JP2564514B2 - Liquid crystal device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Application of the Invention The present invention relates to a liquid crystal device using a smectic liquid crystal which is one of the typical examples of liquid crystal, particularly a ferroelectric liquid crystal (hereinafter referred to as FLC), a microcomputer, A liquid crystal device for thinning the display portion of a word processor or a television,
Furthermore, the present invention relates to a liquid crystal device applied to a memory device such as a disk memory and an audio device such as a speaker.

“Prior Art” Conventionally, when a liquid crystal device is to be manufactured using a liquid crystal,
A method is known in which a pair of electrodes are provided inside a pair of substrates of this liquid crystal, and a symmetrical alignment film is provided on the electrodes.

However, in such a simple matrix structure or an active device structure in which a non-linear device is connected in series to each pixel, the most important factor is that the smectic liquid crystal has a sufficiently large Ec (critical electric field or threshold electric field). is important. This Ec maintains the initial state (for example, non-transmissive) of the liquid crystal below a predetermined electric field,
It is a phenomenon in which it is extremely sharply inverted at a predetermined electric field or more and exhibits another state (for example, transmission), and vice versa. That is, the Ec is the (critical electric field that is observed when adding positive electric field) Ec ^+, Ec conversely ^-
(Electrical field existing when negatively applied). The Ec ⁺ and Ec ^- but is not identical necessarily in absolute value,
The alignment can be made almost the same depending on the process condition of the alignment treatment in contact with the liquid crystal, but the control is extremely difficult.

However, the existence of such Ec ⁺ and Ec ⁻ is extremely poor in the liquid crystal itself, and particularly in the ferroelectric liquid crystal using the chiral smectic C phase, the value of the electric field strength of the pulse electric field for applying the liquid crystal and its pulse width Heavily depends on. Therefore, in the matrix display, the excitation method known as "AC bias method" must be used, and when rewriting in the positive direction, a negative pulse is added once, and then a positive pulse is applied with a predetermined electric field strength. And time are precisely controlled and added. On the contrary, when rewriting in the negative direction, a positive pulse must be applied once, and then a negative pulse must be applied under the precise control of the predetermined electric field strength and time.

"Problems to be solved by the invention" When such a liquid crystal, particularly a ferroelectric liquid crystal, is used, the "AC bias method" described above is used in the conventional technology.
Must be used. However, since this bias method makes the peripheral circuit extremely complicated, a simpler peripheral circuit is required for a display device. For that purpose, it is important that the liquid crystal itself has a sufficiently clear Ec. For this reason, when performing asymmetric alignment treatment (the main components of one alignment treatment layer and the other alignment treatment layer are made different), Ec ⁺ and Ec ⁻ are different, and a bias voltage in series with the liquid crystal must also be applied. . In addition, the fact is that we have to be satisfied with insufficient Ec. In the present invention, when such a ferroelectric liquid crystal is used, it is not required that the liquid crystal itself has Ec, but the liquid crystal and the nitride film on the electrode are regarded as an integral body, and substantially effective as a whole. It is a thing that obtained Ec.

"Means for Solving the Problem" The present invention is particularly effective for a liquid crystal that switches light in the direction of an electric field, not a liquid crystal that switches light depending on the presence or absence of an electric field. Therefore, a ferroelectric liquid crystal (FLC) is used as a liquid crystal material as a typical example. Further, as a factor that determines the Ec of the liquid crystal, a thin film or a cluster of a dielectric film nitride film is provided on both of a pair of substrates in close or substantially close contact with the FLC. Then, the inventors tried to determine Ec of the ferroelectric liquid crystal substantially by the dielectric film.

 The longitudinal sectional view is shown in FIG.

In FIG. 1, a ferroelectric liquid crystal (FLC) (1), dielectric films (2) and (2 '), a pair of translucent electrodes (3) and (3'), and a translucent substrate ( 4), (4 ')
It has an alignment film (5) for aligning liquid crystal molecules in a uniaxial direction.

 The electrical equivalent circuit of FIG. 1 is shown in FIG.

FIG. 2 (A) is an equivalent circuit of FIG. That is, there is a nitride film (2) between the terminals (8) and (9) or a nitride film (2 ') between the terminals (6) and (7).
The nitride coatings (2) and (2 ') were made of the same material type and the same thickness. Then the dielectric (2), having a (2 ') each capacitor (C _1), conductance (G _1). Also, FLC exists between the noses (8) and (7). Since this FLC is insulating, it is similarly expressed as a capacitor (1 / 2C ₂ ) and conductance (2G ₂ ). Further, the voltage applied to C ₁ , G ₁ is V ₁ , 2G ₂ , and the voltage applied for 1 / 2C ₂ is 2V _2, and a voltage of 2V ₀ is applied to the whole. Then Q ₁ is added to C ₁ and the charge of Q ₂ is induced in C ₂ .

