JP4832464B2 - Liquid crystal display - Google Patents

Description

  The present invention relates to a liquid crystal display device used as a display unit of an electronic device or the like, and more particularly, to an MVA mode liquid crystal display device having excellent viewing angle characteristics.

  An MVA (Multi-domain Vertical Alignment) mode liquid crystal display device (hereinafter referred to as “MVA-LCD”) is a vertical alignment (Vertical Alignment) technology that realizes high contrast and high-speed response, and an alignment division that realizes a wide viewing angle. This is a liquid crystal display device combined with (Multi-domain) technology. The MVA-LCD has an alignment regulating structure (a linear protrusion or electrode removal) provided on a substrate in order to realize alignment division. The alignment regulating structure also has the effect that the rubbing process, which is a major cause of the decrease in productivity, becomes unnecessary. For this reason, high productivity is realized in the MVA-LCD.

  However, there are also problems to be improved in the MVA-LCD. FIG. 18 is a graph showing transmittance characteristics (TV characteristics) of a conventional MVA-LCD. The horizontal axis represents the voltage (V) applied to the liquid crystal, and the vertical axis represents the light transmittance (%). A line X1 in the graph indicates a TV characteristic in a direction perpendicular to the display screen (hereinafter referred to as “front direction”), and a line X2 indicates a direction with a polar angle of 60 ° (hereinafter referred to as “oblique direction”) above the display screen. The T-V characteristics of the above are shown. Here, the polar angle is an angle formed with a vertical line standing on the display screen. The display mode of the liquid crystal display device is a normally black mode. As shown in FIG. 18, the TV characteristics in the oblique direction include a gradation area where the transmittance increases and a gradation area where the transmittance decreases compared to the TV characteristics in the front direction. Existing. Therefore, there is a problem that the chromaticity in the oblique direction is deviated from the chromaticity in the front direction. In particular, there is a problem in the region where the transmittance in the oblique direction is larger than the transmittance in the front direction. That is, there is a problem that a dark halftone display image looks whitish from an oblique direction.

  FIG. 19 is a graph showing chromaticity characteristics of a conventional MVA-LCD. A line Y1 indicates a change in chromaticity characteristics due to gradation in the front direction, and a line Y2 indicates a change in chromaticity characteristics due to gradation in an oblique direction. As shown in FIG. 19, the conventional MVA-LCD also has a problem that the chromaticity changes depending on the gradation and the viewing angle. The transmittance at each gradation is determined by the amount of retardation generated in the liquid crystal layer. Since the chromaticity also changes depending on the size of the retardation, a phenomenon occurs in which the chromaticity changes depending on the gradation.

  An object of the present invention is to provide a liquid crystal display device having good chromaticity characteristics and viewing angle characteristics.

  The object is to provide a pair of substrates that are arranged opposite to each other and provided with electrodes on opposite surfaces, a liquid crystal sealed between the pair of substrates, and an effective voltage applied to the liquid crystal from a voltage applied between the electrodes. And a pixel region having a threshold voltage different between the low effective voltage region and another region. The

  As described above, according to the present invention, a liquid crystal display device having excellent chromaticity characteristics and viewing angle characteristics can be realized.

[First Embodiment]
A liquid crystal display device 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. As shown in FIG. 1, the liquid crystal display device includes a TFT substrate 2 including gate bus lines and drain bus lines formed to intersect each other with an insulating film interposed therebetween, and TFTs and pixel electrodes formed for each pixel. have. Further, the liquid crystal display device includes a counter substrate 4 on which a common electrode is formed, and a liquid crystal (not shown) sealed between both the substrates 2 and 4.

  The TFT substrate 2 includes a gate bus line driving circuit 80 on which driver ICs for driving a plurality of gate bus lines are mounted, and a drain bus line driving circuit 82 on which driver ICs for driving a plurality of drain bus lines are mounted. Is provided. These drive circuits 80 and 82 are configured to output scanning signals and data signals to predetermined gate bus lines or drain bus lines based on predetermined signals output from the control circuit 84. A polarizing plate 86 is disposed on the substrate surface opposite to the element formation surface of the TFT substrate 2, and a backlight unit 88 is attached to the surface of the polarizing plate 86 opposite to the TFT substrate 2. On the other hand, a polarizing plate 87 arranged in crossed Nicols with the polarizing plate 86 is attached to the surface of the counter substrate 4 opposite to the common electrode forming surface.

  FIG. 2 is a cross-sectional view showing the basic configuration of the liquid crystal display device according to the present embodiment. FIG. 3 is a perspective view showing a configuration in the vicinity of the region shown in FIG. As shown in FIGS. 2 and 3, a liquid crystal 6 is sealed between the TFT substrate 2 and the counter substrate 4. On the TFT substrate 2, a pixel electrode 16 is formed for each pixel region. The pixel electrode 16 is formed with an alignment regulating slit (electrode removal) 48 that is an alignment regulating structure. A common electrode 42 is formed on almost the entire surface of the counter substrate 4. On the common electrode 42, linear protrusions 44, which are alignment regulating structures, are provided. Each pixel region is divided into a plurality of alignment regions by alignment regulating slits 48 and linear protrusions 44. In each alignment region, the liquid crystal molecules 8 are inclined in substantially the same direction.

  A dielectric layer 50 is formed on the pixel electrode 16 in a partial region (low effective voltage region) B within each alignment region. The dielectric layer 50 is provided in order to lower the effective voltage applied to the liquid crystal 6 in the region B than in the other regions A in the alignment region. As a result, the threshold voltage is higher in the region B than in the region A, and two regions A and B having different threshold voltages are formed in the alignment region. Therefore, when viewed locally, each alignment region has two different TV characteristics. Since the dielectric layer 50 may be disposed between the pixel electrode 16 and the common electrode 42, it may be formed on the common electrode 42.

  FIG. 4 is a perspective view showing a modification of the basic configuration of the liquid crystal display device according to the present embodiment. As shown in FIG. 4, the pixel electrode 16 in a part of the region B in the alignment region is formed with an effective voltage reduction slit (electrode extraction portion) 46 in which electrodes are extracted in a stripe shape. The effective voltage lowering slit 46 is not used as an alignment regulating structure, and the effective voltage applied to the liquid crystal 6 in the region B is applied to the other region A in the alignment region in the same manner as the dielectric layer 50 shown in FIGS. It is provided in order to lower it.

