JP2009053414A - Liquid crystal display panel and liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display panel which prevents an effect of static electricity on a color filter substrate side and the elution of impurity into a liquid crystal layer from a color filter substrate, and hardly causes display irregularity with respect to an in-plane switching (IPS) type liquid crystal display panel. <P>SOLUTION: The liquid crystal display panel of the IPS type liquid crystal display panel in which a plurality of pixels are arrayed in a matrix shape comprises: a first substrate having an electrode pair that generates a transverse electric field in the pixels; a second substrate having a color filter, a transparent conductive film on the color filter, and an overcoat layer on the transparent conductive film; and a liquid crystal layer containing positive liquid crystal interposed between the first substrate and the second substrate, wherein distance between the electrode pair and the transparent electrode film is larger than the interval of the electrode pair. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a horizontal electric field type liquid crystal display panel and a liquid crystal display device.

  In general, in a liquid crystal display device, a thin film transistor array substrate (hereinafter referred to as a TFT substrate) in which a plurality of thin film transistors (TFTs) are provided on a transparent substrate, and a color filter in which a color filter is provided on the transparent substrate. A liquid crystal panel in which liquid crystal is sealed between a substrate (hereinafter referred to as a CF substrate) is used. On the TFT substrate, switching elements and liquid crystal driving electrodes connected to the switching elements are formed in a matrix array. In the CF substrate, pixels including RGB colored layers and a shielding material called a black matrix arranged between the colored layers of each color are arranged so as to correspond to the switching elements.

  Operates by aligning the liquid crystal molecules that are aligned in the horizontal direction in the vertical direction with the electric field applied to the liquid crystal sealed between the TFT substrate and the CF substrate. Conventionally, a liquid crystal driving system represented by a twisted nematic display system (TN system) has been adopted. However, this method has a problem that when the liquid crystal molecules are aligned in the vertical direction by an electric field, the brightness varies depending on the viewing direction and the viewing angle cannot be widened because the liquid crystal molecules have a certain angle with respect to the substrate.

  On the other hand, a horizontal electric field method (InPlane Switching method: hereinafter referred to as an IPS method) in which the direction of the electric field applied to the liquid crystal is made substantially parallel to the substrate interface and the liquid crystal molecules are rotated by the electric field in the horizontal direction. There is a liquid crystal display device. In the IPS liquid crystal display device, the major axis of the liquid crystal layer molecules (hereinafter also simply referred to as liquid crystal molecules) is almost parallel to the substrate surface, and the liquid crystal molecules do not rise in the vertical direction of the substrate. The change in brightness is small and there is almost no so-called viewing angle dependency. That is, it is known as a liquid crystal display device for a monitor application having a very wide viewing angle and excellent display quality as compared with a liquid crystal display device of a twisted nematic display method which is a vertical electric field method.

  An IPS liquid crystal display device performs display by rotating liquid crystal molecules with respect to a substrate in a horizontal plane. In the conventional IPS drive, an arbitrary potential is applied to a signal line on a TFT substrate, a thin film transistor is driven by a signal of a scanning line, and a potential is applied from the signal line to a pixel electrode. Depending on the potential difference between the pixel electrode and the common signal line, the alignment angle of the liquid crystal molecules is changed to change the brightness of the display. A color filter of each color layer is disposed in the transmission part of the light source of the CF substrate, and a black matrix layer is disposed as a light shielding part on the CF substrate side in a region facing the signal lines, thin film transistors, and scanning lines of the TFT substrate.

  In the IPS liquid crystal display device as described above, usually, no electrode is formed on the CF substrate side. Since the CF substrate is electrically insulated, there is a problem that display unevenness occurs due to static electricity of the CF substrate. There is also a problem that alkali metal ions are eluted from the color filter into the liquid crystal layer. As means for solving this, Patent Document 1 describes a method of sequentially laminating a transparent conductive film and an overcoat layer so as to cover a black matrix layer and a color filter layer.

JP 2003-75819 A

  By the method of Patent Document 1, it is possible to prevent the influence of static electricity and the elution of impurities from the CF substrate side to the liquid crystal layer. However, when a prototype liquid crystal display panel having a similar structure was studied, it was found that display unevenness may occur even if the CF substrate having the structure of Patent Document 1 is provided.

  Accordingly, the present invention has been made to solve the above-described problems, and is a horizontal electric field type liquid crystal display panel and liquid crystal display device, in which the influence of static electricity on the CF substrate side and from the CF substrate to the liquid crystal layer is achieved. It is an object of the present invention to provide a horizontal electric field liquid crystal display panel and a liquid crystal display device that prevent the elution of impurities and prevent display unevenness.

  A liquid crystal display panel according to the present invention is a horizontal electric field type liquid crystal display panel in which a plurality of pixels are arranged in a matrix, and includes a first substrate having an electrode pair in the pixel for generating a horizontal electric field, a color filter, A second substrate having a transparent conductive film on the color filter and an overcoat layer on the transparent conductive film, and a liquid crystal layer having a positive liquid crystal sandwiched between the first substrate and the second substrate, A liquid crystal display panel characterized in that the distance between the electrode pair and the transparent electrode film is larger than the distance between the electrode pair.

  According to another aspect of the present invention, there is provided a liquid crystal display device comprising the above-described liquid crystal display panel, a circuit for applying a voltage to the electrode pair, and a circuit for controlling the voltage of the transparent conductive film.

  A liquid crystal display panel according to the present invention is a horizontal electric field type liquid crystal display panel in which a plurality of pixels are arranged in a matrix, and includes a first substrate having an electrode pair for generating a horizontal electric field in the pixel, a color filter, A second substrate having a transparent conductive film on the color filter and an overcoat layer on the transparent conductive film; and a liquid crystal layer having a positive type liquid crystal sandwiched between the first substrate and the second substrate. Since the distance between the electrode pair and the transparent electrode film is larger than the distance between the electrode pair, the influence of static electricity on the CF substrate side and the elution of impurities from the CF substrate to the liquid crystal layer can be prevented, and display unevenness can be prevented. Can do.

