JPH0915645A - Active matrix liquid crystal display element - Google Patents

Abstract

PURPOSE: To detect electrically a defect position of a driver built-in active matrix liquid crystal display element in a short time. CONSTITUTION: TFT analog switches 21, 23 and one TFT switch 16 are turned on. An image signal input SIG is made an H level, and a pulse voltage is applied to scan signal lines Y1 , Y2 ...YN successively, and pixel TFTs 14 are turned on successively, and corresponding pixel capacities 17 are charged. After charging is ended, the TFT analog switch 21 is turned off, and the TFT analog switch 20 is turned on. The pulse voltage is applied successively to the scan signal lines Y1 , Y2 ...YN, and the corresponding TFT analog switch 23 is turned on, and the pixel TFTs 14 are turned on successively, and electric charges storage in the pixel capacities 17 are discharged. A voltage/current pulse caused by the discharge is detected by a discharge detection circuit 19, and when the pulse is detected, the fact that the TFT is normal is judged, and when not, the fact that the TFT is defective is judged.

Description

Detailed Description of the Invention

[0001]

This invention relates to a TFT (thin film)
The present invention relates to an active matrix liquid crystal display element using a thin film transistor (TFT) as an active element, and particularly to an active matrix liquid crystal display element having a driver for driving a liquid crystal and a driver for inspection.

[0002]

2. Description of the Related Art As shown in FIG. 6, a conventional active matrix liquid crystal display device has a pixel area (display area) 1,
Data signal line driver 2 and scanning signal line driver 3
Having. Pixel area 1, a plurality of data signal lines X _1, X ₂ ... X _M provided on an insulating substrate, and is suitably insulated to cross the data signal lines X _1, X ₂ ... X _M on an insulating substrate Y _N provided with a plurality of scanning signal lines Y ₁ , Y ₂ ... Y _N, and active signals provided at each intersection of the data signal lines X ₁ , X ₂ ... X _M and the scanning signal lines Y ₁ , Y ₂ ... Y _N. Pixel TFT4 as an element
And a pixel capacitor 7 which forms a matrix of pixels.

The pixel capacitor 7 is a capacitor formed of a pixel electrode and a counter electrode which are arranged with a liquid crystal layer interposed therebetween.
The pixel electrode and the counter electrode are respectively arranged on a pair of insulating substrates which are arranged to face each other with the liquid crystal layer interposed therebetween.

The source of the pixel TFT 4 is the data signal line X ₁
To X _M , the gates are connected to the scanning signal lines Y _{1 to} Y _N , and the drains are connected to the pixel electrodes forming the pixel capacitance. The counter electrode forming the pixel capacitor 7 is connected to the common potential V _COM . Parasitic capacitors 8 also exist between the data signal lines X _{1 to} X _M and the counter electrodes.

The data signal line driver 2 has a plurality of TFT analog switches 6 provided between each of the data signal lines X _{1 to} X _M and the video signal input SIG, and the TFT analog switch 6 having a clock CLX and an operation input. It has a shift register 5 that is driven (on / off) based on DX. The scanning signal line driver 3 is composed of a shift register that drives the pixel TFT 4 based on the clock CLY and the operation input DY.

In such an active matrix liquid crystal display device, it is difficult to manufacture a defect-free display device, and whether each pixel capacitor has a capability of normally accumulating charges or not, each TFT operates normally. Whether or not, that is, whether or not there is a defect needs to be inspected at the time of shipping the product.

[0007]

However, in an active matrix liquid crystal display element with a built-in driver, when the element is completed, it is usually covered with the opposing glass substrate including the driver circuit section. Therefore, it is difficult to directly investigate the defect by applying a probe needle to each signal line or electrode and measuring the potential thereof.

It is possible to actually display an image (test pattern) and visually detect display defects, but it takes time and it is difficult to quantify the defects.
There is also an apparatus that receives a display image with a detector and detects a defective portion by image processing, but it requires a long inspection time of about 3 minutes and the apparatus itself is expensive.

