JPH04225317A - Active matrix liquid crystal display element - Google Patents

Abstract

PURPOSE:To decrease the rate of disposing the liquid crystal display element which is defect-free in actuality in quality inspection by constituting the element in such a manner as to allow whether the cause for generation of a linear display defect crossing a display region lies in the shorting of a scanning line and a signal line or lies in the connection defect of a driving circuit to be known. CONSTITUTION:Dummy picture element electrodes 5a are provided along the terminal leading out ends of the scanning line 2 and the signal line 3 in the peripheral part within the region facing the liquid crystal layer of one substrate 1. These dummy picture element electrodes 5a are connected respectively to the parts between the terminal parts 2a, 3a of the respective lines 2, 3 and thin-film transistors 4 nearest these parts. Counter electrodes 6 of the other signal 9 are also disposed to face the respective dummy picture element electrodes. Whether the connecting state of the display circuit is good or not is decided from the display state in the parts corresponding to the dummy picture element electrodes 5a.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to active matrix liquid crystal display devices.

0002

2. Description of the Related Art Some active matrix liquid crystal display devices use thin film transistors as active elements for selecting pixel electrodes.

This active matrix liquid crystal display element has a plurality of scanning lines and a plurality of signal lines perpendicular to the scanning lines arranged on one side of a pair of transparent substrates facing each other with a liquid crystal layer in between. Thin film transistors and pixel electrodes connected to the thin film transistors are provided corresponding to the intersections of each scanning line and each signal line, and a counter electrode facing the pixel electrodes is formed on the other substrate. ing.

FIG. 4 is an equivalent circuit diagram of a conventional active matrix liquid crystal display element.

In FIG. 4, 1 is one transparent substrate of a liquid crystal display element, 2 is a scanning line, 3 is a signal line, and 4 is arranged corresponding to the intersection of each scanning line 2 and each signal line 3. The gate electrode of this thin film transistor 4 is connected to the scanning line 2,
The drain electrode is connected to the signal line 3.

Further, in FIG. 4, A is a pixel portion arranged corresponding to the intersection of each scanning line 2 and each signal line 3, and each pixel portion A is connected to a pixel electrode (transparent A pixel a consisting of an electrode, a counter electrode formed on the other transparent substrate (not shown), and a liquid crystal between the two electrodes.
and a storage capacitor 8 provided on the pixel electrode.
It is made up of. The pixel electrode is formed on the gate insulating film and connected to the source electrode of the thin film transistor 4, and the counter electrode is a single electrode covering almost the entire surface of the substrate and connected to the ground terminal.

The storage capacitor 8 is used to accumulate and hold the charge of the image data signal applied from the signal line 3 to the pixel electrode 5 when the thin film transistor 4 is turned on. 8, although its structure is not shown, the pixel electrode and
It consists of a capacitor electrode formed to face a part of this pixel electrode, and an insulating film (gate insulating film of thin film transistor 4) interposed between this capacitor electrode and the pixel electrode.

On the other hand, in FIG. 4, 20 is a scanning side drive circuit, 30 is a signal side drive circuit, and the scanning side drive circuit 20
is connected to the terminal portion 2 a of each scanning line 2 , and the signal side drive circuit 30 is connected to the terminal portion 3 a of each signal line 3 . The scanning side drive circuit 20 and the signal side drive circuit 30 are, for example, film-like wiring in which terminals 22 and 32 corresponding to the terminal portions 2a and 3a of the scanning line 2 and the signal line 3 are arranged on the side edges thereof, respectively. The side edges of the wiring boards 21, 31 are bonded to the terminal arrangement part of the substrate 1 of the liquid crystal display element using an anisotropic conductive adhesive or the like, and the terminal parts 2a, 3a are connected to the terminal parts 2a, 3a. It is connected.

