JPH0728045A - Liquid crystal element - Google Patents

Abstract

PURPOSE:To prevent the leak current between adjacent electrodes and the shorting between upper and lower electrodes and to obtain a good gradation display free from uneven images by providing the surfaces of electrode group with protective layer and specifying the resistivity of the protective layer to a specific value. CONSTITUTION:The electrode group consisting of plural band-shaped transparent electrodes 102, 102' in formed on a pair of substrates 101, 101'. The protective layers 105, 105' are respectively arranged on these transparent electrodes 102, 102'. The protective layers 105, 105' may have multilayered constitution consisting of upper and lower shorting preventive layers and orientation control layers. The resistivity rho of the protective layers satisfies rho>=(2N-3)r.t.L/m, where t(cm) denotes the film thickness of the protective layers, r(OMEGA) denotes the wiring resistance value between the adjacent electrodes, L(cm) denotes an electrode length, m(cm) denotes the distance between the adjacent electrodes, N denotes the number of display gradations, respectively. The resistivity rhoof the protective layers of the liquid crystal element to be used as an ordiary display is preferably in a 10<5>OMEGA.cm<=rho<=10<5>OMEGA.cm range.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal element suitable for gradation display, and particularly, a ferroelectric liquid crystal (hereinafter referred to as "FLC").
The present invention relates to a liquid crystal element using.

[0002]

2. Description of the Related Art Recently, as an improved type of conventional liquid crystal elements,
The use of a liquid crystal device having bistability is clarified by Clar.
k) and Lagerwall, both of which are proposed in JP-A-56-107216, U.S. Pat. No. 4,367,924, and the like. As the bistable liquid crystal, FLC having a chiral smectic C phase (SmC ^* ) or H phase (SmH ^* ) is generally used, and in these states, the first optical response is made in response to an applied electric field. It has either the stable state or the second optical stable state, and has the property of maintaining that state when no electric field is applied, that is, bistability, and has a quick response to changes in the electric field and high speed. Moreover, it is expected to be widely used in the field of memory type display devices and the like.

[0003]

FL having bistability
The C element is generally formed to have an extremely thin liquid crystal layer thickness of 2 μm or less, and there is a problem that a short circuit occurs between the upper and lower electrodes through fine particles or the like mixed in the element.
Therefore, an insulating film is required on each electrode.

However, JP-A-63-121020
As described in detail in the publication, it has been pointed out that a FLC element having an insulator layer is disturbed in bistability in the switching process of liquid crystal molecules due to the bias of charges due to spontaneous polarization. It is disclosed that the resistivity ρ of the insulator layer is set to 1 × 10 ⁸ Ω · cm or less in order to solve the problem.

On the other hand, as can be easily inferred, when the resistance of the insulating layer becomes low, current leakage occurs between adjacent electrodes, and as a result, a voltage distribution occurs in the longitudinal direction of the electrodes. That is, the potential is distributed near the entrance and the end where a voltage is applied on one electrode, and the voltage applied to each corresponding pixel is distributed.

Such voltage distribution becomes a problem in gradation display, particularly in gradation display by precisely controlling the voltage, and results in image unevenness.

[0007]

SUMMARY OF THE INVENTION The present invention is a liquid crystal device which solves the above-mentioned problems, in which a liquid crystal is sandwiched between a pair of electrode substrates arranged facing each other, and a scanning electrode group and information provided on each electrode substrate. A liquid crystal element having a pixel at the intersection with the electrode group, and having a resistivity ρ on at least one of the electrode groups on the substrate.
(Ω · cm) and a film thickness t (cm) are provided, the wiring resistance of the electrode group in which the protective layer is arranged is r (Ω), the electrode length is L (cm), and the distance between adjacent electrodes is When the distance is m (cm) and the number of display gradations is N, the resistivity ρ of the protective layer satisfies the following relationship ρ ≧ (2N−3) r · t · L / m. To do.

The present invention will be described in detail below.

FIG. 1 shows one embodiment of the liquid crystal element of the present invention. FIG. 2 is a cross-sectional view of the liquid crystal element of FIG. 1, (a), (b)
Indicate different aspects.

A liquid crystal element 100 shown in FIGS. 1 and 2 is a pair of substrates 101 made of a glass plate or a plastic plate.
And 101 'are held at a predetermined interval by a spacer 104, and have a cell structure in which a pair of substrates are adhered with an adhesive agent 106 for sealing, and a plurality of transparent electrodes 102 are formed on the substrate 101. An electrode group (for example, a scanning voltage applying electrode group in the matrix electrode structure) is formed in a predetermined pattern such as a strip pattern. Board 1
On 01 ′, an electrode group (for example, a signal voltage applying electrode group in the matrix electrode structure) including a plurality of transparent electrodes 102 ′ intersecting with the transparent electrode 102 is formed.

In the present invention, the transparent electrodes 102 and 10 described above are used.
An alignment control film and a short-circuit preventing protective film, which will be described later, can be provided as a protective layer on at least one transparent electrode 2 '.

