JPH06160878A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To obtain an active matrix type liquid crystal display device having such features that the contrast is high, visual angle property is good, a multi- level display can be easily performed, and that the display is bright and the cost is reduced. CONSTITUTION:The device has such a structure that an electric field 7 parallel to a substrate surface is impressed on a liquid crystal composition layer by a thin film transistor provided with a drain electrode 12 and a common electrode 2 which are extending over plural picture elements and a source electrode 1 extending in a direction same as that of the electrodes.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin film transistor type liquid crystal display device having good mass productivity, low cost and good viewing angle characteristics.

[0002]

2. Description of the Related Art In a conventional thin film transistor type liquid crystal display device, transparent electrodes which are formed on the interface between two substrates and face 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 is adopted, which operates by making the direction of the electric field applied to the liquid crystal substantially perpendicular to the substrate interface. On the other hand, as a method for making the direction of the electric field applied to the liquid crystal substantially parallel to the substrate interface, a method using a comb-teeth electrode pair has been proposed in, for example, Japanese Patent Publication No. 63-21907. In this case, the electrodes do not have to be transparent, and it is possible to use an opaque metal electrode having high conductivity.

[0003]

In the above-mentioned prior art, it is necessary to use a vacuum system manufacturing equipment such as a sputtering apparatus in order to form a transparent electrode typified by ITO, resulting in a huge equipment cost. It was Also, the use of vacuum manufacturing equipment involves the work of removing contamination in the vacuum furnace,
This requires a great deal of time, which significantly increases the manufacturing cost. Further, in general, the transparent electrode has irregularities of about several tens of nm on its surface, which makes it difficult to process a fine active element such as a thin film transistor. In addition, the protrusions of the transparent electrode often come off and mix into other parts such as electrodes, causing dot-shaped or line-shaped display defects,
The yield was remarkably reduced. For these reasons, it has been impossible to stably provide a low-cost liquid crystal display device that meets market needs. Further, the above-mentioned conventional techniques have many problems in terms of image quality. In particular, the change in luminance is remarkable when the viewing angle direction is changed, and when performing halftone display, the gradation level is inverted due to each strong direction, which is a practical problem. Further, due to the concavo-convex structure of the thin film transistor element, an alignment defect domain is generated in the periphery of the thin film transistor element, a light-shielding film having a large area is required as a countermeasure, and the light utilization efficiency is significantly reduced.

On the other hand, if the comb-teeth electrode disclosed in Japanese Patent Publication No. 63-21907 is not used, it is possible to solve the above problems by eliminating the need for using transparent electrodes. Not not. That is, in this known technique, since the comb-teeth electrode pairs that interlock with each other are used, the pattern in the pixel becomes fine and complicated, and the mass productivity is extremely low. In particular, in a display with a large amount of display information and a small pixel size, it is almost impossible to put an electrode having a comb-tooth structure in one pixel. Even if it is put, the aperture ratio is extremely low, and most light can be effectively used. Can only achieve a dark display. In principle, the aperture ratio can be expanded to a practical level by reducing the electrode width of the comb-teeth electrode to about 1 to 2 μm, but in reality, such fine lines are formed uniformly over the entire surface of a large substrate without any breakage. It is extremely difficult to do. That is, in the above-mentioned conventional technology, the pixel aperture ratio and the manufacturing yield have a trade-off relationship because the comb-teeth-shaped electrodes that interlock with each other are used, and it is not possible to provide a liquid crystal display device having a bright image at low cost. It was difficult.

The present invention is intended to solve these problems at the same time. The object of the present invention is, first of all, to achieve high contrast without a transparent electrode and to realize mass production with low cost equipment at high yield and at low cost. An object is to provide a thin film transistor type liquid crystal display device. Secondly, it is to provide a thin film transistor type liquid crystal display device that can be driven at a low voltage, has good viewing angle characteristics, and can easily perform multi-gradation display. Thirdly, the degree of freedom in selecting usable liquid crystal compositions and alignment film materials is increased, thereby increasing the latitude of processes such as liquid crystal panel fabrication, and achieving both high aperture ratio and suppression of pixel deterioration.
Another object of the present invention is to provide a brighter thin film transistor type liquid crystal display device having an increased light transmittance. Fourthly, to provide a thin film transistor type liquid crystal display device having a simple structure and a high manufacturing yield in addition to the first to third objects.

[0006]

In order to solve the above problems and achieve the above object, the present invention uses the following means.
A pair of substrates, at least one of which is transparent, 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 thin film transistor element provided for each pixel and connected to a pixel electrode, a signal wiring electrode and a scanning wiring electrode, a common electrode separated from and in contact with the thin film transistor element, a voltage signal waveform for changing the light transmittance or reflectance of the pixel In the liquid crystal display device having a means for applying, the pixel electrode and the signal wiring electrode are provided between the pixel electrode and the common electrode by means for applying a voltage signal waveform,
An electric field is applied substantially parallel to the surface of the substrate (this electric field is referred to as a lateral electric field), and it is arranged so as to change the light transmittance or reflectance of the pixel according to the strength of the electric field. [Means 1] The pixel electrode In the pixel, it extends in a first direction, and the signal wiring electrode and the common electrode extend in the first direction and across a plurality of pixels to the end of the display portion. Liquid crystal display device.

[Means 2] The pixel electrodes are paired so as to sandwich the signal wiring electrode in one pixel, and the pixel and the signal wiring electrode are sandwiched by a pair of common electrodes. The liquid crystal display device according to means 1.

[Means 3] Means 1 or 2 characterized in that all of the pixel electrode, the signal wiring electrode, the common electrode and the scanning wiring electrode are arranged on one of the pair of substrates. The described liquid crystal display device.

By the means 1 to 3 described above, the transparent electrode is unnecessary, and the structure is much simpler than the conventional technique using the comb-teeth electrode pair, and the aperture ratio is high and the manufacturing yield is high. Also, a thin film transistor type liquid crystal display device that meets the fourth object is obtained.

[Means 4] The pixel electrode and the common electrode are in the same layer, and an insulator is interposed between any one of the pixel electrode, the common electrode, or an adjacent pixel electrode and the scanning wiring. 4. A liquid crystal display device according to means 3, wherein the liquid crystal display device forms a capacitive element.

[Means 5] At least two kinds of color filters having different colors are provided on a substrate facing the substrate having the thin film transistor element among the pair of substrates.
3. The liquid crystal display device according to means 1 or 2, wherein a boundary of the color filter overlaps any one of the pixel electrode, the signal wiring electrode, and the common electrode.

According to the means 5, the light shielding layer which has conventionally covered the boundary of the color filter having low color purity can be omitted, and a thin film transistor type liquid crystal display device of lower cost can be obtained.

[Means 6] At least two kinds of color filters having different colors are provided on the other substrate facing the substrate having the pixel electrode, the signal wiring electrode, the common electrode and the scanning wiring electrode, An organic polymer for flattening the surface is laminated on the color filter, the organic polymer is a transparent polymer, and the surface of the transparent polymer is rubbed to control the alignment of liquid crystal molecules on the interface in a predetermined direction. 4. The liquid crystal display device according to means 3, which is used as an alignment film.

According to the means 6, the organic polymer for flattening the unevenness of the color filter can be used also as the alignment film for controlling the alignment of the liquid crystal molecules, which is effective for cost reduction.

[Means 7] A pair of substrates, at least one of which is transparent, a liquid crystal composition layer having a dielectric anisotropy and a refractive index anisotropy which are sandwiched between the substrates and have an orientation, a polarizing means, and a matrix shape. A plurality of arranged pixels, a thin film transistor element provided for each pixel and connected to a pixel electrode, a signal wiring electrode and a scanning wiring electrode, a common electrode separated from and connected to the thin film transistor element, a light transmittance or reflection of the pixel In the liquid crystal display device having a means for applying a voltage signal waveform for changing the rate, the pixel electrode and the signal wiring electrode are provided on the substrate between the pixel electrode and the common electrode by means for applying a voltage signal waveform. The thin film transistor element and the liquid crystal composition are arranged so that an electric field is applied substantially parallel to the surface and the light transmittance or reflectance of the pixel is changed according to the strength of the electric field. The liquid crystal display device, wherein a organic insulating layer in direct contact with the layer are provided.

