KR20040013787A - Liquid Crystal Display Panel and Method of Fabricating the same - Google Patents

Abstract

PURPOSE: A liquid crystal display panel and a method for manufacturing the same are provided to minimize loss of light at a pixel boundary area, thereby improving brightness and a contrast ratio. CONSTITUTION: A liquid crystal panel is formed of a liquid crystal layer(48) formed between an upper substrate(40) and a lower substrate(50) which are bonded with each other. The liquid crystal layer includes light-hardened monomers. The liquid crystal panel has pixel areas(A,C) arranged in a plurality of matrices, and a pixel boundary area(B) formed at a boundary part of the pixel areas. Polymer networks(62) in a band alignment state are formed at the pixel areas by optically hardening monomers of the pixel areas. Another polymer networks in a vertical alignment state are formed at the pixel boundary area by applying light to the pixel boundary area.

Description

Liquid Crystal Display Panel and Method of Fabricating the same

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display panel, and more particularly, to a liquid crystal display panel and a method for manufacturing the same, which can improve brightness and increase contrast ratio by using a polymer network.

In general, a liquid crystal display ("LCD") displays an image by adjusting the light transmittance of the liquid crystal using an electric field. To this end, the LCD includes a liquid crystal panel in which liquid crystal cells are arranged in a matrix, and a driving circuit for driving the liquid crystal panel. The liquid crystal panel is provided with pixel electrodes and a reference electrode, that is, a common electrode, for applying an electric field to each of the liquid crystal cells. The pixel electrode is formed for each liquid crystal cell on the lower substrate, while the common electrode is integrally formed on the front surface of the upper substrate. Each of the pixel electrodes is connected to a thin film transistor (hereinafter referred to as "TFT") used as a switching element. The liquid crystal cell is driven along with the common electrode in accordance with the data signal supplied through the TFT. Such LCDs can be miniaturized compared to CRTs, and are widely used in personal computers and notebook computers, as well as office automation devices such as photocopiers, mobile phones and pagers.

Referring to FIG. 1, a conventional OCB (Optically Compensated Bend) liquid crystal display panel includes a color filter array 12 including a black matrix (not shown) on an upper substrate 10 and a common electrode 14 thereon. ) And the top electrode layer 16 on which the aligned upper alignment layer 16 is sequentially stacked, the pixel electrode 22 including the TFT array 24 formed on the lower substrate 20, and the aligned lower alignment layer 26 formed thereon. A lower plate consisting of a lower plate, a spacer (not shown) that maintains a gap between the upper plate and the lower plate, and the upper plate and the lower plate are bonded by a sealant (not shown) and injected into a space between the upper and lower plates. 18).

The black matrix formed on the upper plate is formed by coating an opaque metal such as opaque resin and chromium on the upper substrate 10 and then patterning the black matrix. The black matrix is formed in a matrix form on the upper substrate 10 to divide the surface of the upper substrate 10 into a plurality of cell regions in which the color filters 12 are to be formed and to prevent optical interference between adjacent cells. do. The black matrix is formed to overlap the gate line, data line and TFT array 24 of the lower plate.

The color filter 12 is located in the cell regions divided by the black matrix. The color filter 12 is formed by coating and then patterning a material that absorbs a white light source on the front surface of the upper substrate 10 on which the black matrix is formed and transmits only a light having a specific wavelength (red, green, or blue).

The common electrode 14 is supplied with a common voltage and is formed by depositing a transparent conductive film.

The upper and lower alignment layers 16 and 26 are coated with polyimide on the entire surface, followed by a rubbing process to align the pretilt angle, and the alignment treatment directions are made in the same direction.

In the lower panel, the TFT is formed by sequentially stacking a gate electrode, a gate insulating film, an active layer and an ohmic contact layer, and a source and a drain electrode. In this case, the gate electrode is connected to the gate line GL, and the source electrode is connected to the data line DL. The drain electrode is in contact with the pixel electrode 22 through a contact hole formed in the protective layer for protecting the TFT.

The liquid crystal 18 injected between the upper and lower plates forms the OCB mode liquid crystal cell by the upper and lower alignment layers 16 and 26 oriented in the same direction on the upper and lower plates.

The operation principle of the OCB mode liquid crystal cell with reference to FIGS. 2A to 2B is as follows.

