JPH054138U - Active matrix LCD panel - Google Patents

Abstract

(57) [Summary] [Objective] In an active matrix type liquid crystal panel, an auxiliary capacitor having a small decrease in aperture ratio is formed. [Structure] Metal electrode 1 for auxiliary capacitance on rear glass substrate 2
1 is overlapped with the pixel electrode 10 and the insulating film 12 by 13
The areas (shaded areas) overlap. This overlap 13
Is the auxiliary capacity. A metal electrode 11 for auxiliary capacitance,
The auxiliary capacitance portion of the pixel electrode 10 is uneven. Therefore, the surface area of the electrode is larger than that of the conventional auxiliary capacitance formed in a flat shape, and the capacitance is large.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a structure of an active matrix type liquid crystal panel.

[0002]

[Prior Art]

 FIG. 5 is a perspective view of a conventional active matrix type liquid crystal panel, and FIG. 6 is a plan view of one pixel thereof. As shown in FIG. 5, in a conventional active matrix type liquid crystal panel, a front glass substrate 1 and a rear glass substrate 2 are arranged to face each other, and a spherical or cylindrical resin spacer (not shown) having a diameter of several μm is used. The liquid crystal layer 3 is provided between the liquid crystal layers 3 at regular intervals and the periphery is closed (the sealing portion is not shown). On the side of the front glass substrate 1 facing the rear glass substrate 2, a color filter 4, a translucent common electrode 5, and an alignment film 6 are sequentially laminated. On the other hand, on the side of the rear glass substrate 2 facing the front glass substrate 1, the gate bus lines 7 and the drain bus lines 8 are formed in a grid shape and are isolated from each other. A switching element (hereinafter, referred to as a TFT) 9 including, for example, an amorphous silicon thin film transistor is formed at an intersection with the line 8. Further, an alignment film (not shown) is formed on the entire surface.

As shown in FIG. 6, the TFT 9 has a gate electrode 9 connected to the gate bus line 7. ₁ And a drain electrode 9 connected to the drain bus line 8₂And a source electrode 9 connected to the translucent pixel electrode 10.₃And amorphous silicon (not shown). FIG. 7 is a waveform diagram of the drive voltage applied to the TFT in the conventional active matrix type liquid crystal panel.

In FIG. 5 to FIG. 7, the scanning signal V _G is applied to the gate bus line 7, and the TFT 9 is turned on in the period of T _H (for example, 40 μsec) at the cycle of T _V (for example, 16 msec). The voltage V _GH (for example, 20 V) for turning the TFT 9 on and the voltage V _GL (for example, OV) for making the TFT 9 non-conductive during the other period. In addition, a data signal V _D having a center voltage V _DC synchronized with the scanning signal V _G is input to the drain bus line 8.

FIG. 8 is an equivalent circuit diagram of one pixel of a conventional active matrix type liquid crystal panel. 5 to 8, V_LCIs the potential of the pixel electrode 10, V_COMIndicates the voltage applied to the common electrode 5. Gate bus line 7 and gate electrode 9₁Potential is V_G, Drain bus line 8 and drain electrode 9₂Potential is V_DBecomes Also, C _LC Is the liquid crystal capacity, C_GSIs a stray capacitance generated at the intersection of the gate electrode and the source electrode, C _GD Is a stray capacitance generated at the intersection of the gate electrode and the drain electrode. Furthermore, C _ST Is the storage capacity or additional capacity (collectively referred to as auxiliary capacity), and will be described in detail later.

In FIGS. 7 and 8, V is used as a scanning signal._GHIs applied, stray capacitance C_GDAnd C _GS The charge is stored in. Then T_HAfter the passage, V_GAs V_GLIs applied and the TFT 9 becomes non-conductive, the gate-source stray capacitance C_GSIs redistributed to the source side capacitance, the potential V of the pixel electrode 10_LCA potential drop (hereinafter referred to as a level shift) occurs at. This level shift is dV_PExpress. dV_PThe value of is dV_P= C_GS(V_GH-V_GL) / (C_GS+ C_LC+ C_ST)… (1) If dV_PIs a constant value, the voltage V of the common electrode 5 is_COMBecomes a constant value as shown in equation (2). V_COM= V_DC-DV_P(2) However, V_DCIs the data signal V_DIs the center voltage of.