  FIG. 5 is a graph showing TV characteristics of the liquid crystal display device according to the present basic configuration. The horizontal axis represents the voltage (V) applied to the liquid crystal, and the vertical axis represents the light transmittance (%). A line A1 in the graph indicates the TV characteristic in the front direction, and a line A2 indicates the TV characteristic in the oblique direction. As shown in FIG. 5, the TV characteristics of the liquid crystal display device according to the basic configuration are averaged in the regions A and B having different threshold voltages, and the conventional liquid crystal display device shown in FIG. Compared with the TV characteristic, the difference in transmittance between the front direction and the oblique direction is small. Therefore, in the liquid crystal display device according to the present basic configuration, it is possible to obtain a good gradation viewing angle characteristic with little chromaticity shift of the display image between the front direction and the oblique direction.

  Further, in the liquid crystal display device according to this basic configuration, the chromaticity change due to gradation and the chromaticity change due to viewing angle are greatly improved. Providing regions having partially different threshold voltages in the pixel region (alignment region) also provides regions having different retardations in the pixel region. That is, when an arbitrary voltage is applied to the liquid crystal, the tilt angle of the liquid crystal molecules is different in each region, so that the retardation value depending on the tilt angle of the liquid crystal molecules is also different in each region. Therefore, the retardation difference between pixels of each color in an arbitrary gradation is alleviated, so that the change in chromaticity due to gradation and viewing angle is reduced.

  Further, by adjusting the retardation value of each color pixel according to the transmission spectrum of the color filter layer, the difference in Δn · d / λ between the pixels of each color can be further reduced. That is, parameters such as the retardation value in each region where the threshold voltage is different, the transmission spectrum of the color filter layer, the wavelength dispersion of the birefringence of the liquid crystal layer, and the voltage applied to the liquid crystal layer different for each color Optimization is performed so that the difference of Δn · d / λ between pixels of each color is minimized. As a result, it is possible to obtain good display characteristics in which chromaticity changes due to gradation and viewing angle hardly occur.

  A general liquid crystal display device uses three color filters of red, green, and blue (R, G, and B). The center transmission wavelength of each color filter is about 600 nm for R, about 550 nm for G, and about 450 nm for B. The retardation Δn · d is about 350 nm. Therefore, in the conventional liquid crystal display device, a difference of Δn · d / λ of about 0.2 is generated between the R pixel and the B pixel. Therefore, by setting the difference of Δn · d / λ between the pixels of each color to 0.2 or less, which is smaller than the conventional one, it is possible to obtain good display characteristics in which almost no change in chromaticity due to gradation or viewing angle is visually recognized.

  That is, the central transmission wavelength of the N color filter layers is λk (k = 1, 2,..., N; N> 2), the birefringence of the liquid crystal molecules with respect to the wavelength λ is Δn (λ), and the center When the cell thickness of a pixel having a color filter layer having a transmission wavelength of λk is dk, the following relationship is satisfied between pixels each having at least two different color filter layers.

| Δn (λi) · di / λi−Δn (λj) · dj / λj | <0.2
(I, j = 1, 2,..., N; i ≠ j)

  Thereby, it is possible to obtain good display characteristics in which almost no change in chromaticity due to gradation or viewing angle is visually recognized. More preferably, the difference of Δn · d / λ between pixels of each color is set to 0.05 or less. As a result, very good display characteristics can be obtained in which no change in chromaticity due to gradation or viewing angle is visually recognized.

  There are the following two methods for reducing the difference of Δn · d / λ between pixels of each color. FIG. 6 shows a cross-sectional configuration of a liquid crystal display device to which the first method is applied. As shown in FIG. 6, in the first method, the cell thickness d of each pixel is controlled by making the film thickness of the color filter layer 40 different between pixels of each color of R, G, and B.

  FIG. 7 shows a cross-sectional configuration of a liquid crystal display device to which the second method is applied. As shown in FIG. 7, in the second method, the effective voltage applied to the liquid crystal is varied by varying the film thickness of the dielectric layer 50 between pixels of each color. Alternatively, as shown in FIG. 8, the voltage applied to the liquid crystal layer is made different between pixels of each color without changing the film thickness of the color filter layer 40 and the dielectric layer 50. In these configurations, the cell thickness d of each color pixel is substantially constant, and the effective retardation Δn (λ, θ) of the liquid crystal layer is controlled to satisfy the following relationship.

| Δn (λi, θi) · d / λi−Δn (λj, θ j ) · d / λj | <0.2
(I, j = 1, 2,..., N; i ≠ j)

  In order to obtain the maximum transmittance in the normally black mode (maximum contrast in the normally white mode), it is necessary to select the retardation of the liquid crystal layer. When the cell thickness d is controlled to reduce the difference of Δn · d / λ between pixels of each color, in order to obtain the maximum transmittance, a pixel having a color filter whose center transmission wavelength λ is closest to 545 nm The retardation Δn (λk) · dk of (G in the configuration of R, G, B) needs to be set between 250 and 450 nm, preferably around 345 nm (250 nm <Δn (λk) · dk <450 nm). In order to obtain the maximum transmittance, when the effective retardation Δn (λ, θ) of the liquid crystal layer is controlled to reduce the difference in Δn · d / λ between pixels of each color, the TV curve is The retardation Δn (λk) · dk of a pixel (B in the configuration of R, G, B) having the shortest central transmission wavelength λ that is the steepest is set between 250 and 450 nm, preferably around 345 nm. (250 nm <Δn (λk) · d <450 nm).

