JPH09179109A - Liquid crystal display device - Google Patents

Abstract

(57) Abstract: A liquid crystal display element is provided which has a color filter provided on electrodes and which can be driven in a time-division manner at a high duty while lowering a drive voltage. A liquid crystal display device in which electrodes 3 and 4 are respectively formed on the inner surfaces of a pair of substrates 1 and 2 that face each other with a liquid crystal LC sandwiched between them, and a color filter CF is provided on an electrode 4 of one substrate 2. In, the conductive particles 10 were dispersed in the color filter CF.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device that displays a color image.

[0002]

2. Description of the Related Art Liquid crystal display devices for displaying color images are
In general, electrodes are formed on the inner surfaces of a pair of substrates that face each other with a liquid crystal in between, and a color filter is provided on one of the substrates.

[0003]

By the way, in the above-mentioned liquid crystal display device, the electrodes on the side of the substrate on which the color filters are provided are formed on the color filters, and the electrodes are formed on the substrate. Some have a color filter provided on an electrode, but a liquid crystal display element having a color filter provided on an electrode has a problem that it must be driven at a high driving voltage.

This is because the voltage applied between the electrodes of both substrates causes a voltage drop corresponding to the impedance of the color filter to be applied to the liquid crystal, so that the effective voltage applied to the liquid crystal is applied between the electrodes. This is because the voltage is blunted and the voltage value (absolute value) is lower than that of the applied voltage.

Therefore, the liquid crystal display element having the color filter provided on the electrodes has a high threshold voltage Vth,
Since the γ characteristic is poor, it is necessary to drive with a high drive voltage, so it is necessary to use a drive circuit element such as an LSI having a high breakdown voltage.

Moreover, in this liquid crystal display element, since the effective voltage applied to the liquid crystal is a voltage whose waveform is distorted compared with the voltage applied between the electrodes, the responsiveness is poor, and therefore the high duty ratio is achieved. Time division drive is difficult. This is a problem particularly in a simple matrix type liquid crystal display device.

It is an object of the present invention to provide a liquid crystal display element, which is provided with a color filter on an electrode and which can be driven in a time division manner with a high duty while lowering a driving voltage. .

[0008]

SUMMARY OF THE INVENTION The present invention is a liquid crystal in which electrodes are formed on the inner surfaces of a pair of substrates which face each other with a liquid crystal in between, and a color filter is provided on the electric electrodes of one of the substrates. In the display element, conductive particles are dispersed in the color filter.

In the present invention, the conductive particles may be transparent particles having a diameter substantially the same as the thickness of the color filter, and fine particles having a diameter sufficiently smaller than the thickness of the color filter, for example, having a diameter of The particle size may be 0.1 μm or less.

According to the present invention, since the conductive particles are dispersed in the color filter, the conductivity of the color filter is apparently increased, the impedance is lowered, and the voltage drop due to the color filter is reduced. The rounding of the waveform of the effective voltage applied to the device and the decrease in the voltage value (absolute value) are reduced.

Therefore, according to the liquid crystal display element of the present invention, although the color filter is provided on the electrode, the threshold voltage Vth can be lowered and the γ characteristic can be improved. It is possible to lower the value and drive with high duty in a time division manner.

In the present invention, the conductive particles may be transparent particles having a diameter substantially the same as the thickness of the color filter, and the conductive particles may be brought into contact with the electrodes below the color filter. A voltage with almost no voltage drop due to the color filter is applied to the liquid crystal in the corresponding portion, and a voltage with a voltage drop due to the color filter is applied to the liquid crystal in the portion not corresponding to the conductive particles. Therefore, the rising alignment state of liquid crystal molecules when a voltage is applied between the electrodes is partially different in each pixel portion,
A wide viewing angle can be obtained by reducing the apparent viewing angle dependence of the entire pixel portion.

Further, in the present invention, if the conductive particles are fine particles having a diameter sufficiently smaller than the thickness of the color filter, the conductivity of the color filter can be made substantially uniform over the entire filter. It is possible to reduce the scattering of the light passing through the color filter by the conductive particles, and to obtain a good display with less light leakage. In particular, if the diameter of the conductive particles is 0.1 μm or less, the light leakage will not occur. You can almost eliminate it.

