JPH07311389A - Active matrix liquid crystal display device - Google Patents

Abstract

PURPOSE:To provide an active matrix liquid crystal display device of a reflection type with which the loss of the light quantity by light absorption in the substrates and polarizing plates of a liquid crystal cell is lessened, bright display is obtd. by increasing the opening rate and the capacitance value of compensation capacitors in sufficiently assured. CONSTITUTION:One sheet of the polarizing plate is arranged on the front surface side of the liquid crystal cell 10 having TFTs (thin-film transistors) 14 as active elements and pixel electrodes 13 to be formed on the inside surface of the rear surface side substrate 11 of the liquid crystal cell 10 are set to be light reflection films. The pixel electrodes 13 are disposed to cover the TFTs 14 on protective insulating films 21 covering the TFTs 14. Further, on the surface of gate insulating film 16, first capacitor electrodes 22 formed integrally with the source electrodes 19s of the TFTs 14 are provided and on the surface of the rear surface side substrate 11, second capacitor electrodes are provided. The compensation capacitors CS are composed of these capacitor electrodes 22, 23 and the gate insulating films 16 therebetween.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reflection type active matrix liquid crystal display device.

[0002]

2. Description of the Related Art Conventionally, in a reflection type active matrix liquid crystal display device, a pair of front and back polarizing plates are arranged across an active matrix type liquid crystal cell, and a reflection plate is arranged on the back surface of the back side polarizing plate. It is composed.

As the above-mentioned active matrix type liquid crystal cell, one using a thin film transistor as an active element is generally used, and this liquid crystal cell is one of a pair of transparent substrates facing each other with a liquid crystal layer interposed therebetween. A plurality of transparent pixel electrodes and a plurality of thin film transistors respectively corresponding to these pixel electrodes are arranged in a matrix on the inner surface of the substrate, and a transparent counter electrode facing the pixel electrodes is provided on the inner surface of the other substrate. It has been configured.

The thin film transistor includes a gate electrode formed on the one substrate, a transparent gate insulating film formed on almost the entire surface of the substrate to cover the gate electrode, and the transparent gate insulating film formed on the gate insulating film. The semiconductor film is formed so as to face the gate electrode, and the source electrode and the drain electrode are formed on both sides of the semiconductor film. The pixel electrode is formed on the gate insulating film while avoiding the thin film transistor. At the same time, it is connected to the source electrode of the corresponding thin film transistor at the end of the pixel electrode.

In an active matrix type liquid crystal cell using a thin film transistor as an active element, a capacitor electrode facing the edge of the pixel electrode is provided on the one substrate with the gate insulating film of the thin film transistor interposed therebetween. The capacitor electrode, the pixel electrode, and the gate insulating film therebetween form a compensation capacitance (storage capacitor) that compensates the holding voltage of the pixel in the non-selected period.

The reflection type active matrix liquid crystal display device uses external light such as natural light or indoor illumination light for display, and the light incident on the liquid crystal display device from the surface side is a polarizing plate on the surface side. Is converted into linearly polarized light, and this linearly polarized light enters the liquid crystal cell.

The alignment state of the liquid crystal molecules of the liquid crystal cell is
Since the birefringence effect of the liquid crystal layer changes according to the voltage applied between the pixel electrode and the counter electrode of both substrates and the alignment state of the liquid crystal molecules, the linearly polarized light incident on the liquid crystal cell is The light having a polarization state according to the orientation state of the molecules enters the polarizing plate on the back surface side.

Then, this light becomes image light due to the analyzing action of the back side polarizing plate, and this image light is reflected by the reflecting plate, and the back side polarizing plate, the liquid crystal cell and the front side polarizing plate are combined. The light is emitted to the front surface side of the liquid crystal display device.

That is, in the above liquid crystal display device, an optical image displayed by the polarizing action of the front side polarizing plate, the birefringence effect of the liquid crystal cell, and the analyzing action of the back side polarizing plate is displayed on the back side reflecting plate. It is reflected and observed from the front side of the liquid crystal display device.

[0010]

However, in the above-mentioned conventional reflection type active matrix liquid crystal display device, the light incident from the front surface side passes through the front surface side polarizing plate, the liquid crystal cell and the back surface side polarizing plate and is reflected by the reflection surface. Since the light is reflected by the plate and again passes through the back-side polarizing plate, the liquid crystal cell, and the front-side polarizing plate, the light passes through both substrates of the liquid crystal cell and the front and back polarizing plates twice in the process. Therefore, there is a problem that the light amount loss due to the light absorption by these substrates and the polarizing plate is large and the display becomes dark.

Further, in the above-mentioned conventional active matrix liquid crystal display device, since the pixel electrode provided on one substrate of the liquid crystal cell is formed avoiding the thin film transistor, the area of the pixel electrode is small and therefore the aperture ratio is low, This has also been a factor in darkening the display.

Further, in the active matrix type liquid crystal cell, as described above, the capacitor electrode is provided on the substrate provided with the pixel electrode and the thin film transistor, and the compensation capacitance is provided by the capacitor electrode, the pixel electrode and the gate insulating film therebetween. However, the conventional liquid crystal display device cannot secure a sufficient capacitance value of the compensation capacitance.

That is, the capacitor electrode is generally formed of the same metal film as the gate electrode of the thin film transistor. However, in the conventional liquid crystal display device, the light incident from the front surface side of the thin film transistor has the front side polarizing plate and the liquid crystal cell. And is reflected by the reflection plate through the back surface side polarizing plate in order, and this reflected light is emitted through the back surface side polarizing plate, the liquid crystal cell and the front surface side polarizing plate in sequence, so that among the light that has entered the liquid crystal cell, Light incident on the portion where the capacitor electrode is provided is blocked by the capacitor electrode.

