JP2001005025A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To decrease the probability of short circuits between electrodes which constitute auxiliary capacitance elements and to improve the production yield of a liquid crystal display unit by determining the capacitance and properly distributing according to the capacitance of the auxiliary capacitor element required for each pixel. SOLUTION: Auxiliary capacitor elements 32 are formed by overlapping capacitance lines CS (CS1 to CSn) through a dielectric material on pixel electrodes 13 arranged in a matrix. The electrode areas of auxiliary capacitance elements 32 at least on both ends in a row of the auxiliary capacitance elements 32 are changed to produce different capacitance so as to decrease the probability of short circuits between electrodes due to defects in the dielectric insulating film and to improve the yield.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an active matrix type liquid crystal display device using a thin film transistor as a switching element, and more particularly to a probability of occurrence of a defect due to a short between capacitor electrodes when an auxiliary capacitance element is formed. The present invention relates to a liquid crystal display device in which the yield of a liquid crystal display unit is improved by lowering the ratio.

[0002]

2. Description of the Related Art Conventionally, an active matrix type liquid crystal display device using a thin film transistor (TFT) as a switching element has a gate which turns on a TFT in a scanning line.
By sequentially supplying the pulse in the row direction, the TFT
Are sequentially turned on in response to the gate pulse, and a display signal such as a video signal synchronized with the gate pulse is sequentially supplied to the pixel electrode from the signal line, so that a predetermined charge is charged to the capacitive element. Reserved during the credit period. By sequentially performing scanning in this manner, each liquid crystal display element is driven to reproduce an image.

FIG. 3 is a circuit diagram showing a conventional liquid crystal display device.
1 to Xn extend in the row direction, and a plurality of signal lines Y1 to Yn from the signal line driving circuit 102 extend in the column direction so as to intersect the scanning line X. At the intersection of the scanning line X and the signal line Y, a thin film transistor (TF
T) 103 is arranged, the gate of the TFT 103 is connected to the scanning line X, and one end of the drain D / source S channel, for example, the drain D is connected to the signal line Y.
The other end of the drain D / source S channel of the TFT 103, for example, the source S, is connected to the liquid crystal display element 104 and to one end of a capacitive element 105. It is connected to the capacitance lines CS1 to CSn of the line drive circuit 101.

Accordingly, the gate pulse from the scanning line driving circuit 101 is sequentially supplied to the scanning lines X in a line-sequential driving manner from X1 to Xn, and the TFTs 103 on one scanning line X are simultaneously turned on. The signal line driving circuit 1 is synchronized with this scanning.
02 to the TFT via the signal lines Y1 to Yn.
To the capacitor 105 connected to the drain D / source S channel of the TFT 103.
The signal charge is accumulated through the drain D / source S channel of the TFT 103. By maintaining the signal charge during the scanning period of the next frame, the liquid crystal display elements 104 of all pixels connected to the scanning line X are continuously excited to display an image. I do. The other end of the capacitor 105 is driven by an earth or an opposite-phase gate pulse via the capacitor line CS.

[0005] In theory, when the internal resistance of the TFT 103 when turned off is sufficiently large, or when the electric capacity or specific resistance of the liquid crystal display element 104 is sufficiently large, a capacitive element for accumulating signal charges is required. Although it is possible to omit 105, in order to maintain good display quality, the gate pulse is turned off from on, and charges are accumulated so that the pixel potential does not change until the next turn on. There is a need.

In order to prevent the pixel potential from dropping below a predetermined potential, the load capacitance which is the capacitance of the liquid crystal display element 104 and the off-resistance of the TFT 103 and the resistance of the liquid crystal layer of the liquid crystal display element 104 are determined. You need to increase the constant. Normally, in order to supplement the capacitance of the liquid crystal layer of the liquid crystal display element 104, a pixel electrode is provided to constitute the capacitance element 105, and further, an auxiliary capacitance element which constitutes a part of the capacitance element 105 is added. Is generally configured to form a capacitor having a predetermined capacitance value.

