WO2012165312A1 - Liquid crystal display panel and liquid crystal display device - Google Patents

Abstract

The present invention provides a liquid crystal display panel and liquid crystal display device whereby opposite electrodes suppress unevenness of display and whereby burn-in is adequately reduced. This liquid crystal display panel comprises a first substrate, a second substrate, and a liquid crystal layer interposed between the two substrates, the first substrate having an electrode to which an alternating current voltage is applied, and the second substrate having a pair of comb electrodes.

Description

Liquid crystal display panel and liquid crystal display device

The present invention relates to a liquid crystal display panel and a liquid crystal display device. More specifically, the present invention relates to a liquid crystal display panel and a liquid crystal display device in which an oblique electric field is applied to a liquid crystal layer using a pair of comb electrodes and a counter electrode.

A liquid crystal display panel is configured by sandwiching a liquid crystal display element between a pair of glass substrates and the like, taking advantage of its thin, lightweight, and low power consumption characteristics, such as personal computers, televisions, car navigation systems, and other portable devices. The display of a portable information terminal such as a telephone is indispensable for daily life and business. In these applications, liquid crystal display panels of various modes related to electrode arrangement and substrate design for changing the optical characteristics of the liquid crystal layer have been studied.

As a display method of a liquid crystal display device in recent years, a vertical alignment (VA) mode in which liquid crystal molecules having negative dielectric anisotropy are vertically aligned with respect to a substrate surface, or a positive or negative dielectric constant difference is used. In-plane switching (IPS) mode in which lateral liquid crystal molecules are oriented horizontally with respect to the substrate surface and a transverse electric field is applied to the liquid crystal layer, and fringe field switching (FFS) Is mentioned. Various liquid crystal display panels suitable for each mode have been studied and developed.

For example, a signal voltage that is the sum of an AC voltage component and a DC voltage component Vdc is applied between the pixel electrode and the common electrode, and the amplitude Vac and the DC voltage component Vdc of the AC voltage component are changed to substantially optimize the DC. A method for developing a specific liquid crystal display panel is disclosed in which the component fluctuation range ΔVdc is measured, and the configuration or constituent material of the liquid crystal display device is determined so that ΔVdc is a predetermined value or less (see, for example, Patent Document 1). ).

JP 2009-187022 A

Generally, the optimum offset voltage can be adjusted by the method described in Patent Document 1, and in the case of an element configuration in which no counter electrode is arranged, there is no problem because the offset voltage does not shift with voltage application. However, in a liquid crystal display device including a facing electrode and a comb electrode such as an FFS structure comb electrode, charge accumulation occurs at an interface of an overcoat layer (also referred to as OC in the present specification), and the like. As the voltage is applied, the optimum offset voltage shifts and the optimum value cannot be specified. As a result, image sticking occurs in a liquid crystal display element that includes an opposing planar electrode and a comb electrode such as an FFS structure comb electrode and uses an oblique electric field. In Patent Document 1, there is no disclosure regarding means for solving such burn-in.
In Patent Document 1, the rectangular AC voltage is applied only to the pixel electrode, and FIG. 3 of Patent Document 1 also describes the pixel applied voltage.

The cause of image sticking is as follows. When an oblique electric field is applied using a comb electrode and a counter electrode, an oblique electric field is generated even in the overcoat layer. This electric field distribution causes charge accumulation at the liquid crystal-overcoat interface and shifts the optimum offset voltage. As a result, burn-in occurs.

The present invention has been made in view of the above situation, and a liquid crystal display panel having a comb-teeth electrode and a counter electrode and a liquid crystal display device that suppress display unevenness and sufficiently reduce the occurrence of burn-in, and An object of the present invention is to provide a liquid crystal display device.

The inventors of the present invention have studied to achieve both suppression of display unevenness and reduction of image sticking in a liquid crystal display panel and a liquid crystal display device. It was also found that by applying an alternating voltage (AC voltage) to the counter electrode side, it is possible to provide a liquid crystal display element that prevents accumulation of charges in a specific region such as an overcoat layer and does not cause burn-in. That is, by applying an AC voltage to the counter electrode to control the electric field distribution, it is possible to eliminate the accumulation of charges in a specific region such as on the overcoat layer, and to sufficiently prevent burn-in.

Furthermore, as an additional effect, it is possible to provide a liquid crystal display panel and a liquid crystal display device in which display unevenness at the time of low gradation display is difficult to see. That is, a display device having a counter electrode has a lower threshold and a change in transmittance with respect to a voltage change is smaller than a display device without a counter electrode, so that display unevenness can be reduced. Because it occurred, it could not be realized. The present inventors have found that it is possible to suppress both display unevenness and image sticking by using this method, and have arrived at the present invention by conceiving that the above problems can be solved brilliantly. Is.

That is, the present invention is a liquid crystal display panel comprising a first substrate, a second substrate, and a liquid crystal layer sandwiched between both substrates, wherein the first substrate has an electrode to which an alternating voltage is applied, The second substrate is a liquid crystal display panel having a pair of comb electrodes.

The AC voltage is a voltage whose magnitude periodically changes with time. Usually, the potential changes so that the amplitudes are substantially the same magnitude above and below the center voltage. Examples of the alternating current waveform include a sine wave, a rectangular wave, and a triangular wave. Among these, a sine wave is preferable.

