WO2007136215A1

WO2007136215A1 - Multi-domain vertical alignment lcd

Info

Publication number: WO2007136215A1
Application number: PCT/KR2007/002471
Authority: WO
Inventors: Bong Gyu Rho
Original assignee: Sesim Photonics Technology Co., Ltd.
Priority date: 2006-05-22
Filing date: 2007-05-22
Publication date: 2007-11-29
Also published as: KR20070112493A; KR100877218B1

Abstract

A multi-domain vertical alignment LCD (MVA-LCD) is disclosed, which forms multi- domains by means of lateral electric fields that are caused by a difference between vertical electric fields that are formed between the electrodes of the MVA-LCD. When the lower electrodes and the lower common electrodes are biased at the same voltage or the lower common electrodes are floated, a difference between vertical electric fields, which are formed between the upper electrodes and the lower electrodes, and vertical electric fields, which are formed between the upper electrodes and the lower common electrodes, caused lateral electric fields. Such lateral electric fields allow multi-domain to be formed in the liquid crystal layer.

Description

Description MULTI-DOMAIN VERTICAL ALIGNMENT LCD

Technical Field

[1] The present invention relates to vertical alignment technology for LCD's. More particularly, this invention relates to a multi-domain vertical alignment LCD (MVA-LCD) that forms multi-domains by means of lateral electric fields that are caused by a difference between vertical electric fields that are formed between the electrodes of the MVA-LCD. Background Art

[2] In general, a vertical alignment LCD is fabricated in such a way that vertical alignment films are disposed on the substrates of the LCD, and liquid crystal having an anisotropic characteristic and negative dielectric constant is injected into the gap between the substrates. When the electrodes formed on the substrates are not biased at a voltage, the longitudinal axes of liquid crystal molecules are aligned perpendicular to the plane of the alignment films. On the contrary, when a voltage above a threshold voltage is applied to the electrodes, the longitudinal axes of liquid crystal molecules are horizontally aligned in a particular direction.

[3] Since the vertical alignment LCD can orient LC molecules in each unit pixel in many directions, it has a wide viewing angle. Such a vertical alignment LCD may be sorted into a protrudent vertical alignment LCD, a surrounding electrode vertical alignment LCD, and a pattern vertical alignment (PVA) LCD, etc., each of which is described in detail referring to the drawings.

[4] Figure 1 is a cross-sectional view depicting a conventional protrudent vertical alignment LCD.

[5] The protrudent vertical alignment LCD as constructed in the figure is fabricated as follows. Firstly, a protrusion 13 is formed on the upper electrode 11 of the upper glass substrate 10. The protrusion 13 and upper electrode 11 are coated with a vertical alignment film 12. The upper glass substrate 10 is coupled to and spaced apart from the lower glass substrate 30 having the lower electrode 31 and lower alignment film 32. After that, a liquid crystal material is injected into the space, i.e., the cell gap, between the upper glass substrate 10 and the lower glass substrate 30.

[6] In such a protrudent vertical alignment LCD, the liquid molecules on the flat portion of the upper glass substrate 10 are vertically aligned. On the contrary, the liquid molecules on the protrusion 13 are aligned according to the slope of the protrusion 13. That is, the initial alignment directions of the liquid molecules on the protrusion 13 are determined by the slope of the protrusion 13. When a voltage greater than a threshold voltage is applied to the LCD, the liquid molecules on the protrusion 13 keep their initial alignment directions. As such, the protrudent vertical alignment LCD achieves the multi-domain liquid crystal alignment.

[7] Figure 2 is a cross-sectional view depicting a conventional alignment- induced-electrode vertical alignment LCD.

[8] As shown in Figure 2, the initial alignment direction of liquid crystal molecules

20-1 is determined by horizontal electric fields between the lower electrode 31-1 and the alignment inducing electrode 33, which are formed on the lower glass substrate 30-1. Here, the lower electrode 31-1 and the alignment inducing electrode 33 are coated with the lower alignment film 32-1. When a voltage greater than a threshold voltage is applied between the upper electrode 11-1 and the lower electrode 31-1, the liquid crystal molecules 20-1 lean at a relatively wide angle, as a result of the horizontal electric fields between the upper electrode 11-1 and the lower electrode 31-1. In the conventional alignment inducing vertical alignment LCD, since the upper glass substrate 10-1, the upper electrode 11-1, and the upper alignment film 12-1, shown in the structure of general LC panel, are known, their detailed description will be omitted.