When the cell thickness d is controlled to reduce the difference of Δn · d / λ between pixels of each color, the chromaticity change due to viewing angle is automatically adjusted by adjusting so that there is no chromaticity change due to gradation. Improved. However, when the effective retardation Δn (λ, θ) of the liquid crystal layer is controlled to reduce the difference in Δn · d / λ between pixels of each color, the liquid crystal display panel without a polarizing plate is transmitted or It is necessary to make the difference between the chromaticity (x0, y0) of the reflected incident light source and the chromaticity (x1, y1) at the time of white display smaller than 0.1 (((x0−x1) ² + (y0− y1) ² ) ^1/2 <0.1). The difference between both chromaticities is more preferably 0.01 or less. When only the chromaticity change due to the gradation in the front direction is improved, there is no need to reduce the difference of Δn · d / λ between the pixels of each color, so any chromaticity may be adjusted. However, in order to improve both the chromaticity change due to the gradation and the chromaticity change due to the viewing angle, it is necessary to align the retardation when viewed from an oblique direction. Therefore, Δn · d / λ between pixels of each color The difference needs to be reduced. For example, in a transmissive liquid crystal display device using a backlight, a liquid crystal display device having a desired chromaticity can be obtained by adjusting the chromaticity of light emitted from the backlight.

  FIG. 9 is a graph showing the chromaticity characteristics of a liquid crystal display device in which the retardation value of each region having different threshold values, the transmission spectrum of the color filter, and the wavelength dispersion of the birefringence of the liquid crystal layer are optimized. A line B1 indicates a change in chromaticity characteristics due to gradation in the front direction, and a line B2 indicates a change in chromaticity characteristics due to gradation in the oblique direction. Compared with the gradation chromaticity change characteristic of the conventional liquid crystal display device shown in FIG. 19, it can be confirmed that the chromaticity change due to gradation is greatly reduced in both the front direction and the oblique direction. In addition, the chromaticity difference between the front direction and the diagonal direction is also reduced, and the problem that the color changes depending on the viewing angle is solved.

  As described above, according to the present embodiment, it is possible to realize a liquid crystal display device in which the gradation viewing angle characteristic and the gradation chromaticity change characteristic are significantly improved and a superior display quality can be obtained. Hereinafter, description will be made using specific examples.

(Example 1-1)
First, a liquid crystal display device according to Example 1-1 of this embodiment will be described. The liquid crystal display device according to this example has the same configuration as that shown in FIGS. For example, in the region B on the TFT substrate 2 side of the MVA-LCD provided with alignment regulating structures such as the linear protrusions 44 and the alignment regulating slits 48, the effective voltage applied to the liquid crystal layer is controlled to increase the threshold voltage. A dielectric layer 50 is formed.

  The counter substrate 4 has color filter layers 40 of three colors of R, G, and B. A common electrode 42 is formed on the color filter layer 40. On the common electrode 42, linear protrusions 44 having a height of 1.4 μm and a width of 10 μm are formed at a pitch of 70 μm.

  The TFT substrate 2 has a pixel electrode 16 for each pixel region. In the pixel electrode 16, slits 48 for alignment regulation having a width of 10 μm are formed at a pitch of 70 μm. A substantially rectangular parallelepiped dielectric layer 50 having a width of 50 μm and a height (thickness) of 0.5 μm is formed on the pixel electrode 16 with the alignment regulating slit 48 as the center. Columnar spacers are formed on one of the substrates 2 and 4 so as to obtain a cell thickness of 3.6 μm. In addition, the substrates 2 and 4 are each coated with a vertical alignment film (manufactured by JSR) on each facing surface, and are bonded so that the linear protrusions 44 and the alignment regulating slits 48 are alternately arranged. Between the two substrates 2 and 4, n-type liquid crystal (made by Merck) of Δn = 0.1 is filled. 2 and 3 show only a part of the four alignment regions divided in one pixel. Actually, the inclination directions of the liquid crystal molecules in each alignment region in one pixel are 45 °, 135 °, 225 °, and 315 ° (for example, the right side of the display screen is set to 0 °). The area of each alignment region is substantially uniform within one pixel.

  Further, as a comparative example with respect to Example 1-1, a liquid crystal display device in which the dielectric layer 50 for controlling the effective voltage was not formed was manufactured.

(Example 1-2)
As Example 1-2, in order to maximize the transmittance, a liquid crystal display device having a cell thickness of 4.3 μm was fabricated so that the sum of transmittances in a plurality of regions having different threshold voltages was maximized. .

(Example 1-3)
As Example 1-3, in order to further improve the gradation chromaticity change, a liquid crystal display device as shown in FIG. 7 in which the thickness of the dielectric layer 50 is different in each of the R, G, and B pixels is manufactured. did. The thickness of the dielectric layer 50 in each pixel is 0.3 μm for the R pixel, 0.5 μm for the G pixel, and 0.7 μm for the B pixel.

(Example 1-4)
As Example 1-4, in order to further improve the gradation chromaticity change, a liquid crystal display device as shown in FIG. 6 in which the cell thickness was changed for each of R, G, and B pixels was produced. The cell thickness in each pixel is 4.7 μm for the R pixel, 4.3 μm for the G pixel, and 3.5 μm for the B pixel.

(Example 1-5)
As Example 1-5, in order to further improve the change in gradation chromaticity, a signal conversion board provided with a correction gradation conversion table for each of R, G, and B in the same liquid crystal display panel as Example 1-2 A liquid crystal display device as shown in FIG. 8 was produced in which the input data voltage was optimized between R, G, and B pixels.

  In Examples 1-1 to 1-5, the dielectric layer 50 has a substantially rectangular parallelepiped shape, but the same effect can be obtained with other shapes. For example, the effective voltage is controlled by providing a stripe-shaped dielectric layer 50 having a formation width L and a gap width S of L / S = 3.0 μm / 3.0 μm in a direction orthogonal to the alignment regulating structure. In addition to the effect, an effect of strengthening the orientation control ability regulated by the orientation regulating structure can be obtained. Therefore, it is possible to control the orientation more firmly, and it is possible to improve the transmittance and avoid various display defects.

  In Example 1-3, the thickness of the dielectric layer 50 was changed in each of the R, G, and B pixels in order to improve the gradation chromaticity change, but the area ratio and shape of the dielectric layer 50 were changed. The same effect can be obtained by changing the value. In the case where the stripe-shaped dielectric layer 50 is provided, the same effect can be obtained by optimizing the width and period of the dielectric layer 50 between the R, G, and B pixels.

(Example 1-6)
A liquid crystal display device according to Example 1-6 of this embodiment will be described. The liquid crystal display device according to this example has the same configuration as that shown in FIG. An effective voltage lowering slit (electrode extraction portion) 46 is formed in the pixel electrode 16 in a part of the region B in the alignment region. The effective voltage lowering slit 46 is provided to lower the effective voltage applied to the liquid crystal 6 than the other area A in the alignment area, and to increase the threshold voltage.