  In addition, since the liquid crystal display device of the present invention includes the above-described liquid crystal display panel, a circuit for applying a voltage to the electrode pair, and a circuit for controlling the potential of the transparent conductive film, stable display unevenness can be prevented. Can do.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In addition, the same code | symbol is attached | subjected about the same component and it abbreviate | omits without repeating the description.

Embodiment 1 FIG.
FIG. 1 is a perspective view showing the overall configuration of the liquid crystal display device according to Embodiment 1 of the present invention. A liquid crystal display panel 50 in which the liquid crystal layer 1 is sandwiched between the transparent CF substrate 4 and the transparent TFT substrate 7, a drive circuit 51 for driving the liquid crystal display panel 50, and from the back side of the liquid crystal display panel 50 to the front direction. A light source 53 for irradiating light and a light source control circuit 54 for controlling the light source 53 are provided. A plurality of pixels are arranged in a matrix in the display area 55 of the liquid crystal display panel 50. An electric signal corresponding to image data to be displayed is input to the data input unit 52 of the drive circuit 51. The drive circuit 51 controls the transmittance for each pixel based on the input signal. As a result, the brightness of light emitted from the light source 53 through the liquid crystal display panel 50 in the front direction is controlled for each pixel, and an image is displayed in the display area 55. The light source control circuit 54 receives a signal related to image display from the drive circuit 51, and blinks the light source 53 or changes the brightness according to the signal. Although not shown in the figure, the liquid crystal display panel 50 has a structure in which the CF substrate 4 and the TFT substrate 7 are sealed at their peripheral portions and the liquid crystal layer 1 is enclosed. The light source 53 is, for example, a light guide plate in which a lamp or LED is installed at one end, a surface emitting LED, or the like. Further, the drive circuit 51 may be formed on the TFT substrate 7 outside the display area 55.

  FIG. 2 is a cross-sectional view showing the structure of the liquid crystal display panel of the liquid crystal display device according to Embodiment 1 of the present invention, and shows a part of the cross section of the pixel of the liquid crystal display panel 50 in FIG. In FIG. 2, the liquid crystal layer 1 is a transparent TFT substrate 7 on which an electrode pair composed of an electrode b9 and an electrode a8 for controlling the orientation direction of the liquid crystal molecules 2 of the liquid crystal layer 1 is formed, and a transparent on which a color filter 5 is formed. Sandwiched between CF substrates 4. The electrode b9 and the electrode a8 are formed with an interval of d2, and each of them forms an electrode pair for applying a voltage from different wirings to generate a horizontal electric field on the substrate surface. The color filter 5 is made of, for example, a resin that transmits one of blue, red, and green light. In the pixels for displaying these colors, the color filter 5 is surrounded by a black matrix layer 6 made of a black resin formed as a light shielding portion.

  A transparent conductive film 3 is formed on the liquid crystal layer 1 side of the color filter 5, and an overcoat layer 10 is formed on the liquid crystal layer 1 side of the transparent conductive film 3. An alignment film 12 is formed on the liquid crystal layer 1 side of the overcoat layer 10. An alignment film 11 is formed on the surfaces of the electrodes b9 and a8 on the liquid crystal layer 1 side of the TFT substrate 7. These alignment films 11 and 12 are for aligning the liquid crystal molecules 2 in contact with them in a certain direction.

  A distance d3 between each of the electrodes a8 and b9 and the transparent conductive film 3 formed on the CF substrate 4 is set to be longer than a distance d2 between the electrodes a8 and b9. Although not shown in the drawing, a spacer for determining the thickness d1 of the liquid crystal layer 1 is provided between the CF substrate 4 side and the TFT substrate 7 side. The transparent conductive film 3 and the alignment film 11 are thin, and d3 is mainly determined by the sum of d1 and the thickness d4 of the overcoat layer 10. Therefore, the thickness of the overcoat layer 10 and the height of the spacer are set so that the sum of d4 and d1 is larger than d2. In addition, when it has an electrode structure from which the height of the electrode a8 and the electrode b9 differs, the distance with the electrode close | similar to the transparent conductive film 3 is set to d3. The electrode interval d2 is the interval at which the electrode a8 and the electrode b9 generate a transverse electric field, and is the interval between the end of the electrode a8 and the end of the electrode b9 as shown in FIG. However, when the width of the electrode a8 and the electrode b9 is significantly smaller than the thickness d1 of the liquid crystal layer 1, the center of each electrode may be set as the interval.

  Each of the CF substrate 4 and the TFT substrate 7 has a polarizing plate 14 and a polarizing plate 15 on the side opposite to the liquid crystal layer 1. The light from the light source arranged under the TFT substrate becomes linearly polarized light through the polarizing plate 14, passes through the liquid crystal layer 1, becomes light that is strongly colored with a specific wavelength by the color filter 5, and the CF substrate 4. Light is emitted to the front side of the liquid crystal display panel through the polarizing plate 15 on the side. From the liquid crystal display panel to the front side, the intensity of light changes depending on the direction of the transmission axis of the polarizing plates 14 and 15 on both sides and the degree of rotation of the polarized light when passing through the liquid crystal layer 1.