The scanning side drive circuit 20 is connected to each scanning line 2.
A gate signal is sequentially outputted to turn on the thin film transistor 4, and the gate signal outputted to each scan line 2 is applied to the gate electrode of the thin film transistor 4 to turn on the thin film transistor 4. Further, the signal side drive circuit 30 captures and holds image data signals for one scanning line from an image processing circuit (not shown), and outputs the image data signals for one scanning line from the scanning side drive circuit 20. The image data signal is output to each signal line 3 in accordance with the output timing of the gate signal, and the image data signal output to each signal line 3 is applied to the pixel electrode 5 via the thin film transistor 4 which is turned on by the gate signal. .

[0010] The pixel a of each pixel portion A performs a display operation by changing the alignment state of the liquid crystal due to the voltage of the image data signal applied to the pixel electrode (the electric field between the pixel electrode and the counter electrode). In this case, the image data signal applied from the data line 3 to the pixel electrode 5 is only applied during the time when the thin film transistor 4 is in the ON state, that is, during the selected time when the gate signal is applied to the thin film transistor 4. However, the image data signal applied from the signal line 3 to the pixel electrode when the pixel electrode is selected is also supplied to the storage capacitor 8, and its charge is stored in the storage capacitor 8.
Due to the charges accumulated in the pixel a, the pixel a is maintained in a display operation state even when it is not selected.

By the way, the quality inspection of the liquid crystal display element is performed by connecting the scanning side drive circuit 20 and the signal side drive circuit 30 to the scanning line 2 and signal line 3, respectively, and then displaying a test image on the liquid crystal display element. It is done by letting
If a display defect occurs, the liquid crystal display element is discarded as a defective product.

0012

[Problems to be Solved by the Invention] However, conventionally, the liquid crystal display element cannot be used even when the above-mentioned display defect occurs partially or when a display defect occurs over the entire length of the scanning line 2 or the signal line 3. Because the product is determined to be defective, liquid crystal display elements that actually have no defects may end up being discarded.

That is, the causes of display defects in liquid crystal display elements include the scanning line 2 and the signal line 3.
In addition to disconnection defects and short circuit defects between the scanning line 2 and the signal line 3, the scanning side drive circuit 20 and the signal side drive circuit 3
There is a connection failure of 0.

Among these causes, the display defect when there is a disconnection defect in the scanning line 2 and signal line 3 occurs when the line is disconnected from the disconnection point to the end of the line (on the opposite side from the terminals 2a and 3a). This is a partial defect that occurs only in the edge portion), but it is a display defect that occurs due to a short circuit between the scanning line 2 and the signal line 3, and a display defect that occurs only in the drive circuits 20 and 30.
The display defects caused by poor connections are all linear defects that cross the display area.

In other words, when the scanning line 2 and the signal line 3 are short-circuited, the image data signal applied to the signal line 3 which is short-circuited to the scanning line 2 is transferred from this signal line 3 to the short-circuited signal line 3. Therefore, the image data signal that should be applied from the signal line 3 via the thin film transistor 4 is no longer applied to each pixel a along this signal line 3. All pixels a along the line stop displaying, and a linear display defect occurs that crosses the display area in the signal line direction.

This linear display defect also occurs in the scanning line direction. In other words, the gate signal applied to the scanning line 2 that is short-circuited to the signal line 3 is connected from this scanning line 2 to the signal line that is short-circuited to it, so that all the gate signals connected to this scanning line 2 are A signal in which the image data signal and the gate signal are superimposed is supplied to the thin film transistors 4 of the thin film transistors 4, and a normal gate signal is no longer applied.
Since it becomes an FF state or an ON state, the above scanning line 2
Image data signals are no longer applied to all pixels a along the line, and a linear display defect occurs that crosses the display area in the scanning line direction.

Furthermore, the scanning side drive circuit 20 and the scanning line 2
If there is a poor connection between the
This is similar to the case where the signal line 3 and the signal line 3 are short-circuited, and the gate signal is not applied to the scanning line 2 whose connection state with the scanning side drive circuit 20 is poor. All thin film transistors 4
remains in an OFF state, and no image data signal is applied to all pixels a along this scanning line 2, resulting in a linear display defect that crosses the display area in the scanning line direction.

The same applies when there is a connection failure between the signal side drive circuit 30 and the signal line 3. The image data signal is no longer applied to all the pixels a along the line 3, and a linear display defect that crosses the display area in the signal line direction occurs.

