JPH08248387A - Liquid crystal display - Google Patents

Abstract

(57) [Abstract] [PROBLEMS] To provide a liquid crystal display device capable of preventing display unevenness due to a delay of a drive voltage waveform applied to an electrode and applying an electric field substantially parallel to a substrate surface to a liquid crystal layer. . A plurality of active elements formed in a display region on one substrate, a plurality of pixel electrodes respectively connected to the plurality of active elements, and a plurality of scanning voltages applied to the respective active elements in the row direction. A plurality of common electrodes that apply an electric field substantially parallel to the substrate surface between the scan electrodes, a plurality of signal electrodes that apply a signal voltage to each active element in the column direction, and each pixel electrode in the row direction to the liquid crystal layer. In a liquid crystal display device including at least an electrode, a liquid crystal layer sandwiched between a pair of substrates, a scanning electrode driving unit, a signal electrode driving unit and a common electrode driving unit, a scanning electrode driving unit and a common electrode driving unit are provided. Are arranged on the same side of the display area.

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, and more particularly to an active matrix type liquid crystal display device having high image quality without display unevenness.

[0002]

2. Description of the Related Art Conventional TFT (Thin Film Tr)
2. Description of the Related Art A liquid crystal display device of an anistor type is known in which a display type represented by a twisted nematic display type is adopted.

A TFT type liquid crystal display device adopting a display system typified by the twisted nematic display system uses two transparent electrodes as electrodes for driving a liquid crystal layer, and the respective transparent electrodes face each other on a substrate interface. The liquid crystal layers are arranged side by side and the orientation of the liquid crystal is controlled by making the direction of the electric field applied to the liquid crystal layer substantially perpendicular to the substrate interface.

In the TFT type liquid crystal display device adopting the above-mentioned display system, the luminance change remarkably when the viewing angle direction is changed. Especially, when the halftone display is performed,
There is a practical problem such that the gradation level is inverted depending on the viewing angle direction.

On the other hand, when a display system in which the direction of the electric field applied to the liquid crystal is substantially parallel to the substrate interface (hereinafter referred to as the horizontal electric field display system) is adopted as the display system of the liquid crystal display device, the brightness is reduced. It is described in Document I below that the viewing angle dependency of is almost eliminated.

Further, an example of a TFT type liquid crystal display device adopting a lateral electric field display method using a pair of comb-teeth electrodes is described in, for example, the following publication II. The liquid crystal display device has not yet been put to practical use.

I “R. Kiefer, B. Webe
r, F. Windscheid and G.W. Bau
r, Proceedings of the Twelf
th International Display Re
search Conference (Japan Di
spray, '92) pp. 547-550 "II Japanese Patent Publication No. 63-21907.

[0008]

However, in Document I, there is a thin film transistor (Thin Film Tr).
There is no description of the driving method suitable for the configuration of the anistor) and the lateral electric field display method.

Further, in the structure described in Document I, in order to maintain a sufficient light transmittance and contrast ratio, for example, it is necessary to apply a high voltage of 8 V or more,
It is necessary to use a high withstand voltage drive IC with high power consumption.

In addition, the gap between the electrodes is only 10 μm.
Therefore, it is extremely difficult to secure a high aperture ratio, which is extremely narrow compared to the pixel pitch of a normal TFT type liquid crystal display device and is essential for increasing the light transmittance of the liquid crystal display panel and increasing the brightness.

On the other hand, when the gap between the electrodes is widened to secure a high aperture ratio, the electric field strength between the electrodes is lowered, and a higher driving voltage is required to maintain a sufficient light transmittance.

On the other hand, the publication II (Japanese Patent Publication No. 63-2190).
No. 7) describes a structure of a TFT type liquid crystal display device adopting a lateral electric field display system, in which a pair of comb-teeth electrodes that interlock with each other is connected to a thin film transistor.

However, the publication II (Japanese Patent Publication No. 63-
21907), 17 comb-teeth electrodes are introduced in one pixel, and in order to maintain a sufficient pixel aperture ratio (for example, 30% or more), It is necessary to make the electrode width as narrow as 1 to 2 μm or less.

In order to expand the aperture ratio to a practical level and to apply a high electric field, it is necessary to introduce a large number of electrodes having an extremely narrow width and to make the gap between the pair of electrodes as narrow as possible. .

However, it is extremely difficult to form such fine lines uniformly over the entire surface of a large-sized substrate and without breaks.

That is, the publication II (Japanese Patent Publication No. 63-2190).
In the liquid crystal display device of the TFT method adopting the horizontal electric field display method described in No. 7), there is a trade-off relationship between a low driving voltage, a high pixel aperture ratio and a manufacturing yield, and a liquid crystal display device having a bright image can be manufactured at a low cost. There was a problem that it was difficult to provide in.

Therefore, the present applicant has already applied for a TFT type liquid crystal display device which solves the above-mentioned problems and adopts a horizontal electric field display system.

According to the TFT type liquid crystal display device adopting the lateral electric field display method, which has already been applied by the applicant,
A low driving voltage and a high pixel aperture ratio can be realized, and driving can be performed with a low power consumption driving IC, whereby bright and good visual characteristics can be obtained, and cost can be reduced. Is possible.

However, in the TFT type liquid crystal display device adopting the lateral electric field display method, which has already been filed by the present applicant, there is a problem that display unevenness occurs due to the delay of the drive voltage waveform applied to the electrodes. It was

The present invention has been made in order to solve the above-mentioned problems of the prior art, and an object of the present invention is to apply electrodes to electrodes in a liquid crystal display device in which an electric field substantially parallel to the substrate surface is applied to the liquid crystal layer. It is an object of the present invention to provide a technique capable of preventing display unevenness due to delay of applied drive voltage waveform.

