JPS632023A - Driving method for optical modulation element - Google Patents

Abstract

PURPOSE:To execute a display and a gradation display which are free from unevenness of display and stable, by forming a potential gradient in the surface of the first conductive film, or the first conductive film and the second conductive film, and impressing an information signal on which an offset voltage has been superposed, to the first conductive film or the second conductive film. CONSTITUTION:A potential gradient is provided in the surface of a display use conductive film 32 by a signal voltage which has been impressed to an electric transmission electrode 33, and a potential difference gradient is generated in an electric field between the film and an opposed electrode 34. When a prescribed signal voltage Va is impressed to the electric transmission electrode being adjacent to the electric transmission electrode which has been connected to a reference potential point, such as the electric transmission electrode 33a and 33c, a potential gradient of Va can be provided to a lengthwise direction l1 and l2 in the surface of the conductive film 32 between the electric transmission electrodes 33a, 33b, or 33b, 33c. In this case, when -Vb is impressed to the opposed electrode 34, a potential difference Va+Vb exceeding an inversion threshold voltage Vth is impressed to a ferroelectric liquid crystal corresponding to a lengthwise direction m1 and m2 in the surface of the conductive film 32. Accordingly, by applying Vb by a value corresponding to a gradation at every picture element, the gradation property can be expressed.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for driving an optical modulation element for a display panel, and more particularly to a method for driving an optical modulation element for a display panel. The present invention relates to a method for driving a liquid crystal optical element suitable for a panel, particularly for gradation display.

[Conventional technology]

In LCD television panels using the conventional active matrix drive system, thin film transistors (TPT)
Arrange the matrix for each pixel.

A gate-on voltage is applied to the TPT to bring the source and drain into a conductive state, and at this time, a video image (No. , TN-liquid crystal) are driven, and gradation display is performed by simultaneously modulating the voltage of the video signal.

[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 the TPT has a complicated structure, it requires a large number of structural steps, which poses a problem with high U and manufacturing. There are problems such as it is difficult to spread the coating and form a film over the entire area.

- On the other hand, TNM is a product that can be manufactured at low (・manufacturing cost)
A display panel using a passive matrix drive method is known, but as the number of scanning lines (N) increases in this display panel.

The time during which an effective electric field is applied to one selected point while scanning one screen (one frame) (duty ratio) decreases at a rate of 1/'N.

For this reason, crosstalk occurs and images with high contrast cannot be obtained. Arrangement 1. Not suitable for a number of display panels, especially LCD television panels.

[Means for Solving the Problems] and [Operations] The object of the present invention is to eliminate the above-mentioned drawbacks, and more specifically, to improve the driving method of a display panel having high-density pixels over a wide area, and in particular, to improve gradation. An object of the present invention is to provide a driving method for an optical modulation element suitable for display.

That is, the present invention provides a first substrate having a first conductive film, a second substrate having a second conductive TL film facing the first conductive film, and a first substrate and a second conductive film. an optical modulating substance disposed between the substrate and the first conductive film, or a potential gradient in the plane of the first conductive film and the second conductive film; The method of driving the optical modulation element is characterized by applying an information signal on which a canceling voltage is superimposed to the conductive film of the optical modulator. In other words, one aspect of the present invention is to apply an in-plane potential gradient to at least one of two opposing conductive films constituting one pixel, and apply a Barne signal or a gradation having a peak value corresponding to the gradation to the other conductive film. It is characterized by a driving method that expresses gradation by applying a signal with a corresponding Varne width or number of pulses to form regions within one pixel in which the inversion threshold voltage is exceeded and regions in which it is not exceeded.

〔Example〕

1. The present invention will be explained below with reference to the drawings. 4. Optical modulating substances used in the driving method of the present invention.

It has a first optically stable state (for example, a bright state is formed) and a second optically stable state (for example, a dark state is formed) depending on the applied electric field. That is, a material having at least two stable states with respect to an electric field, particularly a liquid crystal having such properties, is used.

As the liquid crystal having bistability that can be used in the driving method of the present invention, a chiral numectic liquid crystal having ferroelectricity is most preferable.
Phase (SmC*).