[0014]

1 to 3 show a first embodiment of the present invention, and FIG. 1 is a sectional view of a part of a liquid crystal display device. The liquid crystal display element of this example is of a simple matrix type, and is formed on the inner surface of one of the pair of substrates 1 and 2 facing each other across the liquid crystal LC (lower substrate in FIG. 1). Has a plurality of scanning electrodes 3 formed in parallel with each other in the row direction (left-right direction in the drawing), and the inner surface of the other substrate (upper substrate in FIG. 1) 2 has a column direction (perpendicular to the paper surface in the drawing). A plurality of signal electrodes 4 are formed in parallel with each other.

The pair of substrates 1 and 2 are transparent substrates made of glass or the like, and are composed of the scanning electrodes 3 and the signal electrodes 4.
Is a transparent electrode made of indium tin oxide (ITO) or the like.

On the inner surface of one of the pair of substrates 1 and 2, for example, the inner surface of the substrate 2 on which the signal electrode 4 is formed,
Color filters C of a plurality of colors, for example, three colors of red, green and blue
F is provided in a thickness of 1 μm to 2 μm.

Each color filter CF of each color is formed in a stripe shape slightly wider than the signal electrode 4, and on each signal electrode 4, a red filter R,
The green filters G and the blue filters B are alternately arranged in this order.

The color filter CF is obtained by adding a pigment to a transparent filter base material and coloring it in a desired color. In each color filter, indium oxide.
Transparent conductive particles 10 made of tin or the like are dispersed.

The conductive particles 10 are color filters C.
The spherical particles have a diameter substantially the same as the thickness of F (1 μm to 2 μm), and are dispersed so as to be distributed almost evenly over the entire color filter.

In the color filter CF, for example, on the substrate 2 on which the signal electrode 4 is formed, a predetermined amount of the conductive particles 10 is mixed in a filter material obtained by adding a pigment to a filter base material made of a photocurable resin. It is formed by repeating the steps of applying a substance, exposing it to a predetermined pattern, and developing it to form a filter of one color. The conductive particles 10 in the filter are formed on the substrate 2 side. Is in contact with the surface of the signal electrode 4.

Note that, in FIG. 1, the filters R, G, and B of the respective colors are shown to have the same thickness for the sake of convenience, but the transmittance of the color filters has wavelength dependence, and the short wavelengths in the visible light band are short. Since the transmittance of light in the range is lower, the blue filter B for transmitting light in the short wavelength range is made slightly thinner than the green filter G for transmitting light in the intermediate range in this embodiment. The thickness of the red filter R that transmits light in the long wavelength range is made slightly thicker than that of the green filter G so that the transmittances of the filters R, G, B of the respective colors are substantially equal, and the filters R, G, In B, conductive particles having the same diameter as the thickness are dispersed.

On the inner surfaces of the pair of substrates 1 and 2 (on the scanning electrode 3 on one substrate 1 and on the color filter CF on the other substrate 2), alignment films 5 and 6 made of polyimide or the like, respectively. Are provided and these alignment films 5 and 6 are provided.
Are oriented in a predetermined direction.

The pair of substrates 1 and 2 are bonded to each other with their inner surfaces facing each other via a frame-shaped sealing material (not shown), and the liquid crystal LC is sandwiched between the substrates 1 and 2. The molecules of this liquid crystal LC are
Between the specified twist angles (approximately 9 in TN mode)
The twist orientation is 0 °, and 180 ° to 270 ° in the STN mode).

Further, polarizing plates 7 and 8 are arranged on the outer surfaces of both substrates 1 and 2, respectively, and the transmission axes of the polarizing plates 7 and 8 are oriented so that the liquid crystal molecules are in an initial twist alignment state (no voltage is applied). In addition, the transmittance of the liquid crystal display element becomes the lowest when the voltage is applied, and the transmittance increases as the liquid crystal molecules rise and align with respect to the substrates 1 and 2 while maintaining the twist alignment state. Is set to be high.

