JPS63316024A - Optical modulating element - Google Patents

Abstract

PURPOSE:To facilitate the formation of a display panel which has high-density picture elements over a wide area by connecting resistance bodies electrically to every (n) striped conductive films of at least one of 1st or 2nd electrode group and providing a reference potential point on every (n) films. CONSTITUTION:This is an optical modulating element which has an optical modulating material sandwiched between 1st substrate 11 and 2nd substrate, and at least one of the 1st substrate 11 and 2nd substrates is constituted by connecting and wiring every (n) striped conductive films 12 and 14 arranged on the substrate electrically by the resistance bodies 13 and 15 and also providing the reference potential point of at least one line on every (n) electrodes. Namely, voltages applied to the respective electrodes are different in value, line by line, owing to voltage drops across the resistance bodies. For the purpose, a pulse signal with a crest value corresponding to gradation or signal with pulse width or pulse number corresponding to the gradation is applied to form an area where the inverted threshold voltage of ferroelectric liquid crystal is applied and an area which does not exceed the threshold value, thereby obtaining the gradation by area variation.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an optical modulation element for a display panel, and more specifically to a display panel using ferroelectric liquid crystal as a liquid crystal material having bistability. In particular, the present invention relates to a liquid crystal optical element suitable for gradation display.

[Summary of the Disclosure] This specification and drawings describe a plurality of striped conductive films in at least one electrode group of a first electrode group or a second electrode group in an optical modulation element for a display panel. By electrically connecting the lines with a resistor and providing at least one line of reference potential points for every three lines, it is possible to easily create a display panel with high density pixels over a wide area, and also to improve gray scale. This invention discloses a technique for making an optical modulation element suitable for display.

C. Prior Art] In a liquid crystal television panel using a conventional active matrix driving method, thin film transistors (TPTs) are arranged in a matrix for each pixel, and a gate-on pulse is applied to the TPTs to bring the source and drain into a conductive state. At this time, a video image signal is applied from the source and stored in the capacitor, and a liquid crystal (e.g. twisted nematic liquid crystal) is driven in response to this stored image signal, and at the same time modulates the voltage of the video signal. Gradation display is performed by doing this.

[Problems to be Solved by the Invention] However, in the active matrix drive type television panel using such a thin-N liquid crystal, the TPT used is
Because TPT has a complicated structure, the number of structural steps is large, resulting in high manufacturing costs. There are problems in that it is difficult to form a film over a long period of time.

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. 1 while scanning
The time during which an effective electric field is applied to one selected point (duty ratio) decreases at a rate of 1/H, which causes crosstalk and has drawbacks such as not providing a high-contrast image. Moreover, when the duty ratio becomes low, it becomes difficult to control the gradation of each pixel by voltage modulation, making it unsuitable for display panels with a high density of wiring, especially liquid crystal television panels.

The present invention has been made in order to solve the above-mentioned conventional problems, and it is possible to easily create a display panel having high-density pixels over a wide area, and also to provide an optical modulation element suitable for gradation display. The purpose is to provide

[Means for Solving the Problems] The present invention provides an optical modulation element in which an optical modulation substance is sandwiched between a first substrate and a second substrate, in which at least one of the first substrate and the second substrate includes: A plurality of striped conductive films disposed on the substrate are electrically connected and wired every n by a resistor, and at least one line of reference potential point is provided for every n of the electrode group. This is an optical modulation element.

[Function] Since the electrodes grouped every n are connected to each other via a resistor, the voltage applied to each electrode has a different value for each line due to the potential drop of the resistor. In other words, n types of potentials are created by n electrodes. therefore.

By applying a pulse signal with a peak value corresponding to the gradation, or a signal with a pulse width or number of pulses corresponding to the gradation, and forming regions exceeding the inversion threshold voltage of the ferroelectric liquid crystal and regions not exceeding the inversion threshold voltage, Gradation is expressed through changes.

[Example] Embodiments of the present invention will be described below with reference to the drawings.

