JPH07122703B2 - Optical modulator - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to an optical modulation element for a display device, and more particularly to an optical modulation element that performs halftone display by using an inversion region partially formed in a pixel. And a display method using the same.

[Prior Art] A liquid crystal display device using a twisted nematic (TN) liquid crystal is known that uses a display panel of a passive matrix drive system and an active matrix drive system.

In an active matrix drive type liquid crystal television panel, thin film transistors (TFT) are arranged in a matrix for each pixel, and a gate-on pulse is applied to the TFT to establish a conduction state between the source and the drain. At this time, a video image signal is applied from the source. Then, the TN liquid crystal is driven in response to the stored image signal and stored in the capacitor, and at the same time, gray scale display is performed by modulating the voltage of the video signal.

Such a gradation display method is called luminance gradation,
The halftone display in this case controls the light transmittance of the entire pixel.

[Problems to be Solved by the Invention] However, in an active matrix driving type television panel using such a TN liquid crystal, the light transmittance completely depends on the applied electric field. Will fluctuate.

Moreover, since the viewing angle is narrow, the appearance of the halftone state changes depending on the viewing position.

Alternatively, in a passive matrix drive type display panel that can be manufactured at low manufacturing cost, an effective electric field is applied to one selection point while scanning one screen (one frame) as the number of scanning lines (N) increases. The time (duty ratio) is reduced at a rate of 1 / N, which causes crosstalk. Moreover, in addition to having a technical problem to be solved in that a high-contrast image is not obtained, it becomes difficult to control the gradation of each pixel by voltage modulation when the duty ratio becomes low. In particular, it was not optimal for a liquid crystal television panel.

[Means for Solving the Problems] An object of the present invention is to solve the above problems, and more specifically, it is suitable for easily producing a display panel having high-density pixels over a wide area and for displaying a gradation. An object is to provide an optical modulator and a display method.

That is, the present invention provides a two-dimensional pixel having a pixel having a first electrode and a second electrode facing each other, and an optical modulation substance arranged between the first electrode and the second electrode. In the optical modulation element arranged in the above, a projection for increasing the electric field strength formed when an electric field is applied to the pixel according to the gradation information, when the electric field is applied to the pixel. However, so as to partially form an inversion region in which the state of the optical modulation material is inverted in the pixel,
A plurality of regularly arranged optical modulation elements on the inner surface of the pixel, or a first electrode and a second electrode facing each other, the first electrode and the second electrode And a pixel having an optical modulation material disposed between
In the optical modulation element arranged in a dimension, a means for supplying an electric signal according to gradation information to the pixel is provided, and in order to enhance the electric field strength formed when an electric field is applied to the pixel by the electric signal. The optical modulation element is characterized in that a plurality of parts are regularly arranged on the inner surface of the pixel so as to partially form an inversion region in which the state of the optical modulation material is inverted in the pixel. To do.

[Operation] According to the present invention, the inversion region is partially formed in the pixel, that is, it is possible to suppress the change of the state due to the halftone display depending on the size of the inverted area in the unit pixel. However, it is possible to display stable halftones with excellent reproducibility.

Furthermore, by controlling the position at which the reversal is started, the reproducibility and stability can be further enhanced, and gradation display over a wide range can be performed.

EXAMPLES The present invention will be described below with reference to the drawings. The optical modulation material that can be used in the present invention is the first one depending on the applied electric field.
A substance having an optical stable state (for example, to form a bright state) and a second optical stable state (for example, to form a dark state), that is, at least two stable states against an electric field, A liquid crystal having such properties is most suitable.

As the liquid crystal having at least two stable states that can be used in the optical modulator of the present invention, a chiral smectic liquid crystal is most preferable, and among them, a chiral smectic C phase (SmC *), H phase (SmH *), I Phase (SmI *), F
Phase (SmF *) and G phase (SmG *) liquid crystals are suitable.

For this ferroelectric liquid crystal, please refer to “Le Journal de Physique Lettle”
("LE JOURNAL DE PHYSIQUE LETTRE") Volume 36 (L-69)
1975 "Ferroelectric Liquid Crystals:": "Applied Physics Letters"("Appl
ied Physics Letters ") dai36kann, No. 11, 1980," Submicro Second Bistable Electrooptic Switching "in" Liquid Physics Letters "
Switching in Liquid Crystals ”):“ Solid State Physics 16 (141) 1981 “Liquid Crystal” and the like, and the ferroelectric liquid crystal disclosed therein can be used in the present invention.

More specifically, examples of the ferroelectric liquid crystal compound used in the present invention include desiloxybenzylidene-P'-amino-2-methylbutylcinnamate (DOBAMBC) and hexyloxybenzylidene-P'-amino-2. -Chloropropyl cinnamate (HOBACPC) and 4-0- (2-
Methyl) -butyl resorcylidene-4'-octylaniline (MBRA8) and the like.