The capacitance value of the compensation capacitance increases as the area where the capacitor electrode and the pixel electrode face each other increases, but in the conventional liquid crystal display device described above, when the capacitor electrode is formed large, that amount is increased. Since the light transmission area of the pixel portion becomes small, the aperture ratio of the liquid crystal display device further decreases.

Therefore, conventionally, the size of the capacitor electrode is determined in consideration of the aperture ratio of the liquid crystal display device.
In this case, the capacitance value of the compensation capacitance cannot be sufficiently secured, so that the holding voltage of the pixel in the non-selection period changes, causing flicker in the display.

Although the present invention is of a reflective type, the light quantity loss due to light absorption by the substrate and the polarizing plate of the liquid crystal cell can be reduced, and the aperture ratio can be increased to obtain a bright display. It is an object of the present invention to provide an active matrix liquid crystal display device capable of sufficiently securing the capacitance value of the capacitance.

[0017]

An active matrix liquid crystal display device of the present invention comprises an active matrix type liquid crystal cell having a thin film transistor as an active element and a polarizing plate arranged on the surface side of the liquid crystal cell, ,
The liquid crystal cell is one in which a plurality of pixel electrodes and a plurality of thin film transistors respectively corresponding to these pixel electrodes are arranged on the inner surface of the back side substrate, and a counter electrode is provided on the inner surface of the front side substrate, The thin film transistor includes a gate electrode formed on the back surface side substrate, a gate insulating film formed on almost the entire surface of the back surface side substrate to cover the gate electrode, and the gate electrode formed on the gate insulating film. The thin film transistor comprises a semiconductor film formed to face each other and a source electrode and a drain electrode formed on both sides of the semiconductor film, and the thin film transistor is covered with a protective insulating film provided over substantially the entire surface of the back side substrate. The pixel electrode is formed of a metal film that reflects light, and is provided on the protective insulating film to cover the thin film transistor. A contact hole formed in the protective insulating film is connected to the source electrode of the thin film transistor, and further, a first capacitor electrode electrically connected to the source electrode of the thin film transistor is provided on the gate insulating film, A second capacitor electrode that faces the first capacitor electrode across the gate insulating film is provided on the back-side substrate, and by the capacitor electrode and the gate insulating film between them,
It is characterized in that a compensation capacitor for compensating the holding voltage of the pixel in the non-selected period is formed.

In the present invention, the first capacitor electrode is preferably formed integrally with the source electrode of the thin film transistor, and the second capacitor electrode is preferably formed of the same metal film as the gate electrode of the thin film transistor.

[0019]

In the active matrix liquid crystal display device of the present invention, the incident light from the front surface side is incident on the liquid crystal cell through the polarizing plate, and the light passing through the liquid crystal layer is on the inner surface of the rear side substrate of the liquid crystal cell. The light reflected by the pixel electrode made of a metal film that reflects light is incident on the polarizing plate through the liquid crystal layer again, and the light transmitted through the polarizing plate is emitted to the front surface side of the liquid crystal display device.

That is, in this liquid crystal display device, the pixel electrode provided on the inner surface of the back surface side substrate of the liquid crystal cell also serves as a reflection film, so that the light incident from the front surface side of the liquid crystal cell on the back surface side substrate can be reflected. In addition to reflecting on the inner surface, a single polarizing plate is provided only on the surface side of the liquid crystal cell, and the polarizing action that makes the incident light from the outside into linearly polarized light and the light whose polarization state has been changed are image light. It has both the function of analyzing light.

In this liquid crystal display device, of both substrates of the liquid crystal cell, light passes through only the front surface side substrate and only one polarizing plate. It is possible to reduce the light amount loss due to light absorption.

In addition, in this liquid crystal display device, the thin film transistor provided on the inner surface of the back side substrate of the liquid crystal cell is covered with a protective insulating film, and the pixel electrode also serving as a reflective film is provided, and the thin film transistor is provided on the protective insulating film. Since it is provided so as to cover it, the area of this pixel electrode can be increased to increase the aperture ratio.

Furthermore, in this liquid crystal display device, since the pixel electrode reflects light, the capacitor electrode provided on the back side of the pixel electrode does not affect the aperture ratio, and therefore the area of the capacitor electrode is small. Can be arbitrarily selected, and the first capacitor electrode electrically conducting with the source electrode of the thin film transistor is provided on the gate insulating film, and the gate insulating film is sandwiched between the first capacitor electrode and the back side substrate. Since the second capacitor electrode facing the first capacitor electrode is provided and the compensation capacitor is constituted by these capacitor electrodes and the gate insulating film between them, the insulating film of the compensation capacitor can be made thin. It is possible to sufficiently secure the capacitance value of the compensation capacitor.

In the liquid crystal display device according to the present invention, if the first capacitor electrode is formed integrally with the source electrode of the thin film transistor and the second capacitor electrode is formed of the same metal film as the gate electrode of the thin film transistor,
The compensation capacitor may be formed by using a thin film transistor forming process.

[0025]

1 is a sectional view of a part of an active matrix liquid crystal display device showing an embodiment of the present invention, and FIG. 2 is an enlarged sectional view of a part of a back side substrate of the liquid crystal cell. The active matrix liquid crystal display device of this embodiment displays a color image, and is composed of a liquid crystal cell 10, one polarizing plate 30, and one retardation plate 40. Is disposed on the front surface side of the liquid crystal cell 10, and the retardation plate 40 is disposed between the liquid crystal cell 10 and the polarizing plate 30.

