JP3265802B2 - Liquid crystal display - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low-cost thin-film transistor liquid crystal display device which is composed of an IC with low power consumption, is bright, has good viewing angle characteristics and is low in cost.

[0002]

2. Description of the Related Art In a conventional thin film transistor type liquid crystal display device, transparent electrodes formed on the interface between two substrates and opposed to each other are used as electrodes for driving a liquid crystal layer. this is,
This is because a display method typified by a twisted nematic display method, which operates by setting the direction of an electric field applied to the liquid crystal to a direction substantially perpendicular to the substrate interface, is employed. On the other hand, as a method of making the direction of the electric field applied to the liquid crystal substantially parallel to the substrate interface, a method using a pair of comb electrodes has been proposed, for example, in Japanese Patent Publication No. 63-21907, but as a display device. Not practical.

[0003]

In the display device of the prior art described above, the luminance change when the viewing angle direction is changed is remarkable. In particular, when a halftone display is performed, the gradation level is inverted depending on the viewing angle direction. This was a practical problem. On the other hand, it has been clarified that the viewing angle dependency of the brightness is almost eliminated by using a method in which the direction of the electric field applied to the liquid crystal using the pair of comb electrodes is made substantially parallel to the substrate interface. See, R. Kiefer, B. Weber, F. Winds
cheid and G. Baur, Proceedings of the Twelfth Inte
rnational Display Research Conference (Japan Displa
y, 92 ') pp. 547-550). However, this publication does not describe the structure of a thin film transistor and a driving method suitable for this method. Further, in the configuration shown here, it is necessary to apply a high voltage of, for example, 8 volts or more to maintain a sufficient light transmittance and contrast ratio.
It is necessary to use a high-withstand-voltage drive IC with high manufacturing cost and high power consumption. In addition, the gap between electrodes is only 10
μm, which is extremely narrower than the pixel pitch of an ordinary liquid crystal display device, and it is extremely difficult to secure a high aperture ratio which is essential for increasing the light transmittance of the panel and increasing the brightness. On the other hand, if the gap between the electrodes is widened to ensure a high aperture ratio, the electric field strength between the electrodes will decrease, and the driving voltage required to maintain a sufficient light transmittance will increase further, resulting in an obstacle. Was.

On the other hand, Japanese Patent Publication No. 63-21907 proposes a structure in which a pair of interdigitated comb-teeth electrodes is connected to a thin-film transistor. Here, as many as seventeen comb-teeth electrodes are introduced in one pixel. Therefore, in order to maintain a sufficient pixel aperture ratio (for example, 30% or more), it is necessary to extremely narrow the width of the comb-teeth electrode to about 1 to 2 μm or less. In order to increase 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 and without disconnection over the entire surface of a large substrate. That is, in the above-mentioned prior art, a low drive voltage, a high pixel aperture ratio and a manufacturing yield have a trade-off relationship, and it has been difficult to provide a liquid crystal display device having a bright image at low cost.

The present invention solves these problems at the same time. A high pixel aperture ratio thin film transistor type liquid crystal which can be driven by an IC having a practically sufficiently low breakdown voltage with a small number of electrodes and without significantly reducing the gap between the electrodes. A display device is provided.

[0006]

Means for Solving the Problems In order to solve the above problems and achieve the above object, the present invention uses the following means.
At least one of a pair of transparent substrates, a liquid crystal composition layer sandwiched between the substrates and having oriented dielectric anisotropy and refractive index anisotropy, polarizing means, a plurality of pixels arranged in a matrix, A liquid crystal display device provided for each pixel, comprising: a thin film transistor element connected to a pixel electrode, a signal wiring electrode and a scanning wiring electrode; a common electrode; and means for applying a voltage signal waveform between the pixel electrode and the common electrode. [Means 1] the pixel electrode and the common electrode are arranged so as to apply an electric field between the pixel electrode and the common electrode by means for applying a voltage signal waveform and substantially parallel to a substrate surface; The alignment state of the liquid crystal composition layer and the configuration of the polarizing means are such that the brightness is substantially zero when the voltage _VLC applied between the pixel electrode and the common electrode is substantially zero, and the voltage _VLC is changed from zero. It is set so that the brightness increases after going through a voltage region where the brightness does not substantially change as the voltage _VLC is gradually increased, or the brightness decreases and takes the minimum value as the voltage _VLC is gradually increased from zero. Voltage waveforms V _D and V _C synchronized with the scanning signal waveform V _S applied to the scanning wiring electrode are applied to the signal wiring electrode and the common electrode, respectively, and are applied to the signal wiring electrode and the common electrode. The voltage waveforms V _D and V _C are determined so that the effective voltage V _LC applied to the pixel is higher than when the amplitude V _C of the voltage waveform from the common electrode is zero,
Further, by changing the peak value of the voltage applied to the signal wiring electrode in accordance with the image information, the effective voltage _VLC applied to the pixel is in the vicinity of the voltage V _OFF where the brightness is minimum, and the voltage at which the state becomes brighter. A liquid crystal display device characterized by being driven so as to change between V _ON and V _ON .

[0007] According to the means 1, by using a small number of electrodes,
It is possible to provide a wide-viewing-angle thin-film transistor liquid crystal display device that can be driven by an IC having a sufficiently low withstand voltage for practical use without reducing the gap between the electrodes so much. Use of an IC having a low withstand voltage results in low power consumption at the same time.

