JP2018017773A - Liquid crystal display device - Google Patents

Abstract

A liquid crystal display device capable of effective transflective display is provided. A liquid crystal layer is sandwiched between two substrates. The polarizing layer 24 is provided on the liquid crystal layer 40 side of at least one of the two substrates 10 and 50. And it has the contact hole 28 which electrically connects the board | substrate side conductive layer 22 provided in the board | substrate 10 side of the polarizing layer 24, and the liquid crystal side conductive layer 26 provided in the liquid crystal layer 40 side of the polarizing layer 24. [Selection] Figure 1

Description

  The present invention relates to a liquid crystal display device in which a polarizing layer is disposed on a liquid crystal layer side of a substrate.

  Conventionally, a liquid crystal display (LCD) has been widely used. Various types of liquid crystal display devices are known. As a liquid crystal drive system, a VA (vertical alignment) type, an IPS (in-plane switching) system, and the like are used in addition to TN (twist nematic). Further, as a display method, there are a reflection method, a semi-transmission method, and the like in addition to a transmission method that transmits light to the liquid crystal. Further, LCDs that are flexible and bendable by using a resin substrate (plastic substrate) as a whole are also known.

  FIG. 7 shows a configuration of a conventional transflective liquid crystal display device. A liquid crystal layer 114 is disposed between the TFT substrate 110 and the counter substrate 112. A polarizing layer 122 is provided outside the TFT substrate 110 via a phase difference compensation plate 120, and a polarizing layer 122 is provided outside the counter substrate 112 via a phase difference compensation plate 120. In addition, a stepped portion 130 that protrudes toward the liquid crystal layer 114 is provided on a part of the TFT substrate 110 on the liquid crystal layer 114 side (reflection region), and a reflector 132 is provided thereon.

  In the transmission region, light is directed upward from the lower side in the drawing in the order of the polarizing layer 122, the retardation compensation plate 120, the TFT substrate 110, the liquid crystal layer 114, the counter substrate 112, the retardation compensation plate 116, and the polarizing layer 118. Pass through. On the other hand, in the reflection region, the polarizing layer 118, the phase difference compensation plate 116, the counter substrate 112, the liquid crystal layer 114, the reflection by the reflection plate 132, the counter substrate 112, the phase difference compensation plate 116, and the polarization layer 118 are arranged in this order from the top in the drawing. Light passes through.

  Thus, in the case of the transflective method, since light passes through the liquid crystal layer 114 twice in the reflection region, the cell gap of the reflection region (the thickness of the liquid crystal layer 114) is set to make the display in the reflection region equivalent to the transmission portion. A step portion 130 is provided so as to be ½ of the transmission region, and a reflecting plate 132 is disposed thereon. Further, when the normal structure is maintained, the black and white are reversed between the reflection portion and the transmission portion. Therefore, the phase difference compensating plates 116 and 120 are used, and the light passing through the liquid crystal layer 114 is circularly polarized. In this manner, display in both the transmissive region and the reflective region is performed by controlling the voltage application to the pixel electrode on the TFT substrate 110.

  In the liquid crystal display device, display is performed by passing polarized light through the liquid crystal layer and changing the polarization state. Therefore, a polarizing layer is required. As this polarizing layer, in addition to iodine-based ones, dye-based polarizing layers are known (see Patent Documents 1, 2, and 3).

JP 2013-47842 A JP 2014-167089 A WO2007 / 138980

  Here, in the case of the semi-transmissive method, the stepped portion 130 is required. For this reason, a process for forming the stepped portion 130 is added, the process becomes complicated, and further, light leakage occurs at the edge portion of the stepped portion 130 and the display quality is deteriorated. When the IPS method is used, it is difficult to use circularly polarized light, and it is difficult to use a semi-transmissive method. Further, in a flexible LCD, a phase difference is generated according to the position by bending the resin substrate. For this reason, the state of the polarized light passing through it changed, and the contrast was likely to deteriorate.

