JP3735107B2 - Active matrix liquid crystal display device - Google Patents

Description

The present invention relates to an active matrix type liquid crystal display device with good mass productivity, low cost and high image quality.

  In a conventional active matrix type liquid crystal display device, transparent electrodes formed on the interface between two substrates and opposed to each other are used as electrodes for driving a liquid crystal composition layer. This is because a display method represented by a twisted nematic (TN) display method, which operates by setting the direction of the electric field applied to the liquid crystal composition layer to a direction substantially perpendicular to the substrate interface, is adopted. Hereinafter, a display method in which the main electric field direction applied to the liquid crystal composition layer is a direction substantially perpendicular to the substrate interface is referred to as a vertical electric field method.

  Further, for example, Japanese Patent Publication No. 63-21907 proposes a method of applying an electric field to a liquid crystal composition layer using a comb-like electrode pair formed on one substrate. The comb-like electrode pair referred to here is an arrangement in which two electrodes having a comb-like shape as indicated by 1 and 2 in FIG. 5 are arranged so that their teeth do not overlap each other. It is. In this case, the electrode for driving the liquid crystal composition layer does not need to be transparent, and an opaque metal electrode having high conductivity can be used. In addition, the liquid crystal composition molecules can be oriented in a homogeneous orientation, 90 ° twist orientation, or homeotropic orientation in a state where no voltage is applied between the electrodes. A voltage effect type display method such as a refraction (ECB) mode or a current effect type dynamic scattering (DS) mode display method can be used. Hereinafter, a display method in which the main electric field direction applied to the liquid crystal composition layer is a direction substantially parallel to the substrate interface is referred to as a horizontal electric field method.

  The operation principle of the horizontal electric field method will be described with reference to FIGS.

  2A and 2B are sectional views showing the operation of the liquid crystal in the liquid crystal display device, and FIGS. 2C and 2D are plan views thereof. In FIG. 2, the active element is omitted, and a part of the comb-like electrode pair in the pixel is shown.

  FIG. 2A shows a sectional view when no voltage is applied, and FIG. 2C shows a plan view at that time. A pair of pixel electrodes 1 and 2 having a comb-like shape are formed on opposite surfaces of a pair of substrates 3 at least one of which is transparent, and an alignment film 4 is applied and aligned. A liquid crystal composition is sandwiched between them. The rod-like liquid crystal molecules 5 are aligned so as to have a slight angle with respect to the long side direction of the comb-like pixel electrode pair 1 and 2 when no voltage is applied between the pixel electrodes 1 and 2. Here, the case where the alignment directions of the liquid crystal molecules 5 on the upper and lower interfaces are parallel will be described as an example. In addition, the dielectric anisotropy of the liquid crystal composition is assumed to be positive.

  Next, when a voltage is applied between the comb-like pixel electrode pair 1 and 2 and an electric field 7 is applied to the liquid crystal composition layer, the liquid crystal molecules 5 are oriented in the direction of the electric field 7 as shown in FIGS. Changes its direction. By disposing the polarizing plate 6 at a predetermined angle, the light transmittance can be changed by applying an electric field. As shown in FIG. 3, when the effective value of the applied voltage is increased, the relative light transmittance changes. As described above, according to the horizontal electric field method, it is possible to perform display that provides contrast without using a transparent electrode.

  In FIG. 2, the comb-like pixel electrode pairs 1 and 2 are formed on the surface of one substrate. However, the effect does not change even if divided into a pair of substrates. However, in view of miniaturization of wiring and various deformations due to heat, external force, etc., it is desirable to provide one of the substrates because higher-precision alignment is possible. Further, although the dielectric anisotropy of the liquid crystal composition is assumed to be positive, it may be negative. In that case, the initial alignment state is aligned so as to have a slight angle from the direction perpendicular to the long side direction of the pixel electrode. Furthermore, if the angle at which the polarizing plate 6 is disposed is changed, it is possible to obtain characteristics having an inclination opposite to that in FIG.

  In the conventional vertical electric field type active matrix liquid crystal display device, in order to prevent the voltage fluctuation of the transparent electrode, a capacitive element for charge storage is connected to the transparent electrode. However, in the above-described vertical electric field method, when the size of the capacitive element is reduced in order to improve the light utilization efficiency as much as possible, an extremely high voltage of about 1012 Ωcm or more is required to hold the charge accumulated in the transparent electrode. It is necessary to use a liquid crystal composition having a high specific resistance. For this reason, the freedom degree of selection of the liquid crystal composition which has a low optical threshold voltage, an appropriate magnitude | size birefringence, etc., and is hard to be contaminated with an impurity was limited significantly. Furthermore, since the specific resistance of the liquid crystal composition layer also depends on the alignment film material that controls the alignment of liquid crystal composition molecules on the substrate interface in a predetermined direction, it is necessary to use an alignment film material that keeps the specific resistance of the liquid crystal composition layer high. There is. For this reason, materials that can be used as an alignment film that expresses an appropriate pretilt angle (tilt angle of liquid crystal composition molecules on the substrate interface) and hardly retains DC charges have been limited. For these reasons, image quality deterioration such as display unevenness and afterimages is likely to occur.

  Further, in the conventional lateral electric field method, since no capacitive element for charge storage is connected, it is impossible to suppress the voltage fluctuation of the comb-like electrode pair, and display unevenness is likely to occur. Furthermore, since the comb-like electrode pair is used, the light utilization efficiency is remarkably lowered, and it is difficult to improve the brightness of the liquid crystal display device.

  Further, even in the conventional lateral electric field method, there is a problem that an electric field component in a direction perpendicular to the substrate interface is generated in the vicinity of the pixel electrode, and the contrast ratio viewed from an oblique direction is lowered due to light leakage in this portion.

  The present invention solves these problems at the same time, and a first object of the invention is to widen the degree of freedom in selecting a usable liquid crystal composition and alignment film material and to prevent image quality deterioration.

  The second object is to improve the brightness of the liquid crystal display device.

  A third object is to provide a method for realizing a lateral electric field method having a high contrast ratio as viewed from an oblique direction.

  In order to achieve the above object, the following means are used.

A pair of substrates at least one of which is transparent, a liquid crystal composition layer and a color filter sandwiched between the substrates, a plurality of scanning wirings arranged in a matrix on the facing surface of any one of the substrates, and A signal line; a pair of first and second pixel electrodes; an active element connected to one of the first and second pixel electrodes; the scan line; and the signal line; In a liquid crystal display device comprising scanning line driving means connected to wiring and signal wiring driving means connected to each signal wiring,
[Means 1]
One of the first and second pixel electrodes includes an electrode that extends in the signal wiring extending direction and is shared between adjacent pixels in the scanning wiring extending direction.

  According to the means 1, one of the first and second pixel electrodes has an electrode that extends in the signal wiring extending direction and is shared between adjacent pixels in the scanning wiring extending direction. As a result, the number of electrodes can be reduced as compared with the case where each pixel is provided independently and not shared, and the area occupied by the electrodes in the pixel can be reduced, so that the aperture ratio can be improved.

[Means 2]
The color filter has a boundary between pixels adjacent in the scanning wiring extending direction, and the boundary is positioned on an electrode shared between pixels adjacent in the scanning wiring extending direction.

  According to the means 2, the aperture ratio is further improved by setting the boundary of the color filter on the pixel electrode which becomes the boundary of the adjacent pixel.

[Means 3]
An electrode shared between adjacent pixels in the scanning wiring extending direction is a common electrode.

  According to the means 3, since the electrode shared between the adjacent pixels in the scanning wiring extending direction is a common electrode, the same potential can be applied between the adjacent pixels, and the common between the adjacent pixels can be applied. Uneven luminance can be prevented by matching the potentials.

[Means 4]
One of the first and second pixel electrodes, which is an electrode shared between pixels adjacent in the scanning wiring extending direction, is shared between pixels adjacent in the signal wiring extending direction, and the other The electrode is connected to the active element in each pixel.

  According to the means 4, since the shared electrode is shared by the pixels in the vertical direction and the horizontal direction around the electrode, the potential is stable between the upper, lower, left and right pixels, and the luminance unevenness is reduced. Improvement can be achieved.

[Means 5]
A capacitive element is formed between one electrode of the first and second pixel electrodes, which is an electrode shared between pixels adjacent in the scanning wiring extending direction, and the other electrode.

  According to the means 5, both the signal applied to the first electrode and the signal applied to the second electrode are signals from the signal wiring, one of which intersects the plurality of scanning signal lines and is affected by the scanning signal lines, The other crosses a plurality of scanning signal lines to become a common electrode affected by the scanning signal lines, and by forming a capacitance between them, it is possible to form a capacitance that works in a direction that cancels the influence from the scanning signal to each other. Further improvements can be made.

[Means 6]
The other electrode different from one of the first and second pixel electrodes, which is an electrode shared between adjacent pixels in the scanning wiring extending direction, and the upper and lower sides of the pixel A capacitive element is formed between the other electrode of the two scanning signal lines to be connected and the scanning signal line on the side not connected by the active element.

  According to the means 6, the capacity can be increased, and the display unevenness can be eliminated by suppressing the voltage fluctuation.

[Means 7]
The first pixel electrode and the second pixel electrode are arranged in the same layer.

  According to the means 7, the misalignment of the electrodes is suppressed to be small, the variation in capacitance between the electrodes is suppressed, and the display unevenness can be eliminated.

[Means 8]
A protective film is formed on the color filter.

A pair of substrates at least one of which is transparent, a liquid crystal composition layer and a color filter sandwiched between the substrates, a plurality of scanning wirings arranged in a matrix on the facing surface of any one of the substrates, and A signal line; a pair of first and second pixel electrodes; an active element connected to one of the first and second pixel electrodes; the scan line; and the signal line; In a liquid crystal display device comprising scanning line driving means connected to wiring and signal wiring driving means connected to each signal wiring,
[Means 9]
Either one of the first and second pixel electrodes includes an electrode extending in the signal wiring extending direction and shared between adjacent pixels in the scanning wiring extending direction, It is formed between the color filter and the alignment film on the substrate on which the electrode is formed.

  According to the means 9, when positioning the boundary of the color filter in the region of the electrode extending in the signal wiring extending direction and shared between the pixels adjacent in the scanning wiring extending direction, the electrode and the color filter Alignment on the same substrate improves alignment accuracy and facilitates alignment. As a result, the width of the electrode can be supplemented by the reduction in misalignment, and the aperture ratio is further improved.

A pair of substrates at least one of which is transparent, a liquid crystal composition layer and a color filter sandwiched between the substrates, a plurality of scanning wirings arranged in a matrix on the facing surface of any one of the substrates, and A signal line; a pair of first and second pixel electrodes; an active element connected to one of the first and second pixel electrodes; the scan line; and the signal line; In a liquid crystal display device comprising scanning line driving means connected to wiring and signal wiring driving means connected to each signal wiring,
[Means 10]
Either one of the first and second pixel electrodes includes an electrode extending in the signal wiring extending direction and shared between adjacent pixels in the scanning wiring extending direction, It is formed between the protective film and the alignment film on the substrate on which the electrode is formed.

  According to the means 10, by positioning the electrode between the protective film and the alignment film, the electrode can be formed on the flattened underlayer, and defects such as disconnection can be reduced. Further, since the distance of the electrode to the liquid crystal composition layer is short, the electric lines of force from the electrode are strong, and the driving voltage required to achieve the target electric field strength can be reduced.

[Means 11]
The protective film is an organic film.

  According to the means 11, the flattening effect of the underlayer can be increased, and further the disconnection of the electrode is reduced.

[Means 12]
An electrode shared between adjacent pixels in the scanning wiring extending direction is a common electrode.

  According to the means 12, the electrode shared between the pixels adjacent in the scanning wiring extending direction is a common electrode, so that the same potential can be applied between the adjacent pixels, and common between the adjacent pixels. Uneven luminance can be prevented by matching the potentials.

[Means 13]
One of the first and second pixel electrodes, which is an electrode shared between pixels adjacent in the scanning wiring extending direction, is shared between pixels adjacent in the signal wiring extending direction, and the other The electrode is connected to the active element in each pixel.

  According to the means 13, since the shared electrode is shared by the pixels in the vertical direction and the horizontal direction around the electrode, the potential is stable between the upper, lower, left and right pixels, and the luminance unevenness is reduced. Improvement can be achieved.

[Means 14]
A capacitive element is formed between one electrode of the first and second pixel electrodes, which is an electrode shared between pixels adjacent in the scanning wiring extending direction, and the other electrode.

  According to the means 14, both the signal applied to the first electrode and the signal applied to the second electrode are signals from the signal wiring, one of which intersects the plurality of scanning signal lines and is affected by the scanning signal lines, The other crosses a plurality of scanning signal lines to become a common electrode affected by the scanning signal lines, and by forming a capacitance between them, it is possible to form a capacitance that works in a direction that cancels the influence from the scanning signal to each other. Further improvements can be made.

[Means 15]
The other electrode different from one of the first and second pixel electrodes, which is an electrode shared between adjacent pixels in the scanning wiring extending direction, and the upper and lower sides of the pixel A capacitive element is formed between the other electrode of the two scanning signal lines to be connected and the scanning signal line on the side not connected by the active element.

  According to the means 15, the capacity can be increased, and the display unevenness can be eliminated by suppressing the voltage fluctuation.

[Means 16]
The active matrix etching display device is a lateral electric field type.

  According to the means 16, because of the horizontal electric field method, the common electrode formed on the entire surface as in the conventional TN method or the stripe shape that must be separated for each pixel as in the STN method. None of the common electrodes is required, and an electrode that is shared between adjacent pixels and patterned can be formed.

[Means 17]
The channel layer of the active element is polycrystalline silicon.

  According to the means 17, since the mobility of the channel layer is higher than that of amorphous silicon, the image quality is further improved.

A pair of substrates at least one of which is transparent, a liquid crystal composition layer sandwiched between the substrates, and a plurality of scanning wirings and signal wirings arranged in a matrix on the facing surface of one of the substrates, A pair of pixel electrodes; an active element connected to the pixel electrode and the scanning wiring and signal wiring; scanning wiring driving means connected to each scanning wiring; and signal wiring connected to each signal wiring. In a liquid crystal display device comprising a driving means,
[Means 18]

The paired pixel electrodes have a strip shape, the long side direction of one of the electrodes is substantially parallel to the long side direction of the other electrode, and at least one of the paired pixel electrodes; A capacitive element is formed between the scanning wirings via an insulator. Alternatively, one of the paired pixel electrodes is connected to one of the paired pixel electrodes in an adjacent pixel and insulated from the other of the paired pixel electrodes. A capacitor element is formed through an object. In particular, the capacitive element is formed through an insulator having a specific resistance of 10 ¹⁰ Ωcm or more.

[Means 19]
The specific resistance of the liquid crystal composition is 10 ¹⁰ Ωcm or more. Desirably, a member is used in which the product of the specific resistance and dielectric constant of the insulator constituting the capacitive element is equal to or greater than the product of the specific resistance and dielectric constant of the liquid crystal composition. Further, it is desirable to set one vertical scanning period in the drive signal output from the scanning wiring driving means to be smaller than a time constant represented by a product of a specific resistance and a dielectric constant of an insulator constituting the capacitive element.

[Means 20]
The length of the short side of the paired pixel electrodes is made shorter than the distance between the paired pixel electrodes. In addition, a member having two or more non-conductive constituent members and a dielectric constant of at least one of them being smaller than a dielectric constant of the liquid crystal composition is used. Preferably, a member having a dielectric constant smaller than that of the liquid crystal composition is used as a member in contact with the liquid crystal composition layer.

  According to the means 19, the paired pixel electrodes have a structure in which an electric field parallel to the substrate interface is applied to the liquid crystal composition layer, and the distance between the electrodes is a conventional vertical electric field type active matrix. Larger than the distance between transparent electrodes opposed to each other in the liquid crystal display device. Also, the equivalent cross-sectional area can be kept smaller than the conventional one. Therefore, the electrical resistance between the paired pixel electrodes according to the present invention can be increased by an order of magnitude between the transparent electrodes opposed to each other in the conventional active matrix liquid crystal display device. Further, the capacitance between the paired pixel electrodes according to the present invention is connected in parallel with the capacitive element, and a capacitive element having sufficiently high electrical resistance can be realized. As a result, it becomes easy to hold the charge accumulated in the pixel electrode, and a liquid crystal composition having a lower specific resistance than before can be used. Further, since the pixel electrode has a simple shape as compared with the comb-like electrode pair, the light use efficiency is improved. Furthermore, the electric field component in the direction perpendicular to the substrate interface generated in the vicinity of the pixel electrode can be suppressed smaller than the lateral electric field component. In addition, when one of the paired pixel electrodes is connected to one of the paired pixel electrodes in an adjacent pixel, it is almost the same as the common electrode in the conventional active matrix liquid crystal display device. Equivalent action.

  Further, according to the means 20, it is possible to form a liquid crystal composition layer having an electric resistance sufficient to hold charges accumulated in the pixel electrode even when a liquid crystal composition having a specific resistance lower than that of the conventional one is used. Furthermore, since it is possible to suppress the leakage of the charge accumulated in the pixel electrode within one vertical scanning period, it is easy to suppress the voltage fluctuation of the pixel electrode sufficiently small.

  In addition, since the electric field tends to concentrate on the liquid crystal composition layer, a horizontal electric field can be efficiently applied to the liquid crystal composition layer, and the electric field component in the direction perpendicular to the substrate interface generated in the vicinity of the pixel electrode is compared with the horizontal electric field component. It becomes possible to keep it small.

  As described above, according to the present invention, the specific resistance of the liquid crystal composition may be lower than that of the related art, so that the degree of freedom in selecting the liquid crystal composition and the alignment film material is expanded. Therefore, if it has a specific resistance sufficient to hold the charge accumulated in the pixel electrode, it has a low optical threshold voltage, an appropriate magnitude of birefringence, etc., and is hardly contaminated by impurities. The liquid crystal composition can be used. In addition, even with an alignment film material that can easily reduce the specific resistance of the liquid crystal composition layer, an alignment film that exhibits an appropriate pretilt angle and hardly retains direct current charge can be used. For this reason, it is possible to prevent image quality deterioration such as display unevenness and afterimage.

  In addition, since the strip-shaped pixel electrode having a large distance between the electrodes has a simple shape as compared with the comb-like electrode pair, the light use efficiency can be improved. For this reason, the brightness of the liquid crystal display device can be improved.

  Furthermore, since a lateral electric field can be efficiently applied to the liquid crystal composition layer, the electric field component in the direction perpendicular to the substrate interface generated in the vicinity of the pixel electrode can be suppressed to be smaller than the lateral electric field component. For this reason, light leakage due to the rise of liquid crystal molecules in this portion is reduced, and the contrast ratio viewed from an oblique direction can be improved.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1A is a part of a plan view of an active matrix type liquid crystal display device in this embodiment. 1B is a cross-sectional view taken along the line AA ′ of FIG. 1A, and FIG. 1C is a cross-sectional view taken along the line BB ′ of FIG. Two glass substrates whose surfaces were polished were used as the substrates. As shown in FIG. 1A, scanning wirings 10 are arranged in parallel to each other on one substrate 31 to form a gate insulating film 13 made of silicon nitride and a channel layer 16 made of amorphous silicon with a film thickness of about 300 nm. The strip-shaped first pixel electrode 1 and the signal wiring 11 are both arranged in a direction intersecting with the scanning wiring 10. Thereby, a thin film transistor which is an active element is formed in the vicinity of each intersection of the scanning wiring 10 and the signal wiring 11. The other pixel electrode to be paired with the first pixel electrode 1 is connected between adjacent pixels, and formed as a striped second pixel electrode 2 on the other substrate 32 as shown in FIG. 1B. did. The second pixel electrode has substantially the same function as the common electrode in the conventional active matrix type liquid crystal display device. Thereby, an electric field 7 is applied to the liquid crystal composition layer 50 between the first pixel electrode 1 and the second pixel electrode 2, and a lateral electric field method in which the direction is substantially parallel to the substrate interface can be realized. Since the paired pixel electrodes 1 and 2 have a simpler shape than the conventional comb-like electrode pair, the light utilization efficiency is as follows. When the pixel pitch is 80 μm in the horizontal direction (that is, the interval between the common electrodes 2) and 240 μm in the vertical direction (that is, the interval between the scanning wirings 10), the dimensions of each part are set to the width of the first pixel electrode 1 (the length of the short side). ) Is 4 μm, the width (short side length) of the common electrode 2 is 12 μm, and the distance between the first pixel electrode 1 and the second pixel electrode 2 is 23 μm. The length of the short side of each pixel electrode 2 could be made shorter than the distance between them. At this time, if the light use efficiency is defined as the effective display area in the pixel area,
It becomes 50.3%. Therefore, the transmittance of the active matrix liquid crystal display device according to this example was 8.4%. As shown in FIG. 1C, the capacitor element 12 was formed to have a structure in which the first pixel electrode 1 was extended by 27 μm on the scanning wiring 10 and the gate insulating film 13 was sandwiched therebetween. Therefore, the capacitance of the capacitive element 12 is about 21.4 fF.

Further, transparent organic polymers 14 and 15 made of an epoxy resin were laminated on the surface as a protective film, and an alignment film 4 made of a polyimide resin was laminated. The alignment film 4 on each substrate is rubbed so that the pretilt angle is about 0.5 degrees, the rubbing direction 8 on the interface between both substrates is substantially antiparallel to each other, and the angle formed with the applied electric field direction 7 is 85 degrees. Treated. A nematic liquid crystal composition 50 having a positive dielectric anisotropy and a value of 4.5 between both substrates and a birefringence of 0.072 (589 nm, 20 ° C.) was sandwiched. The gap was 4.5 μm when the liquid crystal was sealed. As a result, the electrostatic capacitance between the first pixel electrode 1 and the second pixel electrode 2 was about 2.14 fF. A polarizing plate 6 is disposed outside one substrate so that its polarization transmission axis is substantially parallel to the rubbing direction 8, and a polarizing plate 6 is disposed outside the other substrate so as to be orthogonal thereto. Thereby, a normally closed characteristic is obtained. A scanning wiring driving LSI and a signal wiring driving LSI (not shown) were connected to each scanning wiring 10 and each signal wiring 11, respectively.
The electric charge accumulated in the first pixel electrode 1 is accumulated in about 23.5 fF, which is a capacitance obtained by connecting the capacitance between the first pixel electrode 1 and the second pixel electrode 2 and the capacitive element 12 in parallel. Thus, even if the specific resistance of the liquid crystal composition 50 is 5 × 10 ¹⁰ Ωcm, the voltage fluctuation of the first pixel electrode 1 can be suppressed. For this reason, image quality deterioration could be prevented.

The liquid crystal composition 50 used in this example has a specific dielectric constant of 6.7 and a specific resistance of 5 × 10 ¹⁰ Ωcm, and silicon nitride used as an insulator constituting the capacitor 12 has a relative dielectric constant. 6.7, specific resistance 5 × 10 ¹⁶ Ωcm. That is, the specific resistance of the liquid crystal composition 50 and the insulator constituting the capacitive element 12 is 10 ¹⁰ Ωcm or more, and the product of the dielectric constant and specific resistance of silicon nitride is about 3 × 10 ⁴ seconds. The product of dielectric constant and specific resistance is greater than about 0.03 seconds. Further, one vertical scanning period in the driving signal output from the scanning wiring driving LSI is about 16.6 ms in a normal liquid crystal display device, which is much smaller than about 3 × 10 ⁴ seconds. For this reason, it is possible to take a sufficiently large time constant for the charge accumulated in the first pixel electrode 1 to leak, and it becomes easy to suppress the voltage fluctuation of the first pixel electrode 1 to be sufficiently small. The liquid crystal composition 50 used in this example has a characteristic that it is not easily contaminated by impurities, and the alignment film 4 used in this example has a characteristic that no DC charge remains. Therefore, image quality deterioration such as display unevenness and afterimages can be prevented.

  Further, the alignment film 4 used in this example has a value of a relative dielectric constant of 3.4. That is, the alignment film 4, which is a nonconductive member in contact with the liquid crystal composition layer 50, has a relative dielectric constant smaller than that of the liquid crystal composition layer 50. According to the theory of electromagnetism, the electric field tends to concentrate on a portion having a high dielectric constant, so that the electric field tends to concentrate on the liquid crystal composition layer 50 rather than the alignment film 4. Further, since the electric field has a property of entering and exiting in a direction perpendicular to the electrode surface, a vertical electric field component in a direction perpendicular to the substrate interface is generated in the vicinity of the surfaces of the first pixel electrode 1 and the second pixel electrode 2. . However, the electric field bends between the first pixel electrode 1 and the second pixel electrode 2 so as to maintain the continuity, thereby forming a lateral electric field. In this embodiment, the lengths of the short sides of the first pixel electrode 1 and the second pixel electrode 2 are made shorter than the distance between the first pixel electrode 1 and the second pixel electrode 2, thereby The region of the transverse electric field component can be made larger than the region of the electric field component. For these reasons, the electric field tends to concentrate on the liquid crystal composition layer 50, and a lateral electric field can be efficiently applied to the liquid crystal composition layer 50, which is generated in the vicinity of the first pixel electrode 1 and the second pixel electrode 2. The electric field component in the direction perpendicular to the substrate interface can be suppressed smaller than the lateral electric field component 7. Therefore, since liquid crystal molecules are prevented from rising in the vicinity of the first pixel electrode 1 and the second pixel electrode 2, light leakage due to this can be prevented, and the contrast ratio viewed from an oblique direction is 100 or more. became.

  In this embodiment, a glass substrate is used. However, a transparent plastic substrate may be used, and either one of the substrates may be opaque such as a silicon substrate. Further, the shape of each wiring is not limited to the shape shown in FIG. Further, as the gate insulating film, not only silicon nitride but also an insulator such as silicon oxide, aluminum oxide, tantalum oxide, and titanium oxide may be used, or a laminate thereof. Further, in that case, the dielectric constant and specific resistance of the member used may satisfy the requirements of the present invention even if they are not the numerical values described in this embodiment. The channel layer may be made of not only amorphous silicon but also a semiconductor such as polycrystalline silicon or cadmium selenide, and the number of thin film transistors serving as active elements may be plural. Further, the dimensions and distances of the respective electrodes do not necessarily need to adopt the values of this embodiment, and the dimensions and distances may be changed according to the pixel pitch and screen size of the active matrix liquid crystal display device. Further, the protective film does not necessarily need to be a transparent organic polymer made of an epoxy resin, and the alignment film does not necessarily need to be a polyimide resin, and the dielectric constant and characteristics of these members satisfy the requirements of the present invention. It only has to satisfy. Further, the pretilt angle and rubbing angle of the alignment film may not be the numerical values described in this embodiment, and the protective film may also serve as the alignment film depending on the member. Further, even if the liquid crystal composition does not have the dielectric anisotropy, birefringence, specific resistance, or specific dielectric constant described in the present example, it is sufficient that the specific resistance or dielectric constant satisfies the requirements of the present invention. . Furthermore, the alignment of the liquid crystal composition molecules may be homogeneous alignment, 90 ° twist alignment or homeotropic alignment, and may be a TN mode, GH mode, ECB mode or the like. Further, the gap may be changed so that desired characteristics can be obtained. Further, the angle at which the polarizing plate is disposed can be changed according to the rubbing angle and the orientation of the liquid crystal composition molecules. One vertical scanning period is not limited to about 16.6 ms, and may be changed within a range that satisfies the requirements of the present invention. Thus, this example does not completely limit the present invention.

[Comparative Example 1]
An active matrix liquid crystal display device using a twisted nematic (TN) system, which is a conventional vertical electric field system, is used as a first comparative example. As shown in FIG. 4, in this system, transparent pixel electrodes 1 are arranged in a matrix on the substrate 31 side on which active elements are formed, and a common electrode 2 ′ covering the entire display area is formed on the surface of the substrate 32 facing the transparent pixel electrodes 1. Forming. As the material for the nematic liquid crystal composition 50 and the alignment film 4, the same members as those in Example 1 were used, the gap was 7.3 μm, and the twist angle of the liquid crystal molecules was 90 degrees.

  Since the specific resistance of the liquid crystal composition 50 used in this comparative example is 5 × 10 10 Ωcm, the specific resistance is low for use in a vertical electric field type active matrix liquid crystal display device. For this reason, the charge accumulated in the pixel electrode 1 is likely to leak, making it impossible to suppress the voltage fluctuation of the pixel electrode 1 to be small, and image quality degradation has occurred. In addition, since the pretilt angle of the alignment film 4 used in this comparative example is about 0.5 degrees, alignment defects such as reverse tilt and reverse twist of the liquid crystal molecules are present in the part where the surface of the substrates 31 and 32 has a gap structure. A domain occurred. Due to this light leakage, the contrast ratio as viewed from the front as well as in the oblique direction also decreased to 10 or less.

  As described above, the liquid crystal composition and the alignment film material which cannot be used in the conventional TN type active matrix liquid crystal display device can be sufficiently used in Example 1 according to the present invention. The degree of freedom of selection increases.

