JP4519691B2 - Liquid crystal display panel and liquid crystal display device including the same - Google Patents

Description

  The present invention relates to a liquid crystal display panel used in a display unit of an electronic device and a liquid crystal display device including the same.

A vertical alignment method in which liquid crystal molecules are aligned perpendicularly to the substrate like the MVA method can realize a wide viewing angle characteristic. However, in the vertical alignment method, generally, the transmittance characteristic (TV characteristic) with respect to the voltage applied to the liquid crystal is different between the normal direction (front direction) of the display screen and the oblique direction. For this reason, even when the TV characteristic in the normal direction of the screen is optimally adjusted, the TV characteristic is distorted depending on the image displayed on the screen when viewed from an oblique direction when halftone is displayed. The color changes whitish. A capacitively coupled MVA liquid crystal display panel is known as a technique for improving gradation viewing angle characteristics (brownish).
JP-A-6-337419 JP 2002-169161 A Japanese Patent Laid-Open No. 2001-209074

  However, the capacitively coupled MVA type liquid crystal display panel has a problem of being easily burned. A conventional MVA type liquid crystal display panel which is not a capacitive coupling type is more noticeable in image sticking as the display is on the lower gradation side. On the other hand, in the capacitively coupled MVA liquid crystal display panel, there is a tendency that larger burn-in is observed on the high gradation side than on the low gradation side. The image sticking on the high gradation side is a phenomenon peculiar to the capacitively coupled MVA type liquid crystal display panel. This occurs particularly because the region on the pixel electrode side (high threshold voltage side) that is capacitively coupled and is in a floating state is easily burned.

  The capacitively coupled MVA type liquid crystal display panel easily accumulates charges in the pixel region on the high threshold voltage side even when positive and negative symmetrical alternating voltages are continuously applied, and the charges are capacitively coupled MVA type liquid crystal display panel. It turned out to be the cause of peculiar seizure. In general, the liquid crystal display panel is driven while being fixed at an optimum common voltage that minimizes flicker generated on the display screen. However, in the capacitively coupled MVA liquid crystal display panel, the optimum common voltage fluctuates with the voltage application time and increases in most cases.

  FIG. 12 is a graph showing evaluation results of residual direct current (DC) voltage in a capacitively coupled evaluation liquid crystal display panel. The horizontal axis represents voltage application time (minutes), and the vertical axis represents residual DC voltage (V). A curve A connecting the asterisk in the figure indicates the characteristics of the evaluation sample A, and a curve B connecting the □ in the figure indicates the characteristics of the evaluation sample B. In addition, a straight line C indicated by a broken line in the drawing indicates a characteristic of a conventional MVA liquid crystal display panel that is not a capacitive coupling type as a comparative example. Evaluation samples A and B are produced under the same conditions. The evaluation is performed by applying an AC voltage having a frequency of 30 Hz and a voltage of 5 V under an environment of an ambient temperature of 50 ° C.

  As shown in FIG. 12, when a positive and negative symmetric AC voltage is applied, the conventional MVA liquid crystal display panel has a residual DC voltage of about 0.04 V and becomes constant. However, even if positive and negative symmetric AC voltages are applied, the residual DC voltages of the capacitively coupled evaluation samples A and B rapidly increase until about 10 minutes have elapsed since the start of application of the AC voltage. Thereafter, the residual DC voltage gradually increases to about 0.14 V after about 120 minutes from the start of application of the AC voltage. Thus, in the capacitively coupled evaluation samples A and B, a DC voltage component remains even when an AC voltage is applied. Due to the residual DC voltage component, the optimum common voltage (for example, the voltage that minimizes flicker) varies in an actual liquid crystal display panel. The seizure occurs due to the deviation of the common voltage from the initial setting value (optimum value) caused by this variation.

  An object of the present invention is to provide a liquid crystal display panel capable of obtaining good display characteristics and a liquid crystal display device including the same.

  The object is to provide a gate bus line, a drain bus line formed intersecting the gate bus line through an insulating film, a gate electrode electrically connected to the gate bus line, and the drain bus line. A transistor having an electrically connected drain electrode; a first pixel electrode electrically connected to a source electrode of the transistor; and a source electrode of the transistor opposed to each other with an insulating film interposed therebetween, A second pixel electrode formed separately from the first pixel electrode; and a first alignment film formed on the first and second pixel electrodes and determining an initial alignment state of the liquid crystal material. The transistor substrate comprising: a transistor substrate; and a second alignment film that is different in structure and state from the first alignment film and determines an initial alignment state of the liquid crystal material. It is achieved by a liquid crystal display panel and having a face arranged opposite a substrate.

  ADVANTAGE OF THE INVENTION According to this invention, the liquid crystal display panel from which a favorable display characteristic is acquired, and a liquid crystal display device provided with the same are realizable.

[First Embodiment]
A liquid crystal display panel and a liquid crystal display device including the same according to a first embodiment of the present invention will be described with reference to FIGS. FIG. 1 shows a schematic configuration of a liquid crystal display device according to the present embodiment. FIG. 2 shows an equivalent circuit of the configuration of one pixel of the liquid crystal display device according to this embodiment. As shown in FIGS. 1 and 2, the liquid crystal display device includes a gate bus line 12 and a drain bus line (data bus line) 14 that are formed so as to cross each other through an insulating film, and a TFT 20 that is formed for each pixel. And a TFT substrate 2 having first and second pixel electrodes 16 and 17. In the liquid crystal display device, a counter substrate 4 facing the TFT substrate 2 with a predetermined cell gap is disposed. For example, a liquid crystal having negative dielectric anisotropy is sealed between the TFT substrate 2 and the counter substrate 4. A color filter (CF) and a common electrode 42 are formed on the liquid crystal side surface of the counter substrate 4. The liquid crystal display panel includes a TFT substrate 2, a counter substrate 4, and liquid crystal sealed between the substrates 2 and 4.

