JPS62238533A - Driving method for optical modulation element - Google Patents

Abstract

PURPOSE:To have high-density picture elements over a wide area and to make an element particularly suitable for a gradation display by providing the specific 1st and 2nd steps to the element and forming a region where an inversion threshold voltage is exceeded and a region where said voltage is not exceeded. CONSTITUTION:This element is provided with the 1st step to clear all the picture elements to white display state 71 by using a conductive film 32 as an electrode and impressing the voltage exceeding the threshold voltage of an optical modulation material between the electrode 32 and a counter electrode 34, and the 2nd step to write the selected picture elements to a black display state 72 by using the conductive film 32 as a resistance film and impressing the voltage signal to an electric transmission line. A potential gradient is formed within at least one conductive film 32 plane to constitute the picture elements and a gradation signal modulated by a voltage value or pulse width or number of pulses, etc., is impressed as an input signal. Gradation display and simultaneous turning on and off of the plural picture elements are thereby executed.

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 specifically, the present invention relates to a method for driving an optical modulation element for a display panel. Display panel, +v 1
Palanquin 1 = 1 = -; 2 -de +/81 axis
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(Prior art) In a liquid crystal 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. At this time, a video image signal 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 the stored image signal, and at the same time, by modulating the voltage of the signal. Gradation display is performed.

[Problem that the invention seeks to solve]

However, in active matrix drive type panels using such TN liquid crystals, the TPT used has a complicated structure, so the number of structural steps is large, and high manufacturing costs are a bottleneck. There are problems in that it is difficult to form a film over a wide area of the thin film semiconductor (eg, polysilicon, amorphous silicon) that constitutes the TPT.

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 (one frame) During scanning, the time during which an effective electric field is applied to one selected point (duty ratio) decreases at a rate of 1/N, resulting in crosstalk and problems such as not being able to obtain high-contrast images. In addition to having drawbacks, when the duty ratio becomes low, it becomes difficult to control the gradation of each pixel by voltage modulation, so that it is not suitable for a display panel with a high density of wiring.

[Means for Solving the Problems] and [Operations] The purpose 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, especially 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 is a system in which a potential gradient is formed within a pixel and driving is performed based on this potential gradient.
an optical modulating material disposed between the substrate and the second substrate; a conductive film disposed on at least one of the first substrate and the second substrate; and a plurality of low resistances electrically bonded to the conductive film. A method of driving an optical modulation element having an electrical transmission line, in which a conductive film is used as an electrode, and a voltage exceeding the threshold voltage of the optical modulation material is applied between the electrode and a counter electrode to make all pixels white. a first step of clearing the display state (based on the first stable state of the optical modulation material); Displays pixels in black display state (
A method of driving an optical modulation element has a 41F feature, with a second step of writing to a second stable state of the optical modulation material. Furthermore, another feature of the present invention is that a pulse signal with a peak value corresponding to the gradation, or a signal with a pulse width or the number of pulses depending on the gradation is applied to at least one of the two opposing transmission electrode lines constituting one pixel. This is a driving method that expresses gradation by applying voltage and forming regions within a pixel in which the inversion threshold voltage is exceeded and regions in which it is not exceeded.

〔Example〕

The present invention will be explained below with reference to the drawings. The optical modulation substance used in the driving method of the present invention has a first optically stable state (for example, a bright state) and a second optically stable state (for example, a dark state) depending on the applied electric field. ), that is to say has at least two stable states with respect to an electric field, in particular liquid crystals having such properties are used.

As the liquid crystal having bistability that can be used in the driving method of the present invention, chiral smectic liquid crystal having ferroelectricity is most preferable, and among these, chiral smectic liquid crystal
Phase (SmC*), H phase (SmH end), I phase (SmI book)
, F phase (SmF lines) or G phase (5m0 lines) liquid crystals are suitable. Regarding this ferroelectric liquid crystal, the ferroelectric liquid crystal is
OURNAL DEPHYSIQtJE LETT
RE”) Volume 36 (L-69) 1975 “Ferroelectric Liquid Crystals” (rFerroelectric LiquidCr
ystalsJ);
ette, rs”) Volume 36.

