KR100378355B1 - Liquid crystal display - Google Patents

Abstract

A liquid crystal display device is disclosed. In the liquid crystal display device, a lower substrate, a lower electrode layer, a lower alignment layer, a liquid crystal layer, an upper alignment layer, an upper electrode layer, and an upper substrate are sequentially stacked, and the liquid crystal layer is filled with ferroelectric liquid crystal, and a plane parallel to the alignment layer between the upper and lower alignment layers. When the long axis of the ferroelectric liquid crystal phase is rotated around the one end according to the presence or absence of a predetermined electric field, the other end of the liquid crystal is provided with a spacer formed along a plurality of rows parallel to the line connecting the points which are respectively located before and after the electric field application do. Such a liquid crystal display device can reduce alignment defects by arranging spacers such that leakage light is suppressed in consideration of the turning direction of the liquid crystal due to the application of an electric field. In addition, by forming the black matrix on a position corresponding to the spacer arrangement direction according to the present invention, contrast reduction can be suppressed. In particular, when the spacer is formed into a stripe-shaped partition wall along the arrangement direction according to the present invention, leakage light can be more effectively suppressed.

Description

Ferroelectric liquid crystal display device {Liquid crystal display}

The present invention relates to a ferroelectric liquid crystal display device, and more particularly, to a ferroelectric liquid crystal display device with improved spacer arrangement.

Ferroelectric liquid crystals, unlike twisted nematic liquid crystals, have spontaneous polarization and have a response speed of more than 500 times faster. In addition, the ferroelectric liquid crystal is pivoted about one point in a direction orthogonal to the electric field direction applied above and below the liquid crystal layer, thereby providing a viewing angle close to the CRT and having a low driving voltage. That is, when no electric field is applied, the liquid crystals are arranged side by side in a predetermined direction on a plane parallel to the alignment layer, and when the electric field is applied, the long axis pivots at a predetermined angle with respect to one point.

As the ferroelectric liquid crystal is known, when the temperature is changed from high temperature to low temperature, phase transition is performed in an isotropic (ISO) -cholestic * -Sc * step. Ferroelectric liquid crystals usually maintain a gap of about 15 μm in the liquid crystal layer in which the liquid crystal is filled in order to obtain high contrast. In order to maintain the gap of the ferroelectric liquid crystal layer at a desired thickness, a ball-shaped spacer or stripe-shaped partition wall is provided between the upper and lower alignment layers facing the liquid crystal layer.

In a conventional ferroelectric liquid crystal display device, spacers were installed in a square parallel to the rubbing direction of the alignment layer, and a method of arranging such spacers is disclosed in a document (Japanese Liquid Crystal Society 1998 Preview 206p. Liquid Crystal 1997 vol 23, 43).

However, a ferroelectric liquid crystal has a disadvantage in that leakage light occurs along a direction orthogonal to the center line of the cone angle formed while the long axis is rotated on a plane parallel to the alignment layer according to the application of an electric field, and the conventional spacer array structure cannot suppress such leakage light. There is this.

The present invention has been made to solve the above problems, and an object thereof is to provide a ferroelectric liquid crystal display device capable of improving contrast by suppressing leakage light caused by driving of a ferroelectric liquid crystal.

1 is a cross-sectional view showing a ferroelectric liquid crystal display device to which the present invention is applied;

2 is a plan view schematically showing a spacer arrangement according to an embodiment of the present invention;

3 is a plan view schematically showing a spacer arrangement according to another embodiment of the present invention;

4 is a graph showing light transmission characteristics with respect to an applied voltage of a ferroelectric liquid crystal display device according to the present invention;

5 is a photograph showing light leakage by a spacer arrangement of a conventional ferroelectric liquid crystal display device.