  The present invention is a liquid crystal display device in which a liquid crystal layer is sandwiched between two substrates, the polarizing layer provided on the liquid crystal layer side of at least one of the two substrates, and the substrate of the polarizing layer A substrate-side conductive layer provided on the side, a liquid crystal-side conductive layer provided on the liquid crystal layer side of the polarizing layer, and provided on the polarizing layer, electrically connecting the substrate-side conductive layer and the liquid crystal-side conductive layer A contact hole.

  The polarizing layer is preferably a dye-based polarizing layer obtained by dyeing PVA with a dichroic dye.

  The substrate on which the polarizing layer is provided is a TFT substrate that controls application of an electric field to the liquid crystal layer by a thin film transistor, and it is preferable that the thin film transistor on the TFT substrate and the electrode on the polarizing layer are connected by the contact hole. is there.

  In the counter substrate which is another substrate which is not the TFT substrate, it is preferable to provide a second polarizing layer on the opposite side to the liquid crystal layer.

  It is preferable to provide a retardation compensation plate between the counter substrate and the second polarizing layer.

  By disposing the polarizing layer on the liquid crystal layer side of the substrate, it is possible to easily adopt the transflective method even in the TFT. Further, the semi-transmission method can be adopted even in the IPS method. In the case of flexibility, the display deteriorates due to the birefringence of the resin substrate (plastic substrate), which can be prevented by the present technology.

It is a figure which shows the structure of the liquid crystal display device which concerns on embodiment. It is a figure which shows the plane of the liquid crystal display device which concerns on embodiment. It is a figure which shows the structure of a pixel circuit. It is a figure which shows the structure of an auxiliary capacity. It is a figure which shows the structure of the liquid crystal display device which concerns on other embodiment. It is a figure which shows the structure of the liquid crystal display device which concerns on other embodiment. It is a figure which shows the structure of the transflective liquid crystal display device of a prior art.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the present invention is not limited to the embodiments described herein.

<Configuration>
FIG. 1 is a cross-sectional view (schematic diagram) showing a configuration example of the liquid crystal display device according to the embodiment, and a data line DL is not shown. FIG. 2 is a plan view of the TFT substrate 36, and the gate oxide film 16 is omitted in addition to the substrate 10, the polarizing layer 24, the photosensitive layer 38, and the alignment film 34. Each is a schematic diagram, and the scale and the like are changed so that each part can be easily seen.

  On a transparent substrate 10 formed of glass, resin, or the like, pixel circuits and wirings including TFTs (thin film transistors) are formed. Note that a data driver, a gate driver, and the like may be disposed in the peripheral portion of the substrate 10.

On the substrate 10, a TFT 12 is arranged for each pixel. In the figure, two TFTs 12 are shown. A gate electrode 14 connected to the gate line is disposed at a substantially lower portion (on the substrate 10) of the TFT 12. A gate insulating film 16 is formed to cover the gate electrode 14, and a semiconductor layer 18 is formed to cover the gate insulating film 16. The gate insulating film 16 is formed of an insulator such as SiO ₂ , for example. The semiconductor layer 18 is formed of amorphous silicon or polysilicon, and a portion immediately above the gate electrode 14 is a channel region having almost no impurities, and both sides are a source region and a drain region to which conductivity is imparted by impurity doping. It has become.

  A metal (for example, aluminum) drain electrode 20 is disposed (electrically connected) on the drain region of the TFT 12, and a metal (for example, aluminum) source electrode 22 is disposed (electrically connected) on the source region. It is connected. As will be described later, the drain electrode 20 is connected to a data line to which a data voltage is supplied. Therefore, the data voltage of the data line is taken in the state where the TFT 12 is turned on according to the signal of the gate line.

  A polarizing layer 24 is formed so as to cover the TFT 12. The polarizing layer 24 is a dyeing-type polarizing layer in which a PVA (polyvinyl alcohol) resin is dyed with a dichroic dye. The polarizing layer 24 covers and insulates the TFT 12 and flattens the surface.

  A display electrode 26 is provided on the surface of the polarizing layer 24. The display electrode 26 is an individual electrode separated for each pixel, and is a transparent electrode made of, for example, ITO (indium tin oxide).