  On the TFT substrate 2, a gate bus line driving circuit 80 on which driver ICs for driving a plurality of gate bus lines 12 are mounted, and a drain bus line driving circuit 82 on which driver ICs for driving a plurality of drain bus lines 14 are mounted. And are connected. These drive circuits 80 and 82 output a scanning signal to a predetermined gate bus line 12 based on a control signal output from the control circuit 84, and output a gradation signal to a plurality of drain bus lines 14. ing. A polarizing plate 87 is disposed on the surface opposite to the liquid crystal side surface of the TFT substrate 2, and a polarizing plate 86 is disposed on the surface opposite to the liquid crystal side surface of the counter substrate 4 in a crossed Nicol manner. Yes. A backlight unit 88 is disposed on the surface of the polarizing plate 87 opposite to the TFT substrate 2.

  As shown in FIG. 2, the gate electrode G of the TFT 20 is connected to the gate bus line 12, and the drain electrode D is connected to the drain bus line 14. The source electrode S of the TFT 20 is electrically connected to the first pixel electrode 16, the storage capacitor electrode 19, and the connection electrode 25. The first pixel electrode 16, the common electrode 42 on the counter substrate 4 side facing the first pixel electrode 16, and the liquid crystal sandwiched between the first pixel electrode 16 and the common electrode 42 are the first. Liquid crystal capacitance Clc1 is formed. The storage capacitor Cs is formed by the storage capacitor electrode 19, the storage capacitor bus line 18 facing the storage capacitor electrode 19, and an insulating film sandwiched between the storage capacitor electrode 19 and the storage capacitor bus line 18. . A control capacitor Cc is formed by the connection electrode 25, the second pixel electrode 17 facing the connection electrode 25, and an insulating film sandwiched between the connection electrode 25 and the second pixel electrode 17. Further, the second pixel electrode 17, the common electrode 42 on the counter substrate 4 side facing the second pixel electrode 17, and the liquid crystal sandwiched between the second pixel electrode 17 and the common electrode 42. A second liquid crystal capacitor Clc2 is formed. In this example, the same potential is applied to the storage capacitor bus line 18 and the common electrode 42.

  As described above, in the pixel according to the present embodiment, the second liquid crystal capacitor Clc2 and the control capacitor Cc are connected in series, and the first liquid crystal capacitor Clc1 and the storage capacitor Cs are connected in parallel. It has a configuration. When the TFT 20 is turned on, the gradation signal supplied to the drain bus line 14 is applied to the first pixel electrode 16, the storage capacitor electrode 19, and the connection electrode 25, while the storage capacitor bus line 18 and the common electrode 42 have A common potential (common potential) is applied. As a result, the second pixel electrode 17 is maintained at a potential lower than the potential of the gradation signal applied to the first pixel electrode 16 by a predetermined amount.

  FIG. 3 shows a planar configuration of one pixel among a plurality of pixels formed in a matrix of the liquid crystal display panel according to the present embodiment. FIG. 4 shows a cross-sectional configuration of the liquid crystal display panel taken along line XX in FIG. As shown in FIGS. 3 and 4, a plurality of gate bus lines 12 and a plurality of drain bus lines 14 formed so as to intersect the gate bus lines 12 with the insulating film 30 interposed therebetween are, for example, on the glass substrate 10. Is formed. In the vicinity of the intersection position of the gate bus line 12 and the drain bus line 14, a TFT 20 formed for each pixel is disposed. A part of the gate bus line 12 functions as the gate electrode G of the TFT 20. On the gate bus line 12, an operating semiconductor layer of the TFT 20 and a channel protective film (both not shown) are formed via an insulating film. On the gate electrode G and on the channel protective film of the TFT 20, the drain electrode D and the underlying n-type impurity semiconductor layer (not shown), the source electrode S and the underlying n-type impurity semiconductor layer (not shown) Are opposed to each other with a predetermined gap therebetween.

  A storage capacitor bus line 18 extending in parallel with the gate bus line 12 is formed across the pixel region defined by the gate bus line 12 and the drain bus line 14. On the storage capacitor bus line 18, a storage capacitor electrode (intermediate electrode) 19 is formed for each pixel via an insulating film. The storage capacitor electrode 19 is connected to a connection electrode 25 that is electrically connected to the source electrode S of the TFT 20. The storage capacitor Cs is formed by the storage capacitor bus line 18, the storage capacitor electrode 19, and the insulating film 30 sandwiched between them.

  A pixel region defined by the gate bus line 12 and the drain bus line 14 is divided into a subpixel A and a subpixel B. For example, the trapezoidal sub-pixel A is arranged on the left side of the central portion of the pixel area, and the sub-pixel B is arranged on the upper, lower, and central right end of the pixel area excluding the sub-pixel A area. The arrangement of the sub-pixels A and B in the pixel region is substantially line symmetrical with respect to the storage capacitor bus line 18, for example. A first pixel electrode 16 is formed in the sub-pixel A. In the sub-pixel B, the second pixel electrode 17 separated by the first pixel electrode 16 and the slit 46 is formed. Both the first and second pixel electrodes 16 and 17 are formed of a transparent conductive film such as ITO. The first pixel electrode 16 is electrically connected to the storage capacitor electrode 19, the connection electrode 25, and the source electrode S of the TFT 20 through a contact hole 24 in which a protective film 32 is opened. The second pixel electrode 17 has a region overlapping the connection electrode 25 through the protective film 32. In this region, the control capacitor Cc is formed by the connection electrode 25, the second pixel electrode 17, and the protective film 32 sandwiched between the electrodes 17 and 25. The second pixel electrode 17 is in an electrically floating state.

