JPH1114556A - Method and apparatus for inspection of tft liquid-crystal panel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To discriminate the OFF-defect of a thin-film transistor(TFT) by a simple contrivance in an all-over turning-on inspection before a driver IC is attached. SOLUTION: While a common TFT ON-test signal is being applied to all gate bus lines which are exposed on the short side 10b of a liquid-crystal substrate 10, a common display test signal is applied to all data bus lines which are exposed on the long side 16a of the liquid-crystal substrate 10, and the display state of all pixels on the liquid-crystal substrate 10 is inspected. At this time, the level of the display test signal is made different between the active period and the inactive period of the TFT ON-test signal. In the case of a TFT in which an OFF-defect is generated, a pixel voltage is rewritten in the inactive period of the TFT ON-test signal, and the display level of a screen is changed. Consequently, when its change is confirmed visually, a defective pixel can be discriminated easily.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin film transistor (TFT) for a switching element.
Inspection method and device for an active matrix type liquid crystal panel (hereinafter, referred to as TFT liquid crystal panel) using the method, and particularly, an inspection method called “solid lighting inspection” performed at a stage before mounting a driver IC and an apparatus therefor About.

2. Description of the Related Art A TFT liquid crystal panel controls a liquid crystal sandwiched between a pixel electrode and a counter electrode by controlling a voltage (hereinafter referred to as a pixel voltage) written in a capacitor between the two electrodes. This is to obtain a display gradation.
It has a feature that accurate pixel voltage can be written by switching operation of a TFT and a delicate halftone can be displayed, and is widely used in various display devices including personal computers. However, on the other hand, it also has the disadvantage of low yield due to TFT manufacturing defects,
There is a need to provide useful technologies that contribute to yield improvement.

[0003]

2. Description of the Related Art In general, the yield of a TFT liquid crystal panel is dominated by a rubbing step and a bonding step among the steps before mounting a driver IC. This is because in the rubbing process, the alignment film is easily rubbed, which may cause poor alignment or light leakage, or the TFT or the alignment film is liable to be broken by abrasion charging. Is likely to occur. If the TFT liquid crystal panel before the driver IC is mounted is referred to as a liquid crystal substrate for the sake of convenience, defects in the liquid crystal substrate have been screened by a technique called "solid lighting inspection".

In FIG. 8, reference numeral 1 denotes a liquid crystal substrate. The liquid crystal substrate 1 has a gate bus line and a data bus line intersectingly arranged on one of two glass plates and a TFT at each intersection.
And a liquid crystal electrode are formed, and a common electrode is formed on the other glass plate. In the figure, one data bus line 2, one gate bus line 3, a TFT 4, and a liquid crystal electrode 5 are provided.
Are representatively shown. The ends of the gate bus lines and the data bus lines are exposed on at least two sides of the liquid crystal substrate 1, respectively. TAB (tapeautomate
d bonding), and the driver IC is not yet mounted at this stage.

In the conventional solid lighting test, a common TFT ON test signal Sg is applied to all the gate bus lines,
A common display test signal Sd is applied to all data bus lines. Note that the potential of the common electrode (Vco
m) is omitted. One cycle Tg of Sg substantially corresponds to the cycle of the horizontal scanning frequency of the liquid crystal substrate 1, for example, 60H
For a display image of z, Tg is 16.6 ms. Sg
Is set to a level sufficiently exceeding the threshold value of the TFT 4, and the TFT 4 is turned on during this active period. On the other hand, Sd is set to a potential level corresponding to any one display gradation (typically, a black level or a white level), and at a period of Tg around Vcom to prevent liquid crystal deterioration. AC drive is performed alternately for positive and negative.

When the gradation of Sd is set to the black level, the liquid crystal substrate 1
The entire surface of the liquid crystal substrate 1 is displayed in black, and when the white level is set, the entire surface of the liquid crystal substrate 1 is displayed in white. Therefore, the defective pixel looks white in the former case and the defective pixel looks black in the latter case, so that the quality of the liquid crystal substrate 1 can be determined based on the degree of the defect.

[0007]

However, in such a conventional solid lighting inspection, the off defect of the TFT (incomplete off state; specifically, a state in which the source and drain are connected with a small resistance value). If there is, the liquid crystal substrate 1
There is a problem that this defect cannot be found from the display state of (1).

