JPH08184854A - Liquid crystal display panel - Google Patents

Abstract

PURPOSE: To make it possible to drive liquid crystals with AC without excessively increasing auxiliary capacitance of a liquid crystal display panel. CONSTITUTION: The liquid crystals 10 are held between a pair of substrates 12 and 14 facing each other. The one substrate 12 is provided with gate bus lines 20, drain bus lines and nonlinear type elements connected to the gate bus lines 20 and drain bus lines as well as pixel electrodes 16 connected to these nonlinear elements. The other substrate 14 is provided with striped common electrodes 18a, 18b divided to extend in parallel with the gate bus lines.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display panel which realizes bright display.

[0002]

2. Description of the Related Art A liquid crystal display panel is one in which liquid crystal is sealed between a pair of substrates. Recently, active matrix development has been actively carried out with the increase in size and definition of liquid crystal display panels. There is. The active matrix includes a gate bus line, a drain bus line, a non-linear element connected to the gate bus line and the drain bus line, and a pixel electrode provided on one substrate. A TFT (thin film transistor) is often used as the non-linear element. A common electrode having a solid surface is provided on the other substrate.

In a TN liquid crystal panel, liquid crystal molecules are aligned substantially parallel to the substrate surface when no voltage is applied, and the liquid crystal molecules move from one substrate to the other substrate by 90 degrees.
It is designed to twist once. When a voltage is applied, the liquid crystal molecules rise almost vertically to the substrate surface. Therefore, the channel of the TFT is opened by the voltage of the positive pulse applied to the gate bus line, and the voltage of the drain is written in the pixel electrode. In this way, display is performed by applying a voltage between the common electrode and the pixel electrode. Gradation display can be performed by adjusting the signal voltage supplied from the drain bus line.

[0004] In such a liquid crystal display panel includes a liquid crystal and the electrode is considered to form a capacitance C _LC, write the pixel electrode as described above is performed by applying an electric field to the capacitor C _LC. Further, an auxiliary capacitance electrode is provided below the pixel electrode, and the auxiliary capacitance C _S is arranged in parallel with the liquid crystal capacitance C _LC.
Are formed. The auxiliary capacitance C _S is arranged in parallel with the capacitance C _LC of the liquid crystal and serves to adjust the voltage or current applied to the liquid crystal. Furthermore, it is known that an undesired parasitic capacitance C _gs can be produced. The parasitic capacitance C _gs can be formed, for example, between the gate electrode and the source electrode of the TFT.

FIG. 10 is a diagram showing drive voltage waveforms in a conventional liquid crystal display panel. V _g is a pulse voltage supplied to the gate bus line, and V _D is a signal voltage supplied to the drain bus line. When V _g and V _D are applied, the pixel electrode potential V _p is applied and a signal is written in the liquid crystal. Here, there is a problem that the pixel electrode potential V _p decreases by ΔV at the writing end stage. That is, since the pixel electrode is connected to the gate bus line by capacitive coupling by the parasitic capacitance C _{gs, the} pixel electrode potential V _p decreases by ΔV according to the potential difference ΔV _g when the gate voltage decreases from the peak value to the base value. The lowered voltage ΔV is calculated by the following formula. This reduced voltage ΔV is a DC component.

[0006]

When a direct current component is applied to the liquid crystal, problems such as flicker, a reduction in contrast, and deterioration of the liquid crystal and the alignment film occur. Therefore, the liquid crystal is usually driven by an alternating current. Therefore, the signal voltage V _D is an alternating current with 0 potential at the center. The pixel electrode potential V _p should also be a corresponding alternating current, but since the lowered voltage ΔV is a direct current component, the pixel electrode potential V _p is not an alternating current centered on 0 potential. Therefore, conventionally, a constant voltage V _C corresponding to the lowered voltage ΔV is applied to the common electrode so that the pixel electrode potential V _p becomes an alternating current centered on V _C.