  As shown in FIG. 4, the first alignment film 5 that determines the initial alignment state of the liquid crystal molecules of the liquid crystal layer 6 is formed on the glass substrate 10 so as to cover the first and second pixel electrodes 16 and 17. On the other hand, a CF resin layer 40 and a common electrode 42 are formed in this order on, for example, the counter glass substrate 11 disposed to face the glass substrate 10. At least one of the glass substrate 10 and the counter glass substrate 11 is formed to be transparent. A linear protrusion 44a as an alignment regulating structure that regulates the orientation direction of the liquid crystal molecules of the liquid crystal layer 6 is formed at a position that protrudes from the counter glass substrate 11 and faces the connection electrode 25 that extends obliquely in FIG. Yes. Further, linear protrusions 44 b that are formed so as to protrude from the counter glass substrate 11 are formed at positions that are substantially line-symmetric with respect to the storage capacitor bus line 18. Furthermore, a V-shaped linear protrusion 44c is formed on the first pixel electrode 16 on the left side of the center of the pixel region. The linear protrusion 44 c is substantially line symmetric with respect to the storage capacitor bus line 18. The second alignment film 7 that determines the initial alignment state of the liquid crystal molecules of the liquid crystal layer 6 is formed on the counter glass substrate 11 so as to cover the linear protrusions 44a, 44b, and 44c. The first and second alignment films 5 and 7 are formed so that at least one of the structure and the state is different.

  In the sub-pixel A, a liquid crystal capacitor Clc1 is formed by the first pixel electrode 16, the common electrode 42, and the liquid crystal layer 6 sandwiched between both the electrodes 16, 42. In the sub-pixel B, a liquid crystal capacitance Clc2 is formed by the second pixel electrode 17, the common electrode 42, and the liquid crystal layer 6 sandwiched between the electrodes 17 and 42. Between the glass substrate 10 and the counter glass substrate 11, the liquid crystal capacitor Clc2 is connected in series with the control capacitor Cc.

In the liquid crystal display panel according to the present embodiment, the first alignment film 5 formed on the TFT substrate 2 and the second alignment formed on the counter substrate 4 so that charges accumulated by the residual DC voltage are canceled out. The film 7 has an asymmetric structure.
Hereinafter, a liquid crystal display panel and a liquid crystal display device including the same will be described in more detail using examples.

(Example 1-1)
The liquid crystal display panel according to this embodiment is characterized in that the first and second alignment films 5 and 7 have an asymmetric structure with different imidization ratios. The materials having different imidization rates can be used, or the imidization rates of the first and second alignment films 5 and 7 can be made different by changing the baking temperature although the materials have the same imidization rate.

  The liquid crystal display panel according to this embodiment has the pixel structure shown in FIGS. 3 and 4, and a SiN film is used as the insulating film 30. As shown in FIGS. 3 and 4, the gate bus line 12 and the drain bus line 14, which are metal electrodes, and the first and second pixel electrodes 16, 17 and the like are patterned as necessary. The first and second pixel electrodes 16 and 17 have a fine pattern, and the slit 46 that separates both the electrodes 16 and 17 functions as an alignment regulating structure. Therefore, the TFT substrate 2 and the counter substrate 4 are bonded together. The liquid crystal display panel has an MVA structure.

  The alignment regulating structure formed on the counter substrate 4 may be point-like protrusions instead of the bank-like linear protrusions 44a, 44b, 44c shown in FIG. The linear protrusions 44a, 44b, and 44c are formed by patterning a resist material. For example, a soluble polyimide type vertical alignment material A (manufactured by JSR) is formed on the TFT substrate 2 by a spinner, and a soluble polyimide type vertical alignment material B (manufactured by JSR) is formed on the counter substrate 4 by a spinner. Next, the alignment film A with an imidization rate of a% and the alignment film B with an imidization rate of b% are subjected to post-baking under the same conditions, and the first and second alignment films 5 and 7 are formed. The vertical alignment materials A and B may be formed by printing instead of forming by spin coating. Alternatively, one vertical alignment material may be formed by spin coating and the other may be formed by printing.

  FIG. 5 is a graph showing the evaluation results of the residual DC voltage of the liquid crystal display panel according to this example. The horizontal axis represents voltage application time (minutes), and the vertical axis represents residual DC voltage (V). A curve A connecting the X marks in the figure indicates the characteristics of the liquid crystal display panel of this embodiment. Also, a curve B connecting ▲ in the figure shows the characteristics of the liquid crystal display panel according to Example 1-2 described later, and a curve C connecting □ in the figure shows the characteristics of the liquid crystal display panel according to Example 1-6 described later. The characteristics are shown. Further, a curve D connecting ● marks in the figure shows the characteristics of a conventional capacitively coupled MVA type liquid crystal display panel as a comparative example. The evaluation is performed by applying an AC voltage having a frequency of 30 Hz and a voltage of 5 V under an environment of an ambient temperature of 50 ° C.

  As shown in FIG. 5, in the conventional capacitively coupled MVA liquid crystal display panel, the residual DC voltage increases as the voltage application time increases. On the other hand, by making the imidation ratios of the first and second alignment films 5 and 7 different so as to have an asymmetric structure, the residual DC voltage can be made substantially zero even when an AC voltage is applied for about 120 minutes. it can. As a result, the liquid crystal display panel according to this embodiment can prevent the occurrence of burn-in of the display screen because the deviation of the common voltage from the initial setting value (optimum value) is extremely reduced. Therefore, the liquid crystal display device provided with the liquid crystal display panel of this embodiment can obtain good display characteristics.

(Example 1-2)
The liquid crystal display panel according to the present embodiment includes the first and second alignment films 5 and 7 having an asymmetric structure by changing the amount of the cross-linking material contained in the same component material to vary the degree of film formation. It has a feature in that. The liquid crystal display panel of this embodiment has the pixel structure shown in FIGS. For example, a soluble polyimide type vertical alignment material C (manufactured by JSR) is formed on the TFT substrate 2 by a spinner, and a soluble polyimide type vertical alignment material D (manufactured by JSR) is formed on the counter substrate 4 by a spinner. Next, a cross-linking material component is added to the vertical alignment material C, and post-baking is performed under the same conditions without adding a cross-linking material component to the vertical alignment material D, so that the first and second alignment films 5 and 7 are formed. It is formed.

