JPH0792490A - Method for inspecting liquid crystal display element with thin-film transistor - Google Patents

Abstract

PURPOSE:To inspect liquid crystal characteristics and spot defects before packaging of a driving circuit by separately wiring common electrode lines and additive capacitance lines and applying a specific voltage to the common electrode lines and the additive capacitance lines. CONSTITUTION:The common electrode lines 9 and additive capacitance lines 10 of the liquid crystal display element with thin-film transistors(TFTs) in the course of a production line are formed as the separate wirings which are not electrically connected. Further, the additive capacitance lines 10 for each of respective pixels are shorted and the source wirings and gate wirings for each of the respective lines are respectively short circuited. While the TFTs 6 are held off, the voltage shifted in phase by 180 deg. is applied to the common electrode lines 9 and the additive capacitance lines 10. Then, the voltage based on the capacity ratio of a liquid crystal capacitance CLC and an additive capacitance CS is eventually directly applied on the liquid crystal layer 4. The common voltage is eventually applied to all the pixels according to such driving method and, therefore, a raster display is obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for inspecting a liquid crystal display device with a thin film transistor, and more particularly to a method for inspecting a liquid crystal display device with a thin film transistor for inspecting liquid crystal characteristics and point defects.

[0002]

2. Description of the Related Art In recent years, a matrix type liquid crystal display device incorporating a liquid crystal display element in which a thin film transistor (hereinafter, also referred to as a TFT) is added to each pixel has a high contrast display without crosstalk due to a switching action of the TFT. Therefore, use as an image / character display device is being promoted.

Generally, in the manufacturing line of the liquid crystal display device as described above, the liquid crystal characteristics of the liquid crystal display element with a thin film transistor (specifically, voltage holding characteristics, VT characteristics, etc.)
Is being inspected. As is well known, the voltage holding characteristic is a characteristic of the liquid crystal layer based on a quantitative value of how much the liquid crystal layer can hold the voltage from the time when the TFT is switched off, and the VT characteristic is , Refers to the characteristic of the liquid crystal layer that represents the transmittance with respect to the applied voltage.

Conventionally, as a method of inspecting a liquid crystal display device with a thin film transistor, a liquid crystal display device with a thin film transistor having a structure and an equivalent circuit for each pixel shown in FIGS. 3 (A) and 3 (B) is manufactured. A liquid crystal display device for quality control (as is clear from FIGS. 4 (A) and 4 (B)) whose configuration and equivalent circuit for each pixel can be represented by FIGS. 4 (A) and 4 (B), respectively. , A liquid crystal display device with no TFT added) is manufactured in the same lot.
An inspection method is known in which a voltage is directly applied to the liquid crystal layer of the liquid crystal display element for quality control to inspect its liquid crystal characteristic, so that the liquid crystal characteristic of the liquid crystal element with a thin film transistor is indirectly inspected. . In addition, as shown in FIG.
In (B), 1 is a transparent insulating substrate (eg, glass substrate), 2 is a color filter, 3 is a common electrode, 4 is a liquid crystal layer, 5 is a transparent insulating substrate (eg, glass substrate), 6 is a thin film transistor (TFT), and 6a. Is a source electrode of the TFT 6, 6b is a drain electrode of the TFT 6, 6c is a gate electrode of the TFT 6, 7 is a pixel electrode, 8 is an additional capacitance, 8a is an additional capacitance electrode, 9 is a common electrode line, 10 is an additional capacitance line, C _LC
Represents the capacity of the liquid crystal layer 4, that is, the liquid crystal capacity, and C _S represents the additional capacity. In FIGS. 4A and 4B, 11 is a transparent insulating substrate (eg, glass substrate), 12 is a common electrode, 13 is a liquid crystal layer, 14 is a transparent insulating substrate (eg, glass substrate), 15 is a pixel electrode, C _LC represents the capacity of the liquid crystal layer 13, that is, the liquid crystal capacity.

[0005]

However, according to the above-mentioned conventional inspection method, the number of steps for manufacturing the quality control liquid crystal display element is increased, and the quality control liquid crystal display element is inspected, so that the thin film transistor Since the liquid crystal display element is indirectly inspected, there is a problem that the inspection result does not always match the liquid crystal characteristics of the liquid crystal display element with a thin film transistor.