Further, a method of electrically detecting a defect in an active matrix liquid crystal display device with a built-in driver is described in "JAPAN DISPLAY '92 Paper S14-2, P. 561".
Is shown in The method disclosed in this document detects a short circuit defect from a leak current between a data signal line and a scanning signal line, determines whether the output of the scanning signal line driver reaches the end of the scanning signal line, and disconnects the wiring. To detect. But,
Since current measurement is performed to detect a short-circuit defect, measurement time is long. Also, only some short circuits can be detected.

As described above, it has been difficult to detect a display defect at a low cost in a short time with an active matrix liquid crystal display element having a built-in driver.

The present invention has been made in view of the above situation, and in an active matrix liquid crystal display element with a built-in driver, the presence or absence of a defect and the defective portion can be detected electrically and in a short time. The purpose is to provide a device.

[0012]

In order to achieve the above object, an active matrix liquid crystal display device according to the present invention has an active element and a pixel electrode connected to one end of a current path of the active element in a matrix. One substrate formed, another substrate on which a counter electrode facing the pixel electrode is formed, liquid crystal disposed between the one substrate and the other substrate, and a current path of the active element. A data signal line connected to the other end of the active element, a scanning signal line connected to the control end of the active element, the scanning signal line and the data signal line, and the active element via the scanning signal line. Charging means for sequentially turning on, and applying a voltage to the data signal line to charge a pixel capacitance formed by the pixel electrode and the facing portion of the counter electrode and the liquid crystal therebetween. Connected to the scan signal line and the data signal line, the active elements are sequentially turned on through the scan signal line to discharge the electric charge accumulated in the pixel capacitance, and the voltage of the data signal line due to the discharge or It is characterized by comprising an inspection means for inspecting the presence or absence of a defect by checking a change in current.

[0013]

According to the active matrix liquid crystal display element having the above-described structure, the electric current or voltage pulse generated when the electric charge is stored in the pixel capacitance or the auxiliary capacitance connected to each active element and then discharged is detected. To do. If the pixel capacitance is normally charged by the charging means, and if it is discharged, a predetermined current pulse or voltage pulse is generated. On the other hand, when the pixel capacitance is not normally charged due to disconnection or short circuit, the current pulse or the voltage pulse is not generated even if the pixel capacitance is discharged. The same applies when the active element does not operate normally. Therefore, by detecting the current pulse or the voltage pulse, it is possible to detect the presence or absence of a defect, the position of the defect, and the like.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 3 shows a sectional structure of an active matrix liquid crystal display element according to an embodiment of the present invention. As shown in the figure, this active matrix type liquid crystal display element is
A pair of insulating transparent substrates 31 and 32, and substrates 31 and 32
A liquid crystal cell 38 composed of a sealing material SC for joining and a liquid crystal 37 sealed between the substrates 31 and 32;
A pair of polarizing plates 41 and 4 arranged with the liquid crystal cell 38 in between.
2 is provided.

Pixel electrodes 33 and pixel TFTs 14 as active elements are arranged in a matrix on the substrate 31, as shown in FIGS. 3 and 4. Pixel TFT14
Is composed of a gate electrode, a gate insulating film, a semiconductor layer, a source electrode and a drain electrode formed on the substrate 31. An alignment film 3 is formed on each pixel electrode 33 and the pixel TFT 14.
5 are arranged.

Further, on the substrate 31, the compensation capacitance line CS which faces the pixel electrodes 33 of each row via the gate insulating film is provided.
Are formed.

As shown in FIG. 4, the gate electrode of each pixel TFT 14 is a scanning signal line (gate line) Y of the corresponding row.
₁ , Y ₂ ... Y _N , the drain electrode is connected to the corresponding pixel electrode 33, and the source electrode is connected to the data signal lines X ₁ , X ₂ ... X _M in the corresponding column. Each scanning signal line Y ₁ , Y ₂ ... Y _N is connected to the scanning signal line driver 13 formed on the substrate 31, and the data signal lines X ₁ , X ₂ ... X _M and the compensation capacitance line CS are provided on the substrate 31. It is connected to the formed data signal line driver 12.