The center voltage of the AC voltage is preferably in the range of 1V to 10V, for example. The amplitude of the AC voltage is preferably in the range of 1V to 10V, for example. Furthermore, it is preferable that the voltage is equal to or less than an intermediate voltage applied to the pair of comb-shaped electrodes, and the amplitude of the AC voltage is equal to or less than half of the voltage difference applied between the pair of comb-shaped electrodes. The center voltage of the AC voltage is less than or equal to the intermediate voltage of the voltages applied to the pair of comb electrodes, and the amplitude of the AC voltage is less than half of the voltage difference applied between the pair of comb electrodes. It is preferable. More preferably, the center voltage of the AC voltage is a substantially intermediate voltage between the voltages applied to the pair of comb electrodes, and the amplitude of the AC voltage is a voltage applied between the pair of comb electrodes. Is substantially half of the difference.

The first substrate preferably further has an overcoat layer. By having the overcoat layer, the lateral electric field strength on the counter substrate side (upper part of the liquid crystal layer) is increased. Thereby, the utilization efficiency of light can be improved and the transmittance can be increased. The overcoat layer has an action of flattening the color filter layer, for example, when the substrate is a substrate having a color filter. When the overcoat layer is provided, charges may accumulate in a specific region on the overcoat layer. However, by applying an AC voltage to the electrode of the first substrate as in the present invention, such a problem can be sufficiently obtained. Can be resolved.
The overcoat layer is obtained using a general insulating material. Specifically, an organic insulating film such as acrylic resin having a thickness of about 1 to 3 μm and a dielectric constant of about 3 to 4, or an inorganic insulating film such as silicon nitride having a thickness of about 50 to 150 nm and a dielectric constant of about 6 to 7 Etc.

As the material for the overcoat layer, organic resins that are generally used at present can be used. Also, from the viewpoint of forming a flat uniform film that is an insulator, it is usually a dielectric layer composed of a dielectric (insulator).

The pair of comb electrodes may be anything as long as it can be said that the two comb electrodes face each other when the substrate main surface is viewed in plan. Since the pair of comb electrodes can generate a transverse electric field between the comb electrodes, when the liquid crystal layer includes liquid crystal molecules having positive dielectric anisotropy, the transmittance is excellent. Become.

The pair of comb electrodes may be provided in the same layer, and may be provided in different layers as long as the effects of the present invention can be exhibited, but provided in the same layer. Is preferred. A pair of comb electrodes is provided in the same layer when each comb electrode has a common member (for example, an insulating layer, a liquid crystal layer side and / or a side opposite to the liquid crystal layer side). A liquid crystal layer, etc.).

In the pair of comb-tooth electrodes, it is preferable that the comb-tooth portions are respectively along when the main surface of the substrate is viewed in plan. In particular, it is preferable that the comb-tooth portions of the pair of comb-tooth electrodes are substantially parallel, in other words, each of the pair of comb-tooth electrodes has a plurality of substantially parallel slits.

It is preferable that the pair of comb electrodes can have different potentials at a threshold voltage or higher. The threshold voltage means, for example, a voltage value that gives a transmittance of 5% when the transmittance in the bright state is set to 100%. The potential different from the threshold voltage can be any voltage as long as it can realize a driving operation with a potential different from the threshold voltage. This makes it possible to suitably control the electric field applied to the liquid crystal layer. Become. A preferable upper limit value of the different potential is, for example, 20V. As a configuration that can have different potentials, for example, one of the pair of comb electrodes is driven by one TFT and the other comb electrode is driven by another TFT. A pair of comb electrodes can be set to different potentials by conducting with the lower electrode of the other comb electrode. The width of the comb tooth portion in the pair of comb electrodes is preferably 2 μm or more, for example. In addition, the width between the comb tooth portions (also referred to as a space in the present specification) is preferably 2 μm to 7 μm, for example.

Each of the first substrate and the second substrate preferably includes a polarizing plate. The polarizing plate is usually disposed on the opposite side of the liquid crystal layer with respect to the first substrate and the second substrate.

The liquid crystal layer in the liquid crystal display panel of the present invention usually contains liquid crystal molecules that are aligned in the horizontal direction with respect to the substrate main surface at a threshold voltage or higher due to an electric field generated between a pair of comb electrodes. “Orienting in the horizontal direction” may be anything that can be said to be oriented in the horizontal direction in the technical field of the present invention. Thereby, the transmittance can be improved. It is preferable that the liquid crystal layer is substantially composed of liquid crystal molecules that are aligned at a threshold voltage or higher and oriented in the horizontal direction with respect to the main surface of the substrate.

The liquid crystal layer preferably includes liquid crystal molecules that are aligned in a direction perpendicular to the main surface of the substrate at a voltage lower than the threshold voltage. In the technical field of the present invention, the term “orienting in the direction perpendicular to the main surface of the substrate” may be anything that can be said to be oriented in the direction perpendicular to the main surface of the substrate. Including. It is preferable that the liquid crystal layer is substantially composed of liquid crystal molecules which are less than a threshold voltage and are aligned in a direction perpendicular to the main surface of the substrate. Such a vertical alignment type liquid crystal display panel is an advantageous system for obtaining a wide viewing angle, high contrast characteristics, and the like, and its application is expanding.

