JP3029319B2 - Liquid crystal display - Google Patents

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 thin film transistors as switching elements.

[0002]

2. Description of the Related Art Conventionally, LCD (Liquid Cr)
2. Description of the Related Art A liquid crystal display device adopting a simple matrix system as a display system of the Yeast Display is widely used. However, when the number of scanning lines is increased in order to increase the definition of the screen, there has been a problem that the contrast is reduced due to a decrease in the effective voltage applied to the liquid crystal and the visual range is narrowed.

In recent years, as a display method, a screen is divided into tens of thousands to hundreds of thousands, and each pixel has a nonlinear element,
For example, an active matrix method in which a thin film transistor (TFT) is provided and the operation of each pixel is controlled using its switching characteristics does not cause a decrease in contrast, visual range, or response speed even when the number of scanning lines is increased. It is attracting attention. FIG. 12 is a schematic circuit diagram of a conventional TFT-LCD using the active matrix method.

This LCD has a configuration in which basic pixels 1 each including a TFT 3, an electrode pixel 5, and an auxiliary capacitor 7 are arranged in a matrix. The gate, source, and drain of the TFT 3 are a scanning line G _n , a signal line S _m , and a pixel electrode 5, respectively.
, And the storage capacitor 7 is connected to the pixel electrode 3.

In the LCD using the basic pixel 1 configured as described above, the scanning signal applied to the scanning line _Gn causes the T.
With FT3 ON / OFF is selected, the liquid crystal by applying a pulse signal which is amplitude-modulated by a video signal applied to the scanning signal to the synchronization signal lines S _m, a pixel electrode 5 through the drain of the TFT3 (Not shown) orientation is controlled.

However, since the structure and the manufacturing process are complicated, there is a problem that when the size of the screen is increased, the yield is sharply reduced. For example, 64
To realize a color display of 0 × 480 pixels, 640 ×
Since 3 × 480 = 920,000 pixels are required, it is necessary to eliminate defects such as disconnection and short-circuiting over all 920,000 TFTs, 1920 signal lines, and 480 scanning lines.

[0007] Such defects cause display defects on the screen. Display defects include line defects and point defects.
Point defects are more likely to occur. There are several causes of point defects, one of which is a TFT defect. TFT
As a countermeasure against a point defect due to the defect of the above, an active matrix system of a plural TFT system has been proposed.

FIG. 13 shows a conventional T using such a method.
A schematic circuit diagram of the FT-LCD is shown. This differs from that described above in that two TFTs 3a and 3b are provided for each basic pixel 1, respectively.

That is, the gate, source and drain of the TFT 3a are connected to the scanning line G _n , signal line S _m and pixel electrode 5, respectively, and the gate, source and drain of the TFT 3b are scanning line, respectively. G _{n + 1} , the signal line S _m , and the pixel electrode 5. When the TFTs 3a and 3b are both normal, the output signal of the TFT 3b is controlled to be supplied to the pixel electrode 5. Therefore, when the TFT 3a is defective, the TFT 3a is connected to the pixel electrode 5 using a laser or the like.
Or LCD repair by disconnecting from the signal line S _m.

When the TFT 3b is defective, TF
The TFT3b in the same manner as T3a disconnected from the pixel electrode 5 or the signal lines S _m perform LCD repair. However, in this case, the signal of the TFT 3a is not a regular signal, but the same signal as the signal of the TFT of the pixel immediately above. For example, in an OA LCD, there is a problem that an image changes. In an LCD for a television or the like, the image does not greatly change even if one pixel is shifted, but the image quality is deteriorated because the defect of the TFT also appears as a point defect.

Furthermore, it is difficult to find a defective TFT from the shape even by using a microscope or the like, so that there is a problem that it is not known which TFT should be repaired. This is because the shape of a defective TFT is often normal.

Therefore, it has been proposed to increase the number of scanning lines or signal lines per pixel in order to send a normal signal to a pixel having a defective TFT. However, in this case, there is a problem that the aperture ratio is reduced due to an increase in the wiring area, and that short-circuiting between adjacent wirings is likely to occur.

