JPH0656463B2 - Liquid crystal display - Google Patents

Description

TECHNICAL FIELD The present invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device suitable for a large-sized liquid crystal matrix display.

[Conventional technology]

The most commonly used conventional liquid crystal display device is of the twisted nematic type. This has a 90 ° twisted spiral structure made of nematic liquid crystal having a positive dielectric anisotropy between two electrode substrates, and a polarizing plate (or absorption axis) on the outside of both electrode substrates. The axes were arranged so as to be orthogonal or parallel to the liquid crystal molecules adjacent to the electrode substrate.

To orient the liquid crystal molecules so that they form a spiral structure twisted by 90 ° between the two electrode substrates, for example, by rubbing the surface of the electrode substrate in contact with the liquid crystal in one direction with a cloth, the so-called rubbing method. Done. The rubbing direction at this time, that is, the rubbing direction is the alignment direction of the liquid crystal molecules. The two electrode substrates thus oriented are made to face each other with a gap so that the rubbing directions intersect each other at about 90 degrees, and the two electrode substrates are adhered with a sealant to form the gap. When a nematic liquid crystal having a positive dielectric anisotropy is enclosed in, the liquid crystal molecules have a helical molecular arrangement that rotates about 90 degrees between the electrode substrates. Polarizing plates are provided above and below the liquid crystal cell constructed in this manner, and the polarization axis or absorption axis thereof is made substantially parallel to the alignment direction of the liquid crystal molecules adjacent to the respective electrode substrates (Japanese Patent Publication No. 57-13666). Issue).

Here, the time division driving will be briefly described by taking a dot matrix display as an example. As shown in FIG. 7, stripe-shaped Y electrodes (signal electrodes) 12 are formed on the lower electrode substrate.
A striped X electrode (scan electrode) on the upper electrode substrate
43 is formed, and characters or the like are displayed by turning on or off the liquid crystal at the intersection of the X and Y electrodes. In the figure, N scanning electrodes are repeatedly line-sequentially scanned with X ₁ , X ₂ , ... X, X ₁ , X ₂ , ... When a certain scanning electrode is selected, a display signal of selection or non-selection is simultaneously applied to all the pixels on the electrode from the signal electrodes 12, Y ₁ , Y ₂ , ... . In this way, lighting or non-lighting of the intersection is selected by the combination of the voltage pulses applied to the scanning electrodes and the signal electrodes. The number of scan electrodes X in this case corresponds to the number N of time divisions.

In such a liquid crystal display device, a driving method based on a voltage averaging method is generally adopted in order to prevent crosstalk that occurs because the electro-optical phenomenon of liquid crystal is bipolar and does not have a steep threshold characteristic. However, the operating margin α (= selected pixel voltage Vs / non-selected pixel voltage Vns) decreases as the number of time divisions N increases, and N =
16, 32, 64, 128 with α = 1.24, 1.19, 1.13,
It becomes 1.09. On the other hand, the steepness γ (= Vsat (voltage at which the brightness becomes 50%) / Vth (voltage at which the brightness becomes 10%)) of the conventional liquid crystal is about 1.15 at most, so that the display Considering the viewing angle dependence and temperature dependence of the above, the time division number N was at most about 32, or even about 64 even if the liquid crystal material was further improved (Magazine "Electronic Materials" April 1984 Issue 17).
Page 6).

[Problems to be solved by the invention]

Conventionally, there has been a problem that an attempt to increase the number N of time divisions causes a decrease in operation margin, a decrease in contrast, and a decrease in viewing angle range.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a liquid crystal display device which eliminates a decrease in operation margin, a decrease in contrast and a decrease in viewing angle range when the number of display pixels is increased.

[Means for solving problems]

The above problems can be solved by forming the scanning electrodes from a photoconductive material and irradiating the scanning electrodes at selected positions with light.

[Action]

Since the resistance of only the scan electrodes at the selected position becomes low and the resistance of the scan electrodes at the remaining positions remains high, crosstalk does not occur.

