KR100697365B1 - Fringe field switching mode lcd - Google Patents

Abstract

The present invention discloses a fringe field drive liquid crystal display device capable of preventing residual DC. The present invention discloses an upper and lower substrate facing each other at a predetermined distance; A liquid crystal layer interposed between the upper and lower substrates; A counter electrode formed on the lower substrate and formed of a transparent material; A pixel electrode made of a transparent material, overlapping the counter electrode on the lower substrate, the pixel electrode having a plurality of combs to form a fringe field with the counter electrode; An insulating film insulating between the counter electrode and the pixel electrode; A lower alignment layer interposed between the surface of the lower substrate resultant on which the counter electrode and the pixel electrode are formed and the liquid crystal layer; And an upper alignment layer interposed between the upper substrate surface and the liquid crystal layer, wherein each of the liquid crystal layer, the lower alignment layer, and the insulating layer has a product of a dielectric constant and a specific resistance within the same range.

Description

Fringe field drive liquid crystal display device {FRINGE FIELD SWITCHING MODE LCD}

1 is a cross-sectional view of a conventional fringe field driving liquid crystal display device.

2 is a cross-sectional view of a fringe field driving liquid crystal display device according to the present invention;

(Explanation of symbols for the main parts of the drawing)

21-Board 22-Counter Electrode

23-first insulating film 25-second insulating film

30-pixel electrode 31-lower alignment layer

39-liquid crystal layer

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display, and more particularly, to a method of manufacturing a fringe field switching liquid crystal display capable of reducing residual direct current (DC).

In general, a liquid crystal display device operated by a fringe field has been filed in Korean Patent Application No. 98-9243 to improve the low aperture ratio and transmittance of a general IPS mode liquid crystal display device.

In the fringe field driving liquid crystal display, the counter electrode and the pixel electrode are formed of a transparent conductor, and the gap between the counter electrode and the pixel electrode is formed to be narrower than the gap between the upper and lower substrates, and the fringe field is formed on the counter electrode and the pixel electrode. By forming the filed), all of the liquid crystal molecules present on the electrodes are operated.

1 is a cross-sectional view of a typical fringe field driving liquid crystal display device.

Referring to FIG. 1, a counter electrode 2 is formed in a plate shape in each unit pixel region of the transparent lower substrate 1 having a unit pixel region defined therein. After the first insulating film 3 made of a silicon oxide film is formed on the lower substrate 1 on which the counter electrode 2 is formed, the gate bus line 4 is formed in a predetermined region of the lower substrate. On the gate bus line 4 and the first insulating film 3, the second and third insulating films 5 and 6 and the channel layer 7 serving as the gate insulating film are sequentially stacked. In this case, silicon nitride oxide (SiON) having excellent insulating properties is used as the first and second insulating films 3 and 5, and the third insulating film 6 has a silicon nitride film having excellent adhesion property with the channel layer 7 ( SiN) is used. In addition, the channel layer 7 and the third insulating film 5 are formed in an active form existing only on a predetermined portion of the gate bus line 4. Source and drain electrodes 9a and 9b are formed on both sides of the channel layer 7 around the gate bus line 4 to form a thin film transistor. Here, a doped amorphous silicon layer 8 as an ohmic layer is disposed between the source and drain electrodes 9a and 9b and the channel layer 7, respectively. The pixel electrode 10 is disposed on the second insulating layer 5 to overlap the counter electrode 2. In this case, the pixel electrode 10 is formed of an ITO layer similarly to the counter electrode, and is formed in a comb-tooth shape to be in contact with the drain electrode of the thin film transistor. An alignment layer 12 is formed on the resultant surface of the lower substrate 1 on which the thin film transistor and the pixel electrode 10 are formed.

On the other hand, a color filter (not shown) is formed on the inner surface of the upper substrate 15 to be bonded to the lower substrate 1, and the alignment film 17 is also formed on the color filter surface.

The liquid crystal layer 19 is interposed in the space portion between the lower substrate 1 and the upper substrate 15.

In the fringe field driving liquid crystal display device configured as described above, since the gap and width between the pixel electrode 10 and the counter electrode 2 are sufficiently narrow, a fringe field is formed to form a gap between the electrodes 10, 2 and the electrodes 10,. 2) All liquid crystal molecules on the top are operated.