  The counter substrate 4 has color filter layers 40 of three colors of R, G, and B. A common electrode 42 is formed on the color filter layer 40. On the common electrode 42, linear protrusions 44 having a height of 1.4 μm and a width of 10 μm are formed at a pitch of 70 μm.

  The TFT substrate 2 has a pixel electrode 16 for each pixel region. In the pixel electrode 16, slits 48 for alignment regulation having a width of 10 μm are formed at a pitch of 70 μm. Further, the pixel electrode 16 has a finer stripe-shaped (L / S = 3.5 μm / 5.0 μm) effective voltage lowering slit extending perpendicularly to the alignment regulating slit 48 around the alignment regulating slit 48. 46 is provided. Except for the above, the configuration is the same as that of Example 1-1.

  The liquid crystal display device according to the present embodiment can further reduce the loss of transmittance by performing optimization so that the sum of the transmittances of regions having different threshold values is maximized, similarly to the embodiment 1-2. . Further, as in Example 1-3, by optimizing the shape, width, and period of the alignment regulating slit 48 in each of the R, G, and B pixels, more excellent gradation chromaticity characteristics can be obtained. Further, as in Example 1-4, by optimizing the cell thickness for each of the R, G, and B pixels, more excellent gradation chromaticity characteristics can be obtained. Further, as in Example 1-5, by optimizing the input data voltage for each of the R, G, and B pixels, more excellent gradation chromaticity characteristics can be obtained.

  FIG. 10 is a graph collectively showing the characteristics of Examples 1-1 to 1-6 and the comparative example (Ref.). The horizontal axis represents the normalized transmittance as a logarithm. The normalized transmittance is 100% when white is displayed. The vertical axis represents the ratio of the transmittance in the oblique direction to the transmittance in the front direction (transmittance ratio). In the graph shown in FIG. 10, the gradation viewing angle characteristic is superior when the transmittance ratio is constant, that is, the profile is flat regardless of the normalized transmittance. Further, the closer the transmittance ratio is to 1.0, the better the gradation viewing angle characteristics. As shown in FIG. 10, in Examples 1-1 to 1-6, the transmittance ratio at the low transmittance, which was high in the conventional transmittance ratio, is lowered and the profile is flattened. The transmittance ratio is close to 1.0. Therefore, it can be seen that the gradation viewing angle characteristics are greatly improved as compared with the comparative example in any of the examples.

  FIG. 11 is a table collectively showing the structures and optical characteristics of Examples 1-1 to 1-6 and the comparative example. The transmittance is expressed as a ratio when the transmittance of the comparative example is 1.0. The gradation chromaticity change indicates the chromaticity change width when the gradation is changed from black to white (corresponding to the length of each line when plotting is performed as shown in FIGS. 9 and 19). . In addition, the gradation viewing angle characteristic and gradation chromaticity change characteristic when visually confirming a general demonstration display image are evaluated in four stages of ◎, ○, Δ, and X in order from the superior one. . As shown in FIG. 11, all of the examples can obtain the gradation viewing angle characteristics and the gradation chromaticity change characteristics that are remarkably excellent without substantially losing the transmittance as compared with the comparative example, and are extremely high as a whole. Display performance is obtained.

  In the above embodiment, various display defects can be avoided by providing the region where the dielectric layer 50 and the effective voltage lowering slit 46 are provided in the region close to the end of the pixel. That is, by increasing the threshold voltage in the region close to the edge of the pixel, it is possible to prevent display defects that have conventionally occurred during white display. In particular, the effective cell thickness can be reduced by providing the dielectric layer 50 in a region near the edge of the pixel. Therefore, since the alignment control ability is improved, a liquid crystal display device that is resistant to display defects can be realized.

  In the above embodiment, the area ratio of the region where the effective voltage is lowered is a parameter indicating which gradation region the gradation viewing angle display characteristics are mainly improved. The threshold voltage difference is a parameter indicating how much characteristic improvement can be obtained. Therefore, the area ratio is preferably 0.5 to 0.9 in order to improve display characteristics at an extremely low gradation, which is a problem in the MVA-LCD. More desirably, when the area ratio is 0.6 to 0.8, more excellent display characteristics can be obtained over all gradations. Since the difference in threshold voltage is in a trade-off relationship with the transmittance, it is preferably 0.1V to 2.0V. More desirably, when the difference in threshold voltage is 0.5 V to 1.0 V, there is almost no loss of transmittance, and more excellent display characteristics can be obtained over all gradations.

Moreover, although the said Example is an example which applied this Embodiment to MVA-LCD, the same effect will be acquired even if this Embodiment is applied to the liquid crystal display panel of another switching mode.
Further, the above embodiment is an example in which the present embodiment is applied to an MVA-LCD in which alignment division is realized by the linear protrusions 44 and the alignment regulating slits 48. However, the present embodiment is applied to other alignment regulating structures. The same effect can be obtained even if it is applied to an MVA-LCD provided with an object.

  In the above embodiment, the dielectric layer 50 and the effective voltage lowering slit 46 are provided at the center of the alignment regulating slit 48. However, the same effect can be obtained even if they are arranged in other regions. However, since the dielectric layer 50 and the slit for reducing effective voltage 46 also have a function of regulating the alignment direction of the liquid crystal, they are arranged so as not to contradict the alignment direction of the liquid crystal regulated by the alignment regulating structure. Is desirable. Further, the dielectric layer 50 and the effective voltage lowering slit 46 are formed so as to overlap the alignment regulating structure, or arranged so as to overlap with the alignment regulating structure on the other opposing substrate. The symmetry of the alignment of the liquid crystal is improved, and the overall alignment control ability is improved. In practice, it is desirable to perform an appropriate layout design in consideration of the above conditions and pixel layout.

  Further, in the above embodiment, the dielectric layer 50 and the effective voltage lowering slit 46 are arranged so as to divide one alignment region, and regions having different threshold voltages are provided in the alignment region. When a plurality of alignment regions are present in one pixel, the dielectric layer 50 and the effective voltage lowering slit 46 may be formed in at least one of the alignment regions. The same effect can be obtained if the above-mentioned division ratio and threshold voltage difference are obtained by averaging the entire pixels. In addition, depending on the size of the pixel and the pixel layout, the difference in threshold voltage can be clarified.