Also, the charge (Q ₂₁ ) is applied to the nose (8) and the charge (Q) is applied to the nose (7).
There are _twelve . In such a case, the equivalent circuit can be modified as shown in FIG.

This equivalent circuit can be expressed vertically symmetrical (mirror-symmetrical) with respect to AA ', and (10) and (10') have the same voltage. Therefore, the upper side of the circuit of FIG. 2 (B) can be transformed into FIG. 2 (C). Therefore charge Q present in both ends of the FLC (1) can be represented by _{Q = Q 21 -Q 12 Q 21} = -Q 12 Q = 2Q 21.

 Therefore, in the following, consideration will be given with reference to FIG.

In FIG. 2 (C), when a voltage V ₀ is applied between these terminals, the voltage V ₁ applied to C ₁ and G ₁ and the voltage applied to the charges Q ₁ , C ₂ and G ₂ are V ₂ and If the charge is Q ₂ , then V ₀ = V ₁ + V ₂ At t = 0.

At this time, the thickness of the nitride film is less than 1000Å
Since C has a thickness of 2-3 μ, C ₁ is sufficiently larger than C ₂ . As a result, V ₂ ≒ V _{0 in} the initial state, and almost all of the applied voltage is applied to the FLC in the initial state.

Further, Q ₂₁ accumulated after t seconds at the interface between the nitride film and the FLC is given by the following equation.

In this general formula, consider the condition that C ₁ > C ₂ described above. The resistance (reciprocal of conductance) is about 2 for liquid crystal.
If it has a thickness of μ and one pixel is 300 μ × 300 μ, it has an order of 10 ⁹ Ω.

On the other hand, the nitride film has an order of 10 ¹² Ω or more at a thickness of 1000 Å, and has a resistance sufficiently higher than that of liquid crystal. Therefore, the following equation is obtained by transforming the above equation with G ₁ ≈0.

Given in. Then, as a result, V ₁ and V ₂ are Transform the above formula Given in.

Furthermore, when to this V ₁ t is sufficiently large, it approaches V ₁ = V _0.

That is, in the initial stage of application, most of the voltage applied between the electrodes is applied to the FLC, and with respect to that value, most of the voltage is applied to the nitride film. In other words, first put the FLC in motion. Thereafter, this voltage is applied to the nitride film, and charges are stored in the nitride film. Inversion or non-inversion of the FLC having a sufficiently small Ec is determined by the type and amount of this charge.

As a result, even if the FLC does not have sufficient Fc, by variably controlling the type and amount of charges stored in the nitride film, the FLC follows the dependency, and as a result, the FLC apparently has a large Ec. be able to. From the above results, the idea of the present invention is to allow a nitride film to exist in series with the smectic liquid crystal and to determine the inversion and non-inversion of the liquid crystal according to the kind and amount of charges stored in the nitride film.

And the types of nitride coatings (2) and (2 ') in FIG.
C ₁ , G ₁ , C ₂ , G ₂ can be changed by changing the thickness, and E
c ^-, it can control the value of EC ^+. Also, as the thickness increases, Ec increases, so when considering practical driving, 100
The range of ~ 4000Å was suitable. In order to make the values of Ec ⁻ and EC ⁺ absolute, the nitride films (2) and (2 ′) on the pair of substrates can be controlled to the same film by using the same material and the same process. I liked it.

 Hereinafter, examples of the present invention will be described.

Embodiment 1 FIG. 1 is a vertical sectional view of the constitution of the present invention.

In the drawing, transparent conductive films (3) and (3 ′), for example, ITO (indium tin oxide) are provided on glass substrates (4) and (4 ′), and a silicon nitride film (as a dielectric film) is formed on the upper surface of one of them. 2) Similarly, a silicon nitride film (2 ') is provided on the upper surface of another electrode (2').

That is, silane (Si
A silicon nitride film is formed from nH ₂ n + 2, n ≧ 1) and ammonia (NH ₃ ) or nitrogen. In particular, when the dielectric film is formed by the photo-CVD method, the dielectric film can be formed without damaging the underlying ITO film, and a liquid crystal device with good interface characteristics can be provided with a sharp (steep) Ec. Can be given. The thickness of this silicon nitride was about 50 to 4000 Å, and about 1000 Å with little attenuation of the amount of transmitted light was good. When the average thickness was less than 200Å, the two were in a cluster or in a mixed state in the middle. In the present invention, a known alignment film (5) such as nylon, PVA, polyimide or the like is formed on one side (2) of the dielectric film, and a known organic rubbing treatment is applied to the alignment film. (Alignment treatment layer)
And

Next, the peripheral portions of the pair of substrates each having the alignment film formed on one side thereof were sealed (not shown) with each other and filled with FLC by a known method. As the liquid crystal to be filled, a liquid crystal having a switching characteristic in the direction of the electric field, particularly FLC, was used. For example, a mixture of ester biphenyl FLC in a ratio of 2: 3 was used. The liquid crystal used is preferably 50 ° C to 0 ° C.
It is preferable that it exhibits ferroelectricity in the temperature range of about ° C.

