JPH1078585A - Ferroelectric liquid crystal display element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve a memory characteristic and to enable display with high fineness in a case by display control with an inexpensive simple matrix system by using a specific liquid crystal material as a liquid crystal layer and setting the film thickness of oriented films for orienting liquid crystals smaller than conventional general numerical values. SOLUTION: Polarizing plates 111, 112, transparent glass substrates 121, 122, transparent electrodes 131, 132, insulating films 141, 142 and oriented films 151, 152 are successively laminated and formed from both outer sides around the liquid crystal layer 107. Liquid crystal materials exhibiting a book shelf layer structure or pseudo book shelf layer structure are packed between both oriented films 151 and 152, by which the liquid crystal layer 107 is formed. The film thickness of the oriented films 151, 152 is made smaller than 600Å of the conventional devices. The more adequate thickness is <=500Å at which a high memory rate is obtainable by aligning the orientation. More preferably, the film thickness of <=200Åat which the change with lapse of time does not substantially arise and just one time of the orientation treatment at the time of sealing the liquid crystals is necessitated is more adequate.

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 display device, and more particularly to a surface stabilized ferroelectric liquid crystal display device capable of displaying in a simple matrix system.

[0002]

2. Description of the Related Art Conventionally, information devices such as word processors and personal computers have been reduced in size and weight, and liquid crystal displays have been widely used as one of means for achieving the object. In recent years, in particular, portable information devices for personal use have become widespread, and liquid crystal displays have not only been reduced in size and weight, but also have reduced power consumption, higher definition, larger capacity, lower cost, etc. It is also expected from the aspect.

[0003] As a display control method of a liquid crystal display element, two methods, a simple matrix method and an active matrix method, are generally used. In the latter active matrix method, TF is generally used for each pixel.
T (Thin Film Transistor) as switching element 1
A drive circuit corresponding to one-to-one correspondence is required, which complicates the configuration and relatively increases the manufacturing cost. However, in the former simple matrix system, only transparent so-called parallel electrodes that are orthogonal to each other need only be arranged on both sides of the liquid crystal layer, so that the configuration is simple and the manufacturing cost is relatively low. However, the liquid crystal material conventionally used in the simple matrix system has a drawback such as a relatively slow response speed to the application of an electric field. From such a viewpoint, a ferroelectric liquid crystal display device which can perform display control by a simple matrix method and has an extremely high speed response is expected.

[0004] A conventional technique relating to a ferroelectric liquid crystal display device will be described below with reference to the schematic diagrams of FIGS. In a cell in which a ferroelectric liquid crystal is used for the liquid crystal layer, and the helical axis of the ferroelectric liquid crystal is parallel to the substrate and the layer is vertical, when the layer thickness of the liquid crystal layer is reduced to about 1 to 2 μm, the figure shows From the state shown in FIG. 2 (a), as shown in FIG. 2 (b), the helix of each liquid crystal molecule was released to exhibit a smectic layer structure, which was stabilized on the layer surface. Surface Stabilized states: SS
State).

The state of the ferroelectric liquid crystal molecules in the SS state is schematically shown in FIG. In FIG. 1, reference numeral L denotes individual liquid crystal molecules, P denotes spontaneous polarization of each liquid crystal molecule L, and E denotes an electric field applied to the cell.

In such ferroelectric liquid crystal molecules in the SS state, it is possible to use the ferroelectric property of the ferroelectric liquid crystal, ie, reversal of spontaneous polarization. Liquid crystal (Surface Stabilized Ferroelectric
Liquid Crystal: SSFLC).

As shown in FIG. 2B, in a cell having a relatively thin liquid crystal layer, ferroelectric liquid crystal molecules L
Liquid crystal molecules L corresponding to the upward and downward spontaneous polarization P of
Is inclined to the right and left sides by θ with respect to the layer normal direction, and is in a bistable state. As described above, even if the state of initially tilting to the right and the state of tilting to the left are mixed, as shown by the solid line in FIG. 1, when the electric field E is applied upward by the transparent electrode, As shown in FIG. 2C, the whole liquid crystal molecules L are inclined rightward. In this state, when the electric field E is inverted and applied downward as shown by a broken line, the entire liquid crystal molecules L are inclined to the left as shown in FIG.