First, the liquid crystal cell 10 will be described. The liquid crystal cell 10 is a thin film transistor (hereinafter, T).
(Hereinafter referred to as FT) is an active matrix type cell in which an active element is used. In this embodiment, molecules of liquid crystal 27 are twist-aligned between the substrates 11 and 12.

Of the pair of substrates 11 and 12 facing each other across the liquid crystal layer of the liquid crystal cell 10, the substrate on the back surface side (see FIG. 1).
The lower substrate 11 in FIG. 1 is an insulating substrate made of a glass plate or the like (however, it does not have to be transparent). The electrodes 13 and a plurality of TFTs 14 corresponding to the respective pixel electrodes 13 are arranged in a matrix in the row direction and the column direction, and a transparent alignment film 24 is provided thereon.

The TFT 14 has a gate electrode 15 formed on the substrate 11, a gate insulating film 16 formed on almost the entire surface of the substrate 11 so as to cover the gate electrode 15, and the gate insulating film 16 formed on the gate insulating film 16. An i-type semiconductor film 17 made of a-Si (amorphous silicon) or the like formed to face the gate electrode 15, and an n-type semiconductor made of a-Si or the like in which both sides of the i-type semiconductor film 17 are doped with impurities. The TFT 14 is composed of a source electrode 19s and a drain electrode 19d formed via a film 18.
Protective insulating film 2 provided on almost the entire surface of substrate 11
Covered with 1.

Reference numeral 20 denotes a blocking insulating film formed on the channel region of the i-type semiconductor film 17, and the blocking insulating film 20 protects the i-type semiconductor film 17 when the n-type semiconductor film 18 is patterned. It is provided for this purpose.

Although not shown, the back side substrate 11 is also provided.
A gate line (address line) for supplying a gate signal to the gate electrode 15 of the TFT 14 and a data line for supplying a data signal corresponding to image data to the drain electrode 19d of the TFT 14 are wired on the upper side. .

The gate line is formed integrally with the gate electrode 15 of the TFT 14 on the substrate 11,
The gate line is covered with the gate insulating film 16 except for its terminal portion. Also, the above data line is
It is formed on the gate insulating film 16, and this data line is connected to the drain electrode 19d of the TFT 14.

The pixel electrode 13 is provided on the protective insulating film 21 so as to cover the TFT 14, and each pixel electrode 13 corresponds to the contact hole 21a formed in the protective insulating film 21. TFT1
4 is connected to the source electrode 19s.

The pixel electrode 13 is made of a metal film that reflects light, for example, a metal film having a high reflectance such as Al alloy. That is, the pixel electrode 13 also serves as a light reflection film, and its surface (reflection surface) is almost a mirror surface.

Further, on the gate insulating film 16,
The TFT is placed below a part of the pixel electrode 13 and
A first capacitor electrode 22 electrically connected to the source electrode 19 s of 14 is provided, and a first capacitor electrode 22 facing the first capacitor electrode 22 is provided on the back surface side substrate 11 with the gate insulating film 16 interposed therebetween. Two capacitor electrodes 23 are provided, and the capacitor electrodes 22 and 23 and the gate insulating film 16 between them form a compensation capacitance Cs for compensating the holding voltage of the pixel in the non-selection period.

The first capacitor electrode 22 has the T
The first capacitor electrode 22 is made of the same metal film as the source and drain electrodes 19s and 19d of the FT14.
Are formed integrally with the source electrode 19s.

In this embodiment, the TFT 14 described above is used.
After forming the gate electrode 15 on the substrate 11, the gate insulating film 16, the i-type semiconductor film 17, and the blocking insulating film 2 are formed.
0 is sequentially formed to pattern the blocking insulating film 20, and then an n-type semiconductor film 18 and a source / drain electrode metal film are sequentially formed to form the metal film, the n-type semiconductor film 18 and The i-type semiconductor film 17 is formed on the TFT 14
Of the metal film and the n-type semiconductor film 18, and the source and drain electrodes 19s,
It is formed by patterning into a shape of 19d,
Therefore, below the first capacitor electrode 22,
The i-type semiconductor film 17 and the n-type semiconductor film 18 are left.

The second capacitor electrode 23 is
It is made of the same metal film as the gate electrode 15 of the TFT 14, and the second capacitor electrode 23, the gate electrode 15 and the gate line are formed by forming a metal film on the substrate 11, and the metal film is formed by a photolithography method. And are simultaneously formed by patterning.

Although not shown, a capacitor line formed integrally with the second capacitor electrode 23 is laid on the back side substrate 11, and the second capacitor electrode 23 connects the capacitor line. To the reference potential.

On the other hand, the front surface side substrate (upper side substrate in FIG. 1) 12 of the liquid crystal cell 10 is a glass plate or a transparent substrate (glass plate in the figure) made of a transparent resin film or the like,
On the inner surface of the front-side substrate 12, that is, the surface facing the liquid crystal layer, a transparent counter electrode 25 that faces all the pixel electrodes 13 on the back-side substrate 11 is provided, and a transparent alignment film 26 is formed thereon. It is provided. The counter electrode 25
Is a single film electrode facing all of the pixel electrodes on the back substrate 11.

Although not shown, the back-side substrate 11 and the front-side substrate 12 are bonded to each other via a frame-shaped sealing material at the outer peripheral edge thereof, and the liquid crystal 27 is provided on both substrates 1.
The region surrounded by the sealing material between 1 and 12 is filled.

The liquid crystal 27 is a nematic liquid crystal having a positive dielectric anisotropy, and the molecules of the liquid crystal 27 are formed on both substrates 1.
The orientation films on the substrates 11 and 12 are regulated by the orientation films 24 and 26 provided on the substrates 1 and 12, respectively.
The twist orientation is provided between the first and the second portions. The alignment films 24 and 26 are horizontal alignment films made of polyimide or the like, and the film surfaces thereof are subjected to an alignment treatment by rubbing.