Liquid crystals of H phase (f', S m H tree), 1 phase (SmI book), F phase (: S mF book), and G phase (', S m G tree) are suitable.

Regarding this ferroelectric liquid crystal, please refer to “6 le journard”.
LE JOURNAL
36th
＠ (L-139) 1975 “Ferro Electric Liquid Cry 7 Tarnu” (rFerroele
ctrFc LiquidCrystal
s J); “Applied” Physiic 7
・Letterspa (A p p, li e dPhys
ics Letters”) Volume 36, No. 11, 1
980's "Submicro Second High Stipple"
"Electro-optic Nuitsching in Liquid Cry7 Tarnu" (rsubmicro 5ec
ondBistableElectrooptic
Switching in LiquidCrys
tels”);”Solid State Physics 6 (141) 1981
ferroelectric liquid crystals disclosed in these documents can be used in the present invention.

More specifically, an example of a ferroelectric liquid crystal compound used in the method of the present invention is decyloxyhenzylidene-P'-amino-2-methylbutylcinnamate (DoBAMB
C), hexyloxybenzylidene-P'-amino-2
-chloropropyl cinnamate (HOBACPC) and 4-o-(', 2-methyl)-butyl resolsiliten-4'-octylphuniline (MBRA8).

When constructing an element using these materials.

The liquid crystal compound is SmC wood, SmH*, SmI wood, SmF
*, In order to maintain the temperature state such that it becomes an SmG tree, 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 In2O3゜S n02 or IT
It is a substrate (glass plate) coated with a transparent electrode such as O (indium tin oxide), and a SmC main phase liquid crystal in which the liquid crystal molecular layer 12 is oriented perpendicular to the glass surface is sealed between the substrates. . A thick line 13 represents a liquid crystal molecule.

Dipole moment (P±)1 in the direction perpendicular to the molecule
It has 4. When a voltage equal to or higher than a certain threshold is applied between the electrodes on the substrates 11 and 11', the helical structure of the liquid crystal molecules 13 is unraveled, and the liquid crystal molecules 13 are adjusted so that the y and phase moments (P soil) 14 are all directed 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 short axis direction. It is easy to understand that this results in a liquid crystal optical modulation element whose optical properties change depending on the polarity of applied voltage. Furthermore, if the thickness of the liquid crystal cell is made sufficiently thin (for example, Ig), the helical structure of the liquid crystal molecules will unravel even when no electric field is applied, as shown in Figure 2.
(non-helical structure), its dipole moment P or P' is oriented either upward (24) or downward (24'). When an electric field E of different polarity above a certain threshold value E' is applied to such a cell as shown in FIG. Accordingly, the liquid crystal molecules are oriented either in the first stable state 23 (bright state) or in the second stable state 23' (dark state).

There are two advantages to using such a strong vi-electric liquid crystal as an optical modulation element. Firstly, it has an extremely fast response speed, and secondly, it has bistability due to the alignment of liquid crystal molecules. To explain the second point using, for example, Fig. 2, '
When the electric field E is applied, the liquid crystal molecules are oriented in the first stable state 23, but this first stable state 23 is maintained even when the electric field is turned off, and when the electric field E' in the opposite direction is applied, , the liquid crystal molecules are aligned to the second stable state 23' and change their orientation, but they remain in this state even when the electric field is turned off, and each stable state has a memory function. In order to effectively realize such fast response speed and bistability, it is preferable for the cell to be as thin as possible; generally 0.5 g to 20 tiles, especially 1JL to 5L. Suitable Q・ru. A liquid crystal-electro-optical device having a matrix electrode structure using a strongly electrostatic liquid crystal of this type is disclosed in, for example, Clark and Ragapal, U.S. Pat.
This is proposed in Book II.

Next, details of the liquid crystal optical element used in the present invention will be explained with reference to FIG.

31 in FIG. 3 is one of the substrates. 32 is display conductivity 1
1ffi and is laminated on 31 substrates. Reference numeral 33 denotes power transmission electrodes made of a low-resistance metal film, which are stacked on the display conductive film 32 in parallel at equal intervals. Further, the other substrate (not shown) faces the substrate 31.

A counter conductive film (counter electrode) 34 is disposed on the other substrate in a region corresponding to the region of pixel A in the figure. The above-mentioned optical modulation material is sandwiched between the display conductive film 32 and the counter electrode 34.