  As the liquid crystal molecules 2 of the liquid crystal layer 1, positive type liquid crystal which is liquid crystal having positive dielectric anisotropy is used. The liquid crystal molecules 2 are aligned along the direction of the electric field generated between the electrode b9 and the electrode a8. The electrode b9 and the electrode a8 disposed so as to face the TFT substrate 7 form a lateral electric field in the liquid crystal layer 1 in a direction along the surface of the substrate 7. This lateral electric field causes the liquid crystal molecules 2 to rotate in a plane parallel to the surface of the liquid crystal display panel, thereby controlling the amount of rotation of the polarization of light passing through the liquid crystal layer 1 and consequently controlling the intensity of light emitted from the panel. The The strength of the electric field between the electrode b9 and the electrode a8 is controlled by the drive circuit of FIG. As described above, the liquid crystal display device according to the first embodiment controls the light by rotating the liquid crystal molecules 2 along a plane parallel to the panel, and is generally referred to as a horizontal electric field method or an IPS method. Device.

  FIG. 3 is a cross-sectional view showing the structure of the liquid crystal display panel of the liquid crystal display device according to Embodiment 1 of the present invention. FIG. 3 shows a state in which a voltage difference is generated between the electrode b9 and the electrode a8. Yes. The alignment film 12 and the alignment film 11 align the liquid crystal molecules 2 in parallel in a direction shifted by 5 to 15 ° from the depth direction of the paper surface. When an electric field is generated between the electrodes b9 and a8 arranged in the horizontal direction in the drawing due to the voltage difference, the liquid crystal molecules 2 rotate along the electric lines of force 40 indicating the direction of the electric field. Since the liquid crystal alignment direction and the electrode depth direction are deviated by 5 to 15 °, the rotation direction of the liquid crystal molecules is uniformly determined when a voltage is applied between the electrodes, and the generation of domains can be suppressed. When the voltage difference is eliminated, the liquid crystal molecules 2 in the liquid crystal layer 1 return to the alignment according to the alignment films 11 and 12 again as shown in FIG.

  FIG. 4 is a plan view showing the structure of the liquid crystal display panel of the liquid crystal display device according to the first embodiment of the present invention, and shows the configuration in the pixel region 20 on the TFT substrate. 2 and 3 correspond to a cross section taken along the line AA of FIG. The electrode b9 and the electrode a8 on the TFT substrate 7 each have a comb shape within the substrate surface, and have an interdigital arrangement in which the comb teeth are combined with each other. Since the comb teeth of the electrode b9 and the comb teeth of the electrode a8 are close to each other and parallel to each other, and the distance between them is constant, an electric field having the same intensity is generated along the same direction in the plane. To do. In addition, it is good also as a structure which combined the electrode which has two or more directions of a comb tooth so that there may be two or more electric field directions in a surface. Further, if the direction of the electric field generated by the electrode b9 and the electrode a8 and the intensity are substantially the same, each may not be a comb shape. For example, even if one side has a shape like a fish bone and the other side is configured such that the comb teeth are located between the bones, the electrodes are parallel to each other at a certain distance, and the electric field direction and strength Can be generally the same. In addition, although the comb tooth portions of the electrode a8 and the electrode b9 are straight lines parallel to each other, they may be curved or polygonal teeth having a constant interval.

  In the pixel region 20, a source line 24, a gate line 22, and a common line 23 are connected. Electrical signals are sent from the drive circuit 51 to the pixel region 20 through these lines. In the figure, the source line 24 and the gate line 22 intersect, and the common line 23 and the gate line 22 are parallel. The common line 23 and the source line 24 may be parallel.

  A transistor 25 whose on / off is controlled according to the signal of the gate line 22 is provided in the pixel region 20. The source 25 side of the transistor 25 is connected to the source line 24, the drain 29 side is connected to the electrode b 9, and the gate 27 is connected to the gate line 22. The transistor 22 is turned on by the electric signal of the gate line 22, and the potential of the source line 24 is transmitted to the electrode b9. A constant voltage is applied to the common line 23 within one frame period. Since the electrode a8 is connected to the common line 23, a constant voltage is applied. Thus, the potentials of the electrode a8 and the electrode b9 are given from the common line 23 and the source line 24. Note that a capacitor between the electrode a8 and the electrode b9, and although not shown in the figure, a storage capacitor is provided between the electrode b9 and the common line 23, so that the transistor 25 is turned on next to the gate line 22. The potential of the electrode b9 is held until a signal is input.

  FIG. 5 is a plan view showing the structure of the liquid crystal display panel of the liquid crystal display device according to Embodiment 1 of the present invention, in which the black matrix layer 6 of the CF substrate 4 is superimposed on the structure of the TFT substrate of FIG. is there. As shown in the figure, the periphery of the pixel region 20 is surrounded by a black matrix layer 6 that absorbs light. Although not shown in the drawing, the color filter 5 is formed in the opening 35 surrounded by the black matrix layer 6. The opening 35 is located above the region where the electrode b9 and the electrode a8 generate an electric field, and the black matrix layer 6 is located above the source line 24, the gate line 22, the common line 23, and the transistor 25. This prevents external light from the front side from being diffusely reflected by each wiring, and light that is not subjected to electric field control from being emitted from the back side to the front and lowering the contrast.

  FIG. 6 is a plan view for explaining the structure of the liquid crystal display device according to Embodiment 1 of the present invention, and shows the positional relationship between the pixels and the transparent conductive film on the CF substrate. As shown in the figure, the transparent conductive film pattern Q is opposed to the entire display region 55 composed of pixels arranged in a matrix. Common lines C1,... C5 and gate lines G1,... G5 are connected to the pixels from the scanning circuit 57, and source lines S1,. Note that the connection relationship between these wirings in the pixel, the electrode a8, the electrode b9, and the transistor 25 is the same as that in FIG. 4, and therefore, only the upper left pixel is shown and the other pixels are omitted. The image data to be displayed is input to the data input unit 52 of the image signal processing circuit 56, and signal compensation or the like according to the characteristics of the panel is performed by the image signal processing circuit 56, and the image data is transferred to the scanning circuit 57 and the signal circuit 58. A corresponding electrical signal is output. In response to the electrical signal, the scanning circuit 57 outputs a signal so as to sequentially scan the gate lines C1,... C5, and sequentially turns on and off the transistors 25 of the pixels connected by the gate lines. A potential to be applied to the pixel is supplied from the signal circuit 58 to the electrode b of the pixel in which the transistor 25 is turned on by the signal of the gate line. Although the potential of the electrode a which is a common electrode is output from the scanning circuit 57 side in the drawing, it may be output from another circuit.

