JP2007183299A - Liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress image persistence in a liquid crystal display device driven by a lateral electric field in FFS (fringe-field switching) techniques or the like. <P>SOLUTION: In conventional FFS techniques, a pixel electrode layer 32 is laminated on a common electrode layer 28 through an insulating layer 30, and the pixel electrode layer 32 is provided with a plurality of slit-like electrode apertures 50. Consequently, the insulating layer 30 is present between the common electrode layer 28 and the pixel electrode layer 32. The insulating layer 30 functions as a capacitive element which easily causes image persistence. In order to suppress image persistence, the insulating layer 30 in portions corresponding to the electrode apertures 50 is provided with insulating layer apertures 52. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device in which liquid crystal is sandwiched between a pair of substrates facing each other and the liquid crystal is driven by an electric field generated between a common electrode and a pixel electrode.

  In general, a liquid crystal display device that constitutes a display device such as a television or a graphic display is mainly of an active matrix type and driven by a vertical electric field. That is, this type of liquid crystal display device includes a pair of transparent glass substrates and a liquid crystal sealed between the glass substrates, and at least one of the glass substrates includes a thin film transistor and a pixel. An electrode is formed, and a color filter and a common electrode are formed on the other glass substrate. The liquid crystal is an electric field generated between the pixel electrode on the glass substrate on one side and the common electrode on the glass substrate on the other side by the drive circuit, that is, the in-plane direction of the glass substrate is defined as the lateral direction. It is driven by a vertical electric field perpendicular thereto.

  Liquid crystal display devices are required to have higher definition, smaller size, and wider viewing angle. In recent years, as one means for increasing the viewing angle, an electric field in the in-plane direction, that is, a transverse electric field is generated with respect to the glass substrate, and the liquid crystal molecules are rotated in a plane parallel to the substrate by the transverse electric field. Thus, a technique of a method of providing an optical switching function for changing the transmittance has been put into practical use.

  For example, Patent Document 1 describes an IPS mode (In Plane Switching Mode) liquid crystal display element that uses a parallel field parallel to the surface of a glass substrate, and Patent Document 2 further improves the IPS technology. A liquid crystal display device that improves the aperture ratio using FFS (Fringe-Field Switching) technology is described. Here, in the FFS technique, a pixel electrode is disposed on a common electrode through an insulating layer, a slit is provided in the pixel electrode, and the slit is used to generate an electric field from the pixel electrode to the common electrode. Yes. This electric field has a strong electric field component in the direction perpendicular to the substrate in the vicinity of the edge of the electrode as well as the lateral electric field, so that the liquid crystal molecules located above the electrode can also be driven. Therefore, if a transparent electrode is used, the electrode portion can also contribute to the display and the aperture ratio is improved.

Japanese Patent Laid-Open No. 10-62767 JP 2002-296611 A

  As described above, the use of the horizontal electric field method is useful because a wide viewing angle can be realized in a liquid crystal display device.

  In a liquid crystal display device that uses a switching element to drive liquid crystal molecules, a bias voltage is applied to the control terminal of the switching element due to a parasitic capacitance between the control terminal of the switching element and the output terminal connected to the pixel electrode. May occur. This bias voltage is related to the control potential applied to the control terminal, the liquid crystal capacitance component, and the other storage capacitance component. Although this bias voltage is minimized by optimizing the common electrode potential, it differs depending on the image to be displayed. Therefore, the bias voltage cannot be completely removed and causes burn-in.

  The electric field used for driving the liquid crystal by the FFS technique is applied between the pixel electrode and the common electrode through an insulating layer for insulating the pixel electrode and the common electrode. Since this insulating layer acts as a capacitive component, a liquid crystal display device using the FFS technique may have a problem of image sticking more strongly than a liquid crystal display device using other methods.