[Comparative Example 2]
A horizontal electric field type active matrix liquid crystal display device using a conventional comb-like electrode pair as shown in FIG. 5 is used as a second comparative example. This comparative example is the same as Example 1 except that the pixel electrode is a comb-like electrode pair and no capacitive element is formed. In this method, it was impossible to make the minimum dimension 4 μm or less from the viewpoint of electrode processing accuracy. For this reason, if the width (short side length) of the portion corresponding to the comb teeth of the comb-like pixel electrodes 1 and 2 is set equal to the interval between the comb teeth (the distance between the paired electrodes), the use of light The efficiency decreased to 15.2%, and the transmittance of the active matrix type liquid crystal display device of this comparative example was 2.5%. In addition, the electric field component in the direction perpendicular to the substrate interface generated in the vicinity of the comb-like pixel electrodes 1 and 2 cannot be suppressed to be smaller than the lateral electric field component. For this reason, the contrast ratio seen from the diagonal direction fell to 10 or less. In addition, since no capacitive element is provided in parallel with the comb-like pixel electrodes 1 and 2, it is impossible to suppress voltage fluctuations of the comb-like pixel electrodes 1 and 2, and display unevenness occurs.

  As described above, when the conventional comb-like electrode pair is used, the light use efficiency is lowered and the brightness is lowered as compared with the first embodiment according to the present invention. Unevenness occurred and the contrast ratio viewed from an oblique direction decreased.

[Comparative Example 3]
This comparative example is the same as Example 1 except that the specific resistance of the insulator constituting the capacitive element is as low as 5 × 10 ⁹ Ωcm. In this case, the product of the specific resistance and the dielectric constant of the insulator constituting the capacitive element 12 is about 0.003 seconds (= 3 ms), and the product of the specific resistance and the dielectric constant of the liquid crystal composition layer 50 is 0.03 seconds. small. In a normal liquid crystal display device, one vertical scanning period in the drive signal output from the scanning wiring driving LSI is about 16.6 ms. If this one vertical scanning period is set to be smaller than about 3 ms, the scanning wiring driving LSI and It is necessary to operate the signal line driving LSI at a speed five times higher than usual, which causes a problem that a very expensive LSI must be used. On the contrary, if one vertical scanning period in the drive signal output from the scanning wiring driving LSI is set to about 16.6 ms, the comparative example includes the capacitive element 12 in parallel with the first pixel electrode 1. Even in such a case, it is impossible to take a sufficiently large time constant for the charge accumulated in the first pixel electrode 1 to leak. For this reason, it is impossible to suppress the voltage fluctuation of the first pixel electrode 1 sufficiently small, and display unevenness occurs.

[Comparative Example 4]
This comparative example is the same as Example 1 except that the specific resistance of the liquid crystal composition layer is as low as 5 × 10 ⁹ Ωcm. In this case, even if the capacitor 12 is provided in parallel with the first pixel electrode 1, the resistance of the liquid crystal layer is small, so that the time constant at which the charge accumulated in the first pixel electrode 1 leaks is sufficiently large. It becomes impossible to take. For this reason, it is impossible to suppress the voltage fluctuation of the first pixel electrode 1 sufficiently small, and display unevenness occurs.

  The configuration of the present embodiment is the same as that of the first embodiment except for the following requirements.

  FIG. 6A is a part of a plan view of the active matrix liquid crystal display device in this embodiment. 6B is a cross-sectional view taken along the line AA ′ in FIG. 6A, and FIG. 6C is a cross-sectional view taken along the line BB ′ in FIG. As shown in FIG. 6C, the capacitor element 12 having the structure in which the gate insulating film 13 made of silicon nitride is sandwiched between the pixel electrode 1 and the scanning wiring 10 in the first embodiment is used. The structure is such that the liquid crystal composition layer 50 is sandwiched between the pixel electrodes 2. In the present embodiment, the capacitance of the capacitive element 12 can be completely connected in parallel with the capacitance between the first pixel electrode 1 and the second pixel electrode 2. The influence of the fluctuation does not reach the first pixel electrode 1. For this reason, voltage fluctuations of the first pixel electrode 1 can be further suppressed, and display unevenness does not occur.

  Even in the active matrix liquid crystal display device of this example, image quality did not deteriorate, and the same effect as in Example 1 was obtained.

  The configuration of the present embodiment is the same as that of the first embodiment except for the following requirements.

  All electrode groups arranged on both of the pair of substrates were formed on one substrate. FIG. 7A is a part of a plan view of the active matrix liquid crystal display device in this embodiment. 7B is a cross-sectional view taken along the line AA ′ in FIG. 7A, and FIG. 7C is a cross-sectional view taken along the line BB ′ in FIG. The second pixel electrode 2 was formed on the substrate 31 on which the active element was formed. In general, the alignment accuracy of a photomask is significantly higher than the alignment accuracy between two opposing substrates. In this embodiment, since all of the four types of electrode groups are formed on one substrate 31, the alignment between the first pixel electrode 1 and the second pixel electrode 2 is performed only by the photomask. Compared to the cases of Examples 1 and 2, the misalignment between both electrodes is suppressed to be small. As a result, in this embodiment, variation in capacitance between the first pixel electrode 1 and the second pixel electrode 2 in one active matrix type liquid crystal display device can be suppressed, and display unevenness is generated at all. In addition, no conductive member is provided on the opposing substrate 32. Therefore, in the configuration of this embodiment, even if conductive foreign matter is mixed in during the manufacturing process of the active matrix type liquid crystal display device, a short circuit between the electrode on one substrate and the electrode on the other substrate is possible. There was no property, and no defect was caused by this.