[Means 8] The organic insulating layer covering the thin film transistor element is rubbed so that the organic insulating layer has both functions of a protective film of the thin film transistor element and a liquid crystal molecule alignment control film. 8. A liquid crystal display device according to means 7, characterized in that

According to the means 7 to 8, the conventional C
An inorganic insulating film formed in a vacuum system such as a VD (Chemical Vapor Deposi-tion) method can be replaced with an organic insulating layer that can be manufactured at a lower cost, which is effective for cost reduction.

Means 9 and below represent a method for realizing the second object of good viewing angle characteristics and excellent multi-gradation display capability.

[Means 9] The dielectric constant anisotropy of the liquid crystal composition layer is positive, and the angle | φ _LC | formed between the liquid crystal molecule alignment direction and the electric field direction on at least one substrate interface is 45.
5. The liquid crystal display device according to any one of means 1 to 4, which is not less than 90 degrees and not more than 90 degrees. However, -90
Degree ≦ φ _LC ≦ 90 degrees.

[Means 10] The dielectric constant anisotropy of the liquid crystal composition layer is negative, and the angle | φ _LC | formed by the orientation direction of liquid crystal molecules and the electric field direction on at least one substrate interface is 0.
5. The liquid crystal display device according to any one of means 1 to 4, wherein the liquid crystal display device is above 45 degrees and above 45 degrees. However, -9
0 degree ≦ φ _LC ≦ 90 degrees.

[Means 11] Regarding the orientation in the liquid crystal composition layer, the angle φ of the orientation direction of the liquid crystal molecules on the interface of one of the substrates.
_LC1 and the liquid crystal molecule orientation direction angle φ _LC2 on the other substrate interface are substantially parallel to each other (φ _LC1 ≈ φ _LC2 ), and the product d · of the thickness d of the liquid crystal composition layer and the refractive index anisotropy Δn. 11. The liquid crystal display device according to means 9 or 10, characterized in that Δn is between 0.21 μm and 0.36 μm.

[Means 12] A retardation R _f lower than the product d · Δn of the thickness d of the liquid crystal composition layer and the refractive index anisotropy Δn.
Is inserted so as to compensate for the phase difference caused by the liquid crystal composition layer, and the difference in absolute value |
12. The liquid crystal display device according to means 11, characterized in that d · Δn | − | R _f | is set between 0.21 μm and 0.36 μm.

According to the means 9 to 12, high contrast and wide viewing angle characteristics due to the birefringence mode can be obtained.

[Means 13] Regarding the orientation in the liquid crystal composition layer, the angle φ of the orientation direction of the liquid crystal molecules on the interface of one substrate.
Intersects the liquid crystal molecular alignment direction angle phi _LC2 and each other in _LC1 and the other substrate surface, the angle | φ _LC1 -φ _LC2 | is less than 100 degrees 80 degrees, and the thickness d of the liquid crystal composition layer
And the product d · Δn of the refractive index anisotropy Δn is between 0.40 μm and 0.60 μm.

According to the means 13, a high contrast and a wide viewing angle characteristic due to the optical rotation mode can be obtained.

[Means 14] The liquid crystal display device according to means 11 or 13, wherein the tilt angle of the liquid crystal molecules is 4 degrees or less on any interface.

[Means 15] The dielectric constant anisotropy of the liquid crystal composition layer is positive, the polarizing means is a pair of polarizing plates sandwiching the liquid crystal composition layer, and the long axis of the liquid crystal molecules on the interface. The angle φ _LC formed by the direction and the electric field direction is larger than the angle φ _P of the transmission axis (or the absorption axis) of one of the pair of polarizing plates A, and the difference | φ _LC −φ _P | Is more than 3 times 15
10. The liquid crystal display device according to means 9, wherein the liquid crystal display device has a temperature of not more than 100 degrees.

[Means 16] The dielectric constant anisotropy of the liquid crystal composition layer is negative, the polarizing means is a pair of polarizing plates sandwiching the liquid crystal composition layer, and the long axis of the liquid crystal molecules on the interface. Angle φ _LC between the direction of the electric field and the direction of the electric field is smaller than the angle φ _P of the absorption axis or the transmission axis of the polarizing plate, and the difference _| φ _P −φ
_11. The liquid crystal display device according to means 10, characterized in that _LC | is 3 degrees or more and 15 degrees or less.

[Means 17] An image signal is applied to the second electrode, and a voltage signal waveform is applied to the common electrode so that the voltage applied to the liquid crystal composition layer is further increased. 17. The liquid crystal display device according to the means 15 or 16.

[Means 18] The polarizing means is a pair of polarizing plates sandwiching the liquid crystal composition layer, and the polarizing means is set to a bright state when a low voltage V _{L is} applied and a dark state when a high voltage V _{H is} applied. 14. A liquid crystal display device according to means 11 or 13, wherein a transparent medium for compensating for the residual phase difference at the interface of the liquid crystal layer when V _{H is} applied is inserted between the pair of polarizing plates.

The means 14 to 18 solve the problem that the threshold voltage rises when the lateral electric field drive which is the basic constitution of the present invention is adopted and it is necessary to use a drive circuit having a higher breakdown voltage. To do. According to this, as in the embodiment, it is possible to operate even a drive circuit having a sufficiently low output voltage of less than 10 volts.

[0032]

First, the angle φ _P formed by the polarization transmission axis of the polarizing plate with respect to the direction of the electric field, the angle φ _LC formed by the liquid crystal molecule major axis (optical axis) direction near the interface, and inserted between the pair of polarizing plates. The definition of the angle φ _R formed by the fast axis of the retardation plate is shown (Fig. 6). Since there are a pair of the polarizing plate and the liquid crystal interface above and below, respectively, they are denoted as φ _P1 , φ _P2 , φ _LC1 , and φ _LC2 as necessary. 6 corresponds to the front view of FIG. 1 described later.

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

1 (a) and 1 (b) are side cross sections showing the operation of the liquid crystal in the liquid crystal panel of the present invention, and FIGS. 1 (c) and 1 (d) are front views thereof. In FIG. 1, the thin film transistor element is omitted. Further, in the present invention, a plurality of pixels are formed by forming a striped electrode, but only one pixel portion is shown here. FIG. 1A shows a cross section of the cell side when no voltage is applied, and FIG. 1C shows a front view at that time. Linear electrodes 1 and 2 are formed inside a pair of transparent substrates, and an alignment control film 4 is applied and aligned on the linear electrodes 1 and 2. A liquid crystal composition is sandwiched between them. The rod-shaped liquid crystal molecules 5 have a slight angle with respect to the longitudinal direction of the electrodes 1 and 2, that is, 4
Oriented such that 5 ° ≦ | φ _LC | <90 °. The orientation directions of liquid crystal molecules on the upper and lower interfaces are parallel here,
That is, φ _LC1 = φ _LC2 will be described as an example. The dielectric anisotropy of the liquid crystal composition is assumed to be positive. Next, when an electric field 7 is applied, the liquid crystal molecules change their directions in the direction of the electric field as shown in FIGS. By arranging the polarizing plate 6 at a predetermined angle 9, the light transmittance can be changed by applying an electric field. As described above, according to the present invention, it is possible to provide a display with contrast even without the transparent electrode. Incidentally, FIG.
In (b), the angle between the surface of the substrate and the direction of the electric field is large and it does not seem to be parallel, but this is the result of enlarging the thickness direction and is actually 20 degrees or less. Hereinafter, in the present invention, those of 20 degrees or less are collectively referred to as a lateral electric field.
Further, in FIG. 1, the electrodes 1 and 2 are formed separately on the upper and lower substrates, but the effect does not change even if they are provided on one substrate. Rather, when patterns such as wiring are miniaturized, heat,
In consideration of various deformations due to external force and the like, it is preferable to equip one of the substrates because more accurate alignment is possible. Although the dielectric anisotropy of the liquid crystal composition is assumed to be positive, it may be negative. In that case, the initial orientation state is slightly different from the direction (electric field direction 7) perpendicular to the longitudinal direction of the electrodes 1 and 2 | φ _LC | (that is, 0 degree <| φ _LC | ≦ 45 degree)
To be oriented.