Further, the polarizing plate 30 is a polarizing plate whose one surface, for example, the surface, is a light scattering surface A, and this light scattering surface A is shown by enlarging a partial cross section thereof in FIG. As described above, the transparent film 31 having minute irregularities is formed on the surface of the polarizing plate 30.

The transparent film 31 is made of a resin having a high light transmittance such as an acrylic resin, and the transparent film 31 is transferred and printed on the surface of the polarizing plate 30 by using a printing material having a minute unevenness made of a resin material. Curing, a method in which the resin material is applied to the surface of the polarizing plate 30 to a uniform thickness, and then unevenness is formed by embossing, followed by curing, or transparent fine particles such as silica are mixed in the resin material. It is formed by any of the methods of applying an object to the surface of the polarizing plate 30 and curing it.

The average height h of the irregularities of the transparent film 31 (the difference between the heights of the concave surface and the convex surface) h is 1 to 5 μm, the average pitch p of the irregularities is 5 to 40 μm, and the haze value of the light scattering surface A is Is 9 to 14%.

The haze value is measured according to JIS K 67.
It is a value measured by an integrating sphere type light transmittance measuring device (haze meter) according to 14. This haze value is calculated by the following formula.

Total light transmittance; Tt (%) = T2 / T1 parallel light transmittance; Tp (%) = Tt-Td diffuse transmittance; Td (%) = [T4-T3 * (T2 / T1)]
/ T1 haze value; H (%) = (Td / Tt) × 100 T1; Incident light amount T2; Total light transmitted light amount T3; Measuring device diffused light amount T4; Test piece (transparent film 31) and diffused light amount by measuring device Further, the retardation plate 40 is made of a uniaxially stretched film such as polycarbonate, and the retardation plate 40 is provided between the liquid crystal cell 10 and the polarizing plate 30 disposed on the surface side of the liquid crystal cell 10. The retardation plate 40 is arranged with the slow axis (stretching axis) and the transmission axis of the polarizing plate 30 obliquely displaced by a predetermined angle. The retardation plate 40 is adhered to the surface of the liquid crystal cell 10 (the outer surface of the front substrate 12),
The polarizing plate 30 is adhered to the surface of the retardation plate 40.

In the liquid crystal display device of this embodiment,
An alignment direction of liquid crystal molecules on both substrates 11 and 12 of the liquid crystal cell 10 (rubbing direction of the alignment films 24 and 26),
The direction of the transmission axis of the polarizing plate 30 and the direction of the slow axis of the retardation plate 40 are set as follows.

In this embodiment, the orientation direction of the liquid crystal molecules on the rear substrate 11 of the liquid crystal cell 10 is 0 °.
Of the liquid crystal cell 10 on the front side substrate 12 of the liquid crystal cell 10 and the polarizing plate 30.
The transmission axis direction and the slow axis direction of the retardation plate 40 are set.

That is, FIG. 4 shows the alignment direction of the liquid crystal molecules of the liquid crystal cell 10 and the retardation plate 40 in the liquid crystal display device.
11 is a plan view showing the slow axis of the liquid crystal cell 10 and the transmission axis of the polarizing plate 30. In FIG.
The orientation direction of the liquid crystal molecules on the upper side, 12a is the liquid crystal cell 10
3 shows the alignment direction of liquid crystal molecules on the front surface side substrate 12.

As shown in FIG. 4, the liquid crystal molecule alignment direction 12a on the front surface side substrate 12 of the liquid crystal cell 10 is the surface with respect to the liquid crystal molecule alignment direction 11a on the rear surface side substrate 11, that is, the azimuth angle of 0 °. 9 from left to right
It is offset by 0 °, and the molecules of the liquid crystal are twist-aligned between the substrates 11 and 12 at a twist angle of approximately 90 °.

Further, in FIG. 4, reference numeral 30a denotes a polarizing plate 30.
Of the transmission axis 30a of the polarizing plate 30.
Is approximately 45 ° counterclockwise as viewed from the front side with respect to the direction of 0 ° azimuth. That is, this polarizing plate 30
Of the transmission axis 30a of the liquid crystal cell 10 is obliquely shifted by about 45 ° with respect to the liquid crystal molecule orientation direction 12a on the front surface side substrate 12 of the liquid crystal cell 10.

Further, in FIG. 4, reference numeral 40a denotes a slow axis of the retardation plate 40. The slow axis 40a of the retardation plate 40 is viewed from the front side with respect to the direction of the azimuth angle of 0 °. It is about 140 ° counterclockwise. In other words, the slow axis 40a of the retardation plate 40 is deviated from the transmission axis 30a of the polarizing plate 30 obliquely by approximately 95 ° counterclockwise when viewed from the surface side.

This liquid crystal display device displays by utilizing external light such as natural light or indoor illumination light, and external light incident from the surface side passes through the polarizing plate 30 and the phase difference plate 40. Light incident on the liquid crystal cell 10 and passing through the liquid crystal layer is reflected by the pixel electrode 13 also serving as a reflective film provided on the inner surface of the back surface side substrate 11 of the liquid crystal cell 10, and again the liquid crystal layer and the retardation plate 40. The light that has passed through the polarizing plate 30 and passes through the polarizing plate 30 is emitted to the surface side of the liquid crystal display device.