Similar to the general liquid crystal display, the fringe field drive liquid crystal display device has a reaction power of an AC component and a drive speed of several tens of kilowatts. However, when driving an fringe field driving liquid crystal display by supplying AC power, the liquid crystal molecules in the liquid crystal layer 19 do not react according to the frequency of the driving voltage but only change in polarity. Accordingly, a direct current generated by the direct current power source is generated between the counter electrode 2 and the pixel electrode 10. To offset this DC current, the voltage of the counter electrode is usually offset. However, even if the offset is made in this manner, since the DC current component cannot be completely removed, a residual DC current (hereinafter, referred to as residual DC) remains between the pixel electrode and the counter electrode, and the residual DC is accumulated over time.

That is, the residual DC is, for example, when one of the counter electrode 2 and the pixel electrode 14 exhibits a positive charge state, and as time passes, the negative charge among contaminants in the liquid crystal layer 19 or the like. Particles with ions gather around the electrode, which exhibits a positive charge state, and a parasitic electric field is generated between the electrode and the contaminated particle. At this time, the parasitic electric field is canceled by the external power source. When the external power source is applied in this way, the voltage retention of the liquid crystal layer 19 is lowered, and afterimages occur on the screen.

Here, the charged contaminants are generated because impurities are not removed in a timely manner, and the films are disposed in the paths of the electric fields E1 and E2 formed between the counter electrode 2 and the pixel electrode 10. That is, it is generated due to the difference in the degree of polarization of the liquid crystal layer 19, the alignment film 12, the second insulating film 5 and the first insulating film (3).

In addition, since the polarization degree of the liquid crystal layer 19, the alignment film 12, the second insulating film 5, and the first insulating film 3 is different, the polarization of the remaining films continues to occur even if the polarization of any one film is eliminated. Excess residual DC components remain.

Accordingly, an object of the present invention is to provide a fringe field driving liquid crystal display device which can reduce residual DC and prevent afterimages on a screen.

A fringe field driving liquid crystal display device according to an exemplary embodiment of the present invention for achieving the above object includes an upper and lower substrates facing each other at a predetermined distance; A liquid crystal layer interposed between the upper and lower substrates; A counter electrode formed on the lower substrate and formed of a transparent material; A pixel electrode made of a transparent material, overlapping the counter electrode on the lower substrate, the pixel electrode having a plurality of combs to form a fringe field with the counter electrode; An insulating film formed of a silicon nitride film to insulate between the counter electrode and the pixel electrode, the dielectric constant and the resistivity of which are controlled by changing a ratio of silicon and nitrogen gas; A lower alignment layer interposed between the surface of the lower substrate resultant on which the counter electrode and the pixel electrode are formed and the liquid crystal layer; And an upper alignment layer interposed between the upper substrate surface and the liquid crystal layer, wherein the liquid crystal layer, the lower alignment layer, and the insulating layer have a product of a dielectric constant and a specific resistance within the same range.

The product of the dielectric constant and the specific resistance of each of the liquid crystal layer, the lower alignment layer, and the insulating film is 2.0 × 10 ¹⁴ to 2.5 × 10 ¹⁴ Ωcm, or 6.1 × 10 ¹³ to 8.1 × 10 ¹³ Ωcm, or 1.0 × 10 ¹³ to 1.5 × 10 ¹³ Ωcm.

The liquid crystal layer has a dielectric constant (ε) of 5 to 7.5 and a specific resistance (ρ) of 2.0 × 10 ¹² to 5.0 × 10 ¹³ Ωcm, and a dielectric constant (ε) of the lower alignment layers 3 to 5.5 and 2.0 × 10 ^12. To 7.0 × 10 ¹³ Ωcm, and the insulating film has a dielectric constant (ε) of 6.5 to 10 and a specific resistance of 1.1 × 10 ¹³ to 2.1 × 10 ¹⁴ Ωcm, wherein the insulating film is made of silicon nitride. When the proportion of silicon is increased and the proportion of nitrogen is decreased, the membrane quality is porous, and the dielectric constant and resistivity are increased.