FIG. 4 is a configuration diagram showing an example of a case where the capacitance element 105 is formed by adding such an auxiliary capacitance element. That is, components having the same functions as the components of the liquid crystal display device described with reference to FIG.
1 includes a plurality of TFTs 103 to which gates G are connected.
Are arranged in the column direction. The drain D of the TFT 103 and the drain D forming one end of the source S channel
Is connected to the signal line Y1, and the source S constituting the other end of the drain D / source S channel is provided with a pixel electrode 111.
Is connected.

The individual components configured as described above are arranged in a matrix in the row direction and the column direction to form the display pixel array 112. Further, the pixel electrode 111
Above, a capacitor line CS is arranged and connected over the pixel electrode 111 in the row direction in parallel with the scanning line X via a dielectric (not shown), and is connected to the liquid crystal display element 105 on the same scanning line.
An auxiliary capacitance element 113 composed of a pixel electrode 111 and an electrode of a capacitance line CS, which are opposed to each other with a dielectric interposed therebetween, is added.

The auxiliary capacitance element 113 is formed by two conductive films, that is, the pixel electrode 11 during the manufacturing process of the liquid crystal display device.
1 and the capacitance line CS, an insulating film is interposed between them. By adding the auxiliary capacitance element 113, the time constant can be increased. That is, the pixel electrode 111 and the capacitance line CS
An intervening short may occur. Moreover, in order to increase the capacitance value of the auxiliary capacitance element 113, it is necessary to increase its area. Therefore, enlarging this area results in an increase in the probability of a short between the electrodes of the auxiliary capacitance element 113, As a result, the yield of the liquid crystal display unit may be reduced. Therefore, it is desirable to make the auxiliary capacitance element 113 as small as possible.

FIG. 5 shows signal potential waveforms of pixels on the same signal line Y connected to the upper scanning line X1 of the display screen and pixels connected to the lower scanning line Xn of the display screen. FIG.

FIG. 5A shows the gate pulse A supplied to the scanning line X1 from the scanning line driving circuit 101 at the top of the screen, and FIG. 5B shows the gate pulse A supplied to the scanning line Xn at the bottom of the screen. FIG. On the other hand, the signal line Y1
The display signal C shown in FIG. 5C is supplied, and the signal potential center of the display signal C is SC indicated by a broken line in the figure. As a result, the pixel potential shown in FIG. 5D is accumulated in the capacitor 105 of the TFT 103 connected to the scanning line X1, and the pixel potential shown in FIG. Will be accumulated. In the pixel at the top of the screen, during the holding period of the pixel potential, the pixel potential and the signal line Y
Since one potential is substantially the same, that is, the potential difference between the drain D and the source S of the TFT 103 is small, the leakage of the TFT 103 is small.

On the other hand, in the pixel at the lower portion of the screen, the difference between the pixel potential and the potential of the signal line Y1 increases during the holding period of the pixel potential.
The potential difference between the electrodes S increases, and the leakage in the TFT 103 increases. For this reason, in order to maintain the pixel potential at a predetermined value, the capacitance value of the auxiliary capacitance element 113 had to be increased.

[0013]

In the conventional liquid crystal display device, in order to maintain the display quality of the entire screen, the capacitance of the pixel that requires the largest capacitance value of the capacitance element, that is, the capacitance of the pixel located at the bottom of the screen. The capacitance value of the entire display screen is uniquely set according to the capacitance value of the element. And, since the auxiliary capacitance elements of all the pixels in the screen are uniformly and simultaneously formed by the capacitance lines, the pixels located in the screen, especially in the upper part of the screen,
A configuration in which an auxiliary capacitance element having a capacitance value larger than necessary is added. In other words, an excessively large inter-electrode area is used for forming the auxiliary capacitance element more than necessary, which increases the probability of an inter-electrode short, which lowers the yield of the liquid crystal display unit. .

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems, and has the following features.
An object of the present invention is to provide a liquid crystal display device in which the yield of the liquid crystal display unit is improved by lowering the probability of a short between electrodes.

