JPS62231934A - Optical modulating element - Google Patents

Abstract

PURPOSE:To easily form a display panel which has high-density picture elements over wide area and to obtain an optical modulating element which is driven suitably by providing an area where orientation control force which orients an optical modulating material is mutually different among the picture elements. CONSTITUTION:Liquid crystal molecules 13 have dipole moment (Prt. angle)14 at right angles to the molecules. A voltage higher than a certain threshold value is applied between electrodes on substrates 11 and 11' and then the spiral structure of the liquid crystal molecules 13 are loosened and the orientation direction of the liquid crystal molecules 13 is changed so that the dipole moment (Prt. angle)14 is all put in an electric field direction. The liquid crystal molecules 13 are thin and long and have refractive index anisotropy between long-axis and short- axis direction, so polarizers are placed in mutually crossed nicols position relation on both sides of, for example, a glass surface to obtain a liquid crystal optical modulating element which changes in optical characteristics according to the polarity of the applied voltage.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to optical modulation elements for display panels, and in particular to display panels using liquid crystals having at least two stable states, such as ferroelectric liquid crystals.

[Conventional technology]

In a liquid crystal television panel using a conventional active matrix driving method, thin film transistors (TPTs) are arranged in a matrix for each pixel, and a gate-on pulse is applied to the TPTs to bring the source and drain into a conductive state. is applied from the source and stored in the capacitor, and a liquid crystal (for example, twisted nematic: TN-liquid crystal) is driven in response to this stored image signal.At the same time, by modulating the voltage of the video signal, gradation display is performed. It is being done.

[Problem that the invention seeks to solve]

However, in active matrix drive type television panels using such TN liquid crystals, the TPT used is
Because TPT has a complicated structure, there are many structural steps, high manufacturing costs are a bottleneck, and the thin film semiconductors (e.g., polysilicon, amorphous silicon) that make up TPT are required to cover a wide area. However, there are problems such as difficulty in forming a film.

On the other hand, a passive matrix drive type display panel using TN liquid crystal is known as a device that can be manufactured at low manufacturing cost, but in this display panel, as the number of scanning lines (N) increases, one screen (l frame) During scanning, the time during which an effective electric field is applied to one selected point (duty ratio) decreases at a rate of l/N, which causes crosstalk and causes problems such as not being able to obtain high contrast images. In addition to having drawbacks, such as the fact that when the duty ratio becomes low, it becomes difficult to control the gradation of each pixel by voltage modulation, it is not suitable for display panels with a high density of wiring, especially liquid crystal television panels.

[Means for Solving the Problems] and [Operations] The object of the present invention is to eliminate the above-mentioned drawbacks. Specifically, it is an object of the present invention to easily create and drive a display panel having high-density pixels over a wide area. An object of the present invention is to provide an optical modulation element suitable for.

Another object of the present invention is to provide an optical modulation element particularly suitable for gradation display.

The present invention provides an optical modulation element in which pixels are two-dimensionally arranged, each having a first electrode and a second electrode facing each other, and an optical modulation substance disposed between the first electrode and the second electrode. The liquid crystal element is characterized in that the alignment regulating force for aligning the optical modulation substance has different regions within the pixel. Furthermore, it is possible to provide an optical modulation element that expresses gradation within a pixel by additionally applying a pulse signal with a peak value corresponding to the gradation, or a signal with a pulse width or pulse number depending on the gradation. I can do it.

<Example> The present invention will be explained below with reference to the drawings.The optical modulating substance that can be used in the present invention includes
a second optically stable state (e.g. shall form a bright state) and a second optically stable state (e.g. shall form a dark state), i.e. at least two stable states with respect to the electric field. Materials, especially liquid crystals, having these properties are most suitable.