  An object of the present invention is to provide a liquid crystal display device capable of suppressing a burn-in phenomenon. Another object is to provide a liquid crystal display device capable of suppressing the image sticking phenomenon when driven by a lateral electric field. Still another object is to provide a liquid crystal display device capable of suppressing a burn-in phenomenon when driven by FFS technology. The following means contribute to at least one of these purposes.

  The liquid crystal display device according to the present invention is a liquid crystal display device in which liquid crystal is sandwiched between a pair of substrates facing each other, and the liquid crystal is driven by a driving electric field generated by a first electrode and a second electrode, An insulating layer is formed between the first electrode and the second electrode, and an opening is provided in the insulating layer.

  The liquid crystal display device according to the present invention is a liquid crystal display device in which liquid crystal is sandwiched between a pair of substrates facing each other, and the liquid crystal is driven by a lateral electric field generated between a first electrode and a second electrode, An insulating layer is formed between the first electrode and the second electrode, and an opening is provided in the insulating layer.

  The liquid crystal display device according to the present invention is a liquid crystal display device in which liquid crystal is sandwiched between a pair of substrates facing each other, and the liquid crystal is driven by a lateral electric field generated between a first electrode and a second electrode. The at least one of the pair of substrates includes the first electrode, an insulating layer stacked on the first electrode, and the second electrode stacked on the insulating layer, The second electrode has a plurality of electrode openings having a predetermined opening size, and the first electrode is arranged at least at a part of the second electrode corresponding to each electrode opening, The insulating layer is characterized in that at least a part of a portion corresponding to each of the electrode openings of the second electrode is opened.

  Moreover, it is preferable that the said insulating layer opens smaller than the predetermined opening dimension of the said electrode opening so that the location corresponding to each of each electrode opening of the said 2nd electrode may not short-circuit between said 1st electrodes. .

  The first electrode and the second electrode are each preferably a transparent electrode.

  In the liquid crystal display device according to the present invention, it is preferable that the first electrode is a common electrode common to a plurality of pixels, and the second electrode is a pixel electrode for each of the pixels.

  The liquid crystal display device according to the present invention preferably includes a plurality of pixels arranged in a matrix and each having a pixel electrode, and a plurality of switching elements provided for each of the pixels.

  When an insulating layer is formed in the path of the driving electric field between the first electrode and the second electrode, an opening is provided in the insulating layer in the path of the driving electric field due to at least one of the above configurations. . Therefore, since the capacitance component due to the insulating layer can be suppressed, the image sticking phenomenon can be suppressed.

  In addition, in at least one of the above structures, in a liquid crystal display device using a lateral electric field method, when an insulating layer is formed in the path of the driving electric field between the first electrode and the second electrode, An opening is provided in the insulating layer in the path portion. Accordingly, since the capacitance component due to the insulating layer can be suppressed, the image sticking phenomenon in the horizontal electric field liquid crystal display device can be suppressed.

  According to at least one of the above structures, in the liquid crystal display device using the lateral electric field method, the second electrode is disposed on the first electrode through the insulating layer, and the second electrode has a predetermined opening size. In a liquid crystal display device using a plurality of electrode openings, that is, a liquid crystal display device using FFS technology, at least a part of the insulating layer corresponding to each electrode opening of the second electrode is opened. Therefore, since the capacitive component due to the insulating layer between the first electrode and the second electrode can be suppressed, the image sticking phenomenon in the liquid crystal display device using the FFS technique can be suppressed.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the following description, the liquid crystal display device is assumed to be an active matrix type and uses FFS technology. However, a liquid crystal display device of a horizontal electric field type including an IPS method may be used. Further, if the liquid crystal display device is driven by a driving electric field generated by the first electrode and the second electrode and has an insulating layer in the path of the driving electric field, it is generally implemented by modifying the following embodiment. can do. In this case, the following embodiment can be modified and implemented by expanding to a liquid crystal display device other than the active matrix system, for example, a passive matrix system. In addition, although the description will be made assuming that a TFT (Thin Film Transistor) is used as the switching element, other switching elements such as a diode element may be used. In the following description, each electrode is described as a transparent electrode, but a metal electrode other than the transparent electrode may be used if there is no practical problem with respect to the aperture ratio. In the case of providing the reflective region, it may be a reflective electrode or a laminated structure of a transparent electrode and a reflective film. In addition, the drive electric field is described as being formed between the common electrode and the pixel electrode, but in general, the drive electric field only needs to be formed between two electrodes and does not depend on the type of electrode. Moreover, the dimension etc. which are demonstrated below are an example, Comprising: The dimension other than that may be sufficient.