  Further, as in the first to fifth embodiments, as a technique for optimizing the input data voltage, a method of providing a scaler circuit in each of R, G, and B, or a method of software conversion represented by an ICC profile or the like and so on. Since both have the same correction function, an optimum method can be selected according to the use environment and cost of the liquid crystal display device.

  As described above, according to the present embodiment, an MVA-LCD having favorable viewing angle characteristics can be realized.

[Second Embodiment]
Next, a liquid crystal display device according to a second embodiment of the present invention will be described with reference to FIGS. In recent years, the viewing angle characteristics of liquid crystal display devices have been greatly improved with the advent of MVA mode, IPS mode, and the like. However, it still does not reach the viewing angle characteristics of CRT. In particular, the MVA-LCD has a problem that a halftone display image appears whitish from an oblique direction.

  As a countermeasure against this, Japanese Patent Application (Japanese Patent Application No. 2002-52303) by the applicant of the present application describes that a photocurable composition mixed in liquid crystal is cured so as to have partially different pretilt angles within one pixel. Techniques to make it have been proposed. According to this technique, regions having different TV characteristics such as threshold voltage can be formed in one pixel, and the gradation viewing angle characteristics are improved.

  In addition, in the Japanese patent application (Japanese Patent Application No. 2001-98455; hereinafter referred to as “Patent Application 1”) filed by the applicant of the present application, the following technique is proposed as a method for providing a pretilt angle. The pretilt of liquid crystal molecules can be imparted by adding a monomer or oligomer that undergoes a polymerization reaction with light or heat to the liquid crystal and polymerizing the monomer or oligomer after liquid crystal injection. The pretilt angle can be varied by changing the voltage applied to the liquid crystal during the polymerization. The greater the applied voltage, the smaller the pretilt angle. Here, the pretilt angle is an inclination angle of the liquid crystal molecules from the substrate surface when no voltage is applied to the liquid crystal layer. That is, “the pretilt angle is decreased” means that the tilt angle from the complete vertical alignment is increased, that is, closer to the horizontal alignment.

However, the above-described method has a problem in that it is difficult to form regions having different TV characteristics in one pixel because there is a limit to the difference in the pretilt angle to be formed. In addition, the above method has a problem that the manufacturing process of the liquid crystal display device is complicated.
An object of the present embodiment is to provide a liquid crystal display device having good viewing angle characteristics by forming regions having different TV characteristics in one pixel by an easy manufacturing process.

  FIG. 12 schematically shows a cross-sectional configuration of almost one pixel of the liquid crystal display device according to the present embodiment. As shown in FIG. 12, a relatively thick insulating film 34 is formed in a region C that is a part of the pixel region. For this reason, the cell thickness d1 of the region C is thinner than the cell thickness d2 of the other region D (d1 <d2). The liquid crystal 6 is formed with a polymer in which polymerizable components such as monomers and oligomers are polymerized.

  When distribution is provided in the cell thickness in this way, after the monomer or oligomer is solidified by UV, different TV characteristics depending on the region can be obtained within one pixel. In the region C where the cell thickness d1 is thin, the pretilt angle of the liquid crystal molecules is larger than that in the region D (that is, close to the vertical alignment), and the TV characteristic is shifted to the high voltage side. Therefore, after the monomer or oligomer is solidified by UV, the liquid crystal 6 in the region D reacts at a lower voltage than the liquid crystal 6 in the region C. Note that the regions C and D do not have to be divided so as to divide the pixel into two equal parts, and both the regions C and D may be mixed more finely. In addition to the regions C and D, other regions having different cell thicknesses may be formed.

  In the method described in Patent Application 1 in which the pretilt angle is controlled using a polymerizable monomer or oligomer, the change in the TV characteristic due to the change in cell thickness is several times larger than that in the case where no monomer or oligomer is used. For this reason, in the present embodiment, the difference in TV characteristics between the regions C and D becomes clear, and the liquid crystal in the region D reacts at a lower voltage than the liquid crystal in the region C.

  Furthermore, if the pretilt setting is changed between the regions C and D and the pretilt angle of the region D is set to be small, the change in the TV characteristic becomes larger. This is because even when the cell thicknesses d1 and d2 are the same, the TV characteristics change depending on the pretilt angle, and the region with the smaller pretilt angle is on the lower voltage side.

  As a method for changing the pretilt angle, there is a technique for changing a voltage value applied to a liquid crystal when a monomer or oligomer is polymerized. In this case, the higher the voltage, the smaller the pretilt angle.

  Further, as a method of changing the pretilt angle, a technique of mixing a monomer or a polymerization initiator in the alignment film may be used. FIG. 13 schematically shows a cross-sectional configuration of almost one pixel of the liquid crystal display device according to the present embodiment using the technology. As shown in FIG. 13, monomers and polymerization initiators are mixed in the alignment film 35 'in the region D in the pixel. In the alignment film 35 in the region C, the monomer and the polymerization initiator are mixed at a lower concentration than the region D or the monomer and the polymerization initiator are not mixed (in other words, the monomer and the polymerization initiator are at a concentration of 0). Mixed). By doing so, the pretilt angle of the region D can be made smaller than that of the region C. Of course, the monomer and the polymerization initiator may be mixed on the alignment film 36 side. Further, this method may be combined with the method shown in FIG. In this case, the pretilt angle of the region D is further reduced by setting the concentration of the monomer or the like in the alignment film 35 in the region D of FIG.

(Example 2-1)
As a liquid crystal display device according to Example 2-1 of the present embodiment, a liquid crystal display panel having a configuration as shown in FIG. 12 was produced. The size of one pixel was about 100 × 300 μm, and the sizes of the regions C and D were about 100 × 150 μm, respectively. As the insulating film 34, PC403 (manufactured by JSR) which is an acrylic insulating film was used, and the film thickness was set to 1.8 μm. The cell thickness was 2.2 μm in region C and 4.0 μm in region D. The liquid crystal (Δε = −3.8; NI point: 71 ° C.) 6 was mixed with 0.5% of acrylic monomer. After injecting the liquid crystal 6 into the panel, the liquid crystal 6 was irradiated with UV light of about 1 J / cm ² while applying a voltage of 10 V between the electrodes 16 and 42. In this example, as compared with a normal liquid crystal display panel having a uniform cell thickness (4.0 μm) in all regions, a good display was obtained even when viewed from an oblique direction.

