JPH0317617A - Ferroelectric liquid crystal color display device - Google Patents

Abstract

PURPOSE:To obtain the brightness uniform over the entire part of a display screen by so determining the intensity, per unit time, of the incident light on a cell for display that the intensity on the side of the scanning electrode to be selected last is larger than on the side of the scanning electrode to be selected first and maintaining the ratio of the change thereof nearly constant. CONSTITUTION:The light emitted from a light source 50 is first made incident on the cell 30 for the light source. Only the parts where red color filters of the cell for the light source exist are turned on at the time of displaying of red. The display of red is executed if the display is made by successively selecting the 1st scanning electrode, the 2nd scanning electrode,... the 400th scanning electrode of the cell for display in this state. The displays of green and blue are then executed by the similar method. The display of all of the red, green and blue is executed at a high speed by the same picture elements in this way, by which the display is viewed as white to the human eyes. The light source 40 is provided to the side of the scanning electrode to be selected last of the cell for display in such a manner, by which the differences in the lengths of the on state by the scanning electrodes in the display of the respective colors is offset with the intensity of the incident light on the cell for display. The brightness over the entire surface of the cell for display is thus uniformized.

Description

[Detailed Description of the Invention] [Prior Art] Ferroelectric liquid crystals, which have been the subject of worldwide research in recent years, have faster response speeds and wider viewing angles than TN-type liquid crystals, which have been conventionally used in watches, calculators, etc. It has the advantage of being wide. However, while TN liquid crystal displays using the optical rotation of the liquid crystal, ferroelectric liquid crystal displays using the anisotropy of the refractive index of the liquid crystal. Uniformity in the thickness of the liquid crystal layer is particularly required compared to TN type liquid crystal.

By the way, when colorizing a liquid crystal display device, the most common method is to install a color filter inside the cell.

This is because if the filter is placed outside the cell, the position of the liquid crystal and the filter will be far apart, and depending on the angle at which the cell is viewed, a different color will be seen than what is actually intended to be displayed.

Normal color filters are R (red) and G (green).
, B (blue). For example, in order to display white, light passing through R, light passing through G, and B are used.
All light passing through must have the same intensity.

If we try to equalize the intensity of the three colors of light, R, G,
B. The thickness of each color filter is not necessarily the same. For this reason, when a color filter is formed in a cell, the thickness of the liquid crystal layer in each of R, G, and B pixels is not necessarily equal. The optical rotation of the liquid crystal is j
In the case of a TN-type liquid crystal, which is used for display purposes, slight differences in the thickness of the liquid crystal layer do not cause color unevenness, so this is fine, but the display is performed using the refractive index anisotropy of the liquid crystal. In the case of ferroelectric liquid crystals, color unevenness occurs due to variations in the thickness of the liquid crystal layer. It is not impossible to calculate color unevenness and use a filter to display white, but
This is extremely difficult when considering cost, yield, precision, etc. in the manufacturing process.

Furthermore, conventional LCD color display devices have three pixels per pixel.
I was only able to display one minute. In other words, the colors that each pixel displays are determined: red, green, and blue.
For example, when displaying white, display all three pixels,
Taking advantage of the fact that the human eye cannot recognize each of the three pixels, white is displayed as the sum of the three colors. Therefore, since the display for one pixel is performed using three pixels of the electrode patterned in a dot shape, the result is the same as when one pixel is large, so that a precise display cannot be achieved.

In order to solve these problems, the applicant filed a patent application in
No. 3-335629 proposed that a color display device using ferroelectric liquid crystal could be manufactured by using a display cell and a light source cell.

The color display device using ferroelectric liquid crystal proposed by the present applicant has a display cell in which a ferroelectric liquid crystal is interposed between a pair of substrates having transparent electrodes, and a color display device that uses red light emitted from a light source. , green, and blue, and the structure of this display cell is as follows:
Similar to black and white display devices using normal ferroelectric liquid crystals,
The structure has a ferroelectric liquid crystal interposed between a pair of transparent substrates with transparent electrodes, and the structure of the light source cell has a color filter, and a liquid crystal is interposed between a pair of transparent substrates with transparent electrodes. It is a structure that interposes.

The purpose of the light source cell used here is to change the color of the light from the light source to the color of the color filter being used after passing through the light source cell, so the transparent electrode of the light source cell is shaped like a dot. There is no problem even if the electrodes are shaped like a stripe, but it is easier to make the electrodes shaped like stripes on one substrate and spread them across the front surface of the substrate. Even the structure that was under threat was sufficient. The same was true for color filters.