A panel is prepared in which a cell in an SSFLC state as shown in FIG. 1 is inserted between two polarizing plates whose polarization axes are orthogonal to each other. At this time, for example, the entire liquid crystal molecules L
So that if the major axis of
The polarization axis of one polarizing plate is made to coincide with the long axis of the liquid crystal molecules L. In such a state, when the electric field E is inverted and the long axis of the entire liquid crystal molecules L is tilted to the left, light is transmitted by birefringence and a bright field is obtained. The amount of light I transmitted at that time is expressed by the following equation (1).

I = I _O sin ² 2α · sin ² (πΔnd / λ) (1) where, d: panel gap (alignment film gap) Δn: refractive index of liquid crystal λ: wavelength α: difference between optical axis of liquid crystal and one polarization axis Eggplant

When the polarization axis of one of the polarizing plates coincides with the long axis of the liquid crystal molecules L, α = 0.
= 0, that is, a dark state. When the electric field E is inverted, the liquid crystal molecules L are tilted in the opposite direction, and α = 2θ.
The light passes through to a bright state. Here, θ is the tilt angle of the ferroelectric liquid crystal, and 2θ is the opening angle of the ferroelectric liquid crystal.

As described above, the ferroelectric liquid crystal panel utilizing the SS state is bistable, that is, stable even when inclined to the left or right with respect to the layer normal. Even if the application of the electric field E is stopped after this state, as shown in FIG. 2 (e), the previous state is maintained. The property of maintaining such a state is called a memory effect, and large-capacity display is possible by performing display control in a simple matrix system using the memory effect of the ferroelectric liquid crystal. Further, the ferroelectric liquid crystal display element can perform scanning per line in a very short time of about 100 μsec, and has a high-speed response. Further, in the ferroelectric liquid crystal display element, since the major axis of the liquid crystal molecules L is always parallel to the substrate (glass substrate) regardless of the presence or absence of an applied voltage, there is practically no view angle of display characteristics. The viewing angle is so wide that it may be acceptable.

FIG. 3 is a schematic sectional view of a conventional ferroelectric liquid crystal display device. In FIG. 3, the polarizing plates 11 and 12, the transparent glass substrates 21 and 22, and the transparent electrode 3 are sequentially arranged from both outer sides toward the liquid crystal layer 7 around the liquid crystal layer indicated by reference numeral 7.
1, 32, insulating films 41 and 42, and alignment films 51 and 52 are formed by lamination. The two alignment films 51 and 52 are opposed at a predetermined interval by the spacer 6, and a gap (gap) between the two alignment films 51 and 52 is provided.
Is filled with a liquid crystal material to form a liquid crystal layer 7. The gap between the two alignment films 51 and 52 is 1-2.
The gap is as narrow as about μm.

The transparent electrodes 31 and 32 are electrodes for applying an electric field to the pixel portion of the liquid crystal layer 7, and are generally made of ITO (Indium Tungsten).
in Oxide) is used. Generally, the insulating films 41 and 42
SiO ₂ or the like is used. Generally, polyimide is used for the alignment films 51 and 52, and conventionally, it is often formed to a thickness of about 600 °.

As shown in the schematic diagram of FIG. 4, the transparent electrodes 31 and 32 are provided with a plurality of linear transparent electrodes 31 arranged at equal intervals in one direction and at equal intervals in a direction orthogonal to these. And a plurality of linear transparent electrodes 32, each pixel is formed at a portion where the transparent electrodes 31, 32 cross each other, and a display device in which pixels are arranged in a matrix as a whole is configured. You.

The polarizing axes of the polarizing plates 11 and 12 are orthogonal to each other, and the direction of the polarizing axis of one of the polarizing plates 11 (or 12) and the direction of the long axis of the liquid crystal molecules of the liquid crystal layer 7 are matched. The liquid crystal display element is formed by inserting the configuration between the transparent glass substrates 21 and 22 between the polarizing plates 11 and 12.

[0016]

As described above, one of the major features of the ferroelectric liquid crystal display element is a memory effect, which enables display control by a relatively inexpensive simple matrix system. In the conventional ferroelectric liquid crystal display device, high memory characteristics could not be obtained even immediately after the alignment of liquid crystal was adjusted at the time of manufacturing. In addition, the memory characteristics deteriorate with the lapse of time after the liquid crystal is aligned, and it is necessary to realign the liquid crystal in some way to perform display.