The liquid crystal display panel is configured such that liquid crystal molecules in a liquid crystal layer are aligned in a direction perpendicular to the main surface of the substrate by an electric field generated between a pair of comb electrodes or between a first substrate and a second substrate. It is preferable that

The electrode of the first substrate is preferably a planar electrode. In the present specification, the planar electrode includes a form electrically connected within a plurality of pixels, for example, as a planar electrode of the first substrate, a form electrically connected within all pixels, A form in which they are electrically connected in the same pixel column is preferable. The second substrate preferably further includes a planar electrode. Thereby, a vertical electric field can be applied suitably and high-speed response can be achieved. In particular, when the electrode of the first substrate is a planar electrode and the second substrate further has a planar electrode, a vertical electric field can be suitably generated by a potential difference between the substrates at the time of falling. Can be made to respond quickly. In order to suitably apply a horizontal electric field and a vertical electric field, the liquid crystal layer side electrode (upper layer electrode) of the second substrate is used as a pair of comb-teeth electrodes, and the electrode (lower layer) opposite to the liquid crystal layer side of the second substrate. A form in which the electrode is a planar electrode is particularly preferable. For example, the planar electrode of the second substrate can be provided below the pair of comb electrodes on the second substrate (the layer on the side opposite to the liquid crystal layer as viewed from the second substrate) via an insulating layer.

The planar electrode of the second substrate is usually formed via a pair of comb electrodes and an electric resistance layer. The electrical resistance layer is preferably an insulating layer. The insulating layer may be an insulating layer in the technical field of the present invention. It is preferable that a pair of comb electrodes are disposed on the liquid crystal layer side of the planar electrode of the second substrate.

The planar electrode of the first substrate and / or the second substrate may be any surface shape in the technical field of the present invention, and has an alignment regulating structure such as a rib or a slit in a partial region thereof. The alignment regulating structure may be provided at the center of the pixel when the main surface of the substrate is viewed in plan, but those having substantially no alignment regulating structure are suitable.

The liquid crystal layer preferably includes liquid crystal molecules (positive liquid crystal molecules) having positive dielectric anisotropy. The liquid crystal molecules having positive dielectric anisotropy are aligned in a certain direction when an electric field is applied, and the alignment control is easy, and a faster response can be achieved. More preferably, the liquid crystal molecules are substantially composed of liquid crystal molecules having positive dielectric anisotropy. The liquid crystal layer preferably also includes liquid crystal molecules having negative dielectric anisotropy (negative liquid crystal molecules). Also by this, the effect of the present invention can be exhibited, and in particular, the transmittance can be improved. That is, it is preferable that the liquid crystal molecules are substantially composed of liquid crystal molecules having positive dielectric anisotropy from the viewpoint of high-speed response, and the liquid crystal molecules are negative from the viewpoint of transmittance. It can be said that it is preferable to be substantially composed of liquid crystal molecules having a dielectric anisotropy of The form in which the liquid crystal layer includes negative liquid crystal molecules can be suitably applied to, for example, a liquid crystal display panel having a three-layer electrode structure in which the alignment of liquid crystal molecules is controlled by an electric field at both rising and falling.

The first substrate and the second substrate usually have an alignment film on at least one liquid crystal layer side. The alignment film is preferably a vertical alignment film. Examples of the alignment film include alignment films formed from organic materials and inorganic materials, and photo-alignment films formed from photoactive materials. The alignment film may be an alignment film that has not been subjected to an alignment process such as a rubbing process. By using an alignment film that does not require alignment treatment, such as an alignment film formed from an organic material or an inorganic material, or a photo-alignment film, the cost can be reduced by simplifying the process, and reliability and yield can be improved. it can. In addition, when rubbing treatment is performed, there is a risk of liquid crystal contamination due to impurities from rubbing cloth etc., point defects due to foreign materials, display unevenness due to non-uniform rubbing within the liquid crystal panel, These disadvantages can be eliminated. Furthermore, the liquid crystal molecules contained in the liquid crystal layer preferably have a tilt angle. The tilt angle usually refers to the tilt angle (pretilt angle) in the initial alignment state. For example, it is preferable that the liquid crystal molecules are aligned so as to be tilted to such an extent that the liquid crystal molecules have a tilt angle from the direction perpendicular to the main surface of the substrate, less than the threshold voltage. More preferably, a photo-alignment process is performed as a means for expressing the tilt angle. Further, for example, a photo-alignment treatment (using a UV exposure machine or the like) such as FPA (Field-induced Photo-reactive Alignment) or PSA (Polymer Stabilized Vertical Alignment) is performed, and the tilt angle is set to the liquid crystal molecules in contact with the alignment film By realizing the imparted initial alignment state, a faster response can be achieved. The tilt angle exceeds 0 ° and is preferably 2 ° or less. If it exceeds 2 °, the CR (contrast ratio) may be lowered. In this specification, it can be said that the liquid crystal molecules having a tilt angle in the initial alignment state are aligned in the direction perpendicular to the main surface of the substrate below the threshold voltage. The first substrate and the second substrate preferably have a polarizing plate on the side opposite to at least one liquid crystal layer side. The polarizing plate is preferably a linear polarizing plate. With such a configuration, the contrast and viewing angle characteristics can be excellent.

The first substrate and the second substrate included in the liquid crystal display panel of the present invention are a pair of substrates for sandwiching a liquid crystal layer. For example, an insulating substrate such as glass or resin is used as a base, and wiring and electrodes are formed on the insulating substrate. It is formed by making a color filter or the like.

It is preferable that at least one of the pair of comb-teeth electrodes is a pixel electrode, and the second substrate including the pair of comb-teeth electrodes is an active matrix substrate. The liquid crystal display panel of the present invention may be any of a transmissive type, a reflective type, and a transflective type.