[Means 2] With respect to the alignment in the liquid crystal composition layer, the liquid crystal molecule alignment direction angle φ on one substrate interface
_LC1 and the liquid crystal molecule orientation angle φ _LC2 on the other substrate interface are substantially parallel to each other (φ _LC1 ≒ φ _LC2 ≡φ _LC ), and the thickness d of the liquid crystal composition layer and the refractive index anisotropy Δn Product d
2. The liquid crystal display device according to claim 1, wherein Δn is between 0.21 μm and 0.36 μm.

According to the means 2, the liquid crystal display mode can be optimized and the brightness can be maximized.

[Means 3] The liquid crystal composition layer has a positive dielectric anisotropy, and the angle | φ _LC | between the major axis direction of the liquid crystal molecules on the interface and the electric field direction exceeds 45 degrees and exceeds 90. Degrees, and the polarizing means is a pair of polarizing plates sandwiching the liquid crystal composition layer, and the angles φ _P and φ of the transmission axis (or absorption axis) of one of the polarizing plates A of the pair of polarizing plates. the angle between the _LC | _{φ LC}
3. The liquid crystal display device according to claim 2, wherein -φ _P | is 2 degrees or less. However, -90 degrees ≦ φ _LC ≦ 90 degrees.

[Means 4] The angle | φ _LC | between the major axis direction of the liquid crystal molecules on the interface and the electric field direction is more than 85 degrees and less than 90 degrees, and the thickness d and refraction of the liquid crystal composition layer The product d · Δn of the rate anisotropy Δn is from 0.26 μm to 0.36 μm
3. The liquid crystal display device according to claim 3, wherein

[Means 5] The liquid crystal composition layer has a positive dielectric anisotropy, and the angle | φ _LC | between the major axis direction of the liquid crystal molecules and the electric field direction on the interface exceeds 45 degrees and exceeds 90 degrees. Degrees, and the polarizing means is a pair of polarizing plates sandwiching the liquid crystal composition layer, and is larger than the angle φ _P of the transmission axis (or absorption axis) of one of the pair of polarizing plates. 3. The liquid crystal display device according to claim 2, wherein the difference | φ _LC −φ _P | is not less than 2 degrees and not more than 30 degrees.

[Means 6] The angle | φ _LC | between the major axis direction of the liquid crystal molecules on the interface and the electric field direction is 80 degrees or more and less than 90 degrees, and the angle difference | φ _LC −φ _P | is 2 degrees. 6. The liquid crystal display device according to claim 5, wherein the angle is not less than 10 degrees.

[Means 7] The dielectric anisotropy of the liquid crystal composition layer is negative, and the angle | φ _LC | between the major axis direction of the liquid crystal molecules and the electric field direction on the interface exceeds 0 degrees and exceeds 45 degrees. Degrees, and the polarizing means is a pair of polarizing plates sandwiching the liquid crystal composition layer, and the angles φ _P and φ _LC of the transmission axis (or absorption axis) of one of the pair of polarizing plates. Angle with the angle | φ _LC
3. The liquid crystal display device according to claim 2, wherein -φ _P | is 2 degrees or less. However, -90 degrees ≦ φ _LC ≦ 90 degrees.

[Means 8] The angle | φ _LC | between the major axis direction of the liquid crystal molecules on the interface and the electric field direction is more than 0 degree and less than 5 degrees, and the thickness d and refraction of the liquid crystal composition layer 8. The liquid crystal display device according to claim 7, wherein the product d · Δn of the ratio anisotropy Δn is between 0.26 μm and 0.36 μm.

[Means 9] The dielectric anisotropy of the liquid crystal composition layer is negative, and the angle | φ _LC | between the major axis direction of the liquid crystal molecules and the direction of the electric field on the interface exceeds 0 degrees and exceeds 45 degrees. Degrees, and the polarizing means is a pair of polarizing plates sandwiching the liquid crystal composition layer, and is smaller than the angle φ _P of the transmission axis (or absorption axis) of one of the pair of polarizing plates. 3. The liquid crystal display device according to claim 2, wherein the difference | φ _LC −φ _P | is not less than 2 degrees and not more than 30 degrees.

[Means 10] The angle | φ _LC | between the major axis direction of the liquid crystal molecules on the interface and the electric field direction is more than 0 degree and less than 10 degrees, and the angle difference | φ _LC −φ _P | The liquid crystal display device according to claim 9, wherein the liquid crystal display device has an angle of 2 degrees or more and 10 degrees or less.

Means 3 to 10 provide concrete measures for optimizing the liquid crystal and the polarizing plate so as to operate with an IC having a low withstand voltage.

[Means 11] A voltage waveform having an amplitude level of at least three values is applied to the scanning wiring electrode, and during the scanning selection period, the resistance between the signal wiring of the thin film transistor element and the pixel electrode is significantly reduced. It has a sufficient high level, and to apply the highest level V _GH, the non-scanning selection period, in accordance with the increase or decrease of the voltage V _C applied to the common wiring electrode, different levels of 2 or more values of the voltage ( The liquid crystal display device according to claim 1, _wherein a maximum value is defined as V _GLH and a minimum value is defined as _VGLL ) to reduce a potential difference between the scanning wiring electrode and the common electrode.

Means 11 is a method of applying an electric field parallel to the substrate surface, which is a problem when applying an electric field to the common electrode, which is generated in the entire means 1 and means 10, and is a parasitic capacitance generated between the scanning electrode and the pixel electrode. Diving voltage ΔV generated by C _GS
It is possible to suppress the influence of voltage fluctuation due to _GS .