The electrodes of this cell were 1 mm × 1 mm, and they were arranged in a matrix, and a voltage of ± 5 V was applied between the electrodes while scanning.
Then, even if this electric field is applied, it becomes possible for the pixel to have a very clean Ec which cannot be seen by the conventional method using only the silane coupling type.

Then, once the positive charge of Ec ⁺ or more is applied, the previous state is maintained even if the voltage is removed. On the other hand, it can be seen that when a negative voltage of Ec- or higher is applied, the previous state can be similarly maintained even if the voltage is removed.

FIG. 3 (b) shows the results measured by the measuring system of FIG. 3 (a). The vertical axis represents the normalized photomultiplier sensitivity and the horizontal axis represents the applied voltage. Curves (20) and (20 ') shown as comparative examples in this drawing have a cell structure in which a dielectric film is formed on only one side. In the present invention, the curves (19) and (19 ′) can be obtained, and Ec ⁺ and EC ⁻ which are extremely clean and symmetrical can be obtained. And this Ec ^+, EC ^- be less voltage is applied, transmission, non-transmitted does not change. Therefore, matrix display is possible. Because it has such a clear symmetrical Ec, for example
It may be possible to make a display with no crosstalk even for a large area display having 720 × 480 pixels.

In the present invention, further clearing (alignment is performed by unilaterally shifting a minute distance after filling the liquid crystal)
It is effective to replace the rubbing method and the temperature gradient method with the rubbing method or to carry out the rubbing method.

"Effect" As described above, the present invention provides a nitride film on both of a pair of electrodes in a thin film form or a cluster form.
Therefore, it was possible to obtain a liquid crystal device in which Ec is more clear and absolute values of Ec ⁺ and EC ⁻ are equal to each other as compared with the conventional method in which the nitride film is not used at all or only one of them is used.

Thus, if the absolute values of Ec ⁺ and EC ⁻ are equal, a wide margin can be obtained when driving the liquid crystal device.

The nitride film may be selectively formed only on the electrodes in FIG. 1 or the like, or may be formed on the entire surface including the electrodes.

In addition, this dielectric film has a function of preventing impurities from entering from the substrate and the transparent conductive film. The dielectric film is preferably a nitride film having stable properties such as silicon nitride, aluminum nitride, boron nitride, magnesium nitride, tin nitride, antimony nitride, indium nitride, or a mixture thereof.

This liquid crystal device can be applied not only to a display but also to a speaker, a printer or a disk memory, and can be applied to all liquid crystal devices using the optical anisotropy of smectic liquid crystals.

[Brief description of drawings]

 FIG. 1 is a longitudinal sectional view of the liquid crystal device of the present invention. FIG. 2 shows an equivalent circuit diagram of the present invention. FIG. 3 shows an example of the characteristics of the present invention and the conventional example. (1) ...... Liquid crystal (2) (2 ') ...... Nitride film (3) (3') ...... Electrode (4) (4 ') ...... Substrate (5) ...... Alignment treatment (film) (12) ) (14) …… Polarizer (15) …… Photomul (13) …… Sample

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshiji Hamaya 7-21-21 Kitakarasyama, Setagaya-ku, Tokyo Inside Semiconductor Energy Laboratory Co., Ltd. (72) Toshiharu Yamaguchi 7-21-21 Kitakarasyama, Setagaya-ku, Tokyo No. 21 Semiconductor Energy Laboratory Co., Ltd. (72) Inventor Takashi Inujima 7-21-21 Kitakarasuyama, Setagaya-ku, Tokyo Semiconductor Energy Laboratory Co., Ltd. Examiner Motofumi Tabe (56) References JP 60-156043 (JP) , A)

Claims (1)

(57) [Claims] 1. A liquid crystal device in which liquid crystals are filled inside a pair of substrates, wherein electrodes are provided on inner surfaces of the pair of substrates, and a nitride film is provided on both of the electrodes. An alignment treatment layer for aligning the molecular long axes of the liquid crystal is provided on at least one of the coatings, and the type of charges accumulated near the interface between the nitride coating or the nitride coating and the electrode, and A liquid crystal device, wherein the liquid crystal is in a first state or a second state depending on an amount.