JP2016048330A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an FFS liquid crystal display device with improved light transmissivity and luminance, and a driving method of the display device.SOLUTION: The liquid crystal display device comprises: a TFT element and a first pixel electrode 5 formed on an intersection of a gate signal line on a surface of a first substrate 1 on a liquid crystal 8 side and an image signal line; a first common electrode 7 formed sandwiching and facing the first pixel electrode 5 and a first insulation layer 6, and including a slit 7a extending in a predetermined direction; a second pixel electrode 11 formed on a surface of a second substrate 15 on the liquid crystal 8 side; and a second common electrode 9 formed sandwiching and facing the second pixel electrode 11 and a second insulation layer 10, and including a second slit 9a extending in a predetermined direction. The first and second pixel electrodes 5, 11, the first and second common electrodes 7, 9, and the first and second slits 7a, 9a are positioned so as to substantially overlap respectively in plain view, and a common voltage signal with the same polarity is applied to the first and second common electrodes 7, 9.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a liquid crystal display (LCD) having a fringe field switching (FFS) type electrode structure and a driving method thereof.

  2. Description of the Related Art Conventionally, an active matrix type LCD has a TFT array side substrate on which a large number of pixel electrode portions including TFT elements are formed and a color filter side substrate on which a color filter and a black matrix are formed facing each other. Are bonded together at a predetermined interval, and a liquid crystal is filled and sealed between the substrates.

  An example of the basic configuration of a conventional active matrix LCD is shown in FIG. For example, the TFT array side substrate has a plurality of gate signal lines GLl, GL2, GL3,... GLn formed in a first direction (for example, a row direction) thereon and a first crossing the first direction. A plurality of image signal lines SLl, SL2, SL3... SLm formed to intersect the gate signal lines GLl to GLn in two directions (for example, the column direction), and the gate signal lines GLl to GLn and the image signal lines. The pixel portion Pll, P12, P13... Pnm including the TFT element 51 and the pixel electrodes PE11, PE12, PE13... PEnm, which are formed at the intersections of SL1 to SLm. In addition, when the common electrode (not shown) and the common electrode 52 that supplies the common voltage (Vcom) to the common electrode form a vertical electric field to be applied to the liquid crystal between the pixel electrodes PE11 to PEnm, A planar electrode (solid electrode) is provided on the color filter side substrate. Further, the common electrode 52 is formed on the TFT array side substrate when a horizontal electric field (in-plane field) or an edge electric field (Fringe Field) is applied between the pixel electrodes PE11 to PEnm. Is provided. In FIG. 6, 53 is a gate signal line drive circuit, and 54 is an image signal (source signal) line drive circuit.

  The TFT element 51 has a semiconductor layer made of amorphous silicon (a-Si), low-temperature polycrystalline silicon (LTPS), or the like, and has three terminal portions including a gate electrode portion, a source electrode portion, and a drain electrode portion. It is the structure which has. Then, by applying a voltage (for example, 6 V) of a predetermined potential to the gate electrode portion, it functions as a switching element (gate transfer element) that causes a current to flow through the semiconductor layer (channel) between the source electrode portion and the drain electrode portion. . The pixel electrodes PE11 to PEnm are generally composed of a transparent conductor layer made of indium tin oxide (ITO) or the like.

  A conventional FFS LCD is shown in FIGS. FIG. 3 is an enlarged plan view showing the four pixel electrodes 27 in the conventional FFS type LCD in an enlarged manner. FIG. 4 is an enlarged plan view showing four common electrodes 28 in an LCD having a conventional FFS-type electrode structure. FIG. 5 shows an example of a conventional FFS LCD, and is a cross-sectional view taken along line A1-A2 of FIG. As shown in FIG. 3, the pixel electrode 27 is a rectangular planar electrode (solid electrode), and is formed in each pixel portion. In FIG. 3, 21 is a gate signal line, 22 is an image signal line, and 23 is a TFT element. As shown in FIG. 4, a common electrode 28 is formed so as to face the pixel electrode 27, and the common electrode 28 is formed with a slit 28a extending from one end side to the other end side in the column direction. The slit 28a is formed corresponding to each pixel portion.

  As shown in FIG. 5, the FFS LCD has an electrode structure in which a pixel electrode 27 and a common electrode 28 are provided on a TFT array side substrate, and the common electrode 28 and the pixel electrode 27 sandwich an insulating layer 35. Are formed to face each other. Further, an electric field in the horizontal direction (row direction) is generated between the pixel electrode 27 and the common electrode 28 through a slit 28a formed in the common electrode 28 so as to extend in the column direction.

  Then, the liquid crystal molecules 36a are aligned along the electric field in the lateral direction in the vicinity of the side of the slit 28a, so that a large luminance with high light transmittance is obtained in the vicinity of the side of the slit 28a. An insulating layer 32 is laminated on the upper surface (surface on the liquid crystal 36 side) of the glass substrate 31 that is the TFT array side substrate, and an image signal line (source signal line) 22 is formed on the insulating layer 32. A passivation film 33 is formed to cover the upper surface and the image signal line 22. A planarization film 34 is formed on the passivation film 33, and a pixel electrode 27 made of a transparent electrode such as indium tin oxide (ITO) is formed on the planarization film 34, covering the upper surface of the planarization film 34 and the pixel electrode 27. An insulating layer 35 is formed, and a common electrode 28 made of a transparent electrode such as ITO having a slit 28 a is formed on the insulating layer 35. A color filter 38 and a black matrix 39 are formed on the lower surface (surface on the liquid crystal 36 side) of the glass substrate 40 that is the color filter side substrate, and an overcoat 37 is formed to cover the color filter 38 and the black matrix 39. By arranging the glass substrate 31 and the glass substrate 40 so that the common electrode 28 and the color filter 38 and the black matrix 39 face each other, and filling the liquid crystal 36 therebetween to seal the outer peripheral portions of both substrates. LCD is constructed.