  As shown by the curve B in FIG. 5, the residual DC voltage is almost zero even when the first and second alignment films 5 and 7 having an asymmetric structure with different amounts of the crosslinking material contained in the same component material are used. Can be. Therefore, the liquid crystal display device provided with the liquid crystal display panel according to the present embodiment can obtain the same effects as those of the embodiment 1-1.

(Example 1-3)
In the liquid crystal display panel according to the present embodiment, the first alignment film 5 is formed of, for example, a polyamic acid material, and the second alignment film 7 is formed of, for example, a material made of soluble polyimide, thereby forming the first and second alignment films. It is characterized in that the films 5 and 7 have an asymmetric structure. Even in this structure, the residual DC voltage can be made substantially zero. Therefore, the liquid crystal display device including the liquid crystal display panel according to the present embodiment can obtain the same effects as those of the above embodiments 1-1 and 1-2.

(Example 1-4)
In the liquid crystal display panel according to the present embodiment, for example, the first alignment film 5 is formed of a material made of polyamic acid or soluble polyimide, and the second alignment film 7 is formed of an inorganic material, for example. The second feature is that the two alignment films 5 and 7 have an asymmetric structure. Even in this structure, the residual DC voltage can be made substantially zero. Therefore, the liquid crystal display device including the liquid crystal display panel according to the present embodiment can obtain the same effects as those of the above embodiments 1-1 to 1-3.

(Example 1-5)
In the liquid crystal display panel according to this embodiment, the first and second alignment films 5 and 7 are asymmetrical by making the film thickness d1 of the first alignment film 5 different from the film thickness d2 of the second alignment film 7. It is characterized by its structure. Even in this structure, the residual DC voltage can be made substantially zero. Therefore, the liquid crystal display device provided with the liquid crystal display panel according to this embodiment can obtain the same effects as those of the above embodiments 1-1 to 1-4.

(Example 1-6)
As shown in FIG. 3, the capacitively coupled liquid crystal display panel includes a sub-pixel B having a second pixel electrode 17 capacitively coupled to the connection electrode 25 and a first pixel electrode 16 directly coupled to the connection electrode 25. A pixel region is composed of the sub-pixels A. According to the liquid crystal display panels of Examples 1-1 to 1-5, the burn-in of the sub-pixel B can be eliminated. However, due to the asymmetric structure of the first and second alignment films 5 and 7, there is a possibility that image sticking may occur in the sub-pixel A. In such a case, a liquid crystal containing a monomer that can be polymerized by light or heat is filled between the TFT substrate 2 and the counter substrate 4, and only the monomer in the pixel region of the sub-pixel A is solidified. The second alignment films 5 and 7 are fixed to the surface. In this way, by the polymer alignment support (PSA) in which the monomer is mixed into the liquid crystal and the inclination direction of the liquid crystal molecule is memorized by polymerizing the monomer in a state where the liquid crystal molecule is inclined by applying a voltage. Due to the effect, it is possible to suppress burn-in in the sub-pixel A.

  The liquid crystal display panel according to this example has the pixel structure shown in FIGS. Moreover, the same 1st and 2nd alignment films 5 and 7 as the said Example 1-1 are formed. As the liquid crystal composition of the liquid crystal layer 6, a negative liquid crystal M containing a monomer (manufactured by Merck) is used. In this embodiment, by using a mask that can irradiate only the sub-pixel A with UV light, each pixel region is partially converted to PSA.

  As shown by the curve C in FIG. 5, the residual DC voltage can be made substantially zero by converting the subpixel A to PSA. Therefore, the liquid crystal display device including the liquid crystal display panel according to the present embodiment can obtain the same effects as those of the above embodiments 1-1 to 1-5.

The present embodiment is not limited to the above embodiment, and various modifications can be made.
Although the liquid crystal display panels of Examples 1-1 to 1-6 have the alignment regulating structure, the present embodiment is not limited to this. For example, even in a liquid crystal display panel that does not have an alignment regulating structure, the same effect as in the above embodiment can be obtained.

[Second Embodiment]
The present embodiment relates to a liquid crystal display panel used in a display unit of an electronic device such as a television receiver or a monitor device, and a liquid crystal display device including the same.

  The liquid crystal display device includes a liquid crystal display panel including two substrates and liquid crystal sealed between the two substrates. In a liquid crystal display device, optical switching is performed by electrical stimulation using the electro-optical anisotropy of liquid crystal. A predetermined voltage is applied to the liquid crystal layer to control the tilt angle of the liquid crystal molecules, thereby changing the direction of the axis of refractive index anisotropy of the liquid crystal molecules. By utilizing the optical rotation and birefringence generated thereby, the light transmittance is changed, and the brightness of each pixel of the liquid crystal display panel is controlled. The vertical alignment method is one such liquid crystal display panel technology. As represented by an MVA liquid crystal display panel, a vertical alignment liquid crystal display device has been put to practical use as a display method capable of realizing a wide viewing angle.

  However, in such a vertical alignment type liquid crystal display panel, when the display screen is viewed from an oblique direction (when viewed from an angular direction), a phenomenon in which an image of an image near a halftone becomes whitish occurs. As a method for solving the phenomenon in which an image becomes whitish, a technique has been proposed in which regions having different pretilt angles of liquid crystal molecules are formed in one pixel to form regions having different rising voltages of TV characteristics.

  Proposed a method to inject liquid crystal to which a monomer or oligomer that undergoes a polymerization reaction with light or heat is added so that different pretilt angles are given to the liquid crystal molecules, and to change the potential applied to the liquid crystal during polymerization of the monomer or oligomer. Has been. In this method, the pretilt angle of the liquid crystal molecules decreases as the applied voltage increases. Here, the decrease in the pretilt angle of the liquid crystal molecules means that the tilt angle from the complete vertical alignment is increased, that is, closer to the horizontal alignment. However, this method requires preparation of a plurality of pretilt angles in one pixel, and is complicated including problems such as handling of a polymerizable material.