As shown in FIG. 2A, the OCB mode liquid crystal cell maintains a splay state, which is an initial alignment state, below the transition voltage Va. That is, the liquid crystal molecules are arranged at tilt angles of θ and -θ ° on the upper and lower surfaces, respectively, and the tilt angle decreases toward the center of the liquid crystal cell so that the tilt angle of the liquid crystal molecules is zero at the center of the liquid crystal cell. It becomes °.

As shown in FIG. 2B, the liquid crystal molecules having such a splay state transition to a band state at a voltage higher than the transition voltage Va. Here, the time taken for the liquid crystal molecules in the splay state to transition to the band state is called a transition time. The liquid crystal molecules of the pixel areas A and C, in which the liquid crystals are normally driven because the pixel electrode 22 is formed, maintain the band state above the transition voltage Va. However, the splay state is maintained in the pixel boundary region B in which the pixel electrode 22 on the gate line or data line 32 formed to correspond to the black matrix 34 is not formed.

The tilt angle of the liquid crystal molecules in the band state is ± θ, which is an initial pretilt angle value (θ is usually about 5 to 15 °), and the tilt angle increases toward the center of the liquid crystal cell, thereby increasing the center of the liquid crystal cell. 90 ° at.

3 is a diagram illustrating light transmittance according to a voltage of an OCB mode liquid crystal cell.

As shown in FIG. 3, the light transmittance is irregular when the voltage applied to the OCB mode liquid crystal cell is lower than the transition voltage Va, and the light transmittance linearly decreases as the voltage increases above the transition voltage Va. Able to know. Since gray scale can be realized only when the light transmittance is changed linearly according to the voltage, the liquid crystal molecules must have a band-like arrangement in normal driving. In other words, the liquid crystal molecules must be initially transferred from the splay state to the band state in a short time. In fact, it takes a few seconds to several tens of seconds for the liquid crystal molecules to transition.

However, the liquid crystal molecules transitioning from the splay state to the band state may return to the splay state orientation near the transition voltage Va after the transition. Therefore, the voltage Vb having a more stable band state is used as the maximum white voltage without making the transition voltage Va, which is the voltage having the maximum luminance, the white voltage. As such, by using the white voltage as the Vb voltage instead of the transition voltage Va, as shown in FIG. 3, it can be seen that the light transmittance falls from Ta to Tb, thereby decreasing the luminance.

4 is a diagram illustrating an alignment state of an OCB mode liquid crystal cell in which a black voltage is applied to the liquid crystal display panel. Here, the black voltage refers to the Vc voltage shown in FIG.

When the black voltage is applied to the OCB mode liquid crystal cell during normal driving, the liquid crystals have a tilt angle only on the molecules of the upper and lower surfaces in the pixel regions A and C, and have a vertical alignment with respect to the upper and lower plates in the bulk region. do. Here, since the liquid crystals in the OCB mode liquid crystal cell do not transmit light at the black voltage, we see a black image.

In general, the liquid crystal display panel is driven by a dot inversion method. In the dot inversion method, all adjacent liquid crystal cells on the gate line and the data line are charged with data voltages having opposite polarities.

In the pixel boundary region B, the OCB liquid crystals receive a strong transverse electric field due to data voltages of opposite polarities between adjacent liquid crystal cells and maintain a splay state, thereby causing light leakage. This light leakage phenomenon is also present in the TN mode liquid crystal cell, but the OCB mode liquid crystal cell has a wider area of light leakage, resulting in increased black brightness and lower contrast ratio compared to the TN mode.

In order to solve this problem, by widening the width of the black matrix to widen the area to prevent light leakage and to increase the contrast ratio. However, when the width of the black matrix is widened, the aperture ratio decreases, resulting in a decrease in luminance.

Accordingly, an object of the present invention is to provide a liquid crystal display panel and a method of manufacturing the same, which can improve brightness and increase contrast ratio by using a polymer network.

1 is a view showing a conventional OCB mode liquid crystal display panel.

2A and 2B are diagrams showing a state transition of an OCB mode liquid crystal cell with or without voltage applied thereto.

3 is a graph showing light transmittance according to the voltage of the OCB mode liquid crystal cell shown in FIG.

4 is a view illustrating a state of an OCB liquid crystal when a black voltage is applied to the liquid crystal display panel illustrated in FIG. 1.