The present invention is also a liquid crystal display device including the liquid crystal display panel of the present invention. The preferred form of the liquid crystal display panel in the liquid crystal display device of the present invention is the same as the preferred form of the liquid crystal display panel of the present invention described above. Examples of the liquid crystal display device include in-vehicle devices such as personal computers, televisions, and car navigation systems, and displays of portable information terminals such as mobile phones.

The configuration of the liquid crystal display panel and the liquid crystal display device of the present invention is not particularly limited by other components as long as such components are formed as essential, and the liquid crystal display panel and the liquid crystal display are not limited. Other configurations normally used in the apparatus can be applied as appropriate.

Each form mentioned above may be combined suitably in the range which does not deviate from the gist of the present invention.

According to the liquid crystal display panel and the liquid crystal display device of the present invention, the display unevenness can be suppressed and the occurrence of image sticking can be sufficiently reduced by having the comb electrode and the counter electrode.

1 is a schematic cross-sectional view of a liquid crystal display panel according to Embodiment 1. FIG. 4 is a graph showing a waveform applied to a counter electrode of the liquid crystal display panel according to Embodiment 1. 4 is a schematic plan view of picture elements of the liquid crystal display panel according to Embodiment 1. FIG. 6 is a graph showing VT characteristics of the liquid crystal display panel according to Embodiment 1, the liquid crystal display panel according to Comparative Example 1, and the liquid crystal display panel according to Comparative Example 2. 3 is a schematic cross-sectional view of the liquid crystal display panel according to Embodiment 1 when an AC voltage is applied. FIG. It is a simulation result when the counter voltage of the liquid crystal display panel which concerns on Embodiment 1 is 0V. It is a graph which shows the transmittance | permeability distribution for every observation point of the liquid crystal display panel shown in FIG. It is a simulation result when the counter voltage of the liquid crystal display panel which concerns on Embodiment 1 is 1.5V. It is a graph which shows the transmittance | permeability distribution for every observation point of the liquid crystal display panel shown in FIG. It is a simulation result when the counter voltage of the liquid crystal display panel which concerns on Embodiment 1 is 2.5V. 11 is a graph showing a transmittance distribution for each observation point of the liquid crystal display panel shown in FIG. 10. It is a simulation result when the counter voltage of the liquid crystal display panel which concerns on Embodiment 1 is 3.5V. 13 is a graph showing a transmittance distribution for each observation point of the liquid crystal display panel shown in FIG. It is a simulation result when the counter voltage of the liquid crystal display panel which concerns on Embodiment 1 is 5V. It is a graph which shows the transmittance | permeability distribution for every observation point of the liquid crystal display panel shown in FIG. 4 is a graph showing the transmittance for each applied voltage when a center voltage of 2.5 V and an amplitude voltage of 2.5 V are applied as AC voltage pressures applied to the counter electrode of the liquid crystal display panel according to Embodiment 1. Transmittance with respect to the applied voltage when the center voltage is set as the intermediate voltage between the comb electrodes and the amplitude voltage is set to half the voltage between the comb electrodes as the AC voltage applied to the counter electrode of the liquid crystal display panel according to Embodiment 2. It is a graph which shows. 10 is a graph showing VT characteristic curves for a liquid crystal display panel according to Embodiment 2, a liquid crystal display panel having a counter electrode [common electrode], and a liquid crystal display panel having no counter electrode. Transmission with respect to each applied voltage when the center voltage is set as an intermediate voltage between the comb-teeth electrodes and the amplitude voltage is set to half the voltage between the comb-teeth electrodes as an AC voltage applied to the counter electrode of the liquid crystal display panel according to Embodiment 3. It is a graph which shows a rate. 10 is a graph showing VT characteristic curves for a liquid crystal display panel according to Embodiment 3, a liquid crystal display panel having a counter electrode [common electrode], and a liquid crystal display panel having no counter electrode. 6 is a schematic cross-sectional view of a liquid crystal display panel according to Embodiment 3. FIG. 6 is a schematic cross-sectional view of a liquid crystal display panel according to Comparative Example 1. FIG. FIG. 23 is a more detailed view of FIG. 10 is a schematic cross-sectional view of a liquid crystal display panel according to Comparative Example 2. FIG.

Embodiments will be described below, and the present invention will be described in more detail with reference to the drawings. However, the present invention is not limited only to these embodiments. In this specification, a pixel may be a picture element (sub-pixel) unless otherwise specified. Furthermore, as long as it can be said that the planar electrode is a planar electrode in the technical field of the present invention, for example, dot-shaped ribs and / or slits may be formed, but the planar electrode has a substantially alignment regulating structure. What is not preferred is preferred. Of the pair of substrates sandwiching the liquid crystal layer, the substrate on the display surface side is also referred to as an upper substrate, and the substrate on the opposite side to the display surface is also referred to as a lower substrate. In addition, when the electrodes arranged on the substrate are arranged in two layers, the electrode on the display surface side is also referred to as an upper layer electrode, and the electrode on the side opposite to the display surface is also referred to as a lower layer electrode. Furthermore, the circuit substrate (second substrate) of this embodiment is also referred to as a TFT substrate or an array substrate because it includes a thin film transistor element (TFT). 6, 8, 10, 12, and 14, which will be described later, the scale represented by (# 1) indicates the height of the insulating layer of the lower substrate (second substrate), and (# 2 The scale represented by () represents the height of the liquid crystal layer, and the scale represented by (# 3) represents the height of the overcoat layer of the upper substrate (first substrate). In addition, in each embodiment, the member and part which exhibit the same function are attached | subjected the same code | symbol.