However, the liquid crystal has a dielectric anisotropy, and its value changes depending on the direction of the liquid crystal molecules. Therefore, the capacitance C _LC of the liquid crystal is, for example, as shown in FIG. It changes as shown in the capacitance characteristic diagram. Here, C _LC = C _A (> C _B ) means that a sufficiently high voltage is applied to the liquid crystal layer 3 and the long axis direction of the liquid crystal molecules is oriented in a direction close to the plane normal to the plane of the pixel electrode 10. The capacitance of the liquid crystal layer 3 is shown, and C _LC = C _B means that the applied voltage is sufficiently low and the long axis of the liquid crystal molecules is oriented in a direction close to the direction parallel to the plane of the pixel electrode 10. Shows the capacity of. Therefore, since C _LC changes according to the voltage applied to the liquid crystal layer 3, the level shift dV _D has a maximum value dV _PMAX and a minimum value dV _PMIN as follows, and changes between them. _{dV PMAX = C GS (V GH} -V GL) / (C GS + C B + C ST) ... (3) dV PMIN = C GS (V GH -V GL) / (C GS + C A + C ST) ... (4) Therefore, the liquid crystal cannot be completely AC driven, and the DC component remains to be driven, which has a great influence on the image quality and reliability of the active matrix type liquid crystal panel.

Therefore, in order to reduce the amount of change in the level shift dV _P , a method has been proposed in which a capacitance component (that is, auxiliary capacitance) is provided in parallel with the capacitance of the liquid crystal layer 3. In this case, as shown in the equations (3) and (4), the difference between dV _PMAX and dV _PMIN can be reduced by adding a large auxiliary capacitance C _ST . FIG. 10 is a plan view of one pixel of an active matrix type liquid crystal panel in which a conventional auxiliary capacitor is installed and a wiring portion in the vicinity thereof, and FIG. 11 is a part (AB of FIG. 10) sectional view thereof.

Here, 7 _N is a gate bus line of an arbitrary Nth stage of the gate bus line 7, and 7 _N-1 is a (N-1) th stage gate bus line of a pixel adjacent thereto, 11 Indicates a metal electrode for auxiliary capacitance. The auxiliary capacitance metal electrode 11 is overlapped with the pixel electrode 10 in the region of overlap 13 (hatched portion) with the insulating film 12 interposed therebetween. The overlapping portion 13 is a storage capacitor.

[0010]

[Problems to be solved by the device]

 However, in the conventional active matrix type liquid crystal panel described above, in the structure in which the storage capacitor is not added to the liquid crystal, the application of the DC component due to the change in the level shift amount of the pixel electrode potential causes the image quality deterioration such as flicker and image sticking and the liquid crystal display. There are problems such as deterioration of reliability due to electrochemical deterioration of the material.On the other hand, in the configuration where the auxiliary capacitance is installed by using a new metal electrode and the application of DC component is reduced, a large capacity can be obtained with a limited aperture. However, there is a problem in that the area of the pixel electrode is inevitably reduced when the auxiliary capacitance is installed, the aperture ratio is reduced, and the utilization efficiency of the backlight light is reduced.

It is an object of the present invention to solve the above problems and provide an active matrix type liquid crystal panel having high reliability and good display quality.

[0012]

[Means for Solving the Problems]

 In order to solve the above problems, the present invention provides a gate bus line, a drain bus line that intersects the gate bus line in an insulated state, a switching element arranged at the intersection, and a pixel connected to the switching element. An active matrix including a first substrate having electrodes, an alignment film covering the entire surface, a second substrate having a common electrode and an alignment film covering the entire surface, and liquid crystal arranged between the alignment films In the liquid crystal panel of the liquid crystal panel, an auxiliary capacitance metal electrode that overlaps with a part of the pixel electrode via an insulating film is formed on the first substrate, and an unevenness is formed on the auxiliary capacitance metal electrode and a part of the pixel electrode.

[0013]

[Action]

 According to the present invention, since the active matrix type liquid crystal panel is constructed as described above, due to the unevenness formed on the metal electrode for the auxiliary capacitance and the pixel electrode, the electrode of the capacitor formed by the overlapping portion of those electrodes is formed. The surface area of is increased compared to the case where there is no unevenness. As a result, the capacitance of the capacitor also increases.