  Further, a transparent conductive film control circuit 59 for controlling the potential of the transparent conductive film pattern Q is provided. The transparent conductive film control circuit 59 is connected to the scanning circuit 57 so that the potential of the transparent conductive film pattern Q is between the common line potential and the source line potential. Thereby, the potential of the transparent conductive film pattern Q can be stabilized. Note that the image signal processing circuit 56, the scanning circuit 57, the signal circuit 58, and the transparent conductive film control circuit 59 in FIG. 6 are circuits constituting the drive circuit 51 in FIG.

  In addition, although the transparent conductive film control circuit 59 is provided, the potential of the transparent conductive film pattern Q may be a floating potential that is affected by the voltages of the electrodes a8 and b9 in the entire display region 55. Although a stable potential cannot be obtained, a potential between the potential of the common line and the potential of the source line can be obtained.

FIG. 7 is a cross-sectional view showing a manufacturing process of the liquid crystal display panel 50 of the liquid crystal display device according to the first embodiment of the present invention. First, as shown in (a), the pattern of the color filter 5 and the black matrix layer 6 are formed on the CF substrate 4 by using a printing method or a photoengraving method using a resin having a dye or a pigment and a black resin. To do. Next, as shown in (b), a transparent conductive film 3 such as ITO (Indium Tin Oxide) or AZO (ZnO ₂ : Al ₂ O ₃ ) is formed on the surface of the color filter 5 and the black matrix layer 6 by sputtering or vapor deposition. To do. For example, when ITO is used, the thickness may be 200 nm or less. Next, as shown in (c), the overcoat layer 10 is formed by coating. At this time, the thickness of the overcoat layer 10 is adjusted so that the distance d3 between the electrodes on the transparent conductive film 3 and the TFT substrate 7 is larger than the comb-shaped electrode distance d2 on the TFT substrate 7.

  The distance between the transparent conductive film 3 and the electrode on the TFT substrate 7 is determined by the total thickness of the alignment film 12, the liquid crystal layer 1, and the overcoat layer 10. Among these, the thickness of the alignment film 12 is about 100 nm, which is 1/10 or less of the thickness of the liquid crystal layer 1 or the overcoat layer 10 and can be ignored. The thickness of the liquid crystal layer 1 is designed so that the product of the birefringence Δn of the liquid crystal and the liquid crystal layer thickness d is λ / 2 (λ is the wavelength of visible light). The range of birefringence Δn of the liquid crystal used in the IPS liquid crystal panel is about 0.08 to 0.11, and when λ is 560 nm, the range of the liquid crystal layer thickness d is 2.5 to 3.5 μm. The degree is small. For this reason, by increasing the thickness of the overcoat layer 10, the distance d3 between the electrodes on the transparent conductive film 3 and the TFT substrate 7 can be made larger than the comb-shaped electrode distance d2 on the TFT substrate 7.

  On the other hand, on the TFT substrate 7 side, the transistor 25, the electrode a8, the electrode b9, and each wiring are formed on the TFT substrate 7 as shown in FIG. Although not shown in the drawing, an alignment film made of polyimide or the like is formed on the surface of the CF substrate 4 in (c) and the surface of the TFT substrate 7 in (d). Finally, as shown in (e), the CF substrate 4 and the TFT substrate 7 are opposed to each other with the spacer 16 interposed therebetween, and the periphery is sealed in a state where the distance between the substrates is constant, and liquid crystal is injected into the gap. The liquid crystal layer 1 is formed. A liquid crystal display panel is completed by the above procedure. The spacers 16 are spherical, and the CF substrate 4 and the TFT substrate 7 are sandwiched between the CF substrate 4 and the TFT substrate 7 after the spherical spacers 16 are dispersed on the CF substrate 4 or the TFT substrate 7. Columnar spacers may be formed in advance.

  As described above, the liquid crystal display panel 50 according to the first embodiment has a transparent conductive film and overcoat so as to cover the black matrix layer and the color filter layer, as described in JP-A-2003-075819. A CF substrate in which layers are sequentially stacked is used. For this reason, the influence of static electricity on the CF substrate side and the elution of impurities from the CF substrate to the liquid crystal layer can be prevented.

  However, when a liquid crystal display panel having a similar structure was prototyped, it was found that display unevenness may occur even when the CF substrate having the structure of Patent Document 1 is provided. As a result of the examination, it was speculated that the cause was due to the influence from the electrode and wiring on the TFT substrate 7 side. Therefore, the liquid crystal display panel 50 according to the first embodiment adjusts the thicknesses of the liquid crystal layer 1 and the overcoat layer 10 so that the distance d3 between the transparent conductive film 3 and the distance d2 between the electrode pairs on the TFT substrate 7 side is set. Increased. Thereby, display unevenness can be made difficult to occur.

  Further, by providing the transparent conductive film control circuit 59 for controlling the potential of the transparent conductive film 3 so that the difference between the potentials of the electrodes a8 and b9 and the potential of the transparent conductive film 3 is reduced, stable display is achieved. Unevenness can be made difficult to occur.