According to the present invention, the polarization characteristics of the liquid crystal layer, the alignment film, and the insulating film formed in the path where the electric field is formed are made similar. Accordingly, as the polarization characteristics of the liquid crystal layer, the alignment film, and the insulating film become similar, generation of charged impurity ions can be fundamentally prevented.

As such, as the polarization characteristics of the liquid crystal layer, the alignment layer, and the insulating film are similar, the polarization canceling point is almost similar, and no additional residual DC is generated.

(Example)

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

2 is a cross-sectional view of a fringe field driving liquid crystal display device according to the present invention.

Referring to FIG. 2, a counter electrode 22 made of an ITO layer is formed on each unit pixel of the lower substrate 21 made of a transparent insulator in which unit pixels are defined. In this embodiment, the counter electrode 22 is formed in the form of a square plate or a comb teeth, for example. Then, a first insulating film 23 made of a silicon oxide film or a silicon oxynitride film is formed on the lower substrate 21 on which the counter electrode 22 is formed. Next, a MoW metal film, an Al—Nd alloy film, or a laminated film of Mo / Al is deposited over the first insulating film 23, and then patterned to a predetermined portion to form a gate bus line 24. At the same time as the process of forming the gate bus line 24, a common electrode line (not shown) for transmitting a common signal to the counter electrode 22 is formed.

On the first insulating film 23 having the gate bus line 24 formed thereon, the second insulating film 25 made of silicon nitride oxide, the third insulating film 26 made of silicon nitride film, and the amorphous silicon film for channel (a-Si: 27) ) And the doped semiconductor layer (n ⁺ a-si: 28) are sequentially deposited by plasma enhacned chemical vapor deposition (PECVD). Then, the doped semiconductor layer 18, the amorphous silicon layer 27, and the third insulating film 26 are patterned to a predetermined portion so as to surround the predetermined portion of the gate bus line 24, thereby forming an active region.

On the resulting product of the lower substrate 21, a metal film for data bus lines, for example, an opaque metal film such as Mo / Al / Mo lamination or MoW, is formed to a predetermined thickness. Then, the metal film is partially patterned so as to be disposed on both sides of the gate bus line 24 to form source, drain electrodes 29a and 29b and a data bus line (not shown).

Then, the ITO layer for the pixel electrode is deposited on the resultant by sputtering, and patterned in the shape of a comb to form the pixel electrode 30. In this case, the pixel electrode 30 overlaps the counter electrode 22 with the first and second insulating layers 23 and 25 interposed therebetween. In this case, the pixel electrode, the comb teeth 30 of the pixel electrode in the drawing, may form a fringe field and a portion of the counter electrode 22 opened through the space between the comb teeth 30 and the pixel electrode comb 30 of the pixel electrode. It is formed at a predetermined interval and a predetermined width so that it can be. The lower alignment layer 31 is coated on the resultant surface of the lower substrate 21.

On the other hand, the upper substrate 35 to be bonded to the lower substrate 21 includes a color filter (not shown) on the inner side, and the upper alignment layer 37 is also coated on the color filter surface.

The liquid crystal layer 39 is interposed in the space portion between the lower substrate 21 and the upper substrate 35. At this time, the liquid crystal layer 39 has a dielectric constant ε of about 5 to 7.5 and a specific resistance ρ of about 2.0 × 10 ¹² to 5.0 × 10 ¹³ Ωcm. Therefore, the polarization characteristic of the liquid crystal layer 39, that is, the function of the product of the dielectric constant epsilon and the specific resistance p is about 1.4 x 10 ¹³ to 2.5 x 10 ¹⁴ Ωcm.

