JP2586195B2 - Liquid crystal display - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a color liquid crystal display suitable for color image display and color graphic display.

Conventionally, it has been impossible to realize a multi-color display of a liquid crystal display in the following points.

One is that the number of dots or the number of lines of the liquid crystal panel itself could not be increased. The dynamic drive that is usually performed has a limit of 1/16 duty, and it is full to realize at most 16 lines. On the other hand, color display is meaningless unless it has at least 100 lines due to its nature, and for this purpose, liquid crystal drive at 1/100 duty must be realized.

In the two, there is no liquid crystal multicolor display means. There is a method of coloring by mixing a dye such as a guest host liquid crystal, but it is very difficult to generate multiple colors in one substrate. There is also a method of superimposing panels of several colors. However, this method is expensive in terms of structure, and it is impossible to produce colorful colors in multiple layers. Light bleeding occurs when the shutter is opened and light is transmitted. For example, when only the shutter corresponding to the red filter is open, blue on both sides of it,
There is a problem that light goes around the edge of the green filter and light leaks from the shutter of the red filter, which causes a problem of lowering color reproducibility.

For the reasons described above, it is difficult to realize a multi-color display panel using liquid crystal.

Accordingly, an object of the present invention is to provide a means for easily realizing a multicolor color display panel by improving the above-mentioned disadvantages, and a main object is to prevent light leakage from an adjacent shutter. Aim.

In a liquid crystal display device of the present invention, a liquid crystal substance is sealed between a pair of substrates, pixel electrodes arranged in a matrix are arranged on one of the substrates, and the pixel electrodes are arranged on the other substrate. A liquid crystal display device having a color filter arranged corresponding to each of the above, wherein the area of the color filter corresponding to the pixel electrode is larger than the area per pixel of the pixel electrode, and the color filter Are arranged so as to include the pixel electrode.

FIG. 1 shows a basic configuration example of the present invention. First, a color filter is formed on the glass substrate 1. For example, a red filter 8, a green filter 9, and a blue filter 10 are formed in a mosaic or stripe shape.

A protective film 6 of SiO ₂ or the like is formed on the upper portion, and a transparent electrode 5 serving as a liquid crystal drive electrode is formed on the upper portion. The opposite counter electrode forms an element layer 3 on which a switching element for an active matrix and a non-linear element are arranged on a glass substrate 2 (the drawing is simplified). The transparent drive electrode layer 4 corresponding to each dot of the filter is formed.

Next, the two glass substrates 1 and 2 face each other, the periphery is sealed, and the liquid crystal 7 is sealed. When this display panel is used in a transmission type, light is introduced from below through a polarizing plate below the glass substrate 1 and a black negative guest-host liquid crystal is used as a liquid crystal body. The drive electrodes 4 corresponding to the filter units 8, 9, and 10 of each color are opened and closed to transmit light having a wavelength corresponding to a predetermined color.

The gap between the drive electrodes 4 is always kept black by using a negative-type guest host so as not to transmit light. As a result, the portion of the liquid crystal that exhibits black (the liquid crystal becomes OF
No light is transmitted through the area where F is applied, and light of the wavelength corresponding to the optical filter corresponding to the area where the liquid crystal is transparent (the area where the liquid crystal is ON) is transmitted. 7 colors can be displayed. Also, if the driving of the liquid crystal is not completely turned on and off, but a gradation display function is added by controlling the halftone, that is, the state where the liquid crystal becomes translucent,
All colors can be realized with various luminances, and a color image display can be realized.

The above is one example of the present invention. Next, the structure of each part will be described to show another configuration example.

FIG. 2 shows a configuration example of an optical color filter. A water-soluble organic resin layer such as polyvinyl alcohol or gelatin is formed on a transparent glass substrate 20, and black, red, blue, and green dyes are printed thereon in a pattern such that a predetermined filter arrangement is formed. Dye the resin layer.