As the liquid crystal having at least two stable states that can be used in the optical modulation element of the present invention, chiral smectic liquid crystal having ferroelectricity is most preferable, and among these, chiral smectic C phase (SmC*), H phase (5m8
), I phase (SmI*), F phase (SmF*), and G phase (
SmG*) liquid crystal is suitable. Regarding this ferroelectric liquid crystal, please refer to "LE JOURNAL DE P
HYSIQUE LETTRE゛) Volume 36 (L-6
9) 1975 “Ferroelectric Liquid
Crystals” (rFerroelectric L
iquidCrystalSJ)
: ”Applied φ Business Letters (“Ap
pliedPhysics Letters') 3rd
Volume 6, No. 11, 1980 "Submicro Second Φ Bi-Stipple Φ Electro-optic Switching in Liquid Fist Ristars J (rsub
micro 5econdBistable El
electrooptic Switching in
LiquidCrystals'): solid state physics 6 (1
41) 1981 r Liquid Crystal, etc., and the ferroelectric liquid crystal disclosed therein can be used in the present invention.

More specifically, examples of ferroelectric liquid crystal compounds used in the method of the present invention include decyloxybenzylidene-y-amino-2-methylbutylcinnamate (DOBAMBC).
, hexyloxybenzylidene-y-amino-2-chloropropylcinnamate (HoBACPC) and 4-
Examples include o-(2-methyl)-butylresolsiliten-4'-octylaniline (MBRA8).

When constructing an element using these materials, the liquid crystal compound is SmC*, 5m8 pieces, SmI wood, SmF wood, Sm
In order to maintain the temperature state such that G-tree is obtained, the element can be supported by a copper block or the like in which a heater is embedded, if necessary.

FIG. 1 schematically depicts an example of a ferroelectric liquid crystal cell. 11 and 11' are I n203 .

It is a substrate (glass plate) coated with a transparent electrode such as Sn02 or ITO (indium tin oxide), between which is a SmC main phase 0 liquid crystal oriented so that the liquid crystal molecular layer 12 is perpendicular to the glass surface. It is enclosed. A thick line 13 represents a liquid crystal molecule, and this liquid crystal molecule 13 has a dipole moment in the direction perpendicular to the molecule.
(P top) It has 14. When a voltage higher than a certain threshold is applied between the electrodes on the substrate 11 and l l', the liquid crystal molecules 1
The helical structure of 3 unravels and a dipole moment) (on P)
The alignment direction of the liquid crystal molecules 13 can be changed so that all of the liquid crystal molecules 14 are oriented in the direction of the electric field. The liquid crystal molecules 13 have an elongated shape and exhibit refractive index anisotropy in the long axis direction and the short axis direction. Therefore, for example, if polarizers are placed above and below the glass surface in a crossed nicol positional relationship, the voltage will be reduced. It is easily understood that this results in a liquid crystal optical modulation element whose optical characteristics change depending on the applied polarity. Furthermore, when the thickness of the liquid crystal cell is made sufficiently thin (for example, IP), the helical structure of the liquid crystal molecules unravels (non-helical structure) even when no electric field is applied, as shown in Figure 1. The dipole moment) P or y is oriented either upward (24) or downward (24'). When an electric field E or r of different polarity above a certain threshold value is applied to such a cell as shown in FIG. change the
Accordingly, the liquid crystal molecules enter the first stable state 23 (bright state)
or the second stable state 23' (dark state).

There are two advantages to using such a ferroelectric liquid crystal as an optical modulation element. First, the response speed is extremely fast.
Second, the alignment of liquid crystal molecules has bistability.

To explain the second point with reference to FIG. 2, for example, when the electric field E is applied, the liquid crystal molecules are oriented in the first stable state 23, but even when the electric field is turned off, the first stable state 23 is maintained. , and when an electric field E' in the opposite direction is applied, the liquid crystal molecules align to the second stable state 23' and change their orientation, but they remain in this state even after the electric field is cut off, and each stable state remains unchanged. It has a memory function. In order to effectively realize such fast response speed and bistability, it is necessary to
It is preferable for the cell to be as thin as possible, and generally 0
．． 5 m to 20 m, especially 1 μm to 5 gm are suitable. A liquid crystal-electro-optical device having a matrix electrode structure using ferroelectric liquid crystals of this kind has been proposed, for example, by Clark and Ragaval in US Pat. No. 4,367,924.