[0013]

As described above, in the conventional liquid crystal display device employing the active matrix system, when the screen is enlarged, the number of TFTs becomes very large.
There is a problem that a point defect due to a defect in T easily occurs and image quality is deteriorated. Several solutions have been proposed to solve these problems, but their disadvantages have become more pronounced,
There was nothing to be expected yet.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a liquid crystal display device which can easily find a defective TFT and has few point defects.

[0015]

The gist of the present invention is to provide a plurality of field effect transistors for each pixel and to insert a variable resistor between a signal line and a pixel electrode via one of these field effect transistors. Has been established.

That is, according to the present invention, the orientation of the liquid crystal is
The pixel electrode controlled by
Connected to the pixel electrode and the other source / drain
Lines, and gates connected to scan lines.
Pixels having field effect transistors are arranged in a matrix.
In the liquid crystal display device, the plurality of transistors
Between the signal line and the pixel electrode via any of the
Characterized in that a two-terminal variable resistor is inserted in
You. Further, the present invention controls the orientation of the liquid crystal by an input signal.
The pixel electrode to be controlled and one source / drain
Electrode and the other source / drain is connected to the signal line.
Multiple field-effect transistors whose gates are connected to scan lines.
Pixels having transistors are arranged in a matrix
In the liquid crystal display device, any of the plurality of transistors
3 terminals between the signal line and the pixel electrode via the
Is inserted and the control terminal of the variable resistor is
A means for supplying a constant potential is connected.
You.

[0017]

When the liquid crystal display device is driven in a state where the variable resistor has a low resistance, that is, when all the field transistors in the pixel are electrically connected to the pixel electrode, the defective field effect transistor does not operate normally. Therefore, it is possible to find a pixel having a defective field-effect transistor based on the quality of display and electric response.

Next, when the liquid crystal display device is driven with the variable resistor in a high resistance state, that is, when the electric field transistor connected to the variable resistor and the pixel electrode are electrically disconnected, the liquid crystal display device is connected to the variable resistor. The display and the electrical response are different between the case where the field-effect transistor is defective and the case where the field-effect transistor not connected to the variable resistor is defective. Therefore, it is possible to specify which field-effect transistor is defective.

Since a defective field-effect transistor can be specified in this manner, generation of a point defect can be prevented by separating the field-effect transistor from a pixel electrode or a signal line.

[0020]

Embodiments will be described below with reference to the drawings. FIG. 1 is a schematic circuit diagram of a unit pixel of a liquid crystal display device according to a first embodiment of the present invention.

The unit pixel 1, gate -: it is connected to the scanning line G _n, source - scan, drain each signal line S _m, 2 two TFT3a connected to the pixel electrode 5, and 3b, the pixel electrode 5 Auxiliary capacitance 7 inserted between ground line GND _n
And a variable resistor 9 inserted between the drain of the TFT 3 a and the pixel electrode 5. FIG. 2 is a plan view of an LCD formed using the unit pixels 1 configured as described above, and FIG. 3 is a cross-sectional view taken along line AA 'of FIG. FIG.
The TFT 3a is an inverted stagger type TFT in which a gate electrode 13 is formed below an active layer 17 via a gate insulating film 15 as shown in FIG.

That is, the TFT 3a is provided on a light-transmitting insulating substrate 11 such as a glass substrate, and a gate electrode 13 connected to the scanning line _Gn and a gate electrode provided on the gate electrode 13. a gate insulating film 15, the gate - a gate insulating film 15 active layer 17 made of amorphous silicon provided on a protective layer 19 provided on the active layer 17, connected to the signal line S _n, impurity And a drain electrode 25 connected to the variable resistor 9 via the contact layer 21 to which the active layer 17 is added. Note that TFT3
The configuration of b is the same as that of the TFT 3a.

The variable resistor 9 has basically the same structure as that of the TFT 3a except for the gate electrode.
7 is connected to the pixel electrode 5. Variable resistor 9
The material and the formation process of the active layer 17 are the same as those of the TFT 3a. Further, the resistance of the variable resistor 9 is set to be sufficiently small by the irradiation of the backlight light of normal intensity.