In the liquid crystal optical element configured as described above, the power transmission electrode 33
By applying a potential gradient in the plane of the display conductive film 32 by the signal voltage applied to the display conductive film 32, a potential difference gradient is generated in the electric field between the display conductive film 32 and the counter electrode 34. At this time, the transmission electrode 33
b to the reference potential point VEf' (for example, 0 port),
Base IP, potential point like the transmission electrodes 33a and 33c! When a predetermined signal voltage Va is applied to the nine consecutive transmission electrodes and the adjacent transmission electrodes, as shown in FIG. 1 and 2 can be given a potential gradient of Va. In this poem, the inversion threshold voltage vth of ferroelectric liquid crystal is V
When -vb is applied to the counter electrode 34, the first
1 (b), the in-plane length direction m1 of the conductive film 32
A potential difference Va+vb greater than the inversion threshold voltage vth is applied to the ferroelectric liquid crystal corresponding to ml and m2, and the regions corresponding to ml and l1n2 can be inverted from a bright state to a dark state, for example. Therefore, in the present invention, gradation can be expressed by applying vb to each pixel with a value corresponding to the gradation. At this time, the voltage value of the voltage signal -vb applied to the counter electrode 34 may be modulated according to the gradation information, or the pulse width may be modulated depending on the gradation information, or the pulse width may be modulated depending on the gradation information. The gradation can be controlled by modulating the number.

In the present invention, before applying the above-mentioned gradation signal,
After going through an erasing step which places the pixel in either a bright state or a dark state.

It is necessary to apply an inversion voltage to the ferroelectric liquid crystal in a manner that is controlled according to the gradation to invert the state.

Furthermore, one preferred and specific example of the present invention will be given and explained.

In FIG. 3, a Sn02 film, which is a transparent conductive film, having a thickness of about 20 mm was formed on a Galanus substrate 31 by the Nubatta ring method to form a conductive film 32 for display. The sheet resistance of this 5n02 film was 105 Ω/mouth.Next, A pattern was vacuum-deposited with a thickness of 1000 Ω on the above-mentioned Sn02 film, and by buttering again, a plurality of electrical transmission electrodes 33 were formed as shown in Fig. 3. The book was formed. In this example, the interval between the transmission electrodes 33 is 230
The sheet resistance of this transmission electrode 33 used for this purpose was approximately 0.4Ω.
/ mouth, and its width was about 20μ. - On the other hand, an ITO film covering area A is placed on the opposite substrate as the opposite electrode 3.
It was set as 4. The sheet resistance of the ITO film serving as the counter electrode 34 was approximately 20 Ω/mm.

A polyvinyl alcohol layer of about 500 years old was formed as a liquid crystal alignment film on the surface of each of the two substrates thus produced, and then subjected to a rubbing treatment.

Next, the two substrates were placed opposite each other and the gap was adjusted to be approximately tp, and the ferroelectric liquid crystals (', p -n-octyloxybenzoic acid-P'-(2-methylbutyloxy) phenyl ester and P -η-nonyloxybenzoic M-P'-(
A feed crystal composition containing 2-methylbutyloxy)phenyl ester as a main component was injected. The shape of the partial pixel A where the display conductive film 32 and the counter electrode 34 overlap is 230g x 23
0μ, and the capacitance after liquid crystal injection was about 3PF. However, the width of 5 pixels A is on both sides of the liquid crystal cell formed in this way.

The polarizing plates were arranged in a crossed nicol configuration, and the optical characteristics were observed.

FIG. 4 schematically shows a method of applying an electric signal, and FIGS. 5 and 6 are 'electrical signals.' (:a)
The waveforms in FIG. 6 (+) to (v) are the waveforms of the drive circuit 4 in FIG.
4 represents the waveform of signal (b) generated at 4.

Now, Signal (a) Toshichi 12V (7) 200g
5ec pulse and 8v 20 as signal (b)
An erasure step is provided in which 0g5ec parnu is applied in advance in synchronization (this is called an erasure pulse). Then,
The rare item is switched to the first stable state, and the entire pixel A becomes a bright state (the cross polarizing plates are arranged in this way).