  The effect will be described below. FIG. 8 is a cross-sectional view showing the operating state of the liquid crystal display device according to Embodiment 1 of the present invention, and shows the electric fields generated by the electrodes a8 and b9. Note that the potential of the transparent conductive film 3 is intermediate between the potential of the electrode a8 and the potential of the electrode b9. In the figure, dotted lines indicate electric lines of force corresponding to the electric field. The relative dielectric constant in the minor axis direction of the liquid crystal molecules of the positive liquid crystal used in the lateral electric field type liquid crystal display device is about 4, which is almost the same as the relative dielectric constant of the organic film forming the overcoat layer 10. Since the distance d3 between the electrodes a8 and b9 and the transparent conductive film 3 formed on the CF substrate 4 is larger than the distance d2 between the electrodes a8 and b9, the electric field generated by the electrodes a8 and b9 is transparent. It can be seen that it is difficult to reach the film 3. On the other hand, FIG. 9 is a cross-sectional view showing the operating state of the liquid crystal display device according to the comparative example of the first embodiment of the present invention, and shows the state of the electric field generated by the electrodes a8 and b9. In the comparative form, d3 and d2 are the same. In the comparative form, the lines of electric force drawn into the transparent conductive film 3 increase, indicating that the transparent conductive film 3 is strongly influenced by the potential of the electrode pair. When the distance from the electrode is closer than the electrode interval d2, the influence of the potential of the electrode pair on the transparent conductive film 3 increases rapidly.

  As described above, the liquid crystal display panel 50 of the liquid crystal display device according to the first embodiment has the transparent conductive film 3 on the color filter 5, so that the color filter 5 and the CF substrate 4 side have the electrodes a8 and b9 and the source. It becomes difficult to be affected by a local electric field from the line 24 or the gate line 22, and it is possible to prevent display unevenness due to the localized electric charges on the CF substrate 4 side due to the electric field. Further, the transparent conductive film 3 has an effect of reducing the influence of the electric field that the liquid crystal layer 1 receives from the outside of the liquid crystal display panel 50. In addition, it is effective to prevent impurities from diffusing from the color filter 5 to the liquid crystal layer 1. In addition, since the driving voltage leaking to the transparent conductive film 3 side can be reduced, the driving power can be reduced.

  When the distance d3 between the electrodes a8 and b9 and the transparent conductive film 3 formed on the CF substrate 4 is closer than the distance d2 between the electrodes a8 and b9, the electric field generated by the electrodes a8 and b9 is transparent. The effect on the conductive film 3 side is large, and local electric field distribution occurs in the transparent conductive film 3 itself, resulting in display unevenness. However, since d3 is made larger than d2 as described above, this influence is greatly reduced. Display unevenness is reduced.

  The liquid crystal display panel as described above is particularly effective when a colorant having a photoconductive property is used as the color filter 5. If the pigment is contained at a high concentration in order to widen the color reproducibility, the color filter 5 is likely to have photoconductivity. If charges are accumulated in the color filter 5 due to an electric field from the TFT substrate side, display unevenness occurs. Similarly, when the charge is accumulated in the black matrix layer 6 as well, display unevenness occurs. In the liquid crystal display panel 50 as described above, since the electric field is shielded by the transparent conductive film 3, display unevenness can be made difficult to occur.

  Further, by connecting the transparent conductive film control circuit 57 to the transparent conductive film pattern Q, the potential of the transparent conductive film is controlled, so that it is possible to stably prevent display unevenness.

  Further, the potential of the transparent conductive film pattern Q is set to the potential between the potential of the electrode a8 and the potential of the electrode b9, but may be the same as the potential of the common line 23, that is, the potential of the electrode a8. Since there is no potential difference between the electrode a8, the common line 23, and the transparent conductive film pattern Q, an electric field to the transparent conductive film pattern Q is mainly generated between the electrode b9. Also in this case, since d3> d2 as described above, the influence from the electrode b9 can be reduced.

  In FIG. 6, the transparent conductive film control circuit 59 is connected to the scanning circuit 57, but the transparent conductive film control circuit 59 may be connected to the signal circuit 58. When controlling the potential of the transparent conductive film 3 with reference to the potential of the common line, the transparent conductive film control circuit 59 is connected to the scanning circuit 57 that outputs the potential of the common line. It is preferable to output the potential of the transparent conductive film 3 from the transparent conductive film control circuit 59 in response to the above signal. When the control is performed using the potential of the source line as a reference, the transparent conductive film control circuit 59 is connected to the signal circuit 58 and receives the output signal of the potential of the source line to receive the transparent conductive film 3 from the transparent conductive film control circuit 59. It is preferable to output a potential of.

  As described above, the liquid crystal display panel 50 of the liquid crystal display device according to the first embodiment of the present invention is a horizontal electric field type liquid crystal display panel in which a plurality of pixels are arranged in a matrix, and is arranged at a predetermined interval d2. A TFT substrate 7 having a pair of electrodes for generating a lateral electric field in the pixel, a color filter 5, a transparent conductive film 3 on the color filter 5, and an overcoat layer 10 on the transparent conductive film 3; A liquid crystal layer 1 having a positive liquid crystal sandwiched between a TFT substrate 7 and a CF substrate 4, and a distance d3 between the electrode pair and the transparent electrode film 3 being larger than a predetermined distance d2 between the electrode pair. Therefore, the influence of static electricity on the CF substrate 4 side and the elution of impurities from the CF substrate 4 to the liquid crystal layer can be prevented, and display unevenness can be made difficult to occur.

  Further, since the liquid crystal display panel 50, a circuit for applying a voltage to the electrode pair, and the transparent conductive film control circuit 59 for controlling the potential of the transparent conductive film are provided, stable display unevenness can be prevented. it can.

Embodiment 2. FIG.
FIG. 10 is a cross-sectional view showing the structure and operating state of the liquid crystal display device according to Embodiment 2 of the present invention, and shows the electric fields generated by electrodes a8 and b9. The liquid crystal display device according to the second embodiment of the present invention is basically the same as the first embodiment, but the thickness d4 of the overcoat layer 10 is larger than the thickness d1 of the liquid crystal layer 1.