The above and other objects and novel features of the present invention will become apparent from the description of this specification and the accompanying drawings.

[0022]

Of the inventions disclosed in the present application, a representative one will be briefly described below.
It is as follows.

(1) A pair of substrates, a plurality of active elements formed in a display region on the one substrate, and a plurality of pixels formed on the one substrate and connected to the plurality of active elements, respectively. An electrode, a plurality of scanning electrodes formed in a row direction on the one substrate and applying a scanning voltage to respective active elements in the row direction, and a plurality of active electrodes in a column direction formed in the column direction on the one substrate. An electric field, which is formed in a row direction on one of the substrates and applies a signal voltage to the element, and a pixel electrode in the row direction, and which is substantially parallel to the substrate surface, is applied to the liquid crystal layer. A plurality of common electrodes, a liquid crystal layer sandwiched between the pair of substrates, a scanning electrode driving unit that drives the scanning electrodes, a signal electrode driving unit that drives the signal electrodes, and a driving unit of the common electrodes. A common electrode driving means that, in the liquid crystal display device having at least a common electrode driving means and said scanning electrode driving means, characterized in that arranged on the same side of the display region.

(2) In the above-mentioned means (1), the scan electrode driving means and the common electrode driving means are constituted by the same integrated circuit.

[0025]

According to each of the above-mentioned means, a plurality of active elements are arranged in a matrix and each pixel electrode in the row direction connected to the plurality of active elements and a plurality of common electrodes formed in the row direction are provided. In a liquid crystal display device in which an electric field that is substantially parallel to the substrate surface is applied to the liquid crystal layer, a plurality of scan electrodes and common electrodes formed in the row direction that apply a scan voltage to each active element in the row direction are displayed. A drive voltage is applied from the same side of the area.

As a result, the delay of the scan voltage waveform of the scan electrode in each pixel electrode and the delay of the voltage waveform of the common electrode facing each pixel electrode become substantially the same, and it is possible to prevent the occurrence of display unevenness. Therefore, it becomes possible to obtain good display characteristics.

[0027]

Embodiments of the present invention will be described below in detail with reference to the drawings.

In all the drawings for explaining the embodiments, parts having the same function are designated by the same reference numerals, and the repeated description thereof will be omitted.

FIG. 1 is a diagram showing the operation of liquid crystal in a liquid crystal panel used in a liquid crystal display device according to an embodiment of the present invention. FIGS. 1 (a) and 1 (b) are side sectional views thereof. , Figure 1
(C), (d) shows the front view.

In FIG. 1, 1 is a common electrode (common electrode), 2 is a gate insulating film, 3 is a signal electrode (drain electrode), 4 is a pixel electrode (source electrode), 5 is an alignment control film,
6 is liquid crystal molecules in the liquid crystal composition layer, 7a and 7b are substrates, 8
Is a polarizing plate, 9 is an electric field direction, and 10 is a molecular long axis orientation direction on the interface (rubbing direction).

Further, FIG. 2 shows the angle (φLC) formed by the liquid crystal molecule major axis (optical axis) direction 10 near the interface with respect to the electric field direction 9 corresponding to FIGS. FIG. 3 is a diagram showing a definition of an angle (φP) formed by a polarization transmission axis 11.

Since there are a pair of the polarizing plate 8 and the liquid crystal interface on the upper and lower sides, if necessary (φP1, φP2, φLC1, φLC
2)

In FIG. 1, the thin film transistor is omitted and a part of the wiring electrode structure is shown. Further, the liquid crystal display device of the present embodiment is composed of a plurality of pixels, but here, a part within one pixel is shown. Shows only.

FIG. 1A is a sectional view of the cell side when no voltage is applied.
The front view at that time is shown in FIG.

A linear common electrode 1 and a pixel electrode 4 are formed on the inside of a pair of transparent substrates (7a, 7b), and an alignment control film 5 also serving as a protective film is applied and oriented on the linear common electrode 1. The liquid crystal composition is sandwiched between them.

The rod-shaped liquid crystal molecules 6 are
The electrodes 1 and 4 are oriented to have a slight angle with respect to the longitudinal direction (front view of FIG. 1X (c)), that is, 45 ° ≦ | φLC | <90 °.

In FIG. 1 and FIG. 2, the major axis alignment (rubbing) direction 10 of the liquid crystal molecules 6 on the interface is indicated by an arrow.

The alignment direction of the liquid crystal molecules 6 on the upper and lower interfaces is
As a preferable example, parallel, that is, φLC1 = φLC2 (= φL
C).

The dielectric anisotropy of the liquid crystal composition is assumed to be positive.

Here, when different electric potentials are applied to the pixel electrode 4 and the common electrode 1 and a potential difference is applied between them to apply an electric field 9 to the liquid crystal composition layer, the dielectric anisotropy and electric field of the liquid crystal composition are applied. 1 (b) and FIG.
As shown in (d), the liquid crystal molecules 6 react and change their direction to the direction of the electric field.

At this time, the brightness changes due to the interaction between the refractive index anisotropy of the liquid crystal composition layer and the polarizing plate.

Next, the operation of changing the alignment direction of the liquid crystal molecules 6 as described above and changing the brightness accordingly will be described.

Generally, the light transmittance T / To when a uniaxial birefringent medium is inserted between two polarizing plates 8 arranged orthogonally to each other.
Is represented by the following equation.

[0044]

## EQU1 ## T / To = sin ² (2χeff) sin ² (πdeffΔn / λ) (1) where χeff is the effective optical axis direction of the liquid crystal composition layer (effective molecule Angle formed by the long axis direction and the polarization transmission axis), d
eff is the thickness of the effective liquid crystal composition layer having birefringence, Δn is the refractive index anisotropy, and λ is the wavelength of light.