That is, in the case of a normal TFT, the TFT is turned on during the active period of Sg, the level of Sd is written to the pixel electrode 5, and turned off simultaneously with the fall of Sg until the next rise of Sg. The write potential is maintained, but in the case of a TFT having an off defect, Sg
Does not enter the off state even if falls, so that Sd is continuously written to the liquid crystal electrode 5. In each case, the display state of the liquid crystal substrate 1 is exactly the same, and the normal TF
It is indistinguishable between T and a TFT having an off defect.

The off-defect of a TFT can be identified by applying Sg sequentially while selecting gate bus lines line by line instead of applying Sg to all gate bus lines at once. For example, when Sg is applied to the gate bus line in the i-th row and a pixel other than the i-th row is displayed (Sd level), it can be identified that the TFT of the pixel has an off defect. .

However, for this purpose, it is necessary to make electrical contact with each of the gate bus lines of the liquid crystal substrate 1. However, since the pitch of the gate bus lines is extremely narrow, the machining accuracy of the contact jig is required. In addition, the alignment accuracy must be sufficient, which ultimately leads to an increase in inspection cost. Therefore, the present invention provides a driver I
An object of the present invention is to identify an off defect of a TFT by a simple device in a solid lighting inspection before attaching C.

[0011]

The present invention provides a TFT common to all gate bus lines exposed on the short side of a liquid crystal substrate.
When applying a common display test signal to all data bus lines exposed on the long side of the liquid crystal substrate while applying the ON test signal, when inspecting the display state of all the pixels of the liquid crystal substrate, The level of the display test signal is different between the active period and the inactive period of the TFT ON test signal.

For convenience of explanation, the levels of the display test signal during the active period of the TFT ON test signal are represented by Va and TF.
Assuming that the level of the display test signal during the inactive period of the T-on test signal is Vb, in the case of a normal TFT,
Since the pixel voltage (Va) written during the active period of the TFT-on test signal is maintained during the inactive period of the TFT-on test signal, the display level of the screen corresponds to Va, but an off defect occurs. In the case of TFT,
Since the pixel voltage is rewritten to Vb in the inactive period of the TFT ON test signal, the display level of the screen changes from Va to Vb. Therefore, by visually confirming this change, a defective pixel can be easily identified.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 and FIG. 2 are views showing one embodiment of a method and an apparatus for inspecting a TFT liquid crystal panel according to the present invention. In FIG. 1, reference numeral 10 denotes a liquid crystal substrate (corresponding to a conventional liquid crystal substrate 1) before a driver IC is mounted, and reference numeral 11 denotes an electrical connection to all data bus lines exposed on the long side 10a of the liquid crystal substrate 10. Data contacts, 12
Is a gate contact electrically connected to all gate bus lines exposed on the short side 10b of the liquid crystal substrate 10. Although the data contact 11 and the gate contact 12 are separated from the liquid crystal substrate 10, this is convenient for illustration.

Reference numeral 13 denotes a gate signal generator, and reference numeral 14 denotes a data signal generator. These signal generators 13, 14
Is for generating a test signal synchronized with a predetermined timing signal (horizontal / vertical synchronizing signal or clock signal corresponding to the display signal of the liquid crystal substrate 10) and applying it to the gate contact 11 and the data contact 12. Yes, the gate signal generator 13 and the gate contact 12 integrally constitute "first means" described in the claims,
Also, the data signal generator 14 and the data contact 1
1 is an integral part of the "second means" described in the claims.
And "third means".

The TFT on test signal Sg applied from the gate signal generator 13 to the gate contact 12 is the same as that of the conventional example, but the display test applied from the data signal generator 14 to the data contact 11 is performed. Signal Sd '
Differs from the conventional example in the following points. That is, FIG. 2 is a waveform diagram of Sg and Sd 'of the present embodiment. In the same manner as in the conventional example, Sg represents an active period (a period of a level exceeding the threshold value of the TFT) and an inactive period in one cycle Tg. (Period below the threshold of TFT)
Sd ′ is the level of the active period of Sg (for convenience, V
Level of inactive period same as a) (Vb for convenience)
And are different. It is natural that AC driving is performed to prevent the deterioration of the liquid crystal. Va and Vb in this embodiment are also positive and negative with a cycle of Tg around com (a minus sign after Va and Vb indicates a negative polarity). (Representing).