[0019] If the cause of a linear display defect that crosses the display area is a poor connection between the drive circuits 20 and 30, the display defect can be eliminated by reconnecting the drive circuits. However, conventionally, the cause of the linear display defect that crosses the display area is due to a short circuit between the scanning line 2 and the signal line 3, or due to the drive circuit 20.
, 30, it was not possible to know whether it was due to a poor connection, so even if the display defect was a partial defect,
Furthermore, even in the case of a linear defect that crosses the display area, the liquid crystal display element has no choice but to be determined as a defective product, and as a result, even liquid crystal display elements that are actually defect-free have to be discarded.

An object of the present invention is to find out whether the cause of a linear display defect that crosses a display area is due to a short circuit between a scanning line and a signal line, or a poor connection in a drive circuit. An object of the present invention is to provide an active matrix liquid crystal display element that can improve the yield by reducing the disposal rate of liquid crystal display elements that are actually defect-free during quality inspection.

[0021]

[Means for Solving the Problems] The present invention wires a large number of scanning lines and a large number of signal lines perpendicular to the scanning lines on one side of a pair of transparent substrates facing each other with a liquid crystal layer in between. At the same time, a thin film transistor whose gate electrode is connected to the scanning line and whose drain electrode is connected to the signal line is provided, corresponding to each intersection of each scanning line and each signal line, and a pixel electrode connected to the source electrode of this thin film transistor. In an active matrix liquid crystal display element, in which a counter electrode facing the pixel electrode is formed on the other substrate, each of the scanning lines and each signal line is provided in a peripheral portion of the liquid crystal layer opposing region of the one substrate. A large number of dummy pixel electrodes are provided along the terminal lead-out edge of at least one of the lines, and each dummy pixel electrode is connected to a portion between the terminal portion of each line and the thin film transistor closest to the terminal portion. At the same time, the counter electrode of the other substrate is also opposed to each of the dummy pixel electrodes.

[0022]

[Operation] That is, the present invention determines whether the connection state of the drive circuit is good or bad based on the display state of the portion corresponding to the dummy pixel electrode, and the drive circuit and the line are connected in a conductive state. If so, the signal (gate signal or image data signal) applied to the above line from the drive circuit
is also applied to the dummy pixel electrode, and a driving electric field is applied to the liquid crystal between this dummy pixel electrode and the counter electrode.If the connection between the driving circuit and the above line is poor, a signal is not transmitted from the driving circuit to the above line. If no driving electric field is applied, no driving electric field will be applied to the liquid crystal between the dummy pixel electrode and the counter electrode. By looking at the display state of the portion corresponding to the dummy pixel electrode, it can be determined whether the linear display defect is due to a poor connection in the drive circuit.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. 1 to 3. 1 and 2 show a dummy pixel electrode forming portion of a liquid crystal display element, and FIG. 3 shows an equivalent circuit of the liquid crystal display element. In addition, in FIGS. 1 to 3, the same parts as shown in FIG. 4 are denoted by the same reference numerals, and the explanation thereof will be omitted.

The active matrix liquid crystal display element of this embodiment has a scanning line 2, a signal line 3, a thin film transistor 4, and a pixel electrode 5 of a pair of transparent substrates 1 and 9 facing each other with a layer of liquid crystal 7 in between. The terminal leading edge of each scanning line 2 and each The same number of transparent dummy pixel electrodes 5a as the number of scanning lines and the number of signal lines are provided along the terminal lead-out edges of the signal lines 3, and each dummy pixel electrode 5a is connected to the terminal portion 2a of each scanning line 2. The terminal portion 2a is connected to the portion between the terminal portion 2a and the thin film transistor 4 closest to the terminal portion 2a, and the portion between the terminal portion 3a of each signal line 3 and the thin film transistor 4 closest to the terminal portion 3a is connected to the other substrate 9. The counter electrode 6 is formed in such an area that its peripheral portion faces each of the dummy pixel electrodes 5a.