[9] Sanyo Electric Co., Ltd. first presented technology for the alignment- induced-electrode vertical alignment LCD at the Symposium on Information Displays (SID) in 1995.

[10] Figure 3 is a cross-sectional view depicting a conventional patterned vertical alignment (PVA) LCD.

[11] As shown in FIG. 3, the PVA LCD is fabricated to etch the upper electrode 11-2 and the lower electrode 31-2 to form slits. Lateral electric fields (not shown) are formed around the slits. The leaning directions of the vertically aligned liquid crystal molecules are determined by the lateral electric fields. Since the upper glass substrate 10-2, lower glass substrate 30-2, upper alignment film 12-2, and lower alignment film 32-2 are well known, their detailed description will be omitted. Reference numeral 20-2 denotes a liquid crystal molecule.

[12] However, the conventional LCD's have drawbacks that will be described in detail as follows.

[13] The conventional vertical alignment LCD is disadvantageous because the fabricating methods are complicate and thus failure rates are high.

[14] The conventional protrudent vertical alignment LCD is disadvantageous in that, when a voltage is not applied to the liquid crystal layer, liquid crystal molecules are not vertically aligned with the upper portions of the protrusion. Instead, the liquid crystal molecules are leaned horizontally at a certain angle. Therefore, when the protrudent vertical alignment LCD operates, light leakage occurs and thus contrast ratio is decreased.

[15] The conventional induced-electrode vertical alignment LCD is disadvantageous in that, since a residual DC voltage is accumulated at the induced electrode portion, a residual image is generated when displaying images.

[16] The conventional patterned vertical alignment (PVA) LCD is disadvantageous in that the display characteristic worsens due to the tolerance caused as the upper and lower glass substrates are coupled to each other. Disclosure of Invention Technical Problem

[17] Therefore, the present invention has been made in view of the above problems, and it is an object of the present invention to provide a multi-domain vertical alignment LCD (MVA-LCD) that forms multi-domains by means of lateral electric fields that are caused by a difference between vertical electric fields that are formed between the electrodes of the MVA-LCD. Technical Solution

[18] In accordance with an aspect of the present invention, the above and other objects can be accomplished by the provision of a multi-domain vertical alignment (MVA) LCD including: a lower glass substrate; an upper glass substrate located spaced apart from the lower glass substrate at a certain distance; and a liquid crystal layer located between the lower and upper glass substrates.

[19] Here, the lower glass substrate includes: lower common electrodes formed on the side thereof that faces the upper glass substrate; a dielectric film coated on the lower common electrodes; lower electrodes formed in such a way to have slits on the dielectric film; and a lower alignment film formed on the dielectric film and the lower electrodes. The upper glass substrate comprises: upper electrodes formed on the side thereof that faces the lower glass substrate; and an upper alignment film formed on the upper electrodes.

[20] When the lower electrodes and the lower common electrodes are biased at the same voltage or the lower common electrodes are floated, a difference between vertical electric fields, which are formed between the upper electrodes and the lower electrodes, and vertical electric fields, which are formed between the upper electrodes and the lower common electrodes, causes lateral electric fields, thereby forming multi- domain in the liquid crystal layer.

[21] Preferably, the MVA LCD further includes a color filter substrate between the lower common electrodes and the lower glass substrate.

[22] Preferably, the MVA LCD further includes a smoothing film between the lower common electrodes and the lower alignment film. [23] Preferably, the dielectric film has a thickness above 0.5μm.

[24] Preferably, each of the lower electrodes is angled, at 45°, or shaped as a rectangle.

[25] Preferably, each of the lower common electrodes is shaped as a plate.