[0021]

First, according to FIG. 2, the angle φ between the liquid crystal molecule major axis (optical axis) direction 10 near the interface and the electric field direction 9 is shown in FIG.
_LC, shows the definition of the angle phi _P polarization transmission axis 11 of the polarizer. Phi _P1 optionally Since the polarizer and the liquid crystal interface is a pair up and down, respectively, φ _P2, φ _LC1, referred to as phi _LC2.
FIG. 2 corresponds to a front view of FIG. 1 described later.

Next, the operation of the present invention will be described with reference to FIG.

FIGS. 1A and 1B are side sectional views showing the operation of the liquid crystal in the liquid crystal panel of the present invention, and FIGS. 1C and 1D are front views thereof. FIG. 1 shows a part of the wiring electrode structure without the thin film transistor element part. Although the display device of the present invention includes a plurality of pixels, only a part of one pixel is shown here. FIG. 1A shows a cross section of the cell when no voltage is applied, and FIG. 1C shows a front view at that time. Linear electrodes 1 and 4 are formed inside a pair of transparent substrates, and an orientation control film 5 serving also as a protective film is applied and oriented thereon. A liquid crystal composition is sandwiched between the two. When no electric field is applied, the rod-shaped liquid crystal molecules 6
A slight angle with respect to the longitudinal direction (FIG. 1 (c) front view),
That is, they are oriented so that 45 degrees ≦ | φ _LC | <90 degrees. In FIG. 1 and FIG. 2, the liquid crystal molecule major axis alignment (rubbing) direction 10 on the interface is indicated by an arrow. The liquid crystal molecule alignment direction on the upper and lower interfaces is preferably parallel, that is, φ _LC1.
= And has a φ _LC2 (= φ _LC). The dielectric anisotropy of the liquid crystal composition is assumed to be positive.

Here, when a different potential is applied to each of 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 of the liquid crystal composition and the electric field 1 (b) and 1 (d), the liquid crystal molecules react to change 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. The first of the main configurations of the present invention is optimization of electro-optical characteristics, and the second is optimization of driving conditions. The operation of each will be described below.

(1) Optimization of Electro-Optical Characteristics (First Configuration) First, the operation of changing the alignment direction of the liquid crystal molecules as described above and changing the brightness in accordance with the change will be described. General light transmission T / T _o when inserted between two polarizing plates were orthogonally arranged uniaxial birefringent medium is expressed by the following equation. Here, χ _eff is the effective optical axis direction of the liquid crystal composition layer (the angle between the effective molecular major axis direction and the polarization transmission axis), and d _eff is the effective birefringent liquid crystal composition layer. Represents the refractive index anisotropy, and λ represents the wavelength of light. Here, the purpose of setting the optical axis direction of the liquid crystal composition layer as an effective value is that liquid crystal molecules are fixed on the interface in the actual cell, and all liquid crystal molecules are parallel to each other in the cell when an electric field is applied. In addition, in consideration of the fact that the orientation is not uniform and large deformation occurs particularly in the vicinity of the interface, the average value thereof is treated as an apparent value when a uniform state is assumed.

T / T _o = sin ² (2χ _eff ) · sin ² (πd _eff · Δn / λ) (1) When changing the brightness, the dark and the high voltage are applied when the low voltage V _{OFF is} applied. There are two types of normally closed characteristics, in which a bright state occurs when V _{ON is} applied, and normally open characteristics, in which the brightness is reversed. A first configuration of the present invention is to set a polarizing plate or the like such that the brightness decreases as the _VLC increases and takes a minimum value. Therefore, in order to obtain normally closed characteristics, the angle φ _P between the polarization transmission axis 11 of the polarizing plate 8 and the electric field direction 9 is slightly larger than the angle φ _LC between the rubbing direction 10 and the electric field direction 9 (2 degrees or more and 30 degrees). (Hereinafter, preferably 3 degrees or more and 10 degrees or less)). By so doing, while applying a certain bias voltage (V _OFF to be described later), a light transmission T / T _o be 0 corresponding to the chi _eff becomes zero brightness in (1). On the other hand, when a higher electric field (V _ON described later) is applied, the value of χ _eff increases in accordance with the intensity, and reaches a maximum at 45 degrees. On the other hand, in order to obtain normally open characteristics, the angle φ _P between the polarization transmission axis 11 of the polarizing plate 8 and the electric field direction 9 is set to the rubbing direction 1.
Significantly larger than angle φ _LC between 0 and electric field direction 9 (45 degrees or more)
It may be arranged at a small angle. For any characteristic, effective d is achromatic to maximize transmittance.
_eff · Δn may be set to 0.28 μm, which is a half wavelength (here, the wavelength of light is assumed to be 0.555 μm).
Actually, there is a margin, so it is sufficient if the rubbing angle | φ _LC | is as small as 10 degrees or less, especially when the dielectric anisotropy is positive and the rubbing angle | φ _LC | It is preferable to set a slightly higher value between 0.27 and 0.33 μm.

FIG. 4 shows an example of a curve of the applied voltage dependence of the brightness, which is the main first configuration of the present invention. When the voltage _VLC applied between the pixel electrode 4 and the common electrode 1 is gradually increased from almost zero, the brightness temporarily decreases, takes a minimum value, then increases again, and finally when the applied voltage is almost zero. Take a value higher than the brightness. Here, such a characteristic that a bright state is displayed on the high voltage side is called a normally closed characteristic. On the other hand, FIG. 5 shows an example of a normally open characteristic in which a dark state occurs on the high voltage side. Here, in each case, the birefringence mode was adopted, and the polarization transmission axes of the two polarizing plates sandwiching the liquid crystal composition layer were substantially perpendicular to each other. However, the present invention is not limited to this as long as it is a means for realizing a characteristic capable of displaying two states of light and dark. In the present invention, the voltage at which the brightness becomes substantially the minimum value for any characteristic is defined as V _OFF, and the voltage for obtaining a brighter state is defined as V _ON (FIGS. 4 and 5).