[0008]

The liquid crystal is in a state crystal that leans against the substrate surface when a voltage is not applied, and stands up against the substrate surface when a voltage is applied. The dielectric constant ε of the liquid crystal differs depending on whether the liquid crystal is standing or not. Since the capacitance C _LC of the liquid crystal is a function of the dielectric constant of the liquid crystal epsilon, different and capacity C _LCOFF state where the liquid crystal is sleep, the capacitance C _LCON state where the liquid crystal is standing. Therefore, the above equation becomes as follows.

[0009] This ΔV is a DC component, and its value changes according to the display state. Therefore, even if a constant voltage V _C is applied to the common electrode, the pixel electrode potential V _p cannot be made completely alternating.

For this reason, the display may appear as burn-in, which is a serious problem in display. As a countermeasure against this, the auxiliary capacitance C _S is set to a sufficiently large value, but the auxiliary capacitance electrode is usually formed of the same metal as the gate bus line, and when the area of the auxiliary capacitance electrode is increased, the aperture ratio is increased. And the transmittance of the liquid crystal display panel decreases. Even so, it was not possible to make ΔV completely zero.

Further, if the auxiliary capacitance C _S is added, the load on the TFT increases correspondingly, and the current I flowing through the TFT is increased.
It is necessary to increase d. For that purpose, the TFT becomes large, and when the TFT becomes large, the parasitic capacitance C _gs becomes large due to the overlapping of the gate electrode and the source electrode, and therefore, it becomes necessary to further increase the value of the auxiliary capacitance C _S. Due to this vicious circle, a considerably large auxiliary capacity C
_S is required.

An object of the present invention is to provide a liquid crystal display panel which can drive liquid crystal by an alternating current without excessively increasing the auxiliary capacitance. Another object of the present invention is to provide a liquid crystal display panel having a high aperture ratio without making the auxiliary capacitance excessively large.

[0013]

A liquid crystal display panel according to the present invention includes a liquid crystal 10 between a pair of substrates 12 and 14 facing each other.
, And the gate bus line 20,
A drain bus line 22, a non-linear element 24 connected to the gate bus line and the drain bus line, and a pixel electrode 16 connected to the non-linear element are provided, and the other substrate is provided in parallel with the gate bus line. It is characterized in that the striped common electrodes 18a, 18b, and 18c are provided so as to extend.

In another feature, the liquid crystal display panel according to the present invention has a pair of substrates 12 and 14 facing each other.
The liquid crystal 10 is sandwiched between the two, and one of the substrates is connected to the gate bus line 20, the drain bus line 22, the non-linear element 24 connected to the gate bus line and the drain bus line, and the non-linear element. The pixel electrode 16 is provided, the common electrode 18 is provided on the other substrate, and the non-electrode portion 40 having a size of 10 μm or less is provided on at least one of the pixel electrode and the common electrode.

[0015]

In the structure described above, the common electrode is provided in the form of a divided stripe extending parallel to the gate bus line. Therefore, if a constant voltage V _C is applied to one of the divided striped common electrodes and the voltage applied to the other common electrode can be adjusted according to the display state as in the conventional case. , The liquid crystal can be driven by alternating current.

In addition, in the configuration of another feature,
At least one of the pixel electrode and the common electrode, for example, the pixel electrode is provided with a non-electrode portion having a size of 10 μm or less, for example, a groove or a slit. However, by providing the non-electrode portion, the load capacitance C _LC is reduced, so that the current Id flowing in the TFT can be reduced, and thus the TFT
Since it is not necessary to increase the storage capacitance C _S and the auxiliary capacitance C _S , the aperture ratio can be increased. No voltage is applied to the liquid crystal in the non-electrode portion, but the liquid crystal rises due to intermolecular force.

[0017]

1 and 2 are views showing a first embodiment of a liquid crystal display panel according to the present invention. The liquid crystal display panel is composed of a liquid crystal 10 enclosed between a pair of transparent substrates 12 and 14. A transparent pixel electrode 16 is formed on the inner surface of one substrate 12.
And an alignment film (not shown), and the other substrate 1
A color filter (not shown), transparent common electrodes 18a and 18b, and an alignment film (not shown) are provided on the inner surface of 4.