Advantageous Effects

[26] As described above, the present invention provides a multi-domain vertical alignment LCD that can form multi-domains by means of the lateral electric fields caused by a difference between vertical electric fields, which are formed between the upper electrodes and the lower electrodes, and vertical electric fields, which are formed between the upper electrodes and the lower common electrodes, when the lower electrodes and the lower common electrodes are biased at the same voltage or when the lower common electrodes are floated. This allows the MVA-LCD to have a relatively wide viewing angle. Brief Description of the Drawings

[27] The above and other objects, features, and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

[28] Figure 1 is a cross-sectional view depicting a conventional protrudent vertical alignment LCD;

[29] Figure 2 is a cross-sectional view depicting a conventional alignment- induced-electrode vertical alignment LCD;

[30] Figure 3 is a cross-sectional view depicting a conventional patterned vertical alignment (PVA) LCD;

[31] Figure 4 is a cross-sectional view depicting a multi-domain vertical alignment LCD according to an embodiment of the present invention;

[32] Figure 5 is views describing shapes of a lower electrode and a lower common electrode of a vertical alignment LCD according to an embodiment of the present invention;

[33] Figures 6 to 8 are cross-sectional views depicting a vertical alignment LCD to describe the alignment of liquid crystal; and

[34] Figure 9 is a cross-sectional view depicting a lower substrate of a vertical alignment

LCD according to an embodiment of the present invention.

[35] <Brief Description of Symbols in the Drawings>

[36] 100: upper glass substrate

[37] 101: upper electrode

[38] 102: vertical alignment film

[39] 120: liquid crystal layer

[40] 130: lower glass substrate [41] 131, 131-1, 131-2: lower electrode

[42] 132: lower alignment film

[43] 133: lower common substrate

[44] 134: dielectric film

[45] 135: color filter substrate

Best Mode for Carrying Out the Invention

[46] Now, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[47] Figure 4 is a cross-sectional view depicting a multi-domain vertical alignment LCD according to an embodiment of the present invention.

[48] The upper glass substrate 100 is fabricated as the upper electrode 101 and upper alignment film 102 are formed in order. The lower glass substrate 130 is fabricated as the lower common electrode 133 and dielectric film 134 are formed in order. Lower electrodes 131 are disposed on the dielectric film 134. Slits are formed between the lower electrodes 132. After forming the lower electrodes 131 and the slits, a lower alignment film 132 is formed. After that, the upper glass substrate 100 is coupled to and spaced apart from the lower glass substrate 130 at a certain distance, which is called a gap. That gap forms a space between the upper alignment film 102 and the lower alignment film 132. The gap is filled with liquid crystal materials, thereby forming a liquid crystal layer 120.

[49] The lower electrode 131 inputs a specific voltage. The lower common electrode 133 may input the same voltage as that of the lower electrode 131, but is floated.

[50] Region A including the lower electrode 131 is affected by vertical electric fields between the lower electrode 131 and the upper electrode 101.

[51] In region B corresponding to the slit of the lower electrode 131, a difference in voltage between the lower common electrode 133 and the upper electrode 101 is divided into the liquid crystal layer 120 and the dielectric film 134. Therefore, the liquid crystal layer 120 above the slit is affected by vertical electric fields of different strengths and by a horizontal electric field of a certain of strength. Accordingly, the vertical alignment LCD forms multi-domains using the horizontal electric fields generated on the slit pattern.

[52] The lower electrode 131 and the lower common electrode 133 are described in detail in association with their shapes.

[53] Figure 5 is views describing shapes of a lower electrode 131 and a lower common electrode 133 of a vertical alignment LCD according to an embodiment of the present invention.

[54] The lower common electrode 133 may be formed as a plate electrode without any pattern, as is a common electrode disposed on a color filter of a TN-type TFT LCD. The alignment directions of vertical alignment liquid crystal molecules are determined according to the shape of the lower electrode 131.

[55] As shown in FIG. 5, if a lower electrode is formed as a rectangle shape 131-1, the vertical alignment liquid crystal molecules are aligned to form double domains, such as -X, X, -X and X. If the lower electrode is formed as an angled shape 131-2 angled at 45°, the vertical alignment liquid crystal molecules are aligned in four alignment directions.

[56] Such alignment directions of the vertical alignment LCD are described in detail referring to the figures.

[57] Figures 6 to 8 are cross-sectional views depicting a vertical alignment LCD to describe the alignment of liquid crystal.

[58] Both the lower electrode 131 and lower common electrode 133 are biased at 0 volts, and the upper electrode 101 is biased at 8 Volts. The dielectric film 134 has a dielectric constant of 4 and a thickness of lμm. The lower electrode 131 is lOμm in width and the slit is also lOμm in width.

[59] Under the condition, at the initial time, the liquid crystal molecules maintain the vertical alignment state, as shown in Figure 6. When a voltage is applied to the electrodes, lateral electric fields are generated and then the liquid crystal molecules are divided into both sides with respect to the center of the slit and lean, as shown in Figure 7. Once a certain period of time has elapsed, the liquid crystal molecules are arrayed to show domains that are alternately aligned at left and right with respect to the center of each slit, and this is repeated, as shown in Figure 8.