〔Example〕

The occurrence of crosstalk always exists as a problem in executing matrix driving (time-division driving) in an element material system such as liquid crystal in which the threshold voltage for operation is not clear.

As shown in FIG. 8, in a normal liquid crystal X, Y matrix display device, a scanning electrode group 43 (Xi) and a signal electrode group 12 (Yj) are used.
A leak path 37 other than the selection point 36 is formed between and through the liquid crystal, and crosstalk occurs.

According to the present invention, as shown in FIG. 9, the scanning electrode group 43 acts as the high resistance body 36 when it is not selected, and the conductor only when it is selected.
By acting as a 38, it cuts off the cause of crosstalk.

Since the scan electrode group 43 normally forms a stripe shape, the stripe electrode group 43 is formed of a photoconductor, and when a scan electrode 43 is selected, only the scan electrode is irradiated with light. Make the resistance low and turn it on.

Embodiments of the present invention will be described below with reference to the drawings.

Example 1 As shown in FIG. 1, in the liquid crystal cell 1, a transparent substrate is used.
A striped transparent electrode 12 in the vertical direction is formed on the inner surface of the transparent substrate 11, and the transparent substrate of the transparent substrate 21 is arranged to face the transparent substrate 11.
Lateral stripe-shaped photoconductive electrodes 13 made of a photoconductive material are formed on the inner surface on the 11 side. Transparent substrate 11 and transparent substrate
A nematic liquid crystal 35 containing a pleochroic dye 34 is sandwiched between 21. That is, the liquid crystal cell 1
Utilizes the guest-host effect, and the liquid crystal layer in the portion to which a sufficient voltage is not applied is configured to block the light incident on it.

In the liquid crystal cell 2, each of the striped transparent electrodes 14 having the same pitch and the same width as the striped photoconductive electrodes 13 is provided on the surface of the transparent substrate 21 where the striped photoconductive electrodes 13 are not formed. It is formed so as to face each of the conductive electrodes 13. A transparent substrate arranged to face the transparent substrate 21.
Striped transparent electrodes 15 are formed on the inner surface of the transparent substrate 21 side of 31 at positions facing the respective striped transparent electrodes 14. The liquid crystal cell 1 is provided between the transparent substrate 21 and the transparent substrate 31.
A nematic liquid crystal 35 containing a pleochroic dye 34 is sandwiched in the same manner as in. A polarizing plate 16 is provided outside the transparent substrate 11.
However, a polarizing plate 17 is arranged outside the transparent substrate 31 with their polarization axes aligned with each other.

In order to turn on an arbitrary intersection of the stripe-shaped transparent electrode 12 in the vertical direction of the liquid crystal cell 1 and the stripe-shaped photoconductive electrode 13 in the horizontal direction, that is, to form a light transmission region, the stripe-shaped transparent electrode 12 that forms this intersection is formed. A voltage equal to or more than a threshold value is applied between the stripe-shaped photoconductive electrode 13 and the stripe-shaped transparent electrode 14 of the liquid crystal cell 2 facing the stripe-shaped photoconductive electrode 13 passing through this intersection, and the stripe-shaped transparent electrode.
A voltage equal to or higher than the threshold value may be applied between the transparent transparent electrode 15 and the stripe-shaped transparent electrode 15 facing the electrode 14. That is, when a sufficient voltage is applied to a certain pair of the stripe-shaped transparent electrode 14 and the stripe-shaped transparent electrode 15, the stripe-shaped liquid crystal layer region to which the voltage is applied is the light source 18 due to the guest-host effect.
From which the stripe-shaped photoconductive electrode 13 facing this region has a low resistance, while the remaining stripe-shaped photoconductive electrodes 13 have a high resistance. . Therefore, the above-mentioned crosstalk does not occur, so that the voltage is applied only to the intersection of the intended stripe-shaped transparent electrode 12 and the stripe-shaped photoconductive electrode 13, and since lighting due to crosstalk does not occur, only the above-mentioned intended intersection is generated. Light from the light source 18 is transmitted to the observer 19 side to form pixels.