(2) Optimization of Driving Conditions (Second Configuration) Next, the voltage of the driving IC is obtained by combining the above-described main first configuration and the following main second configuration driving method. Will be described below. FIG. 10 shows a drive circuit system according to the present invention. In the present invention, the scan electrode drive circuit 18 and the signal electrode drive circuit 1 are provided in the same manner as the drive circuit of a general thin film transistor type display device.
9, and a drive circuit 20 for applying a voltage waveform also to the common electrode. FIG. 9 shows an example of a driving waveform by this circuit. 9 (a) is a scanning waveform V _G supplied from the scan electrode driving circuit, FIG. 9 (b) shows the signal waveforms V _D which played an image information supplied from the signal electrode driving circuit. FIG. 9C shows a waveform V _C supplied to the common electrode, and FIG. 9D shows a voltage V _S applied to the source electrode which is a pixel electrode.
And FIG. 9 (e) shows the voltage _VLC applied to the liquid crystal.
Here, the waveform V _C supplied to the common electrode is synchronized with the signal waveform V _D and its phase is reversed, so that the effective voltage applied to the liquid crystal is such that the amplitude V _C of the voltage waveform from the common electrode is zero. It is made to be significantly higher than the case.

In the present invention, the drive circuit 20 for applying a voltage waveform to the common electrode is also provided. By combining the above-mentioned electro-optical characteristics with this simple circuit, the most frequently used and the image information can be used. It is possible to reduce the cost of the signal electrode drive circuit which becomes expensive to carry. The reduction in the cost of the signal electrode driving circuit, which accounts for a considerable portion of the total circuit cost, greatly contributes to the reduction in the cost of the entire display device. Generally, the manufacturing cost of a drive IC strongly depends on the withstand voltage (maximum output voltage), and the lower the cost, the easier it is to reduce. On the other hand, the common electrode drive circuit basically requires only one output terminal, and it is not necessary to carry image information, and a slight increase in output voltage does not lead to a significant increase in cost. As is clear from FIG. 9, when a voltage waveform having a phase opposite to the signal voltage waveform is applied to the common electrode, the effective voltage _VLC applied to the liquid crystal increases. The effective voltage V _LC applied to the liquid crystal is a voltage obtained by subtracting the voltage V _C from the common electrode from the voltage V _S applied to the source electrode which is a pixel electrode. In addition, the amplitude ΔV _S of the voltage applied to the pixel electrode (source electrode) when the gate is off is substantially proportional to the peak-to-peak value | V _DH −V _DL | of the voltage V _D applied to the signal electrode. Therefore, if the voltage applied to the signal electrode, that is, the voltage waveform applied to the pixel electrode (source electrode) and the voltage waveform applied to the common electrode have an opposite phase relationship, the peak-to-peak value of the effective voltage _VLC applied to the liquid crystal is The sum of them is obtained, and a higher voltage is applied to the liquid crystal even if the voltage applied to the signal electrode is lower. As is clear from FIG. 4, the voltage range that can be changed (also called dynamic range) is ΔV
_Since it is _S , the voltage V _OFF at which the minimum value of brightness is obtained by setting the polarizing plate and the like shown as the main first configuration described above.
Then, the voltage width corresponding to the dynamic range of the difference from the voltage V _ON at which sufficient brightness is obtained is narrowed, and the amplitude of the signal voltage waveform is suppressed to be lower.

The difference between V _OFF and V _ON strongly depends on the orientation direction (rubbing direction) of the liquid crystal on the interface. When the dielectric anisotropy of the liquid crystal is positive, the angle | φ _LC | It is effective to take as large as possible within the range. If the dielectric anisotropy of the liquid crystal is negative, the angle | φ _LC | should be made as small as possible within a range exceeding 0 °.

[0031]

EXAMPLES The present invention will be specifically described with reference to examples.

Example 1 The thickness of the substrate was 1.1 mm.
Use two transparent glass substrates whose surfaces have been polished. A thin film transistor was formed on one of these substrates, and an alignment film also serving as an insulating film was formed on the uppermost surface thereof. In this embodiment, polyimide is adopted as the alignment film,
A rubbing treatment for aligning the liquid crystal was performed thereon.
The other substrate was also coated with polyimide and subjected to the same rubbing treatment. The rubbing directions on the upper and lower interfaces are substantially parallel to each other, and the angle between the rubbing directions and the direction of the applied electric field is 88 degrees (φ _LC1 =
φ _LC2 = 88 °). The dielectric anisotropy Δε is positive and 4.5 between these substrates, and the refractive index anisotropy Δn is
Of a nematic liquid crystal composition of 0.072 (589 nm, 20 ° C.). The gap d was 3.9 μm in a state in which liquid crystal was sealed while spherical polymer beads were dispersed and sandwiched between substrates. Therefore, Δn · d is 0.281 μm. The panel is sandwiched between two polarizing plates (G1220DU manufactured by Nitto Denko Corporation)
The polarization transmission axis of one of the polarizing plates is slightly smaller than the rubbing direction, that is, φ _P1 = 80 ° (that is, | φ _LC1 −φ _P1 | =
8 °) and the other is orthogonal to it, ie φ _P2 = -12.
°. As a result, a characteristic (FIG. 4) in which the brightness decreases and takes the minimum value as the voltage _VLC applied to the pixel, which is the first main configuration of the present invention, gradually increases from zero is obtained. In the present embodiment, a normally-closed characteristic is employed in which a dark state occurs at a low voltage (V _OFF ) and a bright state occurs at a high voltage (V _ON ). V _OFF is 6.9V and V _ON is 9.1V.