  The polarizing layer 24 is adhered to the substrate with a water-based adhesive glyoxal, and a photosensitive layer 38 made of photosensitive polyimide (JSR Optoma) is formed thereon with a thickness of 0.5 μm, and a pattern is formed through an exposure / development process. To do. Further, it is immersed in warm water (80 ° C.) to pattern the polarizing layer. By this process, a contact hole 28 is formed above the source electrode 22 of the polarizing layer 24, and the display electrode 26 is filled with ITO so that the source electrode 22 and the display electrode 26 are electrically connected. .

  An insulating layer 30 is formed to cover the display electrode 26, and a common electrode 32 is disposed on the surface of the insulating layer 30. This embodiment is an IPS system, in which a common electrode 32 is formed on the display electrode 26 with a gap, and display is performed by controlling the alignment of the liquid crystal in the horizontal plane by a lateral electric field generated by applying a voltage between the two. . Known arrangements of electrodes for applying a lateral electric field to the liquid crystal can be appropriately employed.

  An alignment film 34 on the substrate 10 side is formed so as to cover the common electrode 32, whereby a TFT substrate 36 is formed.

  A liquid crystal layer 40 is disposed on the alignment film 34 of the TFT substrate 36, and an alignment film 42 on the counter substrate side is disposed above the liquid crystal layer 40. Accordingly, the alignment of the liquid crystal layer 40 is controlled by the alignment film 34 on the lower side and the alignment film 42 on the upper side. That is, the alignment state of the liquid crystal in the liquid crystal layer 40 in the initial stage (when no electric field is applied) is determined by the alignment films 34 and 42. Then, by applying an electric field to the liquid crystal layer 40, the alignment of the liquid crystal is controlled and the transmission / reception of light is controlled.

  A color filter layer 44 is formed on the alignment film 42. In the case of color display, three pixels of normal RGB are combined to function as a display pixel for color display, and a color filter of any color of RGB is arranged for each pixel.

  A glass or resin substrate 50 is disposed on the color filter layer 44, and a diffusion layer 52 is disposed on the substrate 50. The diffusion layer 52 is a transparent material in which small spheres (beads) are dispersed, diffuses transmitted light, and eliminates the strength (glare) due to the location of reflected light.

  A polarizing layer 56 is disposed above the diffusion layer 52 via a phase difference compensation plate 54. Here, the phase difference compensation plate 54 is a composite of a positive A plate and a positive C plate, and has an effect of widening the viewing angle by compensating for a phase difference due to a difference in light wavelength. The polarizing layer 56 is paired with the polarizing layer 24 to transmit or block light.

  Actually, the counter substrate 58 is formed by forming the color filter layer 44 and the alignment film 42 on one surface of the substrate 50 and forming the diffusion layer 52, the retardation compensation plate 54, and the polarizing layer 56 on the other surface. The liquid crystal layer 40 is formed by encapsulating liquid crystal between the TFT substrate 36 and the counter substrate 58 (between the alignment films 34 and 42).

<Action>
Then, for example, the polarization direction of the polarizing layer 24 of the TFT substrate 36 is the 90 ° absorption axis, and the polarization direction of the polarizing layer 56 of the counter substrate 58 is the 0 ° absorption axis.

  When light passes upward from the lower side of the TFT substrate 36 (transmission type), if the change in the polarization direction of the liquid crystal layer 40 is zero due to no application of an electric field, black (non-transmission) display is performed. Further, when the polarization direction changes by 90 ° in the liquid crystal layer 40 by applying an electric field, white (transmission) display is performed. Note that the degree of rotation of the polarization direction in the liquid crystal layer 40 can be controlled by controlling the applied voltage, and thereby the degree of transmission (luminance) is controlled.

  In the present embodiment, the surface of a metal member such as the source electrode 22 is used as a reflector. In this case, when no voltage is applied to the liquid crystal layer 40, the polarized light from the polarizing layer 56 reaches the polarizing layer 24 as it is, so that it cannot be transmitted here and a black display is obtained. On the other hand, when a voltage is applied to the liquid crystal layer 40, the polarized light from the polarizing layer 56 changes the 90 ° polarization direction and passes through the polarizing layer 24. The direction of polarization is reversed (shifted by 180 °) by the reflecting plate, but passes through the polarizing layer 24 as it is, shifted by 90 ° by the liquid crystal layer 40, passes through the polarizing layer 56, and becomes white (transmissive) display. Here, as described above, with respect to the reflected light, the diffusion layer 52 removes the glare due to the partial strength of the light.