The reason why the direction of the optical axis of the liquid crystal composition layer is set to an effective value is that the liquid crystal molecules 6 are present on the interface in the actual cell.
Are fixed, and not all liquid crystal molecules 6 are aligned parallel to each other and uniformly in the cell when an electric field is applied. In particular, large deformation occurs near the interface. The average value of is treated as an apparent value when a uniform state is assumed.

There are two types of behavior when the brightness is changed: a normally closed characteristic in which darkness is applied when a low voltage is applied and a bright state is applied when a high voltage is applied, and a normally open characteristic in which lightness and darkness are reversed.

In this embodiment, the polarizing plate 8 and the like are set so that the brightness decreases as the voltage (VLC) applied between the common electrode 1 and the pixel electrode 4 increases and takes the minimum value. .

Therefore, in order to obtain normally closed characteristics, the angle (φP) formed by the polarization transmission axis 11 of the polarizing plate 8 and the electric field direction 9 is slightly smaller than the angle (φLC) formed by the rubbing direction 10 and the electric field direction 9. (2 degrees or more and 30 degrees or less, preferably 3 degrees
It may be arranged at a small angle (equal to 10 degrees or less).

By doing so, χ eff in equation (1) is applied with a certain bias voltage (VOFF described later) applied.
Becomes "0", and the light transmittance T / To corresponding to the brightness also becomes "0".

On the other hand, when an electric field higher than that (VON which will be described later) is applied, the value of χeff increases in accordance with the strength,
Maximum at 45 degrees.

On the other hand, in order to obtain normally open characteristics, the angle φP formed by the polarization transmission axis 11 of the polarizing plate 8 and the electric field direction 9 is significantly larger than the angle φLC formed by the rubbing direction 10 and the electric field direction 9 (45 degrees or more). ) Place it at a small angle.

For any of the characteristics, the effective deffΔn is halved in order to maximize the transmittance with achromatic color.
The wavelength may be 0.28 μm (here, the wavelength of light is assumed to be 0.555 μm).

In reality, since there is a margin, it suffices if it falls within the range of 0.21 to 0.36 μm. In particular, the dielectric constant anisotropy is positive and the rubbing angle | φLC | is 10 degrees or less. When making it small, it is better to set it to a slightly higher value between 0.27 and 0.33 μm.

FIG. 3 is a graph showing an example of the curve of the applied voltage dependence of the brightness in the liquid crystal display panel used in the liquid crystal display device of this embodiment, which is a normally closed state in which the high voltage side produces a bright state. Show the characteristics.

When the voltage (VLC) applied between the pixel electrode 4 and the common electrode 1 is gradually increased from zero, the brightness is once decreased, reaches the minimum value, and then increases again, and then the applied voltage is increased. It takes a value higher than the brightness when it is almost zero.

FIG. 4 is a graph showing another example of the curve of the applied voltage dependence of the brightness in the liquid crystal display panel used in the liquid crystal display device of this embodiment, which is a normally dark state on the high voltage side. Shows open characteristics.

In each case, the birefringence mode is adopted, and the polarization transmission axes of the two polarizing plates 8 sandwiching the liquid crystal composition layer are the transmission axes of one of the polarizing plates on the interface. When it is almost parallel to the liquid crystal molecule alignment direction (rubbing axis),
In order to realize the normally closed characteristic, the transmission axis of the other polarizing plate may be parallel to it, and in order to achieve the normally open characteristic, it may be vertical.

Further, the present invention is not limited to this as long as it is a means for realizing the characteristic that the two states of light and dark can be displayed in the voltage range of a certain width as described above.

In the liquid crystal display panel used in the liquid crystal display device of this embodiment, the voltage at which the brightness is almost the minimum value is defined as VOFF for any of the characteristics, and a brighter state is obtained. The voltage is defined as VON (see FIGS. 3 and 4).

FIG. 5 is a diagram showing a schematic configuration of a liquid crystal display panel used in the liquid crystal display device of this embodiment.

FIG. 6 is a diagram showing an equivalent circuit of one pixel of the liquid crystal display panel used in the liquid crystal display device of this embodiment.

5 and 6, 7a and 7b are a pair of substrates, 1 is a common electrode, 3 is a signal electrode, 12 is a scanning electrode,
Reference numeral 14 is a thin film transistor, 21 is a display region, CLC is a liquid crystal capacity, and CS is an additional capacity.

As shown in FIG. 5, the liquid crystal display panel is composed of a pair of substrates (7a, 7b), one of which is a substrate 7a.
Are formed in a matrix in the display area 21 of (M
× N) thin film transistors 14 are formed.

The gates of the thin film transistors 14 in the row direction are connected to the scanning electrodes 12, and the drains of the thin film transistors 14 in the column direction are connected to the signal electrodes 3, respectively.
The source of the thin film transistor 14 is connected to the pixel electrode.

Further, the common electrode 1 is arranged so as to face the pixel electrode to which the source of the thin film transistor 14 in the row direction is connected.

7 to 12 are diagrams showing the thin film transistor 14 and various electrode structures on one substrate 7a of the liquid crystal display panel used in the liquid crystal display device of this embodiment.

In the liquid crystal display panel used in the liquid crystal display device of this embodiment, the electrode pattern of the common electrode 1 and the scanning electrode 12 is formed on one substrate 7a, as shown in FIG.

Next, a gate insulating film 2 made of silicon nitride (SiN) or the like is formed on the electrode patterns of the common electrode 1 and the scanning electrode 12, and the gate insulating film 2 is formed on the gate insulating film 2 as shown in FIG.
As shown in, a pixel electrode (source electrode) 4, a signal electrode (drain electrode) 3, and alpha silicon 13 are formed.