FIG. 3 shows the structure of the thin film transistor and various electrodes. FIG. 3A is a front view seen from a direction perpendicular to the substrate surface, and FIGS. 3B and 3C are side sectional views. The thin film transistor element 14 includes a pixel electrode (source electrode) 4, a signal electrode (drain electrode) 3, a scanning electrode (gate electrode) 12, and amorphous silicon 13. The common electrode 1 and the scanning electrode 12, and the signal electrode 3 and the pixel electrode 4 were each formed by patterning the same metal layer. The capacitive element 16 is a region that couples between the two common electrodes 1 (FIG. 3).
(Indicated by a dotted line in FIG. 3)), the pixel electrode 4 and the common electrode 1 sandwich the insulating protective film 2. The pixel electrode is disposed between two common electrodes 1 in a front view (FIG. 3A). The pixel pitch is 69 μm in the horizontal direction (ie, between signal wiring electrodes), and 207 μm in the vertical direction (ie, between scanning wiring electrodes). As for the electrode width, a scanning electrode, a signal electrode, and a common electrode wiring portion (a portion extending in a direction parallel to the scanning wiring electrode (in the horizontal direction in FIG. 3)), which are wiring electrodes extending over a plurality of pixels, are widened to avoid line defects. . The width is 1 each
0 μm. On the other hand, the width of the pixel electrode independently formed in one pixel unit for improving the aperture ratio and the width of the portion of the signal wiring electrode of the common electrode extending in the longitudinal direction are slightly reduced to 5
μm and 8 μm. By reducing the width of these electrodes, the possibility of disconnection due to the incorporation of foreign matter or the like increases, but in this case, a partial defect of one pixel does not result in a line defect. In addition, the common electrode and the signal electrode were slightly overlapped (1 μm) via an insulating film in order to achieve an aperture ratio as high as possible. This eliminates the need for a black matrix in the direction parallel to the signal wiring. Therefore, as shown in FIG. 3C, a black matrix structure that shields light only in the direction of the scanning wiring electrode is adopted. Thus, the gap between the common electrode and the pixel electrode is 20 μm, and the length of the opening in the longitudinal direction is 15 μm.
7 μm, and a high aperture ratio of 44.0% was obtained. The number of pixels was 320 × 160 with 320 signal wiring electrodes and 160 wiring electrodes. FIGS. 13 and 14 show a part of a panel including a plurality of pixels. 13 omits the black matrix, and FIG. 14 shows a state where light is shielded by the black matrix.

Next, the circuit configuration and drive waveforms will be described. Each of the scanning wirings 12 and each of the signal wirings 3 have a scanning electrode driving circuit 18 and a signal electrode driving circuit 19, respectively.
Connected. The common electrode driving circuit 20 was also connected to the common electrode 1 (FIG. 10). A signal waveform having information is applied to the signal electrode 3, and a scanning waveform is applied to the scanning electrode 12 in synchronization with the signal waveform. An information signal is transmitted from the signal electrode 3 to the pixel electrode 4 via the thin film transistor 14, and a voltage is applied between the common electrode 1 and the liquid crystal portion.
In the present invention, a voltage waveform is also applied to the common electrode, and a higher voltage is applied to the liquid crystal layer. FIG. 9 shows the waveform of the voltage applied to each wiring electrode. Note that the amplitude of the voltage waveform in FIG. 9 is V _D-CENTER = 14.0, V _GH = 28.0, V _GL = 0, V _DH
= 15.1, V _DL = 12.9, V _CH = 20.4, V _CL = 4.39, and as a result, the jump voltage ΔV _GS (+) due to the parasitic capacitance between the gate electrode and the source electrode. , ΔV _GS (−), voltage V _S applied to the pixel electrode, and voltage V _LC applied to the liquid crystal are as shown in the table below. The unit of the voltage is hereinafter all volts.

[0035]

[Table 1]

V _ON and V _OFF shown in FIG.
6 volts and 6.85 volts, and a sufficiently high contrast ratio 80 was obtained.

In the present embodiment, the drive voltage waveform supplied to the signal wiring electrode could be driven at a very low amplitude V _DP-P (≡V _DH −V _DL ) of only 2.2 volts.

Comparative Example 1 φ _P1 and φ _P2 of Example 1 were set to 88 ° and −2 °, respectively, to obtain the characteristic of becoming darkest when the voltage was zero (FIG. 4). Other configurations such as the driving voltage waveform were the same as those in the first embodiment. Brightness at V _OFF is 1
There was as much as 2%, and a contrast ratio as low as 8 was obtained.

Comparative Example 2 φ _P1 and φ _P2 of Example 1 were set to 88 ° and −2 °, respectively, to obtain the characteristic of becoming darkest when the voltage was zero (FIG. 4). The drive voltage waveform was also changed in accordance with such a change in the characteristics. That is, V _C in FIG. 9 is a constant level of 12.4 volts, V _DH is 18.5 volts, V _DL is 9.5 volts, and 9.0 volts V _DP-P
I got Therefore, V _DP-P was much higher than 2.2 volts of Example 1.