In general, a ferroelectric liquid crystal display element performs display by line-sequential scanning by a simple matrix system utilizing the memory characteristics of ferroelectric liquid crystal. Specifically, by maintaining the display state between the time when writing is performed on one scanning line and the time when writing is performed on the next line, the line-sequential scanning is performed by relying on the memory characteristics of the liquid crystal. Can be displayed. However, high definition display devices,
As the capacity increases and the number of scanning lines increases, the writing interval to the same scanning line becomes longer, and accordingly, the time required to maintain the display state, in other words, the time required to maintain the memory characteristics, also increases. Become. Therefore, when the memory characteristics of the ferroelectric liquid crystal are low, the change in the display luminance while maintaining the display is large, and the display quality is degraded. This means that it is difficult to increase the definition and capacity of the display.

The present invention has been made in view of the above-mentioned problems of the conventional ferroelectric liquid crystal display device, and does not significantly change the conventional technology, in other words, does not increase the manufacturing cost. The present invention provides a ferroelectric liquid crystal display device capable of high-definition display when display is controlled by an inexpensive simple matrix method by further improving memory characteristics, which is a major feature of a ferroelectric liquid crystal display device. The purpose is to:

[0019]

In order to solve the above problems, in the ferroelectric liquid crystal display device of the present invention, a liquid crystal material having a bookshelf layer structure or a pseudo bookshelf layer structure is used as a liquid crystal layer. It is characterized in that the thickness of the alignment film for aligning the liquid crystal is made thinner than the conventional general value of 600 °.

More specifically, the thickness of the alignment film is 500
Or less, preferably 300 mm or less, more preferably 200 mm or less.
Å The following is desirable. The most preferable, in other words, the theoretically optimal film thickness of the alignment film is the minimum film thickness at which the liquid crystal is aligned.

As described above, the ferroelectric liquid crystal has spontaneous polarization and can respond at high speed. However, when the direction of the spontaneous polarization is changed by the application of an electric field, the liquid crystal molecules are inverted. An anti-electric field is generated. The anti-electric field generated in this manner is an electric field having a polarity opposite to that of the external electric field generated in the cell when the electric field is removed by accumulating charges in the insulating film and the alignment film due to spontaneous polarization of the ferroelectric liquid crystal. . It is considered that the liquid crystal molecules are inverted to the original state before the application of the external electric field due to such a counter electric field, and the memory characteristics are degraded. As a countermeasure against this, it is conceivable to adopt a structure that makes it easy for the charges of the anti-electric field to escape to the outside.

If the light state (or dark state) is maintained for a long time, space charge is generated, and the state is monostabilized, resulting in a dark state (or light state).
It is difficult to return to. This phenomenon causes so-called seizure, and is considered to occur as follows. That is, to keep the liquid crystal molecules in one state means to keep the spontaneous polarization in the same direction, and by this, the impurity ions in the liquid crystal accumulate the electric charge because it tries to cancel this spontaneous polarization. The generated area is generated.
These are space charges, and the electric field degrades the bistability of the liquid crystal molecules and lowers the memory characteristics. As a countermeasure for this, it is conceivable to reduce impurity ions in the liquid crystal material, or to adopt a structure in which electric charges can easily escape to the outside as in the case of the above-described counter electric field.

From the above viewpoints, the inventors of the present invention have found that by promoting the release of extra charges of the ferroelectric liquid crystal to the outside, the memory characteristics can be improved. I got the knowledge that it was good. Details will be described below.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the drawings showing the embodiments. Although the present invention has the same basic configuration as the above-mentioned conventional ferroelectric liquid crystal display element, the dimensions of some constituent elements are devised based on knowledge newly confirmed by the inventor of the present application. Thus, the above-mentioned problems of the prior art are solved.

FIG. 5 is a schematic sectional view of the ferroelectric liquid crystal display device of the present invention. In FIG. 5, polarizing plates 111 and 112, transparent glass substrates 121 and 122 are sequentially arranged from both outer sides toward the liquid crystal layer 107 around the liquid crystal layer indicated by reference numeral 107.
Transparent electrodes 131 and 132, insulating films 141 and 142, and alignment films 151 and 152 are laminated. Both alignment films 151 and 152 are spacers 106
The two alignment films 151, 152
Filling the gap between the liquid crystal material with the liquid crystal layer
107 are formed. The gap between the alignment films 151 and 152 is a narrow gap of about 1 to 2 μm.