Further, the pixel electrode (source electrode) 4,
Signal electrode (drain electrode) 3, Alpha silicon 13
An insulating film 50 made of silicon nitride (SiN) or the like
Then, the alignment film 51 is formed and the alignment control film 5a is formed.

FIG. 9 is a front view of the liquid crystal panel used in the liquid crystal display device of this embodiment, as seen from a direction perpendicular to the surface of the substrate 7a, and FIGS. 10 to 12 are AA ′ in FIG.
The side sectional drawing which followed the line, the BB 'line, and the CC' line is shown.

The thin film transistor 14 includes a pixel electrode (source electrode) 4, a signal electrode (drain electrode) 3, a scanning electrode (gate electrode) 12, and an amorphous silicon 1
It consists of 3.

In this embodiment, the thin film transistor 1
Although an amorphous silicon thin film transistor element was used as 4, a polysilicon thin film transistor element, a MOS type transistor on a silicon wafer, an organic TFT, or an MIM (Metal-Ins) was used.
It is also possible to use a two-terminal element (strictly speaking, it is not an active element, but it is an active element in the present invention) such as an ulator-metal) diode.

The common electrode 1 and the scanning electrode 12, and the signal electrode 3 and the pixel electrode 4 are formed by patterning the same metal layer.

The common electrode 1, the scanning electrode 12, the signal electrode 3,
And the material of the pixel electrode 4 is not particularly limited,
It is possible to use tantalum, aluminum, chromium, polysilicon, or the like, but considering the corrosion at the connection terminal portion with each drive circuit, the common electrode 1, the scan electrode 12, and the signal electrode 3 are anticorrosive. A strong metal is desirable.

Further, the common electrode 1 and the scanning electrode 12
Since a metal having low electric resistance is desirable for the common electrode 1,
Alternatively, the scan electrode 12 may be composed of two or more metal layers.

The additional capacitance element 16 is connected to the pixel electrode 4 in the wiring portion of the common electrode 1 (the portion extending in parallel with the scanning electrode 12 in FIG. 9, that is, the region connecting the two common electrodes 1). It was formed as a structure in which the insulating protective film 2 was sandwiched between the common electrodes 1.

In the front view (FIG. 9), the pixel electrode 4 is
It is arranged between two common electrodes 1.

Further, in order to realize the highest possible aperture ratio, the common electrode 1 and the signal electrode 3 are provided via the gate insulating film 2.
A little (1 μm).

As a result, the light shielding film 22 (black matrix) in the direction parallel to the signal wiring 3 becomes unnecessary.

Therefore, as shown in FIGS. 9 and 10, the black matrix structure is used in which the light shielding film 22 (black matrix) shields light only in the direction parallel to the scanning electrodes 12.

13 and 14 are views showing a liquid crystal display panel used in the liquid crystal display device of this embodiment, which is composed of a plurality of pixels.

In FIG. 13, the light shielding film 22 (black matrix) is omitted, and in FIG. 14, the light shielding film 22 (black matrix) is used to shield light.

FIG. 15 is a sectional view showing a section of the other substrate 7b of the liquid crystal display panel used in the liquid crystal display device of this embodiment.

As shown in FIG. 15, a color filter 33 and a light shielding film 22 are formed on the other substrate 7b of the liquid crystal display panel used in the liquid crystal display device of this embodiment. The color filter 33 and the light shielding film 22 are formed. Flattening film 3 on top
After forming 4, the alignment film 51 is formed and the alignment control film 5b is formed.

Next, a specific example of the liquid crystal display panel used in the liquid crystal display device of this embodiment will be described.

A pair of substrates (7a, 7a) of the liquid crystal display panel
As b), two transparent glass substrates having a thickness of 1.1 mm and having a polished surface were used, and these substrates (7a, 7b) were used.
The thin film transistor 14 was formed on one of the substrates 7a, and the orientation control film 5a which also serves as an insulating film was formed on the uppermost surface thereof.

In this embodiment, polyimide is used as the alignment film 51, and a rubbing process for aligning the liquid crystal is performed thereon.

Polyimide was applied on the other substrate 7a and the same rubbing treatment was performed.

The rubbing directions on the upper and lower interfaces are substantially parallel to each other, and the angle with the direction of the applied electric field is 88 degrees (φLC
1 = φLC2 = 88 °).

Between these substrates, the dielectric anisotropy Δε is positive, its value is 4.5, and the refractive index anisotropy Δn is 0.072.
A nematic liquid crystal composition (589 nm, 20 ° C.) was sandwiched.

The gap d was set to 3.9 μm in a state where liquid crystal was sealed by holding spherical polymer beads dispersed between the substrates (7a, 7b). Therefore, Δn · d is 0.281 μm.

The liquid crystal display panel is sandwiched between the two polarizing plates 8.
The polarization transmission axis of one polarizing plate 8 is slightly smaller than the rubbing direction, φP1 = 80 ° (that is, | φLC1−φP1 | = 8
°) and the other is orthogonal to it, that is, φP2 = -12
°.

As a result, the voltage (VL
We obtained the characteristic (Fig. 3) in which the brightness increased and the maximum value was obtained as C) was gradually increased from zero.

That is, in the first embodiment, the low voltage (VOFF)
It adopts the normally-closed characteristic that it is in a dark state at and a bright state at high voltage (VON).

At this time, the low voltage (VOFF) is 6.9V,
The high voltage (VON) is 9.1V.

The pixel pitch in the liquid crystal display panel of the liquid crystal display device of Example 1 is 69 μm in the horizontal direction (that is, between the signal electrodes 3) and 207 μm in the vertical direction (that is, between the scanning electrodes 12).