  As described above, in this embodiment, switching between black and white (transmission / non-transmission) of transmitted light and reflected light is performed by applying a voltage. Therefore, although it is an IPS liquid crystal display device, it functions as a transflective liquid crystal display device.

  A black matrix for preventing light leakage is arranged between each pixel. Further, large irregularities are formed on the upper surfaces of the drain electrode 20 and the source electrode 22 of the TFT 12. It is not preferable to use such a large uneven portion as a reflector. Therefore, it is also preferable to cover this portion with a black matrix. In addition, small unevenness can be formed on the surface functioning as the reflecting plate to diffuse the reflected light and reduce glare.

<Circuit configuration>
Here, FIG. 3 shows a circuit diagram of the pixel circuit. Thus, the drain electrode 20 of the TFT 12 is connected to the data line Data. The gate electrode 14 of the TFT 12 is connected to the gate line Gate, and the source electrode 22 is connected to the display electrode 26 facing the liquid crystal layer 40. In the illustrated example, the TFT 12 is an n-channel, but may be a p-channel. A common electrode 32 is opposed to the display electrode 26 with a liquid crystal layer 40 interposed therebetween, and the common electrode 32 is connected to a power source having a constant potential, for example, ground.

  The source electrode 22 is connected to one end of the auxiliary capacitor 60, and the other end of the auxiliary capacitor 60 is connected to a power source having a constant potential, for example, ground, via the auxiliary capacitor line 62.

  Here, FIG. 4 shows a configuration example of the auxiliary capacitor 60. An auxiliary capacitance line 62 connected to the ground is formed on the substrate 10, and an insulating film 64 is formed thereon. The auxiliary capacitance line 62 is preferably formed by the same process as the gate electrode 14, and the insulating film 64 is preferably formed by the same process as the gate insulating film 16. Then, a part of the source electrode 22 is extended to be opposed to the auxiliary capacitance line 62 via the insulating film 64, and the auxiliary capacitance 60 is formed.

  The auxiliary capacitor 60 can be formed in a desired region in one pixel, and the source electrode 22 located in the auxiliary capacitor 60 is in the display region (for example, the central portion in the vertical direction of the display region). It is preferable to position and use this as a reflector.

  In a liquid crystal display device, a plurality of pixels are arranged in a matrix. And if it is a stripe type, it assigns in order to RGB color for every row | line | column.

  For example, the data line Data is arranged between the columns of pixels in the column direction, and the gate line Gate is arranged between the rows of pixels in the row direction. The auxiliary capacitance line 62 is arranged in the row direction at an intermediate portion of the pixel row.

  The gate line Gate of each row is set to the H level in order according to the vertical scanning of the screen. The data line Data of each column is sequentially supplied to the data line Data of each column of the column of the row selected by the gate line Gate so that the supplied pixel data is supplied to the corresponding pixel. The

  Therefore, the TFT 12 of each pixel is turned on when the data voltage of its own pixel is supplied to the data line Data, and the data voltage is sequentially stored in the auxiliary capacitor 60 of each pixel. The auxiliary capacitor of each pixel maintains the written data voltage until the next data voltage is written to the auxiliary capacitor 60 even after the TFT 12 of the pixel is turned off. Accordingly, if the data voltage for each frame is written, the auxiliary capacitor 60 maintains the data voltage for the period of one frame, and this data voltage is applied to the liquid crystal layer 40. Therefore, liquid crystal display corresponding to the data voltage is performed in each pixel. In the case of color display, the corresponding color pixel is displayed according to the data voltage supplied for each RGB.