In such a configuration, in the case of a normal TFT, the TFT is turned on during the active period of Sg and becomes Va.
Is written to the pixel electrode and then turned off during the inactive period of Sg, and the written Va is held as it is. Therefore, Vb during the inactive period of Sg
Has no effect on the display. For example, if Va is a black level, the screen display remains black.

On the other hand, in the case of a TFT having an off defect, the pixel is not completely turned off during the inactive period of Sg.
To Vb (or a level close to Vb). Therefore, for example, if Va is a black level and Vb is a white level, the screen display changes from black to white at the defective portion, so that the defect can be easily identified.

In the example of FIG. 2, the active period of Sg
Sd 'during the period of Va, and Sd' during the inactive period as Vb.
And Va> Vb> Vcom (Va on the negative polarity side
<Vb <Vcom), but is not limited to this. Required
Is equal to the level Va of Sd 'during the active period of Sg.
If the level Vb of Sd 'during the active period is different
For example, as shown in FIG. 3, Va> Vb = Vco
m (Va <Vb = Vcom on the negative polarity side)
Then, as shown in FIG. 4, Va and Vb are exchanged (that is,
Sd 'during the active period of Sg is Vb,
Va) may be used for Sd 'in the active period, or as shown in FIG.
Va> Vb = Vcom (Va <Vb = on the negative polarity side)
Vcom). Or ignore the degradation of the liquid crystal
If the inspection time is as short as possible, see Fig. 6 and Fig. 7
Thus, Va> Vb> V in all the cycles without performing the AC drive.
com or Va> Vb = Vcom (Va in FIG. 7)_(-)<
Vb _(-)<Vcom or Va_(-)<Vb_(-)= Vco
m).

Also, from the viewpoint of obtaining a large contrast ratio, the gradation levels corresponding to Va and Vb are naturally
One should be the maximum gradation level and the other should be the minimum gradation level, but if sufficient discrimination performance can be obtained,
An appropriate halftone may be assigned to Va or Vb.

[0020]

According to the present invention, the off-defects can be obtained simply by making the level of the display test signal applied to all the data bus lines different between the active period and the inactive period of the TFT-on test signal. TFT that caused
Pixel can be identified without fail, and a defective liquid crystal substrate can be reliably screened at the solid lighting inspection stage.

As a result, an extremely advantageous effect can be obtained in the field of TFT liquid crystal panels that the manufacturing cost can be largely suppressed by avoiding unnecessary disposal of the driver IC. The reason is that in the prior art, the driver I
TFT with off-defect only in inspection after attaching C
The reason for this is that it was not possible to find out, and it took considerable time and effort to remove the driver IC once attached, so that the entire liquid crystal unit had to be discarded unwillingly.

[Brief description of the drawings]

FIG. 1 is a conceptual configuration diagram of one embodiment.

FIG. 2 is a signal waveform diagram of one embodiment.

FIG. 3 is another signal waveform diagram of the embodiment (part 1).

FIG. 4 is another signal waveform diagram of the embodiment (part 2).

FIG. 5 is another signal waveform diagram of the embodiment (part 3).

FIG. 6 is another signal waveform diagram of the embodiment (part 4).

FIG. 7 is another signal waveform diagram (part 5) of the embodiment.

FIG. 8 is a conceptual diagram of a conventional solid lighting inspection.

[Explanation of symbols]

 Sg: TFT ON test signal Sd ': Display test signal 2: Data bus line 3: Gate bus line 10: Liquid crystal substrate 10a: Long side 10b: Short side 11: Data contact (second means. Means 12: Gate contact (first means) 13: Gate signal generator (first means) 14: Data signal generator (second means; third means)

Continued on the front page (51) Int.Cl. ⁶ Identification symbol FI G09F 9/35 302 G09F 9/35 302

Claims (2)

[Claims] 1. A display common to all data bus lines exposed on the long side of the liquid crystal substrate while applying a common TFT ON test signal to all gate bus lines exposed on the short side of the liquid crystal substrate. In a method of applying a test signal and inspecting a display state of all pixels on the liquid crystal substrate, a level of the display test signal is made different between an active period and an inactive period of the TFT-on test signal. Inspection method for TFT liquid crystal panel. 2. A first means for applying a common TFT on test signal to all gate bus lines exposed on the short side of the liquid crystal substrate, and all data exposed on the long side of the liquid crystal substrate. A second means for applying a common display test signal to a bus line;
3. A TFT liquid crystal panel inspection apparatus, comprising: third means for making an active period and an inactive period of an FT-on test signal different.