From this state, when various pulses as shown in FIGS. 6(i) to (ma) are applied as signals (b) to the facing room 8i34 in synchronization with the pulses in FIG. 5 applied to the transmission electrode 33. Optical state of pixel A of 1! ; is shown in FIG.

Pulse applied voltage -2■ (corresponding to Figure 66a)) and -5
V (corresponding to FIG. 6(b)), no change from the bright state 71 occurs (corresponding to FIG. 7(a)), but the pulse applied voltage is -8V (corresponding to FIG. 6(c)). Then, the liquid crystal near the transmission electrode 33 switches to the dark state 72 (: Fig. 7).
Corresponding to b)), furthermore, the applied pressure is -14V C 6th U
A(d) 4: Corresponding), the area of the dark state 72 becomes wider as shown in the figure (corresponding to FIG. 7(C)), and the applied voltage is 20 V (corresponding to FIG. 6(2)). The pixel A body is switched to the dark state 72 (corresponding to FIG. 7(d)).
In this way, an image with one gradation can be formed.

In addition, various signals (b) with different pulse widths as shown in Fig. 9 (a) to (e) and a signal (a) which is a triangular wave as shown in Fig. 8 were synchronously given. The optical state change illustrated in FIG. 7 above can be shown even at the same time. At this time, the pulse shown in FIG. 8 was applied to the transmission electrode.

Gradation can be expressed by applying the pulses shown in FIGS. 9(a) to 9(e) to the counter electrode 34 according to the gradation in synchronization with this pulse.

In FIG. 4, 41 represents a ferroelectric liquid crystal, preferably a chiral smectic liquid crystal under a bistable state, and 42 represents a counter substrate.

Further, in the present invention, in addition to the aluminum (A-AC) transmission electrode 33 used in the above example, silver and copper are used.

Metals such as gold and chromium can be used as the transmission electrode 33, and preferably have a sheet resistance of 102 Ω/port or less.

Further, as the conductive film 32 to which the TL gradient is applied, a transparent conductive film having a sheet resistance of 10 to LMΩ/' can be used. Such sheet resistance can be designed to an appropriate value by adjusting the thickness of the transparent conductive film.

FIG. 10 shows an example in which the gradation expression method according to the present invention is applied to matrix drive.

The display panel shown in FIG. 10 has a striped conductive film 101 (Iota) on a glass substrate 31.

101b, 101c) are arranged, and low-resistance transmission electrodes 102 (102a, 102b, 1
02c) and 103 (103a, 103b, 103c) are wired. A counter electrode 1 made of a nutripe-shaped conductive film provided on a counter substrate (not shown) facing the substrate 31
04 (104a, 104b) are arranged, and the above-mentioned striped conductor? tll! A ferroelectric liquid crystal is placed between the electrode 101 and the counter electrode 104 .

FIG. 12 shows an electrical equivalent circuit of the display panel shown in FIG. 10, where 121 is a striped conductive film 111
122 and 123 are the resistances of the striped conductive film 111.
This is the resistance of the electrical transmission electrodes that are electrically connected and wired to both ends in the longitudinal direction. Note that each resistance is not concentrated, but distributed in a negative manner (・ru.) Now, the sheet resistance of the striped conductive film 111 is expressed as tOSΩ.
/ mouth, the sheet resistance of the transmission electrode lines 112 and 113 is 0
．． 4Ω/゛mouth. Also.

The width of the transmission electrode lines 112 and 113 is 10 μm, the length is 200 mm, and the interval between the transmission electrodes 112 and 113 is 250 mm.
μm, the terminal 124 was grounded, 1 V was applied to the terminal 125, and the terminals 126 and 127 were left open.

FIG. 13 shows the potential distribution at that time. A curve 131 in FIG. 13(a) is a potential curve showing the potential distribution in the longitudinal direction of the transmission electrode line 112 (between terminals 124 and 126). In addition, a curve 132 in FIG.
7) is a potential curve showing the potential distribution. A curve 133 in FIG. 13(c) shows a shape in which the potential difference in the short direction of the striped conductive film 111 narrowed by the transmission electrode lines 112 and 113 is distributed in the longitudinal direction of the striped conductive film 111. It is a potential difference curve showing; 1st
As can be seen from Figure 3 (C), the potential difference in the short direction of the striped conductive film 111 on the terminals 124 and 125 side is l.
V, but the potential difference decreases as it moves away from the terminals 124 and 125, and on the terminals 126 and 127 side, the potential difference almost approaches Ov.

