. By reducing the thickness of the polymer dispersed liquid crystal layer, it is possible to reduce the voltage. If it is possible to reduce the voltage of the polymer dispersed liquid crystal layer, there is no need to use a high voltage driver.

[0025] However, when the thickness of the polymer dispersed liquid crystal layer is reduced, there is a risk that the scattering luminance when a voltage is applied decreases.

[0026] Therefore, by stacking two display panels with thin polymer-dispersed liquid crystal layers as shown in Figure 1, it is possible to reduce the voltage required for the polymer-dispersed liquid crystal layer and suppress the decrease in scattered brightness.

[0027] 2 is a cross-sectional view showing an example of a schematic configuration of a display device DSP. The display device DSP includes a first display panel PNL1, a second display panel PNL2, a light guide plate LG1, a light guide plate LG2, a light source LS1, and a light source LS2.

[0028] The first display panel PNL1 emits display light DT1 upward. The second display panel PNL2 emits display light DT2 upward. It is assumed that the observer observes the display device DSP from above the display device DSP in the direction opposite to the third direction Z. When the display light DT1 and the display light DT2 reach the observer's eye EYE, the observer can view the display image displayed by the display device DSP.

[0029] The first display panel PNL1 includes a substrate SUB11, a substrate SUB21, and a liquid crystal layer (the above-mentioned liquid crystal layer LC1 (not shown)) provided between the substrates SUB11 and SUB21. The substrates SUB11 and SUB21 are laminated in this order along the third direction Z.

[0030] A light guide plate LG1 is provided on the substrate SUB21. The material of the light guide plate LG1 is, for example, glass. Light from the light source LS1 propagates through the light guide plate LG1, the substrate SUB11, and the substrate SUB21. It is preferable that the light guide plate LG1 has a refractive index similar to that of the substrate SUB11 and the substrate SUB21.

[0031] A light source LS1 is provided at an end of the first display panel PNL1. More specifically, the light source LS1 is provided facing an end of the light guide plate LG1. The light source LS1 has, for example, a light source element that emits red light, a light source element that emits green light, and a light source element that emits blue light. The light source elements are, for example, light emitting diodes (LEDs).

[0032] The second display panel PNL2 is disposed in a position that is line-symmetrical to the first display panel PNL1 with respect to each of the XY plane and the YZ plane. In other words, the second display panel PNL2 is disposed in a position that is upside down with respect to the XY plane and left-right reversed with respect to the YZ plane with respect to the first display panel PNL1.

[0033] The second display panel PNL2 includes a substrate SUB12, a substrate SUB22, and a liquid crystal layer (the above-mentioned liquid crystal layer LC2 (not shown)) provided between the substrates SUB12 and SUB22. The substrates SUB22 and SUB12 are laminated in this order along the third direction Z.

[0034] A light guide plate LG2 is provided below and in contact with the substrate SUB22. The material of the light guide plate LG2 is, for example, glass, similar to the light guide plate LG1. Light from the light source LS2 propagates through the light guide plate LG2, the substrate SUB12, and the substrate SUB22. It is preferable that the light guide plate LG2 has a refractive index similar to that of the substrates SUB12 and SUB22.

[0035] The substrate SUB11 of the first display panel PNL1 and the substrate SUB12 of the second display panel PNL2 are in contact with each other. Of the surfaces of the substrates SUB11 and SUB12, the surface on which the switching elements SW are provided is referred to as the upper surface, and the surface opposite to the main surface is referred to as the lower surface. The lower surfaces of the substrates SUB11 and SUB12 are in contact with each other.

[0036] The light source LS2 is provided at an end of the second display panel PNL2. More specifically, the light source LS2 is provided facing an end of the light guide plate LG2. Like the light source LS1, the light source LS2 has, for example, a light source element that emits red light, a light source element that emits green light, and a light source element that emits blue light. The light source elements are, for example, light emitting diodes.