An active matrix is formed on the substrate 12 having the pixel electrodes 16. The active matrix is a TFT as a non-linear element connected to the gate bus line 20 and the drain bus line 22 and the gate bus line 20 and the drain bus line 22 which are orthogonal to each other.
(Thin film transistor) 24, and the pixel electrode 16 is connected to the TFT 24.

The gate bus line 20 is provided on the surface of the substrate 12, and the gate electrode 26 of the TFT 24 is provided at the same time as the gate bus line 20. Furthermore, the auxiliary capacitance electrode 2
8 is provided on the surface of the substrate 12 with the same metal material as the gate bus line 20. After the gate bus line 20, the gate electrode 26, and the auxiliary capacitance electrode 26 are provided, the insulating layer 3
0 is provided.

A semiconductor layer (not shown) of the TFT 24 is formed on the insulating layer 30 and connected to the semiconductor layer to form a TF.
The drain electrode 32 and the source electrode 34 of T24 are formed. The drain bus line 22 is formed at the same time as the drain electrode 32. An insulating layer (not shown) is provided so as to cover these members, and the pixel electrode 16 is formed on the insulating layer. The pixel electrode 16 is connected to the source electrode 34 via a contact hole provided in the insulating layer. The structure of such a TFT 24 is known.

The other substrate 14 is usually provided with a solid common electrode, but in the present invention, the common electrode 18 is provided.
Reference numerals a and 18b denote divided striped common electrodes extending parallel to the gate bus lines 20. In the same way that each gate bus line 20 extends over a plurality of pixel electrodes 16, the striped common electrodes 18 a, 18 b extend over a plurality of pixel electrodes 16.

In FIGS. 1 and 2, there are two stripe-shaped common electrodes 18a and 18b for one of the display gate lines (the pixel electrode 16 line along the gate bus line 20). A pulse voltage is applied when writing the line corresponding to one line.

Therefore, both the liquid crystal 10 and the pixel electrode 16 are
The through electrodes 18a and 18b have a capacitance C _LC1, C_LC2Forming
I do. Insulating layer 30, pixel electrode 16, auxiliary capacitance electrode 2
8 is the auxiliary capacitance C_STo form Furthermore, the parasitic capacitance C
_gsIs, for example, the gate electrode 26 and the source electrode 3 of the TFT 24.
You can do it with 4. The gate electrode 26 is a gate bus line
20 and the source electrode 34 is connected to the pixel electrode 16
Has been done. Therefore, the pixel electrode 16 has a parasitic capacitance C_gsBy
Will be connected to the gate bus line 20,
As a result, the pixel electrode potential V_pLowering voltage ΔV of
Is as described with reference to FIG.

The drive voltage waveform of each member is shown in FIG. 3, and the equivalent circuit of each capacitor is shown in FIG. 1 and 3, V _g is a pulsed voltage supplied to the gate bus line 20, and V _D is a signal voltage supplied to the drain bus line. When V _g and V _D are applied, the pixel electrode potential V _p is applied and a signal is written in the liquid crystal.

One striped common electrode 18b is
As in the conventional case, a constant voltage V _C is supplied, and the auxiliary capacitance electrode 28 is also supplied with the same constant voltage V _C. The other striped common electrode 18a is supplied with a pulsed voltage V _g ′ in synchronism with the pulse of the gate bus line 20, and otherwise the same constant voltage V _g as one striped common electrode 18b. Supplied with _C.

At the writing end stage, the pixel electrode potential V _p decreases by ΔV. However, in this case, ΔV
Is a composite of the component ΔV ₁ due to the voltage drop ΔV _g and the component ΔV ₂ due to the pulsed voltage V _g ′ as in the conventional case.

[0027]

[0028]

[0029]

Here, C _LC1 and C _LC2 are values that change according to the change in the dielectric constant depending on whether the liquid crystal is in a standing state or in a standing state. In this embodiment, since the changing value exists both in the denominator and the numerator, it is possible to optimize the other parameters C _S and ΔV _g ′ so that they are not affected by the display state. .