5 is a view illustrating an OCB mode liquid crystal display panel according to an exemplary embodiment of the present invention.

6A through 6E are diagrams illustrating a method of manufacturing the liquid crystal display panel illustrated in FIG. 5 in stages.

<Explanation of symbols for main parts of drawing>

10, 40: upper substrate 12, 42: color filter

14, 44 common electrode 16, 26 alignment film

18, 48: liquid crystal 20, 50: lower substrate

22, 54: pixel electrode 24: TFT array

34, 46: black matrix 56: gate line or data line

58 photocurable monomer 62 polymer network

In order to achieve the above object, the liquid crystal display panel according to the present invention is a liquid crystal display between a liquid crystal is injected between the bonded upper plate and the lower plate and composed of a pixel region disposed in a plurality of matrix forms and a pixel boundary region provided at the boundary of the pixel region. In the panel, the polymer network in the band alignment state is formed in the pixel region of the liquid crystal display panel, and the polymer network in the vertical alignment state is formed in the pixel boundary region.

The polymer network is formed by irradiating ultraviolet rays to the photocurable monomer.

The upper plate is formed on the upper substrate corresponding to the pixel boundary region, and includes a black matrix separating the adjacent pixel regions, a color filter formed on the upper substrate corresponding to the pixel region divided by the black mattress, and on the color filter. And a common alignment electrode to be formed and an upper alignment layer to be aligned on the common electrode.

The lower plate may include a gate line, a data line, and a thin film transistor formed in correspondence with a pixel boundary region, a pixel electrode electrically connected to the thin film transistor and formed in the pixel region, and a lower alignment layer aligned in the same direction as the upper alignment layer on the entire lower plate. It characterized by having a.

According to an exemplary embodiment of the present invention, a method of manufacturing a liquid crystal display panel includes bonding a top plate and a bottom plate, injecting a liquid crystal containing a photocurable monomer between the bonded top and bottom plates, and supplying a voltage greater than or equal to a transition voltage to provide a liquid crystal display panel. Transitioning the liquid crystal to a band state, arranging a mask to block light to correspond to the pixel boundary region, and irradiating light to photocure the photocurable monomer in the pixel region to form a band-like polymer network And vertically arranging the liquid crystal corresponding to the pixel boundary region by supplying a maximum normal driving voltage to the liquid crystal display panel, and vertically arranging the photocurable monomers added to the vertically aligned liquid crystals by irradiating light to the pixel boundary region. Forming a polymer network of the characterized in that it comprises.

Light for curing the photocurable monomer is characterized in that the ultraviolet light.

A color filter is formed on at least one of the upper and lower plates, and the light is irradiated onto a substrate on which the color filter is not formed.

In the vertical arrangement of the liquid crystals, the maximum normal driving voltage supplied to adjacent pixel regions with a pixel boundary region therebetween has the same polarity.

Other objects and features of the present invention in addition to the above objects will be apparent from the description of the embodiments with reference to the accompanying drawings.

Hereinafter, exemplary embodiments of the present invention will be described with reference to FIGS. 5 to 6E.

Referring to FIG. 5, in the liquid crystal display panel according to the present invention, the liquid crystals 48 are aligned in a band state by a polymer network in the pixel regions A and C, and the liquid crystals 48 in the pixel boundary region B. Referring to FIG. It is characterized in that the vertically oriented.

The LCD panel includes an upper plate composed of a black matrix 46, a color filter 42, and a common electrode 44 sequentially stacked on the upper substrate 40, and an unshown stacked sequentially on the lower substrate 50. A lower plate composed of a TFT array and a pixel electrode 54 is provided, and a liquid crystal 48 is injected between the upper plate and the lower plate and includes a polymer network.

The liquid crystal 48 contains a photocurable monomer. The liquid crystal 48 initially forms a splay structure by an unillustrated alignment film oriented parallel to each other on the upper and lower substrates 40 and 50, and forms a band state according to application of voltage. At the same time, light is irradiated to cure the photocurable monomer included in the liquid crystal 48 to form a polymer network. In this case, the liquid crystals 48 of the pixel areas A and C have a band state, and the liquid crystals of the pixel boundary area B have a vertical alignment state. Here, the pixel boundary area B becomes an area overlapping with the black matrix 46.

6A through 6E are diagrams illustrating a method of manufacturing a liquid crystal display panel according to an exemplary embodiment of the present invention.