The optical modulating substance used in the present invention is capable of forming a first optically stable state (for example, a bright state) and a second optically stable state (for example, forming a dark state) depending on the applied electric field. ), ie, has at least two stable states with respect to an electric field, and in particular liquid crystals having such properties are most suitable.

As the liquid crystal having bistability that can be used in the present invention, chiral smectic liquid crystal having ferroelectricity is most preferable, and chiral smectic liquid crystal having chiral smectic C phase (
Sac 1, H phase (SmH 1 phase (Sm 1, F phase (S
+sF◆) or G phase (SmG) liquid crystals are suitable.

Regarding this ferroelectric liquid crystal, “LE JOURNAL de physique rutile” (LEJOURNAL D
E P）IYSIQUE LE TINGTERS'')
In 1975, Jiko (L-69) issue, ``Ferroelectric Liquid Crystals J (rFerroe
lectricliquidCrygtalsJ);
“Applied Physics Letters
ed Physics Letters”) 1980
Year, No. 3G (11), “Submicro Second Bistiple Electro-Optic Switching in Liquid Crystals J”
.

5econd B15table Electroop
tic Switching 1nLiquid Cr
7stalsJ); "Solid State Physics", 1981, Ai (141), "Liquid Crystal", etc., and in the present invention, the ferroelectric liquid crystal disclosed in these can be used.

More specifically, examples of ferroelectric liquid crystal compounds used in the present invention include decyloxybenzylidene-E'-amino-2-methylbutylcinnamate (DOBAMBG).
, hexyloxybenzylidene-E'-amino-2-
(HOBACPC) and 4-o-(2-methyl)-butylresolsiliten-4
'-octylaniline (MBRA8) and the like.

When constructing an element using these materials, the liquid crystal compound is 5tsC", SmH', S+sl-SmF"
, In order to maintain the temperature state such that SmG is happy, the element can be supported by a copper block or the like in which a heater is embedded, if necessary.

FIG. 7 schematically depicts an example of a ferroelectric liquid crystal cell. 71 and 71' are 1.03. S! It is a substrate (glass plate) coated with a transparent electrode such as 102 or ITO (indium tin oxide).

In between, a 5llC phase liquid crystal with a liquid crystal molecular layer 72 oriented perpendicular to the glass surface is sealed. A thick line 73 represents a liquid crystal molecule, and this liquid crystal molecule 7
3 is the dipole moment (
P, ) 74. When a voltage higher than a certain threshold is applied between the electrodes on the substrates 71 and 71', the helical structure of the liquid crystal molecules 73 is unraveled, resulting in a dipole moment) (P,)?
The alignment direction of the liquid crystal molecules 73 can be changed so that all of the liquid crystal molecules 4 are oriented in the direction of the electric field. The liquid crystal molecules 73 have an elongated shape and exhibit refractive index anisotropy in the long axis direction and the short axis direction. Therefore, for example, if polarizers are placed above and below the glass surface in a crossed nicol positional relationship, It is easily understood that this is a liquid crystal optical modulation element whose optical characteristics change depending on the polarity of applied voltage. Furthermore, when the thickness of the liquid crystal cell is made sufficiently thin (for example, lu), the helical structure of the liquid crystal molecules unwinds (non-spiral structure) even when no electric field is applied, as shown in Figure 8, and its dipole moment) P or P takes either an upward (74a) or downward (74b) orientation state. When an electric field E or E' with a different polarity above a certain threshold value is applied to such a cell as shown in FIG. 4a or downward direction 74b,
Accordingly, the liquid crystal molecules enter a first stable state 75 (bright state).
Or, it is oriented to either the second stable state 75' (dark state).

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 liquid crystal molecules has bistability.

To explain the second point with reference to FIG. 8, for example, when an electric field E is applied, the liquid crystal molecules are oriented in a first stable state 75, but this first stable state 75 is maintained even when the electric field is turned off. , when an electric field E' in the opposite direction is applied, the liquid crystal molecules align to the second stable state 75' and change their orientation, but they remain in this state even after the electric field is cut off, and each stable state remains unchanged. It has a memory function. In order to effectively realize such fast response speed and bistability, it is preferable for the cell to be as thin as possible, and generally 0.51L to 20L, particularly 1 to 5L, is suitable. ing.

