JPS62231940A - Optical modulation element - Google Patents

Abstract

PURPOSE:To obtain an optical modulation element being suitable for displaying a gradation, by constituting it so that an electric field intensity which is formed at the time when an electric field has been applied between the first and the second electrodes is different in a picture element, and a part where the electric field intensity is different is dispersed and distributed in the picture element. CONSTITUTION:In an optical modulation element, a picture element having the first electrode 32 and the second electrode 35 which are opposed to each other, and an optical modulation substance 1 which has been placed between the first electrode 32 and the second electrode 35 is arranged two-dimensionally. Also, an electric field intensity which is formed at the time when an electric field has been applied between the first electrode 32 and the second electrode 35 is different in the picture element, and such a part where the electric field intensity is different is dispersed and distributed in the picture element. In this way, a pulse signal of a crest value corresponding to a gradation, or a pulse signal of width of a pulse or the number of pulses corresponding to the gradation is applied and an optical modulation element which can express a gradation property in the picture element is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an optical modulation element for a display panel, and in particular to a display panel using a liquid crystal with at least two stable states, such as a ferroelectric liquid crystal.

[Conventional technology]

In LCD television panels using the conventional active matrix drive method, thin film transistors (TPT)
are arranged in a matrix for each pixel, and a gate-on pulse is applied to the TPT to bring the source and drain into a conductive state.At this time, a video image signal is applied from the source and stored in the capacitor, and the capacitor corresponds to the stored image signal. A liquid crystal (for example, a twisted nematic liquid crystal) is driven, and gradation display is performed by simultaneously modulating the voltage of a video signal.

<Problems to be solved by the invention> However, in active matrix drive type television panels using such TN liquid crystals, the TPT used is
Because TPT has a complicated structure, the number of structural steps is large, and high manufacturing costs are a bottleneck. This may cause problems such as difficulty in forming a film over the entire area.

On the other hand, it can be manufactured at low manufacturing cost.
A passive matrix drive type display panel using a liquid crystal is known, but in this display panel, as the number of scanning lines (N) increases, the number of effective points for one selection point increases while scanning one screen (l frame). The time during which the electric field is applied (duty ratio) decreases at a rate of 17N, which causes crosstalk and does not provide a high contrast image. When the voltage becomes low, it becomes difficult to control the gradation of each pixel by voltage modulation, making it unsuitable for display panels with high-density wiring, especially liquid crystal television panels.

[Means for solving problems]

An object of the present invention is to eliminate the above-mentioned drawbacks, and specifically to provide an optical modulation element suitable for easily producing and driving a display panel having high density pixels over a wide area.

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

That is, the present invention provides an optical modulation system 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 wIJl electrode and the second electrode. In the element, when an electric field is applied between the first electrode and the second electrode, the electric field strength that is formed differs within the pixel, and the regions where the electric field strength differs are dispersed within the pixel. It is characterized by distributed optical modulation elements. In particular, the present invention provides an optical modulation element that can express gradation within a pixel by applying a pulse signal with a peak value corresponding to the gradation, or a pulse signal with a pulse width or number of pulses depending on the gradation. can do.

<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 (for example, forming a bright state) and a second optically stable state (for example, forming a dark state). That is, a material that has at least two stable states in response to an electric field, particularly a liquid crystal that has such properties, is optimal.

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 one ferroelectricity is most preferable, and among these, chiral smectic C phase (SmC phase), H phase (5m
8 pieces), I phase (SmI pieces), F phase (SmF tree) and G phase (
Sm0) 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
"Liquid Crystals"): "Applied Physics Letters"("Applfed
Physics Letters”) Volume 36,
No. 11, 1980 “Submicro φ second bistiple electro-optic switching”
Insha Liquid Crystals J (rsubmic
ro 5ecand B15table Ele
ctro.

ptic Switching in Liquor
id Crystals”)”Solid State Physics 16 (141
), 1981 R Liquid Crystal, etc., and the ferroelectric liquid crystal disclosed in these documents 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)-butylresolcylidene=4'-octylaniline (MBRA8).