The protective film 2 is formed on the TFT 3 a and the variable resistor 9.
9 have been deposited. On the translucent insulating substrate 11 (matrix array substrate) on which such basic pixels 1 are arranged in a matrix, an alignment film 31, a liquid crystal 33, an alignment film 3
5, a counter electrode 37, a color filter 39, and a black matrix 41 are provided, and are sandwiched between a matrix array substrate and a translucent insulating substrate 43. The liquid crystal 33
Deflecting plates 43 and 45 are provided on the surfaces of the light-transmitting insulating substrates 11 and 41 on the opposite side from the light-transmitting insulating substrates 11 and 41, respectively.

[0025] The scanning lines G _n and the signal line as shown in FIG. 2 S _m, S _{m + 1} and the cross-section 49a, b, the ground line GN
D _n and the signal line S _m, intersections 49c between the S _{m + 1,} the d are left behind material film of the active layer 17, the contact layer 21,
The interlayer short is reduced by over-etching. In the liquid crystal display device configured as described above, a defective TFT is specified as follows.

First, the TFT is driven to make the display of the entire screen black, and the backlight of the liquid crystal display device is adjusted to irradiate the backlight 51 with normal intensity to the LCD.
Then, the display state is examined by a device utilizing visual observation or image recognition to find a defective pixel, that is, a pixel having a defective TFT.

Next, the display state of the defective basic pixel is examined by reducing the intensity of the backlight light. At this time, if the display of the defective basic pixel is improved, the T
If the FT 3a can be identified as defective and the display of the defective basic pixel does not change, the TFT not connected to the variable resistor 9
3b can be specified as defective. The reason why such a defective TFT can be specified is explained as follows.

If the intensity of the backlight 51 is low, the resistance of the variable resistor 9 increases, so that the output level of the TFT 3a decreases regardless of whether the TFT 3a connected to the variable resistor 9 is good or defective. That is, the state is the same as when the pixel electrode 5 is controlled only by the TFT 3b not connected to the variable resistor 9.

As a result, even if the TFT 3a is defective,
Since the pixel electrode 5 is not affected by that, if the TFT 3b is good, the display is good, and if the TFT 3b is bad, the display remains unchanged. Therefore, by reducing the intensity of the backlight 51, the T of the basic pixel 1 is reduced.
Which of the FTs 3a and 3b is defective can be specified.

Next, the LCD is repaired. That is, laser light such as a YAG laser is irradiated from the back surface of the light-transmitting substrate 11 to disconnect the defective TFT from the pixel electrode. For example,
If the TFT 3a connected to the variable resistor 9 is defective,
The drain electrode 25 or the connection electrode 27 may be cut by irradiating a laser beam. At this time, the gates of the TFTs 3a and 3b
Since the gates are connected to the common scanning line _Gn , the problem that the signal of the immediately preceding basic pixel is applied to the pixel electrode 5 does not occur.

Further, the resistance of the variable resistor 9 becomes sufficiently small by the backlight in the normal operation.
Even when b is defective, a signal of a predetermined level can be given to the pixel electrode 5 only with the TFT 3a.

Further, even when the output level of the TFT 3a is lowered, the display of the basic pixel 1 including the TFT 3a does not become white even if the display of the surrounding pixels is black, so there is no practical problem. Was. In this embodiment, the defective TFT is specified by changing the intensity of the backlight light.
Even if the backlight light intensity is kept constant, poor T
FT can be specified.

That is, after illuminating the back light of the translucent substrate 11 with backlight light having such an intensity that the resistance of the variable resistor 9 becomes sufficiently small, the basic pixel 1 having an abnormal display is found.
The CD is turned over, and backlight is irradiated from the translucent substrate 41 side to specify a defective TFT.

The reason why a defective TFT can be specified is that when backlight light is irradiated from the light transmitting substrate 41 side, light to the variable resistor 9 is blocked by the black matrix 39.