[0014]

【Example】

 Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. However, the overall structure of the liquid crystal panel according to the present invention is the same as that of the conventional example described in detail in FIG. FIG. 1 is a cross-sectional view showing a structure of a storage capacitor of a liquid crystal panel according to an embodiment of the present invention.

The auxiliary capacitance metal electrode 11 on the rear glass substrate 2 overlaps with the pixel electrode 10 via the insulating film 12 in the region of overlap 13 (hatched portion). The portion of this overlap 13 is the auxiliary capacitance. The metal electrode 11 for the auxiliary capacitance and the auxiliary capacitance portion of the pixel electrode 10 are uneven. Here, the unevenness formed on the auxiliary capacitance metal electrode 11 and the unevenness formed on the auxiliary capacitance portion of the pixel electrode 10 are at the same position. Further, the metal electrode 11 for auxiliary capacitance is made of Ta, Al or the like. The plan view of one pixel and its vicinity of the active matrix type liquid crystal panel provided with the auxiliary capacitance according to the embodiment of the present invention is the same as the conventional example described in detail with reference to FIG. ..

In the case of the auxiliary capacitance in this embodiment, the area of the metal electrode for the auxiliary capacitance viewed from the opening direction, the distance between both electrodes, and the film quality of the insulating film 12 are different from those of the conventional auxiliary capacitance shown in FIG. Even if they are the same, the surface area of the auxiliary capacitance metal electrode 11 is large, so that the capacitance is large. Hereinafter, this point will be described. FIG. 2 is a plan view of a metal electrode for auxiliary capacitance according to an embodiment of the present invention, and FIG. 3 is a perspective view thereof.

As shown in FIGS. 2 and 3, the metal electrode 11 for auxiliary capacitance in this embodiment has a radius r on a rectangular plane (area ML) having a vertical length M and a horizontal length L. = M / 2N, and a length L of semi-cylindrical (cylindrical) convex portions arranged in a line. In this case, the surface area of the auxiliary capacitance metal electrode 11 is πML / 2, and in the case of the conventional structure, M × L = ML. Since the capacitance is proportional to the surface area, if the shape on the pixel electrode 10 side is also formed in a similar manner so that the concavities and convexities of both electrodes are made uniform and the distance between the electrodes and the film quality of the insulating film are the same, the structure of the present invention The storage capacitance due to is larger than the storage capacitance due to the structure of the conventional example by π / 2 = 1.57 times. As an example, the results of trial calculation of dVp, dVp _MAX , and dVp _MIN using the above-described formulas (1), (3), and (4) are shown below. However, calculation was performed with C _A = 0.323 pF, C _B = 0.148 pF, C _ST = 0.210 pF, C _GS = 0.019 pF, and V _GH −V _GL = 20V. When the auxiliary capacitor C _ST is not added in the conventional example, dVp = 2.275 to 1.11 [V] When the auxiliary capacitor having the structure of the conventional example is added, dVp = 1.00 to 0.688 [V] When an auxiliary capacity is added by the structure of (1) (provided that the auxiliary capacity of 1.57 times is added by the structural example of the present invention), dVp = 0.76 to 0.56 [V].

As is clear from the above trial calculation, in the case of the conventional example (without adding the auxiliary capacitance) or in the case of the present embodiment, the level shift is more than in the case of adding the auxiliary capacitance according to the structure of the conventional example. The absolute value of the amount dVp is also small, and its change range is also small. As described above, in order to simplify the calculation in the present embodiment, the shape of the unevenness is a semi-cylindrical shape, but it goes without saying that the same effect can be obtained with other shapes such as a hemispherical shape and a conical shape.

Needless to say, the area of the electrode surface can be arbitrarily controlled by the number and shape of the irregularities on the surface of the auxiliary capacitance electrode. FIG. 4 is an explanatory diagram of a method of forming irregularities on the surface of the metal electrode for auxiliary capacitance in the embodiment of the present invention. It is composed of the following processes (1) to (4). (1) A material (for example, the same material as the metal electrode for auxiliary capacitance) that will be the nucleus 15 of the convex portion is formed in advance on the surface of the rear glass substrate 2 on the side where the TFT 9 is formed, and then (2) auxiliary By forming the metal electrode 11 for capacitance, it is possible to make unevenness. Further, if (3) the insulating film 12 is formed and (4) the pixel electrode 10 is formed, the same unevenness as the auxiliary capacitance electrode 11 is formed on the pixel electrode surface at the same position.

