JP2791345B2 - Ferroelectric liquid crystal panel - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ferroelectric liquid crystal panel.

[0002]

2. Description of the Related Art Conventionally, a ferroelectric liquid crystal panel using a ferroelectric liquid crystal generally uses the bistability of a ferroelectric liquid crystal for driving. FIG. 4 is a diagram showing an electro-optical response characteristic of a ferroelectric liquid crystal panel with respect to a driving pulse. In the figure, 4a indicates a drive pulse, and 4b indicates an electro-optical response characteristic (light transmission characteristic).

However, it is not easy to uniformly orient the ferroelectric liquid crystal and at the same time to provide bistability and maintain its characteristics. Therefore, a ferroelectric liquid crystal having a negative dielectric anisotropy is used. In addition, there is a technique of forcibly imparting a memory property by applying a high voltage high frequency in which the direction of an electric field changes at a cycle sufficiently faster than the switching speed at the time of driving, that is, there is a technique called AC stabilization.

[0004]

However, when the above-mentioned one is left in one switching state, that is, a memory state, the state has an advantage over the other state as shown in FIG. In other words, it has a one-sided stable state (in FIG. 4, the stable state when a negative drive voltage is applied has an advantage). There is a problem that a phenomenon called "burn-in" or "ghost" occurs. I was The above problem is that the direction of spontaneous polarization of the ferroelectric liquid crystal is 1
It is pointed out that this is an essential problem of the ferroelectric liquid crystal, which is caused by the formation of an electric double layer by the movement of ionic impurities due to the internal electric field generated due to the alignment. When driving a ferroelectric liquid crystal panel, this phenomenon is caused by the asymmetry that only one side has a memory property, which causes a decrease in contrast, a difference in response speed between two memory states, and when it is further deteriorated, switching is lost at a drive voltage level. In addition, there is a problem that the operation becomes unstable even when driven by the AC stabilization method.

An object of the present invention is to provide a ferroelectric liquid crystal panel free from "burn-in" or "ghost".

[0006]

According to the present invention, electrodes are formed on opposing surfaces of two substrates, and an alignment film is provided on each of the electrodes. In a ferroelectric liquid crystal panel in which a ferroelectric liquid crystal is interposed, a high frequency of a frequency at which the electro-optical response of the ferroelectric liquid crystal cannot follow a voltage high enough to change the layer structure of the ferroelectric liquid crystal is applied to each of the electrodes. By applying a high voltage,
The above object has been achieved by eliminating the bistability and the unidirectional memory property of the ferroelectric liquid crystal when no electric field is applied.

In addition, a low frequency high voltage having a frequency sufficient to change the layer structure of the ferroelectric liquid crystal at a frequency at which the electro-optical response of the ferroelectric liquid crystal is sufficiently saturated is applied to each of the electrodes. Thereafter, by applying a high-frequency high voltage having a frequency that cannot follow the electro-optical response of the ferroelectric liquid crystal at a voltage high enough to change the layer structure of the ferroelectric liquid crystal, the ferroelectric liquid crystal when the electric field is not applied is The above object has been achieved by eliminating the bistability and unilateral memory property of the dielectric liquid crystal.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below with reference to one embodiment shown in the drawings.

In FIG. 1, a transparent electrode 2 made of ITO (tin oxide doped with tin oxide) is selectively formed on one surface of a substrate 1 made of glass or the like. An alignment film 3 formed by obliquely depositing SiO ₂ is selectively provided.

[0010] The transparent electrode 5 made of ITO is on opposite sides of the substrate 1 of the substrate 4 made of glass or the like has selected formed, the was formed thereon by oblique evaporation of SiO ₂ An alignment film 6 is selectively provided.

The space between the substrate 1 and the substrate 4 is held at a predetermined distance by a spacer 7. In this example, the thickness is 2.5μ
m spacers 7 are used. Then, the substrate 1 and the substrate 4
Is fixed by a sealant 8. In this example, an acrylic thermosetting adhesive is used as the sealant 8.

A ferroelectric liquid crystal 9 is sealed in a portion surrounded by the substrate 1, the substrate 4, the sealant 8, and the like. In this example, a ferroelectric liquid crystal SKC102 manufactured by Chisso Petrochemical Co., Ltd. is used as the ferroelectric liquid crystal 9.