Next, details of the liquid crystal optical element according to the present invention will be explained.

FIG. 3 shows an embodiment of the present invention.

31 is one substrate, and glass, plastic, or the like is used. A first electrode 3 made of ITO or the like is placed on this substrate 31.
2 and an orientation control layer 33 are laminated.

The optical modulation material 1 is sandwiched between the other substrate 34 and the substrate 31 which are opposite to this.

On this substrate 34, a second electrode 35 and an alignment control layer 36 are formed.
are stacked, and the distance between the substrates 31 and 34 is controlled by a spacer 37.

FIG. 4 shows a plan view of the orientation control layer 33 formed on one of the substrates 31 described above. This orientation control layer 33 is
It has different alignment regulating force regions, that is, a first alignment regulating force region 101 and a second alignment regulating force region 102, and the first alignment regulating force region 101 is within the second alignment regulating force region 102. It is distributed in a dispersed manner. Therefore.

The first region 101 and the second region 102 have uniaxial alignment axes (for example, rubbing treatment axes) in the same direction, but the alignment regulating forces of the uniaxial alignment axes are different from each other.

The aforementioned orientation control W! As a method for obtaining the substrate 31 provided with the substrate 33, for example, the substrate 31 is made of glass or plastic.
ITO (indium tin oxide) or the like is uniformly deposited on the substrate 31 as an electrode 32 to a thickness of about 3000 mm by sputtering, and then a polyvinyl alcohol aqueous solution is uniformly deposited on the substrate 31 by a spinner or dipping. A polyvinyl alcohol film (corresponding to the second orientation regulating force region 102) having a thickness of about 100 to 2000 mm is hardened by heat treatment at 180° C. for 30 minutes, and a polyimide precursor solution (for example, A solution of a condensate of pyromellitic anhydride and 4,4'-diaminodiphenyl ether dissolved in N-methylpyridone) was applied via spray or mesh, and then heat treated at about 180°C for 1 hour. There is a method of forming polyimide (corresponding to the first orientation regulating force region lot) and further performing a rubbing treatment as a -axial orientation treatment.

In order to form uniaxial alignment axes with different alignment control forces, in addition to the above-mentioned combination of polyvinyl alcohol/polyimide, polyvinyl alcohol/polyamide, polyvinyl alcohol/silane camping agent, polyimide/polyamide, polyimide/silane coupling can be used. Combinations of different organic polymers or monomers such as agents can be used. Further, in the present invention, the first orientation regulating force region 101 is
It is possible to use a combination in which the film is made of an inorganic insulating material such as iO or SiO and the second alignment regulating force region 102 is made of an organic polymer film, or the opposite combination.

Further, in the present invention, as the other orientation control fi 36, a coating formed uniformly with polyvinyl alcohol, polyimide, polyamide, or a silane coupling agent and subjected to a rubbing treatment can be used.

In the present invention, since the uniaxial alignment regulating forces for the ferroelectric liquid crystal in the first alignment regulating force region 101 and the second alignment regulating force region 102 are different from each other, the threshold voltage of the ferroelectric liquid crystal is The area 101 and the second area are different.

Therefore, the inversion start voltages in the first region 101 and the second region 102 are different. For example, in the above-mentioned combination of polyvinyl alcohol/polyimide, the polyimide corresponding to the first region lot is different from the polyvinyl alcohol corresponding to the second region 102. Because it tends to lower the threshold voltage compared to alcohol,
An inversion nucleus is generated in the first region lO1.