  FIG. 1 is a schematic diagram of a configuration of an FFS mode liquid crystal display device 10 that can suppress the image sticking phenomenon. The liquid crystal display device 10 includes a display control unit 12, a display panel 14, and the like. The display control unit 12 is a circuit including a control circuit and a drive circuit for causing the display panel 14 to perform a desired display. A part of the circuit constituting the display control unit 12 can be incorporated in the display panel 14.

  The display panel 14 is an element that takes a form in which the liquid crystal 16 is sandwiched between a pair of glass substrates 22 and 24 and is sealed. This is an active matrix liquid crystal display panel in which pixels are arranged in a matrix. In FIG. 1, a TFT forming layer 26, a common electrode layer 28, an insulating layer 30, a pixel electrode layer 32, an alignment film 34, and the like are sequentially stacked on the lower glass substrate 24. Details of this laminated structure will be described later. In addition, a color filter 36, an alignment film 38, and the like are laminated on the upper glass substrate 22. Here, the liquid crystal 16 is sealed between the alignment films 34 and 38 facing each other. This stacking form is an example, and other stacking elements may be included, and the stacking order may be changed according to the method or application of the liquid crystal display. Here, since the structure for suppressing the image sticking phenomenon is in the part A laminated on the lower glass substrate 24, the contents thereof will be described in detail below.

  2A and 2B show a detailed top view and a cross-sectional view of the lower glass substrate 24 in a state where the respective laminated elements are laminated. In FIG. 2, a range of approximately one pixel is shown. Elements similar to those in FIG. 1 are denoted by the same reference numerals, and detailed description thereof is omitted.

  The lower glass substrate 24 is a glass plate having components and temperature characteristics suitable for a liquid crystal panel. The buffer layer 25 between the lower glass substrate 24 and the TFT formation layer 26 is provided to form a TFT formation layer 26 including a semiconductor layer on the glass substrate 24 with good adhesion and prevent diffusion of impurities. It is done.

  The TFT formation layer 26 includes a semiconductor layer and a gate insulating film layer for forming the TFT element 40 for each pixel. The semiconductor layer can be a low-temperature polysilicon layer, a high-temperature polysilicon layer, an amorphous silicon layer, or the like, and is formed using a thin film deposition technique such as a CVD (Chemical Vapor Deposition) technique and a heat treatment technique such as laser annealing. be able to. As the gate insulating film layer, an oxide film, a nitride film, a composite insulating film combining them, or the like by a CVD method or the like can be used.

  The TFT element 40 is configured by forming a source, a drain, and a channel region therebetween in the semiconductor layer of the TFT formation layer 26, and forming a gate electrode 42 on the channel region with a gate insulating film interposed therebetween. . A source terminal connected to the pixel electrode layer 32 is drawn from the source, and a drain terminal connected to the data line 44 is drawn from the drain. The drain and the source have a compatible structure. Here, the side connected to the pixel electrode layer 32 is the source, but this may be referred to as the drain.