For example, the twist angle of liquid crystal molecules is approximately 90.
In the case of °, one polarizing plate 7 is arranged with its transmission axis substantially orthogonal to or substantially parallel to the alignment direction of liquid crystal molecules in the vicinity of the substrate 1 facing this polarizing plate 7, The other polarizing plate 8 is arranged with its transmission axis substantially orthogonal to the transmission axis of the one polarizing plate 7.

According to this liquid crystal display element, since the conductive particles 10 are dispersed in the color filter CF, the conductivity of the color filter CF apparently increases, the impedance decreases, and the voltage drop due to the color filter CF. Is smaller, the rounding of the waveform of the effective voltage applied to the liquid crystal LC and the decrease of the voltage value (absolute value) are reduced.

That is, in this liquid crystal display element, the conductive particles 10 are transparent particles having a diameter substantially the same as the thickness of the color filter CF, and the conductive particles 10 are brought into contact with the signal electrode 4 below the color filter CF. Therefore, a voltage having almost no voltage drop due to the color filter is applied to the liquid crystal LC in the portion corresponding to the conductive particles 10,
In the liquid crystal LC of the part where the conductive particles 10 do not correspond,
A voltage that causes a voltage drop due to the color filter is applied.

FIG. 2 is an equivalent circuit diagram of one pixel portion of the liquid crystal display element. In the figure, RLC and CLC indicate the resistance and capacitance of the liquid crystal LC, and RCF and CCF indicate the resistance and capacitance of the color filter CF. Shows capacity. Note that this equivalent circuit is a circuit in which the alignment films 5 and 6 are ignored.

As shown in this equivalent circuit diagram, the portion of one pixel portion of the liquid crystal display element to which the conductive particles 10 do not correspond is the impedance of the liquid crystal layer determined by the resistance RLC and the capacitance CLC of the liquid crystal LC. And the impedance of the color filter determined by the resistance RCF of the color filter CF and the capacitance CCF are equivalent to the circuit a connected in series.

Further, the portion corresponding to the conductive particles 10 has a diameter substantially the same as the thickness of the conductive particles 10 penetrating the color filter CF, and the conductive particles 10 under the color filter CF. Since it is in contact with the signal electrode 4, it is equivalent to a circuit b having only the impedance of the liquid crystal layer determined by the resistance RLC and the capacitance CLC of the liquid crystal LC.

Therefore, in each pixel portion of the liquid crystal display element, the circuit a having the impedance of the liquid crystal layer and the impedance of the color filter and the circuit b having only the impedance of the liquid crystal layer are connected in parallel. It is represented by an equivalent circuit.

Then, in the portion where the conductive particles 10 do not correspond, the driving voltage applied between the electrodes 3 and 4 of the substrates 1 and 2 causes a voltage drop due to the impedance of the color filter CF, and the liquid crystal LC. Therefore, the effective voltage applied to the liquid crystal LC in this portion is a voltage whose waveform is blunt and whose voltage value (absolute value) is lower than the drive voltage applied between the electrodes 3 and 4. Becomes

On the other hand, in the portion corresponding to the conductive particles 10, the driving voltage applied between the electrodes 3 and 4 of the substrates 1 and 2 does not cause a voltage drop due to the impedance of the color filter CF and the liquid crystal is generated. Since it is applied to LC,
The waveform of the effective voltage applied to the liquid crystal LC in this portion is almost the same as the drive voltage applied between the electrodes 3 and 4, and there is almost no decrease in the voltage value.

FIG. 3 shows the waveform of the driving voltage applied between the electrodes 3 and 4 of one pixel portion of the liquid crystal display element and the liquid crystal LC.
The waveform of the effective voltage applied to is shown. Note that FIG.
, Ts is a selection period of the pixel portion in one frame, and Tf is a non-selection period.

As shown in FIG. 3, the effective voltage VLC-a applied to the liquid crystal LC in the portion not corresponding to the conductive particles 10.
Is compared with the driving voltage V0 applied between the electrodes 3 and 4,
The voltage is a voltage with a blunted waveform and a low voltage value (absolute value), but the liquid crystal L in the portion corresponding to the conductive particles 10
The effective voltage VLC-b applied to C has a waveform that is almost the same as the drive voltage V0 and has almost no decrease in voltage value.