The display method of this color display device performs display by synchronizing the display cell and the light source cell. For example, first, red is displayed in the display cell, then green is displayed, and then blue is displayed. At this time, when performing this on the red display cell,
Synchronize the light source cells to make the light from the light source red. Similarly, in the case of green and blue, the light source cells are synchronized to make the light from the light source the color of each color filter. A simple tying chart in this case is shown in FIG. In FIG. 4, L1 LGr ts are the red cells of the light source cells. This is a timing chart for the signals applied to the electrodes of the portion where the green and blue color filters are present, and t is the timing chart for the display cell. However, the horizontal axis is time. As shown in the figure, the light source cell and the display cell are synchronized, and at A-B in the figure, the light from the part of the light source cell where the red filter exists is transmitted, and at the same time the red of the display cell is transmitted. A display signal is applied to the electrodes of the part to be displayed to display red. Next, at B-C, light from the portion of the light source cell where the filter is present is transmitted, and at the same time, a display signal is applied to the electrode of the portion of the display cell where green is desired to be displayed, thereby displaying green. Then, in C to D, light from the portion of the light source cell where the blue filter is present is transmitted, and at the same time, a display signal is applied to the electrode of the portion of the display cell where blue is to be displayed, thereby displaying blue. In this way, the display of one screen as a color display device ends at steps A to D.

However, when driving the display cells in a time division manner in this color display device, the light source cells are red, green,
By switching the blue light with a temporal shift, the light from the light source is changed to red, green, and blue, so that when the light incident on the display cell is red, the first scan of the display cell Select the electrode, second electrode...n-th scanning electrode in sequence, and then select the l-th, second...n-th scanning electrode in sequence when the incident light to the display cell is green. Select. Therefore, if a certain pixel on the first scanning electrode is in the on state (light passing state) when red incident light is incident, the lth scanning The on state of the pixel on the electrode is maintained.

Now suppose that the selection time of one scanning electrode is a, then n - 400
Then, the on state of the pixel on the first scanning electrode is 400a
Only lasts. However, after the 400th scan electrode, that is, the scan electrode selected last, is turned on, the scan electrode selected next is the first scan electrode, but at this time, the light after passing through the light source cell has changed from red to green. Therefore, for example, for red display, the on time of the pixel on the first scan electrode is n times longer than the on time of the pixel on the nth scan electrode, so for the viewer, the on time of the pixel on the first scan electrode is The display seemed much brighter than the display on the n-th scanning electrode side, and uniform brightness could not be obtained over the entire display screen.

``Structure of the Invention J'' In order to solve the above problems, the present invention provides a display cell in which a ferroelectric liquid crystal is interposed between a light source, a substrate having a plurality of scanning electrodes, and a substrate having a plurality of control electrodes. A light source cell having a liquid crystal interposed between a pair of substrates having transparent electrodes between a light source and a display cell, and a color filter on the outside of the substrate; and a light source cell having a color filter on the outside of the substrate: polarized light for identifying different states of liquid products. In a color display device using a ferroelectric liquid crystal having means and; when the display cell is time-divisionally driven, the scan electrode selected last with respect to the intensity per unit time of the light incident on the display cell. The side is larger than the side of the first scanning electrode selected, and the rate of change is approximately constant, or the rate of change is at least one type.

In the present invention, a method of increasing the intensity per unit time of light incident on the display cell on the scanning electrode side that is selected last is to use a light diffusing plate, which is normally used to make the light uniform. , the intensity of the emitted light is given a gradient depending on the location, and the location where the intensity is high is placed on the scanning electrode side that is selected last. Alternatively, there are many methods such as arranging the light source on the scanning electrode side that is selected last, and any of these methods can be used in the present invention.

According to the present invention, when driving a display cell in a time-division manner, the intensity per unit time of light incident on the last selected scan electrode side of the display cell is made higher than that on the first selected scan electrode side. large, and the rate of change in intensity per unit time of the light incident on the display cell from the last selected scan electrode side to the first selected scan electrode side is approximately constant or at least one type. Therefore, the difference in the length of the ON time of the scanning electrode can be canceled out by the intensity of the incident light per unit time, so that the brightness of the display screen appears to be extremely uniform to the viewer.