In the time-divisional driving in the configuration of FIG. 1, a scanning signal is sequentially applied to the stripe-shaped photoconductive electrode 13 at each position, and the stripe-shaped electrodes formed at the positions facing the stripe-shaped photoconductive electrode 13 are sequentially applied. 14 and striped electrodes
A voltage having a sufficient value for utilizing the guest-host effect may be sequentially applied between the first and second electrodes 15 to perform the scanning operation, while a signal synchronized with the scanning signal may be applied to the stripe-shaped transparent electrode 12.

Since the crosstalk between the scanning electrodes and the signal electrodes cannot exist functionally due to the structure, the margin of time-division driving is greatly expanded, and high contrast, high-speed driving, and wide viewing angle display are high-time-division driving. But you can do it.

FIG. 2 shows an example of the relationship between voltage and transmitted light intensity when a Heilmeier type liquid crystal is used as the liquid crystal used in the liquid crystal cells 1 and 2. The applied voltage at the time of non-selection may be zero, or an effective value equal to or less than the threshold voltage value may be applied to the electrode at the time of non-selection as a bias voltage. Such a bias voltage improves the response characteristic at the time of selection.

As the photoconductive electrode, a layer of CdS having a thickness of 1 to 2 μm can be used.

The paper "Image Converter with Liquid Crystal and Photoconductor" by Assouline et al. In "Proceding of IEEE", Volume 59 (1971) 1355-1357, has already revealed. Thus, the resistance of the photoconductive film can be made higher than that of the liquid crystal layer when light is not irradiated. When light is irradiated, the resistance of the photoconductive film is lowered and a voltage is applied to the liquid crystal, and the liquid crystal operates.

The writing sensitivity is good at 5 × 10 ^-3 mJ / cm ^2, and the writing response time is
It is 100 μs or less.

The photoconductive electrode 13 can also have a two-layer (laminated) structure of a photoconductor 22 and a transparent electrode 23 such as an ordinary indium oxide as shown in FIG.

As the light source 18, an incandescent lamp, a fluorescent lamp, an electroluminescence cell, etc. are effective.

Example 2 This example uses an electroluminescence (hereinafter abbreviated as EL) cell in place of the liquid crystal cell 2 and the light source 18 in Example 1.

In FIG. 4, the liquid crystal cell 1 is shown in Example 1
Is exactly the same as.

In the EL cell 3, the stripe-shaped electrode is formed on the surface of the transparent substrate 21 on which the stripe-shaped photoconductive electrode 13 is not formed.
Striped transparent electrodes with the same pitch as 13 and almost the same width 14
And is formed so as to face each of the striped photoconductive electrodes 13. A striped back metal electrode 25 is formed on the inner surface of the substrate 26 facing the transparent substrate 21 on the transparent substrate 21 side. An EL material 24 is sandwiched between the transparent substrate 21 and the substrate 26. The EL cell 3 in this example is the same as that in Example 1.
The combination of the liquid crystal cell 2 and the light source 18 in FIG. That is, in order to turn on an arbitrary intersection between the vertical stripe-shaped transparent electrode 12 of the liquid crystal cell 1 and the horizontal stripe-shaped photoconductive electrode 13, that is, a light transmission region, the stripe-shaped transparent electrode forming the intersection is formed. A voltage equal to or higher than a threshold value is applied between the stripe-shaped photoconductive electrode 12 and the stripe-shaped photoconductive electrode 13, and the stripe-shaped transparent electrode 14 of the EL cell 3 facing the stripe-shaped photoconductive electrode 13 passing through this intersection and the stripe-shaped transparent electrode A voltage sufficient to cause the EL material 24 to emit light may be applied between the electrode 14 and the striped back surface metal electrode 25 facing the electrode 14. That is, when a voltage is applied to a certain pair of the striped transparent electrode 14 and the back surface metal electrode 25 to cause the EL substance 24 to emit light, the EL substance 24 emits light in a striped pattern, and therefore the transparent substrate 21 is interposed in this striped light emitting region. The resistance of only the photo-striped photoconductive electrodes 13 facing each other decreases, but the remaining striped photoconductive electrodes 13 remain high in resistance. Therefore, crosstalk does not occur, and the voltage is applied only to the intended intersection of the stripe-shaped electrode 12 and the stripe-shaped photoconductive electrode 13, and lighting due to crosstalk does not occur. In this case, the EL cell 3 also acts as an illumination light source for the liquid crystal cell 1.