  In addition to forming two pretilt regions in this way, a method of providing two potential differences in one pixel has also been proposed. FIG. 13 schematically shows the configuration of one pixel used in the method. As shown in FIG. 13, in one pixel, a TFT 51 in which the gate electrode G is connected to the gate bus line 61 and the drain electrode D is connected to the drain bus line is formed. A pixel electrode 53 is connected to the source electrode S of the TFT 51. A pixel electrode 55 is disposed opposite to the pixel electrode 53 via an insulating film. A control capacitor Cc is formed by the pixel electrode 53, the pixel electrode 55, and an insulating film sandwiched between the electrodes 53 and 55. Thus, a subpixel including the pixel electrode 53 and a subpixel including the pixel electrode 55 are formed in one pixel. A liquid crystal capacitor Clc1 is formed by the pixel electrode 53, the common electrode 57, and the liquid crystal sandwiched between the electrodes 53 and 57. A liquid crystal capacitor Clc2 is formed by the pixel electrode 55, the common electrode 57, and the liquid crystal sandwiched between the electrodes 55 and 57. The liquid crystal capacitor Clc2 and the control capacitor Cc are connected in series, and the circuit configuration is such that the liquid crystal capacitor Clc1 is connected in parallel.

  When the TFT 51 is turned on, the gradation signal supplied to the drain bus line 63 is applied to the pixel electrode 53, while the common potential is applied to the common electrode 57. As a result, the pixel electrode 55 is maintained at a potential that is lower than the potential of the gradation signal applied to the pixel electrode 53 by a predetermined amount. As described above, different voltages can be applied to the pixel electrode 53 directly connected to the source electrode S of the TFT 51 and the pixel electrode 55 not directly connected to the TFT 51. However, the pixel having such a configuration has a problem that when the liquid crystal display device is driven, the center voltage gradually shifts at the pixel electrode 55, and a burn-in phenomenon occurs on the display screen.

  An object of the present embodiment is to provide a liquid crystal display panel capable of obtaining good display characteristics and a liquid crystal display device including the same.

  The object is to provide a gate bus line, a drain bus line formed intersecting the gate bus line through an insulating film, a gate electrode electrically connected to the gate bus line, and the drain bus line. A transistor having an electrically connected drain electrode; a pixel electrode electrically connected to a source electrode of the transistor; and at least an initial alignment state of the liquid crystal material in contact with the liquid crystal material on the pixel electrode A transistor substrate having a first vertical alignment film for determining the first vertical alignment film, and a second vertical alignment film having a resistance value different from that of the first vertical alignment film and determining the initial alignment state in contact with the liquid crystal material And a counter substrate disposed opposite to the transistor substrate. This is achieved by a liquid crystal display panel.

  According to the present embodiment, it is possible to realize a liquid crystal display panel that can obtain good display characteristics and a liquid crystal display device including the same.

  A liquid crystal display panel according to a second embodiment of the present invention and a liquid crystal display device including the same will be described with reference to FIGS. As a result of earnest investigation on the phenomenon in which the center voltage at the pixel electrode 55 shown in FIG. 13 gradually shifts, the following conclusion has been reached. In general, different materials are formed on the surface of the TFT substrate and the counter substrate on which the alignment film is formed. Each of the materials contaminates the alignment films on both substrates in different states. This difference in the degree of contamination forms a unique current flow direction in the liquid crystal display panel (liquid crystal cell), and even if a positive and negative equivalent square wave is applied to the pixel electrode as an external input, it is biased to one polarity. The residual DC voltage component is charged in the liquid crystal cell.

  In this case, in the sub-pixel having the pixel electrode 53 directly connected to the source electrode S of the TFT 51, the charge is hardly accumulated because the charge is input every time the gradation signal is written. However, in the sub-pixel having the pixel electrode 55 forming the capacitor, the electric charge accumulated in the pixel electrode 55 remains without being canceled, so that the center voltage is largely shifted.

  FIG. 6 is a graph showing the measurement result of the center voltage fluctuation when the alignment film of either one of the opposed substrates is contaminated with an organic substance. FIG. 6A shows the center voltage fluctuation at the pixel electrode α directly connected to the TFT. FIG. 6B shows the center voltage fluctuation at the pixel electrode β that is capacitively coupled without being directly coupled to the TFT. The abscissa represents the voltage application time (min), and the ordinate represents the fluctuation (shift) amount (mV) of the center voltage. Note that an alternating current (AC) 5 V square wave is used as the applied voltage. In FIG. 6 (a), the curve connecting the circles with solid lines shows the fluctuation of the center voltage at the pixel electrode α when any of the opposing alignment films on the substrate is contaminated. A curve connecting the two lines with a broken line indicates a center voltage fluctuation in the pixel electrode α when neither alignment film of both substrates as a comparative example is contaminated. In FIG. 6B, the curve connecting the ● mark with a solid line indicates the variation in the center voltage at the pixel electrode β when the alignment film on the one substrate (first substrate) side facing each other is contaminated. The curve connecting the circles with solid lines in the figure shows the fluctuation of the center voltage at the pixel electrode β when the alignment film on the other substrate (second substrate) side is contaminated. The curve shows the fluctuation of the center voltage at the pixel electrode β when neither alignment film of both substrates as a comparative example is contaminated.

  As shown in FIG. 6A, even if one of the substrate-side alignment films is contaminated and an AC5V square wave is applied, the change in the center voltage at the pixel electrode α directly connected to the TFT is almost generated. Absent. Furthermore, the variation of the center voltage at the pixel electrode α is almost the same regardless of the presence or absence of contamination of the alignment film. On the other hand, as shown in FIG. 6B, when an AC5V square wave is applied by contaminating the alignment film on the first or second substrate side, the TFT is compared with the case where the alignment film is not contaminated. The center voltage at the pixel electrode β that is not directly connected changes greatly.