  The interlayer insulating film 27 between the TFT forming layer 26 and the common electrode layer 28 is a layer mainly having a function of protecting the TFT forming layer 26 and separating from the electrode layer laminated thereon. For example, an inorganic insulating film such as an oxide film or a nitride film deposited by a CVD method, or an organic insulating film can be used. In addition, the interlayer insulating film 27 has a multilayer structure, and a wiring layer is provided in the middle. Further, contact holes for connecting each terminal of the TFT element 40 in the TFT forming layer 26 to the wiring layer and the electrode layer are arranged in the vertical direction. Provided. 2B shows a data line 44 from the drain terminal of the TFT element 40, a contact hole 46 from the source terminal to the pixel electrode layer 32, a contact hole 48 from the common wiring to the common electrode layer 28, and the like. Yes.

  The common electrode layer 28 is a transparent electrode film disposed on the interlayer insulating film 27 and can be formed of an ITO (Indium Titanium Oxide) film or the like. The common electrode layer 28 is an electrode layer common to a plurality of pixels arranged in a matrix. FIG. 2B shows a state in which an opening is partially provided in the common electrode layer 28 for the contact hole 46 leading to the pixel electrode disposed on the common electrode layer 28. The common electrode layer 28 is opposed to the entire surface of the pixel electrode for one pixel.

  Prior to the description of the insulating layer 30, the configuration of the pixel electrode layer 32 and the like will be described first. The pixel electrode layer 32 is a transparent electrode film disposed on the common electrode layer 28 with the insulating layer 30 interposed therebetween, and can be formed of an ITO film or the like. The pixel electrode layer 32 is connected to the source terminal of the TFT element 40 through the contact hole 46. Here, a plurality of slit-like openings are provided in the pixel electrode layer 32 in order to apply a lateral electric field to the liquid crystal molecules in the FFS mode. In order to distinguish from the opening of the insulating layer 30 described later, the opening in the pixel electrode layer 32 can be referred to as an electrode opening 50. This is shown in the top view of FIG. Here, eleven elongated slit-like electrode openings 50 are provided in the pixel electrode of one pixel.

  An alignment film 34 rubbed in the rubbing direction 54 indicated by the solid line in FIG. 2A is disposed on the entire surface of the pixel electrode layer 32. The rubbing direction 55 of the alignment film 38 of the upper glass substrate 22 is opposite to the rubbing direction 54 of the alignment film 34 of the lower glass substrate 24, as shown by the broken line in FIG. These rubbing directions 54 and 55 preferably have an angle greater than 0 ° and not more than 45 ° with the longitudinal direction of the electrode opening 50. Although not shown, polarizing plates are arranged on both sides of the pair of substrates, and the transmission axes of the polarizing plates form an angle of 90 ° with each other, and the rubbing direction is 0 ° or 90 °. Make an angle.

  The insulating layer 30 is disposed between the common electrode layer 28 and the pixel electrode layer 32, and has a function of separating the two and a capacitive element sandwiched between these two electrode layers in terms of circuit. It has the function to form. Since this capacitive element is arranged in parallel with the capacitive component of the liquid crystal 16 in circuit, it functions as a so-called holding capacitor. As shown in FIGS. 2A and 2B, the insulating layer 30 is provided with openings at locations corresponding to the respective electrode openings 50. This opening is distinguished from the electrode opening 50 and is called an insulating layer opening 52. This is indicated by a broken line in FIG.

  FIG. 3 shows the laminated structure on the lower glass substrate 24 in more detail by extracting portions of the common electrode layer 28, the insulating layer 30 and the pixel electrode layer 32. 3A is a top view and FIG. 3B is a cross-sectional view. In the cross-sectional view, the magnification in the thickness direction of each layer is enlarged as compared with that in the plane direction. Thus, the insulating layer opening 52 is provided corresponding to the position of the electrode opening 50 and is smaller than the opening size of the electrode opening 50. The dimensional difference is not so large, and can be reduced to such an extent that no short circuit occurs between the common electrode layer 28 and the pixel electrode layer 32. In other words, the insulating layer 30 has a portion corresponding to each electrode opening 50 of the pixel electrode layer 32 smaller than a predetermined opening size of the electrode opening 50 and does not short-circuit with the common electrode layer 28. Open large.