[0037] The light source LS2 is disposed at a position that is line-symmetrical to the light source LS1 with respect to each of the XY plane and the YZ plane. In other words, the light source LS2 is disposed at a position that is upside down with respect to the XY plane and left-right reversed with respect to the YZ plane with respect to the light source LS1. That is, the direction in which the light from the light source LS1 enters the light guide plate LG1 (the direction opposite to the first direction X) and the direction in which the light from the light source LS2 enters the light guide plate LG2 (the first direction) are opposite to each other. In other words, the direction in which the light from the light source LS1 enters the first display panel PNL1 (the direction opposite to the first direction X) and the direction in which the light from the light source LS2 enters the second display panel PNL2 (the first direction) are opposite to each other.

[0038] After entering the light guide plate LG1, the light from the light source LS1 propagates through the light guide plate LG1, the substrate SUB11, and the substrate SUB21 into the first display panel PNL1. In addition, the light from the light source LS1 propagates through the substrate SUB22, the substrate SUB12, and the light guide plate LG2 into the second display panel PNL2.

[0039] After entering the light guide plate LG2, the light from the light source LS2 propagates inside the second display panel PNL2 through the light guide plate LG2, the substrate SUB12, and the substrate SUB22. In addition, the light from the light source LS2 propagates inside the first display panel PNL1 through the substrate SUB21, the substrate SUB11, and the light guide plate LG1.

[0040] Fig. 3 is a cross-sectional view showing an example of a schematic configuration of a display device. The display device DSP includes a first display panel PNL1, a second display panel PNL2, a light guide plate LG1, a light guide plate LG2, and a light source LS1. The configuration example shown in Fig. 3 is different from the configuration example shown in Fig. 2 in that a light source LS2 is not provided.

[0041] In the display device DSP shown in Fig. 3, similarly to Fig. 2, the first display panel PNL1 emits display light DT1 upward. The second display panel PNL2 emits display light DT2 upward. It is assumed that an observer observes the display device DSP from above the display device DSP in the direction opposite to the third direction Z. When the display light DT1 and the display light DT2 reach the observer's eye EYE, the observer can view the display image displayed by the display device DSP.

[0042] In the display device DSP shown in Fig. 3, the second display panel PNL2 is not provided with a light source. However, light emitted from a light source LS1 provided in the first display panel PNL1 propagates through the substrate SUB12, the substrate SUB22, and the light guide plate LG2 of the second display panel PNL2. This allows display on the second display panel PNL2.

[0043] Fig. 4 is a cross-sectional view showing an example of a schematic configuration of a display device. The display device DSP includes a first display panel PNL1, a second display panel PNL2, light guide plates LG1 and LG2, and light sources LS1 and LS2. The configuration example shown in Fig. 4 is different from the configuration example shown in Fig. 2 in that the components of the first display panel PNL1 and the second display panel PNL2 are arranged at the same positions with respect to the XY plane and the YZ plane, respectively.

[0044] In the display device DSP shown in Fig. 4, similarly to Fig. 2, the first display panel PNL1 emits display light DT1 upward. The second display panel PNL2 emits display light DT2 upward. It is assumed that an observer observes the display device DSP from above the display device DSP in the direction opposite to the third direction Z. When the display light DT1 and the display light DT2 reach the observer's eye EYE, the observer can view the display image displayed by the display device DSP.

[0045] In the display device DSP shown in FIG. 4, the first display panel PNL1 is the same as that in FIG. In the second display panel PNL2, the substrate SUB12 and the substrate SUB22 are laminated in this order along the third direction Z. A light guide plate LG2 is provided on the substrate SUB22. A light source LS2 is provided at an end of the light guide plate LG2. The light source LS2 faces the light source LS1 along the third direction Z.

[0046] The second display panel PNL2 shown in Fig. 4 has the same configuration as the first display panel PNL1. That is, as described above, the components of the first display panel PNL1 and the second display panel PNL2 are arranged at the same positions with respect to the XY plane and the YZ plane, respectively.

[0047] The light guide plate LG2 provided on the second display panel PNL2 and the first display panel PNL1 are provided in contact with each other. More specifically, the light guide plate LG2 and the substrate SUB11 are provided in contact with each other.