As a result, the red part 22 and the blue part correspond to the shutter part of the liquid crystal.
23, at the same time that each color filter of the green portion 24 is formed, the boundaries of each color filter are dyed with a black color system in the sense of preventing color bleeding at the filter boundaries for transmitted light,
A black frame 21 is formed. The black frame 21 is indispensable to prevent light from passing through the gap of the shutter when the liquid crystal is a positive type.

In the case of a negative type liquid crystal, the presence of a black frame also serves to reduce light bleeding. In the case of a negative type liquid crystal, when the degree of dyeing in the horizontal direction of the dye is strong, the black frame 21 can be mixed with a substance that prevents dyeing, instead of a black dye. Further, a transparent protective film 25 is provided on the upper portion, a conductive transparent film 26 serving as a liquid crystal drive electrode is formed thereon, and photo-etching is performed in a required pattern to form a lower electrode.

In addition, the dye used for the filter may be reduced in color or damaged when the transparent conductive film is formed. At this time the third
As shown in the figure, a protective film 34 is provided on the filter film 31 on the glass substrate 30.

Alternatively, a transparent conductive film 33 may be separately formed on a thin glass or plastic film 32 and bonded to the glass substrate 30.

FIG. 4 is a structural example of an active matrix formed on an upper substrate used in the present invention. The features of this method are that a drive duty of 100 or more can be easily achieved and that gradation display can be easily achieved. In this example, a transparent glass substrate with a relatively high melting point such as
The transistor is characterized in that it can be relatively easily formed on a transparent substrate as compared with an active matrix on a normal Si single crystal wafer.

FIG. 4 (a) is a plan view showing a cell 41 of one pixel (one dot) of the matrix. Gate line (Y selection line)
44 is a data line (X line) for the gate of the transistor 49
43 is connected to the source of the transistor 49 via the contact hole 47, and the liquid crystal drive electrode 42 is connected to the drain of the transistor 47 via the contact hole 46. The ground line 45 is a capacitor for holding electric charge between the liquid crystal drive electrode 42 and the ground line 45.
Make up 48.

FIG. 4 (b) shows an equivalent circuit of the cell 41. When the transistor 49 is turned on, the voltage input via the data line 43 is changed to the charge holding capacitance 48 or the capacitance between the liquid crystal drive electrode 42 and the counter electrode. Is retained as an electric charge. Therefore, since the leakage current of the transistor and the liquid crystal is small, the charge is held for a considerably long time.
(The time required to write the charge)
That is all. Also, if the area of the liquid crystal drive electrode is large,
48 becomes unnecessary.

FIG. 4C is a cross-sectional view taken along a line AB in FIG. A first-layer Si thin film serving as a channel is formed on the transparent substrate 40 by a low-pressure CVD method, a plasma CVD method, or the like. After patterning, an oxide film obtained by oxidizing the Si layer is formed on the surface, and then a second-layer Si film is formed. A layer is formed, gate lines and GND lines are patterned, and an oxide film is further etched using the pattern as a mask to form a gate insulating film 51 and a gate electrode 50. Thereafter, P ions are implanted into the whole using the gate electrode 50 as a mask to form an N-type layer, thereby forming a lease 53, a channel 55, and a drain 54 of the transistor. After that, an oxide film 52 is formed,
After making a contact hole, attach a transparent conductive film,
By patterning, data lines 43 and drive electrodes 42 are formed.

As a result, the liquid crystal drive electrode functions as an optical shutter, and the color of the filter corresponding to the position of the electrode is transmitted or blocked. Also, the light transmittance of the liquid crystal can be continuously changed according to the level of the voltage input to the data line.
So-called gradation display is possible, and since the three primary colors can be weighted and added and mixed, there is a great advantage that all colors can be reproduced. In addition, since the drive duty can be extremely high as much as possible even in the dot sequential method, a complete color image with 500 × 500 dots can be realized.