(Example 2-2)
As a liquid crystal display device according to Example 2-2 of the present embodiment, a liquid crystal display panel was manufactured under the same conditions as Example 2-1 except for the applied voltage during polymerization. In Example 2-1, UV irradiation was performed all over the surface, but in this example, UV light was irradiated through a mask, and the monomers in regions C and D were polymerized separately. A voltage of 10 V was applied when the region C monomer was polymerized, and a voltage of 16 V was applied when the region D monomer was polymerized. In this example, when viewed from an oblique direction, a better display than that of the liquid crystal display panel of Example 2-1 was obtained.

(Example 2-3)
As a liquid crystal display device according to Example 2-3 of the present embodiment, a liquid crystal display panel having a configuration as shown in FIG. 13 was produced. The size of one pixel was about 100 × 300 μm, and the sizes of the regions C and D were about 100 × 150 μm, respectively. The cell thickness was 4.0 μm. In the alignment film 35 ', an acrylic monomer and a polymerization initiator (Irgacure 651; manufactured by Ciba Specialty Chemicals) each having a weight ratio of 5% with respect to the alignment material (including the solvent) were mixed during printing. No monomer or polymerization initiator was mixed in the alignment films 35 and 36. The liquid crystal (Δε = −3.8; NI point: 71 ° C.) 6 was mixed with 0.5% of an acrylic monomer in the same manner as in Example 2-1. After injecting the liquid crystal 6 into the panel, the liquid crystal 6 was irradiated with UV light of about 1 J / cm ² while applying a voltage of 10 V between the electrodes 16 and 42. In this example, as compared with a normal liquid crystal display panel, a good display was obtained even when viewed from an oblique direction.

(Example 2-4)
As a liquid crystal display device according to Example 2-4 of the present embodiment, a liquid crystal display panel having a configuration as shown in FIGS. 14 and 15 was produced. FIG. 14 shows a configuration of almost three pixels of the liquid crystal display panel according to the present embodiment, and FIG. 15 shows a schematic cross-sectional configuration of the liquid crystal display panel cut along line AA in FIG. As shown in FIGS. 14 and 15, in this embodiment, a dielectric layer 52 is formed on the pixel electrode 16 at the outer periphery of each pixel region defined by the gate bus line 12 and the drain bus line 14. Has been. As the dielectric layer 52, PC403 (manufactured by JSR), which is an acrylic insulating film, was used. The dielectric layer 52 is a transparent body having a transmittance of 90% or more in the visible light region. An opening 56 in which a dielectric layer 52 is opened is formed at the center of the pixel. The pixel electrode 16 is exposed at the opening 56. A TFT 20 is formed in the vicinity of each intersection position of the gate bus line 12 and the drain bus line 14. The size of one pixel is about 100 × 300 μm. The cell thickness at the center of the pixel was 4.0 μm. The liquid crystal (Δε = −3.8; NI point: 71 ° C.) 6 was mixed with 0.5% of an acrylic monomer in the same manner as in Example 2-1. After injecting the liquid crystal 6 into the panel, the liquid crystal 6 was irradiated with UV light of about 1 J / cm ² while applying a voltage of 10 V between the electrodes 16 and 42.

  Further, as a modification of the liquid crystal display device according to this example, a liquid crystal display panel having a configuration as shown in FIGS. 16 and 17 was produced. FIG. 16 shows a configuration of almost three pixels of a liquid crystal display panel according to this modification, and FIG. 17 shows a schematic cross-sectional configuration of the liquid crystal display panel taken along line BB in FIG. As shown in FIGS. 16 and 17, in this modification, the end surface of the dielectric layer 52 formed on the outer periphery of each pixel is inclined toward the opening 56 side. The thickness of the dielectric layer 52 is preferably 0.1 μm or more and half or less of the cell thickness. If the boundary between the inclined surface α and the flat surface β of the dielectric layer 52 is disposed outside the pixel region, the film thickness of the dielectric layer 52 may be equivalent to the cell thickness. In addition, on the common electrode 42 on the counter substrate 4 side, a dot-like protrusion 54 is formed that is disposed substantially at the center of each pixel. The other conditions were the same as in the above example.

  Thus, by providing the dielectric layer 52 on the outer periphery of the pixel, the liquid crystal molecules 8 can be oriented toward the center of the pixel region when a voltage is applied to the liquid crystal layer. However, when a high voltage is suddenly applied, many disclination lines are randomly generated. Therefore, when the monomer is polymerized by irradiating UV light while applying a voltage, a regular disclination line is generated by gradually increasing the applied voltage from a low voltage, and UV solidifies in this state. It is desirable.

  By uniformly applying a voltage of 10 V between the electrodes 16 and 42 of the entire pixel, a voltage of substantially 10 V is applied to the region E of the liquid crystal 6 shown in FIG. 17, and the voltage generated by the dielectric layer 52 is applied to the region F. Since distribution occurs, a voltage of about 6V is applied. By solidifying UV in this state, the difference that the pretilt angle is slightly smaller than 90 ° in the region F and the pretilt angle is smaller than that in the region F in the region E can be realized. As a result, in the regions E and F, the electro-optical characteristics can be made different based on the difference in the substantial voltage and the pretilt angle during driving caused by the presence or absence of the dielectric layer 52. In this example and the modification, a good display was obtained even when viewed from an oblique direction as compared with a normal liquid crystal display panel having a uniform cell thickness (4.0 μm) in the entire region.

  In the configuration shown in FIGS. 16 and 17, one opening 56 and one protrusion 54 are formed in each pixel. However, a plurality of openings 56 and protrusions 54 may be formed in each pixel.

  As described above, according to the present embodiment, regions having different TV characteristics can be formed in one pixel by an easy manufacturing process, and a liquid crystal display device with favorable viewing angle characteristics can be realized.