  Here, in the present embodiment, the polarizing layer 24 is formed inside the TFT 12. Therefore, a metal electrode such as the source electrode 22 constituting the TFT 12 is positioned outside the polarizing layer 24. Accordingly, the light input from above the device also passes through the polarizing layer 24 and is reflected again through the polarizing layer 24 and then passes through the liquid crystal layer 40 and the polarizing layer 56. For this reason, switching is performed by the liquid crystal layer 40 in the same manner as the reflection portion and the transmission portion. Therefore, the IPS system can also be a semi-transmissive type.

  In addition, a high-performance transflective type can be easily realized even in a liquid crystal mode other than the IPS mode. In addition, since the electrode surface of the TFT substrate 36 such as an electrode can be used as a reflection plate, the aperture ratio can be improved compared to the case where a separate reflection plate is provided.

  The polarizing layer 24 functions as an insulating film that electrically separates the TFT 12 and the display electrode 26, and the electrical connection between the TFT 12 and the display electrode 26 is achieved by forming a contact hole 28 therein. Therefore, it is not necessary to form an insulating film separately. Furthermore, the polarizing layer 24 is an organic film (resin film) such as PVA, and can also obtain a flattening effect.

<Polarizing layer 24>
The polarizing layer 24 is formed inside the substrate 10. Here, the normal polarizing layer is formed on the outer side of the substrate 10 (opposite side of the liquid crystal layer 40). This is because the polarizing layer usually uses an iodine-based polarizing layer formed of a material dyed with resin by iodine and an iodine compound. That is, iodine and iodine compounds are vulnerable to heat and are altered by heating at about 100 ° C. On the other hand, it is necessary to form an alignment film 34 on the surface of the substrate 10 in contact with the liquid crystal layer 40. In the case of forming this alignment film 34, it is necessary to heat at least over 100 ° C. and 130 ° C. or higher (preferably higher). Therefore, when it is assumed that an iodine-based dyeing material is used for the polarizing layer, it is essential to form the polarizing layer outside the substrate 10 after forming the alignment film 34.

  On the other hand, Patent Documents 1 and 2 show a polarizing layer using a dye (dichroic dye). This dye is relatively heat resistant. For example, if heating is performed at about 130 ° C. with various dyes disclosed in Patent Documents 1 and 2, alteration can be prevented. In particular, a dye containing an azo compound and a salt thereof described in Patent Document 2 is preferable.

  Therefore, the polarizing layer 24 can be formed inside the substrate 10 by forming the polarizing layer 24 using such a dye.

In addition, as a base material of a polarizing layer, as described in Patent Documents 1, 2, and 3, a stretched PVA resin is preferable.
Specifically, it is preferable to use a polarizing film obtained by the following procedure. The dye of the following structural formula (2) shown in Example 1 of Patent Document 3 is 0.01%, C.I. Direct Red 81 is 0.01%, and Example 1 of Japanese Patent No. 2622748 is shown. 0.03% of the dye represented by the following structural formula (10) and 0.03% of the dye represented by the following structural formula (11) disclosed in Example 23 of JP-A-60-156759 In addition, polyvinyl alcohol having a thickness of 75 μm was immersed in an aqueous solution of 45 ° C. having a concentration of 0.1% sodium sulfate for 4 minutes. This film was stretched 5 times at 50 ° C. in a 3% boric acid aqueous solution, washed with water and dried while maintaining a tension state to obtain a polarizing film of neutral color (gray in parallel position and black in orthogonal position). It was.

  In this example, the polarizing layer 56 is disposed outside the substrate 50, and may be a polarizing layer with low heat resistance that is not a dyeing system. For example, a polarizing layer using iodine and an iodine compound may be used.

  Furthermore, if the alignment film 34 can be formed at a low temperature, the polarizing layer 24 having low heat resistance may be used.

<Other embodiments>
FIG. 5 shows the configuration of another embodiment. In this example, the polarizing layer 56 is disposed inside the substrate 50 of the counter substrate 58. Therefore, a material having high heat resistance is used for the polarizing layer 56. Further, the color filter layer 44, the diffusion layer 52, and the retardation compensation plate 54 are omitted. This is because these are not necessarily required structures, but they may be provided. In addition, when arrange | positioning, the phase difference compensating plate 54 is arrange | positioned inside the polarizing layer 56. FIG.