Regarding the electrode width, the wiring portions of the scanning electrode 12, the signal electrode 3, and the common electrode 1 which are wiring electrodes extending over a plurality of pixels are made wider to 10 μm to avoid line defects.

On the other hand, the width of the pixel electrode 4 formed independently for each pixel in order to improve the aperture ratio and the width of the drive voltage application portion of the common electrode 1 are slightly narrowed to 5 μm and 8 μm, respectively.

By narrowing the widths of these electrodes, the possibility of disconnection due to the inclusion of foreign matter or the like increases, but in this case, a partial defect of one pixel does not lead to a line defect.

Further, as described above, the common electrode 1 and the signal electrode are slightly (1 μm) overlapped with each other with the insulating film 2 interposed therebetween in order to realize the highest aperture ratio, and the light-shielding film 2 (black) in the direction parallel to the signal wiring 3 is formed. Matrix) is unnecessary.

In this way, the common electrode 1 and the pixel electrode 4 are
Gap of 20 μm, length of the opening in the longitudinal direction 15
It was 7 μm, and a high aperture ratio of 44.0% was obtained.

The number of pixels is 320 signal wiring electrodes and 16
The number of wiring electrodes was set to 320 × 160.

In the liquid crystal display panel used in the liquid crystal display device of the present embodiment, light is incident on and modulated by the liquid crystal layer which is transmitted between the common electrode 1 and the pixel electrode 4.

Therefore, as in the conventional TFT type liquid crystal display device adopting the twisted nematic display system, a light-transmitting pixel electrode for controlling the alignment of the liquid crystal molecules 6, for example, a transparent electrode such as ITO. Need not be formed in particular, and since it is formed in the same layer as the signal electrode 3, the manufacturing process of the liquid crystal display panel can be greatly shortened.

FIG. 16 is a diagram showing a drive circuit of the liquid crystal display device of this embodiment.

In FIG. 16, 1 is a common electrode, 3 is a signal electrode, 12 is a scanning electrode, 14 is a thin film transistor, and 17 is a thin film transistor.
Is a control circuit, 19 is a signal electrode drive circuit, 21 is a display region, 23 is a common electrode / scan electrode drive circuit, CLC is a liquid crystal capacitance, and CS is an additional capacitance.

The liquid crystal display device of the present embodiment is a common electrode for applying a scanning voltage to the scanning electrode 12 in order to drive the above-mentioned liquid crystal display panel, similarly to the drive circuit of a general TFT type liquid crystal display device. A scan electrode drive circuit 23 and a signal electrode drive circuit 19 that applies a signal voltage to the signal electrode 3 are provided, and in addition, a common electrode / scan electrode drive circuit 23 that applies a voltage to the common electrode 1 is provided.

FIG. 17 is a diagram showing drive voltage waveforms of the drive circuit of the liquid crystal display device of this embodiment.

In order to make the drive circuit of the liquid crystal display device of this embodiment easier to understand, the drive circuit of the TFT type liquid crystal display device adopting the lateral electric field display system, which has already been filed by the present applicant, will be described.

FIG. 18 is a diagram showing a drive circuit of a TFT type liquid crystal display device adopting the horizontal electric field display method which has already been applied by the present applicant.

In FIG. 18, 1 is a common electrode, 3 is a signal electrode, 12 is a scanning electrode, 14 is a thin film transistor, and 17
Is a control circuit, 18 is a scan electrode drive circuit, 19 is a signal electrode drive circuit, 20 is a common electrode drive circuit, 21 is a display region, CLC is a liquid crystal capacity, and CS is an additional capacity.

FIG. 19 is a diagram showing drive voltage waveforms of the drive circuit shown in FIG.

FIG. 19A shows the scan voltage waveform (VG) supplied from the scan electrode drive circuit 18, as shown in FIG.
Shows the signal voltage waveform (VD) that carries the image information supplied from the signal electrode drive circuit 19, and FIG. 19C shows the voltage waveform (VC) supplied to the common electrode 1.

Further, FIG. 19D shows the voltage (VS) applied to the source electrode, which is the pixel electrode 4, as shown in FIG.
Indicates the voltage (VLC) applied to the liquid crystal layer.

A signal voltage waveform (VD) carrying image information is applied to the signal electrode 3, and a scanning voltage waveform (VG) is applied to the scanning electrode 12 in synchronization with the signal voltage waveform (VD). It

An information signal is transmitted from the signal electrode 3 to the pixel electrode 4 through the thin film transistor 14, and a drive voltage is applied to the liquid crystal layer between the signal electrode 3 and the common electrode 1.

In the drive circuit shown in FIG. 18, the voltage waveform (VC) supplied to the common electrode 1 is the signal voltage waveform (V
D) is synchronized and its phase is reversed.

As is clear from FIG. 19, the common electrode 1
When a voltage waveform having a phase opposite to that of the signal voltage waveform is applied to, the effective voltage (VLC) applied to the liquid crystal can be increased.

The effective voltage (VLC) applied to the liquid crystal is a voltage obtained by subtracting the voltage (VC) applied to the common electrode 1 from the voltage (VS) applied to the source electrode which is the pixel electrode 4.

The amplitude (ΔVS) of the voltage applied to the pixel electrode 4 when the gate is off is the peak-to-peak value (│VDH-VDL│2) of the voltage (VD) applied to the signal electrode.
Vsig) is almost proportional to.

Therefore, the signal electrode 3 (drain electrode)
If the voltage applied to the liquid crystal element, that is, the voltage waveform applied to the pixel electrode 4 (source electrode) and the voltage waveform applied to the common electrode 1 have opposite phases to each other, the effective voltage applied to the liquid crystal ( The peak-to-peak value of VLC) is the sum of them, and a higher voltage can be applied to the liquid crystal even if the voltage applied to the signal electrode 3 is low.