  The electric field generated between the electrode a8 and the electrode b9 has a large amount of horizontal component in the region close to the TFT substrate 7, and the vertical electric field component perpendicular to the substrate increases as the distance from the TFT substrate 7 increases. When a positive type liquid crystal is used as the liquid crystal molecule 2, the liquid crystal molecule 2 is easily aligned in a direction perpendicular to the substrate in a portion where the vertical electric field is large. The liquid crystal molecules 2 aligned in the vertical direction cause a reduction in transmittance and contrast in a horizontal electric field type liquid crystal display device.

  In the liquid crystal display panel of the liquid crystal display device according to the second embodiment of the present invention, since the thickness d4 of the overcoat layer 10 is larger than the thickness d1 of the liquid crystal layer 1, the liquid crystal layer 1 is confined in a region having a large transverse electric field component. Since it is prevented from being affected by a vertical electric field, a high-quality display with a small reduction in transmittance and high contrast can be realized.

  Further, the voltage applied between the transparent conductive film 3 and the electrode on the TFT substrate 7 is divided mainly into the liquid crystal layer 1 and the overcoat layer 10 according to the ratio of the thicknesses. For example, when the thicknesses of the liquid crystal layer 1 and the overcoat layer 10 are the same, half of the voltage applied between the transparent conductive film 3 and the electrode on the TFT substrate 7 is reduced between the liquid crystal layer 1 and the overcoat layer 10. Respectively. For this reason, in a panel where the thickness d4 of the overcoat layer 10 is larger than the thickness d1 of the liquid crystal layer 1, the potential of the transparent conductive film 3 on the color filter 5 is set to the potential of the electrode a8 which is a common electrode on the TFT substrate 7 side. Is set to be the same as that of the liquid crystal layer 1, the voltage applied in the vertical direction is smaller than half of the voltage applied between the comb electrodes. By doing so, the rising displacement in the vertical direction of the liquid crystal molecules is reduced, and the decrease in transmittance can be reduced. In addition, since the driving voltage leaking to the transparent conductive film 3 side can be reduced, the driving power can be reduced.

  Further, when the thickness d1 of the liquid crystal layer is set to be equal to or less than half of the electrode interval d2, the liquid crystal layer 1 is confined in a region having a larger lateral electric field component, so that contrast can be further increased.

  As described above, in the liquid crystal display panel 50 of the liquid crystal display device according to the second embodiment of the present invention, the thickness d4 of the overcoat layer 10 is larger than the thickness d1 of the liquid crystal layer 1 in addition to the configuration of the first embodiment. So the display quality is improved.

Embodiment 3 FIG.
FIG. 11 is a graph showing the driving method of the liquid crystal display device according to the third embodiment of the present invention, and shows the time change of the potential of each electrode and the transparent conductive film. The configuration of the apparatus is the same as that described in the first or second embodiment. In the figure, Va is the potential of the electrode a8, Vb is the potential of the electrode b9, and Vc is the potential of the transparent conductive film. There are two types (a) and (b) of FIG. 11 because of the difference in the driving method of each electrode. 11A and 11B show the magnitude relationship between the potential Va of the electrode a8 and the potential Vb of the electrode b9, that is, the polarity is inverted every frame period (hereinafter referred to as inversion driving). ing.

  FIG. 11 (a) shows a driving method in which Va is a constant voltage and Vb is alternately repeated so as to be larger or smaller than Va every frame period. FIG. 11B shows a driving method in which Va is repeated so that the potentials of the low potential L and the high potential H are repeated every frame period, and Vb is made larger or smaller than Va. Yes. The method (b) is a method in which both Va and Vb are changed every frame period. The signal voltage Vb can be lowered by changing the potential Va of the common electrode every frame period.

  Note that the polarity inversion of the electrode pair may be configured such that, for example, a positive voltage and a negative voltage are alternately switched as long as the magnitude of the voltage is switched. In such inversion driven liquid crystal, the transparent conductive film control circuit 59 sets the potential Vc of the transparent conductive film 3 to Va, Vb or a potential between Va and Vb. Note that this inversion driving is performed to prevent a phenomenon that the liquid crystal is likely to be deteriorated when long-term display is performed with only one polarity.

  The liquid crystal display device according to the third embodiment of the present invention is a display device that is inverted and driven as described above, and controls the potential of the transparent conductive film 3 by the transparent conductive film control circuit 59 in accordance with the inversion of the polarity of the frame. It is.

  11 (a) and 11 (b) both show a driving state in which the difference between Vb and Va is maximum, that is, the electric field generated by the electrode pair is maximum, and Vc is approximately halfway between Va and Vb. An example of a value is shown. The potential Vc of the transparent conductive film 3 is approximately between Va and Vb in the pixel region where the electric field strength is highest, and the transparent conductive film 3 can hardly affect the electric field generated by the electrode pair. . That is, since the voltage difference between the transparent conductive film 3 and the electrode pair is reduced, the electric field generated between the transparent conductive film 3 and the electrode pair can be reduced. In particular, when the maximum and minimum values of Vb are substantially the same as Va as shown in (b), the transparent conductive film control circuit 59 can be simplified by setting Vc to an average value of H and L, that is, a constant voltage.

  As described above, in the display device that performs inversion driving, the transparent conductive film control circuit 59 causes the potential of the transparent conductive film 3 to be between the potentials of the electrode pairs that generate the transverse electric field. 3, the color filter 5 and the black matrix layer 6 are shielded so as to reduce the influence of the electric field generated by the electrode, and the electric field generated between the transparent conductive film 3 and the electrode pair is reduced, thereby reducing the occurrence of display unevenness. can do.