No. 11, 1980, “Submicro φ Second Bistiple Medium Electro-Optic Switching in Liquid Meeting Risterus J (rsubmi
cro 5econdBistable Elec
trooptic Switching in Liq
uidCrystelsJ); “Solid State Physics 6 (141
), 1981r 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-glolopropyrcinamate (HOBACPC) and 4-
Examples include o-(2-methyl)-butylresolsiliten-4'-octylaniline (MBRA8).

When constructing an element using these materials.

Liquid crystal compounds include SmC wood, SmH wood, SmI wood, SmF
In order to maintain the temperature state such that it becomes wood or SmG wood, 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 l l' are In2O3°S n 02
A substrate (glass plate) coated with a transparent electrode such as ITO (indium tin oxide), etc., between which a liquid crystal molecular layer 12 is oriented perpendicular to the glass surface.
It is filled with mC terminal phase liquid crystal. 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 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 all dipole moments (PJ-) 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,
Liquid crystal optical modulation exhibits refractive index anisotropy in the long axis direction and the short axis direction, and therefore, for example, if polarizers are placed above and below the glass surface in a crossed nicol positional relationship, the optical characteristics change depending on the polarity of voltage application. It is easily understood that it becomes an element. Furthermore, when the thickness of the liquid crystal cell is made sufficiently thin (for example, 1K), the helical structure of the liquid crystal molecules unravels (non-helical structure) even when no electric field is applied, as shown in Figure 2, and the bipolar structure child moment) P or y is upward (
24) Or, the direction of the clove moment is changed upward 24 or downward 24' in response to the electric field vector of the tail field E or E', and accordingly the liquid crystal molecules are in the first stable state 23 (bright state) or in the first stable state 23 (bright state). It is oriented in one of two stable states 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. For such a response, it is preferable for the cell to be as thin as possible.
Generally, 0.5 to 20 liters, particularly 1IL to 5 liters, 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 used in the present invention will be explained with reference to FIG.

31 in FIG. 3 is one substrate. Reference numeral 32 denotes a display conductive film, which is laminated on the substrate 31. 33 is a transmission electrode made of a low-resistance metal film, and has 1 display conductivity [
32 are stacked in parallel at equal intervals. Further, another substrate (not shown) is opposed to the substrate 31, and a counter conductive film (counter electrode) 34 is disposed on the other substrate in a region corresponding to the region of the 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
The reference potential point WE (for example, O
When a predetermined signal voltage Va is applied to the electric transmission electrode line 33% - - Notebook #, the 11th
As shown in Figure (a), it is possible to apply a potential gradient of Va to the in-plane length directions of the conductive film 32 between the transmission electrode lines 33a and 33b or 33b and 33c. At this time, when the inversion threshold voltage of the ferroelectric liquid crystal 5 is Vtht-Va and -vb is applied to the counter electrode 34, as shown in FIG. 11(b).
As shown in , a potential difference Va+Vb greater than the inverted dark value voltage vth is applied to the ferroelectric liquid crystal corresponding to the in-plane length directions m1 and m2 of the conductive film 32, and such ml and m2
For example, the area corresponding to the area can be inverted from a bright state to a dark state. 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 signal applied to the counter electrode 34 -
The voltage value of vb may be modulated according to the gradation information,
Alternatively, the pulse width may be modulated according to the gradation information, or the gradation can be controlled by modulating the number of pulses.

Furthermore, in the present invention, prior to applying the above-mentioned gradation signal,
After going through an erasing step that puts the pixel into 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.

Further, preferred specific examples of the present invention will be described.

In FIG. 3, a transparent conductive film of about 200 mm thick is formed by sputtering on a glass substrate 31.
Two films were formed to form a display conductive film 32. This S n O
The sheet resistance of the two membranes was 105Ω7/mouth.
A film of 1,000 layers thick was vacuum-deposited on the SnO2 film described above and patterned again to form a plurality of electrical transmission electrodes 33 as shown in FIG. In this example, the transmission electrode 3
The sheet resistance of the transmission electrode 33 was approximately 0.4Ω/mouth, and the width thereof was approximately 20Ω. On the other hand, the counter board has an IT board that covers area A.
An O film was provided as the counter electrode 34. The sheet resistance of the ITO film serving as the counter electrode 34 was about 20Ω/hole.