The liquid crystal display device according to the first embodiment described above can be summarized as follows.
(Appendix 1)
A pair of substrates disposed opposite each other and provided with electrodes;
Liquid crystal sealed between the pair of substrates;
One or a plurality of low effective voltage regions having an effective voltage applied to the liquid crystal lower than the voltage applied between the electrodes are provided in a predetermined area ratio, and the one or more low effective voltage regions and others And a pixel region having a threshold voltage different from that of the region.

(Appendix 2)
In the liquid crystal display device according to appendix 1,
The pixel region includes a plurality of color filter layers formed on at least one of the pair of substrates and having a center transmission wavelength of λk (k = 1, 2,..., N; N> 2),
When the birefringence of the liquid crystal molecules with respect to the wavelength λ is Δn (λ), the cell thickness dk of the pixel region provided with at least two kinds of the color filter layers, respectively,
| Δn (λi) · di / λi−Δn (λj) · dj / λj | <0.2
(I, j = 1, 2,..., N; i ≠ j)
A liquid crystal display device characterized by satisfying the above relationship.

(Appendix 3)
In the liquid crystal display device according to appendix 1,
The pixel region includes a plurality of color filter layers formed on at least one of the pair of substrates and having a center transmission wavelength of λk (k = 1, 2,..., N; N> 2),
The product of the cell thickness dk of the pixel region having the color filter layer with the central transmission wavelength λk closest to 545 nm and the birefringence Δn (λk) of the liquid crystal molecules with respect to the central transmission wavelength λk,
250 nm <Δn (λk) · dk <450 nm
A liquid crystal display device characterized by satisfying the above relationship.

(Appendix 4)
In the liquid crystal display device according to appendix 1,
The pixel region includes a plurality of color filter layers formed on at least one of the pair of substrates and having a center transmission wavelength of λk (k = 1, 2,..., N; N> 2),
Regardless of the central transmission wavelength λk, the cell thickness d of the pixel region is substantially constant,
The effective retardation Δn (λk, θk) of the liquid crystal layer when the data voltage Vk that gives the tilt angle θk to the liquid crystal molecules is applied between the pixel regions each including at least two types of the color filter layers,
| Δn (λi, θi) · d / λi−Δn (λj, θj) · d / λj | <0.2
(I, j = 1, 2,..., N; i ≠ j)
While satisfying the relationship
The chromaticity (x0, y0) of the incident light source that is transmitted or reflected through the liquid crystal display panel without the polarizing plate, and the chromaticity (x1, y1) during white display,
((X0−x1) ² + (y0−y1) ² ) ^1/2 <0.1
A liquid crystal display device characterized by satisfying the above relationship.

(Appendix 5)
In the liquid crystal display device according to appendix 1,
The pixel region includes a plurality of color filter layers formed on at least one of the pair of substrates and having a center transmission wavelength of λk (k = 1, 2,..., N; N> 2),
Regardless of the central transmission wavelength λk, the cell thickness d of the pixel region is substantially constant,
The product of the cell thickness d of the pixel region having the color filter layer with the shortest central transmission wavelength λk and the birefringence Δn (λk) of the liquid crystal molecules with respect to the central transmission wavelength λk,
250 nm <Δn (λk) · d <450 nm
A liquid crystal display device characterized by satisfying the above relationship.

(Appendix 6)
In the liquid crystal display device according to any one of appendices 1 to 5,
The area ratio is 0.5 or more and 0.9 or less.

(Appendix 7)
In the liquid crystal display device according to any one of appendices 1 to 6,
The threshold voltage of the low effective voltage region is higher than the threshold voltage of other regions by a predetermined voltage difference,
The voltage difference is 0.1 V or more and 2.0 V or less.

(Appendix 8)
In the liquid crystal display device according to any one of appendices 1 to 7,
The liquid crystal display device, wherein the area ratio varies depending on a central transmission wavelength λ of a color filter layer included in the pixel region.

(Appendix 9)
In the liquid crystal display device according to any one of appendices 1 to 8,
The liquid crystal display device, wherein the low effective voltage region has a dielectric layer formed with a predetermined thickness on at least one of the electrodes.

(Appendix 10)
In the liquid crystal display device according to appendix 9,
The liquid crystal display device, wherein the dielectric layer is formed in a stripe shape having a predetermined formation width and a gap width.

(Appendix 11)
In the liquid crystal display device according to any one of appendices 1 to 8,
The liquid crystal display device, wherein the low effective voltage region has an electrode extraction portion formed in at least one of the electrodes.

(Appendix 12)
In the liquid crystal display device according to appendix 11,
The liquid crystal display device, wherein the electrode extraction part is formed in a stripe shape having a predetermined formation width and a gap width.

(Appendix 13)
The liquid crystal display device according to any one of appendices 1 to 12,
The liquid crystal display device, wherein the low effective voltage region is disposed near an end of the pixel region.

(Appendix 14)
The liquid crystal display device according to any one of appendices 1 to 13,
The liquid crystal is a nematic liquid crystal having negative dielectric anisotropy, and an initial alignment is substantially perpendicular to a substrate surface.

(Appendix 15)
In the liquid crystal display device according to appendix 14,
An alignment regulating structure that regulates alignment of the liquid crystal is further provided on at least one of the substrates,
The liquid crystal display device, wherein the pixel region has a plurality of alignment regions in which the liquid crystal is aligned in different directions.

The liquid crystal display device according to the second embodiment described above can be summarized as follows.
(Appendix 16)
A pair of substrates disposed opposite to each other and provided with electrodes on opposite surfaces;
Liquid crystal sealed between the pair of substrates;
A polymer obtained by polymerizing a polymerizable component mixed in the liquid crystal;
And a pixel region including a plurality of regions having different electro-optical characteristics due to different cell thicknesses.

(Appendix 17)
In the liquid crystal display device according to attachment 16,
The pixel region has a different pretilt angle for each of the plurality of regions,
The liquid crystal display device, wherein the pretilt angle is relatively small in a relatively thick region of the cell thickness.

(Appendix 18)
In the liquid crystal display device according to appendix 17,
The liquid crystal display device according to claim 1, wherein the pretilt angle is obtained by varying a voltage applied when the polymerizable component is polymerized for each of the plurality of regions.