It should be noted that the present invention is not limited to the above embodiments, and various modifications can be made based on the spirit of the present invention, and these modifications are not excluded from the scope of the present invention.

[0021]

[Effect of the device]

 As described above in detail, the present invention has the following effects. (1) By adopting a structure in which the metal electrode for the auxiliary capacitance and the pixel electrode in the auxiliary capacitance portion are made uneven, even if the area of the auxiliary capacitance seen from the opening direction is the same, the apparent surface area increases, so Larger capacity.

Therefore, it is possible to reduce the level shift amount of the pixel electrode potential which occurs when the TFT is in the cutoff state. Further, it is possible to reduce the change in the level shift amount due to the change in the capacitance of the liquid crystal layer due to the alignment direction of the liquid crystal molecules. Further, the direct current component applied to the liquid crystal layer is reduced, and it is possible to prevent deterioration of image quality such as afterimage and flicker, and to prevent electrochemical deterioration of the liquid crystal material and improve reliability. (2) Since the surface area of the auxiliary capacitance can be apparently increased in the limited opening, a large auxiliary capacitance can be installed without lowering the opening ratio.

Therefore, it is possible to provide a bright liquid crystal panel with high utilization efficiency of backlight light.

[Brief description of drawings]

FIG. 1 is a sectional view of an essential part showing a structure of a storage capacitor of a liquid crystal panel according to an embodiment of the present invention.

FIG. 2 is a plan view of an auxiliary capacitance electrode according to an embodiment of the present invention.

FIG. 3 is a perspective view of an auxiliary capacitance electrode according to an embodiment of the present invention.

FIG. 4 is an explanatory view of a method for forming irregularities on an electrode surface in the embodiment of the present invention.

FIG. 5 is a perspective view of a conventional active matrix type liquid crystal panel.

FIG. 6 shows a conventional active matrix type liquid crystal panel 1.
It is a top view for pixels.

FIG. 7 is a waveform diagram of a drive voltage applied to a TFT in a conventional active matrix type liquid crystal panel.

FIG. 8: 1 of conventional active matrix type liquid crystal panel
It is an equivalent circuit diagram for pixels.

FIG. 9 is a characteristic diagram of applied voltage vs. capacitance of liquid crystal.

FIG. 10 is a plan view of one pixel of an active matrix type liquid crystal panel provided with a conventional auxiliary capacitor and a wiring portion in the vicinity thereof.

FIG. 11 is a partial (AB in FIG. 10) cross-sectional view of an active matrix type liquid crystal panel in which a conventional auxiliary capacitor is installed.

[Explanation of symbols]

 1 Front Glass Substrate 2 Rear Glass Substrate 3 Liquid Crystal Layer 4 Color Filter 5 Common Electrode 6 Alignment Film 7 Gate Bus Line 8 Drain Bus Line 9 Switching Element 10 Pixel Electrode 11 Auxiliary Capacitance Metal Electrode 12 Insulation Film 13 Overlap

Front page continuation (72) Hiroshi Furuya 1-7-12 Toranomon Minato-ku, Tokyo Oki Electric Industry Co., Ltd.

Claims (1)

Claims for utility model registration: 1. A gate bus line, a drain bus line intersecting with the gate bus line in an insulated state from each other, a switching element arranged at the intersection, and a connection to the switching element. A first substrate having a pixel electrode formed thereon, an alignment film covering the entire surface, a second substrate having a common electrode and an alignment film covering the entire surface, and a liquid crystal disposed between the alignment films. In the active matrix type liquid crystal panel, an auxiliary capacitance metal electrode is formed on the first substrate so as to overlap a part of the pixel electrode via an insulating film, and the auxiliary capacitance metal electrode and a part of the pixel electrode are formed. An active matrix type liquid crystal panel characterized by having irregularities on its surface.