Therefore, a portion of the pixel portion not corresponding to the conductive particles 10 has a high threshold voltage Vth and poor γ characteristics, but a portion corresponding to the conductive particles 10 does not. The threshold voltage Vth is sufficiently low, and the γ characteristic is good.

Therefore, the threshold voltage Vth in the entire pixel portion is an average value of Vth in the portion not corresponding to the conductive particles 10 and Vth in the portion corresponding to the conductive particles 10. Since the γ characteristic is also the characteristic obtained by averaging the characteristics of these portions, according to the liquid crystal display element described above, the threshold voltage Vth is lowered and the γ characteristic is provided even though the color filter CF is provided on the electrode 4. Therefore, it is possible to lower the drive voltage and perform time-division driving with high duty.

In this embodiment, the conductive particles 1 are also used.
Since 0 is a transparent particle having a diameter substantially the same as the thickness of the color filter CF and the conductive particle 10 is brought into contact with the electrode 4 below the color filter CF, the liquid crystal of the portion corresponding to the conductive particle 10 is formed. A voltage having almost no voltage drop due to the color filter is applied to LC, and a voltage having a voltage drop due to the color filter is applied to the liquid crystal LC in the other part (the part 9 to which the conductive particles 10 do not correspond). Therefore, the rising alignment state of liquid crystal molecules when a driving voltage is applied between the electrodes 3 and 4 is partially different in each pixel portion, and the apparent viewing angle dependence of the entire pixel portion is reduced,
A wide viewing angle can be obtained.

That is, according to the above liquid crystal display element, the rising alignment state of the liquid crystal molecules when a voltage is applied differs between the portion corresponding to the conductive particles 10 in the pixel portion and the other portion, and therefore the viewing angle is different. Apparent Δn · d by
Since the change in the value of (the product of the refractive index anisotropy Δn of the liquid crystal and the liquid crystal layer thickness d), that is, the viewing angle dependence of the voltage-transmittance characteristic is different in each of the portions, the apparent viewing angle dependence of the entire pixel The property is reduced, and a wide viewing angle can be obtained even when displaying halftone in gradation display.

The thickness of the color filter CF is 1
Therefore, even if the diameter of the conductive particles 10 is the same as the thickness of the color filter CF, the portions corresponding to the conductive particles 10 and other portions cannot be recognized by the resolution of human eyes. Therefore, the display pixel of the liquid crystal display element is recognized as a pixel having a brightness obtained by averaging the intensities of the emitted light in the two areas.

Next, a second embodiment of the present invention will be described. FIG. 4 is a sectional view of a part of a liquid crystal display device showing a second embodiment of the present invention. In this liquid crystal display element, the thickness of the color filter CF (1
conductive particles 11 which are sufficiently smaller than 1 μm to 2 μm). In this embodiment, the conductive particles 11 are made of indium tin oxide or the like and have a diameter of 0.1 μm or less. Fine transparent particles are used, and the particles 11 are dispersed so as to be distributed almost uniformly over the entire color filter.

The liquid crystal display element of this embodiment is the same as the liquid crystal display element of the first embodiment except for the conductive particles 11 dispersed in the color filter CF. Therefore, duplicate description will be omitted by attaching the same reference numerals to the drawings.

Also in the liquid crystal display element of this embodiment, since the conductive particles 11 are dispersed in the color filter CF, the conductivity of the color filter CF is apparently increased and the impedance is lowered. Since the voltage drop is small, the rounding of the waveform of the effective voltage applied to the liquid crystal LC and the decrease in the voltage value (absolute value) are reduced,
Therefore, since the threshold voltage Vth can be lowered to improve the γ characteristic, it is possible to lower the drive voltage and perform time division driving with high duty.

Further, according to this liquid crystal display element, since the conductive particles 11 are fine particles having a diameter sufficiently smaller than the thickness of the color filter CF, the conductivity of the color filter CF is substantially uniform over the entire filter. In addition, it is possible to reduce the scattering of the light passing through the color filter CF by the conductive particles 11 and obtain a good display with less light leakage.

The effect of reducing the scattering of light by the conductive particles 11 is more remarkable as the diameter of the conductive particles 11 is smaller. As described above, the diameter of the conductive particles 11 is less than 0.
When the thickness is 1 μm or less, the generation of light leakage can be almost eliminated.