At this time, in this embodiment, in order to minimize the residual DC component, the polarization characteristics of the lower alignment layer 31 and the second and first insulating layers 25 and 23 substantially match the polarization characteristics of the liquid crystal layer 39. The polarization characteristics of the lower alignment layer 31 are about 1.0 × 10 ¹³ to 2.1 × 10 ¹⁴ Ωcm, and the polarization characteristics of the second and first insulating layers 25 and 23 are 1.1 × 10 ¹³ to 2.1 × 10 ¹⁴ Ω. About cm is preferable.
In the case of the second and first insulating layers 25 and 23 formed of the silicon nitride layer, the composition ratio of silicon (Si) and nitrogen (N) gases is changed when the second and first insulating layers 25 and 23 are formed. Different polarization characteristics were obtained. For example, the second and first insulating layers 25 and 23 may have a dielectric constant? Of 6.5 and a specific resistance of 1.8 when the composition ratio of silicon (Si) and nitrogen (N) gases is 3: 4. X 10 ¹² Ωcm can be obtained, and when the composition ratio is 3.5: 3.5, the dielectric constant (ε) = 8 and the specific resistance (ρ) = 1.01 x 10 ¹³ Ωcm can be obtained, and the composition ratio is 4: 3. In this case, permittivity (ε) = 10 and specific resistance (ρ) = 2.1 × 10 ¹³ Ωcm can be obtained. In the second and first insulating layers 25 and 23, when the silicon (Si) increases and the ratio of nitrogen (N) decreases, the film quality becomes more porous, thereby increasing the dielectric constant and resistivity. Increases because it does not move easily. Therefore, the second and first insulating layers 25 and 23 are adjusted to have a specific resistance of about 1.1 × 10 ¹³ to 2.1 × 10 ¹⁴ Ωcm by selecting the composition ratio of silicon (Si) and nitrogen (N) gases at the time of formation. shall.
In this way, the product of the dielectric constant ε and the specific resistance ρ of the liquid crystal layer 39, the alignment layer 31, and the second and first insulating layers 25 and 23 has almost similar values, whereby the liquid crystal layer 39, The polarization characteristics of the alignment film 31 and the second and first insulating films 25 and 23 become almost similar. Accordingly, the residual DC can be fundamentally reduced, and since the polarization cancellation point is almost the same, no extra residual DC is generated.

delete

As described in detail above, according to the present invention, the polarization characteristics of the liquid crystal layer, the alignment film, and the insulating film formed in the path where the electric field is formed are similar. Accordingly, as the polarization characteristics of the liquid crystal layer, the alignment film, and the insulating film become similar, generation of charged impurity ions can be fundamentally prevented.

As the polarization characteristics of the liquid crystal layer, the alignment layer, and the insulating film are similar, the polarization elimination point is almost similar, so that no additional residual DC is generated.

Accordingly, afterimages may be prevented from occurring on the screen.

Claims (6)

Upper and lower substrates facing each other at a predetermined distance; A liquid crystal layer interposed between the upper and lower substrates; A counter electrode formed on the lower substrate and formed of a transparent material; A pixel electrode made of a transparent material, overlapping the counter electrode on the lower substrate, the pixel electrode having a plurality of combs to form a fringe field with the counter electrode; An insulating film insulating between the counter electrode and the pixel electrode; A lower alignment layer interposed between the surface of the lower substrate resultant on which the counter electrode and the pixel electrode are formed and the liquid crystal layer; And An upper alignment layer interposed between the upper substrate surface and the liquid crystal layer; The difference between the product of the dielectric constant and the specific resistance of each of the liquid crystal layer, the lower alignment layer, and the insulating film is within a 1 × 10 ¹⁴ Ωcm. The fringe field driving liquid crystal display device according to claim 1, wherein a product of dielectric constant and specific resistance of each of the liquid crystal layer, the lower alignment layer, and the insulating film is 2.0 × 10 ¹⁴ to 2.5 × 10 ¹⁴ Ωcm. The fringe field driving liquid crystal display device according to claim 1, wherein a product of dielectric constant and specific resistance of each of the liquid crystal layer, the lower alignment layer, and the insulating film is 6.1 × 10 ¹³ to 8.1 × 10 ¹³ Ωcm. The fringe field drive liquid crystal display device according to claim 1, wherein a product of dielectric constant and specific resistance of each of the liquid crystal layer, the lower alignment layer, and the insulating film is 1.0 × 10 ¹³ to 1.5 × 10 ¹³ Ωcm. The fringe field driving liquid crystal display device according to claim 1, wherein the insulating film has a dielectric constant of 6.5 to 10 and a resistivity of 1.1x10 ¹³ to 2.1x10 ¹⁴ Ωcm . The fringe field driving liquid crystal display device of claim 5, wherein the insulating layer is made of silicon nitride, and when the ratio of silicon is increased and the ratio of nitrogen is decreased, the film quality is porous, and the dielectric constant and specific resistance are increased.

Images