[Embodiment 2] In this embodiment, φ of Embodiment 1
_LC1 at 88.5 °, φ _P1 and φ _P2 at 88.5 °,-
The angle was set to 1.5 °, and the gap of the liquid crystal was slightly increased to 4.3 μm. Δn · d was 0.310 μm. According to experiments by the inventors, Δn · d is 0.28 which is a half wavelength.
When φ _LC1 is approached to 90 ° while being fixed at about μm, the transmittance becomes maximum when φ _LC1 is about 75 ° and decreases again. This is because the liquid crystal alignment state when voltage is applied is not a simple uniaxial alignment state, but is distributed three-dimensionally. Then, as a result of the inventor's intensive study, especially 90 °
When the value is close to (85 ° or more), the apparent Δn · d is slightly reduced, and a slightly higher value (0.31
(± 0.05 μm). In this embodiment, the gap of the liquid crystal is set in consideration of this point. As a result, the characteristics shown in FIG. 8 were obtained.

When the rubbing direction was parallel to the polarization transmission axis direction of one of the polarizing plates (that is, φ _LC1 = φ _P1 ), the brightness at zero voltage was very low. The maximum value of V _OFF and V _ON were 5.0 volts and 8.8 volts, respectively. According to this characteristic, the voltage V _CP-P / 2 applied to the common electrode
Was also set to 6.9 volts. Other configurations are the same as those of the first embodiment. As a result, the amplitude V _DP-P of the drive voltage waveform supplied to the signal wiring electrode could be set to a low value of 3.8 volts, and the contrast ratio obtained a very high value of 250.

[Embodiment 3] In this embodiment, φ _{P1 of} Embodiment 1 is used.
And φ _P2 were set to 38 ° and −52 °, respectively, and FIG.
The normally open characteristics shown in the following were obtained. Other configurations are the same as those of the first embodiment. Both V _ON and V _OFF were almost equal to those in the first embodiment. A contrast ratio of 60 was obtained.

As in the first embodiment, the amplitude V _DP-P of the drive voltage waveform supplied to the signal wiring electrodes could be driven at a very low value of only 2.2 volts.

[Embodiments 4 to 6] In this embodiment, φ _{LC of} Embodiment 1 was set to 75 °, 88 °, and 89.5 °. Also, | φ
_{LC -φ P1} | was 5 degrees. Other configurations are the same as those of the first embodiment. As a result, characteristics as shown in FIG. 6 are obtained,
V _ON and V _OFF were as shown in the following table, respectively.

[0045]

[Table 2]

In any of the examples, the driving was possible at a low V _DP-P (amplitude of the driving voltage waveform supplied to the signal wiring electrode) of 5.0 volts or less, and a sufficiently high contrast ratio was obtained.

Example 7 The liquid crystal material was ZLI manufactured by Merck.
-2806. The dielectric anisotropy Δε is negative and its value is −4.8, and the refractive index anisotropy Δn is 0.0437. In order to set Δn · d in a desired range, the gap d
Was set to 6.3 μm. Therefore, Δn · d is 0.275. The angle between the rubbing direction and the applied electric field direction is 15
(Φ _LC1 = φ _LC2 = 15 °). The panel is sandwiched between two polarizing plates (G1220DU manufactured by Nitto Denko Corporation), and the polarization transmission axis of one of the polarizing plates has an angle slightly larger than the rubbing direction.
That is, φ _P1 = 20 ° is set, and the other is perpendicular to it, ie, φ
_{P2 was set to} -70 °. Thus, a characteristic (FIG. 7) in which the brightness decreases and takes the minimum value as the voltage _VLC applied to the pixel, which is the first main configuration of the present invention, gradually increases from zero is obtained. In the present embodiment, a normally-closed characteristic is employed in which a dark state occurs at a low voltage (V _OFF ) and a bright state occurs at a high voltage (V _ON ). V _OFF is 2.9V and V _ON is 9.4V. Except for the above points, the other points are the same as those of the first embodiment.

Driving was possible at a low V _DP-P (amplitude of the driving voltage waveform supplied to the signal wiring electrode) of 6.5 volts, and a sufficiently high contrast ratio of 180 was obtained.

Comparative Example 3 φ _P1 and φ _P2 in Example 7 were set to be the same as the rubbing direction, and were set to 15 ° and −75 °, respectively, to obtain the characteristic of darkening when the voltage was zero (FIG. 7). ). Other configurations such as the drive voltage waveform were the same as those of the seventh embodiment. The brightness at V _OFF was as high as 7%, and only a low contrast ratio of 11 was obtained.

Embodiment 8 Each of φ _LC1 and φ _LC2 was 1.
5 °, the gap d was 7.2 μm, and Δn · d was 0.315 μm. The polarization transmission axis of one of the polarizing plates was set substantially parallel to the rubbing direction, ie, φ _P1 = 2.5 °, and the other was perpendicular to it, ie, φ _P2 = -87.5 °. Other conditions are the same as in the seventh embodiment. As a result, the voltage V _OFF for obtaining a dark state
Was 5.2 volts, and the voltage V _ON for obtaining a bright state was 7.8 volts. In accordance with this characteristic, the voltage V _CP-P / 2 applied to the common electrode was also set at 6.5 volts. Other configurations are the same as those of the first embodiment. As a result, the amplitude V _DP-P of the drive voltage waveform supplied to the signal wiring electrode could be as low as 2.6 volts, and the contrast ratio was as high as 160.

[Embodiment 9] This embodiment is the same as Embodiment 1 except that the driving method is different. FIG. 12 shows the driving waveform of the present embodiment. Example 1 differs from those levels of the voltage waveform V _G supplied to the scanning wiring electrode was 2 value of V _GH and V _GL is, V _GL total divided into more V _GLH and V _GLL 3
At the point where the value is reached. V _GLH and V _GLL are V _CH and V, respectively.
Set the same as _CL .