Embodiment 1
FIG. 1 is a schematic cross-sectional view of the liquid crystal display panel according to the first embodiment. The first embodiment has a structure in which the TFT substrate includes only a pair of comb electrodes as electrodes.
The liquid crystal display panel according to Embodiment 1 aligns positive liquid crystal vertically with respect to the main surface of the substrate. In addition, the liquid crystal display panel according to Embodiment 1 includes a pair of comb-shaped electrodes 16 (a pair of comb-shaped electrodes composed of a first electrode 17 and a second electrode 19. The first electrode is also referred to as a first pixel electrode) and the counter electrode 23 (planar electrode) is used to generate an oblique electric field to control the orientation of liquid crystal molecules, thereby controlling the amount of transmitted light. Display mode. Specifically, when the voltage difference between the comb electrodes is equal to or higher than the threshold voltage, the liquid crystal molecules are separated between the comb electrodes by an electric field generated between the pair of comb electrodes 16 formed on the glass substrate 11 (second substrate). The amount of transmitted light is controlled by tilting in the horizontal direction.

The liquid crystal display panel according to Embodiment 1 is characterized in that the counter electrode 23 is driven by AC voltage (AC driving) to control the electric field distribution. FIG. 2 is a graph showing a waveform applied to the counter electrode of the liquid crystal display panel according to the first embodiment. In FIG. 2, the waveform is a sine wave, and a sine wave is preferable, but other waveforms may be used. Further, for example, an AC voltage having a center voltage of 1V to 10V and an amplitude voltage of 1V to 10V can be applied.

The second substrate 10 has a structure that generates a parallel electric field (an electric field substantially horizontal to the main surface of the substrate). On the second substrate 10, a pair of comb-like electrodes 16 are made of IZO (Indium Zinc Oxide) or ITO (Indium Tin Oxide) using photolithography or the like.

FIG. 3 is a schematic plan view of picture elements of the liquid crystal display panel according to the first embodiment. At the timing selected by the scanning signal line, the voltage supplied from the video signal line is applied to the second electrode 19 that drives the liquid crystal material through the semiconductor layer SC of the thin film transistor element (TFT). In this embodiment, the pair of comb electrodes (the first electrode 17 and the second electrode 19) are formed in the same layer, and a form formed in the same layer is preferable, but between the pair of comb electrodes. As long as the effect of the present invention of improving the transmittance by applying a lateral electric field by generating a voltage difference can be formed in another layer. The second electrode 19 is connected to a drain electrode extending from the TFT through a contact hole. In FIG. 1, the counter electrode 23 has a planar shape.

The first substrate 20 facing the second substrate 10 has a structure in which an opposing planar electrode layer 23 and a dielectric layer 25 are deposited.
The cell conditions are as follows.
Electrode width (L) / electrode interval (S) = 3 μm / 8 μm
Insulating layer: thickness 3 μm, ε = 6.9
Dielectric layer 25 (overcoat layer): thickness 2 μm, ε _oc = 3.9
Liquid crystal layer: thickness 3.4 μm, Δn = 0.12, Δε = 22 (25 ° C.)
In addition, although the said insulating layer is not shown in figure, it says the insulating layer between the comb-tooth electrode of a liquid crystal panel, and a glass substrate.

In the present embodiment, the electrode width L of the comb-tooth electrode is 3 μm, but is preferably 2 μm or more, for example. The electrode spacing S of the comb electrodes is 8 μm, but preferably 2 μm or more, for example. In addition, a preferable upper limit is 12 micrometers, for example. The ratio (L / S) between the electrode spacing S and the electrode width L is preferably 0.2 to 3, for example. A more preferable lower limit value is 0.4, and a more preferable upper limit value is 1.5.

The thickness of the liquid crystal layer is 3.4 μm, but may be 2 μm to 7 μm, and is preferably within the range. In the present specification, the thickness of the liquid crystal layer is preferably calculated by averaging all the thicknesses of the liquid crystal layers in the liquid crystal display panel.

Although not shown in FIG. 1, a polarizing plate is disposed on the opposite side of the liquid crystal layers of both substrates. As the polarizing plate, either a circular polarizing plate or a linear polarizing plate can be used, but a linear polarizing plate is preferable. In addition, alignment films are arranged on the liquid crystal layer side of both substrates, and these alignment films are either organic alignment films or inorganic alignment films as long as the liquid crystal molecules stand vertically with respect to the film surfaces. There may be. Further, a photo-alignment process (using a UV exposure machine or the like) such as FPA (Field-induced Photo-reactive Alignment) or PSA (Polymer Stabilized Vertical Alignment) is applied to give a tilt angle to the liquid crystal molecules in contact with the alignment film. Thus, high-speed response can be achieved.

The burn-in and display unevenness were evaluated by visual observation through a commercially available ND (Neutral Density) filter (ND-LCD laminate product manufactured by PANAC). The evaluation was performed in a determination environment in which the illuminance of the external light irradiation part on the panel surface was 150 lux. The evaluation results are shown in Table 1 below. If image sticking and display unevenness are not observed when viewed through an ND filter having a transmittance of 8% or more, there is no practical problem. “Counter AC 5 V” indicates that the first substrate has a counter electrode, and an AC voltage having a center voltage of 2.5 V and an amplitude voltage of 2.5 V is applied to the counter electrode. “Counter AC” indicates that the first substrate has a counter electrode, and an AC voltage is applied to the counter electrode as described later. “Opposite” means that the first substrate has a counter electrode and no voltage is applied to the counter electrode. “No opposing” means that the first substrate does not have an opposing electrode. “No lower layer” means that the second substrate does not have a lower layer electrode. “With lower layer” means that the second substrate has a planar lower electrode. In the table, the numerical value indicated by the unit of% indicates the transmittance of the ND filter used for the measurement. The configurations of Embodiment 2, Embodiment 3, Comparative Example 1 and Comparative Example 2 will be described in detail later.