Specifically, the common electrode layer 28 has a thickness t ₁ of about 100 nm, the insulating layer 30 has a thickness t ₂ of about several hundred nm, and the pixel electrode layer has a thickness t ₃ of about 100 nm. A pitch p between the electrode openings 50 is 10 μm to 15 μm, and an opening size difference 2 s between the electrode openings 50 and the insulating layer openings 52 is 4 μm to 6 μm. Here, it is assumed that the insulating layer opening 52 is slightly smaller than the opening size of the electrode opening 50, in other words, the insulating layer opening 52 opens almost entirely with respect to the electrode opening 50 with a dimensional difference of 2 s. The layer opening 52 may be provided in a part of the electrode opening 50. For example, a smaller opening having a circular or rectangular opening shape may be provided in a part of the insulating layer 30 in the electrode opening 50 portion. The insulating layer 30 may be formed by processing an inorganic film of SiNx or SiO ₂ by photolithography and an etching process, or processing a photosensitive resin by a photolithography process. The latter is easier in terms of process. Examples of the photosensitive resin include acrylic resins.

  The operation of the liquid crystal display device 10 having the above configuration, particularly the operation of the insulating layer opening 52 will be described with reference to FIGS. 4A and 4B are schematic diagrams comparing (a) the state of the electric field by the FFS method of the prior art, and (b) the state of the electric field by the FFS method having the configuration of FIGS. 2 and 3, and FIG. It is a circuit diagram which shows the principle which can be suppressed.

  In the liquid crystal display device 10 having the configuration shown in FIG. 1, when the display is performed due to the difference in the transmittance of the liquid crystal, the display control unit 12 selects the gate line 43 and the data line 44 for a desired pixel, The TFT element 40 which is a switching element is turned on. Thereby, a predetermined drive signal is applied between the common electrode layer 28 and the pixel electrode layer 32 of the pixel. As an example, FIG. 4 shows a case where a negative potential is applied to the common electrode layer 28 and a positive potential is applied to the pixel electrode layer 32.

  4A showing the conventional technique and FIG. 4B showing the technique described in FIGS. 2 and 3, the pixel electrode layer 32 is provided with a plurality of slit-like electrode openings 50. Are the same. Due to the action of the electrode opening 50, the aperture ratio can be improved by the lateral electric field method with a wide viewing angle in accordance with the principle of the well-known FFS method. That is, the electric field 60 generated between the common electrode layer 28 and the pixel electrode layer 32 has a horizontal electric field component parallel to the surface of the glass substrate and the edge of the pixel electrode layer 32, that is, the edge of the electrode opening 50. This part has a strong electric field component in a direction perpendicular to the glass substrate surface. As a result, not only the liquid crystal molecules 17 positioned between the pixel electrode layers 32 but also those positioned above the pixel electrode layers 32 are rotationally driven by the electric field 60 in the plane of the glass substrate, Partial liquid crystal molecules can also contribute to the display.

  In FIG. 4A showing the prior art, the insulating layer 30 exists in the path of the electric field 60 formed between the two electrode layers. On the other hand, in FIG. 4B showing the technique described in FIGS. 2 and 3, the insulating layer 30 does not exist in the path of the electric field 60 formed between the two electrode layers. Since a potential is applied between the common electrode layer 28 and the pixel electrode layer 32, the insulating layer 30 in this portion functions as a capacitor element.

FIG. 5 is a diagram for explaining a mechanism by which a DC component is applied to the liquid crystal layer. The liquid crystal is AC driven, but the DC component is applied for the following reason. The gate voltage V _G, a liquid crystal capacitance C _LC, the storage capacitor C _SC, when the parasitic capacitance formed by the gate electrode and the source electrode and C _G, DC component applied to the liquid crystal layer is shown as follows .
_{· V DC = V G {C} G / (C G + C SC + C LC)}

The potential of the common electrode is adjusted so as to cancel the DC component. However, since the liquid crystal capacitance _CLC changes depending on the display state, the DC component cannot be completely removed. When a DC component is applied to the liquid crystal layer for a long time, if there is an insulating layer on the entire surface as in the prior art, polarization occurs inside the insulating layer, which is held for a certain period of time, and this polarization generates an internal electric field. This causes burn-in.

