JPH06202100A - Liquid crystal display element - Google Patents

Abstract

PURPOSE:To obtain good color characteristics and gradation characteristics by a ferroelectric liquid crystal by changing an electrode area or color filter area according to cell thicknesses. CONSTITUTION:An electrode 41, an insulating film 42 and an oriented film 43 are formed as flat surfaces on one substrate 45 of a pair of the substrates 45, 45'. On the other hand, electrodes 41' are formed for respective picture elements on a member 40 having a slope on the other substrate 45' and the surface thereof is covered with an oriented film 43'. The electrode 41 on the substrate is common to the two picture elements. The cell thickness gradient is such that the cell thickness changes continuously toward the surface of the substrate from d1 to d2 and the area ratio at the respective cell thicknesses d1, (d1<=di<=d2) is standardized according to the cell thickness di in such a manner that the transmittance is equaled, there by the phenomenon of the decrease in the quantity of transmitted light by the cell thickness di is averted. Namely, the specified transmittance is maintained regardless of the cell thickness di by fluctuating the electrode area according to the cell thickness gradient.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a computer terminal,
The present invention relates to a liquid crystal display device used for a display device used in a television receiver, a word processor, a typewriter, a light valve of a projector, a viewfinder of a video camera recorder, and the like.

[0002]

2. Description of the Related Art As a liquid crystal display element, a twisted
Known types include those using nematic (TN) liquid crystals, guest-host type ones, and those using smectic (Sm) liquid crystals.

These liquid crystals are arranged between a pair of substrates, and the light transmittance changes according to the applied voltage. Therefore, the applied electric field strength varies depending on the substrate spacing, that is, the thickness of the liquid crystal layer.

A method for controlling the magnitude of the electric field strength applied to the liquid crystal layer is described in US Pat. No. 4,712,87.
It is described in detail in the specification No. 7.

According to this method, regions having different thicknesses of the liquid crystal layer are formed in the unit pixel, and even if the same applied voltage is applied, the electric field strength applied to the liquid crystal is made different depending on the region.

Such a method can be applied not only to the TN liquid crystal but also to the ferroelectric liquid crystal (FLC) and is characterized in that good gradation display can be performed.

[0007]

However, in such a display element, an image to be displayed may not be an image as designed depending on the degree of gradation.

As a result of repeated research to find out the cause, the inventors found that the intensity of light passing through the liquid crystal varies depending on the region due to the birefringence of the liquid crystal layer. It was

An object of the present invention is to solve the above-mentioned technical problems and to provide a liquid crystal display device capable of displaying an excellent image.

[0010]

Means and Action for Solving the Problems
A liquid crystal display element in which a liquid crystal is sandwiched between a pair of electrode substrates arranged to face each other, and a plurality of filters are arranged on at least one of the electrode substrates, and a pixel area is set for each type of filter corresponding to the pixel. The present invention provides a liquid crystal display device characterized by being changed.

Next, a second aspect of the present invention is a liquid crystal display device comprising a pair of electrode substrates arranged opposite to each other and sandwiching a ferroelectric liquid crystal, wherein each pixel is formed at the intersection of the upper and lower substrates. Areas and / or shapes of the color filters or electrode crossing so that three or more types of color filters are arranged on the electrodes of the color filters and the transmittance of the liquid crystal layer of the transmitted light passing through the color filters becomes constant according to the cell thickness. It is intended to provide a liquid crystal display device characterized in that the area and / or the shape of a part are changed.

A third aspect of the present invention is a liquid crystal display device in which a ferroelectric liquid crystal is sandwiched between a pair of electrode substrates arranged to face each other, each pixel being formed at the intersection of the upper and lower substrates. The unevenness is provided for each pixel on the electrode, the gradient of the cell thickness is provided within one pixel, and the area and / or the shape of the electrode crossing portion is changed according to the cell thickness to change the transmittance with respect to the input voltage. The liquid crystal display element is characterized in that the threshold distribution of the ferroelectric liquid crystal in each pixel is set so that is logarithmic.

Further, a fourth aspect of the present invention is a liquid crystal display element comprising a pair of electrode substrates arranged opposite to each other and sandwiching a ferroelectric liquid crystal, wherein each pixel is formed at the intersection of the upper and lower substrates. Concavity and convexity are provided for each pixel on the electrode to provide a cell thickness gradient within one pixel, and at least one of the electrode substrates is provided with three or more types of color filters and passes through each color filter according to the cell thickness. The present invention provides a liquid crystal display device characterized in that the area and / or shape of a color filter or the area and / or shape of an electrode intersection portion is changed so that the brightness of transmitted light becomes constant.

Further, a fifth aspect of the present invention is a liquid crystal display device comprising a pair of electrode substrates arranged opposite to each other and sandwiching a ferroelectric liquid crystal, wherein each pixel is formed at the intersection of the upper and lower substrates,
Concavity and convexity are provided for each pixel on one electrode to provide a cell thickness gradient within one pixel, and at least one type of electrode substrate is provided with three or more types of color filters to form a display unit with a plurality of pixels. The present invention provides a liquid crystal display device characterized in that the areas of the plurality of pixels are different depending on the cell thickness, and there are a portion where the area of the plurality of pixels decreases and an area where the area increases as the cell thickness increases. .

In addition, a sixth aspect of the present invention is a liquid crystal display device in which a ferroelectric liquid crystal is sandwiched between a pair of electrode substrates arranged to face each other, each pixel being formed at the intersection of the upper and lower substrates. Unevenness is provided on each electrode of each pixel to provide a cell thickness gradient within one pixel, and at least one of the electrode substrates is provided with three or more kinds of color filters to form a display unit with a plurality of pixels. An object of the present invention is to provide a liquid crystal display device characterized in that the areas of the plurality of pixels are different depending on the cell thickness, and the total area of the plurality of pixels is substantially the same regardless of the cell thickness.