[0048] In FIG. 4, the direction in which light from light source LS1 enters light guide plate LG1 (opposite direction to first direction X) is the same as the direction in which light from light source LS2 enters light guide plate LG2 (opposite direction to first direction X).

[0049] Fig. 5 is a cross-sectional view showing an example of a schematic configuration of a display device. The display device DSP includes a first display panel PNL1, a second display panel PNL2, a light guide plate LG1, a light guide plate LG2, and a light source LS1. The configuration example shown in Fig. 5 is different from the configuration example shown in Fig. 4 in that a light source LS2 is not provided.

[0050] In the display device DSP shown in Fig. 5, similarly to Fig. 2, the first display panel PNL1 emits display light DT1 upward. The second display panel PNL2 emits display light DT2 upward. It is assumed that an observer observes the display device DSP from above the display device DSP in the direction opposite to the third direction Z. When the display light DT1 and the display light DT2 reach the observer's eye EYE, the observer can view the display image displayed by the display device DSP.

[0051] In the display device DSP shown in Fig. 5, no light source is provided in the second display panel PNL2. However, similar to the display device DSP shown in Fig. 3, in the display device DSP shown in Fig. 5, light emitted from a light source LS1 provided in the first display panel PNL1 also propagates inside the substrate SUB12, the substrate SUB22, and the light guide plate LG2 of the second display panel PNL2. This makes it possible to perform display on the second display panel PNL2.

[0052] 6 is a plan view showing the configuration of the pixel PX1 on the substrate SUB 11. The substrate SUB 11 includes a scanning line GL, a signal line SL, a switching element SW, an organic insulating layer OI, a metal wiring ML, a capacitance electrode CSE, and a pixel electrode PE.

[0053] 6 shows only pixel PX1, the second display panel PNL2 also includes a pixel (hereinafter referred to as pixel PX2) having a similar configuration to pixel PX1. The substrate SUB12 has a similar configuration to the substrate SUB11.

[0054] The two scanning lines GL each extend along a first direction X and are arranged side by side at an interval in the second direction Y. The two signal lines SL each extend along the second direction Y and are arranged side by side at an interval in the first direction X. The pixel PX1 corresponds to an area defined by the two signal lines SL and the two scanning lines GL.

[0055] The switching element SW is disposed at an intersection of the scanning line GL and the signal line SL. A specific configuration of the switching element SW will be described later. The switching element SW may be a bottom gate type in which a gate electrode is located below a semiconductor layer. The switching element SW may be a top gate type in which a gate electrode is located above a semiconductor layer. The semiconductor layer is formed of, for example, amorphous silicon, but may also be formed of polycrystalline silicon or an oxide semiconductor.

[0056] The organic insulating layer OI is patterned and formed in a lattice shape in plan view in Fig. 6. That is, the organic insulating layer OI overlaps each of the scanning lines GL, the signal lines SL, and the switching elements SW.

[0057] The organic insulating layer OI includes a first portion OX overlapping the scanning line GL and a second portion OY overlapping the signal line SL. The first portion OX has a first side E1 and a second side E2 opposite to the first side E1. The first side E1 and the second side E2 extend along the first direction X. The second portion OY has a third side E3 and a fourth side E4 opposite to the third side E3.

[0058] In this embodiment, the region where the organic insulating layer OI is arranged is defined as a first region PA1 of the substrate SUB11, and the region where the organic insulating layer OI is not arranged is defined as a second region PA2 of the substrate SUB11. The second region PA2 is located inside the region surrounded by the first region PA1. The second region PA2 is located inside the region surrounded by the two signal lines SL and the two scanning lines GL.

[0059] The metal wiring ML is disposed in the first region PA1, and is formed in a lattice shape in plan view in Fig. 6. That is, the metal wiring ML overlaps the scanning lines GL, the signal lines SL, and the switching elements SW. The metal wiring ML includes a first wiring portion MX overlapping the scanning lines GL and the first portion OX, and a second wiring portion MY overlapping the signal lines SL and the second portion OY.