In the case of the liquid crystal display panel including the counter electrode 223 according to the comparative example 1, display unevenness does not occur because it has a low threshold and a broad transmittance characteristic, but noticeable image sticking occurs at the interface of the dielectric layer 225 (overcoat layer). appear. Further, in the case of the liquid crystal display panel without the counter electrode of Comparative Example 2, image sticking does not occur, but the rate of change in transmittance with respect to voltage change is steep, and display unevenness is likely to occur during low gradation display.

FIG. 4 shows VT characteristics (transmittance [%] with respect to applied voltage [V]) for the liquid crystal display panel according to the first embodiment, the liquid crystal display panel according to comparative example 1, and the liquid crystal display panel according to comparative example 2. It is a graph to show. At the same time, the liquid crystal display panel according to the first embodiment provides a display panel that has a gentle VT characteristic curve (the graph of “opposite AC” shown in FIG. 4) and has no display unevenness during low gradation display. Is possible. In Comparative Example 2 (without a counter electrode), the VT characteristic curve is not smooth as in Embodiment 1, and display unevenness cannot be sufficiently suppressed. That is, the liquid crystal display panel according to Embodiment 1 includes the counter electrode 23 and AC driving the counter electrode 23, thereby enabling to provide a high-quality liquid crystal display element that hardly causes image sticking or display unevenness. is there. 4 will be further described later.

As described above, the liquid crystal display panel according to Embodiment 1 is characterized in that the counter electrode 23 is AC driven. FIG. 5 is a schematic sectional view when an AC voltage is applied to the counter electrode 23 of the liquid crystal display panel according to the first embodiment. As shown in FIG. 5, by constantly changing the region where charge accumulation occurs on the surface of the overcoat layer, it is possible to prevent burn-in as shown below.

The electric field distribution in the liquid crystal cell when the voltage applied to the counter electrode 23 was changed was simulated by LCD-MASTER manufactured by Shintech. The simulation conditions are as follows.
Electrode width (L) / electrode interval (S) = 3 μm / 8 μm
Insulating layer: thickness 3 μm, ε = 6.9
Dielectric layer 25 (overcoat layer): thickness 2 μm, ε _oc = 3.9
Liquid crystal layer: thickness 3.4 μm, Δn = 0.12, Δε = 22 (25 ° C.)

The simulation results are shown in FIGS. 6 to 15, in the liquid crystal display panel according to the first embodiment, when white display is performed (5 V for the first pixel electrode (one of the pair of comb electrodes), and the second electrode (the other of the pair of comb electrodes). The voltage distribution and the transmittance distribution are shown when the counter voltage is changed to 0V, 1.5V, 2.5V, 3.5V, and 5V when 0V is applied. That is, FIG. 6 shows a simulation result when the counter voltage is 0V. FIG. 7 is a graph showing the transmittance distribution for each observation point of the liquid crystal display panel shown in FIG. FIG. 8 shows a simulation result when the counter voltage is 1.5V. FIG. 9 is a graph showing the transmittance distribution for each observation point of the liquid crystal display panel shown in FIG. FIG. 10 shows a simulation result when the counter voltage is 2.5V. FIG. 11 is a graph showing the transmittance distribution for each observation point of the liquid crystal display panel shown in FIG. In FIG. 10, it can be said that the electric field distribution is in a neutral state. FIG. 12 shows a simulation result when the counter voltage is 3.5V. FIG. 13 is a graph showing the transmittance distribution for each observation point of the liquid crystal display panel shown in FIG. FIG. 14 shows a simulation result when the counter voltage is 5V. FIG. 15 is a graph showing the transmittance distribution for each observation point of the liquid crystal display panel shown in FIG.

From the simulation results, it was confirmed that the electric field distribution can be controlled by changing the applied voltage to the counter electrode. This means that the region where charge accumulation occurs on the overcoat layer can be moved by AC driving the counter electrode. Therefore, when an AC voltage is applied to the counter electrode, the region where charge accumulation occurs constantly changes, and the image sticking phenomenon does not occur.

FIG. 16 shows a VT characteristic curve (transmittance with respect to each applied voltage) when a center voltage of 2.5 V and an amplitude voltage of 2.5 V are applied as the AC voltage applied to the counter electrode of the liquid crystal display panel according to the first embodiment. It is a graph to show. In FIG. 16, “opposite 0 V”, “opposite 1 V”, “opposite 2 V”, “opposite 3 V”, “opposite 4 V”, and “opposite 5 V” respectively indicate the amount of AC voltage applied to the counter electrode. Show. Although there is a fluctuation width for applying the AC voltage, when these are averaged, the VT characteristic according to the first embodiment shown in FIG. 4 is obtained. From FIG. 4, it was confirmed that the liquid crystal display panel of the present invention had a gentle VT characteristic as compared with Comparative Example 2. That is, reduction in display unevenness at the time of low gradation display was realized.