  As another conventional example, there has been proposed an LCD in which an FFS-type electrode arrangement is employed on at least one of a pair of substrates (see, for example, Patent Document 1).

JP 2002-296611 A Republished patent WO2009 / 157313

  However, in the conventional FFS type LCD shown in FIGS. 3 to 5, since the FFS type electrode structure is formed only on the TFT array side substrate, the liquid crystal molecules 36a have the layer thickness d1 of the liquid crystal 36, That is, there is a problem that the liquid crystal molecules 36a are difficult to align over the entire distance (gap) d1 between the TFT array side substrate and the color filter side substrate. For example, the thickness d2 at which the liquid crystal molecules 36a are aligned is about two-thirds of d1, and when d1 is about 3 μm, d2 is about 2 μm. Therefore, these characteristics are insufficient for LCDs that require high light transmittance and high brightness. In particular, for LCDs for applications such as a head up display (HUD) that requires high light transmittance and high brightness, it is desired to further improve their characteristics.

  In addition, Patent Document 1 describes that an FFS-type electrode arrangement can be adopted for both substrates, but nothing is disclosed about the detailed configuration, the driving method, and the like.

  Accordingly, the present invention has been completed in view of the above problems, and an object of the present invention is to realize an FFS-type LCD with improved light transmittance and luminance and a driving method thereof.

  The liquid crystal display device of the present invention includes a plurality of gate signal lines formed in a first direction on a liquid crystal side surface of a first substrate, and the gate signal in a second direction intersecting the first direction. A plurality of image signal lines formed to intersect with the lines; thin film transistor elements and first pixel electrodes formed at intersections of the gate signal lines and the image signal lines; the first pixel electrodes; A first common electrode having a first slit extending in a predetermined direction so as to face each other with one insulating layer interposed therebetween, and a second pixel formed on a liquid crystal side surface of a second substrate An electrode, and a second common electrode having a second slit extending in the predetermined direction, which is formed to face the second pixel electrode with a second insulating layer interposed therebetween. , The first and second pixel electrodes, the first and second common electrodes, the first Beauty second slit, together are positioned so as to substantially superimpose in a plan view, respectively, said first and second common electrode has a configuration common voltage signal of the same polarity is applied.

  In the liquid crystal display device of the present invention, preferably, the liquid crystal has negative dielectric anisotropy.

  In the liquid crystal display device of the present invention, it is preferable that the common voltage signal having the same polarity is simultaneously applied to the first and second common electrodes.

  In the liquid crystal display device of the present invention, it is preferable that the first and second common electrodes are applied with the common voltage signal having a ground potential, and the first and second pixel electrodes are pixels having the same potential. While the voltage signal is applied, the pixel voltage signal is driven to invert the polarity.

  The liquid crystal display device driving method according to the present invention includes a plurality of gate signal lines formed in a first direction on a liquid crystal side surface of a first substrate, and a second direction intersecting the first direction. A plurality of image signal lines formed to intersect with the gate signal lines; a thin film transistor element and a first pixel electrode formed at an intersection of the gate signal lines and the image signal lines; and the first pixel. A first common electrode having a first slit extending in a predetermined direction and facing the electrode across the first insulating layer; and a first common electrode formed on a liquid crystal side surface of the second substrate. Two pixel electrodes, and a second common electrode having a second slit extending in the predetermined direction and formed so as to face the second pixel electrode with a second insulating layer interposed therebetween. The first and second pixel electrodes, and the first and second common electrodes. The first and second slits are driving methods of a liquid crystal display device positioned so as to substantially overlap each other in plan view, and a common voltage signal having the same polarity is applied to the first and second common electrodes. It is the structure to apply.

  The liquid crystal display device of the present invention includes a plurality of gate signal lines formed in a first direction on a liquid crystal side surface of a first substrate, and gate signal lines in a second direction intersecting the first direction. A plurality of image signal lines formed by crossing, a thin film transistor element and a first pixel electrode formed at an intersection of the gate signal line and the image signal line, a first pixel electrode, and a first insulating layer. A second common electrode formed on the liquid crystal side surface of the second substrate; a second pixel electrode formed on the liquid crystal side of the second substrate; And a second common electrode having a second slit extending in a predetermined direction and facing the pixel electrode with the second insulating layer interposed therebetween. The first and second The pixel electrode, the first and second common electrodes, and the first and second slits are substantially in plan view. Since the common voltage signal having the same polarity is applied to the first and second common electrodes, the first electrode and the second common electrode are applied over the entire gap (gap) between the first substrate and the second substrate. Liquid crystal molecules are aligned laterally along the electric field. As a result, the retardation of the liquid crystal is increased, and the light transmittance and luminance are improved. In addition, the lines of electric force are not coupled between the first common electrode and the second common electrode, that is, the first common electrode and the second common electrode are not electromagnetically coupled. Disturbances in lateral orientation do not occur. Therefore, the light transmittance and the luminance are further improved. Further, since the responsiveness and orientation of liquid crystal molecules are improved, low voltage driving is possible and power consumption can be reduced. Furthermore, when driving at a voltage equivalent to the conventional voltage, a liquid crystal having a low viscosity and a small | Δε | (absolute value of dielectric anisotropy) can be used, so that the response speed can be improved.