In this embodiment, the thin film transistor 4 is of an inverted stagger type. As shown in FIGS. 1 and 2, this inverted staggered thin film transistor 4 includes a gate electrode G formed on the substrate 1, and a semiconductor layer 12 formed on the gate electrode G with a gate insulating film 11 interposed therebetween. At the same time, a source electrode S is formed on this semiconductor layer 12.
and a drain electrode D are formed. Gate insulating film (transparent insulating film) 11 of this thin film transistor 4
is formed over almost the entire surface of the liquid crystal layer facing region of the substrate 1, and the scanning line 2 to which the gate electrode G of the thin film transistor 4 is connected is wired on the substrate 1, and the scanning line 2 is connected to the drain electrode D.
The signal line 3 to which is connected is wired on the gate insulating film 11.

The pixel electrode 5 and the dummy pixel 5a are formed of a transparent conductive film such as ITO on the gate insulating film 11, and each pixel electrode 5 is connected to the source electrode of the corresponding thin film transistor 4. The dummy pixel electrode 5a is directly connected to the scanning line 2 and signal line 3.

In FIG. 1, reference numeral 13 denotes a capacitor electrode (transparent electrode) constituting the storage capacitor 8. This capacitor electrode 13 is formed on the substrate 1 in parallel with the scanning line 2, and is used for each scanning. It faces each pixel electrode 5 lined up along line 2 with a gate insulating film 11 interposed therebetween.

The quality inspection of the liquid crystal display element of this example was also carried out as follows:
After connecting the scanning side drive circuit 20 and the signal side drive circuit 30 to the scanning line 2 and signal line 3, respectively, a test image is displayed on the liquid crystal display element.

In this liquid crystal display element, as described above, each of the scanning lines 2, the signal lines 3, the thin film transistors 4, and the pixel electrodes 5 are provided in the peripheral part of the liquid crystal layer opposing area of the one substrate 1. Dummy pixel electrodes 5a are provided corresponding to the scanning line 2 and each signal line 3, respectively.
This dummy pixel electrode 5a is connected to the terminal portion 2a of each scanning line 2.
and the thin film transistor 4 closest to this terminal section 2a, and the terminal section 3a of each signal line 3 and this terminal section 3.
Since the counter electrode 6 provided on the other substrate 9 is also connected to the portion between the thin film transistor 4 closest to the thin film transistor 5a and the upper dummy pixel electrode 5a, each dummy pixel is It is possible to determine whether the connection state of the drive circuits 20 and 30 is good or bad from the display state of the portion corresponding to the electrode 5a.

That is, display defects caused by a short circuit between the scanning line 2 and the signal line 3 and the drive circuits 20 and 30
As explained in the [Problem to be Solved by the Invention] section, display defects caused by poor connections are linear defects that cross the display area, so it cannot be determined from the situation of occurrence of display defects alone. , whether this linear defect occurred due to a short circuit between the scanning line 2 and the signal line 3, or
I don't know if this was caused by a poor connection on the 30.

However, in the above embodiment, the drive circuit 20,
30 and the scanning line 2 and signal line 3 are connected in a conductive state, each line 2 is connected from the drive circuits 20 and 30.
, 3 (gate signal or image data signal) is also applied to the dummy pixel electrode 5a, a driving electric field is applied to the liquid crystal 7 between the dummy pixel electrode 5a and the counter electrode 6, and the driving circuit 20 , 30 and each line 2, 3 is defective, and the drive circuit 20, 30 disconnects each line 2, 30 from the drive circuit 20, 30.
If no signal is applied to the dummy pixel electrode 5, the dummy pixel electrode 5
Since no driving electric field is applied to the liquid crystal 7 between the dummy pixel electrode 5a and the counter electrode 6, when a linear display defect across the display area occurs, the display state of the portion corresponding to the dummy pixel electrode 5a is as follows. , it can be seen whether the linear display defect is due to a poor connection between the drive circuits 20 and 30.