The transparent electrodes 131 and 132 are electrodes for applying an electric field to the pixel portion of the liquid crystal layer 107, and are generally formed of ITO (Indium).
Tin Oxide) is used. For the insulating films 141 and 142, general SiO ₂ or the like is used. Ordinary polyimide is used for the alignment films 151 and 152, and in the past, it was often formed to a thickness of about 600 °, but in the present embodiment, as described later, various polyimides are formed in a range of 50 to 620 °. It was formed to a thickness.

As shown in the schematic diagram of FIG. 4, the transparent electrodes 131 and 132 are composed of a plurality of linear transparent electrodes 131 arranged at equal intervals in one direction and a direction orthogonal to these. And a plurality of linear transparent electrodes 132 arranged at equal intervals.Each pixel is formed at a portion where the transparent electrodes 131 and 132 cross each other, and the pixels are arranged in a matrix as a whole. A display device is configured.

The polarization axes of the polarizing plates 111 and 112 are orthogonal to each other, and the direction of the polarization axis of one of the polarizing plates 111 (or 112) and the direction of the long axis of the liquid crystal molecules of the liquid crystal layer 107 match. The configuration between the transparent glass substrates 121 and 122 is the same as that of the polarizing plates 111 and 1.
A liquid crystal display element is formed by inserting the liquid crystal display element between the two.

In a configuration basically similar to the conventional one as shown in the schematic diagram of FIG. 5, the thickness of each of the alignment films 151 and 152 is changed in the range of 50 to 620 ° as follows. In this way, a ferroelectric liquid crystal display device was manufactured, and its memory characteristics were examined in detail.

First, ITO transparent electrodes 131 and 132 having an electrode width of 0.185 mm and a pitch of 0.2 mm are laminated on a glass plate.
On top of this, two transparent glass substrates 121 and 122 were formed by laminating SiO ₂ insulating films 141 and 142 each having a thickness of about 1000 °. After cleaning these transparent glass substrates 121 and 122, the insulating film 14
Polyimide as an alignment film 151, 152 was coated on each of 1, 142 with a spin coater in eight different thicknesses in the range of 50 to 620 ° and baked at 200 ° C. for 1 hour. Note that the alignment films 151, 1
The film thickness of polyimide as 52 is actually measured as 50, 118,
162, 225, 294, 403, 492 and 618 km.

Next, the surfaces of the alignment films 151 and 152 are rubbed with a cloth made of rayon, and two transparent glass substrates 121 and 122 are attached to the two alignment films 151 and 122 using glass spheres having an average particle diameter of 1.6 μm as spacers 106. The liquid crystal panel of 1024 × 768 pixels was fabricated by bonding the substrates 152 to each other.

The gap of the panel obtained as described above, that is, the distance between the two alignment films 151 and 152 was about 2 μm as measured. In the gap of this panel, a ferroelectric liquid crystal material containing a naphthalene-based liquid crystal material as a main component, which exhibits a bookshelf layer structure at the time of the smectic layer structure, is filled and a liquid crystal layer 10 is formed.
7 was formed. Next, the liquid crystal panel thus obtained was inserted between two polarizing plates 111 and 112 whose polarization axes were orthogonal to each other. At this time, when the ferroelectric liquid crystal is tilted to one of two stable states, the long axis of the liquid crystal molecule and one of the polarizing plates 111 are tilted.
(Or 112).

As described above, a plurality of identical liquid crystal panels were prepared except that the alignment films 151 and 152 were laminated with various thicknesses, and a memory characteristic was obtained as shown in the graph of FIG. Was defined as a memory ratio, and each memory characteristic was examined. More specifically, FIG. 6 shows that each of the liquid crystal panels (two each) having different thicknesses of the alignment films 151 and 152 is provided.
As shown in (a), a bipolar pulse having a voltage of ± 20 V and a pulse width of 200 μs was applied. And FIG.
As shown in (b), the transmitted light intensity at the time of pulse application
The ratio (Ia / Ib) of Ib and the transmitted light intensity Ia after 0.5 s from the time when the applied pulse voltage was removed is defined as the memory ratio, and the orientation film 1
The change of the memory ratio with the difference of the film thickness of 51 and 152 was examined in time series. Specifically, immediately after the alignment of the liquid crystal molecules in the liquid crystal layer 107 is adjusted (until the liquid crystal becomes isotropic,
Immediately after the liquid crystal alignment was adjusted by raising the temperature to ℃ and then gradually cooling to 25 ℃), after 2 days, 15 days and
Thirty days later, the memory ratio was checked. The results are shown in the graph of FIG.