On the substrate 32, a counter electrode 34 facing the pixel electrode 33, and an alignment film 3 formed on the counter electrode 34.
6 are provided. Compensation capacitance line CS and counter electrode 34
Is applied to the common potential V _COM . The liquid crystal 37
For example, it is a TN liquid crystal or a ferroelectric liquid crystal.

FIG. 1 shows a circuit configuration of the active matrix liquid crystal display device shown in FIGS. As shown in FIG. 1, in the display area 11, data signal lines X ₁ , X ₂ ... X _M
A pixel TFT 14 and a pixel capacitor 17 provided at each intersection of the scanning signal lines Y ₁ , Y ₂ ... Y _N are arranged.

The pixel capacitance 17 is a composite capacitance of the display capacitance formed by the pixel electrode 33, the counter electrode and the liquid crystal 37 between them, and the compensation capacitance formed by the pixel electrode 33, the compensation capacitance line CS and the gate insulating film therebetween. Is. Each data signal line X
_{1 to} X _M and a parasitic capacitance 1 between the counter electrode and the counter electrode, respectively.
There are also eight.

The scanning signal line driver 13 includes a TFT analog switch 2 connected to each scanning signal line Y ₁ , Y ₂ ... Y _N.
3 and a shift register 22 for driving the pixel TFT 14 based on the clock CLY and the operation input DY of the driver. The shift register 22 includes a circuit that controls the TFT analog switch 23 according to the control signal input CONT3.

The data signal line driver 12 includes a plurality of TFT analog switches 16 provided between each of the data signal lines X _{1 to} X _M and a common signal line CL connected to the video signal input SIG, and a TFT analog switch. 16 clock CLX
And a shift register 15 driven based on the operation input DX of the driver.

Further, the data signal line driver 12 includes a discharge detection circuit 19 for detecting a current or voltage pulse due to the discharge of the pixel capacitor 17. A TFT analog switch 20 is provided between the discharge detection circuit 19 and the common signal line CL.
Is provided. Common signal line CL and video signal input SIG
A TFT analog switch 21 is provided between and. Control signals CONT1 and CONT2 are applied to the gates of the TFT analog switches 20 and 21, respectively.

The discharge detection circuit 19, for example, as shown in FIG. 2, is composed of an edge trigger type RS flip-flop FF and an output driver D connected to its Q output. The output driver D is an output terminal PO of the discharge detection circuit 19.
Connected to the edge trigger type RS flip-flop FF
The reset terminal (R) is connected to the reset signal input R of the discharge detection circuit 19. The TFT analog switch 20 is connected to the set terminal (S) of the edge trigger type RS flip-flop FF.

The control signals CONT1 and CONT2 are respectively T
The control signal CONT3 is a signal for turning on / off the FT analog switches 20 and 21, and the control signal CONT3 is a signal for simultaneously turning on the TFT analog switch 23.

Next, the operation of inspecting the active matrix liquid crystal display element constructed as shown in FIGS. 1 to 4 for defects will be described with reference to FIGS. 5 (A) to 5 (C). FIG.
In (A) to (C), the TFT analog switches 16, 20, 21, and 23 are represented by switch symbols for easy understanding.

The operation of detecting a defect in the active matrix liquid crystal display device constructed as shown in FIGS.
(I) a charging step of charging the pixel capacitors 17, and (ii) a detection step of sequentially selecting and discharging each pixel capacitor 17 and detecting a voltage pulse (or a current pulse) generated in the common signal line CL thereby. Is repeatedly performed for each data signal line.

First, as shown in FIG.
As shown in (A), a certain data signal line (referred to as "Xα") is selected (the TFT analog switch 1 connected to the data signal line Xα by the output of the shift register 15).
Turn on 6). Furthermore, the video signal input SIG is set to a high voltage (“H”) and the control signal CONT3 is switched to switch all T
The FT analog switch 23 is turned on.

Next, the shift register 22 sequentially selects the scanning signal lines Y ₁ , Y _2, ... Y _N to output a high voltage pulse, and sequentially turns on the pixel TFTs 14 in each row. The N pixel capacitors 17 connected to the data signal line Xα are TF
T analog switch 21, common signal line CL, TFT analog switch 16, data signal line Xα, pixel TFT 14
The electric charge is sequentially injected from the video signal input SIG via, and is charged.