The operation will be described below according to each of the three objects of the present invention.

(1) High Contrast without Transparent Electrode As a specific structure for imparting contrast, a mode utilizing a state in which liquid crystal molecule alignments on the upper and lower substrates are substantially parallel (interference due to birefringence phase difference) Since color is used, this is called a birefringence mode) and a mode in which the alignment of liquid crystal molecules on the upper and lower substrates intersects and the molecular arrangement in the cell is twisted (polarization plane in the liquid crystal composition layer). Since it uses the optical rotation that rotates, it is called the optical rotation mode here). In the birefringence mode, the direction of the molecular long axis (optical axis) is changed in the plane while the direction of the molecular long axis (optical axis) is almost parallel to the substrate interface by applying a voltage, and the angle formed by the axis of the polarizing plate set to a predetermined angle is changed. Change the transmittance. Similarly, even in the optical rotatory mode, only the orientation of the molecular long axis direction is changed by applying a voltage, but in this case, the change in optical rotatory power due to the unwinding of the line is used.

Next, the quantitative structure and operation for making the display achromatic and increasing the contrast ratio will be described below in two cases of using the birefringence mode and the optical rotation mode.

I. Display in Birefringence Mode Generally, the light transmittance T / T _o when a uniaxial birefringent medium is inserted between two polarizing plates arranged orthogonally is expressed by the following equation. Here, χ _eff is the effective optical axis direction of the liquid crystal composition layer (angle formed by the optical axis and the polarization transmission axis), d _eff is the thickness of the effective liquid crystal composition layer having birefringence, and Δn is Refractive index anisotropy, λ represents the wavelength of light. Here, the purpose of making the optical axis direction of the liquid crystal composition layer an effective value is that the liquid crystal molecules are fixed on the interface in the actual cell and all the liquid crystal molecules are parallel to each other in the cell when an electric field is applied. In view of the fact that a large amount of deformation occurs, especially in the vicinity of the interface, rather than being oriented uniformly, it is treated as an average value of the apparent values when assuming a uniform state.

T / T _o = sin ² (2χ _eff ) · sin ² (πd _eff · Δn / λ) (1) Normally closed, which is dark when a low voltage V _{L is} applied and bright when a high voltage V _{H is} applied To obtain the characteristics, the polarizing plate should be arranged so that the transmission axis (or absorption axis) of one polarizing plate is almost parallel to the liquid crystal molecule alignment direction (rubbing axis), that is, φ _P1 ≈ φ _LC1 =
φ _LC2 and the transmission axis of the other polarizing plate may be perpendicular to it, that is, φ _P2 = φ _P1 +90 degrees. When no electric field is applied,
Since χ _{eff in} equation (1) is 0, the light transmittance T / T _o
Also becomes 0. On the other hand, when an electric field is applied, χ
The value of _eff increases and reaches a maximum at 45 degrees. At this time, assuming that the wavelength of the light is 0.555 μm, the effective d _eff · Δn may be set to 0.28 μm, which is a half wavelength, in order to obtain an achromatic color and maximize the transmittance. In reality, since there is a margin, it may be in the range of 0.21 to 0.36 μm, but it is desirable to set the value in the range of 0.24 to 0.33 μm.

On the other hand, in order to obtain a normally open characteristic in which a bright state is applied when a low voltage V _{L is} applied and a dark state is applied when a high voltage V _{H is} applied, χ in equation (1) is applied when no electric field is applied or when a low electric field is applied.
_The polarizing plate arrangement may be set so that _{eff is} approximately 45 degrees. Contrary to the case of normally closed when the electric field is applied, the value of χ _eff decreases according to its strength. However, even if χ _eff becomes minimum (that is, 0), a considerable amount of light leaks due to the residual phase difference of the liquid crystal molecules fixed near the interface. d · Δn from 0.27 to 0.
According to an experiment conducted by the inventors of the present invention in which the voltage is set to 37 μm and an effective voltage of 3 to 10 V is applied, the value of the interface residual phase difference is about 0.02 to 0.06 μm. Therefore, 0.0
By inserting a retardation plate having a birefringence retardation of about 2 to 0.06 μm (this retardation is represented by R _f ) so as to compensate for the interface residual retardation, the dark state sinks and a high contrast ratio is obtained. Is obtained. Angle φ of the fast axis of the retardation plate
_R is the effective optical axis χ _eff of the liquid crystal composition layer when a voltage is applied.
Parallel to. In order to completely sink the brightness of the dark state, it is necessary to exactly match the residual phase difference when the voltage for displaying the dark state is applied. From the above, in order to achieve both the sinking in the dark state and the transmittance and the whiteness in the bright state, it is sufficient to satisfy the following equation.

[0041] 0.21μm <(d · Δn-R f) <0.36μm ... (2) preferably, 0.23μm <(d · Δn- R f) <0.33μm ... (3) II. When displaying in the optical rotation mode Twisted Nemat
In the ic: TN) method, d.Δn as is generally known.
When the value is set near 0.50 μm, which is the first minimum condition, high transmittance and achromatic color are obtained. Considering the margin, in the TN method, it may be set between 0.40 and 0.60 μm. Regarding the arrangement of the polarizing plates, the transmission axis (or absorption axis) of one polarizing plate is set substantially parallel to the liquid crystal molecule orientation direction (rubbing axis) on the interface, that is, φ _LC1 ≈φ _LC2 . In order to realize the normally closed type, the transmission axis of the other polarizing plate may be parallel to it, and to make it the normally open type, it may be vertical.

In order to completely eliminate the optical rotatory power, it is necessary to make the liquid crystal alignment directions near the upper and lower substrate interfaces substantially parallel to each other. Assuming a 90 ° TN mode, the liquid crystal on one substrate side is assumed. You have to rotate the molecule close to 90 degrees. In the case of displaying in the birefringence mode, the liquid crystal molecule rotation angle may be about 45 degrees, and the threshold voltage is lower in the birefringence mode.

(2) Improvement of viewing angle characteristics In the display mode of the present invention, the major axis of the liquid crystal molecules is almost parallel to the substrate and does not rise, and therefore the change in brightness when changing the viewing angle direction is small. In this display mode, the dark state is not obtained by making the birefringence phase difference almost zero by applying a voltage as in the conventional case, but the angle formed by the long axis of the liquid crystal molecule and the axis of the polarizing plate (absorption or transmission axis) is Change things,
Fundamentally different. In the case of raising the liquid crystal molecule long axis perpendicularly to the substrate interface as in the conventional TN type, the viewing angle direction in which the birefringence phase difference becomes 0 is only the front direction, that is, the direction perpendicular to the substrate interface, and even if slightly inclined. Birefringence phase difference appears,
In the normally open type, light leaks, causing a decrease in contrast and inversion of gradation levels.

(3) Improving the degree of freedom in selection of the alignment film material and the liquid crystal material and thereby expanding the process margin. Further, since the liquid crystal molecules do not rise in this way, a large tilt angle (liquid crystal molecule length) as in the conventional case is obtained. An alignment film that provides the angle between the axis and the interface) is not required. In the conventional method, if the tilt angle is insufficient, two states having different tilt directions and domains at their boundaries may be generated, which may result in display failure. In this method, instead of giving a tilt angle, the liquid crystal molecule major axis direction (rubbing direction) on the substrate interface may be set to a predetermined direction deviated from 0 degree or 90 degrees with respect to the electric field direction. For example, when the dielectric anisotropy of the liquid crystal composition is negative, the angle φ _LC (defined as φ _LC > 0 degree) formed by the direction of the electric field and the long axis direction of the liquid crystal molecules on the substrate interface is 0 degree or more ( Substantially 0.5 degrees or more), preferably 2 degrees or more. If it is completely 0 degrees, two kinds of deformation in different directions occur, two different states and domains of their boundaries occur, which may result in display failure. If it is 0.5 degrees or more, the apparent liquid crystal molecule major axis direction (defined as φ _LC (V)) increases uniformly due to the application of the electric field and its strength, and the tilt in the opposite direction, that is, φ _LC (V) never reaches 0 degree. According to the present method, even if the angle (tilt angle) formed by the interface and the liquid crystal molecules is small in this way, the operation is performed without the domain being generated, and thus it is possible to set a lower tilt angle.
The uniformity of the liquid crystal molecule alignment is good because the process latitude such as rubbing increases as the tilt angle is set to a lower value. Therefore, if this method of applying an electric field parallel to the interface is combined with a low tilt angle, the liquid crystal molecule alignment becomes more uniform, and even if the manufacturing process changes to the same degree, the display unevenness can be suppressed lower than that of the conventional method. . In general, the types of alignment films that give a high tilt angle are less than those that give a low tilt angle,
If this method is used, the degree of freedom in selecting the alignment film material is increased. For example, even if the organic polymer is used for the flattening film on the color filter and the protective film on the thin film transistor and the surface alignment treatment such as rubbing is directly performed, the inclination angle is not necessary, and thus the combined use with the alignment film becomes easier. Further, it is possible to simplify the process and reduce the cost associated therewith. To suppress display unevenness due to manufacturing process fluctuations, the tilt angle should be 4 degrees or less,
It is desirable to set it to 2 degrees or less.

