JPH09171191A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To vary load capacitance matching with the variation of the driving capability of a TFT, and improve the display quality and yield by disconnecting some of plural auxiliary capacitance from a switching element matching with the characteristics of a switching element. SOLUTION: An auxiliary capacitance 8 which is formed while divided into two has one end connected to the TFT 3 and the other end connected to a scanning line 1. In such a constitution, the TFT 3 of a selected pixel is on state while a gate select pulse is applied. At this time electric variation of a source electrode corresponding to an image signal outputted to a signal line 2 at this time is transmitted to a drain electrode and a liquid crystal capacitance 4 and the auxiliary capacitance 8 divided into two are accumulated with electric charges, so that a liquid crystal layer is driven. When the gate select pulse moves to a next scanning line 1, those TFTs 3 turn off state and the accumulated electric charges are held until the scanning the is selected next.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to, for example, a thin film transistor (Thin Film Transistor).
The present invention relates to a liquid crystal display device such as an active matrix liquid crystal display device using r, TFT) as a switching element.

[0002]

2. Description of the Related Art Liquid crystal display devices have become increasingly colorized, and OA
The market is rapidly expanding, centering on equipment, and in particular, the growth of active matrix type liquid crystal display devices has been great due to the demand for higher definition and larger screen and display quality improvement such as moving image display. An active matrix type liquid crystal display device is capable of driving a liquid crystal by selectively applying an image signal to a display electrode by an active switching element such as a thin film transistor (hereinafter abbreviated as TFT) provided for each pixel, It is intended to obtain an image display having a high contrast ratio, a high-speed response, and no crosstalk.

FIG. 5 is an electrical equivalent circuit diagram of a conventional active matrix type liquid crystal display device. In the figure, 1
Is a plurality of scanning lines which are row selection lines, 2 is a plurality of signal lines which are column selection lines, 3 is a TFT which is a switching element provided at each intersection of the plurality of scanning lines 1 and the plurality of signal lines 2, 4 Is the liquid crystal capacitance of the liquid crystal sandwiched between the display electrode connected to the TFT 3 and the common electrode facing the display electrode, and includes the display electrode capacitance of the display electrode. Reference numeral 5 is an auxiliary capacitor connected to the TFT 3. Reference numeral 6 denotes a row selection control circuit that sequentially applies a gate selection pulse to a plurality of scanning lines 1, and reference numeral 7 denotes one of the scanning lines 1 to which the gate selection pulse is applied in synchronization with the gate selection pulse of the row selection control circuit 6. This is a column drive circuit that outputs image signals for lines to a plurality of signal lines 2 and drives the source of the TFT 3 of each pixel.

In the liquid crystal display device having such a configuration, the TFT 3 of the selected pixel is in the conductive state during the time when the gate selection pulse is applied, and is output to the signal line 2 at that time. An electric change of the source electrode according to the image signal is transmitted to the drain electrode, and charges are accumulated in the liquid crystal capacitor 4 and the auxiliary capacitor 5,
The liquid crystal layer is driven. That is, the liquid crystal capacitance 4 and the auxiliary capacitance 5
Is the load capacity to be driven by the TFT 3. When the gate selection pulse moves to the next scanning line 1, the TFT 3 for one line becomes non-conductive, and the accumulated charge is
It will be held until the next selection.

Here, in an ideal operation state, the potential of the drain electrode settles to the same potential as the source electrode to which the image signal is applied, but in reality, the driving capability of the TFT 3 and each load capacitance value are set. Due to the variation, the potential of the drain electrode may not reach the potential of the image signal within the predetermined selection time. Pixels having a large uncharged potential as described above are defective in an electrical operation test or a display test. Generally, the quality is determined by the following two-step inspection process. The first step is an electrical operation test that is performed after the formation of the pixel area on the glass substrate is completed, and the second step is to press the substrate and the counter substrate that have passed the electrical operation test under pressure to inject liquid crystal. It is a display test carried out in the state of the panel. After each of these tests, a defect that may be repaired may be repaired.

Such variations in performance of the TFT 3 and variations in load capacitance are due to the following manufacturing factors. A TFT array substrate of a TFT active matrix type liquid crystal display device is often manufactured by a microfabrication technique by repeating a film forming process and a photolithography and etching process as described in comparison with a semiconductor wafer process. . Since the deposition of silicon nitride film, oxide film, amorphous silicon film, etc. on a large glass substrate may cause variations within the substrate surface,
As a result, the film thickness of various thin film layers may differ depending on the substrate position. Further, in the alignment between the respective patterns in the photolithography process, a shift often occurs due to a mask alignment shift or a deformation of the glass substrate during the process. Particularly when a large panel is divided and exposed using a reticle, the mask alignment deviation amount may differ between the divided exposure areas.

[0007]

Since the conventional liquid crystal display device is constructed as described above, the following problems may occur. In order to form a large number of pixels on a relatively large area glass substrate, the TFT characteristics of each pixel may vary due to variations in the glass substrate surface during mask alignment in the photolithography process, variations in the film thickness within the substrate during film formation, etc. Variation occurs. Therefore, even if the pixels are electrically driven under the same condition, the driving state of the liquid crystal is different,
The result is a different display state. For example, in the photoengraving process, when exposing the inside of the screen using a reticle,
If there is a difference in the amount of mask misalignment for each of the divided exposure regions, uniform display within the screen cannot be obtained, and the boundary between the divided regions is visually recognized, resulting in display failure. This is because the amount of mask misalignment differs for each divided region, and the
This is because there is a difference in the characteristics of T (especially the driving ability during dynamic operation), and the driving conditions of the liquid crystal are not uniform.

In order to eliminate such variations in the photoengraving process, it is conceivable to carry out collective exposure of the pixel area, but division exposure is performed in terms of resolution (high definition), compatibility with large screens, mask prices, etc. There is a more unfavorable situation. Even if ideal planar processing such as photoengraving or etching is performed, if the film formation is not uniform, the TFT characteristics and various capacitance values will vary depending on the position of the glass substrate. This tends to increase the size of the glass substrate used in order to improve productivity, and is also a major obstacle to realizing a large screen display device. The present invention has been made in order to solve the above problems, and an object of the present invention is to obtain a liquid crystal display device capable of improving display quality and yield by making a load capacitance variable in accordance with a change in driving ability of a TFT. The first purpose. A second object is to obtain a liquid crystal display device in which the load capacity can be varied according to the load capacity value driven by the TFT, and the display quality and the yield can be improved.

[0009]

In a liquid crystal display device according to the present invention, a plurality of scanning lines arranged to intersect and a display electrode connected to a switching element arranged at each intersection of a plurality of signal lines. A liquid crystal sandwiched between a common electrode arranged to face the display electrode and a plurality of auxiliary capacitors each having one end connected to a switching element,
A part of the plurality of auxiliary capacitors is separated from the switching element according to the characteristics of the switching element. Also, it is sandwiched between a display electrode connected to a switching element arranged at each intersection of a plurality of scanning lines and a plurality of signal lines arranged to intersect with each other, and a common electrode arranged to face the display electrode. And a plurality of auxiliary capacitors each of which has one end connected to the switching element, and a part of the plurality of auxiliary capacitors is switched depending on the load capacity value including the liquid crystal and the plurality of auxiliary capacitors driven by the switching element. It is separated from the element. Further, the other ends of the plurality of auxiliary capacitors each having one end connected to the switching element are connected to a scanning line in the vicinity. Further, the other ends of the plurality of auxiliary capacitors each having one end connected to the switching element are connected to a common line other than the scanning line.

Further, the other ends of the plurality of auxiliary capacitors each having one end connected to the switching element are grouped for each area, and the other ends of the auxiliary capacitors corresponding to the auxiliary capacitors of the other switching elements arranged in the area are collected. In addition to being connected to the other end, it is also connected to a scanning line in the vicinity. Also,
The other ends of the plurality of auxiliary capacitors each having one end connected to the switching element are grouped for each region, and the other end of the auxiliary capacitor corresponding to each of the plurality of auxiliary capacitors of the other switching devices arranged in the region. In addition to being connected, they are connected to common wirings other than the scanning lines. In addition, the region is a region which is separately exposed in the photolithography process in the manufacturing process. Further, a part of the plurality of auxiliary capacitors connected to one of the switching elements in the specific region corresponds to the part of the plurality of auxiliary capacitors of the other switching elements arranged in the region. It is separated from the switching element together with the auxiliary capacitance.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiment 1 FIG. 1 is an electrical equivalent circuit diagram of a liquid crystal display device according to a first embodiment of the present invention. In the figure,
1 to 4, 6 and 7 are the same as the conventional device, and the description thereof will be omitted. Reference numeral 8 denotes an auxiliary capacitor formed by dividing it into two pieces, one end of which is connected to the TFT 3 and the other end of which is connected to the preceding scanning line 1. Embodiment 1 is
The difference from the conventional device is that a plurality of auxiliary capacitors 8 are formed by being divided into two in this case, as shown by being surrounded by a broken line.

In the liquid crystal display device having such a configuration, the TFT 3 of the selected pixel is in a conductive state during the time when the gate selection pulse is applied, and the image output to the signal line 2 at that time. The electric change of the source electrode according to the signal is transmitted to the drain electrode, and charges are accumulated in the liquid crystal capacitor 4 and the auxiliary capacitor 8 divided into two, whereby the liquid crystal layer is driven. Gate selection pulse
When moving to the next scanning line 1, these TFTs 3 become non-conductive, and the accumulated charges are retained for the time until the next selection.

In practice, the potential of the drain electrode may not reach the potential of the image signal within the predetermined selection time due to variations in the driving capability of the TFT 3 and the load capacitance values. Specifically, a pixel having a TFT 3 in which the driving capability fluctuates to a lower side than a design value due to film formation variation in manufacturing and in-plane variation in fine processing due to mask alignment deviation in a photolithography process. Department or
Even if the driving capability of the TFT3 is relatively uniform, the TFT3
Conventionally, a pixel having a bad balance between the TFT drive capability and the load capacitance and having a large uncharged potential, such as a pixel portion in which the value of the load capacitance connected to is larger, has been a defect in the past.

However, in the first embodiment, in the first step of the inspection process, it is possible to repair the following defects, which were not possible conventionally, by an electric operation test after the formation of the pixel region is completed. That is, when the presence or absence of a pixel whose charge capacity is insufficiently charged and the position thereof are detected by an electrical operation test, one of the divided auxiliary capacitors 8 of the pixel is
For example, a laser can be used to electrically disconnect from the drain electrode of the TFT 3. As a result, the load capacitance on the TFT 3 is relatively reduced, the drain electrode can be charged to a potential corresponding to the image signal applied to the source electrode, and the balance between the driving capability of the TFT 3 and the load capacitance is improved. . Conventionally, it is possible to normally operate a pixel region that is defective as a point defect or a pixel region that is defective as divided display unevenness, and it is possible to relieve a pixel that has been determined to be defective as a defect. This remedy can be implemented even in the display test in the second stage of the inspection process if it is clear that the defective cause of the display defective portion is insufficient charging of the TFT 3. In the first embodiment, the case where the auxiliary capacitor 8 is divided into two has been described, but the same effect can be obtained by dividing the auxiliary capacitor 8 into three or more, and further highly accurate repair can be realized.

Embodiment 2 2 is an electrical equivalent circuit diagram of a liquid crystal display device according to a second embodiment of the present invention.
In the first embodiment, the case where the auxiliary capacitance 8 can be separated for each pixel has been shown, but in the second embodiment, the auxiliary capacitance 8 of each pixel can be separated collectively for each specific region. In addition, one of the separated auxiliary capacitors 8 is collectively connected for each specific region. How to divide into regions
If it is performed so as to correspond to each divided shot of the divided exposure, it becomes possible to repair and remedy what was conventionally defective as divided display unevenness.

Embodiment 3 3 is an electrically equivalent circuit diagram of a liquid crystal display device according to a third embodiment of the present invention.
In the first embodiment, the case where the other end of the auxiliary capacitance 8 connected to the drain electrode of the TFT 3 of each pixel is connected to the preceding scanning line 1 has been described, but in the third embodiment, it corresponds. The case where the other end of the auxiliary capacitance 8 is individually connected to a common line other than the scanning line 1 is shown. For the effect,
This is the same as in the first embodiment.