  In the liquid crystal display device of the present invention, preferably, the liquid crystal has negative dielectric anisotropy, and therefore is close to the first and second common electrodes like the liquid crystal having positive dielectric anisotropy. It is eliminated that the liquid crystal molecules are in an oblique alignment state in which the liquid crystal molecules slightly rise in the vertical direction (vertical direction). As a result, the retardation of the liquid crystal is further increased, and the light transmittance and luminance are further improved.

  In the liquid crystal display device of the present invention, it is preferable that a common voltage signal having the same polarity is applied to the first and second common electrodes at the same time, so that the first and second common electrodes are provided between the first substrate and the second substrate. The liquid crystal molecules are aligned laterally along the electric field in a short time over the entire interval. As a result, the response of the liquid crystal is improved.

  In the liquid crystal display device of the present invention, preferably, the first and second common electrodes are applied with a common voltage signal having a ground potential, and the first and second pixel electrodes are respectively supplied with a pixel voltage signal having the same potential. Since the polarity of the pixel voltage signal is driven while being applied, the electric lines of force are not coupled between the first common electrode and the second common electrode, that is, the first common electrode and the second common electrode are not coupled. Since the common electrodes of the liquid crystal molecules are not electromagnetically coupled, the lateral alignment of the liquid crystal molecules is not disturbed, and the polarity inversion drive is performed to suppress the occurrence of afterimages caused by applying a DC voltage component to the liquid crystal molecules for a long time, so-called image sticking. It can be performed.

  A driving method of a liquid crystal display device according to the present invention includes a plurality of gate signal lines formed in a first direction on a liquid crystal side surface of a first substrate, and a gate in a second direction intersecting the first direction. A plurality of image signal lines formed to intersect with the signal lines; a thin film transistor element and a first pixel electrode formed at an intersection of the gate signal line and the image signal line; the first pixel electrode; A first common electrode having a first slit extending in a predetermined direction so as to face each other with an insulating layer interposed therebetween; a second pixel electrode formed on a liquid crystal side surface of a second substrate; A second common electrode having a second slit extending in a predetermined direction and formed so as to face the second pixel electrode with the second insulating layer interposed therebetween, The second pixel electrode, the first and second common electrodes, and the first and second slits are respectively A driving method of a liquid crystal display device positioned so as to be substantially overlapped in a plan view, since a common voltage signal having the same polarity is applied to the first and second common electrodes, the first substrate and the second substrate The liquid crystal molecules are aligned laterally along the electric field over the entire gap (gap) between the substrates. As a result, the retardation of the liquid crystal is increased, and the light transmittance and luminance are improved. Further, the lines of electric force are not coupled between the first common electrode and the second common electrode, that is, the first common electrode and the second common electrode are not electromagnetically coupled, so that the liquid crystal molecules Disturbance in the horizontal orientation of the film does not occur. Therefore, the light transmittance and the luminance are further improved. Further, since the responsiveness and orientation of liquid crystal molecules are improved, low voltage driving is possible and power consumption can be reduced. Furthermore, when driving at a voltage equivalent to the conventional voltage, a liquid crystal having a low viscosity and a small | Δε | can be used, so that the response speed can be improved.

FIG. 1 is a diagram showing an example of an embodiment of the liquid crystal display device of the present invention, and is a partially enlarged sectional view of the liquid crystal display device. 2A and 2B are diagrams showing another example of the embodiment of the liquid crystal display device of the present invention, and FIG. 2A is a liquid crystal molecule when a liquid crystal having negative dielectric anisotropy is used. FIG. 4B is a partially enlarged cross-sectional view showing the alignment state of the liquid crystal molecules, and FIG. 5B is a partially enlarged cross-sectional view showing the alignment state of liquid crystal molecules when a liquid crystal having positive dielectric anisotropy is used. FIG. 3 is an enlarged plan view showing four pixel electrodes in a conventional FFS mode liquid crystal display device in an enlarged manner. FIG. 4 is an enlarged plan view showing four common electrodes in a conventional FFS mode liquid crystal display device. FIG. 5 shows an example of a conventional FFS mode liquid crystal display device, and is a cross-sectional view taken along line A1-A2 of FIG. FIG. 6 is a block circuit diagram showing an example of a basic configuration of a conventional active matrix liquid crystal display device. FIG. 7 is a diagram showing another example of the embodiment of the liquid crystal display device of the present invention, and is a plan view of first and second slits formed in the first and second common electrodes. FIG. 8 is a diagram showing another example of the embodiment of the liquid crystal display device of the present invention, and is a plan view showing that the positions of the first slit and the second slit are shifted. FIG. 9 is a diagram showing another example of the embodiment of the liquid crystal display device of the present invention, and is a plan view showing that the sizes of the first slit and the second slit are shifted.

  Embodiments of an LCD and a driving method thereof according to the present invention will be described below with reference to the drawings. However, each drawing referred to below shows a main part for explaining the LCD of the present invention among the constituent members in the embodiment of the LCD of the present invention. Therefore, the LCD according to the present invention may include well-known components such as a circuit board, a wiring conductor, a control IC, and an LSI that are not shown in the drawing.