Further, the degree of freedom in selection of the liquid crystal material is increased due to the following reasons. That is, in the present invention, the pixel electrode and the common electrode have a structure in which an electric field is applied to the liquid crystal composition layer mainly in parallel to the substrate interface, and the distance between the electrodes is a conventional vertical electric field type active matrix liquid crystal. The distance can be made larger than the distance between the transparent electrodes facing each other in the display device. Further, the equivalent electrode cross-sectional area can be suppressed smaller than that of the conventional one. Therefore, the electric resistance between the pair of pixel electrodes according to the present invention can be increased by an order of magnitude higher than the electric resistance between the transparent electrodes facing each other in the conventional active matrix liquid crystal display device. Furthermore, the capacitance between the pixel electrode and the common electrode according to the present invention is connected in parallel with the capacitance element, and a capacitance element having a sufficiently high electric resistance can be realized. As a result, it becomes easy to hold the charges accumulated in the pixel electrode, and sufficient holding characteristics can be obtained even if the area of the capacitive element, which has conventionally sacrificed the aperture ratio, is reduced. Further, conventionally, a liquid crystal composition also needs to have an extremely high specific resistance of, for example, 10 ¹² Ωcm, whereas a liquid crystal composition having a lower specific resistance is not a problem. This not only increases the degree of freedom in selecting the liquid crystal material, but also increases the process margin. That is, even if the liquid crystal is contaminated during the process, the image quality is unlikely to be poor. In particular, the margin for fluctuations on the interface with the alignment film described above increases, and defects due to the interface are almost eliminated. Therefore, steps such as inspection and aging can be greatly simplified, which greatly contributes to cost reduction of the thin film transistor type liquid crystal display device. Further, since the pixel electrode according to the present invention has a simpler shape than the comb-teeth-shaped electrode pair, the light utilization efficiency is improved. There is no need to sacrifice the opening to obtain a capacitive element that can store a sufficient amount of electric charges as in the conventional method. Furthermore, if the insulating film that protects the thin film transistor is made of an organic material, the dielectric constant can be made lower than that of an inorganic material, so that the electric field component generated in the vicinity of the pixel electrode in the direction perpendicular to the substrate interface can be suppressed smaller than the lateral electric field component. The liquid crystal operates in a wider area. This also contributes to the improvement of brightness. Further, when the common electrode is shared with the common electrode of the adjacent pixel, the same action as the common electrode in the conventional active matrix type liquid crystal display device can be obtained, and the structure can be further simplified. It is possible to increase the aperture ratio.

(4) Realization of a simple thin film transistor structure with a high aperture ratio and improvement of brightness thereof A comb-shaped electrode disclosed in a known example (Japanese Patent Publication No. 63-21907) concerning a structure in a pixel including a thin film transistor. In the case of using, the aperture ratio is remarkably lowered, which causes a problem that the brightness is lowered. Considering mass productivity, the width of one comb-teeth electrode is required to be about 8 μm, and at least 4 μm or more. For example, as shown in Japanese Patent Publication No. 63-21907, see FIG.
Diagonal with a structure with a total of 17 comb teeth like 9.
It is impossible to construct a pixel of 0.3 × 0.1 mm ² of 4-inch color VGA class. The present invention has devised means for maintaining a sufficient aperture ratio while maintaining the advantages (1) and (2). In place of the structure in which the aperture ratio has to be lowered like comb teeth, a simpler electrode structure has realized a high aperture ratio with practicality. Means 1 to 5 relate to a structure in which the common electrode is formed on the counter substrate or the pixel electrode is formed on the same layer.
In the above-mentioned known example (Japanese Patent Publication No. 63-21907), in order to form the comb-teeth electrode, the lead-out directions of the signal wiring and the common electrode are orthogonal to each other. That is, the signal wiring is arranged in the first direction (Y
Direction), the common electrode is extended in a direction (X direction) orthogonal to the common electrode. On the other hand, according to the present invention, by extending all of the signal wiring, the pixel electrode, and the common electrode in the first direction as in the means 1, a complicated structure such as comb teeth is avoided. The threshold voltage of the liquid crystal can be lowered and the response time can be shortened by narrowing the interval between the pixel electrode and the common electrode. For that purpose, the method of the means 2 can be adopted, which is complicated like comb teeth. It is not necessary to have a simple structure.

[0047]

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

Example 1 A substrate having a thickness of 1.1 mm
Two transparent glass substrates whose surfaces have been polished by are used. Between these substrates, the dielectric anisotropy Δε is positive and its value is 4.5, and the refractive index anisotropy Δn is 0.072 (589 nm, 20
(° C) between the nematic liquid crystal compositions. Rubbing the polyimide-based orientation control film applied to the substrate surface for 3.5
The pre-tilt angle in degrees. The rubbing directions on the upper and lower interfaces are substantially parallel to each other, and the angle formed with the direction of the applied electric field is 8
It was set to 5 degrees (φ _LC1 = φ _LC2 = 85 °). The gap d was 4.5 μm when spherical polymer beads were dispersed and sandwiched between the substrates and the liquid crystal was sealed. Therefore, Δn · d is 0.324.
μm. The panel is sandwiched between two polarizing plates [G1220DU manufactured by Nitto Denko Corporation], and the polarization transmission axis of one polarizing plate is almost parallel to the rubbing direction, that is, φ _P1 = 85 °, and the other is orthogonal thereto, that is, φ _P2 = It was set to -5 °. As a result, normally closed characteristics were obtained.

As for the structure of the thin film transistor and various electrodes, as shown in FIG. 2A (front view) and FIG. 2B (side cross section), the thin film transistor element (hatched portion in FIG. 2) is a pixel electrode (source electrode). 1 and the signal electrode (drain electrode) 12,
And a scanning electrode (gate electrode) 10, the pixel electrode 1 extends in a first direction (which means an up and down direction in the drawing of FIG. 2), and the signal electrode 12 and the common electrode 2 include a plurality of pixels. The thin film transistor elements are arranged between the common electrodes, extending in the first direction over the space (in FIG. 2, meaning pixels arranged in the vertical direction on the paper surface).

A signal waveform having information is applied to the signal electrode 12, and a scanning waveform is applied to the scanning electrode 10 in synchronization with the signal waveform. Amorphous silicon (a-S
i) channel layer 16 and silicon nitride (Si
The thin film transistor including the protective insulating film 15 of N) is arranged between the common electrodes adjacent to each other. An information signal is transmitted from the signal electrode 12 to the pixel electrode 1 through the thin film transistor, and a voltage is applied to the liquid crystal portion between the signal electrode 12 and the common electrode 2. In this embodiment, the common electrode is arranged on the counter substrate side, and
In (b), since the thickness direction is enlarged and shown, the electric field direction 7 seems to be inclined. However, in reality, the thickness of the liquid crystal layer 5 is about 6 μm with respect to the width of 48 μm, and the inclination is almost the same. The applied electric field direction is almost parallel to the substrate surface.

As shown in FIG. 1C, the capacitive element 12 has a structure in which the pixel electrode 1 has a structure in which a gate insulating film 13 is sandwiched on the scanning wiring 10 in which a special portion is formed. The capacitance of the capacitive element 12 was about 21 fF. A scanning wiring driving LSI and a signal wiring driving LSI were connected to each scanning wiring 10 and each signal electrode driving circuit 21, respectively.