In a preferred embodiment of the invention, polyvinyl alcohol/
An alternating current can be applied to a liquid crystal element using an orientation controlling GG film combined with polyimide. The AC used in this case is 1
0Hz to 1KHz, 20V to 200Va degrees,
A ferroelectric liquid crystal compatible with a polyvinyl alcohol alignment control film can be brought into a uniform alignment state with a large tilt angle. The threshold voltage of the ferroelectric liquid crystal in the uniform orientation state is lower than that in the spray orientation state, so the threshold voltage of the ferroelectric liquid crystal corresponding to the polyimide film in the spray orientation state can be ensured. can be as low as possible.

The "uniform orientation state" described in this specification means that the helix of one ferroelectric liquid crystal is unwound under the condition that no voltage is applied, and the projections of liquid crystal molecules adjacent to both substrates onto the substrates are parallel to each other or This refers to a state in which they intersect at an angle close to parallel, and the "spray alignment state" refers to a state in which the projections on both substrates mentioned above intersect with each other at a predetermined angle. When an alternating current is applied to a ferroelectric liquid crystal element, it becomes a uniform alignment state, whereas a ferroelectric liquid crystal element with a polyimide alignment control film does not become a temouniform alignment state when an alternating current is applied, but becomes a spray alignment state. ing. In general, a ferroelectric liquid crystal in a splay alignment state has a smaller threshold voltage than a ferroelectric liquid crystal in a uniform alignment state.

FIG. 5 schematically shows the inversion of molecules due to voltage application in the general cell of the ferroelectric liquid crystal described above.

Immediately after the voltage starts to be applied, a partial inversion 51 occurs in the voltage application part (Fig. 5(a)).After this, the voltage is applied as shown in Fig. 5(b) and (e). As time passes under the voltage, the inverted portion gradually expands around the inverted target 51 to form an inverted region 52. Furthermore, if the voltage is continued to be applied, most of the voltage will reverse (Fig. 5(d)).
, and finally the entire voltage application area is inverted.

This reversal can be seen, for example, in Orihar.
° “Switching Characteristics of Ferroelectric Liquid Crystal Dobanbok” by a) and I, Ishibashi
("Swi t Ch er a
cteristics of Ferroelec
t ric Liquid Cry s t e
IDOBAMBC")-Japanese Journal
of Applied Physics), (Japan
se Journal of Applied P
hysics), Volume 23, No. 10, October 1984
May, pp. 1274-1277.

In addition to the above-mentioned ferroelectric liquid crystal, TN liquid crystal or the like can be used as the optical modulation material in the present invention.

As described above, the present invention is based on a method of intentionally forming an inversion layer in a pixel and forming an inversion region around the inversion layer. For example, the first region 1 formed in the alignment control layer 33
Inversion of the ferroelectric liquid crystal starts around 01, and furthermore, the pulse signal cylinder is turned on. V I+
The size of the reversal area that will grow around the area 101 is determined by taking +Mari 1 of the leaf.

In addition, when applying a matrix electrode formed of a scanning electrode and an information electrode to the optical modulation element of the present invention and performing line sequential writing, the driving method disclosed in Japanese Patent Application Laid-open No. 193427/1983 is adopted. In other words, in the present invention, the ferroelectric liquid crystal is oriented in one stable state that corresponds to the black level of pixels on the write line.

Next, by applying the pulse signals shown in Figures 6 to 8 below from the information electrode, the strong Li and Li liquid crystals are inverted to the other stable state corresponding to the white level, and this operation is performed line by line. By performing this sequentially, one screen of gradation display can be obtained.

Figures 6 to 8 show the first [J4i32 and the second
6 shows the applied pulse width, FIG. 7 shows the number of applied pulses, and 8 shows typical examples of the voltage applied between the L pole 35.
In the figure, a gradation display can be obtained by interpreting the applied pulse voltage values (peak values). (a) to (d) in each of Figs. 6 to 8 are schematically shown in Figs. 5(a) to 8.
This corresponds to (d).