The thickness of the alignment films 151 and 152 is 600 °
In this case, the memory ratio was as low as about 40% immediately after the alignment of the liquid crystal was adjusted (○), and two days after the alignment treatment.
(△) is about 10%, 15 days later (□) and 30 days later
For (x), the memory ratio was substantially "0".

On the other hand, it has been found that when the thickness of the alignment films 151 and 152 is reduced to 500 ° or less, a high memory ratio can be obtained. For example, when the film thickness of the alignment films 151 and 152 is set to 500 直 後, a high memory ratio of 90% or more is obtained immediately after the alignment treatment (、), and two days after the alignment treatment.
(△) also maintained a memory ratio of around 60%.

Further, when the thickness of the alignment films 151 and 152 is reduced to 300 °, for example, immediately after the alignment treatment (○), a high memory ratio of 90% or more is exhibited, and two days after the alignment treatment (△). Also showed a memory rate of 90% or more, and
After 50 days (□) and 30 days (×), the memory ratio was about 50%.

When the orientation films 151 and 152 are further thinned to, for example, 200 ° or less, there is almost no change over time with respect to the memory ratio, immediately after the orientation treatment ((), and 15 days (□) and 30 days ( In X), a sufficient memory ratio of about 80 to 90% was maintained.

By the way, it is possible to return the memory ratio, which has decreased with time, to the initial value by adjusting the orientation again, but for that purpose, it is necessary to raise the temperature of the liquid crystal until it isotropic. It takes some time. However, a memory ratio higher than the initial value cannot be obtained. From the above,
The film thickness of the alignment films 151 and 152 is suitably 500 ° or less, in which a high memory ratio can be obtained by adjusting the alignment, and is preferably 300 ° or less, in which the change over time is small and the number of alignment treatments can be reduced. However, it is more preferable that the film thickness is 200 ° or less, which hardly changes with time and the alignment treatment is required only once when the liquid crystal is sealed.

It has also been found that when the thickness of the alignment films 151 and 152 is further reduced, for example, when it is set to about 50 °, a high memory characteristic with substantially no change over time can be obtained. However, in this case, since the orientation of the liquid crystal was reduced, the transmitted light intensity in the dark state was improved, and the transmitted light intensity in the bright state was lowered, so that the contrast ratio was lowered. Specifically, the film thickness
75: 1 for 500Å, 18: 1 for 50Å
The contrast ratio decreased.

Accordingly, considering not only the memory characteristics but also the contrast ratio at the time of display, it can be said that the film thickness of the alignment films 151 and 152 is theoretically the optimum film thickness at which the liquid crystal is aligned.

Further, in order to support the above findings, the present inventors conducted an experiment on the effect of the thickness of the alignment films 151 and 152 on the polarization reversal peak current of liquid crystal molecules, and examined the results. This experiment was performed in exactly the same manner as the panel used in the above-mentioned experiment, that is, the film thickness of the alignment films 151 and 152 was 50, 118, 162, 225, 294, 403, 492 and 618 ° of 8 mm.
As shown in the waveform diagram of FIG. 8, each process of the polarization inversion peak current and the magnitude of the spontaneous polarization (Ps) were performed using ± 10 V as shown in FIG. A low frequency triangular wave of 1 Hz was applied, and the measurement was performed immediately after the orientation of the liquid crystal layer 107 and 15 days after that. Graphs of the measurement results are shown in FIG.

Each measurement object shown in FIG.
(Ps, Td, Tp, Ip, Tw, Tr) will be described. Ps is the magnitude of spontaneous polarization, and the unit is nC / cm ² . Td is the time between the point in time when the polarity of the applied triangular wave shown in FIG. 8B changes and the point in time when the polarization inversion starts before that. Tp is the time from when the polarity of the applied triangular wave shown in FIG. 8 (b) changes to when the polarization inversion reaches a peak. Ip is the peak current value of polarization reversal, and the unit is μ
A. Tw is the half-width time of Ip. Tr is the latter half of the polarization reversal (time after the peak). Note that Td,
The unit of Tp, Tw, and Tr is time, and specifically, ms.