Accordingly, the dynamic range of the difference between the voltage (VOFF) at which the minimum value of brightness is obtained and the voltage (VON) at which sufficient brightness is obtained is set by setting the polarizing plate 8 and the like. The voltage width is narrowed, and the amplitude of the signal voltage waveform is suppressed to a lower level.

The drive circuit shown in FIG. 18 is provided with a drive circuit 20 for applying a voltage waveform to the common electrode 1 as well, and by combining the above-mentioned electro-optical characteristics with this simple circuit, the most used circuit is obtained. Moreover, it is possible to reduce the cost of the signal electrode drive circuit 19, which is expensive because it carries image information.

By reducing the cost of the signal electrode drive circuit 19 which accounts for a considerable portion of the total circuit cost, it is possible to greatly reduce the cost of the entire liquid crystal display device.

Generally, the manufacturing cost of the driving IC strongly depends on the withstand voltage (maximum output voltage), and the lower the cost, the easier the reduction.

On the other hand, the common electrode drive circuit 20 basically needs only one output terminal, and further, it does not need to carry image information and the output voltage is somewhat high, but the cost is considerably high. It does not lead to rise.

In the drive circuit shown in FIG. 18, the amplitude of the voltage waveform applied to each electrode is set as follows.

VD-CENTER = 14.0, VGH = 28.0, VGL =
0, VDH = 15.1, VDL = 12.9, VCH = 20.4, VCL = 4.39 As a result, as shown in the table below, the jump voltage ΔVGS (+), ΔVGS due to the parasitic capacitance between the gate electrode and the source electrode
(−), The voltage VS applied to the pixel electrode and the voltage VLC applied to the liquid crystal were obtained. The unit of voltage will be all volts hereinafter.

[0129]

[Table 1]

As a result, VON and VOFF shown in FIG.
Since they are 9.16 V and 6.85 V, respectively, a sufficiently high contrast ratio 80 can be obtained.

Further, in the liquid crystal drive circuit using the drive voltage waveform shown in FIG. 19, the amplitude VDP-P (= VDH-VDL) of the drive voltage waveform supplied to the signal electrode 3 is only 2.2 V, which is very large. It can be driven at a low value.

In the liquid crystal display panel used in the liquid crystal display device of the present embodiment, the brightness is changed mainly by applying an electric field parallel to the substrate surface.
The liquid crystal capacitance CLC in the equivalent circuit shown in (1) has a remarkably low capacitance component as compared with the system in which an electric field perpendicular to the substrate surface is applied.

This is due to the fact that the electrodes were planar, but became linear, and the inter-electrode gap widened.

In the equivalent circuit shown in FIG. 6, since the capacitance CLC of the liquid crystal layer becomes small as described above, the scanning electrode 12
The parasitic capacitance CGS formed between the signal electrode 3 and the signal electrode 3 relatively increases.

In the case of this embodiment, the liquid crystal capacitance CLC is 30 f.
Although it is about F, the parasitic capacitance CGS is 20 to 50 fF.
Becomes

This parasitic capacitance CGS controls the magnitude of the jump voltage ΔVGS shown in FIG. 19 and becomes a factor of fluctuation of the effective voltage applied to the pixel.

In order to suppress this phenomenon, in the drive voltage waveform shown in FIG. 17, the potential of the gate electrode is changed to the potential of the gate electrode except the selection period so as to suppress the potential difference between the scanning electrode 12 and the common electrode 1 as much as possible. The scanning voltage (VG) supplied to the scanning electrode 12 is set so that the potential of the common electrode 1 becomes substantially the same.

In addition, the voltage (VC) applied to the common electrode 1 is inverted every line.

Therefore, in the drive waveform shown in FIG. 17, in the drive voltage waveform shown in FIG.
The level of the scanning voltage (VG) to be supplied to the low level voltage (VGL) is the binary level of the high level voltage (VGH) and the low level voltage (VGL).
Are three values of the first Low level (VGLH) and the second Low level (VGLL).

Scanning voltage (VG) supplied to the scanning electrode 12
The first low level (VGLH) and the second low level (VGLL) of the voltage waveform (VC) applied to the common electrode 1 are High level (VCH) and Low level (VC), respectively.
It is set the same as L).

Further, the drive waveform shown in FIG. 17 employs a frame inversion method in which the voltage waveform applied to the common electrode 1 is changed for each frame.

The potential of each drive voltage waveform shown in FIG. 17 is basically the same as that of the drive voltage waveform shown in FIG. 19 except that the level of the potential supplied to scan electrode 12 is three-valued.

When the drive voltage waveforms shown in FIG. 17 are used in the drive circuit shown in FIG. 18, the influence of the parasitic capacitance CGS can be suppressed, the additional capacitance CS can be reduced, and the additional capacitance CS can be removed. Is.

The reduction of the additional capacitance CS is effective in reducing the load of the driving IC, and it becomes possible to apply a cheaper IC.

However, when the drive voltage waveform shown in FIG. 17 is used in the drive circuit shown in FIG. 18, the difference in relative waveform distortion between the common electrode 1 and the scan electrode 12 becomes large,
It becomes difficult to obtain uniform display characteristics.

FIG. 20 is a diagram for explaining relative waveform distortion between the common electrode 1 and the scan electrode 12 when the drive voltage waveform shown in FIG. 17 is used in the drive circuit shown in FIG.

As shown in FIG. 20, the wiring line of the normal scanning electrode 12 has a resistance R and a capacitance C, and the capacitance C has a relatively large capacitance of about 100 pF as a whole. This also applies to the wiring line of the common electrode 1.