In the present invention, the brightness is changed mainly by applying an electric field parallel to the substrate surface. In this case, when the liquid crystal portion is viewed as an electric circuit, it is compared with the current system in which an electric field perpendicular to the substrate surface is applied. And the capacity component is remarkably low. This is because the electrodes were planar instead of planar, and the interelectrode gap was widened. FIG. 11 shows a transmission circuit of one pixel. Since the capacitance C _{LC of the} liquid crystal is reduced as described above, the parasitic capacitance C _{GS that} is continuously formed between the scanning wiring electrode and the signal wiring electrode relatively increases. While in the present embodiment C _LC is approximately 30 fF, C _GS is the 20～50FF. This parasitic capacitance governs the magnitude of the jump voltage ΔV _GS shown in FIG. 9 and is a factor in the variation of the effective voltage applied to the pixel. In the present embodiment, in order to suppress this phenomenon, the potential of the gate electrode and the potential of the common electrode become almost the same except during the selection period so that the potential difference between the scanning wiring electrode and the common electrode is suppressed as much as possible. The drive waveform supplied to the scanning wiring electrode was designed as described above.
The various potentials are basically the same as those of the first embodiment except that the level of the supply potential to the scanning wiring electrode is set to three levels.

In the present embodiment, the frame inversion method of changing the level for each frame as the voltage waveform applied to the common electrode is adopted. However, the line inversion method of changing the level of the voltage waveform applied to the common electrode line by line in line order is adopted. You may adopt it. In either case, the effect of parasitic capacitance can be suppressed,
The load capacity C _S can also be reduced (can be removed). The reduction of the load capacity is effective for further reducing the load of the driving IC, so that a cheaper IC can be applied.

[0054]

According to the present invention, a low driving voltage and a high pixel aperture ratio, which are the drawbacks of the method of switching the liquid crystal by the electric field in the interface direction, are realized. A low-cost thin film transistor liquid crystal display device having good viewing angle characteristics can be provided.

[Brief description of the drawings]

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

FIG. 2 is a diagram showing an angle formed by a molecular long axis alignment direction (rubbing direction) φ _LC and a polarizing plate polarization axis direction φ _P on an interface with respect to an electric field direction.

FIG. 3 is a diagram showing a structure of a thin film transistor, an electrode, and a wiring according to the present invention. (A) Front view, (b), (c) sectional side view.

FIG. 4 is a diagram showing an example of the electro-optical characteristics of the present invention. Example of normally closed type.

FIG. 5 is a diagram showing another example of the electro-optical characteristics of the present invention. Example of normally open type.

FIG. 6 is a diagram showing another example of the electro-optical characteristics of the present invention. Normally closed type.

FIG. 7 is a diagram showing another example of the electro-optical characteristics of the present invention. Normally closed type. When the dielectric anisotropy of the liquid crystal is negative.

FIG. 8 is a view showing still another example of the electro-optical characteristics of the present invention. Normally closed type.

FIG. 9 is a diagram showing a driving waveform according to the present invention.

FIG. 10 is a diagram showing a circuit of the present invention.

FIG. 11 is a diagram showing an equivalent circuit of one pixel of the present invention.

FIG. 12 is a diagram showing another driving waveform according to the present invention. The case where the voltage waveform to the scanning wiring electrode is a ternary level.

FIG. 13 is a diagram showing an arrangement of a plurality of pixels of the display device of the present invention.

FIG. 14 is a diagram showing an arrangement of a plurality of pixels including a black matrix of the display device of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Common electrode (common electrode), 2 ... Insulating protective film, 3 ... Signal electrode (drain electrode), 4 ... Pixel electrode (source electrode),
5: protective insulating film, 6: liquid crystal molecules in the liquid crystal composition layer, 7
... Substrate, 8 ... Polarizing plate, 9 ... Electric field direction, 10 ... Direction of molecular long axis alignment on interface (rubbing direction), 11 ... Polarizing plate polarized light transmission axis direction, 12 ... Scanning electrode (gate electrode), 13 ... Amorphous silicon , 14 ... Thin film transistor part, 15 ... 1
Pixel pitch, 16: additional capacitance element section, 17: control circuit, 18: scan electrode drive circuit, 19: signal electrode drive circuit, 20: common electrode drive circuit, 21: display area, 22
... light shielding layer.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-4-96017 (JP, A) JP-A-1-107237 (JP, A) JP-B-63-21907 (JP, B1) 505247 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) G02F 1/133 550 G09G 3/18

Claims (11)