[0060] As indicated by the dashed line, the capacitance electrode CSE is disposed across the pixels PX1 and further across almost the entire area of ​​the substrate SUB11. That is, the capacitance electrode CSE is disposed in each of the first area PA1 and the second area PA2. In the first area PA1, the capacitance electrode CSE overlaps with each of the switching element SW, the scanning line GL, the signal line SL, and the organic insulating layer OI.

[0061] The capacitance electrode CSE may have a lattice shape similar to the metal wiring ML. The lattice-shaped capacitance electrode CSE covers the scanning lines GL, the signal lines SL, the switching elements SW, and the side surfaces E (the first side surface E1, the second side surface E2, the third side surface E3, and the fourth side surface E4) of the organic insulating layer OI. That is, the lattice-shaped capacitance electrode CSE has an opening at the position of the second region PA2.

[0062] The pixel electrode PE is provided in substantially the entire second region PA2. In the example shown in Fig. 6, the pixel electrode PE is provided inside the region in which the organic insulating layer OI is arranged, and overlaps the capacitive electrode CSE in the second region PA2. The pixel electrode PE may be provided so as to overlap each of the first part OX and the second part OY.

[0063] In the example shown in FIG. 6, the spacer SP overlaps the switching element SW, and forms a predetermined gap between the substrate SUB11 and the substrate SUB21.

[0064] FIG. 7 is an enlarged plan view showing an example of the switching element shown in FIG. 6. The switching element SW includes a semiconductor layer SC, a gate electrode GE, a source electrode SE, and a drain electrode DE. The gate electrode GE is formed integrally with the scanning line GL. The semiconductor layer SC overlaps the gate electrode GE. Two source electrodes SE are formed integrally with the signal line SL and are in contact with the semiconductor layer SC. The drain electrode DE is located between the two source electrodes SE and in contact with the semiconductor layer SC. The drain electrode DE has a connection portion DEA. The connection portion DEA is electrically connected to the pixel electrode PE via an opening CA formed in the capacitance electrode CSE and a contact hole CH.

[0065] 8 is a cross-sectional view of the display panel shown in FIG. 7 taken along line A1-A2. The substrate SUB11 further includes a base material BA1, an insulating layer GI, an insulating layer PAS, an insulating layer DIE, and an alignment film AL1. The substrate BA1 includes a main surface (lower surface) BS1a and a main surface (upper surface) BS1b opposite to the main surface BS1a. The main surfaces BS1a and BS1b are substantially parallel to the XY plane. The main surface (lower surface) BS1a and the main surface (upper surface) BS1b of the substrate BA1 correspond to the lower surface and the upper surface of the substrate SUB11. Similarly, the main surface (lower surface) BS1a and the main surface (upper surface) BS1b of the substrate BA1 correspond to the lower surface and the upper surface of the substrate SUB12.

[0066] The gate electrode GE, which is integral with the scanning line GL, is disposed on the main surface BS1b side. The insulating layer GI covers the gate electrode GE and the scanning line GL and contacts the main surface BS1b. The semiconductor layer SC is located on the insulating layer GI directly above the gate electrode GE.

[0067] Two source electrodes SE integral with the signal line SL are in contact with the semiconductor layer SC, and a part of each of them is located on the insulating layer GI. The drain electrode DE is in contact with the semiconductor layer SC. The insulating layer PAS covers the semiconductor layer SC, the source electrode SE, and the drain electrode DE that constitute the switching element SW, and also covers the insulating layer GI.

[0068] The first portion OX of the organic insulating layer OI is in contact with the upper surface PS2 of the insulating layer PAS directly above the gate electrode GE and the scanning line GL, or directly above the switching element SW. The first wiring portion MX of the metal wiring ML is located on the first portion OX directly above the gate electrode GE and the scanning line GL, or directly above the switching element SW.

[0069] The capacitive electrode CSE covers the first wiring portion MX and the first portion OX in the first region PA1. That is, the first side surface E1 and the second side surface E2 of the first portion OX are covered by the capacitive electrode CSE. The first wiring portion MX is in contact with the capacitive electrode CSE and is electrically connected to each other. In addition, the capacitive electrode CSE is in contact with the upper surface PS2 of the insulating layer PAS in the second region PA2.