In the first embodiment and the subsequent embodiments, a positive liquid crystal is used as the liquid crystal, but a negative liquid crystal may be used instead of the positive liquid crystal. In the case of using a negative type liquid crystal, the liquid crystal molecules are aligned in the horizontal direction due to the potential difference between the pair of substrates, and the liquid crystal molecules are aligned in the vertical direction due to the potential difference between the pair of comb electrodes. As a result, the transmittance is excellent, and the liquid crystal molecules can be rotated by an electric field at both rising and falling, thereby achieving high-speed response.

In addition, the liquid crystal display device provided with the liquid crystal display panel of Embodiment 1 can appropriately include a member (for example, a light source or the like) included in a normal liquid crystal display device. The same applies to the embodiments described later. The liquid crystal display device according to the first embodiment can exhibit the same effects as those exhibited by the liquid crystal display panel of the present invention. For example, a portable device such as a personal computer, a television, a car navigation system, or a mobile phone. It can be suitably used as a display of an information terminal.

Embodiment 2
The liquid crystal display panel according to the second embodiment executes a driving method in which an alternating voltage applied to the counter electrode is changed according to a voltage applied to the pixel. Other configurations of the second embodiment are the same as those of the first embodiment described above. FIG. 17 shows an application when the center voltage is set to the intermediate voltage between the comb-teeth electrodes and the amplitude voltage is set to half the inter-comb electrode voltage as the AC voltage applied to the counter electrode of the liquid crystal display panel according to the second embodiment. It is a graph which shows the transmittance | permeability with respect to a voltage. For example, in the driving method according to the second embodiment, in a gradation in which 3V is applied to the first pixel electrode (one of the pair of comb electrodes) and 0V is applied to the second electrode (the other of the pair of comb electrodes), In this driving method, an AC voltage having a center voltage of 1.5 V and an amplitude of 1.5 V is applied to the counter electrode. In FIG. 17, “opposite 0 V”, “opposite center”, and “opposite high” indicate the amount of AC voltage applied to the counter electrode, respectively. The same applies to FIG. 19 described later. FIG. 18 shows a VT characteristic curve (transmittance [%] with respect to applied voltage [V]) for a liquid crystal display panel according to the second embodiment, a liquid crystal display panel having a counter electrode [common electrode], and a liquid crystal display panel having no counter electrode. ). The VT characteristic of the liquid crystal display panel according to the second embodiment has a fluctuation width because an AC voltage is applied, but on average has the VT characteristic curve shown in FIG. 18 (the graph shown in “second embodiment”).

In the first embodiment, a large voltage having a center voltage of 2.5 V and an amplitude of 2.5 V is applied even at the time of low gradation display with a low pixel application voltage. However, it is ideal to apply a counter AC voltage according to each gradation voltage. If the pixel applied voltage is small, the amplitude of the counter AC voltage may be small. Since burn-in occurs more remarkably at the time of high gradation display, the drive method of the second embodiment can sufficiently improve the burn-in. Further, display unevenness at the time of low gradation display can be reduced, and light leakage at the time of black display that may occur in the first embodiment does not occur.

Embodiment 3
The liquid crystal display panel according to Embodiment 3 has a structure in which an AC voltage is applied to the counter electrode in accordance with the pixel applied voltage, and the TFT side substrate has a lower surface electrode.
FIG. 19 is a graph illustrating the AC voltage applied to the counter electrode of the liquid crystal display panel according to the third embodiment when the center voltage is set to the intermediate voltage between the comb electrodes and the amplitude voltage is set to half the inter-comb electrode voltage. It is a graph which shows the transmittance | permeability with respect to an applied voltage. FIG. 19 shows a fluctuation in VT characteristics caused by applying an AC voltage to the counter electrode. FIG. 20 shows an averaged VT characteristic curve of the third embodiment. The VT for each of the liquid crystal display panel according to the third embodiment, the liquid crystal display panel having a counter electrode (common electrode), and the liquid crystal display panel having no counter electrode is shown. It is a graph which shows a characteristic curve.

FIG. 21 is a schematic cross-sectional view of a liquid crystal display panel according to the third embodiment.
The liquid crystal display panel according to Embodiment 3 has a vertical alignment type three-layer electrode structure using liquid crystal molecules that are positive-type liquid crystals (here, the upper layer electrode of the lower substrate located in the second layer is a comb electrode 117). 119). In the rise, liquid crystal molecules are rotated by a lateral electric field generated by a potential difference between the pair of comb electrodes 117 and 119. At this time, there is substantially no potential difference between the substrates (between the counter electrode 113 and the counter electrode 123).

In addition, the fall rotates the liquid crystal molecules by a vertical electric field generated by a potential difference between the substrates (for example, between the counter electrode 113, the first electrode 117, the second electrode 119, and the counter electrode 123). At this time, the potential difference between the pair of comb electrodes (consisting of the first electrode 117 and the second electrode 119) does not substantially occur.

High-speed response is achieved by rotating liquid crystal molecules by an electric field for both rising and falling. That is, at the rising edge, the lateral electric field between the pair of comb electrodes is turned on to increase the transmittance, and at the falling edge, the vertical electric field between the substrates is turned on to increase the response speed. Further, a high transmittance can be realized by a lateral electric field driven by a comb.