The means for improving the drive duty of the liquid crystal in the present invention is to drive the liquid crystal through a non-linear element. 5 and 6 show examples of the configuration of the nonlinear element.

FIG. 5 is a configuration example of a metal-insulator-metal (MIM) element. The matrix cell 61 is configured to drive the drive electrode 57 from the X drive line 58 via the MIM element 62. (B)
Is a cross section of (a), for example, a Ta film is sputtered and then patterned to form a Ta film 58, and the surface thereof is anodized by 300 to 500 °. Thereafter, a Ta film serving as an upper electrode is sputtered and then patterned to form a Ta layer 60, and further a transparent drive electrode 57 is formed.

FIG. 6 shows an example in which two diodes are faced to each other and connected in series, and an N (P) type region 67, P
It is connected to the liquid crystal drive electrode 65 via the (N) type area 68 and the N (P) type area 69. (B) is a cross-sectional view of (A), showing a transparent substrate.
After forming an island of Si layer on 63, N-type (P) regions 67 and 69 and P-type (N) region 68 are formed by ion implantation, a transparent conductive film is further formed, and X drive line 66 and liquid crystal drive are formed. The electrode 65 is formed.

The non-linear element thus formed has a VI characteristic as shown in FIG. 7, and the current suddenly increases from a certain voltage.

When a liquid crystal cell is driven via this nonlinear element,
It becomes an equivalent circuit as shown in the figure. Non-linear element 80 is non-linear resistance
The liquid crystal 81 can be expressed by the equivalent resistance RL and the capacitance CL by the RM and the capacitance CM. When turning on the liquid crystal, if a voltage higher than VTH is applied, RM will have low resistance and VM will be almost equal to VD,
The applied voltage is mostly applied to the liquid crystal. Then the voltage is VT
When the voltage falls below H, RM becomes very high, and VM discharges with the time constant of CL and RL while the ON voltage applied by the capacitor CL is maintained. In addition, when the liquid crystal is not lit, only a potential lower than VTH is applied, so that VM is almost zero potential.

Therefore, as in the active matrix shown in FIG. 4, the voltage to be turned on is held as VM in the capacitor CL, so that the duty can be increased. In this case as well, FIG.
7. The liquid crystal drive electrode of FIG. 65 functions as a shutter for light corresponding to the color filter.

The feature of this nonlinear element is that its structure is simple,
The driving method may be the same as the conventional simple 1/8 or 1/16 dynamic driving method. Although this method is suitable for graphic display, gradation display is also possible. One is a method in which the voltage level applied from the X line is set to be continuous similarly to the active matrix, and the other is a method in which the driving is performed in a time-divided manner.

The switching element and the non-linear element used in the present invention are formed on a glass substrate and serve as an upper liquid crystal driving electrode, and the other glass substrate on which the filter is formed constitutes a lower liquid crystal driving electrode. This is because forming an element directly on a filter as shown in FIG. 2 not only deteriorates the characteristics of the filter, but also reduces the yield. In order to avoid this, as shown in FIG. 3, an element on the thin glass 32 is formed and bonded to a lower filter to form a lower electrode, and a switching element or a non-linear element is first mounted on a glass substrate. There is a method of forming and then forming a filter layer.

FIG. 9 is a configuration example of a display panel of the present invention. (I)
Is a cross-sectional view, in which a switching element or a non-linear element is formed on a glass substrate 90 as an upper electrode, and a driving electrode 97 is formed. A color filter is provided on the glass substrate 91 as the lower electrode.
The liquid crystal driving electrodes 96 are formed through the protective films 95 and 92, 93 and 94.

Thereafter, the liquid crystal layer 98 is sandwiched between the two glass substrates 90 and 91, and a polarizing plate 99 is further mounted above or below, and light is irradiated from above or below. At this time, the problem is a gap between filters, or a gap between drive electrodes, and when light enters this portion, reproducibility of a beautiful color is poor. For example, when light is transmitted from below, if the liquid crystal shutter is closed, the light that has passed through the gap of the filter leaks from the gap of the drive electrode. One means of preventing this is to use a negative type liquid crystal (a type that does not transmit light when no voltage is applied). Therefore, in this method, light is always blocked in the gap between the drive electrodes 97.