[0070] The insulating layer DIE is disposed in the first area PA1 and the second area PA2, and covers the capacitance electrode CSE. Each pixel electrode PE is located on the insulating layer DIE in the second area PA2. The pixel electrode PE and the capacitance electrode CSE face each other via the insulating layer DIE, and form a storage capacitance necessary for image display in the pixel PX1.

[0071] The switching element SW is located between adjacent pixel electrodes PE along the second direction Y. The first side surface E1 and the second side surface E2 are each located between the switching element SW and the pixel electrode PE along the second direction Y. The alignment film AL1 covers the pixel electrode PE and the insulating layer DIE.

[0072] The substrate SUB21 includes a base material BA2, a light-shielding layer BM, a common electrode CE, a spacer SP, and an alignment film AL2. The base material BA2 includes a main surface (lower surface) BS2a and a main surface (upper surface) BS2b opposite to the main surface BS2a. The main surfaces BS2a and BS2b are substantially parallel to the XY plane. The main surface BS2a faces the main surface BS2b.

[0073] The light-shielding layer BM and the common electrode CE are disposed on the main surface BS2a. The light-shielding layer BM is located directly above the first side surface E1 and the second side surface E2 of the first portion OX, directly above the switching element SW, and directly above the gate electrode GE.

[0074] The common electrode CE is disposed across multiple pixels PX and covers the light-shielding layer BM. The common electrode CE is electrically connected to the capacitive electrode CSE and has the same potential as the capacitive electrode CSE. The spacer SP is provided under the common electrode CE and contacts the alignment film AL1. The spacer SP is located between the organic insulating layer OI and the light-shielding layer BM. The alignment film AL2 covers the common electrode CE.

[0075] The liquid crystal layer LC1 (liquid crystal layer LC) is located between the substrate SUB11 and the substrate SUB21, and is in contact with each of the alignment films AL1 and AL2.

[0076] The base material BA1 and the base material BA2 are insulating base materials having light-transmitting properties, and examples of such base materials include glass and plastic.

[0077] The insulating layer GI, the insulating layer PAS, and the insulating layer DIE are formed of a transparent inorganic insulating material such as silicon nitride or silicon oxide. The insulating layer DIE is preferably made of an inorganic insulating material with a high dielectric constant. The organic insulating layer OI is formed of a transparent organic insulating material such as an acrylic resin.

[0078] The scanning line GL, the signal line SL, and the metal wiring ML are, for example, a laminate in which a plurality of conductive layers are laminated. Such a laminate may be, for example, a laminate in which a conductive layer containing molybdenum (Mo), a conductive layer containing aluminum (Al), and a conductive layer containing molybdenum (Mo) are laminated in this order. However, the laminate is not limited to this. The laminate may be a laminate in which a conductive layer containing titanium (Ti), a conductive layer containing aluminum (Al), and a conductive layer containing titanium (Ti) are laminated in this order.

[0079] The scanning line GL may be a laminate of a conductive layer containing molybdenum (Mo) and a conductive layer containing aluminum (Al), and it is preferable that the conductive layer containing aluminum (Al) is in contact with the main surface BS1b. Aluminum (Al) has a higher light reflectance than molybdenum (Mo). Compared to the case where the conductive layer containing molybdenum (Mo) of the scanning line GL is in contact with the main surface BS1b, it is possible to suppress absorption of the light propagating through the base material BA1 by the scanning line GL.

[0080] The capacitance electrode CSE, the pixel electrode PE, and the common electrode CE are transparent electrodes formed of a transparent conductive material such as indium tin oxide (ITO) or indium zinc oxide (IZO).

[0081] The light-shielding layer BM is, for example, a conductive layer having a lower resistance than the common electrode CE. For example, in the embodiment, the light-shielding layer BM is made of an opaque metal material such as molybdenum, aluminum, tungsten, titanium, or silver.

[0082] The common electrode CE is in contact with the light-shielding layer BM and is therefore electrically connected to the light-shielding layer BM, thereby lowering the resistance of the common electrode CE.