The electric charge accumulated in the pixel electrode 1 is accumulated in about 24 fF which is the capacitance between the pixel electrode 1 and the common electrode 2 and the additional capacitance element 11 connected in parallel. Even if the specific resistance of the object 50 is 5 × 10 ¹⁰ Ωcm, the voltage fluctuation of the pixel electrode 1 can be suppressed. Therefore, it is possible to prevent the deterioration of image quality.

The number of pixels is 40 (× 3) × 30, and the pixel pitch is 80 μm in the horizontal direction (that is, between the common electrodes) and 240 μm in the vertical direction (that is, between the scanning electrodes). The width of the scanning electrode is 1
The gap between adjacent scanning electrodes is 2 μm and 68 μm.
A high aperture ratio of 100% was secured. In addition, stripe-shaped R,
A color filter of three colors G and B was provided. A transparent resin for flattening the surface was laminated on the color filter. An epoxy resin was used as the material of the transparent resin. Further, a polyimide-based orientation control film on this transparent resin was applied. A drive circuit is connected to the panel. The configuration of the drive circuit system of this embodiment is shown in FIG. The signal electrode 23 and the common electrode 31 extend to the end of the display unit. 9 and 10 show the configuration of the optical system. FIG. 9 shows a transmissive type, and FIG. 10 shows a reflective type.

Since the transparent electrode is not required in this embodiment, the manufacturing process can be simplified and the yield can be improved.
The cost can be significantly reduced. In particular, the need for extremely expensive equipment having a vacuum furnace for forming transparent electrodes is eliminated,
It is possible to significantly reduce the amount of manufacturing equipment investment and thereby reduce costs. FIG. 3A shows electro-optical characteristics showing the relationship between the effective value of the voltage applied to the pixel and the brightness in this example.
The contrast ratio is 150 or more when driven by 7V, and the difference in the curves when the viewing angle is changed to the left and right and up and down is extremely small compared to the conventional method (shown in Comparative Example 1), and the display characteristics change almost even when the viewing angle is changed. I didn't. In addition, the liquid crystal alignment was good, and no domain with poor alignment was generated. In addition, the aperture ratio secured a sufficiently high value of 50% by simplifying the thin film transistor and electrode structure, and realized a bright display. The average transmittance of the entire panel was 8.4%. The brightness here is defined as the luminance transmittance when two polarizing plates are arranged in parallel.

[Embodiment 2] In this embodiment, the scanning electrodes are arranged on the opposite substrate side and the scanning electrodes are arranged on the same substrate side in the first embodiment. Other configurations are the same as those in the first embodiment. A cross-sectional structure of the thin film transistor and the electrode is shown in FIG. Pixel electrode 1, signal electrode 1
2. All the scanning electrodes were made of aluminum, and were formed by film formation and etching at the same time. There is no conductive substance on the counter substrate. Therefore, in the configuration of the present embodiment, even if a conductive foreign substance is mixed in during the manufacturing process, there is no possibility of touch between the upper and lower electrodes, and the defective rate of the touch between the upper and lower electrodes is suppressed to zero. The material for the electrode is not particularly limited as long as it is a metallic material having a low electric resistance, and chromium, copper or the like may be used.

Generally, the alignment accuracy of the photomask is significantly higher than the alignment accuracy of the combination between the two glass substrates facing each other. Therefore, as in this embodiment, 4
It is better to form any of the seed electrode groups on one substrate,
Since the alignment at the time of forming each electrode is performed only by the photomask, the misalignment between the electrodes is suppressed to be small. Therefore, this embodiment is effective in forming a finer pattern than in the case where the scanning electrodes are formed on the counter substrate.

Similar to Example 1, a bright display having a wide viewing angle characteristic was obtained.

[Third Embodiment] The configuration of this embodiment is the same as that of the first embodiment except for the following requirements.

The structure of the thin film transistor and various electrodes is shown in FIG. 5, and the signal electrode 1 is provided between the pair of pixel electrodes 1.
2 were arranged, and a pair of common electrodes 2 were arranged outside these electrodes. A signal waveform having information is applied to the signal electrode 12, and a scanning waveform is applied to the scanning electrode 10 in synchronization with the signal waveform. Amorphous silicon (a
The thin film transistor including the -Si) 16 and the protective insulating film 15 of silicon nitride (SiN) is arranged substantially in the center of the pair of common electrodes. The same information signal is transmitted from the signal electrode 12 to the two first electrodes 1 through the two thin film transistors, and the same voltage signal is applied to the liquid crystal portion between the common electrodes on both sides having the same potential. By doing this, the electrode spacing can be reduced to about half without complicating the thin film transistor and electrode structure, and a higher electric field can be applied at the same voltage, thus reducing the drive voltage and achieving high-speed response. To be done.

The wide viewing angle characteristics and brightness of the first embodiment are also realized in this embodiment.

[Embodiment 4] The structure of this embodiment is the same as that of the embodiment 1 except for the following requirements.

A flattening film 14 (FIG. 2B) made of a transparent polymer is laminated as an organic insulating layer on the color filter,
The surface was directly rubbed without forming another film as an orientation control film on it. An epoxy resin was used as the material of the transparent polymer. This epoxy resin has both functions of flattening and controlling the alignment of liquid crystal molecules. The liquid crystal composition layer was in direct contact with the epoxy resin, and the inclination angle at the interface was 0.5 degree. As a result, the step of applying the alignment film was eliminated, and the manufacturing process became easier and shorter. Generally, in the TN type which is the conventional method, the characteristics required for the orientation control film are diverse, and it is necessary to satisfy all of them, so that it is limited to some materials such as polyimide. A particularly important characteristic is the tilt angle. However, as mentioned in the operation, the present invention does not require a large tilt angle, and therefore,
The choice of materials is significantly improved.

When the electro-optical characteristics in this example were measured, the difference in the curves when the viewing angle was changed to the left, right and up and down was very small as in Example 1, and the display characteristics were hardly changed. Further, although the tilt angle was as small as 0.5 degree, the liquid crystal alignment was good and no misalignment domain was generated.

[Embodiment 5] The transparent polymer for flattening of Embodiment 4 is changed from epoxy resin to polyimide resin.
Similarly, the surface of the polyimide resin was directly rubbed to have both the functions of flattening and controlling the alignment of liquid crystal molecules. The tilt angle at the interface was 2 degrees. As a result, the display characteristics hardly changed as compared with the other examples. Also,
The liquid crystal alignment was also good and no misaligned domains were generated.

[Embodiment 6] The configuration of this embodiment is the same as that of Embodiment 1 except for the following requirements.

Protective insulating film 1 for protecting thin film transistors
5 (FIG. 2 (b)) was replaced with an organic insulating layer made of epoxy resin from silicon nitride, and the organic insulating layer was directly rubbed to give the organic insulating layer both functions of a protective film and a liquid crystal molecule alignment control film. It was The tilt angle is 0.5 degrees.

When the electro-optical characteristics in this example were measured, display characteristics which were almost the same as those in Example 1 were obtained. Further, as in the case of Example 4, the tilt angle is 0.5.
Although the liquid crystal orientation was small, the liquid crystal orientation was good and no misaligned domains were generated.

[Embodiment 7] The epoxy resin used for the protective film in Embodiment 6 was changed to polyimide, which similarly serves as an organic insulating layer.

When the electro-optical characteristics in this example were measured, display characteristics which were almost the same as those in Example 1 were obtained. Further, the tilt angle was slightly increased to 2.0 degrees as compared with Example 6. The liquid crystal alignment was good and no misaligned domains were generated.

[Embodiments 8 to 12] The structures of these embodiments are the same as those of the embodiment 7 except for the following requirements.

In Example 8, the liquid crystal molecule major axis directions (rubbing directions) on the upper and lower interfaces are substantially parallel to each other, and the angle formed by the applied electric field direction is 89.5 degrees (φ _LC1 = φ _LC2 = 89.5).
), The polarization transmission axis of one polarizing plate is almost parallel to the rubbing direction (φ _P1 = 89.5 °), and the other is orthogonal to it (φ _P2
= -0.5 °).