A liquid crystal-electro-optical device having a matrix electrode structure using ferroelectric liquid crystals of this kind is disclosed, for example, by Clark and Ragabal in US Pat. No. 4.36? , No. 924.

Next, details of a liquid crystal optical element using the above-mentioned ferroelectric liquid crystal will be explained with reference to FIG.

FIG. 1 is a perspective view showing one substrate of a liquid crystal optical element. Reference numeral 11 in FIG. 0 is the substrate on the scanning electrode side.

12-1.12-2.12-3. -.12-X are scanning electrode lines made of a low-resistance metal film, and are arranged in parallel at equal intervals on the substrate 11. 13-1゜13-2. ...13-(X/n) is a resistor made of the same metal film as the scanning electrode line, and is connected to every 8 scanning electrode lines, and Rat, Ra2+ is connected between each electrode line. ...has a resistance value of Ran.

At a position facing the substrate 11, the other information electrode side substrate (not shown) is arranged, and the information electrode line 14-1.14- is configured in the same manner as the scanning electrode line.
2. ...14-Y and resistor 15-1゜15-2. −
-.l5-CY/m) are formed, and Rbl, Rb2 . ...has a resistance value of Rb1.

In addition, resistors 13-1 to 13-(X/n) and 15-1
The connection between the electrode lines by ~15- (Y/m) is made in areas where the upper and lower substrates do not intersect, and the above-mentioned ferroelectric liquid crystal is sandwiched between the upper and lower substrates.

FIG. 2 is a schematic diagram showing the arrangement of electrode lines and resistors. In FIG. 0, the same symbols as in FIG. 1 represent the same parts. According to the electrode configuration described above, the scanning electrode line 12
-1 to 12-Resistor 13- connected to each Xftn
Due to the potential drop of l-13-(X/n), electrode lines having n types of potential are formed, and similarly, transmission electrodes having m types of potential are formed in the information electrode lines 14-1 to 14-Y. That will happen.

For example, in FIG. 2, when a scanning voltage Va is applied to the scanning electrode line 12-1, at point a-1, Va, a
At −2 points, Va(1−Ra+/(Ral”Ra2
” ..., Ran)), at point a-3 Va(1
-(Ra++Ra2)/(Ra++Ra2” ・++
+Ran)), at point a-n Va(1-(R
a++Ra2” ... +Ra(n-+))/(R
al"Ra2+...+Ran)), and n types of potentials are generated.

Similarly, when information voltage Vb is applied to the information electrode line 14-1, Vb is applied at point b-1, and Vb is applied to point b-2 (1-Rh+/(Rb++Rb2+ -"Rw)
), at point b-3, Vb(1-(Rb++Rb2)
/(Rh++Rb2+...+Rb @) ), b-+
The point s point is Vb(1-(Rh++Rh?+ -+R
b(-+))/(Rh++Rb2+ +++ +Rb5
)), and m types of potentials are generated. Therefore, mXn types of potentials are applied to the liquid crystal optical element in one pixel (nine types in the case of pixel A in Figure 1), and at this time, a voltage exceeding the inversion threshold voltage Vth of the ferroelectric liquid crystal is applied. There are areas where the voltage is applied and areas where it is not applied, resulting in a bright state and a dark state. The bright state and the dark state can be changed by mX by applying a value Va or Vb according to the gradation information to each pixel.
Gradation can be expressed as area gradation where n area is one pixel. At this time, the gradation properties of Va and Vb can also be controlled by modulating their voltage values according to the gradation information or by modulating their pulse widths according to the gradation information.

In addition, in the above driving, prior to applying the above-mentioned gradation signal, an erasing step is provided to put the pixel into either a bright state or a dark state, and an inversion voltage for inverting the state is applied to the gradation level. It is necessary to control the voltage to be applied to the ferroelectric liquid crystal according to the temperature.