[0015]

According to the present invention, there are provided a plurality of signal lines extending in a column direction on an insulating substrate and supplying a display signal;
A plurality of scanning lines which extend in the row direction on the insulating substrate so as to intersect with the signal lines and supply gate pulses; and a plurality of scanning lines which are arranged at intersections of the respective signal lines and the scanning lines, and A thin film transistor having one end connected to the signal line and one gate connected to the scanning line; and a liquid crystal display element having a pixel electrode connected to the other end of the drain / source channel of the thin film transistor; A liquid crystal display device comprising a capacitance element connected to the liquid crystal display element, wherein the capacitance value of the capacitance element is different at least at both ends along the column direction. It is.

The capacitive element includes an auxiliary capacitive element composed of a pixel electrode and a capacitive line disposed on the pixel electrode via an insulating film, and the capacitive line is connected to one end of the pixel electrode in the column direction. It is characterized by being formed relatively wide above.

Further, the pixel electrode has a structure in which the area of the pixel electrode arranged on the other end in the column direction is narrower correspondingly to the pixel electrode on one end on which the capacitance line is formed wider. And

Still further, in the liquid crystal display device, the brightness at the other end is equivalently reduced as compared with the one end in the column direction, so that the brightness can be viewed substantially constant over the entire screen. Features.

[0019]

Next, an embodiment of the present invention will be described. FIG. 1 is a configuration diagram schematically showing an overall configuration when a liquid crystal display device of the present invention is applied to a transmission type color display. The liquid crystal display device of the present invention will be described with reference to FIG.
On top, a plurality of thin film transistors (TF
T) 12 and a transparent pixel electrode 13 paired with each of the TFTs 12 are arranged.
A liquid crystal alignment film 14 is provided on the FT 12.

Similarly, the alignment film 15 and the outside of the alignment film 15 are provided so as to face the first glass substrate 11.
A second glass substrate 18 having a three primary color RGB color filter 17 having a transparent electrode 16 integrated over the entire surface is disposed. Then, a liquid crystal layer 19 is sealed between the first and second glass substrates 11 and 18. The liquid crystal layer 19 is sealed by sealing between the glass substrates 11 and 18 and a sealing material 20.
The thickness of the liquid crystal layer 19 is regulated by a spacer 21 interposed between the first and second glass substrates 11 and 18.

The liquid crystal layer 1 of each of these glass substrates 11 and 18
9 are provided on the outer side opposite to the retardation plates or polarizing plates 22, 23.
Is attached, and the polarizing plate 22 on the first glass substrate 11 side is further attached.
A backlight 24 is arranged on the outside, and a drive circuit 25 for driving the TFT 12 is provided on the first glass substrate 11 to constitute a transmissive color display liquid crystal display device.

In the case of a reflection type liquid crystal display device,
Instead of the backlight 24, the polarizing plate 22 may be made of a light-reflecting film. In the case of monochrome display instead of color display, the color filter 17 may be omitted to cope with the display.

With such a configuration, the driving circuit 25
The TFT 12 performs a switching operation in response to a drive signal from the TFT, and charges based on a video signal are accumulated in a capacitor formed between the pixel electrode 13 and the transparent electrode 16 to excite the liquid crystal layer 19. At this time, the light projected from the backlight 24 is transmitted to the liquid crystal layer 19 via the polarizing plate 22, the first glass substrate 11, and the liquid crystal light distribution film 14. The light that has passed through the liquid crystal layer 19 reaches the second glass substrate 18 through the liquid crystal light distribution film 15, the transparent electrode 16, and the color filter 17, and is further transmitted through the polarizing plate 23 to the outside. Is to display a predetermined color image.

FIG. 2 is a simplified diagram showing a configuration for forming an auxiliary capacitance element relating to the liquid crystal display device of the present invention. 2, elements having the same functions as the elements used in the description of FIG. 1 will be described using the same reference numerals. A plurality of scanning lines X1 to Xn extend in the row direction on the first glass substrate 11. A plurality of signal lines Y1 to Yn extend in the column direction so as to intersect with the scanning line X. Each intersection of the scanning line X and the signal line Y has a T
FT12 is arranged. The gate G of this TFT 12
Is connected to the scanning line X, and the drain D
The drain D, which is one end of the source S channel, is connected to the signal line Y, and the source S, which is the other end of the drain D / source S channel, is an oxide film (ITO) made of, for example, indium and tin. ) Is connected to the pixel electrode 13 formed of a transparent conductive film.