That is, in this liquid crystal display device, the pixel electrode 13 provided on the inner surface of the back surface side substrate 11 of the liquid crystal cell 10 is formed of a metal film that reflects light, so that the liquid crystal cell 10 is incident from the front surface side. The light is reflected by the pixel electrode 13 on the inner surface of the back surface side substrate 11 of the liquid crystal cell 10, and one polarizing plate 30 is provided only on the front surface side of the liquid crystal cell 10, and the incident light is applied to the polarizing plate 30. It is provided with a polarization effect of linearly polarized light and an analysis effect of controlling the emission of light.

The display operation of the liquid crystal display device will be described. In this liquid crystal display device, since the slow axis 40a of the retardation plate 40 is obliquely displaced from the transmission axis 30a of the polarizing plate 30, the polarization The linearly polarized light that has entered through the plate 30 changes its polarization state due to its birefringence effect in the process of passing through the retardation plate 40 to become elliptically polarized light, and this elliptically polarized light passes through the liquid crystal layer of the liquid crystal cell 10 and The polarization state can be further changed by the birefringence effect, and the polarization state can be further changed by the birefringence effect while being reflected by the inner surface of the rear substrate 11 of the liquid crystal cell 10 and passing through the liquid crystal layer and the retardation plate 40 again. It is incident on the polarizing plate 30.

The reflected light that has entered the polarizing plate 30 is non-linearly polarized light whose polarization state is changed by the birefringence effect of the retardation plate 40 and the liquid crystal layer. Only the wavelength light of the polarization component that passes through 30 passes through the polarizing plate 30 and is emitted, and this emitted light becomes colored light corresponding to that wavelength.

That is, this liquid crystal display device includes the retardation plate 4
0 and the birefringence effect of the liquid crystal layer of the liquid crystal cell 10 and the polarizing plate 3
Light is colored by utilizing the polarization of 0 and the analysis function. According to this liquid crystal display device, a very bright colored light is obtained as compared with a liquid crystal display device using a commonly used color filter. Can be obtained.

That is, the color filter absorbs light having a wavelength other than the wavelength range corresponding to the color and colors the light.
Since this color filter also absorbs light in the wavelength range corresponding to that color with a considerably high absorptivity, in a liquid crystal display device that colors light with the color filter, the wavelength that becomes colored light of the light that enters the display device. The amount of colored light passing through the color filter is considerably reduced as compared with the amount of light in the band.

In this respect, since the liquid crystal display device of the above-mentioned embodiment colors the transmitted light without using the color filter, the color filter does not absorb light, and the retardation plate 40 and the liquid crystal layer are Since the polarized state of the transmitted light is only changed and the absorbed light is hardly absorbed, the amount of the colored light which is transmitted through the polarizing plate 30 and emitted after the polarized state is changed by the birefringence effect passes through the polarizing plate 30. Since the amount of light in the wavelength band that becomes the colored light in the linearly polarized light that has entered is substantially the same, colored light with high brightness can be obtained.

Further, in the liquid crystal display device in which light is colored by the color filter, the display color is determined by the color of the color filter, so that one pixel cannot display a plurality of colors. According to the liquid crystal display device, one pixel can display a plurality of colors.

That is, in the liquid crystal display device of the above embodiment, the birefringence effect of the retardation plate 40 does not change, but the birefringence effect of the liquid crystal layer of the liquid crystal cell 10 is between the pixel electrode 13 and the counter electrode 25. It changes as the alignment state of the liquid crystal molecules changes according to the magnitude of the voltage applied to.

When a voltage is applied between the electrodes 13 and 25 of the liquid crystal cell 10 so that the liquid crystal molecules rise and align substantially perpendicularly to the surfaces of the substrates 11 and 12, the birefringence effect of the liquid crystal layer is apparently almost the same. It disappears, but even then, the polarizing plate 3
The light entering through 0 can change its polarization state by the birefringence effect of the retardation plate 40.

Therefore, if the voltage applied to the liquid crystal cell 10 is controlled to change the birefringence effect of the liquid crystal layer,
In accordance therewith, the polarization state of the light passing through the retardation plate 40 and the liquid crystal layer of the liquid crystal cell 10 changes, so that the color of the colored light that passes through the polarizing plate 30 and is emitted can be changed. One pixel can display a plurality of colors.

The display drive of this liquid crystal display device is basically the same as the display drive of a generally known active matrix liquid crystal display device (those using TFTs as active elements), and the liquid crystal cell 10 faces each other. A reference signal having a waveform synchronized with the synchronization signal is supplied to the electrode 25, and a gate signal is sequentially supplied to each gate line in synchronization with the synchronization signal, and in synchronization with that, a potential corresponding to image data is supplied to each data line. It may be performed by supplying a data signal. If the potential of the data signal is controlled according to the image data, the data signal having the potential corresponding to the image data is supplied to the pixel electrode via the TFT 14 during the selection period of the pixels in each row. 1
3 and the charge is stored in the compensation capacitor Cs,
A voltage corresponding to the amount of charge stored in the compensation capacitance Cs is applied between the pixel electrode 13 and the counter electrode 25 during the non-selection period.

The display color of the liquid crystal display device will be described. For example, as described above, the liquid crystal cell 10 is one in which liquid crystal molecules are twist-aligned between the substrates 11 and 12 at a twist angle of about 90 °. Both substrates 11,
Alignment directions 11a and 12a of liquid crystal molecules on 12;
The transmission axis 30a of the polarizing plate 30 and the slow axis 4 of the retardation plate 40
0a are in the directions shown in FIG. 4, respectively, and the value of Δn · d (the product of the refractive index anisotropy Δn of the liquid crystal 27 and the liquid crystal layer thickness d) of the liquid crystal cell 10 is about 1000 nm, and the retardation plate 40
If the retardation value of is about 600 nm, then 1
One pixel can display red, green, blue, and white colors.