A layer of about 500 polyvinyl alcohols was formed as a liquid crystal alignment film on the surface of each of the two substrates thus prepared, and a rubbing treatment was performed.

Next, the two substrates were placed facing each other and the gap was adjusted to about 1°, and the ferroelectric liquid crystal (p-η-octyloxybenzoic acid-y-(2-methylbutyloxy) phenyl ester and p-η -nonyloxybenzoic acid-F'-(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, was 230 g x 230 mm, and the capacitance after the liquid crystal was injected was about 3 PF. However, the width of pixel A was determined by disposing polarizing plates in a crossed nicol configuration on both sides of the liquid crystal cell thus formed, and observing the optical characteristics.

FIG. 4 schematically shows the method of applying an electric signal, and FIGS. 5 and 6 show electric signals. Figure 5(a)
and (b) show the waveforms of the signals C&) generated by the drive circuits 43 and 45 in FIG. 4, and FIG. 6(A) shows the waveform of another pulse from the drive circuit 43 in FIG. (e) represents the waveform of the signal (b) generated by the drive circuit 44 in FIG.

Now, the signal (a) is sent from the drive circuit 43 to FIG. 5(a).
) is output as the signal (C), and the signal waveform shown in FIG. 5(b) is output from the drive circuit 45 as the signal (C).
Output in synchronization with a). This step corresponds to the clear step, and is applied to all pixels as an erase pulse.
A voltage of 0V is applied. Then, the liquid crystal 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).

Note that in the present invention, the pulse width is 1 second and the peak value is −1 as shown in FIG.
It is not limited to 2V and 8V pulses.

At this time, the resistance value of the conductive film F132 is equal to the sheet resistance, and if the sheet resistance of the conductive film 32 is 102Ω/portion to 105Ω/portion, the resistance value is 102Ω to 105Ω. On the other hand, since the capacitance of each pixel is approximately 3 pF per pixel, the maximum value when all the opposing conductive films 34 in FIG.
If oooxt000=1013, the total capacity is 3X I
0-12X I O6 = 3X l O-[iF.

Therefore, its time constant is (102~105)X3X10
4=3×10−4 to 3×10−1 seconds.

Therefore, in the present invention, the pulse width during the clear step can be determined by the above-mentioned time constant. From this state, when various pulses as shown in FIG. 6B(a) to (e) are applied as signals (b) to the transmission electrode line 33 in synchronization with the pulses from the drive circuit 4%, the pixel The optical state of A is shown in FIG. 7, and the drive circuit 44 at this time
The pulses from are shown in FIG. 6(A).

Pulse applied voltage -2V (corresponding to Figure 6B(a)) and -5
V (corresponding to FIG. 6B(b)), no change from the bright state 71 occurs (corresponding to FIG. 7(a)), but the pulse applied voltage is −8 V (corresponding to FIG. 6(c)). Then, the liquid crystal near the transmission electrode 33 switches to the dark state 72 (see FIG. 7).
(corresponding to b)), and further increase the applied voltage to -14V (Fig. 6B).
(d)), 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. 6B(e)). The entire pixel is switched to the dark state 72 (corresponding to FIG. 7(d)). In this way, an image with gradation can be formed.

Furthermore, even when signals (b) with different pulse widths as shown in FIGS. 9(a) to (e) and triangular wave pulses as shown in FIG. The optical state changes illustrated in FIG. 7 can be shown. At this time, the pulse shown in FIG. 8 is applied to the transmission electrode line, and in synchronization with this pulse, the pulse shown in FIGS. 9 (a) to (e) is applied to the counter electrode 34 according to the gradation. It is possible to express gradation.

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.

In addition, in the present invention, the aluminum (Al
In addition to the electrical transmission electrode line 33 of 1, a fully bent material such as silver, copper, gold, or chromium can be used as the electrical transmission electrode line 33, and preferably its sheet resistance can be 10 Ω/port or less. Further, as the conductive film 32 to which a potential gradient is applied, a transparent groove TL film having a sheet resistance of 102Ω/port to 105Ω10 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 another embodiment of the present invention. 1st
The liquid crystal optical element shown in FIG.
A plurality of parallel transmission electrode lines 102 are wired, and each is connected to a terminal S, s2, . . . s7 connected to a scanning signal generating circuit (not shown). Conductive film 1
01 is connected to a drive circuit 45 that generates a signal (C). Electrodes 103 made of a plurality of striped conductive films are arranged to face each other so as to intersect with these transmission electrode lines 102, and the conductive films 101 and striped electrodes 103 described above are arranged opposite to each other.
A ferroelectric liquid crystal is placed between the two. Terminal work 1 + work 2 +---■ of this striped electrode 103
5 are each connected to an information signal generation circuit (not shown). By applying the signal waveforms shown in FIGS. 5(a) and 5(b) between the electrode 103 and the conductive film 101, a plurality of pixels can be brought into a white or black display state at the same time.