Further, on the pixel electrode 13, a capacitance line CS formed of the same material as the pixel electrode 13 is formed via a dielectric (not shown) formed of, for example, a silicon oxide (SiOx) film. , Each pixel electrode 1 in the row direction parallel to the scanning line X
3 are added to the liquid crystal display element 31 including the liquid crystal layer 19 and the transparent electrode 16 on the same scanning line X as the auxiliary capacitance element 32. Therefore, the auxiliary capacitance element 32 is formed between the pixel electrode 13 and the capacitance line CS which is arranged to face the pixel electrode 13 via the dielectric.

Similarly, a plurality of TFTs 12 to which the gates G are connected are also arranged in the column direction on the scanning line Xn located at the bottom of the screen of the liquid crystal display device. On the pixel electrode 13 on which the line CS is arranged, the electrode width of the capacitance line CSn part forming the capacitance is the capacitance line CS1 located on the uppermost part, and in the capacitance line CS1 part located on the pixel electrode 13, It is formed so as to be larger by the width α than the same corresponding electrode width. As a result, the area of the electrode is enlarged, and the capacitance formed by the lowermost capacitance line CSn is larger by the width α than the auxiliary capacitance value formed by the uppermost capacitance line CS1. are doing.

In other words, the pixel electrodes 13 move from the lower part of the display screen toward the pixels located at the upper part of the screen.
The electrode width α of the upper capacitance line CS is gradually reduced, and the area of the overlapping portion between the pixel electrode 13 and the capacitance line CS forming the auxiliary capacitance electrode is reduced, whereby the capacitance of the auxiliary capacitance element 32 is reduced. The value is configured to decrease sequentially from the bottom to the top.

With this configuration, the time constant is increased by increasing the overall value of the capacitance at the lower portion of the display screen, which tends to increase the difference between the pixel potential and the signal line potential as compared to the upper portion of the display screen. And the signal charge stored in the auxiliary capacitance element 32 and the like is transferred until the next frame scan.
By reliably holding the potential so as not to change, the potential difference between the drain D and the source S of the TFT 12 is reduced, and the leak of the TFT 12 is reduced.
The configuration is such that a predetermined display quality can be ensured.

In the above description, the case where the capacitance line CS is formed of a transparent conductive film made of ITO as an electrode constituting the auxiliary capacitance element 32 has been described.
It is also possible to use an opaque conductive film made of an alloy of molybdenum (Mo) and tungsten (Ta) and used as an electrode film of the gate G of No. 2 in this case.
The capacitance line CS constituting the auxiliary capacitance element 32 and the pixel electrode 13
In the overlapping portion with the above, the light is not transmitted.

For this reason, there is a possibility that the area of the aperture through which light is transmitted becomes larger in the upper part of the screen than in the lowermost part of the screen, and the luminance of the screen may change. In order to prevent unbalance, the capacitance line CS goes from the bottom of the screen to the top of the screen.
The area of the pixel electrode 13 is sequentially reduced in accordance with the decrease in the area of the pixel electrode 13 with respect to the pixel electrode 13, and the lowermost pixel electrode 1
3 is formed to be shorter by a length α corresponding to the size of the electrode width α of the capacitance line CSn, which is larger on the capacitor line 3, so that the aperture ratio of all pixels in the screen is not changed, thereby preventing luminance unevenness. can do.

As means for preventing the luminance unevenness, contrary to the above, without changing the electrode area of the capacitance line CS,
Corresponding to an increase in the aperture ratio from the lower part of the screen toward the upper part of the screen, the light transmittance of the polarizing plates 22 and 23 is reduced at the upper part of the screen as compared with the lower part of the screen, so that the same aperture ratio is obtained. Can be secured.