In a preferred embodiment of the present invention, a shift in transmittance within a pixel in halftone display is compensated by the area of a region exhibiting the transmittance within the pixel.

In the pixel, a portion where portions functioning as electrodes, which are usually provided on a pair of electrode substrates, overlap each other, a filter provided if necessary, or a light shielding member similarly provided if necessary, etc. It is specified by the combination with.

The embodiments of the present invention will be described below with reference to specific examples.

In the method of changing the thickness of the liquid crystal layer in the pixel to perform gradation display, the intensity of light passing through the liquid crystal layer is different due to the birefringence of the liquid crystal layer. In general,
Transmission intensity ratio R (intensity ratio between incident light and transmitted light; transmittance)
Is expressed by the following equation by the wavelength λ of light, the thickness d of the liquid crystal layer, and the refractive index anisotropy Δn of the liquid crystal layer.

R∝sin ² (πΔnd / λ) Therefore, depending on the thickness of the liquid crystal layer, that is, the cell thickness d, which wavelength of incident light is likely to be transmitted is different.

FIG. 1 is a graph showing the spectral characteristics of the liquid crystal cell, color filter, optical filter, and light source.

In FIGS. 1A and 1B, FIGS. 1A and 1B show spectral characteristics of transmitted light of a liquid crystal cell having a liquid crystal layer thickness (cell thickness) of 1.0 μm and 1.5 μm. The refractive index anisotropy Δn of the ferroelectric liquid crystal is about 0.15 to 0.19. Figure 1
In (A), the transmittance is high near the wavelength of 400 nm and is low near the wavelength of 650 nm. Conversely, Figure 1
In (B), the transmittance in the vicinity of 400 nm is 650.
It is lower than the transmittance in the vicinity of nm.

400,650 nm near 540 nm
To a lesser extent, there are differences.

The ratio of the spectral intensities, eg (A), (B)
R (650nm), G (540nm), B at
The intensity ratio of the wavelength of (400 nm) is set to R (650 n) of (A).
The following table shows the values when m) is standardized as 1.

[0025]

[Table 1]

When the areas of the cell thick portions of (A) and (B) are set as shown in the following table, the transmittance of the cell thick portion can be set equal for each wavelength.

[0027]

[Table 2]

FIG. 2 is a diagram showing a cross section of a liquid crystal cell used in the present invention, showing a cross section of two pixels.

On one of the pair of substrates 45, an electrode 41, an insulating film 42, and an alignment film 43 are formed as flat surfaces. On the other hand, on the other substrate 45 ', an electrode 41' is formed for each pixel on a member 40 having an inclined surface and is covered with an alignment film 43 '. Here, the electrode 41 on the upper substrate is common to the two pixels.

In the cell thickness gradient shown in FIG. 2, the cell thickness is d ₁
Cell thickness but each has changed continuously toward the surface of the substrate to d ₂ from d _i, the cell thickness to the area ratio, the transmittance is equal to the _{(d 1 <d i <d} 2) By normalizing according to d _i , it is possible to avoid the phenomenon that the amount of transmitted light differs depending on the cell thickness.

FIG. 3 is a schematic diagram showing the cell thickness and the pixel shape. Conventionally, the pixel has a square shape like a broken line, but in the present invention, the width w of the pixel changes depending on the gradient direction of the cell thickness, that is, the L direction. In this way, each pixel is adjusted to increase the amount of transmitted light by increasing the width w in a portion having a small transmittance per unit area, and reduce the amount of transmitted light in a portion having a large transmittance per unit area by decreasing the width w. Has been done.

In an actual liquid crystal cell, there are several methods for changing the area of a pixel.

FIG. 4 is a schematic diagram showing a typical example thereof, and two pixels are taken as an example for easy understanding, but in reality, a large display screen is made up of 100 or more pixels. .

FIG. 4A shows a configuration in which the shape of one electrode is cut out based on the above-mentioned design concept. Of course, such a notch may be formed in the electrode 41 'or both electrodes 41, 41'.

In FIG. 4B, the electrodes 41 and 41 'are not cut out, but the shape of the filter (FT) to be superimposed on the pixel portion is cut out based on the above-mentioned design concept.

If necessary, a light blocking member BM may be provided in the cutout portion. In particular, as will be seen in Examples described later, if the notch portions of other pixels are appropriately combined to increase the pixel arrangement density, the light shielding member BM can be eliminated.

As the liquid crystal used in the present invention, there are known TN liquid crystal, ferroelectric liquid crystal, antiferroelectric liquid crystal and the like. For example, a nematic liquid crystal material such as Schiff base type alkoxybenzylidene alkylaniline, alkylalkoxyazobenzene, phenylbenzoate type liquid crystal, cyanobiphenyl type liquid crystal, cyclohexylcarboxylic acid ester type liquid crystal, 2,3-difluorophenylene type liquid crystal, D
Examples include smectic liquid crystal materials such as OBAMBC and HOBACPC.

As the electrode used in the present invention, a transparent conductive film of tin oxide, indium oxide, indium tin oxide or the like is preferably used, and if necessary, a metal conductive film is partially arranged to reduce the resistance. Is configured.

A member for forming irregularities for producing a difference in cell thickness within a pixel is made of a resin or an inorganic material that transmits light.

When a filter is provided in the present invention, US Pat. Nos. 4,712,874 and 4,80 are used.
The filters disclosed in the specifications such as 2,743, 4,786,148 and the like can be used.

When gradation display is performed, the driving method disclosed in US Pat. Nos. 4,747,671, 4,796,980 and 4,712,877 is used. be able to.

Next, an example in which a liquid crystal cell is constructed by using a ferroelectric liquid crystal as a liquid crystal using the pixel having the above-mentioned structure will be described.