The electro-optical response of the ferroelectric liquid crystal 9 is sufficiently saturated at a voltage high enough to change the layer structure of the ferroelectric liquid crystal 9 between the transparent electrode 2 and the transparent electrode 5 of the ferroelectric liquid crystal panel. AC low frequency high voltage at the frequency of
After applying a square wave of 0 Hz and ± 50 V for 1 minute, an alternating current of a frequency that cannot be followed by the electro-optical response of the ferroelectric liquid crystal 9 at a voltage high enough to change the layer structure of the ferroelectric liquid crystal 9. A voltage, in this example, a 5 kHz, ± 50 V square wave is applied for 10 seconds. First, the orientations of the liquid crystal molecules are aligned by the low frequency high voltage to make the alignment state uniform. Subsequently, the direction of spontaneous polarization is dispersed in the direction perpendicular to the substrate by the high-frequency high voltage to erase the memory property when no electric field is applied.

FIG. 2 is a diagram showing the amount of transmitted light b with respect to an applied voltage a under crossed Nicols of a ferroelectric liquid crystal panel to which an alternating low frequency high voltage and a high frequency high voltage are applied as described above. Thus, the amount of transmitted light c when no electric field is applied is
It is an intermediate value between the two transmitted light amounts at the time of switching between the bright transmitted light amount d and the dark transmitted light amount e. That is, it does not have a memory property when no electric field is applied.

The above-mentioned liquid crystal panel has a uniform alignment state in a pixel and does not have an extinction position under crossed Nicols. This indicates that the directions of the spontaneous polarization are not aligned in the direction perpendicular to the substrate. Therefore, the internal electric field generated by the spontaneous polarization is small, and image sticking is unlikely to occur, and a high contrast can be obtained.

FIG. 3 shows a ferroelectric liquid crystal panel having no memory effect as described above.
FIG. 9 shows optical response characteristics when digit multiplex driving is performed.

In the figure, f is an applied voltage waveform applied to the transparent electrode (segment electrode) 2, g is an applied voltage waveform applied to the transparent electrode (common electrode) 5, and h is the above ferroelectric liquid crystal panel. Shows the amount of light transmission.

In this example, one cycle of driving is divided into four parts, first, a dark state is initialized, then a desired response state is written, and then the write state is held (non-selected) by AC stabilization. The above 1 cycle is 1/4 for each digit
Multiplex driving is performed by shifting the period.

As described above, the ferroelectric liquid crystal panel of the present invention can obtain a stable operation even when driven by the AC stabilization method, can reduce the driving voltage, and can stably drive more digits. Can do it. In addition, since the ferroelectric liquid crystal is used, a fast electro-optical response can be obtained.

In the above example, the low frequency high voltage of 500 Hz is a low frequency high voltage at which the electro-optical response of the ferroelectric liquid crystal 9 is sufficiently saturated at a voltage high enough to change the layer structure of the ferroelectric liquid crystal 9. , ± 50 V square wave is used, but the low frequency high voltage is not limited to this, and can be changed as appropriate depending on the type of ferroelectric liquid crystal used. Similarly, a square wave of 5 kHz and ± 50 V in this example is used as a high-frequency high voltage of a frequency that is high enough to change the layer structure of the ferroelectric liquid crystal 9 and cannot follow the electro-optical response of the ferroelectric liquid crystal 9. However, as described above, the present invention is not limited to this, and can be appropriately changed.

In the above example, an alignment film formed by obliquely depositing SiO ₂ was used. However, the same effect as described above can be obtained by using an alignment film that has been subjected to an alignment treatment by a rubbing method or the like.

In the above, after applying a low frequency high voltage of a frequency at which the electro-optical response of the ferroelectric liquid crystal 9 is sufficiently saturated at a voltage high enough to change the layer structure of the ferroelectric liquid crystal 9, An example is shown in which a high-frequency high voltage is applied at a voltage high enough to change the layer structure of the dielectric liquid crystal 9 and a frequency at which the electro-optical response of the ferroelectric liquid crystal 9 cannot follow. Burning can be eliminated only by applying the above high frequency high voltage without applying the voltage. However, the case where the low frequency high voltage is applied is preferable because the alignment state can be made more uniform.