Therefore, in this example, the terminals S1゜s 2 of the liquid crystal optical element,
A potential gradient is formed by sequentially applying a scanning signal to s7 and connecting terminals to which no such scanning signal is applied to a reference potential point. On the other hand, a gradation screen can be formed by applying a gradation signal to the striped electrodes 103 in synchronization with the scanning signal. or,
In the present invention, a scanning signal is sequentially applied to the striped electrodes 103 described above, and in synchronization with this scanning signal, a gradation signal is applied to the odd-numbered (or even-numbered) transmission electrode line, and the gradation signal is applied to the even-numbered (or odd-numbered) transmission electrode line. Gradation driving can also be performed by connecting the transmission electrode line to a reference potential point. In the above description, it is clear that even if the upper substrate and drive circuit have the same configuration as the lower substrate and drive circuit, it can be applied as is. At this time, the front surfaces of the liquid crystal cells can be turned on or off simultaneously.

In addition to the above-mentioned ferroelectric liquid crystal, twisted nematic liquid crystal, guest host liquid crystal, etc. can be used in the present invention, but ferroelectric liquid crystal, especially ferroelectric liquid crystal having at least two stable states, is most preferable. is suitable.

〔Effect of the invention〕

By forming a potential gradient in the plane of at least one conductive film constituting a pixel and applying a voltage value, or a grayscale signal modulated by the Hahalus width or the number of pulses, etc. as an input signal, single grayscale display and multiple grayscale display can be performed. It is possible to turn on or off the pixels simultaneously.

[Brief explanation of drawings]

1 and 2 are perspective views schematically showing a ferroelectric liquid crystal display used in the present invention. FIG. 3 is a perspective view showing one substrate used in the present invention. FIG. 4 is an explanatory diagram showing a pulse waveform of a liquid crystal optical element used in the present invention. FIGS. 7(a) to 7(d) are schematic diagrams showing the gradation of pixels. FIGS. 8 and 9(a) to 9(e) are explanatory diagrams showing other pulse waveforms used in the present invention. 10th
The figure is a plan view showing another liquid crystal optical element used in the present invention. FIGS. 11(a) and 11(b) are explanatory diagrams schematically representing the potential gradient used in the present invention.

Claims (9)

[Claims] (1) An optical modulation material disposed between the first substrate and the second substrate, a conductive film disposed on at least one of the first substrate and the second substrate, and electrically connected to the conductive film. A first method for driving an optical modulation element having a plurality of low-resistance transmission lines, in which a conductive film is used as an electrode, and a voltage exceeding a threshold voltage of an optical modulation substance is applied between the electrode and a counter electrode.
1. A method for driving an optical modulation element, comprising: a first step, and a second step of applying a voltage signal to a power transmission line using a resistive film as a conductive film. (2) The driving method according to claim 1, wherein the voltage signal applied to the transmission line is a scanning signal. (3) The driving method according to claim 1, wherein the voltage signal applied to the transmission line is an information signal. (4) The driving method according to claim 3, wherein the information signal is a pulse signal with a pulse width depending on the gradation. (5) The driving method according to claim 3, wherein the information signal is a pulse signal with a number of pulses depending on the gradation. (6) The driving method according to claim 3, wherein the information signal is a pulse signal having a peak value corresponding to a gradation. (7) The driving method according to claim 1, wherein the conductive film has a sheet resistance of 10^2 Ω/□ or more. (8) The driving method according to claim 1, wherein the optical modulating substance is a ferroelectric liquid crystal. (9) The driving method according to claim 8, wherein the ferroelectric liquid crystal is a chiral smectic liquid crystal.