Note that the scanning side drive circuit 20 and the scanning line 2
When inspecting the connection to the scanning line 2, if the above quality inspection is performed by supplying a gate signal with a DC component different from a normal gate signal to the scanning line 2 from the scanning side drive circuit 20, the connection to the scanning line 2 is confirmed. By driving the liquid crystal 7 between the dummy pixel electrode 5a and the counter electrode 6, the display state of this portion can be viewed.

As described above, according to the liquid crystal display element of the above embodiment, the cause of the linear display defect that crosses the display area may be due to a short circuit between the scanning line 2 and the signal line 3, or due to the drive circuit. It is possible to know whether the problem is due to a poor connection between terminals 20 and 30.

[0034] If the cause of the linear display defect that crosses the display area is a poor connection between the drive circuits 20 and 30, the display defect can be eliminated by reconnecting the drive circuits 20 and 30. Therefore, it is possible to reduce the disposal rate of actually defect-free liquid crystal display elements during quality inspection and improve yield.

Note that in the liquid crystal display element described above, the display by the dummy pixel electrode 5a is visible in the peripheral area of the display screen, but if the dummy pixel electrode 5a is covered with blind printing or a blind board after quality inspection, the dummy pixel electrode 5a The display will not be visible.

Further, in the above embodiment, the dummy pixel electrode 5a is provided along the terminal leading edge of the scanning line 2 and the terminal leading edge of the signal line 3, but this dummy pixel electrode 5a is not connected to the signal line 3. It may be provided on only one of the terminal leading edge of No. 3 and the terminal leading edge of scanning line 2.

[0037]

According to the active matrix liquid crystal display element of the present invention, the peripheral part of the liquid crystal layer facing area of one of the substrates is provided along the terminal lead-out edge of at least one of each scanning line and each signal line. In addition, a large number of dummy pixel electrodes are provided, and each dummy pixel electrode is connected to a portion between the terminal portion of each line and the thin film transistor closest to this terminal portion, and a counter electrode of the other substrate is connected to the portion between the terminal portion of each line and the thin film transistor closest to the terminal portion. The dummy pixel electrodes are also opposed to each other, and the quality of the connection state of the drive circuit is determined from the display state of the portion corresponding to the dummy pixel electrodes, which prevents the occurrence of linear display defects that cross the display area. This makes it possible to determine whether the cause is a short circuit between the scanning line and signal line, or a poor connection in the drive circuit. It is possible to reduce the waste disposal rate and improve yield.

[Brief explanation of the drawing]

FIG. 1 is a plan view of a dummy pixel electrode forming portion of a liquid crystal display element showing one embodiment of the present invention.

FIG. 2 is an enlarged sectional view taken along line II-II in FIG. 1;

FIG. 3 is an equivalent circuit diagram of a liquid crystal display element.

FIG. 4 is an equivalent circuit diagram of a conventional liquid crystal display element.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1, 9...Substrate, 2...Scanning line, 2a...Terminal part, 3...Signal line, 3a...Terminal part, 4...Thin film transistor, G...
Gate electrode, D...drain electrode, S...source electrode, 5...
Pixel electrode, 6... Counter electrode, 7... Liquid crystal, 8... Storage capacitor, 13... Capacitor electrode.

Claims (1)

[Claims] Claim 1: A plurality of scanning lines and a plurality of signal lines perpendicular to the scanning lines are wired to one side of a pair of transparent substrates facing each other with a liquid crystal layer in between, and each scanning line and each A thin film transistor whose gate electrode is connected to the scanning line and whose drain electrode is connected to the signal line, and a pixel electrode connected to the source electrode of this thin film transistor are provided corresponding to each intersection with the signal line, and a pixel electrode is provided on the other substrate. is an active matrix liquid crystal display element in which a counter electrode facing the pixel electrode is formed, and a terminal of at least one of the scanning line and each signal line is led out in a peripheral portion of the liquid crystal layer opposing region of the one substrate. A large number of dummy pixel electrodes are provided along the edge, and each dummy pixel electrode is connected to a portion between the terminal portion of each line and the thin film transistor closest to the terminal portion, and is connected to a portion of the other substrate. An active matrix liquid crystal display device characterized in that a counter electrode is also opposed to each of the dummy pixel electrodes.