In the time-divisional driving in the configuration of FIG. 4, a scanning signal is sequentially applied to the stripe-shaped photoconductive electrode 13, and the stripe-shaped electrode 14 and the back surface formed at a position facing the stripe-shaped photoconductive electrode 13 are arranged. A voltage for causing the EL material 24 to emit light may be sequentially applied to the metal electrode 25 to perform a scanning operation, and a signal may be applied to the stripe-shaped transparent electrode 12 in synchronization with the scanning signal.

As the EL substance 24, it is possible to use a dispersion type ZnS: Cu type or a thin film type ZnS: Mn type according to the required characteristics.

The scanning method is the stripe-shaped photoconductive electrode of Example 1.
Method for simultaneously applying voltage to striped transparent electrodes 14 and 15 at the same time, voltage application to striped photoconductive electrode 13 and striped transparent electrode of Example 2
Instead of a method of simultaneously and sequentially applying a voltage between 14 and the back metal 25, a constant voltage is always applied to all of the stripe-shaped photoconductive electrodes 13. In Example 1, the stripe-shaped transparent electrode 14 is used. And 15 and in the second embodiment, only the voltage is applied between the striped transparent electrode 14 and the back metal electrode 25, and the scanning may be performed by sequentially changing the position.

The liquid crystal has a cumulative response effect as is well known (see the article "Liquid Crystal Display" in the magazine "Hitachi Kenron", August 1974, page 69). That is, this is a phenomenon in which the line-sequential scanning cannot be turned on once, but can be turned on during repeated scanning. By utilizing such a cumulative response effect of the liquid crystal, even if the actual response time of the liquid crystal is longer than one scanning time, a delay of several frame times is recognized by the repeated pulse application (repetition of several frames) several times. However, the image can be displayed.

Example 3 Instead of the stripe-shaped transparent electrode 12 in Example 1,
As shown in FIG. 5, this is a striped transparent electrode 28.
R, 28G, and 28B are divided into three parts, which are a red signal applying stripe electrode, a green signal applying stripe electrode, and a blue signal applying stripe electrode. Further, a striped red filter 27R, a striped green filter 27G, and a striped blue filter 27B are superposed on these. If a white light source is used as the light source 18 in such a configuration, the stripe electrode 28R and the stripe electrode 28
Arbitrary color display is possible by combining the signals applied to the G and stripe electrodes 28B.

Striped red, green and blue filters 27R, 27G,
27B is arranged at the transparent substrate 21 instead of the transparent substrate 11.
Alternatively, of course, 31 corresponding positions may be used.

Example 4 This example is a stripe-shaped photoconductive electrode 13 of Example 2.
As shown in FIG. 6, each of the three divided liquid crystal cells 5 of a red signal applying stripe photoconductive electrode 29R, a green signal applying stripe photoconductive electrode 29G, and a blue signal applying stripe photoconductive electrode 29B are formed. Each of the striped transparent electrode 14 and the striped back surface metal electrode 25 in Example 2 is similarly divided into three, and 30R, 30G and 30 are respectively formed.
B and 31R, 31G, 31B. A striped EL material 32R that emits red light is provided between the striped transparent electrode 30R and the striped back metal electrode 31R, and a striped green material that emits green light is provided between the striped transparent electrode 30G and the striped back metal electrode 31G. The EL cell 32 is formed by sandwiching the EL substance 32G of the blue light emission between the striped transparent electrode 30B and the striped back metal electrode 31B. In such a configuration, in order to display an arbitrary color, for example, red at an arbitrary position, a red color is applied by applying a voltage between the striped transparent electrode 30R and the striped back surface metal electrode 31R at an arbitrary position. The light emitting EL material 32R is caused to emit light to reduce the resistance of the opposed red signal applying stripe-shaped photoconductive electrode 29R, and a voltage equal to or higher than a threshold value is applied between the photoconductive electrode 29R and the stripe-shaped transparent electrode 12 intersecting with the photoconductive electrode 29R. By applying the voltage, red display can be performed at an intended position. Arbitrary color display (including intermediate colors) can be performed by a combination of light emission of EL materials emitting light of each color.