Another means is to provide a black frame between the filters as shown in FIG. When both are used in parallel, the effect is further doubled. Light bleed occurs when the shutter opens and light passes through. This is a red filter
When only the shutter above the shutter 92 is open, the light from the blue filter 94 and the green filter 93 on both sides of the shutter 92 wraps around and leaks from the shutter above the red filter, which also reduces color reproducibility.

In order to prevent this, the color filter is preferably formed larger than the effective shutter portion of the liquid crystal. For example, for a mosaic filter as shown in FIG. 9 (b), for example, the drive electrodes 97 of the active matrix are made small. In the example of the non-linear element as shown in (c), the intersection of the lower liquid crystal drive electrode 96 and the upper liquid crystal drive electrode 97 becomes the effective shutter portion. The size of this effective shutter portion is smaller than that of the stripe type color filter. Keep it. This is the same for a mosaic filter.

As a display method of such a color liquid crystal display, it is required that the ratio of the transmittance of the liquid crystal when the shutter is open and the transmittance of the liquid crystal when the shutter is closed is large. In the case of a normal TN display, two polarizing plates are arranged above and below the display panel, and the polarization planes are adjusted so as to be a positive type. In this case, the transmittance ratio of the shutter is the ratio between the polarization directions of the two polarizing plates when they are parallel to each other and is determined by the polarizing plates.

Actually, this ratio is at most about 10 in this polarizing plate, and the polarizing plate requires some contrivance. On the other hand, when a guest-host liquid crystal is used, only one polarizing plate is required, so that the brightness is first doubled as compared with the TN liquid crystal, and the transmittance ratio is determined by the liquid crystal material, so that it can be large. For example, a guest-host liquid crystal containing a black dye usually blocks light well, and when a voltage is applied, it is quite transparent and the transmittance ratio exceeds 50. Further, as for the guest-host liquid crystal, the positive type is more excellent in stability and reliability than the negative type, the driving voltage is low, and the transmittance ratio required for the present invention is also better in the positive type.

On the other hand, the positive type liquid crystal is better for eliminating the wraparound, bleeding, and leakage of light as described above, and the positive type liquid crystal of the guest host is most suitable for the color display of the present invention. In particular, a panel with a black pigment is the most excellent in reproducibility of the three primary colors.

FIG. 10 shows an example of an arrangement of filters of a color liquid crystal display of the present invention and a driving method thereof. The three primary color filters 106 are arranged in stripes in the Y direction, and the drive electrodes on the filter side are linear or solid in the same direction as the filters. Further, the upper electrode 105 exists in the X-direction for each pixel (the drawing is simplified and connected).

S shift register 101 from S ₁ by a clock input phi _5
n is output, and the transistor 104 is sequentially turned on to output the video signal VS.
Which is a sequential feed sequential method points X ₁ to X _n. The shift register 102 slide into sequentially selected by the clock phi ₄ the Y ₁ to Y _m. Three color signals VSR, VSB, VSG, the clock phi ₁ to [phi]
₃ is switched for each line of Y, and φ ₁ , φ ₂ ,
phi ₃ in the same pulse width as the phi _4, the pulse period is three times that of phi _4.

The feature of this method is that the color filter is a stripe in the Y direction and the switching frequency of the color signal may be low, so that the number of lines in the Y direction can be increased, and the display resolution is good.
A good color image can be reproduced.