  FIG. 1 is a diagram showing an example of an embodiment of the LCD of the present invention, and is a partially enlarged sectional view of the LCD. As shown in FIG. 1, a plurality of gate signal lines formed in a first direction (for example, a row direction) on a surface on the liquid crystal 8 side of a first substrate 1 made of a glass substrate or the like, and a first direction A plurality of image signal lines formed to intersect the gate signal line in a second direction (for example, the column direction) intersecting the TFT, a TFT element formed at the intersection of the gate signal line and the image signal line, and the first A first pixel electrode 5, a first common electrode 7 having a first slit 7 a extending in a predetermined direction, which is formed to face the first pixel electrode 5 and the first insulating layer 6. The second pixel electrode 11 formed on the surface of the second substrate 15 made of a glass substrate or the like on the liquid crystal 8 side is formed so as to face the second pixel electrode 11 with the second insulating layer 10 interposed therebetween. A second common electrode 9 having a second slit 9a extending in a predetermined direction. There. The first and second pixel electrodes 5 and 11, the first and second common electrodes 7 and 9, and the first and second slits 7 a and 9 a are positioned so as to substantially overlap each other in plan view. In addition, the first and second common electrodes 7 and 9 are configured to be applied with a common voltage signal having the same polarity.

  With the above configuration, the liquid crystal molecules 8a are aligned in the lateral direction along the electric field over the distance (gap) between the first substrate 1 and the second substrate 15, that is, over the entire thickness of the liquid crystal 8. As a result, the retardation Δnd of the liquid crystal 8 (Δn: difference between the refractive index of extraordinary light and the refractive index of ordinary light, d: gap) is increased, and the light transmittance and luminance are improved. Further, the lines of electric force are not coupled between the first common electrode 7 and the second common electrode 9, that is, the first common electrode 7 and the second common electrode 9 are not electromagnetically coupled. In this case, no disturbance occurs in the horizontal alignment of the liquid crystal molecules 8a. Therefore, the light transmittance and the luminance are further improved. In addition, since the responsiveness and orientation of the liquid crystal molecules 8a are improved, low voltage driving is possible and power consumption can be reduced. Furthermore, when driving at a voltage equivalent to the conventional voltage, the liquid crystal 8 having a low viscosity and a small | Δε | can be used, so that the response speed can be improved. In the case of a liquid crystal having negative dielectric anisotropy, for example, Δε = −4.5 and Δε = −3 to −1 are preferable. The distance between the first substrate 1 and the second substrate 15 is, for example, about 3 μm.

  The first and second common electrodes 7 and 9 of the LCD of the present invention have first and second slits 7a and 9a extending in a predetermined direction. For example, as shown in FIG. 4, the first and second slits 7a and 9a are formed to extend in a second direction (column direction: a direction parallel to the image signal line 22). Further, as shown in FIG. 7, the first and second slits 7a and 9a have an inverted "<" shape or the like in which the longitudinal direction extends along the second direction and has a bent portion in the middle. It may be a shape. The first and second slits 7a and 9a may be formed to extend in a direction inclined with respect to the second direction so as to form a predetermined angle with respect to the second direction.

  In the LCD of the present invention, the first and second pixel electrodes 5 and 11, the first and second common electrodes 7 and 9, and the first and second 7 a and 9 a are respectively substantially overlapped in plan view. Although they are located, their position, shape, and size need not be completely the same in plan view. The positions of the first pixel electrode 5 and the second pixel electrode 11 may be shifted by about 4 nm or less. In this case, there is a tendency that the horizontal alignment of the entire liquid crystal molecules 8a is not easily disturbed. The shape and size of the first pixel electrode 5 and the second pixel electrode 11 may be shifted by about 20% or less with respect to one pixel electrode. In this case, there is a tendency that the horizontal alignment of the entire liquid crystal molecules 8a is not easily disturbed. Similarly, the positions of the first common electrode 7 and the second common electrode 9, and the first slit 7a and the second slit 9a may be shifted by about 4 nm or less. On the other hand, the other shape and size may be shifted by about 20% or less.

  FIG. 8 is a diagram showing another example of the embodiment of the LCD of the present invention, and is a plan view showing that the positions of the first slit 7a and the second slit 9a are shifted. FIG. 8 shows a form in which the position of the second slit 9a is slightly shifted from the position of the first slit 7a in the first direction (row direction: direction parallel to the gate signal line 21). Even if it is a form, it should just be in the range of said deviation. Of course, the same applies to the case where the position of the second slit 9a is slightly shifted from the position of the first slit 7a in the second direction and other directions. Moreover, FIG. 9 is a figure which shows the other example of embodiment about LCD of this invention, and is those top views which show that the magnitude | size of the 1st slit 7a and the 2nd slit 9a has shifted | deviated. . FIG. 9 shows a form in which the size of the second slit 9a is slightly larger than the size of the first slit 7a. Even in such a form, it may be within the range of the deviation. Of course, the same applies to the case where the size of the second slit 9a is slightly smaller than the size of the first slit 7a.

  The first and second pixel electrodes 5 and 11 and the first and second common electrodes 7 and 9 are made of, for example, a translucent conductive material. Specifically, conductive materials such as ITO, indium zinc oxide (IZO), indium tin oxide added with silicon oxide (ITSO), zinc oxide (ZnO), silicon (Si) containing phosphorus and boron, etc. Thus, the conductive material has translucency. The first and second pixel electrodes 5 and 11 and the first and second common electrodes 7 and 9 are formed by, for example, a sputtering method, a thin film forming method such as a CVD (Chemical Vapor Deposition) method, a photolithography method, or the like. Is done.