The scanning of the stripe-shaped photoconductive electrode is (29R, 29
Select in G, 29B) units. That is, in the case of the intermediate color display, for example, the yellow display, 29R and 29
29B → 29 and a scanning method that simultaneously selects G and
A method of selecting in the order of G → 29R → 29B → 29G → 29R ...

The brightness modulation can be performed by adjusting the magnitude of the voltage applied to the liquid crystal cell 5.

In the above examples, the liquid crystal cell is constructed by using the guest-host effect, but a twisted nematic liquid crystal cell (Japanese Patent Publication No. 51-13666) may of course be used. is there.

Further, the stripe-shaped photoconductive electrode 13 in Example 1,
Any one of the two striped transparent electrodes 14 and 15, the striped photoconductive electrode 13, the striped transparent electrode 14 and the striped back metal electrode 25 in the second embodiment.
One of the striped photoconductive electrodes 13 and the two striped transparent electrodes 14 and 15 in Example 3, and the striped photoconductive electrode 29 in Example 4
R, 29G, 29B, striped transparent electrodes 30R, 30G, 30
B or striped back metal electrode 31R, 31G, 31B
Either one side or the like may be replaced with a stripe to form a common electrode integrated over the entire display surface.

〔The invention's effect〕

In the present invention, the matrix drive of the liquid crystal can be performed by the cumulative response of the liquid crystal. In the case of time-division driving of a normal liquid crystal matrix, there is a problem of crosstalk, and the liquid crystal capacity cannot be fully exhibited. In order to realize high time-division driving, it is necessary to improve the special performance (time-division driving characteristics) of the liquid crystal material, or specially devise the orientation (tilt angle) of the liquid crystal in the display device or the element structure. .

The liquid crystal material of the present invention may be any liquid crystal material having excellent responsiveness (cumulative responsiveness). The device structure is also a level that can be realized by applying ordinary liquid crystal device technology, and no special device is required.

[Brief description of drawings]

FIG. 1 is a perspective view showing an embodiment of the present invention, and FIG.
A graph illustrating the characteristics of the liquid crystal used in the example of the figure,
3 is a sectional view for explaining a modification of the embodiment shown in FIG. 1, FIG. 4 is a perspective view showing another embodiment, and FIGS. 5 and 6 are sectional views showing still another embodiment. FIG. 7 is a diagram for explaining time division driving, FIG. 8 is a diagram for explaining crosstalk, and FIG. 9 is a diagram for explaining the principle of the present invention. 1, 2, 4, 5 ... Liquid crystal cell, 3, 6 ... EL cell, 1
2,14,15 …… Striped transparent electrode, 13 …… Striped photoconductive electrode, 16,17 …… Polarizing plate, 24 …… EL substance,
25: back metal electrode, 34: polychromatic dye, 35: nematic liquid crystal.

Claims (3)

[Claims] 1. A liquid crystal display device in which a plurality of pixels are formed by facing portions of a scanning electrode and a signal electrode and a liquid crystal sandwiched between the scanning electrode and the signal electrode, wherein the scanning electrode is made of a photoconductive material and is located at a selected position. 2. A liquid crystal display device, characterized in that only the scanning electrodes are irradiated with light for a selected period to reduce the resistance of the scanning electrodes. 2. The light irradiation is performed by a plurality of pairs of transparent electrodes arranged to face the scanning electrodes, an optical shutter composed of a liquid crystal layer sandwiched between these transparent electrodes, and a light source for making light incident on the optical shutter. The liquid crystal display device according to claim 1, wherein: 3. The light irradiation is performed by an electroluminescence cell which is arranged so as to face the scanning electrode and is configured to selectively emit light at a light emitting position. The described liquid crystal display device.