Alternatively, the brightness of the backlight 24 can be reduced from the lower part of the screen to the upper part of the screen to prevent the unevenness of the luminance. It is only necessary to configure so as to be visually recognizable, and other methods can be adopted.

Further, the electrode area of the capacitance line CS located on the pixel electrode 13 has been described as being continuously reduced from the lower pixel of the screen to the upper pixel of the screen, but a substantially predetermined potential can be secured. A case in which a plurality of pixels in the column direction are collectively configured as a unit, and the electrode widths of the capacitance lines CS located on the pixel electrodes 13 in this configuration are configured to be all the same width, and viewed in the entire row direction. In addition, it is also possible to adopt a configuration in which the change is performed in a stepwise manner. In this case, although the quality is slightly degraded as compared with the case of continuously decreasing,
This is advantageous in terms of mask design and manufacturing.

It should be noted that the present invention is not limited to these embodiments, and various improvements and modifications can be made. It is apparent that those which do not depart from the gist of the present invention are included in the scope of the present invention. It is.

[0035]

According to the present invention, the capacitance value of the liquid crystal display element in the screen is reduced from one end to the other end in the screen row direction, so that the capacitance between the electrodes due to the defect of the insulating film constituting the auxiliary capacitance element is reduced. It is possible to provide a liquid crystal display device capable of improving the yield of liquid crystal display units by lowering the probability of short-based failure.

Also, even when the capacitance line is formed of an opaque conductive film, the structure is devised in various ways, so that the aperture ratio or the brightness of the pixels in the screen is kept constant, and the brightness of the screen is kept constant. , A liquid crystal display device in which the constant can be visually recognized.

[Brief description of the drawings]

FIG. 1 is a sectional view schematically showing an embodiment of a liquid crystal display device according to the present invention.

FIG. 2 is a configuration diagram showing a liquid crystal display pixel array constituting the liquid crystal display device of the present invention.

FIG. 3 is a circuit configuration diagram showing a circuit configuration of a conventional liquid crystal display device.

FIG. 4 is a configuration diagram showing a liquid crystal display pixel array of a conventional liquid crystal display device.

FIG. 5 is a waveform chart showing potential waveforms at various parts of a liquid crystal display element constituting a conventional liquid crystal display device.

[Explanation of symbols]

 11: glass substrate (insulating substrate) 12: thin film transistor (TFT) 13: pixel electrode 31: liquid crystal display element 32: auxiliary capacitance element X: scanning line Y: signal line CS: capacitance line

Claims (4)

[Claims] 1. A plurality of signal lines extending in a column direction on an insulating substrate and supplying a display signal, and supplying a gate pulse extending in a row direction on the insulating substrate so as to intersect with the signal lines. A plurality of scanning lines, a thin film transistor disposed at an intersection of each of the signal lines and the scanning lines, one end of a drain / source channel connected to the signal line, and a gate connected to the scanning line; The drain of this thin film transistor
In a liquid crystal display device including a liquid crystal display element having a pixel electrode connected to the other end of the source channel, and a capacitor connected to the liquid crystal display element, the capacitance value of the capacitance element is set at least in a column. A liquid crystal display device characterized in that both ends along the direction are different. 2. The capacitive element includes an auxiliary capacitive element composed of a pixel electrode and a capacitive line disposed on the pixel electrode via an insulating film, and the capacitive line is connected to one end of the pixel electrode in a column direction. 2. The liquid crystal display device according to claim 1, wherein said liquid crystal display device is formed relatively wide. 3. The pixel electrode according to claim 1, wherein an area of the pixel electrode arranged at the other end in the column direction is made smaller correspondingly to one end of the pixel electrode on which the capacitance line is formed wider. 3. The liquid crystal display device according to claim 1, wherein: 4. The liquid crystal display device according to claim 1, wherein the brightness at the other end is reduced equivalently to the one end in the column direction so that the brightness is substantially constant over the entire screen. 4. The liquid crystal display device according to claim 1, wherein: