JPS62239127A - Optical modulating element - Google Patents

Abstract

PURPOSE:To write to a display panel at a light speed by providing low- resistance parts and high-resistance parts on at least one of the first and second conductive films and setting the difference of film thickness between them to a specific value or smaller. CONSTITUTION:High-resistance parts 32 used as display conductive films are formed in stripes on one substrate 31. Low-resistance parts 33 formed in stripes are formed in parallel at equal intervals in a conductive film 30. The film thickness of high-resistance parts 32 and low-resistance parts 33 is set to <=100Angstrom to attain picture elements in which a ferroelectric liquid crystal is oriented without causing orientation defects. Thus, quick write to the display panel is possible, and a gradation signal modulated by a voltage value, a pulse width, the member of pulses, or the like is applied as the input signal to display gradations.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical modulation element for a display panel, and more particularly to a display panel using a liquid crystal material having bistability, particularly a ferroelectric liquid crystal, The present invention relates to a liquid crystal optical element suitable for displaying images.

[Conventional technology]

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

However, in active matrix drive type television panels using such TN liquid crystals, the TPT used is
Because TPT has a complicated structure, it requires a large number of structural steps and high manufacturing costs, and it is difficult to spread the thin film semiconductor (e.g. polysilicon, amorphous silicon) that makes up TPT over a large area. There are problems such as difficulty in forming a film over the entire area.

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

Means for Solving the Problems and Effects The object of the present invention is to solve the above-mentioned drawbacks, and specifically, to provide a display panel having high density pixels over a wide area, particularly suitable for gradation display. An object of the present invention is to provide an optical modulation element.

That is, the present invention provides an optical modulation device having a first substrate provided with a first conductive film, a second substrate provided with a second conductive film, and an optical modulation material disposed between the first substrate and the second substrate. In the element, at least one of the first conductive film and the second conductive film has a low resistance part and a high resistance part having a higher resistance than the first conductive film, and the low resistance part and the high resistance part have an II thickness. The difference is 1oooλ
The optical modulation element has the following characteristics. Furthermore, another feature of the present invention is that a potential gradient is applied to one pixel, and 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 each pixel, The present invention provides an optical modulation element suitable for a driving method that expresses gradation by forming regions within a pixel that exceed an inversion threshold voltage and regions that do not exceed an inversion threshold voltage.

<Example> The present invention will be described below with reference to the drawings. As the optical modulating substance that can be used in the present invention, the first
a second optically stable state (e.g. forming a bright state) and a second optically stable state (e.g. forming a dark state), i.e. having at least two stable states with respect to an electric field; In particular, liquid crystals having such properties are most suitable.

As the liquid crystal having bistability that can be used in the optical modulation element of the present invention, chiral smectic liquid crystal having ferroelectricity is most preferable, and among these, chiral smectic C phase (0 Sm), H phase (0 SmH), 1 Phase (Sm
l*), F-phase (SmF), and G-phase (SmG) liquid crystals are suitable. Regarding this ferroelectric liquid crystal.

"Le Journal de Feuisique L'Etre" (
” L E J O U R N A L D E
PHYSIQUE LETTRE”) Volume 36 (L
-69) 1975 “Ferroelectric-Liquid Crystals J”
c Liquid CrystalS”): “Applied Red Physics Letters” (“App
lied Physics Letters”) M2S
Volume, No. 11.

1980's "Submicro Second Bistiple Electro-Optic Self-Switching-in-Liquid List" (rsubmicro 5ec
ond B15table Electroopt
ic Switching in Liquid
Cryste+s”):”Solid State Physics↓6 (141)
1981 "Liquid Crystal", etc., and the ferroelectric liquid crystal disclosed in these documents can be used in the present invention.

More specifically, an example of the ferroelectric liquid crystal compound used in the method of the present invention is decyloxybencylidene-y-amino-2-methylbutylcinnamese (DOBAMBC
), hexyloxypensyritene-y-amino-2-
Chloropropyl cinnamate (HOBACPC) and 4-o-(2-methyl)-butylresolsiliten-4'
-Octylaniline (MBRA8)? can be mentioned.

When constructing an element using these materials, the liquid crystal compound is SmC wood, SmH wood, or SmI wood.

In order to maintain the temperature state such that SmF wood or SmG wood is obtained, 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 I n203.