Therefore, a 10.4 inch liquid crystal display panel was manufactured under the following conditions. Capacitance C when liquid crystal is splashing
_LCOFF is 113 (fF), capacitance C _{LC ON} in a state where the liquid crystal is standing was 266 (fF). These are C _LC1 + C
_{This is} the value of _LC2 . ΔV _g = 25V was set.

FIG. 5 is a diagram showing ΔV _C when C _LC2 is changed under the three conditions of C _S of 0, 50 and 416, with ΔV _g ′ = 25 V. Incidentally, conventionally, when C _S is set to 416 (fF), ΔV _C
Was 0.4V. As C _LC2 is increased, Δ
It can be seen that V _C can be reduced. _{C where} ΔV _C = 0
_LC2 is the optimum value. In FIG. 5, ΔV _C can be set to 0 when C _S is 0 and C _LC2 is 113 (fF). Note that C _LC2 of 113 (fF) means C
_LC1 is 0. Since C _S is 0, the auxiliary capacitance electrode 2
8 is no longer necessary, and the aperture ratio can be increased by 20 to 30%.

When C _S = 50 (fF), C _LC2
Is 30 (fF), ΔV _C = 0. In this case, the area of the auxiliary capacitance electrode 28 can be reduced to 1/6 that of the conventional case. ΔV _g ′ = 25 V, and ΔV _g
= 25V, the striped common electrode 18a
Is connected to the gate bus line 20. However, if ΔV _g ′ is obtained from another existing circuit, it will be smaller than ΔV _g , so normally ΔV _{g ′} will be obtained.
It is preferable that ′ has a small value.

FIG. 6 is a diagram showing ΔV _C when C _S is changed to a different ΔV _g ′ with C _LC2 being a constant value (113 fF). At ΔV _g ′ = 5 V, C _S
= 90 (fF), ΔV _C = 0. Also, Δ
At V _g ′ = 7 V, when C _S = 50 (fF), ΔV
_C = 0. Thus, the area of the auxiliary capacitance electrode 28 can be reduced by the combination of C _LC2 and ΔV _g ′.

FIG. 7 is a diagram showing a second embodiment of the present invention. FIG. 7 shows the substrate 12 on which the active matrix is formed as in FIG.
(See FIG. 1) has a transparent common electrode 18c, which is shown in dashed lines in FIG. 7 (similar to 18a, 18b in FIG. 2).

The transparent common electrode 18c is a divided striped common electrode extending in parallel with the gate bus line 20. Each gate bus line 20 has a plurality of pixel electrodes 16
The stripe-shaped common electrode 18c extends over the plurality of pixel electrodes 16 in the same manner as it extends over. In this embodiment, the stripe-shaped common electrode 18c is the gate line of the display (the pixel electrode 16 along the gate bus line 20).
There is one for each line). Also in this case, a pulsed voltage is applied to the stripe-shaped common electrode 18c in synchronization with the pulse of the gate bus line 20 when writing the corresponding line. The striped common electrode 18c may be provided for each of a plurality of display gate lines.

FIG. 8 is a diagram showing a third embodiment of the present invention. FIG. 8 shows the substrate 12 on which the active matrix is formed as in FIG. Counter substrate 14
(See FIG. 1) has a transparent common electrode, and this common electrode is not necessarily a divided striped common electrode as in the first and second embodiments. be able to.

In FIG. 8, the pixel electrode 16 has a thickness of 10 μm.
The non-electrode portion 40 having a size of m or less is provided. The non-electrode portion 40 is composed of grooves or slits provided in the electrode layer of the pixel electrode 16, and the grooves or slits are arranged long in the direction perpendicular to the long axis direction of the liquid crystal molecules near the substrate 12. That is, the alignment film (not shown) of the substrate 12 is rubbed in the direction of arrow R, and the liquid crystal molecules near the substrate 12 are aligned in the direction of arrow R. The grooves or slits forming the non-electrode portion 40 are arranged in a long array in the direction perpendicular to the arrow R. In the embodiment, the width of the groove or slit forming the non-electrode part 40 is 5 μm, which is 20 μm.
It was arranged at the pitch.