Moreover, as shown in FIG. 13(b), the potential of the transmission electrode is
The voltage drops as the input terminal is moved away from the input terminal. Therefore, the feature of the present invention is to solve this problem by superimposing an offset voltage corresponding to this voltage drop on the information signal (gradation signal). did.

FIG. 14 is a block diagram explaining the present invention.

141 is a display panel, 142 is an information line drive circuit, 143
144 is a scanning line driving circuit, and 144 is a canceling voltage superimposition circuit.

The canceling voltage superimposition circuit 144 exhibits characteristics as shown in FIG. 15. The solid line 151 in FIG. 15 is outside the potential of the transmission electrode! In the potential curve representing rj, a broken line 151 indicates the canceling voltage of the canceling voltage superimposing circuit. By superimposing this offset voltage on each information line, the operating point of liquid crystal driving can be maintained at a constant value of Vs.

FIG. 16 shows a specific example of the canceling voltage superimposition circuit 144. 11 in Figure 16. I2...IN is the gradation information line, Al...AN is the output amplifier, 1
61 is an offset λ power terminal of each output amplifier, and 162 is a dummy wiring for offset voltage. Here, the offset voltage dummy wiring 162 is made of the same material as the transmission electrode 33 and is made of the same material as the transmission electrode 33, and can be formed by making the film thickness, width, and length the same as the transmission electrode 33. .

In this example, the applied voltage was set to 1 V and the ground potential, but 2
It doesn't matter what the potential is.

Furthermore, in the present invention, in addition to the above-mentioned ferroelectric liquid crystal, a twinned-omatic liquid crystal, a guest-host liquid crystal, etc. can be used, but a ferroelectric liquid crystal, especially a ferroelectric liquid crystal having at least two stable states, is most preferably used. LCD is suitable.

〔Effect of the invention〕

According to the present invention, it is possible to perform stable display without display unevenness, and also to apply a voltage value as an input signal, or a gradation signal modulated by Parnu width or Parnu number, etc. It is possible to display the mode.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 and 2 are perspective views schematically showing a ferroelectric liquid crystal element used in the present invention. FIG. 3 is a perspective view showing one substrate used in the present invention. FIG. 4 is a sectional view of a liquid crystal optical element used in the present invention. Figures 5 and 6 (a,) to (e) are used in the present invention (
・It is an explanatory diagram showing a bulk waveform. FIGS. 7(a) to 7(d) are schematic diagrams showing the gradation of pixels. 8 and 9(a) to 9(e) are explanatory diagrams showing other bulk waveforms used in the present invention. FIG. 10 is an explanatory diagram showing another liquid crystal waveform used in the present invention. 11 is a perspective view showing an optical element. FIGS. 11(a) and 11(b) are explanatory diagrams schematically showing potential gradients used in the present invention. FIG. 12 is an equivalent circuit of an element other than the present invention. 13(a) to 13(C) are explanatory diagrams showing the potential distribution at that time. FIG. 14 is a block diagram used in an element of the present invention.
FIG. 5 is an explanatory diagram of the potential distribution used in the present invention. FIG. 16 shows an equivalent concave cold field of the offset voltage superimposition circuit used in the present invention. Patent applicant: Canon Co., Ltd. Confectionery mouth 3 Lale name LI-Figure LL (ICIILfj14/1 (21L) 2 OK) tbL'I
C)IOjDK)tC1+7ICIMCEEC33f)
33azu C33b
:33゜Figure 71.1 Male Figure 15 2θθ(/nrn)

Claims (1)

[Claims] (1) A first substrate having a first conductive film, a second substrate having a second conductive film facing the first conductive film, and between the first substrate and the second substrate. an optical modulating substance disposed in the first conductive film or the first conductive film and the second conductive film; A method for driving an optical modulation element, characterized by applying an information signal on which a canceling voltage is superimposed.