A substrate (glass plate) coated with transparent electrodes such as Sn02 and IT○ (indium tin oxide), and an SmC wood phase liquid crystal with liquid crystal molecular layers 12 oriented directly on the glass surface between them. is included. The thick line 13 represents a liquid crystal molecule, and this liquid crystal molecule 1
3 is the dipole moment (P
Engineering) 14. When a voltage higher than a certain threshold is applied between the substrate 11 and the quasi-pole of l l'-H, the liquid crystal molecules 1
The helical structure of 3 unravels and the dipole moment (P engineering) 1
The inside direction of the liquid crystal molecules 13 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 13 have an elongated shape and exhibit a refractive index anisotropy of 1 in the long axis direction and the short axis direction. Therefore, for example, polarizers arranged in a crossed nicol position above and below the glass surface can be used. It is easily understood that if the device is placed in the same position, it becomes 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, 1μ), 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 its dipole The moment P or y is oriented in either a direction (24) or a direction downward (24').

-M Hee A fP J? +l-L de m
'l) When an electric field E or E' with a different polarity is applied, the electric field vector of the dipole moment electric field E or E' is Correspondingly, E direction 24 or downward direction 2
4', and accordingly the liquid crystal molecules are in the first stable state 23 (four-shaped 7g) or in the second stable state 23' (
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. 2, for example, the electric field E
When is applied, the liquid crystal molecules are oriented in the first stable state 23, or this state remains ``this first stable state even if the upper bound is cut;
23 is maintained and an opposite electric field E' is applied,
The liquid crystal molecules are aligned 1. in a second stable state 23'. However, even if the electric field is changed to pj, the molecules remain in this state, and each stable state has a memory function. In order to effectively realize such speed of response and bistability, it is preferable for the cell to be as thin as possible, and in terms of -M, it is preferable to use a cell with a thickness of 0.5 to 20 mm, especially Ig to 5 AL. Are suitable. A liquid crystal-electro-optical device having a matrix electrode structure using a ferroelectric liquid crystal of this kind has been proposed, for example, by Clark and Ragapal in US Pat. No. 4,367,924, Boo 7.

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 a high resistance portion formed in a stripe shape and used as a display conductive film. 33 is a low resistance portion formed in a stripe shape on the conductive M 30. The low resistance portions 33 are formed in a row in the conductive film 30 at equal intervals. Further, another substrate (not shown) faces 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 optical modulation material described above is sandwiched between the two substrates.

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

In FIG. 3, Zn is added to In2O3 on a glass substrate 31.
EB (Electron Heem) is the addition of ○2 by lO weight ♀%! Depending on how you wear it.

A conductive film 3o was formed. This guide
The root resistance of the other one was 250Ω/□. Then 1
With a thickness of 00, the conductivity of Sn is 111, and the conductivity is 30.
After the empty N arrival 1-, it was patterned into a stripe shape.

Next, the substrate was heated at 1000° C. for 30 minutes in an oxygen atmosphere to thermally diffuse Sn into the conductive film 3°. Thereafter, excess Sn that did not participate in the diffusion was removed by etching to form a low resistance portion 33. At this time, the sheet resistance corresponding to the conductive film, that is, the high resistance portion 32, is lo.

KΩ/□, the sheet resistance of the low resistance part (transmission electrode) 33 is 2
It became 0Ω/'mouth. At this time, the interval between the 33 minutes of the low resistance portion was 230 gm, and the line width was 20 pm. - On the other hand, the high resistance part 32 and the low resistance part 3 are
3 was formed.

A polyvinyl alcohol layer of about 500 layers was formed as a liquid crystal alignment film on the surface of each of the two substrates thus produced, and a lahing process was performed.

Next, the two substrates were placed opposite each other, the gap was adjusted to about 1 p, and the ferroelectric liquid crystal (p-η-octyloxybenzoic acid-y-(2-methylbutyloxy) phenyl ester) and p-η- A liquid crystal composition containing nonyloxybenzoic acid-P'-(2-methylbutyloxy)phenyl ester as a main component was injected.

According to the above-mentioned method, it is possible to form a flattened conductive film in which the difference in film thickness between the one-island resistance part 32 and the low-resistance part 33 is substantially zero, but in the present invention, the high-resistance The difference in film thickness between the portion 32 and the low resistance portion 33 is set to 1000 Å or less, preferably 8 Å or less.
The thickness can be set to 00 Å or less, particularly preferably 500 Å or less. If the film thickness difference mentioned above exceeds 1000 years,
There is a problem in that alignment defects occur in domains of ferroelectric liquid crystals, particularly chiral smectic liquid crystals, and normal switching drive cannot be performed in regions where the alignment defects exist.