The ferroelectric liquid crystal panel configured as described above can be widely used for a liquid crystal shutter and a display device of an optical printer.

[0024]

According to the present invention, electrodes are formed on opposing surfaces of two substrates, and an alignment film is provided on each of the electrodes, and a ferroelectric liquid crystal is interposed between the alignment films. In the ferroelectric liquid crystal panel, a high frequency high voltage of a frequency that cannot be followed by the electro-optical response of the ferroelectric liquid crystal is applied to each electrode at a voltage high enough to change the layer structure of the ferroelectric liquid crystal. By eliminating the bistability and the unidirectional memory property of the ferroelectric liquid crystal when no electric field is applied, image sticking can be eliminated. For example, even when driven by the AC stabilization method, it is stable. Operation can be obtained, the drive voltage can be reduced, and more digits can be driven stably. In addition, since the ferroelectric liquid crystal is used, a fast electro-optical response can be obtained. Also, since the orientation of the ferroelectric liquid crystal in the pixel is uniform and has no defect, high contrast can be obtained.

Before the high frequency high voltage is applied to each of the electrodes, a low enough frequency at which the electro-optical response of the ferroelectric liquid crystal is sufficiently saturated at a voltage high enough to change the layer structure of the ferroelectric liquid crystal. By applying a high frequency voltage, the alignment state can be made more uniform, image sticking can be eliminated in the same manner as described above, and a higher contrast than the above can be obtained.

[Brief description of the drawings]

FIG. 1 is a sectional view showing one embodiment of the present invention.

FIG. 2 is an explanatory diagram showing the optical response characteristics of a ferroelectric liquid crystal panel according to the present invention to an applied voltage under crossed Nicols.

FIG. 3 is an explanatory diagram showing an example of a driving waveform of the ferroelectric liquid crystal panel according to the present invention by the AC stabilization method and an optical response characteristic at that time.

FIG. 4 is an explanatory diagram showing an electro-optical response characteristic of a conventional ferroelectric liquid crystal panel to a driving pulse.

FIG. 5 is an explanatory diagram showing an electro-optical response characteristic of a conventional ferroelectric liquid crystal panel to a driving pulse.

[Explanation of symbols]

 Reference Signs List 1 substrate 2 electrode 3 alignment film 4 substrate 5 electrode 6 alignment film 9 ferroelectric liquid crystal

────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Masanori Fujita 4-1-1, Taihei, Sumida-ku, Tokyo Inside Seikosha Co., Ltd. (56) Reference Literature 3-3-122617 (JP, U) (58) Survey Field (Int.Cl. ⁶ , DB name) G02F 1/133 G02F 1/141 G09G 3/18

Claims (2)

(57) [Claims] An electrode is formed on each of opposing surfaces of two substrates, an alignment film is provided on each of the electrodes, and a ferroelectric liquid crystal is interposed between each of the alignment films. In the liquid crystal panel, by applying to each of the electrodes a high-frequency high voltage of a frequency that cannot be followed by the electro-optical response of the ferroelectric liquid crystal at a voltage high enough to change the layer structure of the ferroelectric liquid crystal, A ferroelectric liquid crystal panel wherein the ferroelectric liquid crystal has no bistability and no unidirectional memory when no electric field is applied. 2. An electrode is formed on each of opposing surfaces of two substrates, and an alignment film is provided on each of the electrodes, and a ferroelectric liquid crystal in which a ferroelectric liquid crystal is interposed between the alignment films. In the liquid crystal panel, after applying, to each of the electrodes, a low frequency high voltage having a frequency sufficient to change the layer structure of the ferroelectric liquid crystal and a frequency at which the electro-optical response of the ferroelectric liquid crystal is sufficiently saturated. By applying a high-frequency high voltage at a frequency that cannot be followed by the electro-optical response of the ferroelectric liquid crystal at a voltage high enough to change the layer structure of the ferroelectric liquid crystal, A ferroelectric liquid crystal panel characterized by eliminating the bistability and unilateral memory properties of the liquid crystal.