(57) [Claims] 1. A liquid crystal composition layer having at least one of a pair of transparent substrates sandwiched between said substrates, having aligned dielectric anisotropy and refractive index anisotropy, polarizing means, and being arranged in a matrix. A plurality of pixels, a thin-film transistor element connected to the pixel electrode, the signal wiring electrode and the scanning wiring electrode, a common electrode, and means for applying a voltage signal waveform between the pixel electrode and the common electrode. In the liquid crystal display device, the pixel electrode and the common electrode are arranged so as to apply an electric field between the pixel electrode and the common electrode and substantially parallel to the substrate surface by means for applying a voltage signal waveform. The alignment state of the liquid crystal composition layer and the configuration of the polarizing means are determined by the voltage V applied between the pixel electrode and the common electrode.
_{When the LC is} almost zero, the brightness is almost zero and the voltage V _LC
As the voltage _VLC gradually increases from zero, the brightness increases after going through a voltage region where the brightness does not substantially change, or as the voltage _VLC gradually increases from zero, the brightness decreases and takes a minimum value. Voltage waveforms V _D and V _C synchronized with the scanning signal waveform V _S applied to the scanning wiring electrode are applied to the signal wiring electrode and the common electrode, respectively. The voltage waveforms V _D and V _C applied to the electrodes are determined so that the effective voltage V _LC applied to the pixel is higher than when the amplitude V _C of the voltage waveform from the common electrode is zero, and By changing the peak value of the voltage applied to the signal wiring electrode in accordance with the image information, the effective voltage _VLC applied to the pixel is in the vicinity of the voltage V _OFF where the brightness becomes minimum, and the voltage V becomes brighter than that. _O Determined is driven to change between a _N, at least three or more values of the amplitude level of the scanning wiring electrode
And a thin-film transistor during the scanning selection period.
The resistance between the signal wiring of the transistor element and the pixel electrode
Have a high enough level to lower and the highest
Level V _GH is applied, and the common wiring is
In response to an increase or a decrease of the voltage V _C applied to the electrodes, different levels
2 or more values of the voltage (the maximum value V _GLH, the minimum value V _GLL the constant of
Is applied, and the potential between the scanning wiring electrode and the common electrode is applied.
A liquid crystal display device characterized by a reduced difference . 2. With respect to the orientation in the liquid crystal composition layer, the liquid crystal molecule orientation angle φ _LC1 on one substrate interface and the liquid crystal molecule orientation angle φ _LC2 on the other substrate interface are substantially parallel to each other (φ _LC1 ≒ _{φ LC2 ≡φ LC)} and is, and the product d · [Delta] n of thickness d and refractive index anisotropy [Delta] n of the liquid crystal composition layer is 0.
The liquid crystal display device according to claim 1, wherein the thickness is between 21 µm and 0.36 µm. 3. The liquid crystal composition layer has a positive dielectric anisotropy, and an angle | φ _LC | between a major axis direction of the liquid crystal molecules on the interface and an electric field direction is more than 45 degrees and less than 90 degrees. Wherein the polarizing means is a pair of polarizing plates sandwiching the liquid crystal composition layer,
The angle | φ _LC −φ _P | formed by the angle φ _P and φ _LC of the transmission axis (or absorption axis) of one polarizing plate A of the pair of polarizing plates is 2 degrees or less. The liquid crystal display device according to claim 2. 4. An angle | φ _LC | between a major axis direction of liquid crystal molecules on the interface and an electric field direction is more than 85 degrees and less than 90 degrees, and the thickness d of the liquid crystal composition layer and the refractive index difference are different. Isotropic Δ
4. The liquid crystal display device according to claim 3, wherein a product d · Δn of n is between 0.26 μm and 0.36 μm. 5. The liquid crystal composition layer has a positive dielectric anisotropy, and an angle | φ _LC | between a major axis direction of liquid crystal molecules and an electric field direction on the interface is more than 45 degrees and less than 90 degrees. Wherein the polarizing means is a pair of polarizing plates sandwiching the liquid crystal composition layer,
The pair of one transmission axis of the polarizing plate of the polarizing plate (or absorption axis) greater than the angle phi _P of, and the difference | phi _LC -
3. The liquid crystal display device according to claim 2, wherein φ _P | is 2 degrees or more and 30 degrees or less. 6. An angle | φ _LC | between a major axis direction of liquid crystal molecules and an electric field direction on the interface is 80 degrees or more and less than 90 degrees,
6. The liquid crystal display device according to claim 5, wherein the angle difference | φ _LC −φ _P | is 2 degrees or more and 10 degrees or less. 7. The liquid crystal composition layer has a negative dielectric anisotropy, and an angle | φ _LC | between a major axis direction of the liquid crystal molecules on the interface and an electric field direction is more than 0 degree and less than 45 degrees. , and the said a pair of polarizing plates polarizing means sandwich the liquid crystal composition layer, of the angle phi _P and phi _LC of the pair of one transmission axis of the polarizing plate of the polarizing plate (or absorption axis) 3. The liquid crystal display device according to claim 2, wherein the angle | φ _LC −φ _P | is 2 degrees or less. 8. An angle | φ _LC | formed between the major axis direction of the liquid crystal molecules on the interface and the electric field direction is more than 0 degree and less than 5 degrees, and the thickness d and the refractive index difference of the liquid crystal composition layer are different. The liquid crystal display device according to claim 7, wherein a product d · Δn of anisotropy Δn is between 0.26 μm and 0.36 μm. 9. The liquid crystal composition layer has a negative dielectric anisotropy, and an angle | φ _LC | between a major axis direction of liquid crystal molecules and an electric field direction on the interface is more than 0 degree and less than 45 degrees. Wherein the polarizing means is a pair of polarizing plates sandwiching the liquid crystal composition layer, and is smaller than an angle φ _P of a transmission axis (or absorption axis) of one of the pair of polarizing plates, and The difference | φ _LC −φ
3. The liquid crystal display device according to claim 2, wherein _P | is not less than 2 degrees and not more than 30 degrees. 10. An angle | φ _LC | formed between the major axis direction of the liquid crystal molecules on the interface and the electric field direction is more than 0 degree and less than 10 degrees, and the angle difference | φ _LC −φ _P | is 2 degrees. 10. The liquid crystal display device according to claim 9, wherein the angle is not less than 10 degrees. 11. In each of the plurality of pixels,
hand, The common electrode is constituted by two common electrodes, The pixel electrode is arranged between the two common electrodes.
The liquid crystal display device according to claim 1, wherein