Next, the structure of the liquid crystal optical element will be explained by giving a specific example.

In FIG. 1, an ITO (Indium-Tin-Oxide) film, which is a transparent electrode with a thickness of about 100 OA, is formed in stripes at intervals of 101 L* by sputtering on a substrate 11 made of a glass plate, and scan electrode lines 1
2-1 to 12-X. The sheet resistance of this electrode is 20
It was Ω/mouth.

At the same time as scanning electrode lines are formed, resistors 13-1 to 13-(
In this embodiment, this resistor is connected to three scanning electrode lines each (n=3), and the resistance value of each is set to Ral.
= 500Ω, Ra2 = 500Ω.

Ra3 = 500 Ω (Rat: Ra2:
Rax = 1:1:1), and the terminal end of Ra3 was set as the reference potential point (GND).

On the other hand, information electrode lines 14-1 to 1 on the substrate on the information electrode side
4-+s has the same configuration as the scanning electrode lines 12-1 to 12-n, and the resistors 15-1 to 15-(Y/m) are connected to three information electrode lines (m=3), respectively. The resistance values are Rbl = 500Ω, Rb2 = 500Ω,
Rb3 = 500Ω (Rbl: Rb2: Rb3
=1:1:1).

Further, the terminal end of Rb3 was set as a reference potential point (GND).

A polyvinyl alcohol layer of approximately 50 OA was formed on the surface of each of the two substrates thus created as a liquid crystal aligning film (not shown), and the resistors 13 of the two substrates were subjected to a rubbing process. -1 to 13-(X/n) and 15
-l-15- (Y/m) is placed at a position where the upper and lower substrates do not intersect, and the substrates are placed opposite each other, and the gap is adjusted to approximately 1p.Then, the ferroelectric liquid crystal is (p
liquid crystal composition containing p'-(2-methylbutyloxy)phenyl ester and p-(eta)-octyloxybenzoic acid-p'-(2-methylbutyloxy) phenyl ester) as main components. In this example, the area where the scanning electrode line intersects with the information electrode line has dimensions of 90×90, and is formed by nine intersections. The dimensions of pixel A were approximately 3001L x 300 IL.

Next, polarizing plates (not shown) were arranged in crossed nicols on both sides of the liquid crystal cell thus formed, and the optical characteristics were observed.

FIG. 3 is a cross-sectional view of the liquid crystal cell, which schematically shows the method of applying an electric signal, and FIG.
The figure shows the electrical signal given at that time. 4 shows the waveform of the signal (a) generated in the drive circuit 16 in FIG. 3, and FIGS. 5(a) to (e) show the waveform of the signal (b) generated in the drive circuit 17 in FIG. 3. It represents.

Now, before displaying, as signal (a) -12
An erasure step is provided in which a 2004 sec pulse of V and a 200 p sec pulse of 8 V are synchronously applied as signal (b) (this is called an erasure pulse). Then, the liquid crystal is switched to the first stable state, and the entire pixel A becomes a bright state (in this embodiment, the crossed polarizing plates were arranged in this way).

In this state, various pulses as shown in FIGS. 5(a) to 5(e) are used as signals (b), and information electrode lines 14-1, 14-4 in FIG. Auto, 14-(x-2
) is applied in synchronization with the pulse from the drive circuit 17, and the optical state (gradation) of the pixel A is shown in FIG.

At this time, the pulses shown in FIG. 4 are used as the pulses from the drive circuit 17.

In addition, the terminal end of Ra3 of the resistors 13-1 to 13-(X/n) and the terminals of Ra3 of the resistors 15-1 to 15-(Y/11) (7) R
The terminal end of b3 is connected to a reference potential point (Ov here).