<Description of the symbols for the main parts of the drawings>

1: first polarizer plate 2: lower substrate

3: lower electrode layer 4: lower alignment layer

5: liquid crystal layer 6: upper alignment layer

7: upper electrode layer 8: upper substrate

9: second polarizer 11a: ball spacer

11c: first stripe-type bulkhead 11d: second stripe-type bulkhead

In order to achieve the above object, according to the present invention, a lower substrate, a lower electrode layer, a lower alignment layer, a liquid crystal layer, an upper alignment layer, an upper electrode layer, an upper substrate are sequentially stacked, and in order to maintain the gap of the liquid crystal layer A liquid crystal display device having a plurality of spacers disposed between an alignment layer and an upper alignment layer, wherein the liquid crystal layer is filled with a ferroelectric liquid crystal, and the spacers have a long axis of the ferroelectric liquid crystal on a plane parallel to the alignment layer. The other end of the liquid crystal is formed along a plurality of rows parallel to the straight line connecting the points which are respectively positioned before and after the electric field application when turning according to whether or not the electric field is applied.

Preferably, the spacers are arranged to be aligned with each other in a direction parallel to the first direction crossing the column at a predetermined angle. Preferably, the first direction coincides with the rubbing direction of the lower alignment layer.

In addition, to prevent crosstalk, a black matrix pattern disposed on a predetermined area between the upper and lower substrates may be formed at a position corresponding to the arrangement direction of the spacers.

Hereinafter, a ferroelectric liquid crystal display device according to a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

1 is a cross-sectional view showing a liquid crystal display device to which the present invention is applied.

Referring to the drawings, the liquid crystal display device may include a first polarizing plate 1, a lower substrate 2, a lower electrode layer 3, a lower alignment layer 4, a liquid crystal layer 5, an upper alignment layer 6, and an upper electrode layer 7. ), The upper substrate 8 and the second polarizing plate 9 are laminated in this order.

A plurality of spacers 11a are provided between the lower alignment layer 4 and the upper alignment layer 6 to maintain the cell gap of the liquid crystal layer 5.

The spacer structure according to the present invention will be described with reference to FIG.

As shown, a plurality of ball spacers 11a are regularly arranged on the lower alignment layer 4.

The lower alignment films 4 are rubbed in parallel with each other along the S direction. The ferroelectric liquid crystal 5a has a characteristic of being arranged along a predetermined direction even without an electric field applied. The direction in which the ferroelectric liquid crystal 5a is arranged on the alignment layer 4 when no electric field is applied varies depending on the type thereof. Typically, the rubbing direction S or the rubbing direction S of the alignment layer 4 and 5 are different. The major axis 5b is arranged inclined within the range within degrees. Here, the long axis 5b generally refers to the longitudinal axis of the liquid crystal 5a having a rod shape.

When the ferroelectric liquid crystal 5a applies an electric field, its major axis 5b is rotated on a plane parallel to the alignment film 4 based on one end thereof.

The straight line 12 represented by a dashed-dotted line in the drawing connects a position before and after applying the electric field of the other end of the liquid crystal 5a that is rotated when an electric field is applied based on one point, along a direction parallel to the straight line 12. The spacer 11a of this invention is arranged. Therefore, the spacers 11a according to the present invention are arranged in rows along the direction parallel to the straight line 12 direction, that is, the direction parallel to the P direction. In the drawings, reference numerals a _n-1 , a _n , a _{n + 1} connect ball spacers 11a arranged along the n-1 th, n th, n + 1 th columns according to the spacer arrangement method of the present invention, respectively. It is a line. Preferably, the space between the columns is equally spaced.

In addition, as shown, the spacers 11a arranged along each column are arranged to be aligned with each other in a direction parallel to the first direction crossing the column direction (P direction) at a predetermined angle. Preferably, the first direction is determined in the rubbing direction (S direction). In the drawings, reference numerals b _n-1 , b _n , b _{n + 1} denote n-1th, nth, n + of spacers aligned in a row with respect to the rubbing direction (s direction) according to the spacer arrangement method of the present invention, respectively. Represents the first row. Preferably, the space between the rows is equally spaced.

In the drawing, γ is an angle formed between the long axis 5b of the liquid crystal 5a and the rubbing direction S in the state where no electric field is applied, and α is the liquid crystal 5a that is displaced relative to one point before the electric field is applied and after the electric field is applied. Is a cone angle formed at the time, and β is an angle formed between the column direction (P direction) and the long axis 5b of the liquid crystal 5a before the electric field application. Referring to the process of determining the arrangement position of the spacer according to the present invention, first when the application of the ferroelectric liquid crystal (5a) applied on the lower alignment layer 4 subjected to the rubbing treatment in one direction without an electric field applied to each other side by side The direction of the major axis 5b of the arranged liquid crystals is found.

Next, after applying a predetermined driving voltage, the cone angle α generated by the turning of the liquid crystal 5a is obtained. Then, β is obtained by the arithmetic equation (β = (π-α) / 2) using the cone angle α obtained above.

The column direction for arranging the spacers 11a is determined in a direction parallel to the direction shifted by the β angle with the direction of the major axis 5b of the liquid crystal 5a before the electric field application. Based on the rubbing direction S, the direction of the heat becomes a direction shifted by the β + γ angle with respect to the rubbing direction S.

What is necessary is just to arrange | position the ball spacer 11a at predetermined intervals along the direction parallel to the direction of the row calculated | required in this way. In addition, the spacers 11a arranged along each row may be positioned so that they are aligned with each other in a direction parallel to the rubbing direction S. FIG.

On the other hand, when the spacer is manufactured from a partition wall extending in a stripe shape without using the ball spacer 11a, the ball spacers 11a of FIG. 2 are respectively formed on positions corresponding to lines interconnected in the column and row directions. The first stripe partitions and the second stripe partitions may be formed. An example of a spacer formed as a stripe-type partition wall corresponding to the arrangement of the ball spacer 11a of FIG. 2 is shown in FIG. 3. In Fig. 3, reference numeral 11c denotes a first strip-shaped partition wall arranged along a column direction determined according to the present invention, and 11d denotes a second strip array arranged along a first direction inclined at a predetermined angle with the column direction determined according to the present invention. It is a vertical bulkhead. Reference numerals C _n-1 , C _n , C _{n + 1} denote first stripe-shaped partition walls formed on positions corresponding to a _n-1 , a _n , a _{n + 1} columns, and d _n-1 , d _n , d _{n + 1} is second stripe-shaped partition walls formed on a position corresponding to the row b _n-1 , b _n , b _{n + 1} .

On the other hand, in order to prevent crosstalk, a pattern of black matrices (not shown) provided on a predetermined area between the upper and lower substrates 8 and 2 is aligned with the arrangement direction of the spacers 11a, 11c, and 11d. It is preferable to form in the corresponding position. As such, when the black matrix is formed in the matrix shape along the spacer arrangement direction according to the present invention, leakage of unwanted light can be more stably suppressed.

An example in which a liquid crystal display device having such a spacer arrangement structure is manufactured will be described below.

First Embodiment

A photoresist is used on the upper and lower electrodes 7 and 3 to form the ball spacers 11a on the upper and lower substrates 8 and 2, respectively, in the form of dots along the arrangement direction according to the present invention. Subsequently, the polyimide-based alignment agent (RN1199) was spin-coated on the substrate 8 (2) to which the ball spacer 11a was attached, and first baked at 80 ° C. for 5 minutes, and then secondary at 180 ° C. for 1 hour. Fire. The upper and lower substrates 8, 2 thus made are bonded together. Injecting ferroelectric liquid crystal (RO319; ISO-cholestic-Sc; T _NC = 64 ° C) having spontaneous polarization at 120 ° C into a cell formed between the upper and lower substrates 8 and 2 bonded together, and then Cooling was performed at a cooling rate of 1 ° C. per minute at 3 ° C. at 66 ° C., which was 2 ° C. higher than the phase transition temperature (T _NC = 64 ° C.) to esc. The optical axis of the oriented liquid crystal (the long axis direction of the liquid crystal before the electric field applied) coincides with the rubbing direction, and the first polarizing plate 1 is attached to the lower substrate 2 so that its optical axis coincides with the rubbing direction of the lower alignment layer 4. The second polarizing plate 9 is attached to the upper substrate 8 so that its optical axis is perpendicular to the rubbing direction of the upper alignment layer 6 to complete the liquid crystal display element.

The result of measuring the electro-optical characteristics of the liquid crystal display device thus manufactured is shown in FIG. 4. As can be seen from the figure, the transmittance changes according to the applied voltage level. Also, as a result of repeating the driving frequency in the range of 0.1-60 Hz for 60 minutes, an optical leakage line corresponding to the diameter of the ball spacer 11a is intermittently intermittent. Although it was seen, the contrast was not lowered by the black matrix formed between the upper and lower substrates 8 and 2 so that the ball spacers 11a corresponded along the arrangement direction. As a result, the response speed was 250μs and the contrast was over 200. The viewing angle was 150 degrees or more in each of the up, down, left, and right directions.

<Example 2>

Only the spacer shape was manufactured in the form of a partition wall as shown in FIG. As a result, no defect of the phase due to light leakage occurred. As a result, it can be seen that spacers extending in the form of barrier ribs more effectively suppress leakage light than spaced-apart ball spacers.

<Comparative Example 1>

The position of the spacer was formed on the substrate so as to be arbitrarily arranged along the rubbing direction at an angle different from that of the conventional method, that is, according to the present invention. . The fabricated device was operated under the same conditions as in Example 1, and as shown in FIG. 5, defect lines due to leakage light were seen along the oblique direction indicated by the arrow f. The contrast was also lowered to 120: 1 than in Example 1.

As described above, the liquid crystal display device according to the present invention can reduce alignment defects by arranging spacers such that leakage light is suppressed in consideration of the turning direction of the liquid crystal according to the application of an electric field. In addition, by forming the black matrix on a position corresponding to the spacer arrangement direction according to the present invention, contrast reduction can be suppressed. In particular, when the spacer is formed into a stripe-shaped partition wall along the arrangement direction according to the present invention, leakage light can be more effectively suppressed.

Claims (6)

The lower substrate, the lower electrode layer, the lower alignment layer, the liquid crystal layer, the upper alignment layer, the upper electrode layer, and the upper substrate are sequentially stacked, and provided with a plurality of spacers disposed between the lower alignment layer and the upper alignment layer to maintain the gap of the liquid crystal layer. In the liquid crystal display device, The liquid crystal layer is filled with a ferroelectric liquid crystal, The spacers are parallel to a straight line connecting the points where the other end of the liquid crystal is positioned before and after the electric field is applied when the long axis of the ferroelectric liquid crystal is rotated around the one end with a predetermined electric field on a plane parallel to the alignment layer. Formed along a plurality of rows, A plurality of first stripe-shaped partition walls continuously formed along the rows at predetermined intervals; And a plurality of second stripe-type barrier ribs continuously formed at a predetermined interval in parallel with the first direction crossing the column at a predetermined angle. The liquid crystal display device of claim 1, wherein the spacers are arranged to be aligned with each other in a direction parallel to the first direction crossing the column direction at a predetermined angle. The liquid crystal display device of claim 2, wherein the first direction corresponds to a rubbing direction of the lower alignment layer. delete The liquid crystal display device of claim 1, wherein the spacers are ball spacers spaced apart from each other along the rows. The liquid crystal display of claim 1, wherein black matrixes are formed at positions corresponding to the arrangement direction of the spacers in a predetermined region between the upper and lower substrates.