When constructing an element using these materials, the liquid crystal compound may be SmC wood, SmH wood, one Sm, 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.

Figure 1 schematically depicts an example of a ferroelectric liquid crystal cell. 11 and 11' are substrates (glass plates) coated with transparent electrodes such as In203SnO2 or ITO (indium tin oxide), and between them, the liquid crystal molecular layer 12 is placed directly on the glass surface. Oriented Sm
A liquid crystal with a C wood phase is enclosed. A thick line 13 represents a liquid crystal molecule, and this liquid crystal molecule 13 has a dipole moment (P) 14 in a direction perpendicular to the molecule. When a voltage higher than a certain threshold is applied between the substrate 11 and the electrodes on l l', the helical structure of the liquid crystal molecules 13 is unraveled, and the liquid crystal molecules 13 are adjusted so that all the dipole moments (on P) 14 are oriented in the direction of the electric field. The orientation direction can be changed. 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 cross-niffle positional relationship with each other, the voltage 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, 1#L), the helical structure of the liquid crystal molecules is unraveled (non-helical structure) even when no electric field is applied, as shown in Figure 2. Its dipole moment P or y is in the 1-direction (
24) or downward; (24'). When an electric field E or E' of different polarity above a certain threshold value E is applied to such a cell as shown in FIG. or downward 24', and accordingly the liquid crystal molecules are aligned in either 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, the electric field E
When the electric field is turned off, the liquid crystal molecules are aligned in the first stable state 23.
3 is maintained, and when an opposite electric field E' 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 turned off.
Each has a steady state memory function. In order to effectively realize such fast response speed and bistability, it is preferable that the cell be as thin as possible, and generally 0.5 m to 20 μm, particularly lkm to 5 gm, is suitable. . A liquid crystal-electro-optical device having a matrix electrode structure using a ferroelectric liquid crystal of this type has been proposed, for example, by Clark and Ragapal 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 or plastic is used. On this substrate 31, a first electrode 3 made of ITO or the like is placed.
2 and orientation control P933 are layered.

Opposed to this, the other substrate 34 is arranged with the optical modulation material l sandwiched between the two substrates, and a second
An electrode 35 and an orientation control layer 36 are provided.

Here, in FIG. 3, the first electrode 32 on the substrate 31
In this case, fine protrusions 40 with dispersed layer thicknesses are formed.

The substrates 31 and 34 are spaced apart by a spacer 37.
It is controlled to ~5gm.

By providing the first electrode 32 with dispersive irregularities as described above, when a voltage is applied between the first electrode 32 and the second electrode 35, the optical modulation material corresponding to the protrusion 40 is The electric field strength acting on the optical modulation material 102 corresponding to the portion 101 and the recess 41 is different, and a dispersive distribution of electric field strength changes is formed. That is, a relatively high electric field acts on the region 101 corresponding to the protrusion 40 with respect to the region 102 . FIG. 4 shows this as a schematic front view of one pixel of the optical modulation element.

41 in FIG. 4 corresponds to the aforementioned protrusion 40, and 42 corresponds to the aforementioned recess 41.

Methods for forming the aforementioned protrusions 40 include the sandglass method as clarified in the examples below, and the method of partially depositing a conductive material on a uniform conductive film as clarified in the examples. There is.

By doing the above, the following effects can be obtained. FIG. 5 schematically shows the inversion of molecules due to voltage application in a general cell of the above-mentioned forced liquid crystal.

First, immediately after the voltage starts to be applied, a reversal phenomenon 51 occurs partially in the voltage application part (FIG. 5(a)), and then as shown in FIGS. 5(b) and 5(C). As time passes under the applied voltage, the inverted portion gradually expands around the inverted target 51 and an inverted region 52 is formed.

Furthermore, if the voltage is continued to be applied, most of the voltage is reversed (FIG. 5(d)), and finally the entire area where the voltage is applied is reversed. This reversal can be seen, for example, in Orihara and Ishibashi.
) by °゛Switching Characteristic Sioux-Sha Ferroelectric Liquid-Crystal
Dobanpok°' (”SwitchingChera
cteristics of Ferroelectr
ic LiquidCrystel DOBAMB
C”) - Japanese Φ Journal of Applied Physics (Japanese J o
urnal of Applied Phys.
sics), Volume 23, No. 10, October 1984,
It is described on pages 1274-1277.

Further, in the present invention, a TN liquid crystal or the like can be used as an optical modulating substance in addition to the above-mentioned ferroelectric liquid crystal.

In this way, the present invention intentionally forms an inversion layer within a pixel,
The method is based on a method of forming an inversion area around the inversion area, and for example, the electric field intensity acting on the portion 101 of the ferroelectric liquid crystal corresponding to the protrusion 40 formed on the first electrode 32 is as follows.
Since the electric field is relatively high, the actual inversion occurs at this location l
ot, and further the number of pulses of the pulse signal,
Depending on the magnitude of the pulse width or peak value, the part 101
The size of the reversal region that grows around is determined.

Further, 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, a driving method disclosed in Japanese Patent Application Laid-open No. 193427/1980 is adopted. In the present invention, the pixels on the write line are oriented in one stable state corresponding to the black level, and then the ferroelectric liquid crystal is oriented in one stable state corresponding to the black level, and then the ferroelectric liquid crystal is aligned as shown in FIGS. By applying a pulse signal from the information electrode, the ferroelectric liquid crystal is inverted to the other stable state corresponding to the white level, and by sequentially performing this operation line by line, one screen of gradation display can be obtained. It will be done.

6 to 8 show typical examples of voltage applied between the first electrode 32 and the second electrode 35. FIG. 6 shows the applied pulse width, and FIG. 7 shows the applied pulse. In FIG. 8, a gradation display can be obtained by selecting the applied pulse voltage value (peak value).

(a) to (d) in each of FIGS. 6 to 8 schematically correspond to FIGS. 5(a) to (d).

WS6 and FIG. 7 are examples of voltage application most suitable for the optical modulation element of the present invention. That is, by applying the pulse waveform (a) in FIGS. 6 and 7 between the electrodes 32 and 35 in FIG. It starts to invert, becomes a nucleus, and the inverted part begins to spread.

If the voltage application is stopped at this point, the current state will be memorized, especially in the case of a bistable optical modulation material.

Next, by applying the voltage or pulse shown in (b) to (d) in Figures 6 and 7, the inverted portion will expand,
The state at the time when voltage application is stopped is memorized, and gradation can be expressed.

According to the method of changing the applied voltage value shown in FIG. 8, the inversion nucleus is formed by the pulse shown in FIG. 8(a), and ? As shown in tIJB diagrams (b) to (d), increasing the voltage value improves the response of the optical modulation material, so
Although the region to be inverted becomes larger, it is thought that at this time as well, the portion where the electric field strength is large is first inverted, and the inverted region expands within the applied pulse width. If the pulse application time in this case is too long, inversion will occur over the entire range even in a low voltage range (for example, near the reversal threshold of the optical modulation material used), so the pulse application time should be adjusted appropriately.

Specific examples are listed below. Example 1 ITO (indium tin oxide) was deposited as a conductive layer on a glass substrate by a sputtering method to a thickness of about 4,000 yen.
The surface of the ITO film was roughened by uniformly distributing it to a thickness of 100 mm, and by evenly colliding the entire surface with #400 to #800 abrasive grains. A Si02 film is formed on the surface as an electrode protective layer to a thickness of about 1000 mm by EB (electron beam) evaporation, and polyimide or polyvinyl alcohol is further formed on this surface as an orientation control layer to a thickness of about 1000 to 2000 mm by spinner or dipping. Established. A rubbing treatment is performed on the orientation control layer to obtain a one-sided substrate. The counter substrate used was a glass substrate on which ITO was uniformly deposited, the polyimide or polyvinyl alcohol was uniformly deposited, and an orientation treatment such as rubbing was performed.

A cell was created using such two glass substrates, and DOBAMBC was injected into this cell to produce a ferroelectric liquid crystal element.

When the pulse signals shown in FIGS. 6(a) to 6(d) were applied to this ferroelectric liquid crystal element, the formation of inverted regions shown in FIGS. 5(a) to 5(d) was observed.

Example 2 Approximately 30% ITO was applied as an electrode on a glass substrate in the same manner as above.
Provided with a thickness of 400 to 800 mesh on the surface.
After masking the mesh and applying ITO again by sputtering to make the surface uneven, 5i02 was applied as an electrode protection layer and polyvinyl alcohol was applied as an orientation control layer as in the previous example, and a rubbing treatment was performed. One side board.

As a result, in Examples 1 and 2, in which the same results as in Example 1 were obtained, the uneven portions were formed only on one side of the substrate, but in the present invention, the above-mentioned uneven portions were formed on both substrates. can do. Further, as another specific example of the present invention, ITO11 is coated on a substrate such as glass or plastic.
4 is provided in the same manner as above, and a relatively high-resistance, for example, SnO2 film is uniformly provided on the surface to a thickness of about 3,000 mm, and then a metal such as Au or A is passed through the mesh or other A is deposited in a dispersive manner by the method described above, the SnO2 film is doped with metal by thermal diffusion, and the remaining metal is removed by etching, resulting in a relatively low resistance of the doped portion.
A film having dispersively different resistance values can be obtained. Thereafter, by forming a substrate by providing an electrode protection layer and an alignment control layer in the same manner as described above, it is possible to impart a subtle dispersive change in the electric field applied to the optical modulation substance.

〔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 an optical shifter, and simply change the pulse width, pulse number, or peak value of a pulse signal according to the gradation. This has the advantage that a ferroelectric liquid crystal element can be used in a display panel that expresses 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 thereof. FIGS. 5(a) to 5(d) are explanatory diagrams schematically showing inverted states of pixels. Figure 6(a)~
(d) Figures 7 (a) to (d) and Figures 8 (a) to (d)
1 is a waveform diagram showing a specific example of a pulse signal used in the present invention.

Claims (9)

[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. ,
The electric field intensity formed when an electric field is applied between the first electrode and the second electrode is different within the pixel, and the areas where the electric field intensity is different are distributed in a dispersed manner within the pixel. An optical modulation element characterized by: (2) Claim 1, wherein the different electric field strength portions correspond to portions where modulation initiation nuclei of the optical modulation substance are generated.
The optical modulation element described in . (3) The optical modulation element according to claim 1, wherein the different electric field strength portions correspond to minute protrusions formed within the pixels. (4) The optical modulation according to claim 1, wherein the different electric field strength regions correspond to low resistance regions formed in at least one of the first electrode and the second electrode in the pixel. element. (5) The optical modulation element according to claim 1, wherein the electric field applied between the first electrode and the second electrode is a pulse signal with a pulse width depending on the gradation. (6) The optical modulation element according to claim 1, wherein the electric field applied between the first electrode and the second electrode is a pulse signal with a number of pulses depending on the gradation. (7) The optical modulation element according to claim 1, wherein the electric field applied between the first electrode and the second electrode is a pulse signal having a peak value corresponding to a gradation. (8) The optical modulation element according to claim 1, wherein the optical modulation substance is a ferroelectric liquid crystal. (9) The optical modulation element according to claim 8, wherein the ferroelectric liquid crystal is a chiral smectic liquid crystal.