In the third embodiment, the planar lower electrode 113 (counter electrode 113) is formed with the insulating layer 115 interposed between the upper layer electrodes 117 and 119 (a pair of comb electrodes). The insulating layer 115 is, for example, or an oxide film SiO _2, nitride SiN or an acrylic resin is used, or a combination of these materials can be used. The liquid crystal display panel of Embodiment 3 is easy to manufacture and can achieve high speed response and high transmittance. The other reference numerals in the drawing according to the third embodiment are the same as those shown in the drawing according to the first embodiment except that 1 is added to the hundreds.

Comparative Example 1
FIG. 22 is a schematic cross-sectional view of a liquid crystal display panel according to Comparative Example 1. FIG. 23 is a more detailed view of FIG. 22 and shows an oblique electric field (solid line) in addition to the contents shown in FIG. 22, and also shows a green color filter 222G, a red color filter 222R, and a blue color. The filter 222B is shown without being omitted. The liquid crystal display panel according to Comparative Example 1 has a counter electrode 223. The counter electrode 223 is a planar common electrode, and no voltage is applied (0 V).

In the case of the liquid crystal display panel provided with the counter common electrode of Comparative Example 1, since it has a low threshold value and broad transmittance characteristics, display unevenness does not occur, but noticeable burn-in occurs at the overcoat layer interface. In addition, the reference numbers of the figure which concerns on the comparative example 1 are the same as that of what was shown to the figure which concerns on Embodiment 1 except having attached 2 to the hundreds place.

Comparative Example 2
FIG. 24 is a schematic cross-sectional view of a liquid crystal display panel according to Comparative Example 2. The liquid crystal display panel according to Comparative Example 2 does not have a counter electrode. In the case of the display device without the counter electrode of Comparative Example 2, image sticking does not occur, but the ratio of the transmittance change to the voltage change is steep and unevenness is likely to occur during low gradation display. In addition, the reference numbers of the figure which concerns on the comparative example 2 are the same as that of what was shown to the figure which concerns on Embodiment 1 except having attached | subjected 3 to the hundreds place.

In summary, the display device of this embodiment is characterized in that the counter electrode voltage is AC driven. In this method, image sticking can be prevented by constantly changing the region where charge accumulation occurs on the surface of the overcoat layer. At the same time, it is possible to provide a display element having a gentle VT characteristic curve and free from display unevenness during low gradation display. That is, by providing the counter electrode and AC driving the counter electrode, it is possible to provide a high-quality liquid crystal display element that is unlikely to cause image sticking or unevenness. As the burn-in improvement effect, as shown in Table 1 above, Embodiment 1 in which an AC voltage of Vpp = 5 V is applied at all gradations is most effective.

In addition, it can confirm that the alternating voltage is applied by observing an applied voltage waveform with an oscilloscope. Further, on the TFT substrate and the counter substrate, the electrode structure and the like according to the liquid crystal display panel and the liquid crystal display device of the present invention can be confirmed by microscopic observation such as SEM (Scanning Electron Microscope).

Each form in embodiment mentioned above may be combined suitably in the range which does not deviate from the summary of this invention.

This application claims priority based on the Paris Convention or the laws and regulations in the country to which the transition is based on Japanese Patent Application No. 2011-125493 filed on June 3, 2011. The contents of the application are hereby incorporated by reference in their entirety.

10, 110, 210, 310: Array substrate 11, 21, 111, 121, 211, 221, 311, 321: Glass substrate 13, 23, 113, 123, 223: Counter electrode 15, 115: Insulating layer 16: Pair Comb electrodes 17, 19, 117, 119, 217, 219, 317, 319: Comb electrodes 20, 120, 220, 320: counter substrate 25, 125, 225: dielectric layer (overcoat layer)
30, 130, 230, 330: liquid crystal layers 231, 331: orientation of liquid crystal molecules 222G: green color filter 222R: red color filter 222B: blue color filter

Claims (12)

A liquid crystal display panel comprising a first substrate, a second substrate, and a liquid crystal layer sandwiched between both substrates,
The first substrate has an electrode to which an alternating voltage is applied,
The liquid crystal display panel, wherein the second substrate has a pair of comb electrodes. The center voltage of the alternating voltage is equal to or lower than the intermediate voltage of the voltages applied to the pair of comb electrodes,
2. The liquid crystal display panel according to claim 1, wherein the amplitude of the alternating voltage is not more than half of a voltage difference applied between the pair of comb electrodes. The liquid crystal display panel according to claim 1, wherein the first substrate further includes an overcoat layer. 4. The liquid crystal display panel according to claim 1, wherein the electrode of the first substrate is a planar electrode. 5. The liquid crystal display panel according to claim 1, wherein the second substrate further includes a planar electrode. 6. The liquid crystal display panel according to claim 1, wherein the liquid crystal layer includes liquid crystal molecules having positive dielectric anisotropy. 6. The liquid crystal display panel according to claim 1, wherein the liquid crystal layer includes liquid crystal molecules having negative dielectric anisotropy. The liquid crystal display panel according to any one of claims 1 to 7, wherein the liquid crystal layer includes liquid crystal molecules that are aligned in a direction perpendicular to a main surface of the substrate at a voltage lower than a threshold voltage. 9. The liquid crystal display panel according to claim 1, wherein the liquid crystal molecules have a tilt angle. The liquid crystal display panel according to claim 9, wherein a photo-alignment process is performed as means for expressing the tilt angle. The liquid crystal display panel according to claim 1, wherein each of the first substrate and the second substrate includes a polarizing plate. A liquid crystal display device comprising the liquid crystal display panel according to any one of claims 1 to 11.

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