First, referring to FIG. 6A, in the OCB mode liquid crystal display panel according to the present invention, the alignment directions of the alignment layers on the upper and lower substrates 40 and 50 are parallel to each other, and the upper and lower plates are bonded to each other. Thereafter, the liquid crystal 48 to which the photocurable monomer 58 is added is injected between the upper and lower plates. At this time, since the reset voltage is not applied to the liquid crystal panel, the liquid crystal 48 maintains the splay state which is the initial alignment state below the transition voltage. That is, the liquid crystals 48 are arranged at tilt angles of θ and -θ ° on the upper and lower surfaces, respectively, and the tilt angle decreases toward the center of the liquid crystal cell, thereby reducing the tilt angle of the liquid crystal molecules at the center of the liquid crystal cell. Becomes 0 °. Monomers 58 added to the liquid crystal 48 are also arranged corresponding to the liquid crystal 48 alignment state.

As shown in FIG. 6B, the liquid crystals 48 having such a splay state transition to a bend state when a voltage equal to or greater than the transition voltage Va is supplied to the liquid crystal cell. Here, the liquid crystal molecules of the pixel regions A and C transition to the band state, but the liquid crystal molecules of the pixel boundary region B formed to correspond to the black matrix 34 do not transition and maintain the splay state. The photocurable monomer 58 has a band-like arrangement in the pixel regions A and C according to the arrangement state of the liquid crystals 48, but has a splay state arrangement in the pixel boundary region B. FIG.

In this state of applying a voltage for inducing the liquid crystal 48 into a band state, as shown in FIG. 6B, after aligning the mask 60 used in forming the black matrix 46, ultraviolet rays (UV) are applied to the liquid crystal panel. Investigate. Here, the color filter 42 formed on the upper plate of the liquid crystal panel is generally formed of a material absorbing ultraviolet light to block the ultraviolet light. Accordingly, since the ultraviolet ray is not irradiated to the photocurable monomer 58 corresponding to the color filter 42, the color filter 42 is not formed to cure the photocurable monomer 58 corresponding to the color filter 42. The bottom panel of the liquid crystal panel is irradiated with ultraviolet light. At this time, ultraviolet rays are not irradiated to the pixel boundary region B of the liquid crystal panel corresponding to the mask 60. If the color filter 42 is not formed on the upper plate of the liquid crystal panel but formed on the lower plate, ultraviolet rays should be irradiated from the upper plate on which the color filter 42 is not formed.

When ultraviolet rays are selectively irradiated to the liquid crystal panel as described above, the photocurable monomers 58 of the pixel areas A and C form the polymer network 62 as shown in FIG. 6C. Since the photocurable monomer 58 having a band-like arrangement is cured, the polymer network 62 also has a band-like state. As a result, when the driving voltage is not applied to the liquid crystal panel, the polymer network 62 in the band state guides the peripheral liquid crystals 48 into the band state and stabilizes the liquid crystal in the band state. The liquid crystals 48 stabilized by the polymer network 62 oriented in the band state can be easily transitioned to a voltage lower than the voltage required for the transition from the splay state to the band state. In other words, not only can the transition voltage and transition time necessary for the transition of the liquid crystal 48 be reduced, but also the luminance can be improved due to the stabilization of the band alignment of the liquid crystal 48.

As described above, after forming the network 62 having the band-oriented alignment of the polymers in the pixel regions A and C, when no driving voltage is applied, the liquid crystal 48 is as shown in Fig. 6C. It has a band state. Since ultraviolet rays are not irradiated to the pixel boundary region B, the liquid crystal 48 containing the monomers 58 has a splay state. In this state, when the black voltage is applied to the liquid crystal cell as shown in FIG. 6D, most of the liquid crystals 48 are arranged perpendicular to the upper and lower plates in the bulk region except for the upper and lower surfaces. At this time, the liquid crystals 48 maintain the initial alignment tilt angle on the upper and lower surfaces.

Conventionally, the vertically aligned liquid crystals are driven in a dot inversion manner to charge adjacent liquid crystal cells with different polarities. Accordingly, light leakage is caused by vertically aligned liquid crystals 48 in the pixel boundary region B being horizontally oriented by a strong transverse electric field. In the present invention, the driving method is not driven in a dot inversion method but driven in a frame inversion method, thereby applying a voltage having the same polarity to each adjacent pixel. As a result, the liquid crystals 48 can maintain the vertical alignment in the pixel boundary region B by reducing the transverse electric field between the pixels. Here, the monomers 58 also maintain the vertical alignment state according to the vertically aligned liquid crystals 48.