When a pulse voltage is applied to the wiring line having the resistance R and the capacitance C, a rise delay occurs in the pulse voltage as shown in FIG.

Therefore, when the scan electrode 12 and the common electrode 1 are driven by the voltage waveform VC and the voltage waveform (VG) as shown in FIG. 17, the waveforms due to the capacitance are located near and far from the drive circuit. Distortion occurs.

Therefore, in the drive circuit as shown in FIG. 18, the common electrode drive circuit 20 and the scan electrode drive circuit 1
When 8 is positioned on the opposite side of the display area 21 and is driven so as to face each other, in the pixel near the common electrode drive circuit 20 and the scan electrode drive circuit 18, the common electrode 1
The difference in relative waveform distortion between the scanning electrode 12 and the scanning electrode 12 becomes large, it becomes difficult to obtain uniform display characteristics, and display unevenness occurs.

In the liquid crystal display device of this embodiment, the common electrode drive circuit 20 is different from the drive circuit shown in FIG. 18 arranged on the opposite side of the scan electrode drive circuit 18 across the display area 21. As shown in FIG. 16, the common electrode / scan electrode driving circuit 23 is arranged on the same side of the display area 21.

Therefore, in the drive circuit of the liquid crystal display device of the present embodiment, the difference in relative waveform distortion between the common electrode 1 and the scan electrode 12 is suppressed to be small at any position in the display area 21, and uniform display is achieved. It is possible to obtain characteristics and prevent occurrence of display unevenness.

It goes without saying that the common electrode / scan electrode driving circuit 23 can be formed of the same semiconductor integrated circuit.

21 to 23 are diagrams showing a configuration example of the common electrode / scan electrode driving circuit 23 shown in FIG.

The common electrode / scan electrode drive circuit 23 shown in FIGS. 21 to 23 is a semiconductor drive circuit chip (CHI).
Is a configuration example using a film carrier package (TCP) mounted on a flexible wiring board.

As a method of reducing the periphery of the frame of the module, a semiconductor drive circuit chip (CH
The chip-on-glass mounting in which I) is directly mounted on the substrate 7a by an anisotropic conductive film or the like can also be configured as a semiconductor drive circuit chip (CHI) described below.

The semiconductor drive circuit chip (CH
In I), the circuit for driving the common electrode and the circuit for driving the scan electrode are alternately designed for each output terminal. Therefore, the size of the semiconductor drive circuit chip (CHI) becomes relatively large, but the common electrode drive is performed. Since there is no intersection between the wiring for scanning and the wiring for driving the scanning electrodes, a good output waveform can be obtained, which is hardly affected by noise.

When a film carrier package (TCP) is used, the output terminals for driving the common electrode and the scan electrode of the semiconductor drive circuit chip (CHI) are electrically connected to the wirings 30 and 31 of the flexible wiring board. And further electrically connected to the common electrode driving wiring 1a and the scanning electrode driving wiring 12a on the substrate 7a.

Power and clock are input to the semiconductor drive circuit chip (CHI) from the wiring on the printed circuit board (PCB) side to the outer lead wiring (TB) of the film carrier package (TCP).

The semiconductor drive circuit chip (CH
In I), the output electrodes for driving the scan electrodes are arranged in a line, and the output terminals for driving the common electrode are designed to have one or two output terminals on the outside thereof.

Therefore, the semiconductor drive circuit chip (CH
The size of I) becomes smaller as the number of output terminals for driving the common electrode decreases.

The common electrode driving wiring 30 uses a flexible wiring substrate having two or more layers, and the scanning electrode driving wiring 31 is used.
And is electrically connected to the output terminal for driving the common electrode of the semiconductor drive circuit chip (CHI).

For chip-on-glass mounting, these cross wirings use the wiring pattern on the substrate 7a.

The semiconductor drive circuit chip (CH
In I), only the output terminals for driving the scan electrodes are arranged in one line, and the common electrode driving voltage is supplied from a dedicated common electrode driving semiconductor driving circuit chip (CHI) (not shown) to the printed circuit board (CHI). It is supplied to the common electrode driving wiring 1a on the substrate 7a via the wiring 32 on the PCB side, the outer lead wiring (TB), and the wiring 30 of the flexible wiring board.

Therefore, the semiconductor drive circuit chip (CH
The size of I) is greatly reduced, which is also advantageous for cost reduction.

Although the present invention has been specifically described based on the embodiments, it is needless to say that the present invention is not limited to the embodiments and various modifications can be made without departing from the scope of the invention.

[0167]

The effects obtained by the typical ones of the inventions disclosed in the present application will be briefly described as follows.

(1) According to the present invention, a liquid crystal that applies an electric field substantially parallel to the substrate surface between each pixel electrode in the row direction and a plurality of common electrodes formed in the row direction. In the display device, a drive voltage is applied from the same side of the display area to a plurality of scan electrodes and a common electrode formed in the row direction that apply a scan voltage to each active element in the row direction.

As a result, the delay of the scan voltage waveform of the scan electrode in each pixel electrode and the delay of the voltage waveform of the common electrode facing each pixel electrode become substantially the same, and the occurrence of display unevenness can be prevented. Therefore, it becomes possible to obtain good display characteristics.

[Brief description of drawings]

FIG. 1 is a diagram showing an operation of a liquid crystal in a liquid crystal panel used in a liquid crystal display device which is an embodiment of the present invention.

FIG. 2 is an angle (φLC) formed by a liquid crystal molecule major axis (optical axis) direction 10 near an interface with respect to an electric field direction 9 corresponding to FIGS. 1C and 1D, and a polarization transmission axis 11 of a polarizing plate 8. Egg angle (φ
It is a figure which shows the definition of (P).