[60] The following is a description of a method for fabricating a vertical alignment LCD having the above described structure, according to the present invention.

[61] Figure 9 is a cross-sectional view depicting a lower substrate of a vertical alignment

LCD according to an embodiment of the present invention.

[62] A color filter substrate 135 is disposed on a lower glass substrate 130. The color filter substrate 135 includes films containing red (R), green (G), and blue (B) dyes. Since the boundaries between the films are uneven, an overcoat layer 134 is generally formed on the R-, G-, and B -color filter. More specifically, before forming the overcoat layer 134, a lower common electrode 133 serving as a plate electrode is disposed on the R-, G-, and B-color filters, and then the overcoat layer 134 is and a lower electrode 131 are formed on the lower common electrode 133, in order. The thickness of the overcoat layer 134 depends on the variation of the thickness of the color filters. The overcoat layer 134 is implemented to be approximately 1.5μm thick, preferably. For example, if the overcoat layer 134 is relatively thick, most of the vertical electric fields on the slit pattern of the lower common electrode 133 are applied to the overcoat layer 134, which requires a high driving voltage. On the contrary, when the overcoat layer 134 is relatively thin, the horizontal electric fields on the slit pattern of the lower common electrode 133 are decreased, which causes response time to be slightly different. Preferably, the overcoat layer 134 is 0.5-1.5μm thick.

[63] The overcoat layer can serve as a dielectric film as well. That is, when the LCD is fabricated in such a way that the overcoat layer can perform the function of a dielectric film as well, the steps for fabricating the LCD can be reduced and the multi-domains can be easily formed.

[64] Since the upper glass substrate can be fabricated through well-known technology, the detailed description will be omitted. Also, the present application will omit the t echnology for coupling the upper glass substrate and lower glass substrate to each other and for injecting liquid crystal materials to the gap, because it has been also well known.

[65] Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims. Industrial Applicability

[66] The multi-domain vertical alignment LCD (MVA-LCD), according to the present invention, can form multi-domains by means of lateral electric fields that are caused by a difference between vertical electric fields that are formed between the electrodes of the MVA-LCD, and thus can be widely used in a variety of display devices that require a wide viewing angle and high contrast.

Claims

[1] A multi-domain vertical alignment (MVA) LCD comprising: a lower glass substrate; an upper glass substrate located spaced apart from the lower glass substrate at a certain distance; and a liquid crystal layer located between the lower and upper glass substrates, wherein: the lower glass substrate comprises: lower common electrodes formed on the side thereof that faces the upper glass substrate; a dielectric film coated on the lower common electrodes; lower electrodes formed in such a way to have slits on the dielectric film; and a lower alignment film formed on the dielectric film and the lower electrodes, the upper glass substrate comprises: upper electrodes formed on the side thereof that faces the lower glass substrate; and an upper alignment film formed on the upper electrodes, and when the lower electrodes and the lower common electrodes are biased at the same voltage or the lower common electrodes are floated, a difference between vertical electric fields, which are formed between the upper electrodes and the lower electrodes, and vertical electric fields, which are formed between the upper electrodes and the lower common electrodes, causes lateral electric fields, thereby forming multi-domain in the liquid crystal layer. [2] The MVA LCD according to claim 1, further comprising a color filter substrate between the lower common electrodes and the lower glass substrate. [3] The MVA LCD according to claim 1 or 2, further comprising a smoothing film between the lower common electrodes and the lower alignment film. [4] The MVA LCD according to claim 1 or 2, wherein the dielectric film has a thickness above 0.5μm. [5] The MVA LCD according to claim 1 or 2, wherein each of the lower electrodes is angled. [6] The MVA LCD according to claim 5, wherein each of the lower electrodes is angled at 45°. [7] The MVA LCD according to claim 6, wherein each of the lower common electrodes is shaped as a plate. [8] The MVA LCD according to claim 5, wherein each of the lower common electrodes is shaped as a plate. [9] The MVA LCD according to claim 1 or 2, wherein each of the lower electrodes is shaped as a rectangle. [10] The MVA LCD according to claim 9, wherein each of the lower common electrodes is shaped as a plate.