The liquid crystal element shown in FIG. 2A has a single-sided substrate 10.
The protective layer 105 'is arranged on the substrate 1', and the liquid crystal element of FIG. 2B has the protective layers 105 and 105 'on the substrates 101 and 101' on both sides.

In the present invention, the protective layer may have a multi-layered structure including an upper and lower short-circuit preventing layer and an orientation control layer.
In that case, the orientation control layer preferably has a lower resistance than the short-circuit prevention layer, for example, an organic polymer film such as polypyrrole, polyparaphenylene, or polyaniline, or an organic polymer film including polyimide or the like. Use a thin film.

Further, in order to improve the signal delay due to the electrode wiring resistance and the rounding of the driving waveform, FIGS. 3A and 3B are used.
As shown in, the metal electrode wiring can be provided along the longitudinal direction of the stripe-shaped transparent electrode. At that time, as the thin wire metal electrode 303, aluminum, molybdenum,
Chromium, titanium, tungsten or their alloys (eg N
A film formed of iCr) can be used.

It is assumed that the voltage V ₀ is applied to any one scanning electrode or information electrode of the liquid crystal element 100 shown in FIG. 1 and all the other electrodes are grounded. For example, in FIG. 1, if the voltage V ₀ is applied to the scan electrode a and all the other electrodes are grounded, a current flows through at least the scan electrodes b and c through the protective layer formed on the scan electrode, As a result, a potential distribution is generated on the scan electrode a. Due to this potential distribution, the voltage V ₀ applied to the pixel A at the entrance of the voltage and the voltage V applied to the pixel B at the end are generally different.

At this time, the voltage V applied to the pixel B can be roughly estimated by the equivalent circuit shown in FIG. 4, for example. In FIG. 4, I ₁ , I ₂ , and I ₃ are currents, r is the wiring resistance of the electrodes, and R is the resistance of the protective layer. In this equivalent circuit, the following four expressions hold.

I ₁ -I ₂ -2I ₃ = 0 (1) V ₀ -I ₁ r -I ₂ r -V = 0 (2) V ₀ -I ₁ r -I ₃ R -I ₃ r = 0 _{3) I 3 r + I 3} R-I 2 r-V = 0 (4) above (1) to (4) than I _1, when erasing the I _2, I ₃ the following equation is obtained.

V = (R + r) V ₀ / (R + 3r) (5) The difference (V ₀ −V) between the voltages applied to the pixel A and the pixel B is
For example, in order to control the gradation by controlling the applied voltage and display an image without unevenness, it is desirable to make it as small as possible. That is, if the number of gradations is N, it is necessary to satisfy at least the following conditions.

V ₀ −V ≦ V ₀ / N (6) Substituting the expression (5) into the expression (6) gives R ≧ (2N−3) r (7).

If the distance between adjacent striped electrodes is m, the length (length from pixel A to pixel B) is L, and the film thickness of the protective layer is t, R = ρ · m / t · L Since equation (8) holds, substituting equation (8) into equation (7) gives
Expression (9) is obtained.

Ρ ≧ (2N−3) r · t · L / m (9) That is, in order to enable good gradation display without image unevenness, the resistivity ρ of the protective layer and the wiring of the electrode The relationship of the resistance r needs to satisfy the expression (9).

On the other hand, so-called VDT such as word processor and personal computer
Considering the screen size and the pixel density of the display used as the above, the electrode length L is 30c.
m, the inter-electrode distance m is several tens of μm, and the wiring resistance r can be set to about 10 kΩ by forming the metal electrode shown in FIG.

Further, in order to prevent the conductive foreign matter from breaking through the protective layer and reaching the transparent electrode, it can be achieved with a film thickness of about 1000Å, although it depends on the hardness thereof.

Further, as the gradation number N, 256 gradations are usually standard.

Under the above conditions, if the resistivity ρ of the protective film is estimated from the equation (9), in order to obtain a good image, ρ
≧ 10 ⁵ Ω · cm (however, L = 30 cm, t = 1
000Å, m = 20 μm, 2r = 10 kΩ, N = 25
6).

Therefore, in the FLC element used as a normal display, in order to eliminate the above-mentioned disorder of the bistability due to the bias of the charge and the unevenness of the gradation due to the leakage between the electrodes, The resistivity ρ of the protective layer is preferably in the range below.

10 ⁵ Ω · cm ≦ ρ ≦ 10 ⁸ Ω · cm (10)

[0028]

【Example】

(Embodiment 1) An embodiment of the present invention will be described below with reference to the drawings.

An ITO film having a thickness of 1000 Å is formed on a 320 × 300 mm glass substrate by a sputtering method, and a photolithography technique is used to form a pitch of 305 μ on the entire surface.
m, a line width of 285 μm is formed, and then an Al film having a thickness of 2000 Å is formed.
05μm line width 12μm, overlapping width with ITO electrode 6
An electrode substrate was obtained by forming a pattern having a configuration shown in FIG.

At this time, the wiring resistance r at both ends of one electrode pattern was about 10 kΩ. 1 on this electrode substrate
A 000 Å SnO ₂ film was formed by a sputtering method, and a polyimide film having a thickness of about 10 Å was applied by a spinner or formed by an LB method, and then baked at a temperature of 200 ° C. or higher.

Aluminum was vapor-deposited on this coating film as an electrode and dried under reduced pressure at 100 ° C. to obtain an aluminum electrode (1 cm).
² ) and the transparent electrode (1 cm ² ) between Y. H. P
(Yokogawa Hewlett Packard) 4192A LF
The resistance was 10 Ω when measured by an IMPEDANCE ANALYZER in an alternating current having a resistance of 20 kHz, and the resistivity ρ was ρ = 1 × 10 ⁶ Ω · cm.

Two electrode substrates were prepared and subjected to rubbing treatment, respectively, and then the two electrode substrates were laminated so that the longitudinal edge directions of the striped transparent electrodes intersect each other at 90 °. The distance between the electrode substrates is 1.5 μm
A SiO ₂ bead having an average particle size of 1.5 μm was placed to hold the cell) to prepare a cell.

A multi-component liquid crystal containing a phenylbenzoate type liquid crystal exhibiting the following phase transition as a main component was injected into this cell,
Further, an electric field treatment with an AC electric field having a frequency of about 10 Hz and a voltage value of about ± 20 V was performed to obtain an orientation in which the domain was relatively easy to control.

[0034]

[Chemical 1]

When a pulse electric field is applied to this liquid crystal cell from a drive circuit and the pulse voltage is changed to attempt gradation display with gradation number N = 256 by domain control, almost uniform display is possible. It was

When the right-hand side ρ _min of the equation (9) in this cell structure is obtained, ρ _min ≡ (2N-3) r · t · L / m≈4 × 10 ⁵ Ω ·
It was confirmed that the value was cm 2 and the expressions (9) and (10) were satisfied.

Example 2 A liquid crystal device was manufactured in the same manner as in Example 1 except that the SnO ₂ film and the polyimide ultrathin film of Example 1 were replaced by an indoped polyaniline film of about 1000 Å.

When the resistivity of the polyaniline film was measured by the same method as in Example 1, it was 1 × 10 ⁷ Ω · cm, and as in Example 1, ρ _min = 4 × 10 ⁵ Ω · cm (9). The expressions (10) and (10) were satisfied.

When gradation display was performed on this liquid crystal cell in the same manner as in Example 1, almost uniform display was possible.

(Comparative Example 1) A liquid crystal element was produced in the same manner as in Example 1 except that the Al film pattern was not formed on the ITO electrode. The wiring resistance r at this time was about 100 kΩ. When gradation display was attempted with the number of gradations N = 256 as in Example 1, uneven brightness was generated in the pixels on the line, and uniform gradation display could not be performed.

The right side of the equation (9) at this time is ρ _min = 3 × 1
Becomes 0 ⁶ Ω · cm, and ρ = 1 × 10 ⁶ Ω as in Example 1.
・ Since it is cm, the formula (9) is not satisfied.

(Comparative Example 2) A liquid crystal element was manufactured in the same manner as in Example 1 except that the SnO ₂ sputtered film was changed to a coating film. When the resistivity of this coating film was measured by the method described above, it was ρ = 1.0 × 10 ⁴ Ω · cm.

When gradation display was attempted with the number of gradations N = 256 in the same manner as in Example 1, uneven brightness occurred in the pixels on the scanning line, and uniform gradation display could not be performed.

At this time, similar to the first embodiment, ρ _min = 4 × 10 ⁵ Ω
・ Since it is cm, the formula (9) is not satisfied.

[0045]

As described above, in the liquid crystal device of the present invention, since the leak current between the adjacent electrodes and the short circuit between the upper and lower electrodes are prevented, good gradation display without image unevenness is realized. To do.

[Brief description of drawings]

FIG. 1 is a plan view of an embodiment of the present invention.

FIG. 2 is a cross-sectional view of one embodiment of the present invention.

FIG. 3 is a cross-sectional view of electrodes used in the liquid crystal element of the present invention.

FIG. 4 is an explanatory diagram of a leak current in a conventional liquid crystal element.

Claims (4)

[Claims] 1. A liquid crystal element in which a liquid crystal is sandwiched between a pair of electrode substrates arranged to face each other, and a pixel is formed at an intersection of a scanning electrode group and an information electrode group provided on each electrode substrate. Resistivity ρ (Ω · cm) on the substrate electrode group,
A protective layer having a film thickness t (cm) is provided, the wiring resistance value of the electrode group in which the protective layer is arranged is r (Ω), the electrode length is L (cm),
When the distance between adjacent electrodes is m (cm) and the number of display gradations is N, the resistivity ρ of the protective layer satisfies the following relation ρ ≧ (2N−3) r · t · L / m. A liquid crystal element characterized by: 2. The liquid crystal element according to claim 1, wherein the resistivity of the protective layer is 10 ⁵ Ω · cm ≦ ρ ≦ 10 ⁸ Ω · cm. 3. The liquid crystal device according to claim 1, wherein the liquid crystal is a ferroelectric liquid crystal. 4. The liquid crystal device according to claim 1, wherein the protective layer has a multi-layer structure including an underlayer and an alignment layer subjected to a uniaxial alignment treatment.