  If the insulating layer is removed as in the above embodiment, the internal electric field as described above does not occur even when a DC component is applied, and no burn-in occurs. As described above, in the liquid crystal display device according to the present invention, it is possible to suppress the occurrence of image sticking by providing the opening in the insulating layer.

1 is a schematic configuration diagram of an FFS mode liquid crystal display device according to an embodiment of the present invention. In embodiment concerning this invention, it is a detailed top view and sectional drawing of the lower side glass substrate in the state by which each lamination | stacking element was laminated | stacked. In the embodiment according to the present invention, a laminated structure on a lower glass substrate is a top view and a cross-sectional view showing a common electrode, an insulating layer, and a pixel electrode part in more detail. It is a figure which compares and shows how to apply an electric field about a prior art and embodiment which concerns on this invention. In an embodiment of the invention, it is a circuit diagram showing a principle which can suppress a burn-in phenomenon.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 Liquid crystal display device, 12 Display control part, 14 Display panel, 16 Liquid crystal, 17 Liquid crystal molecule, 22, 24 Glass substrate, 25 Buffer layer, 26 TFT formation layer, 27 Interlayer insulation film, 28 Common electrode layer, 30 Insulation layer, 32 pixel electrode layer, 34, 38 alignment film, 36 color filter, 40 TFT element, 42 gate electrode, 43 gate line, 44 data line, 46, 48 contact hole, 50 electrode opening, 52 insulating layer opening, 54, 55 rubbing direction, 60 electric field.

Claims (7)

A liquid crystal display device in which liquid crystal is sandwiched between a pair of substrates facing each other, and the liquid crystal is driven by a driving electric field generated by a first electrode and a second electrode;
A liquid crystal display device, wherein an insulating layer is formed between the first electrode and the second electrode, and an opening is provided in the insulating layer. A liquid crystal display device in which a liquid crystal is sandwiched between a pair of substrates facing each other, and the liquid crystal is driven by a lateral electric field generated by a first electrode and a second electrode;
A liquid crystal display device, wherein an insulating layer is formed between the first electrode and the second electrode, and an opening is provided in the insulating layer. A liquid crystal display device in which a liquid crystal is sandwiched between a pair of substrates facing each other, and the liquid crystal is driven by a lateral electric field generated by a first electrode and a second electrode;
At least one of the pair of substrates includes
The first electrode;
An insulating layer stacked on the first electrode;
The second electrode laminated on the insulating layer;
Is placed,
In the second electrode, a plurality of electrode openings having a predetermined opening dimension are arranged,
The first electrode is disposed in at least a part of a location corresponding to each electrode opening of the second electrode,
The liquid crystal display device according to claim 1, wherein the insulating layer has at least a part of a portion corresponding to each of the electrode openings of the second electrode. The liquid crystal display device according to claim 3.
The insulating layer has an opening smaller than a predetermined opening size of the electrode opening so that a portion corresponding to each of the electrode openings of the second electrode does not short-circuit with the first electrode. Liquid crystal display device. The liquid crystal display device according to any one of claims 1 to 4,
The liquid crystal display device, wherein each of the first electrode and the second electrode is a transparent electrode. The liquid crystal display device according to any one of claims 1 to 5,
The first electrode is a common electrode common to a plurality of pixels,
The liquid crystal display device, wherein the second electrode is a pixel electrode for each pixel. The liquid crystal display device according to any one of claims 1 to 6,
A plurality of pixels arranged in a matrix and each having a pixel electrode;
A plurality of switching elements provided for each of the pixels;
A liquid crystal display device comprising:

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