Similarly, in the ninth embodiment, φ _LC1 = φ _LC2 = φ _P1 =
It was set to 88 ° and φ _P2 = −2.0 °. Similarly, in Example 10, φ _LC1 = φ _LC2 = φ _P1 = 75 ° and φ _P2 = −25 °. Similarly, in Example 11, φ _LC1 = φ _LC2 = φ _P1 = 45
And φ _P2 = −45 °. Similarly, in Example 12, φ
_LC1 = φ _LC2 = φ _P1 = 30 ° and φ _P2 = −60 °. The measurement results of the electro-optical characteristics in these examples are collectively shown in FIG. Here, the brightness is expressed as a standardized value in which 100% is the maximum when the applied voltage is in the range of 0 V to 10 V (effective value V _rms ) and 0% is the minimum. By increasing the angle φ _LC , the curve of the threshold characteristic tended to become steeper. In order to perform halftone display with a large voltage tolerance, it is _sufficient to reduce φ _LC , but when it becomes 45 degrees or less, the brightness tends to decrease. The optimum value of the angle φ _LC depends on the number of halftone levels to be displayed, the required value for brightness, the driving voltage, and whether or not the voltage is applied to the common electrode. The designer is φ
_The threshold characteristic can be controlled in a large range by selecting _LC . Considering brightness, it is desirable to set φ _LC to 45 degrees or more. And even more preferably from 60 degrees to 8
It is good to set it between 9.5 degrees.

When the viewing angle characteristics were measured, it was found that the difference in the curves when the viewing angle was changed to the left, right and up and down was very small in all cases, and the display characteristics were hardly changed. In addition, the liquid crystal alignment was good, and no domain with poor alignment was generated.

[Examples 13 to 16] The greatest difference between the above examples and this example is that the value of the dielectric anisotropy of the liquid crystal composition layer is made negative and the rubbing direction is changed accordingly. Is. Δε is -4.8, Δn is 0.0437 (589n)
m, 20 ° C.) nematic liquid crystal composition (Merck, Z
LI-2806) was used. In any of Examples 13 to 16, the liquid crystal molecule major axis directions (rubbing directions φ _LC1 and φ _LC2 ) on the upper and lower interfaces are substantially parallel to each other (φ _LC1
= Φ _LC2 ), and the angle φ _LC1 formed with the direction of the applied electric field is in the range of more than 0 degrees and less than 45 degrees. Also, the polarization transmission axis (φ _P1 ) of one polarizing plate is set to be substantially parallel to the rubbing direction,
The other (φ _P2 ) was orthogonal to it.

That is, in the thirteenth embodiment, φ _LC1 = φ _LC2 = φ _P1
= 1.5 ° and φ _P2 = −88.5 °.

In Example 14, φ _LC1 = φ _LC2 = φ _P1 = 15
And φ _P2 = −75 °.

In Example 15, φ _LC1 = φ _LC2 = φ _P1 = 30
And φ _P2 = -60 °.

In Example 16, φ _LC1 = φ _LC2 = φ _P1 = 45
And φ _P2 = −45 °.

The gap d was set to 6.3 μm when the liquid crystal was sealed, and Δn · d was set to 0.275 μm. The conditions other than the structure of the thin film transistor and the electrode are the same as those in the third embodiment.

The measurement results of the electro-optical characteristics in these examples are collectively shown in FIG. Contrary to the case where the dielectric anisotropy was positive, the curve of the threshold characteristic tended to become steeper as the angle φ _LC was decreased. In order to perform halftone display with a large voltage margin, it is _sufficient to increase φ _LC , but when it becomes 45 degrees or more, the brightness tends to decrease. As with the case where the dielectric anisotropy is positive, the optimum value of the angle φ _LC is the number of halftone levels to be displayed, the required value for brightness, the driving voltage, and whether or not to apply a voltage to the common electrode. Replaced by. The designer can control the threshold characteristic in a large range by selecting φ _LC . Considering brightness, it is more desirable to set φ _LC to 45 degrees or less.

When the viewing angle characteristics were measured, it was found that the difference in the curves when the viewing angle was changed to the left, right, up and down was very small and the display characteristics were hardly changed in all cases. . In particular, no level reversal was observed at half-range display (8 gradations) within ± 50 degrees both vertically and horizontally. In addition, the liquid crystal alignment was good, and no domain with poor alignment was generated.

[Examples 17 to 19] In this example, Example 1 was the best in Examples 13 to 16.
4 (φ _LC1 = φ _LC2 = φ _P1 = 15 °, φ _P2 = −75 °) and the liquid crystal molecule major axis direction and the polarizing plate arrangement are the same, and the thickness d of the liquid crystal composition layer and the refractive index anisotropy Δn are The product d · Δn was changed.
The thickness d of the liquid crystal composition layer of each of Examples 17, 18 and 19 was 4.0, 4.9 and 7.2 μm, that is, d · Δn was 0.1748, 0.2141 and 0.3146 μm, respectively. Although the refractive index anisotropy Δn is constant and only the thickness d of the liquid crystal composition layer is changed here, like other liquid crystal display methods (for example, 90 ° twisted nematic method),
Even if the refractive index anisotropy Δn is changed, similar results can be obtained for the optimum value of brightness. Similar results can be obtained even when the value of the dielectric anisotropy of the liquid crystal composition layer is positive. The results are collectively shown in FIG. 12, including the results of Example 14. Figure 1
2 (a) shows the applied voltage on the horizontal axis, and FIG.
In (a), the applied voltage is fixed to 7 volts and the horizontal axis is d.
-It is expressed as Δn. As is clear from FIG. 12B, the brightness strongly depends on d · Δn, and there is an optimum value. To achieve a practical brightness of 30% or higher, d · Δn should be set between 0.21 and 0.36 μm, and to raise the brightness to 50% or higher, 0.2
It should be between 3 and 0.33 μm. Further, considering mass productivity such as control of the liquid crystal filling time and the thickness of the liquid crystal composition layer, it is desirable that the value of d be 5.0 μm or more and Δn be 0.08 or less as in the present embodiment.

[Embodiments 20 to 22] As is clear from the results of Embodiments 17 to 19, the optimum value of d · Δn is 0.21.
To 0.36 μm, preferably 0.23 to 0.33
between μm. Considering that the thickness of the liquid crystal composition layer having mass productivity is 5.0 μm or more, the refractive index anisotropy Δ
The value of n must be 0.072 or less, preferably 0.066 or less. However, there are very few kinds of liquid crystal compounds having such an extremely low Δn, and it is difficult to be sufficiently compatible with other practically required properties. Therefore, d · Δn of the liquid crystal composition layer is set to be slightly high, and an optically anisotropic medium having a retardation R _f lower than d · Δn of the liquid crystal composition layer is exceeded. Is inserted so as to compensate for the phase difference caused by the liquid crystal composition layer, and as a result, the effective phase difference of the liquid crystal composition layer and the optically anisotropic medium is 0.21 to 0, which is the optimum value. I devised a method to make it enter between 0.36 μm.

In Examples 20 to 22, the same constitution as that of Example 3 was adopted except for the following conditions. The thickness of the liquid crystal composition layer was set to 5.0, 5.2 and 5.5 μm, respectively. Since a nematic liquid crystal composition having a refractive index anisotropy Δn of 0.072 (589 nm, 20 ° C.) is used, the value of d · Δn is 0.360.
It is 0.3744, 0.396 μm. If this goes on,
The value is higher than the range of 0.21 to 0.36 μm in which the brightness and the color tone are good, so that it is colored orange. An optically anisotropic medium of a uniaxially stretched film made of polyvinyl alcohol was laminated on this liquid crystal cell so as to compensate the birefringence phase difference of the liquid crystal when driven at a low voltage (here, 0 V). That is, φ _R was set to 85 °, which is the same as φ _LC1 (= φ _LC2 ). The phase difference R _f is 0.07, 0.08, and 0.10, respectively.
μm, and the value of (d · Δn−R _f ) is 0.29, 0.30.
44, 0.296 μm, with good brightness and color tone of 0.21
To 0.36 μm.

As a result, a bright display with no coloring and a brightness of 50% or more was obtained.