  Also in this example, image quality degradation did not occur, and the same effect as in Example 1 was obtained.

The configuration of the present embodiment is the same as that of the third embodiment except for the following requirements.
FIG. 8A is a part of a plan view of the active matrix liquid crystal display device in this embodiment. 8B is a cross-sectional view taken along the line AA ′ of FIG. 8A, and FIG. 8C is a cross-sectional view taken along the line BB ′ of FIG. 8A. An active element is formed and connected to the second pixel electrode in the third embodiment by providing the channel layer 16 and the common wiring 22 made of amorphous silicon, and the first pixel electrode 1 and the second pixel electrode 2 are connected. The electric field 7 is applied. That is, in this embodiment, no electrode corresponding to the common electrode in the conventional active matrix type liquid crystal display device is provided. The paired pixel electrodes 1 and 2 are connected to the active elements, respectively, but are driven by the common scanning wiring 10, so that they are common between the first pixel electrode 1 and the signal wiring 11 and the second pixel electrode 2. The wiring 22 performs the same on / off switching operation. Therefore, the first pixel electrode 1 and the second pixel electrode 2, the signal wiring 11 and the common wiring 22 are substantially equivalent, and the image signal is transmitted through the signal wiring 11, the common wiring 22, or the signal wiring. 11 and common wiring 22 can also be supplied.

  In this embodiment, since the first pixel electrode 1 and the second pixel electrode 2 are completely equivalent as viewed from the liquid crystal composition layer, the second pixel electrode 2 is also shown in FIG. 8C. The capacitor element 12 was formed in parallel connection so that the gate insulating film 13 was sandwiched between the scanning wirings 10. For this reason, the size of the capacitive element 12 could be halved compared to the first and third embodiments. Therefore, the light utilization efficiency was 55.1%, which can be further improved as compared with Example 3. The transmittance of the active matrix liquid crystal display device according to this example was 9.2%.

  In this example, image quality degradation did not occur, and the same effect as in Example 3 was obtained.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an explanatory diagram of an active matrix liquid crystal display device according to a first embodiment of the present invention. FIG. 5 shows operation of liquid crystal molecules in a horizontal electric field liquid crystal display device. FIG. 6 is a diagram illustrating electro-optical characteristics in a horizontal electric field liquid crystal display device. FIG. 10 is an explanatory diagram of an active matrix liquid crystal display device of Comparative Example 1; Explanatory drawing of the active matrix type liquid crystal display device of the comparative example 2. FIG. Explanatory drawing of the active matrix type liquid crystal display device of Example 2 of this invention. Explanatory drawing of the active matrix type liquid crystal display device of Example 3 of this invention. Explanatory drawing of the active matrix type liquid crystal display device of Example 4 of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... 1st pixel electrode, 2 ... 2nd pixel electrode, 2 '... Common electrode, 3 ... Substrate, 4 ... Alignment film, 5 ... Liquid crystal molecule, 6 ... Polarizing plate, 7 ... Direction of applied electric field, 8 ... Liquid crystal molecule long axis alignment direction (rubbing direction) on the interface, 10 ... scanning wiring, 11 ... signal wiring, 12 ... capacitor element, 13 ... gate insulating film, 14, 15 ... organic polymer as protective film, 16 ... channel layer , 17 ... color filter, 18 ... light shielding layer, 22 ... common wiring, 31, 32 ... substrate, 50 ... liquid crystal composition layer.

Claims (4)

First and second substrates, a liquid crystal composition layer sandwiched between the substrates, a plurality of scanning wirings and signal wirings disposed on the first substrate, and a plurality disposed on the first substrate And a plurality of stripe-shaped second pixel electrodes disposed on the second substrate,
An electric field is applied to the liquid crystal composition layer between the first pixel electrode and the second pixel electrode,
The second pixel electrode is disposed in a space between the adjacent first pixel electrodes;
The first pixel electrode is disposed in a space between the adjacent second pixel electrodes;
The second pixel electrode is formed on the organic polymer, wherein the first pixel electrode is formed on a silicon nitride, and the second image Motoden poles are formed thicker than the first pixel electrode A liquid crystal display device.
  The liquid crystal display device according to claim 1, wherein the display device has a normally closed characteristic.   2. The liquid crystal display device according to claim 1, wherein a bent electric field is formed between the first pixel electrode and the second pixel electrode. 3. The liquid crystal display device according to claim 2, wherein a bent electric field is formed between the first pixel electrode and the second pixel electrode.

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