JPH027074B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a high-performance liquid crystal display device used in information equipment or video equipment.

Conventional configuration and its problems Generally, in an X-Y matrix type liquid crystal display device,
As shown in Figure 1, the X electrode and the Y electrode consist of a group of parallel band-shaped electrodes, which are arranged to be orthogonal to each other across the liquid crystal layer, and the intersection of the electrodes corresponds to one pixel, and the area within one pixel is In this case, if disturbances in the surrounding electric field are ignored, the structure is such that a uniform electric field is applied. However, in matrix type display panels with a large number of pixels to display a large amount of information, each pixel must have a clear threshold characteristic in its electro-optical characteristics in order to prevent crosstalk and achieve clear display. Therefore, expectations are high for improving the properties of liquid crystal materials.

On the other hand, in so-called simple matrix display devices in which a liquid crystal is sandwiched between X-Y electrodes, it is difficult to display large-capacity images such as images due to the insufficient threshold characteristics mentioned above. The so-called active matrix, which adds TFT (hereinafter abbreviated as TFT), MOS-FET, non-linear resistance elements (varistor, diode, MIM, etc.), etc., is actively being developed, and active matrix LCD TVs that have already incorporated TFT and MOS-FET are actively being developed. has reached the point where it is commercially available.

Since the display purpose of such active matrix LCD TVs is video, it is necessary to faithfully reproduce halftones, which is completely different from achieving a large-capacity binary display with a simple matrix. On the contrary, liquid crystals are required to have brightness-voltage characteristics that draw a gentle curve.

Twisted nematic liquid crystals (hereinafter referred to as TN liquid crystals), which are currently widely used, exhibit mediocre characteristics in all applications, such as binary display using a simple matrix with a large number of scanning lines, and gradation reproducibility. All of the active matrix type video displays, which were excellent in quality, were unsatisfactory.

OBJECTS OF THE INVENTION It is an object of the present invention to realize a binary display using a large capacity simple matrix with excellent contrast or an active matrix type video display with excellent gradation reproducibility.

Structure of the Invention In the liquid crystal display device of the present invention, a pair of electrodes sandwiching a liquid crystal layer are formed in a pattern by providing dotted or linear grooves on at least one of them for each pixel. , is characterized in that it forcibly applies a non-uniform electric field to the liquid crystal layer and achieves electro-optical characteristics that could not be achieved with conventional devices configured to apply a uniform electric field.

DESCRIPTION OF EMBODIMENTS The structure of a liquid crystal display device of the present invention will be described below with reference to the drawings.

In a TN liquid crystal cell, the liquid crystal molecules are arranged almost parallel to the electrode surface with a slight tilt angle, and the molecules are oriented so that they are twisted by 90 degrees between the upper and lower electrodes. A pair of polarizing plates are provided so that their polarization axes are parallel to each other (negative type) or perpendicular to each other (positive type). The direction of the polarization axis of the polarizing plate is either coincident with or perpendicular to the direction of the nearest liquid crystal molecules.

The relationship between the brightness B and the applied voltage V of an actual negative-type TN cell is shown by curve 1 in FIG. This is a characteristic when the electrode configuration is as shown in FIG. 1, that is, when substantially equal voltages are applied to the liquid crystal portion corresponding to one pixel. In the brightness-voltage characteristics shown in Figure 2, if the voltage at which the brightness changes by 10% is called the threshold voltage V _T and the voltage at which the brightness changes by 90% is called V _S , then the threshold characteristic γ is γ = V _S /V _T , and in order to realize a large capacity display with a simple matrix, the γ value is required to be as close to 1 as possible.On the other hand, when trying to faithfully reproduce gradations with an active matrix, A liquid crystal that exhibits a γ value as large as possible within the voltage range is required.

That is, the characteristics of curve 2 are desirable for the former purpose, and the characteristics of curve 3 are desirable for the latter purpose. To this end, the main method used in the past was to change the composition of the liquid crystal material according to the above objectives, but changing the γ value inevitably changes the response speed, operating temperature range, threshold voltage, etc. Finding a suitable liquid crystal material composition is an extremely difficult task.
In view of the overall characteristics, the reality is that a considerable compromise is forced on the γ value.

The present invention is based on the discovery that the intensity distribution of the electric field applied to the pixel is also deeply involved in changing the γ value of the cell.

In other words, as shown in Fig. 3, electrodes are formed in a pattern by providing dotted or linear grooves for each pixel, and, unlike the conventional method, a non-uniform electric field is forcibly applied to each pixel. It has been found that when configured to do so, the γ value can be greatly changed, although the threshold voltage V _T is generally fluctuated.