Thus, in the liquid crystal display device of the present embodiment, it is easy to detect a defective TFT, so that a point defect can be completely repaired. As a result, it is possible to prevent a deterioration in image quality. And yield is improved.

FIG. 4 is a schematic circuit diagram of a basic pixel of a liquid crystal display according to a second embodiment of the present invention.
Note that portions corresponding to the basic pixels 1 in FIG. 1 are denoted by the same reference numerals as in FIG. 1, and detailed description thereof is omitted. It differs from the first embodiment of the liquid crystal display device of this embodiment, the variable resistor 9 to the TFT3b source - lies in the inserted between the scan and signal lines S _m.

Also in the LCD using the basic pixel 1 configured as described above, the operation of the TFT 3b can be controlled by changing the resistance of the variable resistor 9 by irradiating the backlight, so that it is the same as the first embodiment. Of course, the variable resistor 9 is formed not in the region where the basic pixels are formed but in the wiring portion, so that the ratio of the basic pixels occupying the translucent substrate 11 can be reduced. There is an effect that the performance index is improved.

FIG. 5 is a schematic circuit diagram of a basic pixel of a liquid crystal display according to a third embodiment of the present invention.
Note that portions corresponding to the basic pixels 1 in FIG. 1 are denoted by the same reference numerals as in FIG. 1, and detailed description thereof is omitted.

The difference of the liquid crystal display device of this embodiment from that of the first embodiment is that the gates of the TFTs 3a and 3b are not formed on the scanning line _Gn , but are branched from the scanning line _Gn. That is formed above.

The same effect as that of the first embodiment can be obtained with the LCD having the above-described structure, and the scanning line G _n can be obtained.
Can be determined independently of the TFTs 3a and 3b, so that the resistance of the scanning line _Gn can be easily controlled.

FIG. 6 is a schematic circuit diagram of a basic pixel of a liquid crystal display according to a fourth embodiment of the present invention.
Note that portions corresponding to the basic pixels 1 in FIG. 1 are denoted by the same reference numerals as in FIG. 1, and detailed description thereof is omitted. The liquid crystal display device of this embodiment differs from that of the first embodiment in that the electrode structure 53 is connected in parallel to the variable resistor 9. FIG.
8 is a plan view of an LCD formed using the basic pixels 1 configured as shown in FIG. 6, and FIGS.
It is -B 'sectional drawing and CC' sectional drawing.

The structure of the electrode structure 53 is basically TF
Same as T3a, 3b. The lower electrode 55 is a connecting electrode 2
3 and overlaps the upper electrode 57 in a planar manner. The point of the electrode structure 53 is that the electrode structure is insulated in terms of direct current, but has a structure capable of shorting the electrode building in a later process. Therefore, the electrode structure 5
3 is not limited to the configuration of the present embodiment.

L using the basic pixels thus configured
Irradiating the backlight with CD also makes the variable resistor 9
By changing the resistance of the TFT 3b, the operation of the TFT 3b can be controlled, and the same effect as in the first embodiment can be obtained.

Further, when the TFT 3a is defective, the lower electrode 5 is formed from the rear surface of the light transmitting substrate 11 by using YAG laser light or the like.
5 is partially melted to short-circuit the lower electrode 55 and the upper electrode 57, whereby there is an advantage that a decrease in the driving ability of the TFT 3b can be prevented.

That is, since the variable resistor 9 is connected in series to the TFT 3b, the driving capability of the TFT 3b may be reduced. However, the output signal of the TFT 3b can be varied by short-circuiting the lower electrode 55 and the upper electrode 57. This can be applied to the pixel electrode 5 via the low-resistance electrode structure 53 without passing through the resistor 9. For this reason, the formation region of the variable resistor 9 is narrow,
Even when the cross-sectional area is small, it is possible to reliably prevent the driving ability of the TFT 3b from decreasing.

FIG. 10 is a schematic circuit diagram of a basic pixel 1 of a liquid crystal display according to a fifth embodiment of the present invention. 1 and 6 are denoted by the same reference numerals as in FIGS. 1 and 6, and the detailed description is omitted.