Example 23 The liquid crystal composition layer of Example 20 had a negative dielectric anisotropy Δε and a value of −2.5,
The nematic liquid crystal composition (ZLI-4518, manufactured by Merck & Co., Inc.) having Δn of 0.0712 (589 nm, 20 ° C.) was used. The other structure is the same as that of the 14th embodiment except the following.
The thickness of the liquid crystal composition layer is 5.5 μm, that is, d · Δn is 0.3.
916 μm. This liquid crystal cell has a phase difference R _f of 0.11.
The optically anisotropic medium of polyvinyl alcohol uniaxially stretched film having a thickness of μm is laminated, and the value of (d · Δn−R _f ) is set to 0.
Good brightness and color tone of 2816μm from 0.21 to 0.36
It was set to be in the range of μm.

As a result, a bright display with no coloring and a brightness of 50% or more was obtained.

[Embodiment 24] The structure of the present embodiment is the same as that of the embodiment 8 except for the following requirements.

The liquid crystal composition layer had a Δn of 0.072 and a gap d of 7.0 μm. Therefore Δn · d is 0.504μ
m. φ _{LC1 is set} to 89.5 degrees and the liquid crystal molecule alignment directions on the upper and lower substrates are made to intersect with each other, and | φ _LC1 −φ _LC2 | = 9
It was 0 degree. The polarizing plates are arranged at right angles to each other (| φ _P2 −φ _P1
│ = 90 °) and φ _LC1 = φ _P1 so that the relationship with the liquid crystal molecule alignment direction is the optical rotation mode. As a result, a normally open type was obtained.

When the electro-optical characteristics in this example were measured, it was found that the brightness was the same except that the threshold voltages V ₁₀ and V ₉₀ were about doubled as compared with the other examples in the birefringence mode. The result is that the difference is 50% or more, the difference between the curves when the viewing angle is changed to the left and right and up and down is very small, and the display characteristics are hardly changed. Also, the liquid crystal alignment is good,
No misaligned domains were generated.

[Embodiments 25 and 26] The construction of this embodiment is the same as that of Embodiment 1 except for the following requirements.

The arrangement of the polarizing plates was set so that a dark state could be obtained when the electric field was not 0 but slightly applied. That is, | φ _LC1 −φ _P1 | is 5 in each of Examples 25 and 26.
And 15 degrees, and | φ _P2 −φ _P1 | = 90 degrees.

Similar to the other examples, good display characteristics were obtained in terms of both brightness and viewing angle. In addition, the liquid crystal alignment was good, and no domain with poor alignment was generated.

[Embodiments 27 and 28] The construction of this embodiment is the same as that of Embodiment 14 except for the following requirements.

The arrangement of the polarizing plates was set so that a dark state could be obtained when the electric field was not 0 but slightly applied. That is, | φ _P1 −φ _LC1 | is 5 in each of Examples 27 and 28.
7 degrees, and | φ _P2 −φ _P1 | = 90 degrees. Also,
The thickness d of the liquid crystal composition layer was 6.3 μm. Therefore, Δ
n · d is 0.275 μm.

The measurement results of the electro-optical characteristics in this example are shown in FIG. In the case of the twenty-seventh embodiment, the dark state voltage V _OFF is 3.0 V and the brightest voltage V _ON is 9.2.
It was a bolt. If driving is performed between V _OFF and V _ON , a sufficiently high contrast can be obtained. Similarly, Example 28
In this case, V _OFF was 5.0 V and V _ON was 9.0 V.

When driven between V _OFF and V _ON , good display characteristics in terms of both brightness and viewing angle were obtained as in the other examples. In addition, the liquid crystal alignment was good, and no domain with poor alignment was generated.

[Embodiment 29] The construction of the present embodiment is the same as that of the embodiment 27 except for the following requirements.

An image signal was applied to the signal electrode and an AC waveform of 3.0 V was applied to the common electrode. As a result, the voltage supplied to the signal electrode is lowered (8.3V⇒6.2V).
Was realized.

In this way, driving was performed between V _OFF and V _ON , and good display characteristics were obtained in terms of both brightness and viewing angle, as in the other examples. In addition, the liquid crystal alignment was good, and no domain with poor alignment was generated.

[Embodiment 30] The construction of this embodiment is the same as that of Embodiment 1 except for the following requirements.

The arrangement of the polarizing plates was set so that a dark state could be obtained when an electric field was applied instead of 0. That is,
| φ _LC1 −φ _P1 | was set to 45 degrees and | φ _P2 −φ _P1 | was set to 90 degrees. As a result, a bright state was applied when a low voltage was applied, and a dark state was applied when a high voltage was applied. The measurement result of the voltage dependence of the brightness at this time is shown by the solid line in FIG.

Similar to the other examples, good display characteristics were obtained in terms of both brightness and viewing angle. The contrast ratio was 35. In addition, the liquid crystal alignment was good, and no domain with poor alignment was generated.

[Example 31] A birefringent medium (uniaxially stretched polyvinyl alcohol film) for compensating for an interface residual retardation between two polarizing plates in the configuration of Example 30.
Inserted. The stretching direction φ _R of this film was set to −45 degrees, and was orthogonal to the polarizing plate transmission axis. The phase difference R _f is 1
It is 5 nm.

As shown by the dotted line in FIG. 14, Example 30 was used.
Compared with the above, light leakage at the time of applying a high voltage was suppressed, and the contrast ratio was further improved to 150.

[0106]

According to the present invention, firstly, it is possible to provide a low-cost thin film transistor type liquid crystal display device which can be mass-produced with high contrast without a transparent electrode and with a high yield in a low-cost facility. Secondly, it is possible to provide a thin film transistor type liquid crystal display device having good viewing angle characteristics and easy multi-gradation display. Thirdly, there is a large process and material margin regarding liquid crystal alignment, and therefore a high aperture ratio. It is possible to provide a brighter thin film transistor type liquid crystal display device with increased light transmittance. Fourth, in addition to the first to third effects, a thin film transistor structure having a simpler structure is provided. It is possible to provide a brighter thin film transistor type liquid crystal display device having a higher light transmittance and a higher light transmittance.

[Brief description of drawings]

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

FIG. 2 is a diagram showing an example of a thin film transistor of the invention.

FIG. 3 is a diagram showing electro-optical characteristics (viewing angle direction dependency) of the present invention (a) and a comparative example (b).

FIG. 4 is a pixel electrode (source electrode), a common electrode, a scanning electrode, a signal electrode (drain electrode) in a thin film transistor.
The figure which shows one Example of this invention which all arrange | positioned on one board | substrate.

FIG. 5 is a diagram showing an embodiment of the present invention in which a pixel electrode (source electrode) and a signal electrode (drain electrode) are arranged in the center of a pixel and one pixel is divided into two.

FIG. 6 is a diagram showing an angle formed by a molecular long axis orientation direction φ _LC , a polarizing plate polarization axis φ _P , and a phase plate fast axis φ _R with respect to an electric field direction.

FIG. 7 is a diagram showing electro-optical characteristics in various examples in which the molecular long axis orientation direction φ _LC on the interface is changed. When the dielectric anisotropy is positive.

FIG. 8 is a diagram showing a liquid crystal display drive circuit system of the present invention.

FIG. 9 is a diagram showing a liquid crystal display transmission type optical system of the present invention.

FIG. 10 is a view showing a liquid crystal display reflection type optical system of the present invention.

FIG. 11 is a diagram showing electro-optical characteristics in various examples in which the molecular long axis orientation direction φ _LC on the interface is changed. When the dielectric anisotropy is negative.

FIG. 12 is a diagram showing electro-optical characteristics in various examples in which the thickness d of the liquid crystal composition layer is changed. When the dielectric anisotropy is negative.

FIG. 13 is a diagram showing electro-optical characteristics when the arrangement of polarizing plates is set so that a dark state can be obtained when an electric field is applied rather than 0.

FIG. 14 is a diagram showing a normally open type characteristic and a characteristic when an interface residual phase difference is compensated.