[0083] The alignment films AL1 and AL2 are horizontal alignment films having an alignment regulating force substantially parallel to the XY plane. In one example, the alignment films AL1 and AL2 are aligned along the first direction X. The alignment treatment may be a rubbing treatment or a photo-alignment treatment.

[0084] The thickness of the liquid crystal layer LC is defined as thickness CG. The thickness CG corresponds to the length in the third direction Z from the alignment film AL1 to the alignment film AL2 in the second region PA2. In other words, the thickness CG corresponds to the length between the alignment film AL1 and the alignment film AL2 in a region where the switching element SW and the light-shielding layer BM are not provided. The thickness CG is preferably 2 μm or less. If the thickness CG is greater than 2 μm, the threshold voltage of the display panel increases.

[0085] However, when the thickness CG of the liquid crystal layer LC of the display panel becomes thin, the scattering luminance decreases. Therefore, by stacking two display panels as described above, the voltage of the polymer dispersed liquid crystal layer is reduced and the decrease in scattering luminance is suppressed.

[0086] FIG. 9 is a diagram showing the relationship between the applied voltage and the scattering luminance with respect to the thickness of the liquid crystal layer. FIG. 10 is an enlarged view of the area surrounded by the dotted line in FIG. 9. In other words, FIG. 10 is an enlarged view of the area in FIG. 9 where the horizontal and vertical axes are approximately 0. The horizontal axis in FIG. 9 and FIG. 10 is the voltage V applied to the liquid crystal layer LC. The vertical axis in FIG. 9 and FIG. 10 is the scattering luminance of the liquid crystal layer LC. The thicknesses CG of the liquid crystal layer LC are 3 μm, 2.5 μm, 2 μm, 1.5 μm, and 1.0 μm, and are shown by the coarse dotted line, two-dot chain line, solid line, one-dot chain line, and fine dotted line, respectively.

[0087] 9, when the thickness CG is small, the scattering intensity LM is small even when the same voltage V is applied. In other words, when the thickness CG is large, the scattering intensity LM is large even when the same voltage V is applied.

[0088] Fig. 11 is a diagram showing the relationship between the thickness of the liquid crystal layer and the threshold voltage. The horizontal axis of Fig. 11 is the thickness CG of the liquid crystal layer LC. The vertical axis of Fig. 11 is the threshold voltage Vth of the liquid crystal layer LC. As shown in Fig. 11, as the thickness CG becomes smaller, the threshold voltage Vth becomes smaller.

[0089] From the above, by reducing the thickness CG, a display panel with a small threshold voltage Vth can be obtained (see FIG. 11). By stacking two such display panels, a display device DSP having the effect of increasing the thickness CG can be obtained. In the display device DSP, the same effect as a display panel with a large thickness CG can be obtained, and therefore the scattering intensity LM becomes large (see FIGS. 9 and 10). Therefore, according to the present disclosure, it is possible to obtain a display device DSP that can be driven at a low voltage and has an increased scattering luminance.

[0090] In this disclosure, the substrates SUB11, SUB21, SUB12, and SUB22 are also referred to as the first substrate, the second substrate, the third substrate, and the fourth substrate, respectively. The liquid crystal layers LC1 and LC2 are also referred to as the first polymer-dispersed liquid crystal layer and the second polymer-dispersed liquid crystal layer, respectively. The light sources LS1 and LS2 are also referred to as the first light source and the second light source, respectively.

[0091] In this disclosure, the pixel PX1 and the pixel PX2 are also referred to as the first pixel and the second pixel, respectively. The first region PA1 and the second region PA2 of the first display panel PNL1 are also referred to as the first region and the second region, respectively. The first region PA1 and the second region PA2 of the second display panel PNL2 are also referred to as the third region and the fourth region, respectively.

[0092] In this disclosure, the alignment films AL1 and AL2 of the first display panel PNL1 are also referred to as the first alignment film and the second alignment film, respectively. The alignment films AL1 and AL2 of the second display panel PNL2 are also referred to as the third alignment film and the fourth alignment film, respectively. The organic insulating layer OI of the first display panel PNL1 is also referred to as the first organic insulating layer, and the organic insulating layer OI of the second display panel PNL2 is also referred to as the second organic insulating layer.