FIG. 11 shows a color filter 116 striped in the Y direction.
Are arranged, which is useful for increasing the number of lines in the horizontal direction, and the dots have a size close to a square, so that the image has a natural feeling. Shift register 112 slide into sequentially selecting driving electrode 115 by signals Y ₁ to Y _m. Drive electrode 1
Shift register while any one of 15 is selected
Reference numeral 111 sequentially selects the filter groups R, G, and B as one unit. Further, R, G, B selection clocks φ ₁ , φ ₂ , φ ₃ are signals obtained by further dividing clock φ ₄ into three phases, and each of the color signals VSR, VSG, VSB is selected one by one in synchronization with this selection clock. And guided to the X drive line.

In this method, the video signal line is divided into three for each color.
Since connected in signal parallel to the sample hold switch 113, the frequency of the transfer clock phi ₅ of the shift register 111 may be a frequency of 1/3 for the same number of dots, the shift register can be reduced the power consumption of the shift register There is a merit that it can be used within a range where the operation speed can afford.

FIG. 12 shows an example in which filters are arranged in a mosaic pattern.
A white filter 124 is further added to the red filter 121, the green filter 122, and the blue filter 123 to make one block, which is repeated in a matrix.

This white part is when the light transmittance to the filter is low,
A state where light is transmitted through all three filters, that is, white color is not clearly produced. In order to solve this, a transparent portion is formed as a white filter, and the luminance signal VSW of the video signal is formed.
When controlled by, the brightness is improved and the white reproducibility is good,
The overall brightness is improved. The driving method in this case is selected by a shift register in the X direction in units of filter blocks, and operates in the same manner as in FIG. The Y-direction is selected by the shift register 126, clock phi half in synchronism with the _third frequency phi ₁ and phi ₂ by VSR and VSB, VSG and VSW are connected alternately.

With the above configuration, the following effects can be obtained.

That is, the area of the color filter corresponding to the pixel electrode is larger than the area per pixel of the pixel electrode, and the color filter is arranged so as to include the pixel electrode. Is transmitted, and light leakage to the adjacent color filters is eliminated. Therefore, color bleeding, color mixing, and the like from adjacent color filters are eliminated.

Further, since the light controlled by the pixel electrode passes only through the corresponding color filter, the color purity of the light passing through the color filter is increased, and a display with high color reproducibility can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration example of the present invention. 1,2 ... Substrate 3 ... Element part 4,5 ... Liquid crystal drive electrode 6 ... Protective film 7 ... Liquid crystal 8,9,10 ... Color filter FIGS. 2 and 3 are used in the present invention. FIG. 4 is a diagram illustrating a configuration example of a color filter. 20, 30 ... substrate 22, 23, 24, 31 ... filter part 21 ... black frame 25, 34 ... protective film 26, 33 ... transparent conductive film 32 ... thin substrate Figure 4 (a) FIGS. 2B and 2C are diagrams illustrating a configuration example of an active matrix substrate used in the present invention. 49... Si thin film transistor FIGS. 5 (a), (b), FIGS. 6 (a), and (b) show examples of the nonlinear element used in the present invention. 62: MIM element 67, 68, 69 ... Si thin film diode FIG. 7 is a VI characteristic diagram of the nonlinear element. FIG. 8 is a drive equivalent circuit diagram. 9 (a), (b) and (c) are views showing a configuration example of the color display device of the present invention. 90, 91 substrate 92, 93, 94 filter 95 protective film 96, 97 liquid crystal drive electrode 98 liquid crystal 99 polarizing plate FIGS. 10, 11, and 12 show the present invention. FIG. 3 is a diagram showing an arrangement of color filters and a driving example of the color display device. 101, 102, 111, 112, 126 ... shift register VSR, VSB, VSG ... video color signal VSW ... luminance signal

Claims (1)

(57) [Claims] A liquid crystal material is sealed between a pair of substrates, pixel electrodes arranged in a matrix on one of the substrates, and each of the pixel electrodes is arranged on the other substrate. In a liquid crystal display device having a color filter arranged correspondingly, the area of the color filter corresponding to the pixel electrode is larger than the area of one pixel of the pixel electrode, and the color filter is the pixel. A liquid crystal display device which is arranged so as to include an electrode.