Next, as shown in FIG. 5B, the signals of the scanning signal lines Y ₁ , Y ₂ ... Y _N are set to 0 V ("L") and the TFT analog switch 21 is turned off. Here, the charge injected in FIG. 5A is held in the pixel capacitor 17.

Next, the process moves to the inspection step (ii) shown in FIG.
As shown in (C), the TFT analog switch 23 of the row to be inspected is turned on, the TFT analog switches 23 of the other rows are turned off, and the TFT analog switch 20 is turned on. Then, the shift register 22 applies a high voltage pulse to the scanning signal line (referred to as “Yβ”) of the inspection target row.

Pixel TFT1 connected to the scanning signal line Yβ
4 is turned on, and the charge accumulated in the pixel capacitor 17 is turned on by the pixel TFT 14, the data signal line Xα, and the turned-on TFT.
It flows into the discharge detection circuit 19 through the analog switch 16, the common signal line CL, and the TFT analog switch 20.
The RS flip-flop FF of the discharge detection circuit 19 is set by using the voltage (or current) pulse having the discharge waveform as shown in FIG. 5C as a trigger signal, and the output terminal PO of the discharge detection circuit 19 is High voltage level. The output signal is received by the measuring instrument M, and it is determined that the voltage is high if the voltage is high, and is defective if the voltage is low. At the time when the measuring device M finishes judging good or bad, a reset pulse is input to the reset terminal R to reset the discharge detection circuit 19.

Then, T of the scanning signal line Yβ which has been inspected
The FT analog switch 23 is turned off, the TFT analog switch 23 of the adjacent scanning signal line Y (β + 1) is turned on, and the scanning signal line Y (β + 1) is set to a high voltage. As a result, the pixel TF connected to the scanning signal line Y (β + 1)
The electric charge accumulated in the corresponding pixel capacitor 17 is discharged via T14. This is measured by the measuring device M in the same manner as described above, and the pass / fail is determined.

Thereafter, in the same manner, the N pixels connected to the same data signal line Xα are inspected. When all the pixels of one data signal line Xα have been inspected,
Returning to the state of FIG. 5A, the data held in the shift register 15 is shifted, the TFT analog switch 16 connected to the next data signal line X (α + 1) is turned on, and the data signal line X is switched in the same manner as described above. Pixels connected to (α + 1) are sequentially inspected.

All the pixels are inspected by repeating the above operation. Note that in FIG. 5C, the TFs other than the inspection target line are
The reason why the T analog switch 23 is turned off is that when there is a defect such as a short circuit defect between the data signal line X and the scanning signal line Y, or between the source and the electrode of the pixel TFT 14, electric charge is passed therethrough. This is to prevent it from being discharged.

As described above, in this embodiment, the display element has a built-in circuit for detecting the discharge of the electric charge charged in each pixel portion of the active matrix. Therefore, the defect inspection can be performed by using a general measuring instrument such as a general-purpose logic tester, and the inspection cost can be reduced. In the above-mentioned inspection, when a defective portion is detected, it is not possible to directly determine whether the defective cause is due to a short circuit or a disconnection. But,
It is possible to estimate the defect content from the distribution of defects by analyzing the inspection results. For example, when the defective portions are dispersed, it is presumed to be the defect of each element. Further, when the defective portions are continuous in the row or column direction, it can be inferred that the scanning signal line or the data signal line is broken. Therefore, it is very effective to use the above-mentioned configuration in order to perform the quality judgment during the manufacturing process at high speed.

In the normal operation, the control signal CONT1
To the L level to turn off the TFT analog switch 20, the control signal CONT2 to the H level to turn on the TFT analog switch 21, and the TFT analog switch 23.
Turn on all. Then, the leading bit of the shift register 22 is set by the signal DY, and thereafter the scanning signal lines are sequentially switched according to the clock signal CLY to apply the gate pulse. Similarly, the leading bit of the shift register 15 is set by the signal DX. Set, then clock signal CL
The TFT analog switch 16 is sequentially turned on according to X, the image signal SIG is written in the pixel capacitor 17, and an image is displayed at the scanning signal line end.