[Explanation of symbols]

1 ... Pixel electrode (source electrode), 2 ... Common electrode (common electrode), 3 ... Substrate, 4 ... Alignment film, 5 ... Liquid crystal molecules in liquid crystal composition layer, 6 ... Polarizing plate, 7 ... Electric field direction, 8 ... Molecular major axis orientation direction on interface (rubbing direction), 9 ... Polarizing axis direction of polarizing plate, 10 ... Gate electrode (scanning wiring), 11 ... Additional capacitance element, 12 ... Signal electrode (drain electrode), 13 ... Gate insulating film , 14: flattening film, 15: protective insulating film, 16: amorphous silicon, 17: color filter, 18: light shielding layer, 19: polarizing plate polarization transmission axis, 20: retardation plate fast axis,
21 ... Signal electrode drive circuit, 22 ... Scan electrode drive circuit, 2
3 ... Signal electrode, 24 ... Scan electrode, 25 ... Lower substrate, 26
... upper substrate, 27 ... control circuit, 28 ... retardation plate, 29 ... backlight, 30 ... reflector, 31 ... liquid crystal composition layer.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masuyuki Ota 4026 Kujimachi, Hitachi City, Ibaraki Prefecture Hitachi Research Laboratory Ltd. Within

Claims (18)

[Claims] 1. A pair of substrates, at least one of which is transparent, said substrate
Dielectric anisotropy and refractive index anisotropy sandwiched between the plates and oriented
A liquid crystal composition layer having
Multiple pixels placed, each pixel has a pixel
Thin film transistor connected to electrodes, signal wiring electrodes and scanning wiring electrodes
Separated from the transistor element and the thin film transistor element
Change the light transmittance or reflectance of the common electrode and the pixel.
Display device having means for applying a voltage signal waveform
In, the pixel electrode and the signal wiring electrode are printed with a voltage signal waveform.
Between the pixel electrode and the common electrode by adding means.
, An electric field is applied almost parallel to the substrate surface, and
To change the light transmittance or reflectance of the pixel
And the pixel electrode extends in the pixel in a first direction,
The signal wiring electrode and the common electrode are arranged in the first direction.
Across multiple pixels to the end of the display
A liquid crystal display device characterized by growth. 2. The pixel electrodes are paired so as to sandwich the signal wiring electrode in one pixel, and the pixel and the signal wiring electrode are sandwiched by a pair of common electrodes. The liquid crystal display device according to item 1. 3. The pixel electrode, the signal wiring electrode, the common electrode, and the scanning wiring electrode are all arranged on one of the pair of substrates. The described liquid crystal display device. 4. The pixel electrode and the common electrode are in the same layer, and a capacitive element is formed between the pixel electrode and the scanning wiring with an insulator interposed therebetween. 1
Item 3. The liquid crystal display device according to item 2. 5. A color filter having at least two kinds of different colors is provided on a substrate facing the substrate having the thin film transistor element among the pair of substrates, and a boundary of the color filters is the pixel electrode and the signal. The liquid crystal display device according to claim 1, wherein the liquid crystal display device overlaps with either the wiring electrode or the common electrode. 6. A color filter comprising at least two kinds of color filters having different colors on the other substrate facing the substrate having the pixel electrode, the signal wiring electrode, the common electrode and the scanning wiring electrode. An alignment film in which an organic polymer for flattening the surface is laminated on the organic polymer, and the organic polymer is a transparent polymer, and the surface of the transparent polymer is rubbed to control the alignment of liquid crystal molecules on the interface in a predetermined direction. The liquid crystal display device according to claim 1, wherein the liquid crystal display device is used as a liquid crystal display device. 7. A pair of substrates, at least one of which is transparent, a liquid crystal composition layer sandwiched between the substrates and having oriented dielectric anisotropy and refractive index anisotropy, polarizing means, and arranged in a matrix. A plurality of pixels, a thin film transistor element provided for each pixel and connected to a pixel electrode, a signal wiring electrode and a scanning wiring electrode, a common electrode separated from and in contact with the thin film transistor element, and a light transmittance or a reflectance of the pixel. In the liquid crystal display device having a means for applying a changing voltage signal waveform, the pixel electrode and the signal wiring electrode are provided on the substrate surface between the pixel electrode and the common electrode by means for applying a voltage signal waveform. An electric field is applied substantially parallel to the thin film transistor element and the liquid crystal composition layer so as to change the light transmittance or the reflectance of the pixel according to the strength of the electric field. The liquid crystal display device, characterized in that the organic insulating layer is provided in contact. 8. The organic insulating layer covering the thin film transistor element is subjected to a rubbing treatment so that the organic insulating layer has functions of both a protective film of the thin film transistor element and a liquid crystal molecule alignment control film. The liquid crystal display device according to claim 7. 9. The liquid crystal composition layer has a positive dielectric anisotropy, and an angle | φ _LC | formed between the liquid crystal molecule alignment direction and the electric field direction on at least one substrate interface is 45 degrees or more 90.
The liquid crystal display device according to any one of claims 1 to 4, wherein the liquid crystal display device has a power of less than 100 degrees. However, -90 degrees ≤ φ _LC
≦ 90 degrees. 10. The liquid crystal composition layer has a negative dielectric anisotropy, and an angle | φ _LC | formed between the liquid crystal molecule alignment direction and the electric field direction on at least one substrate interface exceeds 0 degree. Four
The liquid crystal display device according to claim 1, wherein the liquid crystal display device is less than 5 degrees. However, -90 degrees ≤ φ
_LC ≤ 90 degrees. 11. Regarding orientation in the liquid crystal composition layer, a liquid crystal molecule orientation direction angle φ _LC1 on one substrate interface and a liquid crystal molecule orientation direction angle φ _LC2 on the other substrate interface are substantially parallel to each other (φ _LC1 ≈ φ _LC2 ) and the product d · Δn of the thickness d of the liquid crystal composition layer and the refractive index anisotropy Δn is 0.21.
The liquid crystal display device according to claim 10 or 11, wherein the thickness is in the range of µm to 0.36 µm. 12. A retardation produced by a liquid crystal composition layer is an optically anisotropic medium having a retardation R _f lower than a product d · Δn of a thickness d of the liquid crystal composition layer and a refractive index anisotropy Δn. , And the difference in absolute value | d · Δn |
12. The liquid crystal display device according to claim 11, wherein − | R _f | is set between 0.21 μm and 0.36 μm. 13. Regarding the orientation in the liquid crystal composition layer, a liquid crystal molecule orientation direction angle φ _LC1 on one substrate interface and a liquid crystal molecule orientation direction angle φ _LC2 on the other substrate interface cross each other, and Angle | φ _LC1 −φ _LC2 | is 80 degrees or more 100
And the product d · Δn of the thickness d of the liquid crystal composition layer and the refractive index anisotropy Δn is 0.40 μm to 0.60 μm.
It is between m, The claim 10 or 11 characterized by the above-mentioned.
The liquid crystal display device according to item. 14. The liquid crystal display device according to claim 11, wherein the tilt angle of the liquid crystal molecules is 4 degrees or less on any interface. 15. The liquid crystal composition layer has a positive dielectric anisotropy, and the polarizing means is a pair of polarizing plates sandwiching the liquid crystal composition layer. The angle φ _LC formed with the direction of the electric field is larger than the angle φ _P of the transmission axis (or the absorption axis) of one of the pair of polarizing plates A, and the difference | φ _LC −φ _P | is 3 The liquid crystal display device according to claim 10, wherein the liquid crystal display device has an angle of not less than 15 degrees and not more than 15 degrees. 16. The liquid crystal composition layer has a negative dielectric anisotropy, and the polarizing means is a pair of polarizing plates sandwiching the liquid crystal composition layer. The angle φ _LC formed with the electric field direction is smaller than the angle φ _P of the absorption axis or the transmission axis of the polarizing plate, and the difference | φ _P −φ _LC | is 3 degrees or more and 15 degrees or less. The liquid crystal display device according to claim 11. 17. An image signal is applied to the second electrode, and a voltage signal waveform is applied to the common electrode so that the voltage applied to the liquid crystal composition layer is further increased. Item 15. The liquid crystal display device according to item 15 or 16. 18. The polarizing means is a pair of polarizing plates sandwiching the liquid crystal composition layer, and the polarizing means is set to a bright state when a low voltage V _{L is} applied and a dark state when a high voltage V _{H is} applied, 14. The liquid crystal display device according to claim 11, wherein a transparent medium for compensating for the residual phase difference at the interface of the liquid crystal layer when _{VH is} applied is inserted between the pair of polarizing plates.