Hereinafter, the present invention will be explained in Examples.

Example IJ FIG. 1 shows an example of the ferroelectric liquid crystal color display device of the present invention. Further, FIG. 2 shows a schematic cross-section of a display cell which is a part of the structure of the present invention, and FIG. 3 shows a schematic cross-section of a light source cell.

The display cell (20) uses ITO as a transparent electrode (22).
A substrate (25) formed on soda glass (2L) using a sputtering method, a transparent electrode (ITO) (22) and a liquid crystal alignment film (23) formed on soda glass (21),
The substrates (26) on which spacers were dispersed were bonded together, and ferroelectric liquid crystal (24) was injected between the substrates. However, the spacer is not shown in the drawing.

Here, the transparent electrode has a matrix structure, and the control electrode is 6
The number of electrodes was 40, and the number of scanning electrodes was 400.

The light source cell (30) consists of a substrate (3 pieces) in which a transparent electrode (36) is formed on soda glass (35), and a transparent electrode (36) formed on a soda glass (35).
6) and a substrate (32) in which a liquid crystal alignment film (37) was formed on soda glass (35) were bonded together, and a ferroelectric liquid crystal (24) was injected between the substrates. Note that, before bonding the substrates together, a color filter (33) was attached to the outside of the substrate (32). Here, the transparent electrode was formed on the entire surface without patterning on the substrate (31) side, and the substrate (32) side had a wider width than the electrode of the display cell, that is, had a striped structure.

Furthermore, polarizing plates are arranged on both sides of the display cell (20) and on both sides of the light source cell (30).

When the display cells are time-divisionally driven, a light source (40) is placed on the scanning electrode side that is selected last, that is, the 400th scanning electrode. In this embodiment, the diffuser plate (50) is arranged such that the light passes through the diffuser plate (50) and then enters the display cell.
) was placed.

When using the configuration shown in FIG. 1, which is an example of the present invention, light emitted from a light source (fluorescent lamp) (50) first enters the light source cell (30). In this display device, when displaying red, only the portion of the light source cell where the red color filter exists is turned on (a state through which light passes). At the same time, the area where the green and blue color filters are
By setting it to ff, the light incident on this portion is absorbed by the polarizing plate and does not pass through the light source cell. For this reason,
The light passing through the light source cell becomes red. In this state, the first scanning electrode of the display cell. Second. ...If the 400th scan electrode is selected in order and displayed, red can be displayed.

Next, the light passing through the light source cell is made green in the same manner as in the case of red, and in this state, the display cells are sequentially selected from the first scan electrode to the 400th scan electrode to display green. Next, blue is displayed in a similar manner. This red, green. By displaying all blue at high speed using the same pixel, it appears white to the human eye, and by displaying only red and blue and turning off the pixels in the display cell during the green time period. It is also possible to display purple. Other colors can also be displayed using a combination of red, green, and blue.

By providing the light source (40) on the side of the scanning electrode that is selected last in the display cell as in this embodiment, the difference in the length of the ON state due to the scanning electrode in displaying each color is reflected in the display cell. This can be offset by the intensity of the light, making the brightness uniform across the display cell.

In addition, if you use a diffuser that creates a gradient in the intensity of the emitted light depending on the location, instead of a diffuser that makes the light uniform within the plane, the light intensity of the diffuser will be closer to the scan electrode side that is selected at the end of the display cell. By arranging a large portion, the brightness of the display cell can be further made uniform.

``Cacicle Example 2'' A film of IT◯ was formed as a transparent electrode on the first soda glass by a known DC magnetron sputtering method, and then 720 control electrodes were fabricated by a photolithography method.

Then, polyamic acid is applied by a known offset printing method and heated in a clean open at 280''C for 3 hours to obtain a polyimide thin film.

Furthermore, the polyimide thin film is rubbed with a cotton cloth, that is, a rubbing step is performed.

After 480 scanning electrodes of ITO were similarly fabricated on a second soda glass, fine particles of Si02 with a diameter of 2 μm were sprinkled on this substrate as spacers. After bonding the two substrates together, ferroelectric liquid crystal was injected using a known vacuum injection method to complete the display cell. After that, a polarizing plate was further attached to the outside of the display cell.

In addition, after forming a film of ITO on the third soda glass using the same method, three electrodes were similarly produced using a photolithography process, and red, green, and
A blue color filter was shaped to match the three electrodes.