The present invention is not limited to the above embodiment, and various modifications and applications are possible. For example, although the compensation capacitance line CS is arranged in the above embodiment, the compensation capacitance CS
May be provided as needed. In the above embodiment,
Although the defect is detected for each data signal line, the defect may be detected for each scanning signal line. In addition, all pixel capacity 17
After charging, the batteries may be sequentially discharged.

[0039]

As described above in detail, according to the present invention, after the pixel capacitance connected to each active element is charged, the voltage or current pulse generated when the pixel capacitance is discharged is detected. , Detect defects. Therefore, it becomes possible to detect the defective portion electrically and in a short time.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a configuration of an active matrix liquid crystal display element according to an embodiment of the present invention.

FIG. 2 is a circuit diagram showing a configuration of a discharge detection circuit shown in FIG.

FIG. 3 is a sectional view showing a structure of an active matrix liquid crystal display element according to an embodiment of the present invention.

FIG. 4 is a diagram showing a configuration of one substrate of an active matrix liquid crystal display element according to an embodiment of the present invention.

5A and 5B are views for explaining a process of inspecting the active matrix liquid crystal display element of FIG. 1, in which FIG. 5A shows a charging process, FIG. 5B shows a voltage holding process, and FIG.

FIG. 6 is a circuit diagram showing a configuration of a conventional active matrix liquid crystal display element.

[Explanation of symbols]

11 ... Display area, 12 ... Data signal line driver, 13 ...
Scan signal line driver, 14 ... Pixel TFT, 15 ... Shift register, 16 ... TFT analog switch, 17 ... Pixel capacitance, 18 ... Parasitic capacitance, 19 ... Discharge detection circuit, 20 ... T
FT analog switch, 21 ... TFT analog switch, 22 ... Shift register, 23 ... TFT analog switch, 31 ... Substrate, 32 ... Substrate, 33 ... Pixel electrode, 34
... counter electrode, 35 ... alignment film, 36 ... alignment film, 37 ... liquid crystal, 38 ... liquid crystal cell, 41 ... polarizing plate, 42 ... polarizing plate

Claims (4)

[Claims] 1. A substrate in which an active element and a pixel electrode connected to one end of a current path of the active element are formed in a matrix, and another substrate in which an opposite electrode facing the pixel electrode is formed. A liquid crystal arranged between the one substrate and the other substrate, a data signal line connected to the other end of the current path of the active element, and a scan connected to the control end of the active element. A signal line, connected to the scanning signal line and the data signal line, sequentially turning on the active element via the scanning signal line,
A charging unit that applies a voltage to the data signal line to charge a pixel capacitance formed by the pixel electrode and a facing portion of the counter electrode and a liquid crystal therebetween, and a connecting unit connected to the scanning signal line and the data signal line. Then, the active elements are sequentially turned on through the scanning signal line to discharge the electric charge accumulated in the pixel capacitor, and a change in the voltage or current of the data signal line due to the discharge is checked to detect a defect. An active matrix liquid crystal display element, which is formed by an inspection means for inspecting the presence or absence of the element. 2. The charging means and the inspection means sequentially apply a pulse to the scanning signal line to turn on an active element connected to the scanning signal line, and a predetermined voltage to the data signal line. A voltage applying means for applying the voltage to charge each pixel capacitance through the turned-on active element and a voltage or current due to the charge flowing from each pixel capacitance to the data signal line through the turned-on active element are fetched and checked. 2. The active matrix liquid crystal display element according to claim 1, further comprising: a check unit for performing the operation, and a unit for selectively operating the voltage applying unit and the check unit. 3. The charging means applies a voltage of a predetermined polarity to the data signal line, and the inspection means is in a selected state when a voltage pulse or a current pulse of a predetermined level is not generated in the data signal line. The active matrix liquid crystal display device according to claim 1, wherein the pixel is determined to be abnormal. 4. The active matrix liquid crystal display element according to claim 1, wherein the charging means and the inspection means are formed on the one or the other substrate.