  In this example, a flexible resin substrate is used for the substrates 10 and 50. Therefore, the entire liquid crystal display device is flexible and can be bent.

  Here, as described above, the polarizing layer 56 is disposed inside the substrate 50. Since the polarizing layer 24 is also inside the substrate 10, both the polarizing layers 24 and 56 are located inside the substrates 10 and 50.

  The substrates 10 and 50 are made of resin, but when the resin substrate is bent, a phase difference occurs in the transmitted light depending on the location. Therefore, the transmitted light having a phase difference passes through the polarizing layers 24 and 56, thereby causing unevenness in display.

  According to this embodiment, the polarizing layers 24 and 56 are inside the substrates 10 and 50, and the generation of the phase difference due to the bending of the substrates 10 and 50 affects the control of light transmission and non-transmission by the polarizing layers 24 and 56. It becomes possible to eliminate that.

<Still another embodiment>
FIG. 6 shows the configuration of still another embodiment. This example is a TN liquid crystal display device. Accordingly, the counter substrate 58 has the counter electrode 70, and an electric field is applied to the liquid crystal layer 40 between the display electrode 26 and the counter electrode 70 by applying a voltage to the display electrode 26, thereby polarizing the liquid crystal layer 40. Control direction rotation. In the case of the TN system, white display is normally performed when no voltage is applied, and black display is performed when the voltage is applied.

  In the TFT substrate 36, the display electrode 26 is formed on the polarizing layer 24 for each pixel. An alignment film 34 is formed so as to cover the display electrode 26, and the liquid crystal layer 40 is disposed on the alignment film 34. In the counter substrate 58, the counter electrode 70 is formed inside the substrate 50 through the color filter layer 44. The counter electrode 70 is also a transparent electrode formed of ITO or the like. The counter electrode 70 is one common electrode facing the plurality of display electrodes 26. An alignment film 42 is formed on the lower surface of the counter electrode, and the alignment film 42 faces the liquid crystal layer 40.

  With such a configuration, an electric field based on the data voltage is applied between the display electrode 26 and the counter electrode 70 of each pixel to perform display for each pixel.

  Note that a liquid crystal display device can be configured with a similar configuration even in the VA mode or the like. Further, a flexible device using a receiving substrate as shown in FIG. 5 can be similarly produced.

  10, 50 Substrate, 14 Gate electrode, 16 Gate insulating film, 18 Semiconductor layer, 20 Drain electrode, 22 Source electrode, 24, 56 Polarizing layer, 26 Display electrode, 28 Contact hole, 30 Insulating layer, 32 Common electrode, 34, 42 alignment film, 36 TFT substrate, 40 liquid crystal layer, 44 color filter layer, 52 diffusion layer, 54 retardation compensation plate, 58 counter substrate, 60 auxiliary capacitor, 62 auxiliary capacitor line, 64 insulating film, 70 counter electrode.

Claims (5)

A liquid crystal display device in which a liquid crystal layer is sandwiched between two substrates,
A polarizing layer provided on the liquid crystal layer side of at least one of the two substrates;
A substrate-side conductive layer provided on the substrate side of the polarizing layer;
A liquid crystal side conductive layer provided on the liquid crystal layer side of the polarizing layer;
A contact hole provided in the polarizing layer, electrically connecting the substrate side conductive layer and the liquid crystal side conductive layer;
A liquid crystal display device. The liquid crystal display device according to claim 1.
The polarizing layer is a dye-based polarizing layer obtained by dyeing PVA with a dichroic dye.
Liquid crystal display device. The liquid crystal display device according to claim 1 or 2,
The substrate on which the polarizing layer is provided is a TFT substrate that controls application of an electric field to the liquid crystal layer by a thin film transistor,
The thin film transistor on the TFT substrate and the electrode on the polarizing layer are connected by the contact hole;
Liquid crystal display device. The liquid crystal display device according to claim 3.
In the counter substrate, which is another substrate that is not the TFT substrate, a second polarizing layer is provided on the side opposite to the liquid crystal layer.
Liquid crystal display device. The liquid crystal display device according to claim 4.
A retardation plate is provided between the counter substrate and the second polarizing layer.
Liquid crystal display device.

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