  Since there is a slight difference in the transmittance of pixels due to the difference in polarity, flickering of the screen may occur when the polarities of the pixels in the entire display region are the same. In order to reduce this flicker, the polarities of adjacent pixels may be different. In the case of the driving conditions in FIG. 11A, flickering of the screen can be suppressed by driving (dot inversion) so that the polarities of the pixel electrode potentials Vb of adjacent pixels are different. When the transparent conductive film 3 is not patterned, the potential Vc of the transparent conductive film 3 may be set to the middle of the pixel electrode potential Vb in the entire pixels having different polarities, that is, the same as the common electrode potential Va. In this case, although the effect of reducing the voltage difference between the electrode and the transparent conductive film 3 is small, it is effective to prevent display unevenness from occurring due to the influence of the electric field outside the liquid crystal display panel.

  In the driving condition of FIG. 11B, in order to make the polarities of adjacent pixels different, it is necessary to change not only the pixel electrode potential Vb but also the common electrode potential Va. However, since it is difficult to control the common electrode for each pixel in terms of pattern formation, to reduce screen flicker, the polarity of the pixel must be different for each row, for example, by patterning the common electrode for each row. Must be (line inversion drive). In the case of line inversion driving, there is an advantage that the longitudinal electric field strength generated between the transparent conductive film 3 of the CF substrate and the electrode of the TFT substrate can be halved as compared with the dot inversion driving of FIG.

Embodiment 4 FIG.
FIG. 12 is a plan view showing the configuration of the liquid crystal display device according to Embodiment 4 of the present invention. Although the basic configuration is the same as that of the first and second embodiments, the transparent electrode film 3 for each pixel group connected to the gate lines G1. Is divided. Further, the transparent conductive film control circuit 59 is connected to each of the divided transparent electrode film patterns Q1,.

  FIG. 13 is a schematic diagram showing a driving method of the liquid crystal display device according to the fourth embodiment of the present invention. In the fourth embodiment, the polarities of pixels in a certain frame are different for each row. (A) and (b) of the figure show that the pixels arranged in the matrix have different polarities for each row. Further, (a) and (b) show the polarities in the even and odd frames, respectively, and the arrows in the figure show that the polarity is alternately inverted every frame. As described in the third embodiment, the polarity reversal means that the magnitude relationship between the potential Va of the electrode a8 and the potential Vb of the electrode b9, which is a common potential, is reversed. By doing so, flickering is reduced as compared with the case where a voltage is applied with the same polarity to all the pixels of the display screen.

  The transparent conductive film control circuit 59 controls the potentials of the transparent electrode film patterns Q1,..., Q5 facing the row whose polarity is inverted to be different according to the polarity of the row. For example, as shown in FIG. 11A, when the pixel electrode potential Vb1 in the first row is driven to a high potential and a low potential every frame period, the difference between the common electrode potential Va and the pixel electrode potential Vb1 is W. When the common electrode potential Va is lower than the pixel electrode potential Vb1, the potential Vc1 of the transparent electrode film pattern Q1 is set to Va + W / 2. Since the common electrode potential Va in the second row is higher than the pixel electrode potential Vb2 during this frame period, the potential Vc2 of the transparent electrode film pattern Q2 is set to Va−W / 2. The Q1 potential Vc1 is Va-W / 2 and the Q2 potential Vc2 is Va + W / 2 one frame period after the polarity is inverted. The potentials of the transparent electrode film patterns for the odd and even rows having the same polarity are controlled to be different.

  In this way, the transparent electrode film 3 that is opposed to each pixel group that is connected to the same signal line and the electrode pair is driven with the same polarity is divided, and the potential of the divided transparent conductive film pattern is set to the electrode pair. Therefore, even in line inversion driving, the electric field generated between the transparent electrode film 3 and the electrode pair can be reduced in the entire display region, and display unevenness can be made difficult to occur. . In FIG. 12, the transparent conductive film control circuit 59 is connected to the scanning circuit 57 through the signal lines of T1,... T5, and the potential of the common line in each row is input. In the case where the potential of the transparent conductive film pattern is controlled based on the potential of the source line, the transparent conductive film control circuit 59 may be connected to the signal circuit and input the potential of each source line.

  FIG. 14 is a cross-sectional view of the CF substrate of the liquid crystal display device according to the fourth embodiment of the present invention. (A) of a figure is sectional drawing at the time of dividing | segmenting the transparent electrode film 3 before formation of the overcoat film | membrane 10, (b) of a figure patterns the overcoat film | membrane 10, A transparent electrode film | membrane is used using this pattern. It is sectional drawing at the time of dividing 3. The pattern formation of the transparent electrode film 3 in (a) can be performed by forming a mask pattern with a photoresist, etching the transparent electrode film 3, and removing the mask pattern. In the case of (b), the overcoat film 10 itself is patterned using a photosensitive transparent resin, and the transparent electrode film 3 is etched using this as a mask. Note that the divided areas in the display area are all on the black matrix layer 6. Therefore, the transparent electrode film 3 covers the area of the color filter 5 in the opening of the black matrix layer 6.

  Further, the gaps 38 between the transparent electrode films 3 after being divided as shown in FIG. 14 are considerably smaller than the width of the black matrix layer 6. If the adjacent transparent electrode film 3 patterns have different potentials, an electric field is generated in the gap 38 and the orientation of the liquid crystal changes. However, since the gap 38 is located at the position covered with the black matrix layer 6 when viewed from the front side of the panel, the display is not affected.

  Further, in Embodiment 4 of the present invention, the potential is controlled by dividing the transparent conductive film for each pixel row in which one of the electrode pairs is connected by the common line, but the polarity is inverted for each pixel column connected by the source line. In that case, the potential may be controlled by dividing the transparent conductive film for each pixel column. In addition, when the polarity is reversed for each image arranged in a checkered pattern by meandering the common line, the potential of the transparent conductive film may be divided for each pixel group connected by the meandering common line to control the potential. In the case of inverting the polarity for each of a plurality of pixel rows and a plurality of pixel columns, the potential may be controlled by dividing the transparent conductive film for each of the plurality of pixel rows and the plurality of pixel columns. In addition, the driving method in which the polarity is inverted every other row may be controlled so that the potential of the transparent conductive film every other row is the same. It is preferable to be electrically connected to the outside.

  As described above, the liquid crystal display panel according to the fourth embodiment of the present invention has a plurality of pixel groups each composed of a plurality of pixels connected to the same signal line, and the region in units of these pixel groups is driven with the same polarity. Is done. The transparent conductive film is divided into a region where the electrode pair is driven with the same polarity and a region where the electrode pair is driven with a different polarity. Thereby, for each region, the difference between the potential of the transparent conductive film corresponding to the region and the potential of the electrode pair in those regions can be reduced. Accordingly, in the driving in which the polarity is changed for each pixel region, display unevenness can be suppressed as compared with the case where a transparent conductive film that is not divided is used.

  In addition, the transparent conductive film control circuit 59 independently controls the potential of the transparent conductive film 3 in the pixel region driven with different polarities. Thereby, since the potential of the transparent conductive film 3 in each region can be set to a potential between the potentials of the electrodes of the electrode pair, it is possible to stably suppress display unevenness. In addition, the influence of the electric field outside the liquid crystal display panel can be prevented.

1 is a perspective view illustrating an overall configuration of a liquid crystal display device according to a first embodiment of the present invention. It is sectional drawing explaining the structure of the liquid crystal display device of Embodiment 1 of this invention. It is sectional drawing explaining the structure of the liquid crystal display device of Embodiment 1 of this invention. It is a top view explaining the structure of the liquid crystal display device of Embodiment 1 of this invention. It is a top view explaining the structure of the liquid crystal display device of Embodiment 1 of this invention. It is a top view explaining the structure of the liquid crystal display device of Embodiment 1 of this invention. It is sectional drawing which shows the manufacturing process of the liquid crystal display device of Embodiment 1 of this invention. It is sectional drawing which shows the operation state of the liquid crystal display device of Embodiment 1 of this invention. It is sectional drawing which shows the operation state of the liquid crystal display device of the comparison form of Embodiment 1 of this invention. It is sectional drawing which shows the structure and operating state of the liquid crystal display device of Embodiment 2 of this invention. It is a graph which shows the drive method of the liquid crystal display device of Embodiment 3 of this invention. It is a top view which shows the structure of the liquid crystal display device of Embodiment 4 of this invention. It is a schematic diagram which shows the drive system of the liquid crystal display device of Embodiment 4 of this invention. It is sectional drawing of the liquid crystal display device of Embodiment 4 of this invention.

Explanation of symbols

1 liquid crystal layer, 2 liquid crystal molecules, 3 transparent conductive film, 4 CF substrate, 5 color filter, 6 black matrix layer, 7 TFT substrate, 8 electrode a, 9 electrode b, 10 overcoat layer, 11 alignment film, 12 alignment film , 14 Polarizer, 15 Polarizer, 16 Spacer, 20 Pixel region, 22 Gate line, 23 Common line, 24 Source line, 25 Transistor, 27 Gate, 28 Source, 29 Drain, 35 Opening, 38 Gap, 40 Electric force Line, 50 liquid crystal display panel, 51 drive circuit, 52 data input unit, 53 light source, 54 light source control circuit, 55 display area, 56 image signal processing circuit, 57 scanning circuit, 58 signal circuit, 59 transparent conductive film control circuit, C1 , C5 common line, G1, G5 gate line, S1, S5 source line, T1, T5 signal line, Q, Q1 Q5 transparent conductive film pattern

Claims (8)

A horizontal electric field type liquid crystal display panel in which a plurality of pixels are arranged in a matrix,
A first substrate having in the pixel an electrode pair for generating a lateral electric field;
A second substrate having a color filter, a transparent conductive film on the color filter, and an overcoat layer on the transparent conductive film;
A liquid crystal layer having a positive liquid crystal sandwiched between the first substrate and the second substrate,
The liquid crystal display panel, wherein a distance between the electrode pair and the transparent electrode film is larger than an interval between the electrode pair. The liquid crystal display panel according to claim 1, wherein the overcoat layer is thicker than the liquid crystal layer. A first region composed of a plurality of pixels whose electrode pairs are driven with the same polarity, and a second region composed of a plurality of pixels whose electrode pairs are driven with a polarity different from the pixel region, The liquid crystal display panel according to claim 1, wherein the transparent conductive film is divided between the first region and the second region. 3. A liquid crystal display device comprising: the liquid crystal display panel according to claim 1; a circuit for applying a voltage to an electrode pair; and a circuit for controlling a potential of a transparent conductive film. The liquid crystal display device according to claim 4, wherein the potential of the transparent conductive film is a potential between the potentials of the respective electrodes of the electrode pair. A liquid crystal display panel according to claim 3, comprising a circuit for applying a voltage to the electrode pair, and a circuit for controlling the potential of the transparent electrode in the first region and the transparent conductive film in the second region. Liquid crystal display device. 4. The liquid crystal display panel according to claim 3, a circuit for applying a voltage having a different polarity to the first region and the second region to the electrode pair, a potential of the transparent conductive film in the first region, and the second region And a circuit for independently controlling the potential of the transparent conductive film in the region. 8. The liquid crystal display device according to claim 6, wherein the potential of the transparent electrode in the first region and the transparent conductive film in the second region is a potential between the potentials of the respective electrodes of the electrode pair.

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