As described below, an optical modulation element in which a high resistance part 32 and a low resistance part 33 are formed for each pixel unit is an element suitable for a gradation expression method. The feature is that by setting the film thickness with the portion 33 to 1000 Å or less, the ferroelectric liquid crystal within one pixel can be made into an aligned ferroelectric liquid crystal pixel without causing alignment defects. are doing.

Further, in another specific example of the present invention, the conductive film 30 is made of IT.
○After forming Ili by vapor deposition on the substrate 31, the high resistance part 3
Zn can be diffused into the conductive film in the region corresponding to 2. At this time, the conductivity of the region where Zn is not diffused is
It is possible to use the film as the low resistance portion 33.

The sheet resistance of the low resistance section 33 used in the present invention is 103Ω.
/□ or less, preferably 102Ω/□ or less, and the sheet resistance of the high resistance portion 32 is set to 102Ω/□ or more, preferably 103Ω/□ to IMΩ/□.

In the liquid crystal optical element constructed as described above, a potential gradient is applied in the plane of the high resistance part 32 used as a conductive film for display by a signal voltage applied to the low resistance part 33 used as a transmission electrode line, so that the opposite A potential difference gradient is generated in the electric field between the electrode 34 and the low resistance portions 33a and 33c are connected to a reference potential point VE (for example, O port), and a predetermined signal voltage Va is applied to the low resistance portion 33b. , in the in-plane length direction of the high resistance portion 32 between the low resistance portions 33a and 33b or between 33b and 330 as shown in FIG. 4(a)! ; A potential gradient of Va can be applied to L1 and intersection 2. At this time, the inversion threshold voltage vth of the ferroelectric liquid crystal is set to Va
When -vb is applied to the counter electrode 34, the in-plane length directions m1 and m of the conductive film 32 change as shown in FIG.
A potential difference Va+vb greater than the inversion threshold voltage vth is applied to the ferroelectric liquid crystal corresponding to 2, and the ml
The area corresponding to and m2 can be reversed 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 (peak value) of the voltage signal -vb applied to the counter electrode 34 may be modulated according to the gradation information, or the pulse width thereof may be modulated according to the gradation information. Alternatively, 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 in which the pixel is in either a bright state or a dark state, an inversion voltage that inverts the state IE is controlled according to the gray scale and applied to the ferroelectric liquid crystal. It is necessary to keep

FIG. 5 schematically shows a method of applying electrical signals, and FIGS. 6 and 7 show electrical signals. 6 shows the waveform of the signal (a) generated in the drive circuit 53 of FIG. 5, and FIGS. 7(a) to (e) show the waveform of the signal (b) generated in the drive circuit 54 of FIG. It represents.

Now, as signal (a), -12v 200p-se
200 g of 8V with c pulse as signal (b)
An erasing step is provided in which the s e c pulse is applied synchronously in advance (this is called an erasing pulse). 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).

In this state, when various pulses as shown in FIGS. 7(a) to (e) are applied as signals (b) to the transmission electrode 33b in synchronization with the pulses from the drive circuit 44, the optical The state is shown in FIG. At this time, the drive circuit 44
The pulses from can be the same as those in FIG.

Pulse applied voltages -2V (corresponding to Figure 7(a)) and -5V
(corresponding to Fig. 7(b)), no change from the bright state 81 occurs (corresponding to Fig. 8(a)), but when the pulse applied voltage is -8V (Fig. 7(c)), 'v+ wide) v
l 10 I EJ Okaue *M 7 'E, k tn
:E Azusa's liquid crystal switches to IfS state 82 (corresponding to Figure 8(b)).Furthermore, the applied voltage is changed to 11.
When the length is increased to 4V (corresponding to Fig. 7(d)), the candy-like area of 7.882 becomes wider as shown in the figure (Fig. 8(c)).
), the entire pixel A is switched to the dark state 82 at an applied voltage of 20 V (corresponding to FIG.
d)). In this way, pixels with gradation can be formed.

still,! In Figure J'55, 51 represents a ferroelectric liquid crystal, preferably a chiral smectic liquid crystal under a bistable state, and 52 represents a counter substrate.