(Appendix 19)
The liquid crystal display device according to any one of appendices 16 to 18,
The liquid crystal display device, wherein the pixel region has a dielectric layer formed on one of the electrodes of the pair of substrates and having a relatively thin cell thickness.

(Appendix 20)
In the liquid crystal display device according to appendix 19,
The dielectric layer is formed on the outer periphery of the pixel region,
The liquid crystal display device further comprising an opening in which the dielectric layer is not formed in the pixel region.

(Appendix 21)
In the liquid crystal display device according to attachment 20,
The liquid crystal display device, wherein the dielectric layer has an inclined surface inclined toward the opening.

(Appendix 22)
In the liquid crystal display device according to any one of appendices 19 to 21,
The liquid crystal display device, wherein the dielectric layer has a thickness not less than 0.1 μm and not more than the cell thickness.

(Appendix 23)
In the liquid crystal display device according to attachment 22,
The liquid crystal display device, wherein the dielectric layer has a thickness of 0.1 μm or more and half or less of the cell thickness.

(Appendix 24)
24. The liquid crystal display device according to any one of appendices 20 to 23,
A liquid crystal display device further comprising a protrusion formed on the other of the pair of substrates and disposed substantially at the center of the opening as viewed in the direction perpendicular to the substrate surface.

(Appendix 25)
A pair of opposed substrates;
Liquid crystal sealed between the pair of substrates;
A liquid crystal display device comprising: an alignment film containing a polymerizable component and a polymerization initiator at different concentrations for each of a plurality of regions in a pixel region.

(Appendix 26)
In the liquid crystal display device according to attachment 25,
The pixel region has a different cell thickness for each of the plurality of regions,
The liquid crystal display device characterized in that the concentration is relatively high in the relatively thick region of the cell thickness.

It is a figure which shows schematic structure of the liquid crystal display device by the 1st Embodiment of this invention. It is sectional drawing which shows the basic composition of the liquid crystal display device by the 1st Embodiment of this invention. It is a perspective view which shows the structure of the area | region vicinity shown in FIG. It is a perspective view which shows the modification of the basic composition of the liquid crystal display device by the 1st Embodiment of this invention. It is a graph which shows the TV characteristic of the liquid crystal display device by the 1st Embodiment of this invention. It is sectional drawing which shows the other basic composition of the liquid crystal display device by the 1st Embodiment of this invention. It is sectional drawing which shows the other basic composition of the liquid crystal display device by the 1st Embodiment of this invention. It is sectional drawing which shows the other basic composition of the liquid crystal display device by the 1st Embodiment of this invention. 6 is a graph showing changes in chromaticity characteristics depending on gradation of the liquid crystal display device according to the first embodiment of the present invention. It is a graph which shows collectively the characteristic of Examples 1-1 thru | or 1-6 of the 1st Embodiment of this invention, and a comparative example (Ref.). It is a graph which shows collectively the structure and optical characteristic of Examples 1-1 thru | or 1-6 of the 1st Embodiment of this invention, and a comparative example (Ref.). It is sectional drawing which shows the structure of the liquid crystal display device by the 2nd Embodiment of this invention. It is sectional drawing which shows the other structure of the liquid crystal display device by the 2nd Embodiment of this invention. It is a figure which shows the structure of the liquid crystal display device by Example 2-4 of the 2nd Embodiment of this invention. It is sectional drawing which shows the structure of the liquid crystal display device by Example 2-4 of the 2nd Embodiment of this invention. It is a figure which shows the other structure of the liquid crystal display device by Example 2-4 of the 2nd Embodiment of this invention. It is sectional drawing which shows the other structure of the liquid crystal display device by Example 2-4 of the 2nd Embodiment of this invention. It is a graph which shows the TV characteristic of the conventional liquid crystal display device. It is a graph which shows the change of the chromaticity characteristic by the gradation of the conventional liquid crystal display device.

Explanation of symbols

2 TFT substrate 4 Counter substrate 6 Liquid crystal 8 Liquid crystal molecules 10 and 11 Glass substrate 12 Gate bus line 14 Drain bus line 16 Pixel electrode 20 TFT
34 Insulating films 35 and 36 Vertical alignment film 40 Color filter layer 42 Common electrode 44 Linear protrusion 46 Effective voltage lowering slit 48 Orientation regulating slit 50 and 52 Dielectric layer 54 Projection 80 Gate bus line driving circuit 82 Drain bus line driving Circuit 84 Control circuit 86, 87 Polarizing plate 88 Backlight unit

Claims (8)

A pair of substrates disposed opposite to each other and provided with electrodes on opposite surfaces;
A vertically aligned liquid crystal sealed between the pair of substrates;
A polymer that polymerizes the polymerizable component mixed in the liquid crystal, and gives a pretilt angle to liquid crystal molecules ;
And a pixel region including a plurality of regions having different electro-optical characteristics due to different cell thicknesses. The liquid crystal display device according to claim 1.
The liquid crystal display device, wherein the pixel region has a dielectric layer formed on one of the electrodes of the pair of substrates and having a relatively thin cell thickness. The liquid crystal display device according to claim 2.
The dielectric layer is formed on the outer periphery of the pixel region,
The liquid crystal display device further comprising an opening in which the dielectric layer is not formed in the pixel region. The liquid crystal display device according to claim 3.
The liquid crystal display device, wherein the dielectric layer has an inclined surface inclined toward the opening.   The liquid crystal display device according to claim 3 or 4,
  A protrusion formed on the other of the pair of substrates and disposed substantially in the center of the opening when viewed in a direction perpendicular to the substrate surface;
  A liquid crystal display device.   The liquid crystal display device according to any one of claims 1 to 5,
  The pixel region has a different pretilt angle for each of the plurality of regions,
  The pretilt angle is relatively small in a relatively thick region of the cell thickness.
  A liquid crystal display device. A pair of opposed substrates;
Liquid crystal sealed between the pair of substrates;
An alignment film containing an alignment material ,
The liquid crystal display device , wherein a polymerizable component and a polymerization initiator different from the alignment material are mixed in the alignment film at different concentrations for each of a plurality of regions in the pixel region .   The liquid crystal display device according to claim 7.
  The pixel region has a different cell thickness for each of the plurality of regions,
  In the relatively thick cell region, the concentration is relatively high.
  A liquid crystal display device.

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