In the pixel boundary region B, ultraviolet rays are irradiated onto the lower plate on which the black matrix 46 is not formed while the liquid crystals 48 are vertically aligned. Accordingly, as shown in FIG. 6E, the monomers 58 located in the non-polymerized pixel boundary region B are photopolymerized by ultraviolet rays to form a polymer network having a vertical alignment. In this case, since the ultraviolet rays are not irradiated to the region corresponding to the gate line or the data line 56, the monomers 58 of the region corresponding to the gate line or the data line 56 do not form a polymer network.

However, the liquid crystal display panel according to the present invention can form a polymer network in the vertical alignment of the monomer 58 in the pixel boundary region B, compared to the conventional art, thereby minimizing light leakage caused by the existing transverse electric field. Therefore, not only can the contrast ratio be increased, but also the width of the black matrix 46 can be minimized, thereby ensuring the aperture ratio.

As described above, the liquid crystal display panel and the method of manufacturing the same according to the present invention inject a liquid crystal containing a photocurable monomer into the liquid crystal panel to form monomers in the pixel boundary region into a polymer network in a vertical alignment, thereby causing light leakage in the pixel boundary region. Can be minimized. As a result, the luminance is increased and the contrast ratio can be improved. Here, the liquid crystal display panel and the manufacturing method thereof according to the present invention can minimize the width of the black matrix can ensure the aperture ratio.

Furthermore, the liquid crystal display panel and the method of manufacturing the same according to the present invention can easily transfer the liquid crystals from the splay state to the band state even at low voltage by the polymer network in the band state in the pixel region, and shorten the transition time.

Those skilled in the art will appreciate that various changes and modifications can be made without departing from the technical spirit of the present invention. Therefore, the technical scope of the present invention should not be limited to the contents described in the detailed description of the specification but should be defined by the claims.

Claims (8)

In a liquid crystal display panel comprising a pixel region disposed in a plurality of matrix forms and a pixel boundary region provided at a boundary portion of the pixel region, the liquid crystal is injected between the bonded upper and lower plates, wherein the pixel region of the liquid crystal display panel has a band alignment state. And forming a polymer network and forming a polymer network in a vertical alignment state in the pixel boundary region. The method of claim 1, The polymer network is formed by irradiating ultraviolet light to the photocurable monomer. The method of claim 1, The top plate, A black matrix formed on the upper substrate corresponding to the pixel boundary region and separating adjacent pixel regions; A color filter formed on the upper substrate to correspond to the pixel area divided by the black mattress; A common electrode formed on the color filter; And an upper alignment layer oriented on the common electrode. The method of claim 3, wherein The lower plate, A gate line, a data line, and a thin film transistor formed corresponding to the pixel boundary region; A pixel electrode electrically connected to the thin film transistor and formed in the pixel region; And a lower alignment layer that is aligned in the same direction as the upper alignment layer on the entire lower plate. Bonding the top and bottom plates together; Injecting a liquid crystal to which a photocurable monomer is added between the bonded upper and lower plates; Supplying a voltage equal to or more than a transition voltage to transition the liquid crystal in the pixel region to a band state; Arranging a mask to block light to correspond to the pixel boundary region; Irradiating light to photocur the photocurable monomer in the pixel region to form a band polymer network; Vertically arranging a liquid crystal corresponding to the pixel boundary region by supplying a maximum normal driving voltage to the liquid crystal display panel; And irradiating light to the pixel boundary region to form a polymer network in which the photocurable monomers added to the vertically aligned liquid crystals are in a vertically aligned state. The method of claim 5, wherein The light for curing the photocurable monomer is ultraviolet light. The method of claim 5, wherein And forming a color filter on at least one of the upper plate and the lower plate, wherein the light is irradiated to the photocurable monomer through a substrate on which the color filter is not formed. Method of manufacturing the panel. The method of claim 5, wherein And vertically arranging the liquid crystals to equalize polarities of the maximum normal driving voltages supplied to adjacent pixel regions with the pixel boundary regions interposed therebetween.