In addition to the pattern shown in FIG. 3, various patterns of electrodes can be considered, as shown in FIG. 4, if each pixel is drawn as a unit. In any case, in a normal matrix display panel, the pixel size is generally square or rectangular with a size of about 0.2 to 0.5 mm, and the gap between the electrodes sandwiching the liquid crystal layer is about 5 μm to 10 μm.

In other words, the width of a normal pixel is several tens of times larger than its thickness, so if the part without electrodes (indicated by a black line in the figure) is too thick or sparse compared to the size of the pixel, , undesirable shading occurs inside the pixel that can be discerned with the naked eye. In such a case, it is necessary to subdivide the pattern within one pixel so that one pixel is composed of four patterns as shown in FIG. 3, for example. This makes it difficult to see the shading within one pixel. Note that even if only one of the opposing electrodes is patterned, a non-uniform electric field can be generated in the liquid crystal layer even if both electrodes are formed in the same or different patterns and are faced, so the electrodes should be selected according to the purpose. should be adopted. usually
In TN liquid crystals, the electrodes are transparent electrodes formed by depositing or sputtering tin-containing indium oxide with a thickness of around 1000 Å on a glass or plastic substrate. Can be formed. In any case, if you cross the X and Y strip electrodes, the electrodes will break, so
It is necessary to create a pattern within a range that does not cross.

In an active matrix panel in which thin film transistors, etc. are installed in pixel units, the pixel electrode is on the substrate side that constitutes the TFT array, and the counter electrode side is a uniform common electrode over the entire surface, and the X-Y matrix is , is configured on the substrate side where the TFT is provided. In such a case, each pixel electrode on the TFT substrate side should be configured in a pattern as shown in Figure 4, or should be provided on the common electrode side corresponding to the pixels.
Both may be provided to utilize the combined effect of the upper and lower electrode patterns.

With conventional uniform electrodes, the tilt angle and twist angle of liquid crystal molecules can be considered to be constant in the cross section of the liquid crystal layer parallel to the electrode surface, but in the cell of the present invention, which is driven by a nonuniform electric field, As you can see, the tilt angle and twist angle are not constant even in the cross section of each liquid crystal layer. Factors that affect the γ value include cell configuration parameters such as electrode pattern, electrode groove width, length and groove pitch, and gap between electrodes, as well as the elastic constant and dielectric constant of the liquid crystal,
It is determined by liquid crystal material parameters such as refractive index anisotropy, and we will find a analytical solution to how to set the above cell configuration parameters to make the γ value small or large using a given liquid crystal material. has not yet been reached.

Effects of the Invention In the present invention, using a predetermined liquid crystal material,
It is possible to manipulate the γ value simply by patterning the electrodes, and the cell is not only useful for simple matrix high-duty, large-capacity display, but also capable of achieving gradation reproduction, which is essential for video display. This technology can greatly contribute to improving the performance of information and video equipment that uses liquid crystals.

[Brief explanation of drawings]

Fig. 1 is a configuration diagram showing the X and Y electrode configuration of a conventional X-Y matrix type liquid crystal display panel, Fig. 2 is a characteristic diagram showing the brightness-voltage characteristics of a negative type liquid crystal display cell, and Fig. 3 is a diagram showing the present invention. FIG. 4 is a diagram showing an example of an electrode pattern for applying a nonuniform electric field to a pixel, and FIG. 4 is a diagram showing another example of an electrode pattern that can be used in the present invention. 1...Characteristic curve obtained with the conventional electrode configuration shown in FIG. 1, 2, 3... Characteristic curve obtained with the non-uniform electric field type liquid crystal cell of the present invention.

Claims (1)

[Claims] 1. In an X-Y matrix type liquid crystal display device in which a liquid crystal layer is sandwiched between a pair of substrates having a group of parallel band-shaped electrodes that are orthogonal to each other, For each pixel, at least one of the X or Y electrodes is formed in a pattern by providing dotted or linear grooves to apply a non-uniform electric field to the liquid crystal layer. Characteristic liquid crystal display device. 2. In an active matrix type liquid crystal display device in which a liquid crystal layer is sandwiched between an active matrix array and an electrode facing the active matrix array, a pixel electrode provided on the side of the active matrix array or one of the electrodes facing the active matrix array. A liquid crystal display device characterized in that one of the two is formed in a pattern by providing dotted or linear grooves in units of one pixel, and a non-uniform electric field is applied to the liquid crystal layer. .