Embodiment 4 4 is an electrical equivalent circuit diagram of a liquid crystal display device according to a fourth embodiment of the present invention.
In the second embodiment, the case where the other end of the auxiliary capacitor 8 connected to the drain electrode of the TFT 3 of each pixel is connected to the scanning line 1 in the preceding stage has been described, but in the fourth embodiment, it corresponds. The case where the other end of the auxiliary capacitor 8 is collectively connected to the common wiring which is not the scanning line 1 is shown, and it has the same effect as that of the second embodiment.

[Brief description of the drawings]

FIG. 1 is an electrical equivalent circuit diagram of a liquid crystal display device according to a first embodiment of the present invention.

FIG. 2 is an electrical equivalent circuit diagram of a liquid crystal display device according to a second embodiment of the present invention.

FIG. 3 is an electrical equivalent circuit diagram of a liquid crystal display device according to a third embodiment of the present invention.

FIG. 4 is an electrical equivalent circuit diagram of a liquid crystal display device according to a fourth embodiment of the present invention.

FIG. 5 is an electrical equivalent circuit diagram of a conventional active matrix type liquid crystal display device.

[Explanation of symbols]

1 scanning line, 2 signal line, 3 TFT, 4 liquid crystal capacitance,
8 auxiliary capacity

Claims (8)

[Claims] 1. A plurality of scanning lines, a plurality of signal lines arranged to intersect with the plurality of scanning lines, a switching element arranged at each intersection of the scanning line and the signal line, and connected to the switching element. A liquid crystal sandwiched between a display electrode and a common electrode arranged to face the display electrode, a plurality of auxiliary capacitors each having one end connected to the switching element, and the plurality of storage capacitors according to the characteristics of the switching element. A liquid crystal display device, characterized in that a part of the auxiliary capacitance of is separated from the switching element. 2. A plurality of scanning lines, a plurality of signal lines arranged so as to intersect with the plurality of scanning lines, a switching element arranged at each intersection of the scanning line and the signal line, and connected to the switching element. A liquid crystal sandwiched between a display electrode and a common electrode arranged to face the display electrode, a plurality of auxiliary capacitors each having one end connected to the switching element, and a liquid crystal driven by the switching element and a plurality of liquid crystals. A liquid crystal display device, wherein a part of the plurality of auxiliary capacitors is separated from a switching element according to a load capacitance value including the auxiliary capacitor. 3. The liquid crystal display device according to claim 1, wherein the other ends of the plurality of auxiliary capacitors each having one end connected to the switching element are connected to a scanning line in the vicinity thereof. 4. The liquid crystal display according to claim 1, wherein the other ends of the plurality of auxiliary capacitors each having one end connected to the switching element are connected to a common line other than the scanning line. apparatus. 5. The other ends of the plurality of auxiliary capacitors each having one end connected to the switching element are connected to the other ends of the auxiliary capacitors corresponding to each of the auxiliary capacitors of the other switching elements arranged in the region collectively. The liquid crystal display device according to claim 1 or 2, wherein the liquid crystal display device is connected to a scanning line in the vicinity in addition to being connected to the end. 6. An auxiliary capacitance corresponding to each of a plurality of auxiliary capacitances of other switching elements arranged in the region, the other end of the plurality of auxiliary capacitances each having one end connected to a switching element. 3. The liquid crystal display device according to claim 1, wherein the liquid crystal display device is connected to the other end of the liquid crystal display device and is connected to a common wiring other than the scanning line. 7. The region is a region which is separately exposed in a photoengraving process in a manufacturing process.
Alternatively, the liquid crystal display device according to claim 6. 8. A part of a plurality of auxiliary capacitors connected to one of the switching elements in a specific region, and a part of the plurality of auxiliary capacitors of another switching device arranged in the region. 8. The liquid crystal display device according to claim 5, wherein the liquid crystal display device is separated from the switching element together with the auxiliary capacitance corresponding to.