When an element is constructed using these materials, the element is heated by a heater as necessary in order to keep the liquid crystal compound in a temperature state where it becomes SmC *, SmH *, SmI *, SmF *, SmG *. It can be supported by an embedded copper block or the like.

FIG. 1 schematically shows an example of a ferroelectric liquid crystal cell. 11 and 11 'are In ₂ O ₃ , SnO ₂ and ITO (Indium-
It is a substrate (glass plate) coated with a transparent electrode such as tin-oxide), in which a liquid crystal of SmC * phase in which the liquid crystal molecular layer 12 is oriented perpendicular to the glass surface is enclosed. A thick line 13 represents a liquid crystal molecule, and the liquid crystal molecule 13 has a dipole moment (P⊥) 14 in a direction orthogonal to the molecule. When a voltage above a certain threshold is applied between the substrates 11 and 11'-shaped electrodes, the helical structure of the liquid crystal molecules 13 is unraveled, and all the dipole moments (P⊥) 14 are oriented in the direction of the electric field. You can change direction. The liquid crystal molecule 13 has an elongated shape,
Liquid crystal optical modulators that exhibit refractive index anisotropy in the major axis direction and the minor axis direction, and therefore, for example, if polarizers are placed above and below the glass surface in a positional relationship of crossed Nicols, the optical characteristics change depending on the polarity of voltage application. Is easily understood. Furthermore, when the liquid crystal cell is made sufficiently thin (for example, 1 micron), the helical structure of the liquid crystal molecules is unraveled (non-helical structure) even when no electric field is applied, as shown in FIG. Child moment P or P '
Has either an upward (24) or downward (24 ') orientation. When an electric field E or E'having a polarity different from a certain threshold value is applied to such a cell as shown in FIG. 2, the dipole moment electric field E or E'is directed upward (24) or The liquid crystal molecules are oriented in either the first stable state 23 (bright state) or the second stable state 23 '(dark state) depending on the downward and (24') orientations.

There are two advantages of using such a ferroelectric liquid crystal as an optical modulation element. Firstly, the response speed is extremely fast, and secondly, the alignment of the liquid crystal molecules has bistability. Explaining the second point with reference to FIG. 2, for example, when an electric field E is applied, the liquid crystal molecules are oriented in a second stable state 23 'and change their orientations. It has a memory function in each stable state.

In order to effectively realize such a high response speed and bistability, it is preferable that the cell is as thin as possible, and generally 0.5 μm to 20 μm, particularly 1 μm to 5 μm. Meters are suitable. A liquid crystal-electro-optical device having a matrix electrode structure using a ferroelectric liquid crystal of this kind has been proposed by Clarke and Lagabal in US Pat. No. 4,367,924.

Next, details of the liquid crystal optical element in the present invention will be described.
FIG. 3 shows an embodiment of the present invention. 31 is one of the substrates, and glass or plastic is used. A first electrode 32 such as ITO and an orientation control layer 33 are laminated on the substrate 31. Opposite to this, the other substrate 34 is arranged so as to sandwich the optical modulation substance 1 between both substrates, and the second substrate 34 is placed on the substrate 34.
The electrode 35 and the orientation control layer 36 are provided.

Here, in FIG. 3, the first electrode 32 on the substrate 31 is
The fine protrusions 40 having dispersed layer thicknesses are formed. The distance between the substrates 31 and 34 is controlled by a spacer 37 to be 1 μm to 5 μm. As described above, by providing the first electrode 32 with dispersive unevenness, the optical modulator material 102 corresponding to the protrusion 40 when a voltage is applied between the first electrode 32 and the second electrode 35. The electric field strengths acting on the optical modulation substance 102 corresponding to the portion 101 and the concave portion 41 are different from each other, and a dispersive electric field strength distribution is formed. That is, the portion 101 corresponding to the protrusion 40
A relatively high electric field acts on the part 102 of the device. FIG. 4 is a schematic front view of one pixel of the optical modulator. As shown in this figure, the protrusions 40 are regularly arranged in one pixel.

Reference numeral 41 in FIG. 4 corresponds to the aforementioned projection 40, and 42 corresponds to the aforementioned recess 41.

As a method of forming the above-mentioned protrusion 40, a method of partially adhering a conductive material on the uniform conductive film as revealed in the sand glass method or the example as described in the example below. and so on.

By the above, the following effects can be obtained.
FIG. 5 schematically shows how molecules are inverted by voltage application in the ferroelectric liquid crystal cell. Immediately after the voltage starts to be applied, inversion nuclei 51 are partially generated corresponding to the protrusions 40 in the voltage applied portion (FIG. 5 (a)), and thereafter, FIG. 5 (b) and (c). ), The inversion portion gradually expands with the passage of time under the applied voltage, centering on the inversion nucleus 51, and a partial inversion region 52 is formed. Further, when the voltage is continuously applied, most of the voltage is inverted (d) Finally, the entire voltage application portion is inverted.

A typical state of inversion of a ferroelectric liquid crystal is described, for example, in “Switching Characteristics of Ferroelectric Liquid Crystal Dovanbok” by “Orihara” and “Iwashibashi” (“Swit
ching Cheracteristics of Ferroelectric Liquid Crys
tal DOBAMBC ")-Japanese Journal of appliefs
d physics) Vol. 23, No. 10, October 1984, pages 1274-1277.

As described above, the present invention is based on a method of intentionally forming an inversion nucleus in a pixel and forming an inversion region around the inversion nucleus, and for example, a strong structure corresponding to the protrusion 40 formed on the first electrode 32. Since the electric field strength acting on the part 101 of the dielectric liquid crystal becomes a relatively high electric field, the substantial inversion starts around this part 101, and the pulse number of the pulse signal and the pulse width are as high as a high value. The size of the inversion region that grows around the part 101 is determined in accordance with the above.

In addition, when the matrix electrode formed of the scanning electrode and the information electrode is applied to the optical modulation element of the present invention to perform the line sequential writing, the driving method disclosed in JP-A-59-193427 is adopted. preferable. That is, in the present invention, the pixels on the writing line are once aligned with the ferroelectric liquid crystal in one stable state corresponding to the black level, and then the sixth liquid crystal is aligned.
By applying the pulse signal shown in FIGS. 8 to 8 to the information electrode side, the ferroelectric liquid crystal is inverted to the other stable state corresponding to the white level, and such scanning is sequentially performed for each line to obtain the gradation of one screen. Display is obtained. Figures 6-8 show the first
A typical example of the voltage applied between the electrode 32 and the second electrode 35 is shown. FIG. 6 shows the applied pulse width, FIG. 7 shows the applied pulse number, and FIG. 8 shows the case where the applied pulse voltage value (peak value) is selected according to the gradation information.

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

6 and 7 show examples of voltage application most suitable for the optical modulator of the present invention. That is, by applying the pulse waveform (a) in FIGS. 6 and 7 between the electrodes 32 and 35, the optical modulation substance in the portion (site 101) where a relatively high electric field acts starts to invert, It becomes the core and the inverted part begins to spread.

If the application of the voltage is stopped here, the state as it is is memorized in the case of an optical modulator having a particularly bistable property. Therefore, it is possible to stably display one halftone based on the area of the inversion region.

When the voltage shown in FIGS. 6 and 7 (b) to (d) is applied, or the pulse is applied, the inverted portion is expanded,
The state at the time when the voltage application is stopped is stored in each memory, and a halftone based on the area of another inversion region can be stably displayed. In this way, gradation expression over a wide range is possible.

According to the method of changing the applied voltage shown in FIG. 8, the inversion nucleus is formed by the pulse shown in FIG. 8A, and when the voltage is increased as shown in FIGS. Since the responsiveness of the modulation material is improved, the region of inversion becomes large, but at this time also, the part where the electric field strength is large inverts first, and it is considered that the inversion region first expands within the given pulse width. To be In this case, if the pulse application time is too long, the pulse will be inverted over the entire range even in the low voltage range (for example, near the inversion threshold of the optical modulator used), so the pulse application time is adjusted appropriately.

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

Specific examples will be given below.

(Example 1) ITO was uniformly provided as a conductive layer on a glass substrate to a thickness of about 4000 Å by a sputtering method, and the ITO film surface was roughened by uniformly colliding with # 400 to # 800 abrasive grains. A SiO ₂ film as an electrode protective layer was provided on the surface by EB vapor deposition to a thickness of about 1000Å, and further, polyimide or polyvinyl alcohol was provided on the surface as an orientation control layer by a spinner or dipping to a thickness of about 1000 to 2000Å.
A rubbing treatment is performed on the orientation control layer to form a single-sided substrate. As a counter substrate, ITO is uniformly provided on a glass substrate, and the polyimide or polyvinyl alcohol is uniformly provided, and orientation treatment such as lapping is performed. A cell was prepared using two such glass substrates using the same, and DOBAMBC was injected into the cell to obtain 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, FIG. 5 (a) to (d) were obtained.
The formation of the inversion region shown in FIG.

(Example 2) ITO was used as an electrode on a glass substrate in the same manner as above to about 3000 Å
It is provided with a thickness, and ITO is sputtered again by applying a mask of 400 mesh to 800 mesh on the surface to make irregularities on the surface, and then SiO ₂ or an orientation control layer as an electrode protective layer in the same manner as in the above example. As a single-sided substrate, polyvinyl alcohol or the like was provided as a substrate, and rubbing treatment was performed.

As a result, the same result as in Example 1 was obtained. In Examples 1 and 2 above, the one in which the concavo-convex portion was formed was used, but in the present invention, the above-mentioned concavo-convex portion can be formed in both substrates. Further, as another specific example of the present invention,
An ITO film is provided on a substrate such as glass or plastic in the same manner as above, and a relatively high resistance such as Sn is provided on the surface.
After uniformly providing the O ₂ film to a thickness of about 3000 Å, metal such as Au and Al is dispersedly vapor-deposited through the mesh or other method, and the SnO ₂ film is doped with the metal by thermal diffusion. After that, by removing the remaining metal by etching, the doped portion has a relatively low resistance, and it is possible to obtain a SnO ₂ film having dispersively different resistance values. After that, by forming an electrode protective layer and an orientation control layer in the same manner as described above to form a substrate, it is possible to impart a subtle dispersive change in the electric field applied to the optical modulator.

[Effects of the Invention] According to the present invention, it is possible to provide an optical modulation element suitable for a display panel of high-density pixels or an optical shutter array, and moreover, simply determine the pulse width, the number of pulses or the peak value of a pulse signal. It is possible to provide an optical modulation element suitable for a display panel capable of expressing multi-gradation excellent in reproducibility and stability by being changed according to the tones.

[Brief description of drawings]

FIG. 1 is a schematic diagram for explaining a ferroelectric liquid crystal element used in the present invention. FIG. 2 is a schematic diagram for explaining a ferroelectric liquid crystal element used in the present invention. FIG. 3 is a schematic sectional view of an optical modulator according to an embodiment of the present invention. FIG. 4 is a schematic plan view showing a part of an optical modulator according to an embodiment of the present invention. FIG. 5 is a schematic plan view for explaining the manner of forming the inversion region of the pixel of the optical modulator according to the embodiment of the present invention. FIG. 6 is a diagram showing an example of a waveform of a signal according to gradation information used in the present invention. FIG. 7 is a diagram showing another example of the waveform of the signal according to the gradation information used in the present invention. FIG. 8 is a diagram showing still another example of the waveform of the signal according to the gradation information used in the present invention.

Claims (13)

[Claims] 1. A two-dimensional pixel having a first electrode and a second electrode facing each other, and an optical modulation substance arranged between the first electrode and the second electrode. In the arrayed optical modulation element, a means for supplying an electric signal according to gradation information to the pixel is provided, and a protrusion for increasing the electric field strength formed when an electric field is applied to the pixel by the electric signal. The plurality of optical modulation elements are regularly arranged on the inner surface of the pixel so as to partially form an inversion region in which the state of the optical modulation material is inverted in the pixel. 2. The optical modulation element according to claim 1, wherein the protrusion is formed of a low resistance portion formed on one of the first and second electrodes in the pixel. . 3. The optical modulation element according to claim 1, wherein the electric signal is a pulse signal having a pulse width corresponding to the gradation information. 4. The optical modulation element according to claim 1, wherein the electric signal is a pulse signal having a pulse number corresponding to the gradation information. 5. The optical modulation element according to claim 1, wherein the electric signal is a pulse signal having a peak value according to the gradation information. 6. The optical modulation element according to claim 1, wherein the optical modulation substance is a chiral smectic liquid crystal. 7. The optical modulation element according to claim 1, wherein the optical modulation substance is a ferroelectric liquid crystal. 8. A two-dimensional pixel having a first electrode and a second electrode facing each other, and an optical modulation substance arranged between the first electrode and the second electrode. In the arrayed optical modulation element, a unit for supplying an electric signal corresponding to gradation information to the pixel is provided, and a portion for enhancing an electric field strength formed when an electric field is applied to the pixel by the electric signal, An optical modulation element, wherein a plurality of inversion regions are regularly arranged on the inner surface of the pixel so as to partially form an inversion region in which the state of the optical modulation material is inverted in the pixel. 9. The optical modulation element according to claim 8, wherein the electric signal is a pulse signal having a pulse width corresponding to the gradation information. 10. The optical modulation element according to claim 8, wherein the electric signal is a pulse signal having a pulse number corresponding to the gradation information. 11. The optical modulation element according to claim 8, wherein the electric signal is a pulse signal having a peak value corresponding to the gradation information. 12. The optical modulation element according to claim 8, wherein the optical modulation substance is a chiral smectic liquid crystal. 13. The optical modulation element according to claim 8, wherein the optical modulation substance is a ferroelectric liquid crystal.