FIG. 3 is a graph showing an example of a curve of the applied voltage dependence of brightness in a liquid crystal display panel used in the liquid crystal display device of the present embodiment, showing a normally closed characteristic in which a bright state is obtained on the high voltage side. .

FIG. 4 is a graph showing another example of the curve of the applied voltage dependence of the brightness in the liquid crystal display panel used in the liquid crystal display device of the present embodiment, showing a normally open characteristic in which a dark state is generated on the high voltage side. Show.

FIG. 5 is a diagram showing a schematic configuration of a liquid crystal display panel used in the liquid crystal display device of the present embodiment.

FIG. 6 is a diagram showing an equivalent circuit of one pixel of a liquid crystal display panel used in the liquid crystal display device of the present embodiment.

FIG. 7 is a thin film transistor 1 on one substrate 7a of a liquid crystal display panel used in the liquid crystal display device of the present embodiment.
4 is a diagram showing 4 and various electrode structures. FIG.

FIG. 8 is a thin film transistor 1 on one substrate 7a of a liquid crystal display panel used in the liquid crystal display device of the present embodiment.
4 is a diagram showing 4 and various electrode structures. FIG.

FIG. 9 is a front view of the liquid crystal panel used in the liquid crystal display device of the present embodiment, as viewed from a direction perpendicular to the surface of the substrate 7a.

FIG. 10 is a side sectional view taken along the line BB ′ in FIG.

FIG. 11 is a side sectional view taken along the line AA ′ in FIG.

FIG. 12 is a side sectional view taken along the line CC ′ in FIG. 9.

FIG. 13 is a diagram showing a liquid crystal display panel used in the liquid crystal display device of the present embodiment composed of a plurality of pixels.

FIG. 14 is a diagram showing a liquid crystal display panel used in the liquid crystal display device of the present embodiment, which is composed of a plurality of pixels.

FIG. 15 is a cross-sectional view showing a cross section of the other substrate 7b of the liquid crystal display panel used in the liquid crystal display device of the present embodiment.

FIG. 16 is a diagram showing a drive circuit of the liquid crystal display device of the present embodiment.

FIG. 17 is a diagram showing a drive voltage waveform of the drive circuit of the liquid crystal display device of the present embodiment.

FIG. 18 is a diagram showing a drive circuit of a TFT type liquid crystal display device adopting a horizontal electric field display method which has already been applied by the present applicant.

19 is a diagram showing an example of drive voltage waveforms of the drive circuit shown in FIG.

20 is a diagram for explaining relative waveform distortion between the common electrode 1 and the scan electrode 12 when the drive voltage waveform shown in FIG. 18 is used in the drive circuit shown in FIG.

FIG. 21 is a common electrode / scan electrode driving circuit 2 shown in FIG.
It is a figure which shows the structural example of 3.

22 is a diagram showing a common electrode / scan electrode driving circuit 2 shown in FIG.
It is a figure which shows the structural example of 3.

FIG. 23 is a common electrode / scan electrode driving circuit 2 shown in FIG.
It is a figure which shows the structural example of 3.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Common electrode (common electrode), 1a ... Common electrode drive wiring on a substrate, 2 ... Gate insulating film, 3 ... Signal electrode (drain electrode), 4 ... Pixel electrode (source electrode), 5a, 5b ...
Alignment control film, 6 ... Liquid crystal molecules in liquid crystal composition layer, 7a, 7
b ... Substrate, 8 ... Polarizing plate, 9 ... Electric field direction, 10 ... Molecular long axis orientation direction on interface (rubbing direction), 11 ... Polarization transmission axis direction of polarizing plate 8, 12 ... Scanning electrode (gate electrode), 12
a ... Wiring for scanning electrodes on the substrate, 13 ... Amorphous silicon, 14 ... Thin film transistor, 16 ... Additional capacitance,
17 ... Control circuit, 18 ... Signal electrode drive circuit, 1
9 ... Scan electrode drive circuit, 20 ... Common electrode drive circuit, 21
... Display area, 22 ... Shading layer, 30 ... Common electrode driving wiring of flexible wiring board, 31 ... Scan electrode driving wiring of flexible wiring board, 32 ... Printed circuit board (PCB)
Side wiring, 33 ... Color filter, 34 ... Flattening film, 5
0 ... Insulating film, 51 ... Alignment film, CLC ... Liquid crystal capacity, CS ... Additional capacity, CHI ... Semiconductor drive circuit chip, TCP ... Film carrier package, TB ... Outer lead wiring,
PCB ... Printed circuit board.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Yasuyuki Mishima 3300 Hayano, Mobara-shi, Chiba Hitachi, Ltd. Electronic Device Division

Claims (2)

[Claims] 1. A pair of substrates, a plurality of active elements formed in a display region on the one substrate, and a plurality of pixel electrodes formed on the one substrate and connected to the plurality of active elements, respectively. A plurality of scan electrodes formed in a row direction on the one substrate and applying a scan voltage to each active element in the row direction; and each active element in the column direction formed in the column direction on the one substrate. A plurality of signal electrodes for applying a signal voltage to the liquid crystal layer and a pixel electrode formed on one of the substrates in the row direction and substantially parallel to the substrate surface between the pixel electrodes in the row direction. A plurality of common electrodes, a liquid crystal layer sandwiched between the pair of substrates, a scanning electrode driving unit that drives the scanning electrodes, a signal electrode driving unit that drives the signal electrodes, and a common electrode that drives the common electrodes. A liquid crystal display device having at least a through electrode driving means, wherein the scanning electrode driving means and the common electrode driving means are arranged on the same side of the display area. 2. The liquid crystal display device according to claim 1, wherein the scan electrode driving unit and the common electrode driving unit are configured by the same integrated circuit.