  The thickness of the first and second pixel electrodes 5 and 11 and the thickness of the first and second common electrodes 7 and 9 are about 40 nm to 110 nm. Moreover, the width | variety of the 1st and 2nd slits 7a and 9a formed in the 1st and 2nd common electrodes 7 and 9 like the slit 28a shown in FIG. 4 is 2 micrometers-4 micrometers. . When the widths of the first and second slits 7a and 9a are less than 2 μm, the liquid crystal molecules 8a and the first and second slits 7a and 9a are aligned in the vicinity of the left side of the first and second slits 7a and 9a. It tends to interfere with the liquid crystal molecules 8a aligned in the vicinity of the right side, and the horizontal alignment of the liquid crystal molecules 8a tends to be disturbed. In addition, since the electric field is not sufficiently applied to the liquid crystal molecules 8a, the driving voltage tends to increase. When the widths of the first and second slits 7a and 9a exceed 4 μm, liquid crystal molecules 8a that do not align in the middle in the width direction of the first and second slits 7a and 9a tend to appear. There exists a tendency for the light transmittance in the intermediate part of the width direction of the 2nd slits 7a and 9a to fall.

  The lengths of the first and second slits 7a and 9a are preferably shorter by about 1 μm to 3 μm than the end in the column direction of the pixel electrode facing the first and second slits 7a and 9a. If it is less than 1 μm, depending on manufacturing variations, the upper and lower first and second slits 7a and 9a in the column direction are connected, and as a result, the electric field applied to the liquid crystal molecules 8a becomes weak, and the liquid crystal molecules 8a are aligned in a predetermined direction. Tend to be difficult. When the thickness exceeds 3 μm, the number of liquid crystal molecules 8a aligned in the vicinity of the sides of the first and second slits 7a and 9a is smaller than a desired number, and the light transmittance in the pixel portion tends to decrease.

  The end portions (edges) of the first and second slits 7a and 9a are preferably curved such as a semicircle projecting in the longitudinal direction of the first and second slits 7a and 9a. In this case, the disorder of the alignment of the liquid crystal molecules 8a at the ends of the first and second slits 7a and 9a tends to be small.

  The width of the portion (strip) between the adjacent first and second slits 7a, 9a in the first and second common electrodes 7, 9 is preferably 1.5 μm to 4 μm. When the width of the strip is less than 1.5 μm, the liquid crystal molecules 8a aligned in the vicinity of the left side of the strip and the liquid crystal molecules 8a aligned in the vicinity of the right side of the strip easily interfere with each other, and the horizontal alignment of the liquid crystal molecules 8a is disturbed. Tend. When the width of the strip exceeds 4 μm, liquid crystal molecules 8a that do not align in the middle portion in the width direction of the strip tend to appear, and the light transmittance in the middle portion in the width direction of the strip tends to decrease.

A light-transmitting first insulating layer 6 is provided between the first pixel electrode 5 and the first common electrode 7, and a light-transmitting property is provided between the second pixel electrode 11 and the second common electrode 9. The second insulating layer 10 is formed, and the first and second insulating layers 6 and 10 are made of an inorganic material or an organic material. As the inorganic material, silicon nitride (SiNx), silicon oxide (SiO ₂ ), or the like can be used. As the organic material, acrylic resin, polyimide, polyamide, polyimide amide, benzocyclobutene, polysiloxane, polysilazane, or the like can be used. Polysiloxane has a skeletal structure formed by the bond of silicon (Si) and oxygen (O). The polysiloxane has an organic group containing at least hydrogen as an oxygen substituent, such as an alkyl group or an aromatic hydrocarbon group, and an organic group containing at least hydrogen and a fluoro group as an oxygen substituent. It may be. Polysilazane is a material formed using a polymer material having a bond of silicon (Si) and nitrogen (N) as a starting material. If the first and second insulating layers 6 and 10 are made of an inorganic material, the first and second insulating layers 6 and 10 have a surface that conforms to the surface shape of the pixel electrodes 5 and 11, and the surface can be flattened by increasing the thickness. it can. When the first and second insulating layers 6 and 10 are made of an organic material, the surface flatness can be improved.

  The thickness of the first and second insulating layers 6 and 10 is preferably about 100 nm to 300 nm when they are made of silicon nitride (SiNx). When the thickness of the first and second insulating layers 6 and 10 is less than 100 nm, the pixel capacity increases, writing shortage tends to occur, and the display quality tends to deteriorate. In addition, the production yield is likely to decrease. When the thickness of the first and second insulating layers 6 and 10 exceeds 300 nm, the electric field generated between the first and second common electrodes 7 and 9 and the first and second pixel electrodes 5 and 11 becomes weak. Prone. Also, the pixel capacity tends to be small, and display defects such as crosstalk and flicker tend to be noticeable.