As described above, by providing the non-electrode portion 40, the capacitance C _{LC as} a load is reduced, so that the TFT 2
It is possible to reduce the current Id flowing through the TFT 4, thus reducing the TFT 24 and auxiliary capacitance C _S. Therefore, a liquid crystal display panel having a large aperture ratio can be obtained. In the non-electrode part 40, no voltage is applied to the liquid crystal, but the liquid crystal rises due to the intermolecular force with the liquid crystal molecules around it. In particular, the non-electrode part 40
Is 10 μm or less and is formed to be long in the direction perpendicular to the arrow R, the intermolecular force of the liquid crystal can be used more effectively.

FIG. 9 is a diagram showing a fourth embodiment of the present invention. In this embodiment, a non-electrode part 40 similar to the non-electrode part 40 of FIG. 8 is provided on the common electrode 18 of the other substrate 14. The non-electrode part 40 is provided in a region corresponding to the pixel electrode 16.

[0041]

As described above, according to the present invention,
The auxiliary capacitance electrode can be reduced in size to reduce the aperture ratio, and the liquid crystal can be surely driven by an alternating current.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a liquid crystal display panel of a first embodiment of the present invention.

2 is a plan view showing an active matrix provided on one substrate of the liquid crystal display panel of FIG. 1. FIG.

FIG. 3 is a diagram showing drive voltage waveforms of the liquid crystal display panel of FIGS. 1 and 2.

FIG. 4 is an equivalent circuit diagram of the capacitors shown in FIGS. 1 and 2.

FIG. 5 is a diagram showing a first test result for alternating-current driving a liquid crystal in the liquid crystal display panel of FIGS. 1 and 2.

FIG. 6 is a diagram similarly showing a second test result.

FIG. 7 is a diagram showing a second embodiment of the present invention.

FIG. 8 is a diagram showing a third embodiment of the present invention.

FIG. 9 is a diagram showing a fourth embodiment of the present invention.

FIG. 10 is a diagram showing drive voltage waveforms for explaining a conventional technique.

[Explanation of symbols]

 10 ... Liquid crystal 12, 14 ... Substrate 16 ... Pixel electrodes 18a, 18b, 18c ... Common electrode 20 ... Gate bus line 22 ... Drain bus line 24 ... TFT 40 ... Non-electrode part

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location H01L 29/786 21/336

Claims (6)

[Claims] 1. A liquid crystal (10) is sandwiched between a pair of substrates (12, 14) facing each other, and a gate bus line (20), a drain bus line (22), and the gate bus line are provided on one substrate. And a non-linear element (24) connected to the drain bus line and a pixel electrode (16) connected to the non-linear element, and the other substrate is divided into stripes extending parallel to the gate bus line. -Shaped common electrode (18a, 18b, 18c) is provided, a liquid crystal display panel characterized by the above-mentioned. 2. The stripe-shaped common electrode is provided for each of the display gate lines, and a pulse-like voltage is applied when writing a line corresponding to one of the display gate lines. 1. The liquid crystal display panel according to 1. 3. A stripe-shaped common electrode is provided for one or more display gate lines, and a pulse-shaped voltage is applied when writing a line corresponding to the stripe-shaped common electrode. The liquid crystal display panel according to claim 1, wherein the liquid crystal display panel is a liquid crystal display panel. 4. The liquid crystal display panel according to claim 1, wherein the striped common electrode is connected to a gate bus line. 5. A liquid crystal (10) is sandwiched between a pair of substrates (12, 14) facing each other, and one substrate has a gate bus line (20), a drain bus line (22), and the gate bus line. And a non-linear element (24) connected to the drain bus line and a pixel electrode (16) connected to the non-linear element, and the other substrate is provided with a common electrode (1
8) is provided, and a non-electrode part (40) is provided on at least one of the pixel electrode and the common electrode. 6. The non-electrode portion comprises a groove or slit provided in the electrode material layer, and the groove or slit is long in a direction perpendicular to the major axis direction of liquid crystal molecules near the substrate. The liquid crystal display panel described in.