Display devices using ferroelectric liquid crystal (FLC) are disclosed in US Pat. Nos. 4,639,089 and 4,439.
No. 655,561 and No. 4,681,404. In the present invention, as described in these US patents, a transparent electrode was formed and subjected to orientation treatment.
1 to 3 glass substrates so that the transparent electrode is the inner surface
A liquid crystal cell with a cell gap of about μm
A liquid crystal in which a ferroelectric liquid crystal is injected is used.

The display device using the ferroelectric liquid crystal has two features. One is that since the ferroelectric liquid crystal has spontaneous polarization, the external electric field and the coupling force of the spontaneous polarization can be used for switching, and the other is that the long-axis direction of the ferroelectric liquid crystal molecules is spontaneously polarized. It is possible to perform switching depending on the polarity of the external electrode because it has a one-to-one correspondence with the direction of.

Since the ferroelectric liquid crystal is generally a chiral smectic liquid crystal (SmC ^* , SmH ^* ), the long axis of the liquid crystal molecules exhibits twisted alignment in the bulk state. By injecting the liquid crystal into the cell, the twist of the long axis of the liquid crystal molecule can be eliminated. For this phenomenon, see p213 to p234.
N. A. CLARK et al. , MCLC, 19
83, Vol 94. Etc.

Ferroelectric liquid crystal is used mainly as a binary (bright / dark) display element by setting two stable states to a light transmitting state and a light blocking state, but multivalue display, that is, halftone display is also used. It is possible. One of the halftone display methods is to realize an intermediate light transmission state by controlling the area ratio of the bistable state (light transmission state or light blocking state) in the pixel. The above gradation display method (hereinafter referred to as area modulation method) will be described in detail.

FIG. 5 is a diagram schematically showing the relationship between the switching pulse voltage V of the ferroelectric liquid crystal element and the amount of transmitted light I. A single-polarity single-shot event occurs in a pixel that was initially in a completely light-blocking (dark) state. 6 is a graph in which the amount I of transmitted light after applying a pulse is plotted as a function of the voltage V of a single pulse. When the pulse voltage V is less than the threshold value V _th (V <V _th ), the amount of transmitted light does not change, and the transmission state after pulse application is as shown in FIG. 6 (a) showing the state before application as shown in FIG. 6 (b). does not change. When the pulse voltage V exceeds the threshold value (V _th <V), a part of the pixel transitions to the other stable state, that is, the light transmission state shown in FIG. 6C, and shows an intermediate amount of transmitted light as a whole. The pulse voltage V further increases and exceeds the saturation value V _sat (V _sat <
At V), all the pixels are in a light transmitting state as shown in FIG. 6D, and thus the light amount reaches a certain value (saturates).

That is, in the area gradation method, the voltage applied to the pixel is controlled so that the pulse voltage V satisfies V _th <V <V _sat , and the halftone corresponding to the pulse voltage V is displayed. is there.

However, since the voltage-transmitted light amount relationship shown in FIG. 5 depends on the cell thickness and the temperature, if there is a cell thickness distribution or a temperature distribution in the display panel, it is not possible to apply a pulse voltage having a constant voltage. On the other hand, different gradations may be displayed depending on the location of the display panel.

FIG. 7 is a diagram for explaining this, and is a graph showing the relationship between the pulse voltage V and the amount of transmitted light I, as in FIG. 5, but the relationship between the two at different temperatures, that is, A curve H showing a relationship at a high temperature and a curve L showing a relationship at a low temperature are shown. In general, it is not uncommon for a display having a large display size to have a temperature distribution within the same panel. Therefore, even if the halftone is displayed by a certain driving voltage V _ap , the halftone level in the same panel varies over the range from I ₁ to I ₂ as shown in FIG. 7, resulting in a uniform gradation display state. May not be able to get.

In order to solve the above problems, a driving method (hereinafter referred to as a 4-pulse method) previously proposed by the present applicant in Japanese Patent Application Laid-Open No. 4-218022 has been devised. As shown in FIGS. 8 and 9 of the present application, the “four-pulse method” is a method in which a plurality of pulses (in FIG. 8) are provided for all pixels on the same scanning line in one panel and having different thresholds. By applying the pulses A, B, C, D), finally, as shown in FIG. 9, an equal light transmission amount is obtained. Note that T ₁ , T ₂ , and T ₃ in FIG. 8 are selection times set in synchronization with the pulses (B), (C), and (D). Further, in FIG. 9, Q ₀ , Q ₀ ′, Q ₁ ,
Q ₂ and Q ₃ indicate the gradation level of the pixel, and Q ₀ is black (0
%), Q ₀ 'is white (100%). The pixels in FIG. 9 have a threshold distribution in the pixels, and the threshold increases from the left side to the right side (from V _th to V _sat ) in the figure.

Further, the present applicant has proposed a driving method called a pixel shift method prior to the present invention. The pixel shift method is a method in which different scanning signals are simultaneously input to a plurality of scanning signal lines and selected to create a distribution of electric field intensity across a plurality of scanning lines and display a gradation.

According to this method, the fluctuation of the threshold value due to the temperature change can be absorbed by shifting the writing area over a plurality of scanning lines.

Such a driving method (4 pulse method, pixel shift method) is effective when there is a uniform threshold distribution in the pixel, and driving in a cell having a cell thickness gradient as shown in FIG. Was suitable for.

As described above, in the method of performing gradation display by changing the thickness of the liquid crystal layer in the pixel, the intensity of light passing through the liquid crystal layer is different due to the birefringence of the liquid crystal layer. There is a problem. In general, the transmission intensity ratio R (intensity ratio between incident light and transmitted light; transmittance) is expressed by the following equation based on the wavelength λ of light, the thickness d of the liquid crystal layer, and the refractive index anisotropy Δn of the liquid crystal layer. .

R∝sin ² (πΔnd / λ) Therefore, depending on the thickness of the liquid crystal layer, that is, the cell thickness d, which wavelength of incident light is likely to be transmitted is different.

This means that even if the four-pulse method or the pixel shift method described above is used when a gradation of the cell thickness is formed in a pixel and the gradation is displayed, the central transmission wavelength at the same gradation is changed due to the temperature variation. Are different from each other, which causes coloring due to temperature.

When a color display is performed using a color filter, the transmittance of the wavelengths of each of the three primary colors varies depending on the temperature, so that the colors displayed by combining them also differ. In this way, the tristimulus values (eg, R, G, B) that make up not only the lightness depending on the temperature but also the color
However, the color balance is lost and the quality of the color display device is deteriorated.

The means taken by the present inventors to solve the above problems is to keep the transmittance constant regardless of the cell thickness by changing the electrode area according to the cell thickness gradient. is there. When color display is not performed, good gradation display can be performed by making the electrode area large at a thin cell thickness and small at a thick cell thickness. Further, when it is required to control the wavelength characteristics of transmitted light even when performing color display or during black-and-white display, it is necessary to control the transmittance corresponding to the cell thickness for each color filter. For example, in the case where the area of the color filter is changed by the cell thickness, the red (R) and green (G) filter areas are made larger at the thin cell thickness than the thick one, and conversely the blue (B) Increase the area in thick places and decrease the area in thin places. Then, by controlling the overall size of each filter so that the transmittance of the liquid crystal layer at each gradation level becomes equal, it is possible to reduce color balance disruption depending on the gradation level. Furthermore, even when a temperature compensation method such as a 4-pulse method or a pixel shift method is used, a color change (especially R,
The composite color of G and B) can be reduced.

It is optimum to change both the color filter and the electrode for such an effect. However, even by controlling only the electrode or only the color filter, good gradation display can be achieved depending on the setting of the light-shielding portion. You can

[0061]

【Example】

(Example 1) In the first example, the amount of transmitted light was compensated for in a cell having a cell thickness change as shown in FIG.

In this embodiment, d ₁ in FIG. 2 is the cell thickness of the portion where the electrode gap is the shortest, d ₂ is the gap where the electrode gap is the maximum, and L is the width of one pixel. The electrode 41 ′ in the direction perpendicular to the paper surface is used as the scanning electrode, and the scanning electrode 4
An uneven shape was formed by the member 40 on the 1'side.

First, a UV curable resin was formed in a thin layer on a glass substrate, a mold was pressed against the substrate, and UV exposure was performed to form an uneven shape having an inclined surface.

An ITO film (sheet resistance: about 30 Ω □) was formed on the uneven substrate thus formed and the other substrate by a sputtering method and patterned into an electrode shape. Next, a rubbing treatment was performed on the electrodes of both substrates to form an alignment film of Hitachi Chemical Co., Ltd. (LQ-1802) with a film thickness of about 400 Å. The rubbing treatment was performed in a direction substantially orthogonal to the ridges of the uneven substrate, in a direction common to the upper and lower substrates. In this way, the two substrates were opposed to each other, the ends except the injection port were sealed, and liquid crystal was injected between the two substrates to manufacture a liquid crystal cell exhibiting a smectic phase.

In this cell, d ₁ = 1.0 μm and d ₂ =
It was set to 1.40 μm and L = 200 μm.

Table 3 shows characteristics such as phase transition of the liquid crystal used in this example. This liquid crystal had Δn = 0.18.

[0067]

[Table 3]

FIG. 10A shows one pixel in FIG. 2 in which the cell thickness d ₁ = 1.0 μm in one pixel.
To d ₂ = 1.4 μm continuously changing. Table 4 shows the transmittance of each cell thick portion at the central wavelength (610 nm, 545 nm, 435 nm) when a three-wavelength tube is used as a light source that emits light having the spectral characteristics shown in FIG. showed that.

The transmittance of Table 4 is based on the transmittance of light having a wavelength of 610 nm at a cell thickness of 0.8 μm (1
It is said to be).

Since the numbers in Table 4 represent the transmittance per unit area, in the places where the numbers are different, the amount of transmitted light is different when the pixel area is the same. In order to solve this problem, when the pixel area which gives the same amount of transmitted light is obtained, the value in parentheses in Table 4 is obtained. This number is the reciprocal of the transmittance determined by the wavelength and the cell thickness, and in order to obtain the amount of transmitted light of 1 (assuming a certain reference amount is 1), the pixel area may be configured by the ratio of this reciprocal. It will be.

[0071]

[Table 4]

In the cell having the cell thickness gradient shown in FIG. 10A, the length L in the changing direction of the cell thickness is fixed as shown in FIG. By making it variable, the area of the corresponding cell thickness portion can be changed.

In this embodiment, as shown in FIG.
As shown in (c) and (d), the cell thickness d ₁ = 1.0 μ
The electrode width w at m was set to 142 μm for the electrode with the red color filter, 124 μm for the electrode with the green color filter, and 98 μm for the electrode with the blue color filter. The central wavelength of the color filter used here is in agreement with the three wavelengths shown in Table 4. That is, the center wavelength of red is 610 nm, the center wavelength of green is 545 nm, and the center wavelength of blue is 435 n.
m. In this case, the ratio of the electrode width of each color is based on the ratio of the reciprocal of the transmittance shown in Table 4. In this way, when the electrode width is determined so that each cell thickness part has the area ratio in Table 4, the maximum cell thickness d ₂ = 1.4 μm is obtained. The electrode widths of the red, green, and blue electrodes are 98 μm, 92 μm, and 98 μm, respectively. That is, the electrode having a red color filter has an electrode width of 142
It varies from μm to 98 μm according to the change in cell thickness within one pixel.

In the same way for blue and green, the electrode width within one pixel changes, and it is 124 μm to 92 μm (green) and 98 μm, respectively.
It is changed from μm to 98 μm (blue).

By doing so, even if the cell thickness is different, the amount of light transmitted through the pixels becomes equal, and good color display can be achieved.

(Embodiment 2) In the second embodiment, as in the case of Embodiment 1, a cell having a change in cell thickness as shown in FIG. It was

D ₁ = 1.1 μm, d ₂ = 1.65 μm,
The other structure is the same as that of the first embodiment except that L = 200 μm.

FIG. 11 shows an embodiment. In FIG. 11, (a) shows one pixel in FIG. 2, and the cell thickness within one pixel is from d ₁ = 1.1 μm to d ₂ = 1.65 μm.
Until, it is changing continuously. Table 5 shows the center wavelength (610 nm, 545 nm) when a three-wavelength tube is used as a light source.
nm, 435 nm) is shown for each cell thickness. This transmittance is based on the transmittance of light having a wavelength of 610 nm at a cell thickness of 0.8 μm (this is set to 1). Since this number represents the transmittance per unit area, the amount of transmitted light will be different if the pixel area is the same in different places. In order to solve this problem, when the pixel area that gives the same amount of transmitted light is obtained, the value in parentheses in Table 5 is obtained. This number is the reciprocal of the transmittance determined by the wavelength and the cell thickness, and in order to obtain a transmitted light amount of 1 (assuming a certain reference amount is 1), the pixel area should be constructed with the ratio of this reciprocal. It will be good.

[0079]

[Table 5]

In the cell having the cell thickness gradient as shown in FIG. 11A, the length L in the changing direction of the cell thickness is fixed as shown in FIG. By making it variable, the area of the corresponding cell thickness portion can be changed.

In the second embodiment, (b) of FIG.
As shown in (c) and (d), the cell thickness d ₁ = 1.1 μm
The electrode width w at m was set to 126 μm for the electrode with the red color filter, 110 μm for the electrode with the green color filter, and 94 μm for the electrode with the blue color filter. The center wavelength of the color filter used here is in agreement with the three wavelengths shown in Table 5. That is, the center wavelength of red is 610 nm, the center wavelength of green is 545 nm, and the center wavelength of blue is 435 n.
m. In this case, the ratio of the electrode width of each color is based on the ratio of the reciprocal of the transmittance shown in Table 5. (Indicated as area ratio in Table 5) In this way, when the electrode width is determined so that each cell thickness portion has the area ratio in Table 5, the maximum cell thickness d ₂ =
The electrode widths of the red, green, and blue electrodes at 1.65 μm are 92 μm, 94 μm, and 130 μm, respectively. That is,
The electrode with a red color filter has an electrode width of 126 μm
To 92 μm, it changes according to the change of the cell thickness within one pixel.

In the same way for blue and green, the electrode width within one pixel changes, and 110 μm to 94 μm (green) and 94 μm, respectively.
It becomes from μm to 130 μm (blue).

The fluctuation of the cell thickness is changed from 1.1 μm to 1.65 μm.
By setting m, the electrode width changes of red and blue can be configured complementarily as shown in FIG. Cell thickness d
_{At 1} = 1.1 μm, red has an electrode width of 126 μm and blue has a width of 94 μm. Further, at d ₂ = 1.65 μm, red is 92 μm and blue is 130 μm. As shown in FIG. 12, the planar filling degree of the pixel electrodes R, G, B is improved, the total area of the pixels occupying the liquid crystal panel display surface is increased, and the aperture ratio can be increased.

In FIG. 12, the cell thickness is 1.1 μm
The decrease rate of the aperture ratio when the electrode width is changed by 1.65 μm is 2.1%, and the decrease rate of the aperture ratio when the cell thickness is changed by 1.0 μm to 1.4 μm is 10.4. %, And the aperture ratio could be greatly improved by complementarily configuring the color filter or the electrode with respect to the cell thickness.

(Third Embodiment) As a third embodiment, a specific example in which the relationship between the applied voltage (V) and the transmittance (T) is optimized by changing the electrode area is shown.

When the linear cell thickness distribution as shown in FIG. 2 is provided, the inversion area in the pixel is proportional to the applied voltage V. This will be described with reference to FIG. 13. The thin one in one pixel is set to x = 0, and x is taken in the direction in which the cell thickness increases. The width of the pixel is w, and x varies from 0 to 1. When a certain voltage is applied, x = 0 to x = x ₀ , which is the thinnest cell thickness.
The parts up to are reversed. At that time, the portion [0, x ₀ ] is white, and the portion [x ₀ , w] is black (erasure direction state).
The pixel size is wxm as shown in FIG.
Therefore, when m is constant, gradation display can be achieved at the ratio of the horizontal axis w. When x = 0, the transmittance is 0%, and x = w
Is 100%.

[0087] strength the dielectric liquid is the E _th field intensity required to reverse, when a voltage is applied V, region state reversed exceeds a threshold electric field E _th [0, x] in the following formula Represented.

[0088]

[Equation 1]

This relationship shows the linearity of T with respect to V on a linear axis for both the transmittance T and the applied voltage V.

However, it is known that when the temperature of the liquid crystal cell changes, the response speed of the liquid crystal changes logarithmically, which means that the abscissa is linear.
It shows that the slope of the linearity of the V characteristic cannot be maintained with respect to the temperature change (the T-V characteristic curve does not move in parallel on the horizontal axis). The temperature compensation method (4 pulse method, pixel shift method) for gradation display described in the conventional example requires linearity of the TV characteristic. Therefore, in order to use such a temperature compensation method, it is sufficient to plot the T-V characteristic in a straight line by plotting the abscissa logarithmically. Which is
_It can be seen from the fact that _th changes in parallel even if it changes with temperature.

[0091] _{T = AlogV + B = AlogE th} · d + B E th → E th ' as when you change _{T = AlogE th' · d +} B = AlogE th · d + Alog (E th '/ E th) + B = AlogV + C (II)

Since E _th 'is a constant term that does not depend on V, it is included in C. Relationship T-log V has a constant slope regardless of the E _th.

A TV characteristic curve is shown in FIG. 14A. In the case of a cell having a linear gradient as shown in FIG. 2, as shown by the dotted line (before correction) in the figure, It shows no linearity on the log V axis. In order to correct this to a linear characteristic as shown by the solid line (after correction) in the figure, the electrode width w in FIG. 3 is changed according to the gradient of the cell thickness.

The relationship between the input voltage shown in Table 6 and the position (x) on the pixel in FIG. 13 has a linear relationship as shown in the formula (I). The transmittance before correction is also the input voltage and position (x)
However, in order to convert this into a logarithmic relationship as shown in the formula (II), the width of each electrode is increased by the magnification in Table 6 as compared with that before correction.

[0095]

[Table 6]

It has been described in Embodiments 1 and 2 that the transmitted light amount can be equalized regardless of the cell thickness even before correction.
By further modulating the electrode width at a rate as shown in Table 6, a TV characteristic that translates on the log axis can be obtained.

In FIG. 14 (b), the shapes of the red, green and blue electrodes at that time are shown as a ratio. Further, here, the horizontal axis is taken as the voltage, but the same holds true when the gradation characteristics are grasped by the T-ΔT characteristics taking the pulse width as the pulse width.

(Embodiment 4) In this embodiment, as in Embodiment 2, in FIG. 2, d ₁ = 1.1 μm and d ₂ = 1.65.
μm and L = 200 μm. FIG. 15 shows the pixel shape of this embodiment. In FIG. 15, (a) shows one pixel in FIG. 2, and the cell thickness within one pixel is d ₁ = 1.1 μm.
It continuously changes from m to d ₂ = 1.65 μm.
FIG. 16B shows the wavelength characteristic of the three-wavelength tube used as the light source in this embodiment and the wavelength characteristic of the transmittance of the color filters of R, G, and B colors. The liquid crystal used in the liquid crystal cell was the same as in Example 1. Table 7 shows the transmittances at 615 nm, 540 nm, and 450 nm, which correspond to the peak wavelengths of the transmitted light of the R, G, and B pixels of the light transmitted through the liquid crystal cell. This transmittance is based on the transmittance of light with a wavelength of 615 nm at a cell thickness of 1.1 μm (this is set to 1).

[0099]

[Table 7]

As can be seen from Table 7, when the cell thickness changes, the balance of the transmittance between the three wavelengths changes.
When the pixel area to keep this balance constant is calculated,
It becomes the value in () of Table 7. This number is cell thickness 1.1
The ratio of the transmissivities between the three wavelengths in the μm part is 1: 1.
22: 1.29 was set so as to be kept constant even in other cell thickness portions. In this way, the electrode width is changed according to the change of the cell thickness in FIGS. 15B, 15C, and 15D. Cell thickness d
= 1 μm for the electrode width of 1.1 μm for all R, G, B pixels
It was set to 00 μm. Cell thickness d = 1.1 μm to 1.65
The electrode width while changing up to changes depending on the area ratio shown in () of Table 7. This liquid crystal cell was actually driven by the 4-pulse method described above, and the temperature was changed. FIG. 17 shows how the pixels at this time are observed with a microscope.
(A), (b), (c). At low temperature, the opening was in a portion with a thin cell thickness as shown in (a), and conversely, in an area with a large cell thickness as in (c) under high temperature. In FIG. 16A, in order to investigate the color change associated with the movement of the opening,
Using a colorimeter, turn on only R pixels, turn on G pixels, B
Colors were measured under four conditions of lighting only pixels and simultaneous lighting of R, G, and B. The color change due to temperature change is larger when the opening is narrowed, and each curve in the figure shows the locus on the chromaticity coordinate when the change is the largest, and A indicates that the thin cell side opens at low temperature. While B is open at high temperature, the side where the cell thickness is thick is open.

As described above, by configuring the pixel shape so that the transmittance at the peak wavelength of the transmitted light of each of the R, G, and B pixels is kept constant even when the cell thickness changes,
It was possible to reduce the color change of white when R, G, and B were simultaneously turned on, and good color display was obtained.

(Embodiment 5) As Embodiment 5, by forming a cell thickness distribution in a pixel and distributing the electric field strength applied to the liquid crystal layer in the pixel, the display characteristics of the gray scale display method are shown. An example of improvement is shown.

When there is a distribution of cell thickness within a pixel, a difference occurs in the liquid crystal layer thickness, and as a result, the intensity of transmitted light passing through the liquid crystal layer differs depending on the wavelength. In each of the R, G, and B color filters, the shape of the color filter was configured according to the cell thickness so that the transmitted light intensity (transmittance) was constant regardless of the cell thickness.

However, in the actual liquid crystal element, the light source,
The characteristic of the color filter is not designed to emit or pass monochromatic light.

The amount of light (LL) perceived by the human eye is
The transmitted light φ (λ) of the liquid crystal cell is multiplied by the visual sensitivity ξ (λ) of the human eye for each wavelength, for example, the wavelength range of each filter is 380 n.
It is the amount integrated from m to 780 nm.

[0106]

[Equation 2]

When the amount of transmitted light at a certain wavelength is made constant regardless of the cell thickness as in Example 1, the amount of light (LL) changes depending on the cell thickness.

When gradation display is performed by the above-described 4-pulse method or pixel shift method, it is desirable that the light amount (LL) of the pixels in the portions having different cell thicknesses be constant, so in this embodiment, R , G, and B, the light amount (LL) of each pixel is constant regardless of the cell thickness.

In this embodiment, similarly to the second embodiment, in FIG. 2, d ₁ = 1.1 μm, d ₂ = 1.65 μm, L = 2.
It was set to 00 μm. FIG. 18 shows this embodiment. In FIG. 18, (a) shows one pixel in FIG.
The cell thickness in the pixel is from d ₁ = 1.1 μm to d ₂ = 1.65.
It continuously changes up to μm. The wavelength characteristic of the three-wavelength tube used as the light source in this embodiment is the same as that in FIG. 16B, and shows the wavelength characteristic of the transmittance of the color filters of R, G, and B colors. Table 8 shows the amount of light (LL) that human eyes perceive with respect to the transmitted light when these light sources, each color filter, and the liquid crystal cell are combined. The liquid crystal used in the liquid crystal cell was the same as in Example 1. The numbers represent the light amount per unit area (LL), and the light amount (LL) at the location where the cell thickness of the pixel provided with the R filter is 1.1 μm is used as a reference (this is set to 1).

[0110]

[Table 8]

As can be seen from Table 8, when the cell thickness changes, the balance of the light amount (LL) among the R, G and B pixels changes. When the pixel area for keeping this balance constant is obtained, the value in parentheses in Table 8 is obtained. This number is set so that the luminance ratio of R, G, and B pixels of 1: 2.98: 0.54 in the cell thickness of 1.1 μm is kept constant in other cell thickness portions. In this way, the electrode width is changed according to the change of the cell thickness as shown in FIGS. 18 (b), 18 (c) and 18 (d). The electrode width at the cell thickness d = 1.1 μm was 100 μm for all the R, G, and B pixels. Cell thickness d = 1.1 μm
To 1.65 μm, the electrode width changes depending on the area ratio shown in () in Table 8. The temperature was changed while actually driving the liquid crystal cell by the above-mentioned 4-pulse method. 20 (a), (b), and (c) show how the pixels at this time are observed with a microscope. At low temperature, the opening was in a portion with a thin cell thickness as shown in (a), and conversely, in an area with a large cell thickness as in (c) under high temperature. In FIG. 19, in order to examine the color change due to the movement of the opening, a colorimeter is used, and only R pixels are lit, G pixels are lit, B pixels are lit, and R, G, and B are lit simultaneously. The color was measured under the conditions. The color change due to temperature change is larger when the opening is narrowed, and each curve in the figure shows the locus on the chromaticity coordinate when the change is the largest, and A indicates that the thin cell side opens at low temperature. When
B is open at the side where the cell thickness is thick under high temperature.

In FIG. 19, the hue A of the portion where the cell thickness is thin
It can be seen that the hue B of the thick portion is different.

Even if the shape of the color filter is set so that the light amount (LL) is constant, the hue shift due to the cell thickness cannot be corrected.

In order to improve this, white erase black writing and black erase white writing are performed for each scanning line. White erasing black writing and black erasing white writing are alternately performed for each frame for one scanning line. When such a driving method is adopted, even if the same 10% "white" is written, a 10% "white" domain can be formed in a thick cell portion and a 10% "white" domain in a thin cell portion. When a "black" domain is created, it is averaged spatially () or temporally (), so as shown in Fig. 21 (difference between + mark and ○ mark), hue shift due to cell thickness. Is virtually eliminated. Therefore, when the pixel shift method is used, the threshold value of the liquid crystal changes depending on the temperature and "white" in the pixel
Domain moves from thick cell to thin cell (when the electric field distribution in the pixel is constant and the temperature changes)
Even when it is done, there is virtually no change in "hue".

As described above, in the cell thickness gradient method,
Even when driven by a driving method such as the pixel shift method, it was possible to obtain good characteristics in which the "light amount (LL)" and "hue" of the pixel were not changed depending on the temperature.

FIG. 21 is a block diagram of the drive system of the display device of this embodiment.

The scanning lines of the liquid crystal element 141 serving as a display screen are connected to the common side driving IC 146 as a means for selecting the scanning lines and applying the selection signal, and the information signal lines as the means for applying the gradation information signal. It is connected to the segment side drive IC.

The image information from the image information generator 148 such as an image sensor or a wireless receiver is controlled by the controller 149 into a common side signal and a segment side signal for display. Shift register 147 on the common side
And the scan signal is formed by the drive IC 146 based on the reference voltage distributed by the analog switch of the drive power supply 142.

On the other hand, on the segment side, the digital gradation signal supplied via the shift register 145 and the latch circuit 144 is converted into an analog signal by the D / D converter in the drive IC 143 and supplied to the information signal line. For example, a 4-bit digital signal can be converted into 2 ⁴ or 16 analog signals.

Here, the digital signal is latched before the conversion into the analog signal, but it is also possible to employ a method in which a capacitor is provided in parallel with the driving IC 143 to directly latch the analog signal.

The present invention is not limited to the above-mentioned embodiments, and may be any one that achieves the object of the present invention. Therefore, equivalents in which the constituent elements are replaced with alternatives and the materials are changed are also included in the present invention.

[0122]

As in the above-described embodiments, by changing the electrode area or the color filter area in accordance with the cell thickness, good color characteristics and gradation characteristics can be realized by the ferroelectric liquid crystal. I was able to.

[Brief description of drawings]

FIG. 1 is a graph showing the spectral characteristics of optical means used in a liquid crystal display device of the present invention.

FIG. 2 is a schematic cross-sectional view of a liquid crystal cell used in the liquid crystal display element of the present invention.

FIG. 3 is a schematic diagram for explaining the basic design concept of the pixel configuration of the present invention.

FIG. 4 is a schematic diagram for explaining a configuration of a pixel of the present invention.

FIG. 5 is a diagram schematically showing a relationship between a switching pulse voltage of a liquid crystal element and an amount of transmitted light.

FIG. 6 is a diagram showing a transmission state by a pulse voltage.

FIG. 7 is a graph for explaining a shift in threshold characteristic due to temperature distribution.

FIG. 8 is a diagram showing a timing chart for explaining the 4-pulse method.

FIG. 9 is an explanatory diagram of a 4-pulse method.

FIG. 10 is a schematic diagram for explaining a configuration of a pixel of the liquid crystal element according to the first embodiment.

FIG. 11 is a schematic diagram for explaining a pixel configuration of a liquid crystal element according to a second embodiment.

FIG. 12 is a schematic diagram showing a modified example of the second embodiment.

FIG. 13 is a schematic diagram for explaining the third embodiment.

FIG. 14 is a schematic diagram for explaining the third embodiment.

FIG. 15 is a schematic diagram for explaining a pixel configuration of a liquid crystal element of Example 4.

16 is a diagram showing optical characteristics of Example 4. FIG.

FIG. 17 is a schematic diagram for explaining a display state of the liquid crystal element according to the fourth embodiment.

FIG. 18 is a schematic diagram for explaining a pixel configuration of a liquid crystal element of Example 5.

19 is a diagram showing optical characteristics of Example 5. FIG.

FIG. 20 is a schematic diagram for explaining a display state of the liquid crystal element according to the fifth embodiment.

FIG. 21 is a diagram showing optical characteristics of a modified example of Example 5;

FIG. 22 is a drive system block diagram of a liquid crystal display device according to the present invention.

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Makoto Kojima 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc.

Claims (17)

[Claims] 1. A liquid crystal display device comprising liquid crystal sandwiched between a pair of electrode substrates facing each other, wherein a plurality of filters are arranged on at least one of the electrode substrates, and a pixel area corresponds to the pixel. A liquid crystal display device characterized by being changed for each type. 2. A liquid crystal display element comprising liquid crystal sandwiched between a pair of electrode substrates facing each other, wherein the thickness of a liquid crystal layer is made different within one pixel, and the shape of the pixel is changed according to the thickness. A liquid crystal display device characterized by the above. 3. The liquid crystal display element according to claim 1, wherein an area of the pixel is an area of a portion where a pair of electrodes provided on the electrode substrate overlap each other. 4. The liquid crystal display element according to claim 2, wherein the area of the pixel is an area of a portion where a pair of electrodes provided on the electrode substrate overlap each other. 5. The liquid crystal display element according to claim 2, wherein the pixel is a light transmitting portion in which a filter and a pair of electrodes provided on an electrode substrate overlap each other. 6. The liquid crystal display device according to claim 1, wherein the liquid crystal is a nematic liquid crystal or a smectic liquid crystal. 7. The liquid crystal display element according to claim 1, wherein the electrode substrate is formed by forming a stripe-shaped transparent electrode on an insulating substrate. 8. The liquid crystal display device according to claim 1, further comprising a generation circuit for a gradation display signal applied to the pixel. 9. The liquid crystal display device according to claim 1, which has a backlight. 10. The liquid crystal display device according to claim 1, which has a three-wavelength fluorescent tube. 11. The liquid crystal display device according to claim 1, wherein the pixel has at least three types of pixels of red, blue and green. 12. The method according to claim 1, further comprising a light source that emits light having an emission spectrum having at least three peaks, and a filter having a transmitted light spectrum that overlaps each of the three peaks. Liquid crystal display device. 13. A liquid crystal display device comprising a ferroelectric liquid crystal sandwiched between a pair of electrode substrates facing each other, wherein each pixel is formed at an intersection of upper and lower substrates, and three or more kinds are provided on one electrode. Area and / or shape of the color filter or the area and / or shape of the electrode intersection so that the transmittance of the liquid crystal layer of the transmitted light passing through the color filter becomes constant according to the cell thickness. Liquid crystal display device characterized by changing the. 14. A liquid crystal display device comprising a ferroelectric liquid crystal sandwiched between a pair of electrode substrates facing each other, wherein each pixel is formed at the intersection of upper and lower substrates, and each pixel is provided on one electrode. By providing unevenness on the cell and providing a gradient of the cell thickness within one pixel, and changing the area and / or the shape of the electrode intersection portion according to the cell thickness,
A liquid crystal display device, wherein a threshold distribution of a ferroelectric liquid crystal in each pixel is set so that a change in transmittance is logarithmic with respect to an input voltage. 15. A liquid crystal display device comprising a ferroelectric liquid crystal sandwiched between a pair of electrode substrates facing each other, wherein each pixel is formed at the intersection of upper and lower substrates, and each pixel is provided on one electrode. The unevenness is provided in one pixel to provide a gradient of the cell thickness in one pixel, and at least one of the electrode substrates is provided with three or more kinds of color filters, and the brightness of the transmitted light passing through each color filter depends on the cell thickness. The area and / or the shape of the color filter or the area of the electrode intersection so as to be constant and / or
Alternatively, a liquid crystal display device having a different shape. 16. A liquid crystal display device comprising ferroelectric liquid crystal sandwiched between a pair of electrode substrates arranged facing each other, wherein each pixel is formed at an intersection of upper and lower substrates, and each pixel is arranged on one electrode. The unevenness is provided on one side to form a gradient of the cell thickness within one pixel, and at least one of the electrode substrates is provided with three or more kinds of color filters to form a display unit with a plurality of pixels. The liquid crystal display element is characterized in that the areas of the plurality of pixels are different from each other, and the areas of the plurality of pixels decrease with the increase of the cell thickness and the pixels increase. 17. A liquid crystal display device comprising a pair of electrode substrates facing each other and sandwiching a ferroelectric liquid crystal, wherein each pixel is formed at an intersection of upper and lower substrates, and each pixel is provided on one electrode. The unevenness is provided on one side to form a gradient of the cell thickness within one pixel, and at least one of the electrode substrates is provided with three or more kinds of color filters to form a display unit with a plurality of pixels. And a total area of the plurality of pixels is substantially the same regardless of the cell thickness.