FIG. 5 is a CIE chromaticity diagram showing the color change of the emitted light with respect to the applied voltage of the liquid crystal display device. The liquid crystal display device has a direction of 30 ° with respect to its normal line (the azimuth may be arbitrary). The result of observing the emitted light from the normal direction of the liquid crystal display device is shown by allowing white light to enter.

As shown in FIG. 5, in the liquid crystal display device, as the voltage value applied between the electrodes 13 and 25 of the liquid crystal cell 10 is increased, the color of the emitted light becomes P.
The color changes from point S to point Pe as shown by the arrow, and in the middle of that, the colors become green G, blue B, red R, and white W with high light intensity and good color purity.

The x coordinate value and the y coordinate value of each of the colors G, B, R and W are x = 0.299, y for green G.
= 0.396, blue B x = 0.247, y = 0.23
3, red R x = 0.399, y = 0.402, white W x
= 0.332, y = 0.351, and both have sufficiently satisfactory color purity.

In the above liquid crystal display device, as shown in FIG.
As described above, the color of the emitted light becomes a color close to white W even while the color of the emitted light changes from green G to blue B.
Since the color change with respect to the voltage change is large and the voltage control for displaying this color is troublesome, the white W
It is desirable that the display of (1) is performed with a voltage higher than the voltage for obtaining the display color of red R.

As described above, in the above liquid crystal display device, the colors of the emitted light are green G, blue B, red R, and white W according to the applied voltage, so that red, green, and blue are formed in one pixel. It is also possible to display a white color, or by displaying different colors in a plurality of adjacent pixels, it is possible to display a mixed color of a plurality of colors of red, green, blue, and white.

The liquid crystal display device of the above embodiment is
Green, blue, and white colors are displayed. The display colors of this liquid crystal display device are the applied voltage and both substrates 1 of the liquid crystal cell 10.
Alignment direction 11a, 12a of liquid crystal molecules on 1, 12
And the twist angle of the liquid crystal molecules and the transmission axis 3 of the polarizing plate 30.
Since it is determined by the direction of 0a and the direction of the slow axis 40a of the retardation plate 40, the display color of the liquid crystal display device can be arbitrarily selected by selecting these conditions.

In the above liquid crystal display device, the pixel electrode 13 provided on the inner surface of the back side substrate 11 of the liquid crystal cell 10 also serves as a reflection film, and the pixel electrode 13 is formed on the inner surface of the back side substrate 11 of the liquid crystal cell 10. Since the light is reflected, only the front side substrate 12 of the two substrates 11 and 12 of the liquid crystal cell 10 allows the light to pass therethrough, and since only one polarizing plate 30 is provided, the liquid crystal cell It is possible to reduce the light amount loss due to the light absorption in the substrate and the polarizing plate.

In this liquid crystal display device, light also passes through the phase difference plate 40 and the liquid crystal layer of the liquid crystal cell 10, but since the phase difference plate 40 and the liquid crystal layer absorb little light as described above, There is almost no light loss due to these.

In addition, the above liquid crystal display device has the liquid crystal cell 1
Since the TFT 14 disposed on the inner surface of the back side substrate 11 of 0 is covered with the protective insulating film 21 and the pixel electrode 13 also serving as a reflective film is provided on the protective insulating film 21 to cover the TFT 14, The aperture ratio can be increased by increasing the area of the electrode 13. Therefore, according to the above liquid crystal display device, it is possible to obtain a bright display by reducing the light amount loss due to the light absorption in the substrate of the liquid crystal cell and the polarizing plate and increasing the aperture ratio, though it is of a reflective type. .

Further, since the liquid crystal display device reflects light on the pixel electrode 13, the capacitor electrodes 22 and 23 provided on the back side of the pixel electrode 13 do not affect the aperture ratio. Therefore, the areas of the capacitor electrodes 22 and 23 can be arbitrarily selected, and the first capacitor electrode 22 electrically connected to the source electrode 19s of the TFT 14 is formed on the gate insulating film 16.
And a second electrode facing the first capacitor electrode 22 with the gate insulating film 16 interposed therebetween on the rear substrate 11.
Since the capacitor electrode 23 is provided and the compensation capacitance Cs is formed by the capacitor electrodes 22 and 23 and the gate insulating film 16 between them, the insulation film thickness of the compensation capacitance Cs is thinned to reduce the compensation capacitance Cs. A sufficient capacity value can be secured.

That is, the capacitance value of the capacitance formed by opposing the pair of electrodes with the insulating film sandwiched therebetween is determined by the opposing area of the pair of electrodes and the film thickness of the insulating film, and the opposing area of the electrodes is the same. In some cases, the thinner the insulating film, the larger the capacitance value.

Then, conventionally, a pixel electrode is formed on a substrate on which a pixel electrode and a TFT are provided, the capacitor electrode is covered with a gate insulating film of the TFT, and the pixel electrode is formed on the capacitor electrode, thereby compensating the pixel. The capacitance is formed by the pixel electrode, the capacitor electrode, and the gate insulating film between them, but as described above, the gate insulating film 1
When the pixel electrode 13 is formed on the protective insulating film 21 provided on the substrate 6, the capacitor electrode 2 formed on the substrate 11
When the compensation capacitance Cs is composed of 3 and the pixel electrode 13, the insulating film becomes a two-layer film of the gate insulating film 16 and the protective insulating film 21, and the insulating film of the compensation capacitance Cs becomes thicker, and the capacitance value becomes It gets smaller.