FIG. 9 shows a specific example of applying the gradation expression method according to the present invention to matrix driving.

In the liquid crystal optical element shown in FIG. 9, a plurality of stripe-shaped electrodes 91 are provided on one substrate, and a plurality of stripe-shaped high-resistance portions 92 with opposing round necks intersect with the stripe-shaped electrodes 91. It is provided on the other substrate via a dielectric liquid crystal. Furthermore, the above-mentioned striped high resistance portion 92
Low-resistance portions 93 and 94 are wired as electrical transmission electrode lines at both ends of each.

In the driving method of the present invention, scanning signal pulses are sequentially applied to the striped electrodes 91 as scanning lines SL+S2+53, etc., and in synchronization with the scanning signal pulses, the low resistance portions 9
Information lines I 1 , I 2 , I 3 formed by 3.
By applying an information signal to , it is possible to form one screen of gradation images. At this time, the basic potential point line G1. which is the low resistance portion 93. G2. G3... is, for example, 0
I'll connect you at 7 o'clock. The information signal mentioned above can also be a pulse signal with a pulse width, pulse number, or peak value depending on the gradation. In this case, before writing to the pixel, the pixel is It is necessary to align the display state based on one of the stable states.

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

〔Effect of the invention〕

According to the present invention, high-speed writing to the display panel is possible, and gradation display can be performed by applying a voltage value or a gradation signal modulated by the pulse width or number of pulses as an input signal. I can do it.

Furthermore, according to the present invention, uniform alignment control can be performed over the entire surface of the ferroelectric liquid crystal element, and complete ON-OFF operation of the liquid crystal can be performed.

For this reason, not only the appearance was improved compared to the conventional one having alignment defects due to steps, but also the apparent contrast was improved.

[Brief explanation of drawings]

1 and 2 are perspective views schematically showing a ferroelectric liquid crystal element used in the present invention. FIG. 3 is a perspective view of the present invention. Figure 4(a). (b) is an explanatory diagram schematically representing a potential gradient used in the present invention. FIG. 5 is a sectional view of a liquid crystal optical element used in the present invention. FIG. 6 and FIGS. 7(a) to (e) are explanatory diagrams showing pulse waveforms used in the present invention. FIGS. 8(a) to 8(d) are schematic diagrams showing the gradation of pixels. FIG. 9 is a plan view showing another specific example of the present invention. Patent applicant: Canon Corporation 1jnu! 2) Ll-product L 4

Claims (11)

[Claims] (1) In an optical modulation element having a first substrate provided with a first conductive film, a second substrate provided with a second conductive film, and an optical modulation substance disposed between the first substrate and the second substrate. , at least one of the first conductive film and the second conductive film has a low resistance part and a high resistance part with a higher resistance than the first conductive film, and the difference in film thickness between the low resistance part and the high resistance part is An optical modulation element characterized by having a thickness of 1000 Å or less. (2) The optical modulation element according to claim 1, wherein the low resistance portions and the high resistance portions are alternately formed in a stripe shape. (3) The optical modulation element according to claim 1, wherein the sheet resistance of the low resistance portion is 10^3Ω/□ or less. (4) The optical modulation element according to claim 1, wherein the sheet resistance of the high resistance portion is 10^2 Ω/□ or more. (5) The optical modulation element according to claim 1, wherein the low resistance portion is a member formed by a diffusion method. (6) Claim 1, wherein the low resistance portion is a striped low resistance portion formed by forming a metal film on a conductive film in a stripe shape and then diffusing metal into the inside of the conductive film. The optical modulation element described above. (7) The optical modulation element according to claim 1, wherein the optical modulation substance is a ferroelectric liquid crystal. (8) The optical modulation element according to claim 7, wherein the ferroelectric liquid crystal is a chiral smectic liquid crystal. (9) The optical modulation element according to claim 1, wherein the high resistance portion is formed for each pixel, and a potential gradient is formed in the high resistance portion when writing to the pixel. (10) The difference in film thickness between the high resistance part and the low resistance part is 800
The optical modulation element according to claim 1, wherein the optical modulation element has a thickness of Å or less. (11) The difference in film thickness between the high resistance part and the low resistance part is 500
The optical modulation element according to claim 1, wherein the optical modulation element has a thickness of Å or less.