Thus, as a result of investigating a method for preventing the center voltage at the pixel electrode β from shifting substantially even if the alignment film is contaminated, it has been found that the following method is effective. The first method is to reduce the thickness of the alignment film formed on the other substrate when the contamination of the alignment film from one of the opposed substrates is large. The second method is to form an alignment film having a resistance value lower than that of an alignment film formed on one substrate on the other substrate when contamination from one substrate is large. By using these methods, the degree of shift of the center voltage can be reduced.
Hereinafter, a liquid crystal display panel and a liquid crystal display device including the same will be described in more detail using examples.

(Example 2-1)
A liquid crystal display panel according to Example 2-1 of the present embodiment and a liquid crystal display device including the same will be described with reference to FIG. FIG. 7 shows a cross section of the main part of the liquid crystal display panel according to this embodiment. As shown in FIG. 7, the liquid crystal display panel of the present embodiment includes a TFT substrate 72 and a counter substrate 74 that are disposed to face each other, and a liquid crystal layer 6 that is sealed between the substrates 72 and 74. The counter substrate 74 has a counter glass substrate 11. On the counter glass substrate 11, a red CF resin layer 40r, a green CF resin layer 40g, and a blue CF resin layer 40b are formed as a color filter (CF) resin layer. The plurality of CF resin layers 40r, 40g, and 40b are formed in a matrix within the surface of the counter glass substrate 11. On the CF resin layers 40r, 40g, and 40b, a common electrode 42 and an alignment film 67 that determines an initial alignment state of liquid crystal molecules of the liquid crystal layer 6 are formed in this order.

  On the other hand, the TFT substrate 72 has the glass substrate 10. The glass substrate 10 is formed with a plurality of gate bus lines and a plurality of drain bus lines (both not shown) intersecting via an insulating film (not shown). At least one thin film transistor (TFT) 20 for each matrix unit of a gate bus line and a drain bus line (data bus line) at each position on the glass substrate 10 facing the CF resin layers 40r, 40g, 40b, and the TFT 20 A pixel electrode 69 electrically connected to the pixel electrode 69 is formed. An alignment film 65 that determines the initial alignment state of the liquid crystal molecules of the liquid crystal layer 6 is applied to the glass substrate 10 so as to cover the pixel electrodes 69. The alignment films 65 and 67 are formed in contact with the liquid crystal layer 6. The alignment films 65 and 67 are formed with different resistance values. For example, the respective resistance values can be changed by forming the alignment films 65 and 67 with different materials.

  Since the resistance values of the alignment films 65 and 67 are different, a unique current flow in the liquid crystal display panel can be prevented even if at least one of the alignment films 65 and 67 is contaminated. Thereby, the residual DC voltage component biased to the pixel electrode 69 hardly occurs. Therefore, the occurrence of image sticking can be prevented, and the liquid crystal display panel can obtain good display characteristics. Further, by using the liquid crystal display panel, display characteristics of the liquid crystal display device can be improved.

(Example 2-2)
A liquid crystal display panel according to Example 2-2 of the present embodiment and a liquid crystal display device including the same will be described with reference to FIG. FIG. 8 shows a cross section of the main part of the liquid crystal display panel according to this embodiment. As shown in FIG. 8, the liquid crystal display panel of this embodiment is characterized in that the film thicknesses of the alignment films 65 and 67 are different. The film thickness d1 of the alignment film 65 is smaller than the film thickness d2 of the alignment film 67. Therefore, for example, this is effective when the contamination of the alignment film 67 is larger than the contamination of the alignment film 65. When the contamination on the alignment film 65 side is relatively large, the degree of shift of the center voltage is reduced by forming the film thickness d1 of the alignment film 65 smaller than the film thickness d2 of the alignment film 67. Can do.

  Thus, by changing the film thickness of each of the alignment films 65 and 67, a unique current flow can be prevented in the liquid crystal display panel even if the degree of contamination of the alignment films 65 and 67 is different. Thereby, the residual DC voltage component biased to the pixel electrode 69 hardly occurs. Therefore, the liquid crystal display panel according to the present embodiment and the liquid crystal display device including the same can prevent the display screen from being burned, so that the same effects as those of the embodiment 2-1 can be obtained.

(Example 2-3)
A liquid crystal display panel according to Example 2-3 of this embodiment and a liquid crystal display device including the same will be described with reference to FIG. FIG. 9 shows a cross section of the main part of the liquid crystal display panel according to this embodiment. The liquid crystal display panel of this embodiment is characterized in that it includes vertical alignment films 75 and 77 having different imidization rates. As shown in FIG. 9, the TFT substrate 72 has a vertical alignment film 75, and the counter substrate 74 has a vertical alignment film 77. The liquid crystal material constituting the liquid crystal layer 6 has a negative dielectric anisotropy, and the liquid crystal molecules 79 are aligned substantially perpendicular to the film formation surfaces of the substrates 72 and 75 when no voltage is applied. .

  By the way, generally, the resistance value of the alignment film increases as the imidization ratio increases. Accordingly, when the vertical alignment film 77 side is relatively easily contaminated, the imidization ratio of the vertical alignment film 75 is reduced, and when the vertical alignment film 75 side is relatively easily contaminated, the imide of the vertical alignment film 77 is reduced. By reducing the conversion rate, the degree of shift of the center voltage can be reduced.

  As described above, since the resistance value can be varied by changing the imidization ratio of each of the vertical alignment films 75 and 77, even if the degree of contamination of the vertical alignment films 75 and 77 is different, A unique current flow can be prevented. Thereby, the residual DC voltage component biased to the pixel electrode 69 hardly occurs. Accordingly, the liquid crystal display panel according to the present embodiment and the liquid crystal display device including the same can prevent the display screen from being burned, so that the same effects as those of the embodiments 2-1 and 2-2 can be obtained.

  In this embodiment, the liquid crystal display panel has the vertical alignment films 75 and 77. However, even if the liquid crystal display panel has the alignment films 65 and 67 similar to those in the embodiments 2-1 and 2-2, the same applies. The effect is obtained.