[0093] In the present disclosure, the thickness CG of the first display panel PNL1 is also referred to as the first thickness, and the thickness CG of the second display panel PNL2 is also referred to as the second thickness. Also, in the present disclosure, components of the first display panel PNL1 may be referred to with "first" and components of the second display panel PNL2 may be referred to with "second."

[0094] Although some 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 implemented 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 in the scope and spirit of the invention, and are included in the scope of the invention and its equivalents described in the claims. [Explanation of symbols]

[0095] PA1...first region, PA2...second region, DSP...display device, LC...liquid crystal layer, LG1...light guide plate, LG2...light guide plate, LS1...light source, LS2...light source, OI...organic insulating layer, PNL1...first display panel, PNL2...second display panel, PX...pixel, SUB11...substrate, SUB12...substrate, SUB21...substrate, SUB22...substrate.

Claims

1. a first display panel including a first substrate, a second substrate, and a first polymer dispersed liquid crystal layer provided between the first substrate and the second substrate; a second display panel including a third substrate, a fourth substrate, and a second polymer dispersed liquid crystal layer provided between the third substrate and the fourth substrate; A first light source provided at an end of the first display panel; Equipped with The first substrate is A plurality of first signal lines; A plurality of first scan lines; a plurality of first pixels partitioned by the plurality of first signal lines and the plurality of first scanning lines; A plurality of first switching elements provided in the plurality of first pixels; A first alignment film; Equipped with the second substrate includes a second alignment film facing the first alignment film, The third substrate is A plurality of second signal lines; A plurality of second scan lines; a plurality of second pixels partitioned by the plurality of second signal lines and the plurality of second scanning lines; A plurality of second switching elements provided in the plurality of second pixels; A third alignment film; Equipped with the fourth substrate includes a fourth alignment film facing the third alignment film, the first display panel and the second display panel are disposed in contact with each other, the first polymer dispersed liquid crystal layer is provided between the first alignment film and the second alignment film, the second polymer dispersed liquid crystal layer is provided between the third alignment film and the fourth alignment film, A distance between the first alignment film and the second alignment film is a first thickness; A distance between the third alignment film and the fourth alignment film is a second thickness; The display device, wherein the first thickness and the second thickness are each 2 μm or less.

2. a first light guide plate is provided in contact with the second substrate; The display device according to claim 1 , further comprising a second light guide plate provided in contact with the fourth substrate.

3. a second light source provided at an edge of the second display panel; The first light source is provided to face an end of the first light guide plate, The second light source is provided to face an end of the second light guide plate, Light from the first light source is incident on an end of the first light guide plate, The display device according to claim 2 , wherein the light from the second light source is incident on an end portion of the second light guide plate.

4. The display device according to claim 3 , wherein a direction in which the light from the first light source is incident on the first display panel and a direction in which the light from the second light source is incident on the second display panel are opposite to each other.

5. The display device according to claim 3 , wherein a direction in which the light from the first light source is incident on the first display panel and a direction in which the light from the second light source is incident on the second display panel are the same.

6. The display device according to claim 1 , wherein the first substrate and the third substrate are provided in contact with each other.

7. The display device according to claim 2 , wherein the first light guide plate and the third substrate are provided in contact with each other.

8. the first substrate includes a first organic insulating layer overlapping the first switching element; the third substrate includes a second organic insulating layer overlapping the second switching element, the first pixels have a first region in which the first organic insulating layer is provided so as to overlap the first signal lines and the first scanning lines, and a second region inside the first pixels in which the first organic insulating layer is not provided, the second pixels have a third region in which the second organic insulating layer is provided so as to overlap the second signal lines and the second scanning lines, and a fourth region inside the second pixels in which the second organic insulating layer is not provided, the first thickness is a thickness of the first polymer dispersed liquid crystal layer in the second region, The display device according to claim 1 , wherein the second thickness is a thickness of the second polymer dispersed liquid crystal layer in the fourth region.

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