The liquid crystal display of this embodiment differs from that of the first embodiment in that a spare TFT 3c is provided, and an electrode structure 53 is inserted between the TFT 3c and the pixel electrode 5. .

The L composed of the basic pixels thus configured
In the CD, after the defective TFT is separated from the pixel electrode 5, a short circuit between the lower electrode and the upper electrode of the electrode structure 53 can be repaired.

As a result, the TFT 3c can be used as a substitute for a defective TFT, so that the potential of the pixel electrode can be controlled by the two TFTs, and the element characteristics such as the ON current and the inter-electrode capacitance of the transistor can be adjusted to a normal basic value. It can be the same as the pixel. Therefore, variations in the characteristics of the basic pixels due to restoration can be suppressed, and a liquid crystal display device with better image quality can be obtained. It goes without saying that the liquid crystal display device of the present embodiment can also obtain the same effects as those of the first embodiment.

FIG. 11 is a schematic circuit diagram of a basic pixel of a liquid crystal display according to a sixth embodiment of the present invention. The portions corresponding to the basic pixels in FIG. 1 are denoted by the same reference numerals as those in FIG. 1, and detailed description is omitted.

The liquid crystal display of this embodiment differs from that of the first embodiment in that an FET is used for the variable resistor 9a. The gate, source, and drain of the FET are connected to the storage capacitor 7 and the drain and gate of the TFT 3a, respectively. In the LCD including the basic pixels 1 configured as described above, a defective TFT can be specified by the following procedure.

[0052] First, to drive the TFT, FET Seo and the potential of the ground line GND _n to the high potential - sufficiently reduce the resistance between the scan and the drain. In this state, the display state of the LCD is examined to find a basic pixel having a defective TFT.

[0053] then the potential of the ground line GNDG _n in the low potential TFT3b only by controlling the potential of the basic pixel 5.
At this time, for the same reason as in the first embodiment, if the display of the basic pixel having a defective TFT is improved, the TFT connected to the FET can be identified as defective. If the display state does not change, the connection to the FET is performed. It can be specified that the TFT that is not defective is defective. When the defective TFT is specified, the defective TFT is separated from the pixel electrode or the signal line and the LCD is repaired as in the first embodiment.

L using the basic pixels thus configured
In a CD, the variable resistor 9 can be used without using backlight light.
Has the advantage that it can be applied to a reflection type liquid crystal display device.

In the above embodiment, a normal signal is used to find a defective TFT. However, for example, when the resistance of the variable resistor 9 cannot be reduced, that is, even when the variable resistor 9 is in a low resistance state, When the output level of the TFT 3a does not rise to a predetermined value, a driving signal of the TFT 3a may be increased by supplying a pulse signal having a wider pulse width than a regular pulse signal to the scanning line G.

In the basic pixel 1 using the two TFTs 3a and 3b as in the first to fifth embodiments, the TF
When both T3a and T3b are normal, the capability of the TFT3a cannot be used completely. However, since the ON current is larger than that of only one TFT3b, it is necessary to use a TFT smaller than a basic pixel having only one TFT. it can.

That is, assuming that the driving force and the size of the TFT of one basic pixel are both 1, the TFTs 3a, 3b
Are set to 0.7 and 0.4, respectively, so that the driving force and size of the entire TFT are 1.4 and 0.
8 can be set. The present invention is not limited to the embodiments described above.

For example, in the above embodiment, light is irradiated from the back surface of the light-transmitting substrate 11, but the inspection of the TFT can be performed by irradiating light from the surface of the light-transmitting substrate 41. Alternatively, the resistance may be controlled by changing the temperature instead of irradiating the variable resistor 9 with light. Further, the resistance may be controlled by combining a plurality of control methods, such as controlling the resistance of the variable resistor using light and voltage. Furthermore, instead of using amorphous silicon as the variable resistor 9, polycrystalline silicon may be used.