(Example 2-4)
A liquid crystal display panel according to Example 2-4 of the present embodiment and a liquid crystal display device including the same will be described with reference to FIG. FIG. 10 shows a cross section of the main part of the liquid crystal display panel according to this embodiment. The liquid crystal display panel of the present embodiment is characterized in that a projection 70 is provided as an alignment regulating structure that defines the alignment direction of liquid crystal molecules. As shown in FIG. 10, the counter substrate 74 has a protrusion 70 for each pixel. If the projections 70 are formed of resin, the alignment film 67 is easily contaminated by the resin. Therefore, the film thickness of the alignment film 65 is made thinner than the film thickness of the alignment film 67, or the resistance value of the alignment film 65 is made lower than the resistance value of the alignment film 67 (for example, the imidation ratio of the alignment film 65 is aligned). By making it smaller than the imidation ratio of the film 67, the same effect as in the above Examples 2-1 to 2-3 can be obtained. As described above, the image sticking prevention method according to the present embodiment is particularly effective for the liquid crystal display panel having the protrusions 70 and the liquid crystal display device including the same.

(Example 2-5)
A liquid crystal display panel and a liquid crystal display device including the same according to Example 2-5 of the present embodiment will be described with reference to FIG. FIG. 11 shows a cross section of the liquid crystal display panel according to this embodiment. FIG. 11A shows a cross section of the main part of the liquid crystal display panel, and FIG. 11B shows an enlarged virtual circle A of FIG. 11A. As shown in FIG. 11A and FIG. 11B, the liquid crystal display panel of this embodiment includes a pixel electrode 69 directly connected to the TFT 20 and a pixel electrode (capacitively coupled to the TFT 20 via the pixel electrode 69). It is characterized in that each pixel has a capacitive coupling pixel electrode) 78. A part of each of the pixel electrode 69 and the pixel electrode 78 is disposed to face each other with an insulating film 76 interposed therebetween. Therefore, the control capacitor Cc is formed by the pixel electrode 69, the pixel electrode 78, and the insulating film 76 sandwiched between the electrodes 69 and 78.

  In the pixel structure divided into the sub-pixel having the pixel electrode 69 and the sub-pixel having the pixel electrode 78, as shown in FIG. 6, the difference between the contamination states of the alignment films 65 and 67 appears remarkably. The center voltage at the pixel electrode 78 is likely to fluctuate. However, it is possible to suppress the asymmetry of the contaminated state by changing the imidization ratio of the alignment films 65 and 67. Alternatively, it is possible to suppress the asymmetry of the contamination state by changing the thicknesses of the alignment films 65 and 67 or changing the resistance values. As a result, the fluctuation of the center voltage at the pixel electrode 78 is extremely reduced, so that burn-in occurring on the display screen can be prevented.

  In the liquid crystal display panel of this embodiment, two TV characteristic distributions can be formed by forming sub-pixels to which different gradation signals are applied within one pixel. As a result, the liquid crystal display panel prevents a phenomenon in which the image of the image near the halftone becomes whitish when the screen is viewed from an oblique direction, and the occurrence of image sticking on the display screen. Therefore, the liquid crystal display panel according to the present embodiment and the liquid crystal display device including the same can obtain better display characteristics than the above embodiments 2-1 to 2-4.

The present embodiment is not limited to the above embodiment, and various modifications can be made.
In the liquid crystal display panel of Example 2-5, the pixel electrodes 65 and 67 partially overlap to form the control capacitor Cc. However, the present embodiment is not limited to this. For example, the same effect can be obtained with a pixel structure similar to that of the liquid crystal display panel of the first embodiment.

The liquid crystal display panel according to the first embodiment described above and the liquid crystal display device including the same are summarized as follows.
(Appendix 1)
A gate bus line,
A drain bus line formed to intersect the gate bus line through an insulating film;
A transistor comprising a gate electrode electrically connected to the gate bus line; and a drain electrode electrically connected to the drain bus line;
A first pixel electrode electrically connected to a source electrode of the transistor;
A second pixel electrode disposed opposite to the source electrode of the transistor via an insulating film and formed separately from the first pixel electrode;
A transistor substrate comprising: a first alignment film formed on the first and second pixel electrodes to determine an initial alignment state of the liquid crystal material;
And a counter substrate provided with a second alignment film that is different in structure and state from the first alignment film and determines an initial alignment state of the liquid crystal material and is disposed to face the transistor substrate. LCD panel to be used.
(Appendix 2)
In the liquid crystal display panel according to appendix 1,
The liquid crystal display panel, wherein the first and second alignment films have different thicknesses.
(Appendix 3)
In the liquid crystal display panel according to appendix 1 or 2,
The liquid crystal display panel, wherein the first and second alignment films have different imidization ratios.
(Appendix 4)
In the liquid crystal display panel according to appendix 1 or 2,
The liquid crystal display panel, wherein the first and second alignment films have different amounts of crosslinking material.
(Appendix 5)
In the liquid crystal display panel according to appendix 1 or 2,
The liquid crystal display panel, wherein the first alignment film is made of a polyamic acid material, and the second alignment film is made of a soluble polyimide material.
(Appendix 6)
In the liquid crystal display panel according to appendix 1 or 2,
The liquid crystal display panel, wherein the first alignment film is formed of a polyamic acid material or a soluble polyimide material, and the second alignment film is formed of an inorganic material.
(Appendix 7)
In the liquid crystal display panel according to any one of appendices 1 to 6,
The liquid crystal material has a monomer,
The liquid crystal display panel, wherein the monomer is solidified.
(Appendix 8)
In the liquid crystal display panel according to appendix 7,
The liquid crystal display panel, wherein the monomer is solidified only on the first pixel electrode side.
(Appendix 9)
In the liquid crystal display panel according to any one of appendices 1 to 8,
At least one of the transistor substrate and the counter substrate is formed with an alignment regulating structure that defines an alignment direction of the liquid crystal material.
(Appendix 10)
In the liquid crystal display panel according to any one of appendices 1 to 9,
The liquid crystal display panel, wherein the liquid crystal material has a negative dielectric anisotropy and is aligned substantially perpendicular to the film formation surfaces of the transistor substrate and the counter substrate when no voltage is applied.
(Appendix 11)
A liquid crystal display device comprising the liquid crystal display panel according to any one of appendices 1 to 10.