  The LCD of the present invention has a basic configuration as shown in FIG. An insulating layer 2 is laminated on the upper surface (surface on the liquid crystal 8 side) of the first substrate 1 made of a glass substrate or the like which is a TFT array side substrate, and an image signal line (source signal line) 22 is formed on the insulating layer 2. A passivation film 3 is formed so as to cover the upper surface of the insulating layer 2 and the image signal line 22. A planarizing film 4 is formed on the passivation film 3, and a first pixel electrode 5 made of a transparent electrode such as indium tin oxide (ITO) is formed on the planarizing film 4. A first insulating layer 6 is formed so as to cover the pixel electrode 5, and a first common electrode 7 made of a transparent electrode such as ITO having a first slit 7 a is formed on the first insulating layer 6. . A color filter 13 and a black matrix 14 are formed on the lower surface (surface on the liquid crystal 8 side) of the second substrate 15 made of a glass substrate or the like which is a color filter side substrate, and the color filter 13 and the black matrix 14 are covered and overcoated. 12 is formed. A second pixel electrode 11 is formed on the overcoat 12, and a second insulating layer 10 is stacked on the overcoat 12 and the second pixel electrode 11. A second common electrode 9 is formed on the second insulating layer 10. Then, the first substrate 1 and the second substrate 15 are arranged to face each other so that the first common electrode 7 and the second common electrode 9 face each other, and the liquid crystal 8 is filled between them, and both the substrates are placed. The LCD is configured by sealing the outer peripheries of 1 and 15.

  The color filter 13 and the black matrix 14 are formed on the second substrate 15, but may be formed on the first substrate 1. Further, the TFT element is formed only on the first substrate 1, but in this case, the TFT element may not be formed on the second substrate 15 in the case of an LCD that performs passive static driving. Further, TFT elements may be formed on both the first substrate 1 and the second substrate 15, and in this case, an active matrix type LCD is obtained. When the TFT elements are formed on both the first substrate 1 and the second substrate 15, the upper and lower TFT elements may be arranged so as to substantially overlap in plan view.

  In the LCD of the present invention, the liquid crystal 8 preferably has negative dielectric anisotropy. In this case, like the liquid crystal having positive dielectric anisotropy, the liquid crystal molecules 8a adjacent to the first and second common electrodes 7 and 9 are in an obliquely aligned state in which the liquid crystal molecules 8a slightly rise in the vertical direction (vertical direction). It will be solved. As a result, the retardation of the liquid crystal 8 is further increased, and the light transmittance and luminance are further improved. 2A is a partially enlarged cross-sectional view showing the alignment state of liquid crystal molecules 8aa when a liquid crystal having negative dielectric anisotropy is used, and FIG. 2B is a case where liquid crystal having positive dielectric anisotropy is used. FIG. 6 is a partial enlarged cross-sectional view showing the alignment state of liquid crystal molecules 8ab.

  As shown in FIG. 2B, since the liquid crystal molecules 8ab having positive dielectric anisotropy tend to be aligned along the electric field direction, the liquid crystal molecules 8ab adjacent to the common electrodes 7 and 9 are arranged in the vertical direction (vertical). Oriented in a diagonal direction slightly rising in the direction). As a result, the retardation of the liquid crystal 8 is reduced, and the light transmittance of the liquid crystal 8 is reduced. On the other hand, as shown in FIG. 2 (a), the liquid crystal molecules 8aa having negative dielectric anisotropy tend to be aligned along the direction perpendicular to the electric field direction. Oriented to As a result, the retardation of the liquid crystal 8 is increased, and the light transmittance of the liquid crystal 8 is further improved.

  The material of the liquid crystal 8 having negative dielectric anisotropy is, for example, a compound containing a benzene ring as disclosed in Patent Document 2, which has an alkenyl group or an alkyl group at the end of the main chain. A known compound having 1,4-cyclohexane or 1,4-phenylene in the main chain and hydrogen (H) or fluorine (F) in the side chain may be employed.

  In the LCD of the present invention, it is preferable that a common voltage signal having the same polarity is simultaneously applied to the first and second common electrodes 7 and 9. In this case, the liquid crystal molecules 8a are aligned in the lateral direction along the electric field in a short time over the distance between the first substrate 1 and the second substrate 15, that is, the entire thickness of the liquid crystal 8. As a result, the responsiveness of the liquid crystal 8 is improved. For example, a common voltage signal of about +5 V or about −5 V is applied to each of the first and second common electrodes 7 and 9, and a pixel voltage signal of about 0 V is applied to the first and second pixel electrodes 5 and 11. Apply. When the common voltage signals having the same polarity are simultaneously applied to the first and second common electrodes 7 and 9, they may be applied almost simultaneously.

  In the LCD of the present invention, the first and second common electrodes 7 and 9 are applied with a ground voltage, for example, a common voltage signal of substantially 0 V, and the first and second pixel electrodes 5 and 11 are respectively It is preferable that the pixel voltage signal having the same potential is applied and the pixel voltage signal is driven to invert the polarity. In this case, the electric lines of force are not coupled between the first common electrode 7 and the second common electrode 9, that is, the first common electrode 7 and the second common electrode 9 are not electromagnetically coupled. Therefore, no disturbance occurs in the lateral alignment of the liquid crystal molecules 8a. Further, in this case, the electric current is also generated between the first common electrode 7 and the second common electrode 9 facing the first common electrode 7 and between the first common electrode 7 and the second common electrode 9 opposed to the first common electrode 7 in an oblique direction. The field lines do not combine. At the same time, it is possible to perform polarity inversion driving to suppress the occurrence of afterimages, that is, so-called burn-in, caused by applying a DC voltage component to the liquid crystal molecules 8a for a long time.

  For example, a pixel voltage signal of 5V or -5V is applied to the first and second pixel electrodes 5 and 11, respectively. In addition, when the polarity of the pixel voltage signal is driven, the polarity of the pixel voltage signal applied to the first and second pixel electrodes 5 and 11 is preferably synchronized with the polarity of the pixel voltage signal. In this case, the liquid crystal molecules 8a are aligned in the lateral direction along the electric field over the entire thickness of the liquid crystal 8, and the responsiveness of the liquid crystal 8 is improved. Polarity inversion driving of pixel voltage signals applied to the first and second pixel electrodes 5 and 11 is performed by driving control of control ICs, LSIs, etc. provided on the first and second substrates 1 and 15 or outside. By means.

  The LCD driving method of the present invention includes a plurality of gate signal lines formed in a first direction (for example, a row direction) on the surface of the first substrate 1 on the liquid crystal 8 side, a first direction, A plurality of image signal lines formed to intersect the gate signal lines in a second direction (for example, the column direction) that intersects, the TFT elements formed at the intersections of the gate signal lines and the image signal lines, and the first A first common electrode 7 having a first slit 7a extending in a predetermined direction, which is formed so as to be opposed to each other with the first pixel electrode 5 and the first insulating layer 6 interposed therebetween, A second pixel electrode 11 formed on the surface of the second substrate 15 on the liquid crystal 8 side, and a predetermined direction formed so as to face the second pixel electrode 11 with the second insulating layer 10 interposed therebetween. A second common electrode 9 having a second slit 9a extending to the first and second images. The electrodes 5, 11, the first and second common electrodes 7, 9, and the first and second slits 7a, 9a are LCD driving methods positioned so as to substantially overlap each other in plan view, In this configuration, a common voltage signal having the same polarity is applied to the first and second common electrodes 7 and 9. With this configuration, the liquid crystal molecules 8 a are aligned laterally along the electric field over the entire distance (gap) between the first substrate 1 and the second substrate 15. As a result, the retardation of the liquid crystal 8 is increased, and the light transmittance and luminance are improved. Further, the lines of electric force are not coupled between the first common electrode 7 and the second common electrode 9, that is, the first common electrode 7 and the second common electrode 9 are not electromagnetically coupled. In this case, no disturbance occurs in the horizontal alignment of the liquid crystal molecules 8a. Therefore, the light transmittance and the luminance are further improved. In addition, since the responsiveness and orientation of the liquid crystal molecules 8a are improved, low voltage driving is possible and power consumption can be reduced. Furthermore, when driving at a voltage equivalent to the conventional voltage, the liquid crystal 8 having a low viscosity and a small | Δε | can be used, so that the response speed can be improved.

  The LCD of the present invention is a glass on which an array side substrate (first substrate 1) made of a glass substrate or the like on which many pixel portions including TFT elements are formed, a color filter 13 and a light shielding portion (black matrix) 14 are formed. A color filter side substrate (second substrate 15) made of a substrate or the like is opposed to each other, the substrates 1 and 15 are bonded together at a predetermined interval, and the liquid crystal 8 is filled between the substrates 1 and 15; It is made by encapsulating. Also, on the surface of the color filter side substrate on the liquid crystal 8 side, red (R), green (G), and blue (B) color filters 13 corresponding to the respective pixels are formed, and pass through the respective pixels. A light shielding portion (black matrix) 14 that prevents the light to interfere with each other is formed so as to surround the outer periphery of the color filter 13.

  The LCD of the present invention is not limited to the above-described embodiment, and may include appropriate design changes and improvements.

(Example 1)
The LCDLa1 of the present invention in which the first slits 7a and 9a are formed in the first and second common electrodes 7 and 9 shown in FIG. 1 so as to extend in the column direction (the direction along the image signal line) is as follows. It was configured as follows. The outer shape of the first substrate 1 made of a glass substrate 1 on the side of the liquid crystal 8 is a rectangle having an outer shape of 104 μm in length and 35 μm in width by a sputtering method and a photolithography method. A first pixel electrode 5 made of ITO having a rectangular shape of 32 μm and a thickness of 50 nm was formed. A first insulating layer 6 made of silicon nitride (SiNx) having a thickness of 200 nm was formed on the upper surface of the first pixel electrode 5 by a CVD method. A first common electrode 7 made of ITO having a slit 7a and a thickness of 50 nm was formed on the first insulating layer 6 so as to face the first pixel electrode 5 by sputtering and photolithography. . Five slits 7 a having a width of 3 μm and a length of 205 μm were formed in a portion of the first common electrode 7 facing the first pixel electrode 5. Further, in the first common electrode 7, the width of the portion between the second slits 7a was 3 μm.

  Similarly, the second common electrode 9 having the second pixel electrode 11, the second insulating layer 10, and the second slit 9a on the surface of the second substrate 15 made of a glass substrate on the liquid crystal side, The same structure as that of the first substrate 1 was formed. The first and second pixel electrodes 5 and 11, the first and second common electrodes 7 and 9, and the first and second slits 7 a and 9 a are positioned so as to substantially overlap each other in plan view. In addition, a common voltage signal (0 V) having the same polarity is applied to the first and second common electrodes 7 and 9. The pixel voltage signal of the same potential applied to the first and second pixel electrodes 5 and 11 is set to 5V or −5V, and the polarity is inverted in synchronization. The TFT elements were formed on both the first substrate 1 and the second substrate 15, and the upper and lower TFT elements were arranged so as to substantially overlap in plan view. Further, the color filter 13 and the light shielding portion 14 were formed on the second substrate 15.

  As the liquid crystal 8, a liquid crystal having positive dielectric anisotropy and having Δε = + 6.5 and Δn = 0.12. The thickness of the liquid crystal 8 layer was 3 μm.

  As Comparative Example 1, LCDLb1 having the configuration shown in FIG. That is, the first pixel electrode 5, the first insulating layer 6, the first common electrode 7, and the TFT element were formed only on the first substrate 1 in the same manner as in Example 1. The TFT substrate, the second pixel electrode 11, the second insulating layer 10, and the second common electrode 9 are not formed on the second substrate, but the color filter 13 and the light shielding portion 14 are formed. Same as Example 1.

  LCDLa1 and Lb1 were driven by a dot inversion driving method in which the polarity of the pixel voltage signal is inverted for each pixel portion (dot) and is inverted on the entire screen for each frame. At this time, the light transmittance of the entire LCDLa1 screen was 7.8%, the light transmittance of the entire LCDLb1 screen was 6.8%, and the light transmittance was improved by about 15%. Further, the driving voltage of LCDLa1 was 3.5V and −3.5V, the driving voltage of LCDLb1 was 5V and −5V, and the driving voltage was reduced by about 30%.

(Example 2)
As the LCDLa2 of the present invention, a liquid crystal having negative dielectric anisotropy in the liquid crystal 8 and having Δε = −4.5 and Δn = 0.12. Other configurations were the same as those of LCDLa1 in Example 1 above. Further, as Comparative Example 2, LCDLb2 having the configuration shown in FIG. That is, the liquid crystal 8 having negative dielectric anisotropy and having Δε = −4.5 and Δn = 0.12 is used, and only the first pixel electrode 5 on the first substrate 1 is used. The first insulating layer 6, the first common electrode 7, and the TFT element were formed in the same manner as in Comparative Example 1 above. Other configurations were the same as those in Comparative Example 1.

  LCDLa2 and Lb2 were driven by a dot inversion driving method in which the polarity of the pixel voltage signal is inverted for each pixel portion (dot) and is inverted for the entire screen for each frame. At this time, the light transmittance of the entire LCDLa2 screen was 8.0%, the light transmittance of the entire LCDLb2 screen was 7.6%, and the light transmittance was improved by about 5%. The driving voltage of LCDLa2 was 2.6V, the driving voltage of LCDLb2 was 4.7V, and the driving voltage was reduced by about 45%.

    The active matrix LCD of the present invention can be applied to various electronic devices. The electronic devices include a head-up display device, a projector device, an automobile route guidance system (car navigation system), a ship route guidance system, an aircraft route guidance system, a smartphone terminal, a mobile phone, a tablet terminal, a personal digital assistant (PDA), Video cameras, digital still cameras, electronic notebooks, electronic books, electronic dictionaries, personal computers, copying machines, terminal devices for game machines, televisions, product display tags, price display tags, industrial programmable display devices, car audio, digital There are audio players, facsimiles, printers, automatic teller machines (ATMs), vending machines, digital display watches, and the like.

DESCRIPTION OF SYMBOLS 1 1st board | substrate 5 1st pixel electrode 6 1st insulating layer 7 1st common electrode 8 Liquid crystal 8a Liquid crystal molecule 9 2nd common electrode 10 2nd insulating layer 11 2nd pixel electrode 13 Color filter 14 Light shielding portion 15 second substrate

Claims (5)

  A plurality of gate signal lines formed in a first direction on the liquid crystal side surface of the first substrate and formed in a second direction intersecting with the first direction so as to intersect with the gate signal lines. A plurality of image signal lines, a thin film transistor element and a first pixel electrode formed at an intersection of the gate signal line and the image signal line, and facing each other with the first pixel electrode and the first insulating layer interposed therebetween A first common electrode having a first slit extending in a predetermined direction, a second pixel electrode formed on a liquid crystal side surface of the second substrate, and the second pixel. A second common electrode having a second slit extending in the predetermined direction and formed so as to face the electrode with the second insulating layer interposed therebetween, and the first and second The pixel electrode, the first and second common electrodes, and the first and second slits are Together we are positioned so as to substantially superimposed respectively a plan view, the first and second common electrode a liquid crystal display device common voltage signal of the same polarity is applied.   The liquid crystal display device according to claim 1, wherein the liquid crystal has negative dielectric anisotropy.   The liquid crystal display device according to claim 1, wherein the common voltage signal having the same polarity is simultaneously applied to the first and second common electrodes.   The common voltage signal of the ground potential is applied to the first and second common electrodes, the pixel voltage signal of the same potential is applied to the first and second pixel electrodes, respectively, and the pixel voltage signal is The liquid crystal display device according to claim 1, wherein the liquid crystal display device is driven by polarity inversion.   A plurality of gate signal lines formed in a first direction on the liquid crystal side surface of the first substrate and formed in a second direction intersecting with the first direction so as to intersect with the gate signal lines. A plurality of image signal lines, a thin film transistor element and a first pixel electrode formed at an intersection of the gate signal line and the image signal line, and facing each other with the first pixel electrode and the first insulating layer interposed therebetween A first common electrode having a first slit extending in a predetermined direction, a second pixel electrode formed on a liquid crystal side surface of the second substrate, and the second pixel. A second common electrode having a second slit extending in the predetermined direction and formed so as to face the electrode with the second insulating layer interposed therebetween, and the first and second The pixel electrode, the first and second common electrodes, and the first and second slits are A driving method of a liquid crystal display device is positioned so as to substantially superimposed respectively a plan view, a driving method of a liquid crystal display device for applying a common voltage signal having the same polarity to the first and second common electrode.