FIG. 9 shows the measurement results of Ps. Here, Ps is represented as the area of the protruding portion on the graph as shown in FIG. 9 (a). Here, it is approximated by a triangle, and
The unit is the amount of charge per unit area (nC / cm ² ). FIG.
As shown in (b), Ps is not affected by the thickness of the alignment films 151 and 152 immediately after the alignment treatment (○ is +, △ is −) and after 15 days (● is +, black △ is −). There is no significant difference.

FIG. 10 shows the measurement results of Td. However, Td is the figure
As shown in FIG. 10 (a), this is the time between the time when the polarity of the applied triangular wave changes (broken line) and the time when the polarization inversion starts before that, and the unit is time (ms). Fig. 10 (b)
As shown in the figure, Td is immediately after the alignment treatment (○ is +, △
Both −) and 15 days later (● is +, black triangle is −) are longer as the thickness of the alignment films 151 and 152 increases. This is considered to be due to the effect of the reversal electric field accompanying the polarization reversal.

FIG. 11 shows the measurement results of Tp. Where Tp is
As shown in FIG. 11 (a), this is the time from when the polarity of the applied triangular wave changes (broken line) to when the polarization inversion reaches the peak, and the unit is time (ms). As shown in FIG. 11 (b), Tp was determined immediately after the alignment treatment (○ was +, △ was −).
After 15 days (● is +, black − is −), measurement results were significantly different. Immediately after the alignment treatment, the alignment films 151, 1
Although the value is almost constant irrespective of the film thickness of No. 52, after 15 days, a large difference was observed between the case where the + voltage was applied and the case where the − voltage was applied. Specifically, when a positive voltage is applied, the thickness of the alignment films 151 and 152 increases with increasing thickness.
Tp increases, and conversely, when-voltage is applied, the alignment film
As the film thicknesses of 151 and 152 increase, Tp decreases. This is considered to be because space charges of the same polarity are formed inside the cell when the + voltage is applied.

FIG. 12 shows the measurement results of Ip. Where Ip is
As shown in FIG. 12 (a), this is the peak current value of domain inversion, and the unit is ampere (μA). As shown in FIG. 12 (b), Ip was obtained immediately after the alignment treatment (152 is +, Δ is-) and after 15 days (● is +, black Δ is-). A measurement result was obtained that the smaller the film thickness, the larger the film thickness. However, this tendency is clearly larger after 15 days from the alignment treatment, and tends to show a larger value when the + voltage is applied than when the − voltage is applied.

FIG. 13 shows the measurement results of Tw. However, Tw is a figure
As shown in FIG. 13 (a), it is a half width, that is, a time width of a portion indicating a value of 1/2 of Ip, and a unit is time (ms).
As shown in FIG. 13 (b), Tw is immediately after the alignment treatment (○
The results show that the dispersion was larger 15 days later (● is +, black Δ is-) than + and △ is −), and that the dispersion became larger as the thickness of the alignment films 151 and 152 became larger. Was done. There is also a tendency that Tw itself increases as the thickness of the alignment films 151 and 152 increases.

FIG. 14 shows the measurement results of Tr. However, Tr is a figure
As shown in Fig. 14 (a), the second half of the polarization reversal
(Time after the peak), and the unit is time (ms).
As shown in FIG. 14 (b), Tr is 15 days after the alignment treatment (○ is +, Δ is −), as in the case of Tw described above (●
(+) And black (-) indicate that the variation is larger, and that the variation increases as the thickness of the alignment films 151 and 152 increases. Also, Tr itself is an alignment film.
There is also a tendency that the film thickness increases as the film thicknesses of 151 and 152 increase.

From the above results, when the film thickness of the alignment films 151 and 152 is thin, the value of Td is smaller than when the film thickness is large. It is also considered that uniform polarization reversal is performed from the fact that Ip is large and Tw is small. In addition, as compared with the case where the thickness of the alignment films 151 and 152 is thin, no large conversion is observed in each process of the polarization inversion even after 15 days from the alignment treatment, and the alignment films are stable over time. It is also easily understood.

Therefore, based on these experimental results, the experimental results of examining the above-mentioned memory characteristics, that is, the memory characteristics are higher when the thickness of the alignment films 151 and 152 are thinner than when they are thicker, and the time-dependent conversion is improved. It turns out that the small number is supported.

Finally, based on the above experimental results, the thickness of the alignment films 151 and 152 is set to 600 °
By making it thinner, the memory characteristics are high and
A high-definition, large-capacity display ferroelectric liquid crystal display device having 1024 × 768 pixels at a pitch of 0.2 mm was obtained.