The liquid crystal display panel and the liquid crystal display device including the liquid crystal display panel according to the second embodiment described above can be summarized as follows.
(Appendix 12)
A gate bus line,
A drain bus line formed to intersect the gate bus line through an insulating film;
A transistor comprising a gate electrode electrically connected to the gate bus line; and a drain electrode electrically connected to the drain bus line;
A pixel electrode electrically connected to a source electrode of the transistor;
A transistor substrate comprising: a first vertical alignment film that contacts a liquid crystal material on at least the pixel electrode to determine an initial alignment state of the liquid crystal material;
A counter substrate having a second vertical alignment film that has a resistance value different from that of the first vertical alignment film and is in contact with the liquid crystal material to determine the initial alignment state and is disposed to face the transistor substrate. A liquid crystal display panel characterized by
(Appendix 13)
In the liquid crystal display panel according to appendix 12,
The liquid crystal display panel, wherein the first and second vertical alignment films have different thicknesses.
(Appendix 14)
In the liquid crystal display panel according to appendix 12,
The liquid crystal display panel, wherein the first and second vertical alignment films have different imidization ratios.
(Appendix 15)
In the liquid crystal display panel according to appendix 12,
The counter substrate has a projecting structure that defines the orientation direction of the liquid crystal material,
The liquid crystal display panel according to claim 1, wherein a resistance value of the first vertical alignment film is lower than a resistance value of the second vertical alignment film.
(Appendix 16)
In the liquid crystal display panel according to any one of appendices 12 to 15,
A liquid crystal display panel comprising a capacitively coupled pixel electrode capacitively coupled to the pixel electrode.
(Appendix 17)
In the liquid crystal display panel according to any one of appendices 12 to 16,
The liquid crystal display panel, wherein the liquid crystal material has a negative dielectric anisotropy and is aligned substantially perpendicular to the film formation surfaces of the transistor substrate and the counter substrate when no voltage is applied.
(Appendix 18)
18. A liquid crystal display device comprising the liquid crystal display panel according to any one of appendices 12 to 17.

It is a figure which shows schematic structure of the liquid crystal display device by the 1st Embodiment of this invention. FIG. 2 is an equivalent circuit diagram showing a configuration of one pixel of the liquid crystal display device according to the first embodiment of the present invention. 1 is a plan view showing a configuration of one pixel of a liquid crystal display panel according to a first embodiment of the present invention. 1 is a cross-sectional view illustrating a configuration of one pixel of a liquid crystal display panel according to a first embodiment of the present invention. It is a graph which shows the measurement result of the residual DC voltage of the liquid crystal display panel by the 1st Embodiment of this invention. It is a graph which shows the measurement result of the center voltage fluctuation | variation of the conventional liquid crystal display panel. It is a figure which shows the cross section of the liquid crystal display panel by Example 2-1 of the 2nd Embodiment of this invention. It is a figure which shows the cross section of the liquid crystal display panel by Example 2-2 of the 2nd Embodiment of this invention. It is a figure which shows the cross section of the liquid crystal display panel by Example 2-3 of the 2nd Embodiment of this invention. It is a figure which shows the cross section of the liquid crystal display panel by Example 2-4 of the 2nd Embodiment of this invention. It is a figure which shows the cross section of the liquid crystal display panel by Example 2-5 of the 2nd Embodiment of this invention. It is a graph which shows the measurement result of the residual DC voltage of the conventional liquid crystal display panel. It is a figure which shows typically the structure of 1 pixel of the conventional liquid crystal display panel.

Explanation of symbols

2, 72 TFT substrate 4, 74 Counter substrate 5 First alignment film 6 Liquid crystal layer 7 Second alignment film 10 Glass substrate 11 Counter glass substrate 12 Gate bus line 14 Drain bus line 16 First pixel electrode 17 Second Pixel electrode 18 Storage capacitor bus line 19 Storage capacitor electrode (intermediate electrode)
20 TFT
24 Contact hole 25 Connection electrode 30 Insulating film 32 Protective film 39 Pixel group 40, 40r, 40g, 40b CF resin layer 42 Common electrode 44a, 44b, 44c Linear protrusion 46 Slit 65, 67 Alignment film 69, 78 Pixel electrode 70 Projection 75, 77 Vertical alignment film 79 Liquid crystal molecule 80 Gate bus line driving circuit 82 Drain bus line driving circuit 84 Control circuit 86, 87 Polarizing plate 88 Backlight unit

Claims (5)

A gate bus line,
A drain bus line formed to intersect the gate bus line through an insulating film;
A transistor comprising a gate electrode electrically connected to the gate bus line; and a drain electrode electrically connected to the drain bus line;
A first pixel electrode electrically connected to a source electrode of the transistor;
A second pixel electrode disposed opposite to the source electrode of the transistor via an insulating film and formed separately from the first pixel electrode;
A transistor substrate comprising: a first alignment film formed on the first and second pixel electrodes to determine an initial alignment state of the liquid crystal material;
A counter substrate provided with a second alignment film that is different in structure and state from the first alignment film and determines an initial alignment state of the liquid crystal material and is disposed opposite to the transistor substrate;
In only the pixel region having the first pixel electrode, an alignment support polymer that stores the tilt direction of liquid crystal molecules when a voltage is applied is formed on the first alignment film and the second alignment film. A liquid crystal display panel characterized by The liquid crystal display panel according to claim 1,
The liquid crystal display panel, wherein the first and second alignment films have different thicknesses. The liquid crystal display panel according to claim 1 or 2,
The liquid crystal display panel, wherein the first and second alignment films have different imidization ratios. The liquid crystal display panel according to claim 1 or 2,
The liquid crystal display panel, wherein the first and second alignment films have different amounts of crosslinking material.   A liquid crystal display device comprising the liquid crystal display panel according to claim 1.

Images