Therefore, in the above embodiment, the gate insulating film 1 is formed.
6 is provided with a first capacitor electrode 22 which is electrically connected to the source electrode 19s, and a second capacitor electrode 23 is provided on the rear surface side substrate 11, and these capacitor electrodes 2 are provided.
2, 23 and the gate insulating film 16 between them constitute the compensation capacitance Cs. In this case, since the insulating film thickness of the compensation capacitance Cs is only the gate insulating film 16, the insulating film of the compensation capacitance Cs is formed. It is possible to reduce the thickness and secure a sufficient capacitance value.

Since the area of the capacitor electrodes 22 and 23 can be arbitrarily selected as described above, if the capacitor electrodes 22 and 23 are formed to be large, the capacitance value of the compensation capacitance Cs can be further increased. I can, but
When the capacitor electrodes 22 and 23 are made large, the first capacitor electrode 2 caused by an interlayer short-circuit between the capacitor electrodes 22 and 23 caused by a pinhole defect in the protective insulating film 21 or a pinhole defect caused in the gate insulating film 16.
Since the occurrence rate of the interlayer short circuit between the pixel electrode 13 and the pixel electrode 13 becomes high, it is desirable that the area of the capacitor electrodes 22 and 23 be as small as possible within a range where a desired capacitance value can be obtained.

Further, in the above embodiment, the first capacitor electrode 22 is formed integrally with the source electrode 19a of the TFT 14, and the second capacitor electrode 23 is formed of the same metal film as the gate electrode 15 of the TFT 14. Therefore, the compensation capacitor CS can be formed by using the process of forming the TFT 14, and therefore the liquid crystal cell 10 can be manufactured at low cost, and the pixel electrode 1 of the liquid crystal cell 10 can be manufactured.
Since 3 also serves as a reflection film, there is no need to provide a separate reflection plate, so that the cost of the liquid crystal display device can be reduced.

Further, since the pixel electrode 13 is an extremely thin metal film, the surface of the pixel electrode 13, that is, the reflecting surface is almost a mirror surface. However, in the above embodiment, the polarizing plate 3 is used.
Since the surface of 0 is the light-scattering surface A, the incident light and the outgoing light to the liquid crystal display device can be scattered by the light-scattering surface A. Therefore, even if the reflection surface of the pixel electrode 13 is a mirror surface. , The external image of the display observer's face or its background is not reflected.

That is, since the liquid crystal display device described above colors light without using a color filter and has a high light transmittance, the reflecting surface of the pixel electrode 13 is a mirror surface and the polarizing plate 30 is If you do not have a light scattering function,
An external image such as the face of the display observer or its background appears on the reflecting surface and appears as if it overlaps the display image. However, if the polarizing plate 30 has a light scattering function, the external image is reflected. Does not occur.

In addition, in the above liquid crystal display device, if the reflection surface of the pixel electrode 13 is a mirror surface, the light whose polarization state has been changed by the birefringence effect of the liquid crystal layer is reflected without being scattered and is reflected by the polarizing plate 30. Can be made incident,
Further, when the surface of the polarizing plate 30 is the light scattering surface A, the light incident on the liquid crystal display device from the surface side is scattered and then becomes linearly polarized by the polarizing action of the polarizing plate 30, and the light reflecting surface is The light reflected by is converted into image light by the analyzing action of the polarizing plate 30 and then scattered, so that the light incident through the polarizing plate 30 is scattered until it enters the polarizing plate 30 again. Therefore, it is possible to display a high quality image.

The scattering effect of the light-scattering surface A is determined by the above-mentioned haze value. If the haze value is 25% or more, the light which has become the image light is also largely scattered due to the analyzing action of the polarizing plate 30. When the haze value of the light scattering surface A is in the range of 9 to 14%, a clear display image is obtained although the displayed image becomes unclear and the external image is reflected when the haze value is 6% or less. It is possible to eliminate the reflection of the external image as well as obtain.

In the above embodiment, the i-type semiconductor film 17 and the n-type semiconductor film 18 which are the constituent films of the TFT 14 are left under the first capacitor electrode 22, but the above T
After patterning the i-type semiconductor film 17 of the FT 14, an n-type semiconductor film 18 and a metal film for source / drain electrodes are formed, and the metal film and the n-type semiconductor film 18 are connected to the source / drain electrodes 19s and 19d. When patterned by the method of patterning, the n-type semiconductor film 18 is left under the first capacitor electrode 22. Further, the first capacitor electrode 22 may be formed of a metal film different from the source and drain electrodes 19s and 19d of the TFT 14.

Further, in the liquid crystal display device of the above embodiment, the retardation plate 40 is arranged between the liquid crystal cell 10 and the polarizing plate 30, but the retardation plate 40 may be omitted, and in that case as well. If the transmission axis of the polarizing plate 30 is slanted with respect to the alignment direction of the liquid crystal molecules on the front surface side substrate 12 of the liquid crystal cell 10, the light incident through the polarizing plate 30 will be the liquid crystal layer of the liquid crystal cell 10. The polarization state can be changed by the birefringence effect in the process of passing through, and the polarization state can be further changed in the process of passing through the liquid crystal layer by being reflected by the pixel electrode 13 on the inner surface of the back side substrate 11 of the liquid crystal cell 10. Since the light is incident on the polarizing plate 30, the light of the polarized component that passes through the polarizing plate 30 can be emitted as colored light, and the colored light can be controlled by controlling the voltage applied to the liquid crystal cell 10. It is possible to change the color.