Information electrode line! 4-1, pulse applied voltage -1v ($5
In the case of applying the pulse voltage of -3V (Fig. 5(b)), no change from the bright state 61 occurs at all (see Fig. 6(a)). Line 14-
The liquid crystal near 1 has its threshold voltage (here 10.5V)
Switching to the dark state 62 for electric fields exceeding (
(see Figure 6(b)), and when the applied voltage is further increased to -6V (Figure 6(C)) or -9V (Figure 6(d)), the area exceeding the liquid crystal inversion threshold increases. For,
The area of candy-like s62 becomes wider (Fig. 6 (C), (d)
), the entire pixel A is switched to the dark state at an applied voltage of -24 V (see FIG. 5(e)) (see FIG. 6(d)).
.

In this way, by setting the voltage value of the applied voltage corresponding to the inversion area, it is possible to form an image with gradation.

In the above embodiment, prior to writing, all pixels or a predetermined portion of pixels are set to either a bright state or a dark state at once, or each writing line is After bringing all or a predetermined portion of the scan electrode into either the bright state or the dark state, the scan electrode life 12-1.12-4.12-7.・
-, 12-(X-2) (7) The pulses shown in FIG. 4 are sequentially applied as scanning signals. At this time, it is preferable that the scan selection signal be a pulse having a voltage equal to or slightly smaller than the inversion threshold voltage of the ferroelectric liquid crystal.

On the other hand, information electrode line 14-1.14-4.14-7.
....

14-(Y-2) in the order of scanning electrode lines 12-1.・・・
・.

12-(X-2), pixels on the scanning line are gradated by applying voltage signals according to gradation information as shown in FIGS. 5(a) to (8). You can write according to the key. Therefore, by performing the above-described writing operation in line-sequential writing, it is possible to form one screen with gradation.

Above, in the embodiments of the present invention, ferroelectric liquid crystals, particularly ferroelectric liquid crystals having at least two stable states, have been described as the most preferable example.
It can be applied to twisted nematic liquid crystals, guest-host liquid crystals, and even devices other than liquid crystals.

Also, as a range of one pixel, n=3. Although the example in which m=3 has been described, the combination of m and n is not particularly limited. Furthermore, the resistor that connects the electrodes can be formed by various methods such as a printing method in addition to the sputtering method, and these methods can also be applied to resistors made of other materials.

[Effects of the Invention] As explained above, according to the present invention, the substrate structure can be made simple, so a display panel having high density pixels over a wide area can be easily created. . Furthermore, since the gradation of each pixel can be easily controlled by voltage modulation, it is possible to provide an optical modulation element suitable for gradation display. Furthermore, since the manufacturing process is simplified, costs can be significantly lowered than in the past.

[Brief explanation of drawings]

Figure 1 is a perspective view showing one substrate of a liquid crystal optical element, Figure 2 is a perspective view showing one substrate of a liquid crystal optical element;
The figure is a schematic diagram showing the arrangement of electrode lines and resistors, Figure 3 is a cross-sectional view of a liquid crystal cell, Figure 4 is a waveform diagram of signal (a), Figure 5 is a waveform diagram of signal (b), and Figure 5 is a waveform diagram of signal (b). FIG. 6 is a diagram showing the gradation of pixel A, and FIGS. 7 and 8 are schematic diagrams of a ferroelectric liquid crystal cell. ll: Substrate, 12-1 to 12-X: Scanning electrode line, 14-1 to 1
4-Y: Information electrode line, 13-1 to 13-(X/n
), 15-1 to 15-(Y/m): Resistor, lfi
, 17: Drive circuit.

Claims (1)

[Claims] 1) In an optical modulation element having a matrix structure in which an optical modulation substance is sandwiched between a pair of substrates on which a first electrode group and a second electrode group are provided, the first electrode group or The plurality of striped conductive films of at least one electrode group of the second electrode group are electrically connected every n by a resistor, and at least one line of reference potential point is provided for every n. An optical modulation element. 2) The optical modulation element according to claim 1, wherein the optical modulation substance is a ferroelectric liquid crystal. 3) The optical modulation element according to claim 1, wherein the optical modulation substance is a chiral smectic liquid crystal.