In the above embodiment, the variable resistor 9 is provided only for one TFT, but may be provided for a plurality of TFTs. In this case, it is desirable that the change in the resistance value be different for each TFT so that it is easy to specify which TFT is defective. This can be realized by adjusting the width and length of the variable resistor 9.

Further, in the above-described embodiment, the TFT is inspected after the LCD is manufactured. However, the inspection may be performed in a state of the matrix array substrate. For example, a defective TFT can be found by writing electric charge from a signal line, reading out the electric charge after a certain period of time via a TFT, and examining whether or not a proper electric charge is held. Furthermore, in the above embodiment, the inspection of the TFT has been described. However, the inspection of the auxiliary capacitance 7 can be performed using the same method. Further, the present invention can be applied to a liquid crystal display device using a switching element other than the TFT. In addition, various modifications can be made without departing from the scope of the present invention.

[0061]

As described in detail above, according to the present invention, a defective TFT can be easily found, so that a liquid crystal display device with few point defects can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic circuit diagram of a unit pixel of a liquid crystal display device according to a first embodiment of the present invention.

FIG. 2 is a plan view of an LCD using the unit pixels of FIG.

3 is a sectional view of the LCD of FIG. 2 taken along the line AA ';

FIG. 4 is a schematic circuit diagram of a basic pixel of a liquid crystal display device according to a second embodiment of the present invention.

FIG. 5 is a schematic circuit diagram of a basic pixel of a liquid crystal display according to a third embodiment of the present invention.

FIG. 6 is a schematic circuit diagram of a basic pixel of a liquid crystal display according to a fourth embodiment of the present invention.

7 is a plan view of an LCD using the unit pixels of FIG.

8 is a cross-sectional view of the LCD of FIG. 7 taken along line BB '.

9 is a cross-sectional view of the LCD of FIG. 7, taken along the line CC '.

FIG. 10 is a schematic circuit diagram of a basic pixel of a liquid crystal display according to a fifth embodiment of the present invention.

FIG. 11 is a schematic circuit diagram of a basic pixel of a liquid crystal display device according to a sixth embodiment of the present invention.

FIG. 12 is a schematic circuit diagram of a conventional TFT-LCD.

FIG. 13 is a schematic circuit diagram of a conventional multi-TFT TFT-LCD.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Unit pixel, 3a, 3b, 3c ... TFT, 5 ... Pixel electrode, 7 ... Auxiliary capacitance, 9, 9a ... Variable resistor, 11 ... Translucent insulating substrate, 13 ... Connection electrode, 15 ... Gate insulation Membrane, 1
7 active layer, 19 protective film, 21 contact layer, 2
3, 25, 27 ... connection electrodes, 29, 31 ... protective films, 33
... liquid crystal, 35 ... counter electrode, 37 ... color filter, 39
... black matrix, 41 ... translucent insulating substrate, 43,
45: deflection plate, 49a to 49b: intersection, 51: backlight, 53: electrode structure, 55: lower electrode, 57: upper electrode.

Claims (3)

(57) [Claims] 1. A pixel electrode for controlling the orientation of liquid crystal by an input signal, one source / drain is connected to the pixel electrode, the other source / drain is connected to a signal line, and a gate is connected to a scanning line. In a liquid crystal display device in which pixels having a plurality of field effect transistors are arranged in a matrix, a two-terminal variable resistor is inserted between the signal line and the pixel electrode via any one of the plurality of transistors. A liquid crystal display device, which is provided. 2. The variable resistor is controlled by light or heat.
The liquid according to claim 1, wherein
Crystal display device. 3. A pixel for controlling the orientation of a liquid crystal by an input signal.
The electrode and one of the source and drain are connected to the pixel electrode
And the other source / drain is connected to the signal line,
Multiple field effect transistors with gates connected to scan lines
Liquid crystal display device in which pixels having
Through any of the plurality of transistors.
And a three-terminal variable resistor between the signal line and the pixel electrode.
A constant potential is applied to the control terminal of the variable resistor.
Liquid crystal display, characterized in that means for supplying
apparatus.