That is, when the diameter of the conductive particles 11 dispersed in the color filter CF is large, the conductive particles 1
Even if 1 is a transparent particle, the light transmitted through the color filter CF is refracted at the interface between the conductive particles 11 and the filter material to become scattered light, and the transmission axis of the polarizing plate on the emission side of the light. The light of the polarized component along the line is transmitted through the polarizing plate to be leaked light, but the diameter of the conductive particles 11 is 0.
If the particle size is 1 μm (100 nm) or less, the conductive particles 1
The diameter of 1 is a wavelength in the visible light band (about 400 nm to about 700 n
Since it is much smaller than m), almost no refraction of light occurs at the interface between the conductive particles 11 and the filter material.

Therefore, if the diameter of the conductive particles 11 is set to 0.1 μm or less, the generation of light leakage can be almost eliminated, so that the deterioration of the contrast due to the light leakage can be eliminated and a high quality color image can be displayed. You can

In this embodiment, the conductive particles 1 are
Although a transparent material is used for 1, the conductive particles 11 may be fine particles made of metal. Further, although the liquid crystal display elements of the first and second embodiments are of the simple matrix type, the present invention can be applied to the active matrix type liquid crystal display element.

[0049]

According to the present invention, since the conductive particles are dispersed in the color filter, the conductivity of the color filter apparently increases, the impedance decreases, and the voltage drop due to the color filter decreases. Since the rounding of the waveform of the effective voltage applied to the liquid crystal and the decrease of the voltage value (absolute value) are reduced, the threshold voltage Vth is lowered and the γ characteristic is obtained even though the color filter is provided on the electrode. Therefore, it is possible to lower the drive voltage and perform time-division driving with high duty.

In the present invention, if the conductive particles are transparent particles having a diameter substantially the same as the thickness of the color filter, and the conductive particles are brought into contact with the electrodes below the color filter, the conductive particles will be formed. A voltage with almost no voltage drop due to the color filter is applied to the liquid crystal in the corresponding portion, and a voltage with a voltage drop due to the color filter is applied to the liquid crystal in the portion not corresponding to the conductive particles. Therefore, the rising alignment state of liquid crystal molecules when a voltage is applied between the electrodes is partially different in each pixel portion,
A wide viewing angle can be obtained by reducing the apparent viewing angle dependence of the entire pixel portion.

Further, in the present invention, if the conductive particles are fine particles having a diameter sufficiently smaller than the thickness of the color filter, the conductivity of the color filter can be made substantially uniform throughout the filter, and It is possible to reduce the scattering of the light passing through the color filter by the conductive particles, and to obtain a good display with less light leakage. In particular, if the diameter of the conductive particles is 0.1 μm or less, the light leakage will not occur. You can almost eliminate it. it can.

[Brief description of the drawings]

FIG. 1 is a sectional view of a part of a liquid crystal display element showing a first embodiment of the present invention.

FIG. 2 is an equivalent circuit diagram of one pixel portion of the liquid crystal display element.

FIG. 3 is a diagram showing a waveform of a drive voltage applied between electrodes of one pixel portion of a liquid crystal display element and a waveform of an effective voltage applied to liquid crystal.

FIG. 4 is a partial cross-sectional view of a liquid crystal display element showing a second embodiment of the present invention.

[Explanation of symbols]

 1, 2 ... Substrate 3 ... Scanning electrode 4 ... Signal electrode CF ... Color filter 10, 11 ... Conductive particles 5, 6 ... Alignment film LC ... Liquid crystal

Claims (3)

[Claims] 1. A liquid crystal display element, wherein electrodes are formed on the inner surfaces of a pair of substrates that face each other with a liquid crystal sandwiched therebetween, and a color filter is provided on the electrodes of one of the substrates. A liquid crystal display device, characterized in that conductive particles are dispersed therein. 2. The conductive particle is a transparent particle having a diameter substantially the same as the thickness of the color filter, and the conductive particle is in contact with an electrode below the color filter. 1. The liquid crystal display element according to 1. 3. The liquid crystal display element according to claim 1, wherein the conductive particles are fine particles having a diameter sufficiently smaller than the thickness of the color filter.