However, as in the above embodiment, the liquid crystal cell 1
If the retardation plate 40 is disposed between the polarizing plate 30 and the polarizing plate 30, the light incident through the polarizing plate 30 will pass through the liquid crystal layer of the liquid crystal cell 10 and enter the polarizing plate 30 again. Since the polarization state can be changed also by the birefringence effect of the phase difference plate 40, when a voltage is applied to the liquid crystal cell 10 so that the liquid crystal molecules rise and align substantially perpendicularly to the surfaces of the substrates 11 and 12, that is, the birefringence effect of the liquid crystal layer. Even when apparently almost disappeared, light whose polarization state is changed by the birefringence effect of the retardation plate 40 can be made incident on the polarizing plate 30 to obtain colored light. In this case, two or more retardation plates may be arranged so as to overlap each other.

Further, in the above embodiment, the twist angle of the liquid crystal molecules of the liquid crystal cell 10 is set to about 90 °, but the twist angle of the liquid crystal molecules is not limited to 90 °, but may be 180 to 2 for example.
The liquid crystal cell 10 may be set at 70 °, and the liquid crystal cell 10 may be one in which liquid crystal molecules are aligned in a homogeneous alignment, homeotropic alignment, hybrid alignment or the like.

Further, although the liquid crystal display device of the above embodiment displays a color image by utilizing the birefringence effect of the liquid crystal and the retardation plate, the present invention is the active matrix liquid crystal of TN type or STN type. It can also be applied to a display device.

[0090]

According to the active matrix liquid crystal display device of the present invention, since the pixel electrode provided on the inner surface of the back side substrate of the liquid crystal cell also serves as the light reflecting film, the liquid crystal cell Light passes only through the front side substrate,
Also, since there is only one polarizing plate, it is possible to reduce the light amount loss due to light absorption in the substrate of the liquid crystal cell and the polarizing plate, and to protect the thin film transistor arranged on the inner surface of the back side substrate of the liquid crystal cell Since a pixel electrode which is covered with an insulating film and also serves as a reflective film is provided on the protective insulating film so as to cover the thin film transistor, the area of the pixel electrode can be increased to increase the aperture ratio. However, it is possible to obtain a bright display by reducing the light amount loss due to light absorption in the substrate of the liquid crystal cell and the polarizing plate and increasing the aperture ratio.

Further, in this liquid crystal display device, since the light is reflected by the pixel electrode, the capacitor electrode provided on the back side of the pixel electrode does not affect the aperture ratio. The area can be arbitrarily selected, and the first capacitor electrode electrically conducting with the source electrode of the thin film transistor is provided on the gate insulating film, and the gate insulating film is sandwiched on the back side substrate. Since the second capacitor electrode facing the first capacitor electrode is provided and the compensation capacitance is constituted by these capacitor electrodes and the gate insulating film between them, the insulating film thickness of the compensation capacitance is reduced, It is possible to sufficiently secure the capacitance value of this compensation capacitance.

In the liquid crystal display device according to the present invention, if the first capacitor electrode is formed integrally with the source electrode of the thin film transistor and the second capacitor electrode is formed of the same metal film as the gate electrode of the thin film transistor,
The compensation capacitor may be formed by using a thin film transistor forming process.

[Brief description of drawings]

FIG. 1 is a sectional view of a part of an active matrix liquid crystal display device showing an embodiment of the present invention.

FIG. 2 is an enlarged cross-sectional view of a part of a backside substrate of a liquid crystal cell.

FIG. 3 is an enlarged cross-sectional view of the surface of a polarizing plate.

FIG. 4 is a plan view showing a liquid crystal molecule alignment direction of a liquid crystal cell, a slow axis of a retardation plate, and a transmission axis of a polarizing plate.

FIG. 5 is a CIE showing a color change of emitted light with respect to an applied voltage.
Chromaticity diagram.

[Explanation of symbols]

 10 ... Liquid crystal cell 11 ... Back side substrate 12 ... Front side substrate 13 ... Pixel electrode (reflection film) 14 ... TFT 15 ... Gate electrode 16 ... Gate insulating film 17 ... i-type semiconductor film 18 ... N-type semiconductor film 19s ... Source electrode 19d ... Drain electrode 21 ... Protective insulating film 21a ... Contact hole 22 ... First capacitor electrode 23 ... Second capacitor electrode Cs ... Compensation capacitance 24 ... Alignment film 25 ... Counter electrode 26 ... Alignment film 27 ... Liquid crystal 30 ... Polarizing plate 40 ... Retardation plate

Claims (2)

[Claims] 1. A reflection type active matrix liquid crystal display device comprising an active matrix type liquid crystal cell having a thin film transistor as an active element and a polarizing plate disposed on the surface side of the liquid crystal cell, The liquid crystal cell is one in which a plurality of pixel electrodes and a plurality of thin film transistors corresponding to the respective pixel electrodes are provided on the inner surface of the back surface side substrate, and a counter electrode is provided on the inner surface of the front surface side substrate. Is a gate electrode formed on the back-side substrate, a gate insulating film formed over almost the entire back-side substrate covering the gate electrode, and facing the gate electrode on the gate insulating film. And a source electrode and a drain electrode formed on both sides of the semiconductor film. Is covered with a protective insulating film provided over substantially the entire surface of the back side substrate, the pixel electrode is made of a metal film that reflects light, and the thin film transistor is covered on the protective insulating film. A first capacitor electrode that is provided and connected to the source electrode of the thin film transistor in a contact hole formed in the protective insulating film, and that is electrically connected to the source electrode of the thin film transistor on the gate insulating film. And a second electrode facing the first capacitor electrode across the gate insulating film on the back side substrate.
Active matrix liquid crystal display device, characterized in that: . 2. The first capacitor electrode is formed integrally with the source electrode of the thin film transistor, and the second capacitor electrode is made of the same metal film as the gate electrode of the thin film transistor. The active matrix liquid crystal display device described.