In the above-described embodiment, a liquid crystal material having a bookshelf layer structure is used as the ferroelectric liquid crystal material. However, a ferroelectric liquid crystal material having a pseudo bookshelf layer structure that becomes a bookshelf layer structure by applying an electric field is used. Even when a liquid crystal material is used, substantially the same characteristics are exhibited.

In the above embodiment, the transparent glass substrates 121 and 122 are used, but it is needless to say that plastic or other transparent materials can be used as the substrates.

[0054]

As described in detail above, according to the ferroelectric liquid crystal display device of the present invention, the production cost can be reduced without greatly changing the prior art, specifically, by only thinning the alignment film. It is possible to improve the memory characteristics, which is a great feature of the ferroelectric liquid crystal display element, without increasing the memory characteristics. Further, by improving the memory characteristics, it is possible to provide a high-definition ferroelectric liquid crystal display element by inexpensive simple matrix type image display control.

[Brief description of the drawings]

FIG. 1 is a schematic view of a surface stabilized ferroelectric liquid crystal.

FIG. 2 is a schematic diagram of a state change of a ferroelectric liquid crystal display element.

FIG. 3 is a schematic sectional view of a conventional ferroelectric liquid crystal display device.

FIG. 4 is a schematic diagram of an electrode configuration of a ferroelectric liquid crystal display element.

FIG. 5 is a schematic sectional view of a ferroelectric liquid crystal display device of the present invention.

FIG. 6 is a graph showing definitions of memory characteristics of a ferroelectric liquid crystal display device.

FIG. 7 is a graph showing the relationship between the alignment film thickness and the memory characteristics of the ferroelectric liquid crystal display device of the present invention.

FIG. 8 is a graph showing the influence of the orientation film thickness on the polarization inversion peak current.

FIG. 9 is a graph showing the effect of the orientation film thickness on the polarization inversion peak current.

FIG. 10 is a graph showing the influence of the orientation film thickness on the polarization inversion peak current.

FIG. 11 is a graph showing the influence of the orientation film thickness on the polarization inversion peak current.

FIG. 12 is a graph showing the effect of the orientation film thickness on the polarization inversion peak current.

FIG. 13 is a graph showing the influence of the orientation film thickness on the polarization inversion peak current.

FIG. 14 is a graph showing the influence of the orientation film thickness on the polarization inversion peak current.

[Explanation of symbols]

 121, 122 Transparent glass substrate 151, 152 Alignment film 107 Liquid crystal layer

Continued on the front page (72) Inventor Hiroki Shirato 4-1-1, Kamidadanaka, Nakahara-ku, Kawasaki-shi, Kanagawa Prefecture Inside Fujitsu Limited (72) Inventor Tetsuya Makino 4-1-1, Kamiodanaka, Nakahara-ku, Kawasaki-shi, Kanagawa Inside Fujitsu Limited (72) Inventor Yoshinori Kiyota 4-1-1 Kamikadanaka Nakahara-ku, Kawasaki-shi, Kanagawa Fujitsu Limited

Claims (6)

[Claims] 1. A two-layer substrate in which a transparent electrode for applying an electric field to a liquid crystal and an alignment film for aligning the liquid crystal are arranged to face each other, and a bookshelf layer is provided in a gap between the alignment films. A ferroelectric liquid crystal display device in which a ferroelectric liquid crystal having a structure is sealed, wherein the thickness of the alignment film is 500 ° or less. 2. A two-layer substrate having a transparent electrode for applying an electric field to a liquid crystal and an alignment film for aligning the liquid crystal is disposed to face each other, and a pseudo bookshelf is provided in a gap between the alignment films. A ferroelectric liquid crystal display device in which a ferroelectric liquid crystal having a layer structure is sealed, wherein the thickness of the alignment film is 500 ° or less. 3. The ferroelectric liquid crystal display device according to claim 1, wherein the thickness of the alignment film is 300 ° or less. 4. The ferroelectric liquid crystal display device according to claim 1, wherein the thickness of the alignment film is 200 ° or less. 5. The ferroelectric liquid crystal display device according to claim 1, wherein the thickness of the alignment film is a minimum thickness at which each molecule of the liquid crystal is aligned. . 6. The ferroelectric liquid crystal display device according to claim 1, wherein said alignment film is a polyimide resin.