6 and 7 are examples of voltage application most suitable for the optical modulation element of the present invention. That is, the pulse waveforms (a) in FIGS. 6 and 7 are
By applying the voltage between 1 and 2, the optical modulating material in the region 101 where an inverted nucleus is first formed starts to invert, becomes a nucleus, and the inverted part starts to spread. If you change the voltage application here,
If this is done, the current state will be memorized, especially in the case of a bistable optical modulation material.

Next, if the voltages shown in (b) to (d) in Figures 6 and 7 are applied, or the pulses are applied, the inverted portion will expand, and the state at the time when the voltage application is stopped will be memorized and the level will rise. This allows for tonal expression.

According to the method of changing the applied voltage value shown in FIG. 8, the pulse shown in FIG. 8(a) causes the formation of the inversion nucleus, and the voltage as shown in FIG. 8(b) to (d) is When the value is increased, the responsiveness of the optical modulation material improves, so the region of inversion becomes larger, but even in this case, the part with a small inversion threshold voltage is inverted first, and the region of inversion expands within the peak of the applied pulse. considered to be a thing. In this case, if the pulse application time is too long, the ferroelectric liquid crystal will be inverted in the region 102, so the pulse application time should be set to 31.
! Do 1.

〔Effect of the invention〕

According to the present invention, it is possible to provide an optical modulation element suitable for a high-density pixel display panel or a light shutter array,
Moreover, it has the advantage of being able to provide a ferroelectric liquid crystal element suitable for a display panel that expresses gradation by simply changing the pulse width, number of pulses, or wave height E of a pulse signal depending on the gradation.

[Brief explanation of drawings]

1 and 2 are perspective views schematically showing a ferroelectric liquid crystal element used in the present invention. FIG. 3 is a sectional view of the optical modulation element of the present invention, and FIG. 4 is a plan view of its orientation control layer. FIGS. 5(a) to 5(d) are explanatory diagrams schematically showing inverted states of pixels. Figure 6 (&) - (d), Figure 7 (a) - (d) and Figure 8
Figures (a) to (d) are waveform diagrams showing specific examples of pulse signals used in the present invention. Patent applicant Canon Co., Ltd. Penalty 50 (fl) (0) Moan 1 - ( t

Claims (11)

[Claims] (1) In an optical modulation element in which pixels are two-dimensionally arranged, each having a first electrode and a second electrode facing each other, and an optical modulation substance disposed between the first electrode and the second electrode. ,
An optical modulation element characterized in that the alignment regulating force for orienting an optical modulation substance has different regions within the pixel. (2) The optical modulation element according to claim 1, wherein the optical modulation substance is a ferroelectric liquid crystal. (3) The optical modulation element according to claim 2, wherein the ferroelectric liquid crystal is a chiral smectic liquid crystal. (4) Claim 1, in which the regions of mutually different alignment regulating forces correspond to mutually different regions of the alignment control layer.
The optical modulation element described in . (5) The optical modulation element according to claim 1, wherein the orientation control layer is formed of an organic polymer layer. (6) The pixels are arranged along a plurality of rows and columns, and the pixels in each row are commonly connected to a scanning electrode,
2. The optical modulation element according to claim 1, wherein the pixels in each column are connected to an information electrode, and further comprises means for applying a pulse signal according to a gradation to the information electrode. (7) The optical modulation element according to claim 6, wherein the pulse signal is a pulse signal having a pulse width corresponding to a gradation. (8) The optical modulation element according to claim 6, wherein the pulse signal has a number of pulses depending on the gradation. (9) The optical modulation element according to claim 6, wherein the pulse signal is a pulse signal having a peak value corresponding to a gradation. (10) The optical modulation element according to claim 6, wherein the pulse signal is a signal applied after the optical modulation substance in the pixel is oriented in one stable state. (11) The different alignment regulating force regions have a first alignment regulating force region and a second alignment regulating force region, and the first alignment regulating force region is within the second alignment regulating force region. The optical modulation element according to claim 1, wherein the optical modulation element is distributed in a dispersed manner.