Furthermore, a polyimide thin film is formed as a liquid crystal alignment film on the electrode preparation surface in the same manner as in the case of display cells. Bing process was performed.

Further, ITO was coated on the fourth soda glass in the same manner.

However, since this substrate does not require a plurality of electrodes, a polyimide thin film is formed as a liquid crystal aligning film while ITO is coated on the entire surface. After this, a rubbing process is performed, and SiO2 particles with a diameter of 8 μm are scattered, and 2
Attach the two boards together. However, when bonding, the rubbing directions of the two substrates should be at right angles.

Then, TN-type liquid crystal was injected using the vacuum injection method, and the light source cell was completed. Thereafter, polarizing plates were further attached to both sides of the light source cell.

Then, when a display was performed with the display cell, light source cell, light source, and diffuser plate arranged as shown in Figure 1, Example 1
Similarly, the brightness of the display screen was very uniform.

In this example, a TN type liquid crystal is used for the light source cell, but since the electrodes of the light source cell are very simple (one substrate has a solid surface and the other substrate has three electrodes), the light source cell The red, green, and blue displays can be statically driven, and the viewer cannot distinguish between the red, green, and blue displays, similar to the case using the ferroelectric liquid crystal in Example 1. There were no problems at all.

Furthermore, in this example, when display was performed with the diffuser removed, a display screen with uniform brightness was still obtained.

However, when the light source was placed on the opposite side (the scanning electrode side that is selected first in the display cell), the side where the electrode was placed became very bright, but the side opposite the electrode became very dark. This resulted in a display that was very difficult to read.

This demonstrated that it is very effective to arrange the light source on the scanning electrode side that is selected last in the display cell.

In addition, in this example, a TN type liquid crystal is used for the light source cell, and the spacing between the substrates is relatively thick at 8 μm, which reduces defects such as shorting of electrodes due to foreign matter between the substrates, and increases the yield in the process. did.

[Effect] By using the present invention, it was possible to make the brightness of the display surface of a color display device using ferroelectric liquid crystal very uniform.

[Brief explanation of the drawing]

FIG. 1 shows an example of a color display device using ferroelectric liquid crystal according to the present invention. FIG. 2 schematically shows a cross section of a display cell, which is part I of the structure of the present invention. FIG. 3 schematically shows a cross section of a light source cell that is part of the configuration of the present invention. FIG. 4 shows a timing chart regarding the display of the light source cell and the display cell. 20・ ・ ・ ・ 21, 35・ ・ 22, 36・ ・ 23, 37・ ・ 24・ ・ ・ ・ 25, 26, 31, 30・ ・ ・ ・ 33・ ・ ・ 40・ ・ ・ ・ 50・ ・ ・・・Display cell・Soda glass・Transparent electrode・Liquid crystal alignment film・Ferroelectric liquid crystal 32・Substrate・Light source cell・・Color filter・・Light source・・Diffusion plate

Claims (1)

[Claims] 1. A light source; a display cell in which a ferroelectric liquid crystal is interposed between a substrate having a plurality of scanning electrodes and a substrate having a plurality of control electrodes; a light source and a display cell; A ferroelectric liquid crystal having a liquid crystal interposed between a pair of substrates having a transparent electrode therebetween, a light source cell having a color filter on the outside of the substrate; and polarizing means for identifying different states of the liquid crystal; In the color display device used, when the display cells are driven in a time-division manner, the intensity per unit time of the light incident on the display cells is such that the side of the scan electrode selected last is equal to the side of the scan electrode selected first. A ferroelectric liquid crystal color display device characterized in that the rate of change is large compared to the side and the rate of change is almost constant. 2. A light source; A display cell having a ferroelectric liquid crystal interposed between a substrate having a plurality of scanning electrodes and a substrate having a plurality of control electrodes; A transparent electrode having a transparent electrode between the light source and the display cell; In a color display device using a ferroelectric liquid crystal, the liquid crystal is interposed between a pair of substrates, and has a light source cell having a color filter on the outside of the substrate; and polarization means for identifying different states of the liquid crystal. , when the display cell is time-divisionally driven, the intensity per unit time of the light incident on the display cell is larger on the side of the scan electrode selected last than on the side of the scan electrode selected first. , a ferroelectric liquid crystal color display device characterized in that the rate of change is at least one type.