Usually, most of the defects of the liquid crystal display device with a thin film transistor are due to point defects, but conventionally, the inspection of this point defect is performed only after the drive circuit of the liquid crystal display device with a thin film transistor is mounted. Therefore, if a point defect is found, an expensive drive circuit is wasted. As another example of this point defect inspection method, before mounting the drive circuit, all electrode terminals of the liquid crystal display element with a thin film transistor (usually consisting of several thousand terminals and having a pitch of 10
It is 0 μm to 300 μm. ), A probe (needle) is set up for inspection, but this inspection method is becoming difficult to implement as the definition becomes higher (pitch 100 μm or less).

The present invention has been made to solve the above problems, and an object thereof is to be able to inspect the liquid crystal characteristics of a liquid crystal display element with a thin film transistor itself and to mount it before mounting a drive circuit. An object of the present invention is to provide a method for inspecting a liquid crystal display device with a thin film transistor, which can inspect a point defect.

[0008]

In order to solve the above-mentioned problems, a method of inspecting a liquid crystal display device with a thin film transistor according to the present invention uses a common electrode line and an additional capacitance line as separate wiring, and the common electrode line and the additional capacitance line are added. It is characterized in that a voltage determined by a capacitance ratio of the liquid crystal capacitance and the additional capacitance is directly applied to the liquid crystal layer by applying a voltage having a phase shift of 180 ° to the capacitance line.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS.

FIG. 1A and FIG. 1B are configuration diagrams of respective pixels of a liquid crystal display device with a thin film transistor for explaining an inspection method of a liquid crystal display device with a thin film transistor according to one embodiment. The equivalent circuit diagram is shown. In addition, FIG. 2 is a plan view of the entire liquid crystal display element with a thin film transistor for explaining the above inspection method. In addition, in FIG. 1 (A), (B) and FIG.
3A and 3B are the same as those shown in FIGS. 3A and 3B.
Represents the same thing as.

In carrying out this inspection method, FIG.
As shown in (A) and (B), the common electrode line 9 and the additional capacitance line 10 of the liquid crystal display device with a thin film transistor in the manufacturing line are separated from each other by electrically connecting them to each other.
The common electrode line 9 and the additional capacitance line 10 as shown in (A) and (B) are not electrically connected to form the same wiring.

Further, as shown in FIG. 2, the additional capacitance line 10 for each pixel is short-circuited, and the source line 16 and the gate line 17 for each line are also short-circuited.

While holding the thin film transistor 6 in the off state, the common electrode line 9 and the additional capacitance line 10 are
Voltages 180 ° out of phase are applied. Here, in order to hold the thin film transistor 6 in the off state, a reverse DC bias voltage may be applied to the source electrode 6a and the gate electrode 6b. However, during the liquid crystal process,
Since the source line 16 and the gate line 17 are usually connected to protect the thin film transistor 6 from static electricity, the thin film transistor 6 is kept in an off state without special application of the bias voltage as described above. be able to. Therefore, the liquid crystal layer 4 has a liquid crystal capacitance C _LC.
The voltage based on the capacitance ratio between the capacitance and the additional capacitance C _S is directly applied. For example, when the liquid crystal capacitance C _LC is 1 pF and the additional capacitance C _S is 0.8 pF and a voltage of 10 V is applied between the common electrode 3 and the additional capacitance electrode 8a, the liquid crystal layer 4 has 4.4 V (= 10 V). A voltage of × 0.8 / (1 + 0.8) will be applied. According to such a driving method, since a common voltage is applied to all pixels, raster display is performed.

Next, the inspection method will be described for each main inspection item.

Inspection of voltage holding characteristics Using a voltmeter having an extremely high impedance, a voltage having a 180 ° phase shift is applied to the common electrode line 9 and the additional capacitance line 10 as described above, and then the application is released. Monitor the voltmeter.

Inspection of Point Defects 1) Inspection of Point Defects Due to Short-Circuit between Pixel Electrode 7 and Source Wiring 16 It is inspected whether the brightness of the pixel is changed by changing the source voltage.

2) Inspection of Point Defect Due to Short Circuit between Pixel Electrode 7 and Gate Wiring 17 It is inspected whether the brightness of the pixel is changed by changing the gate voltage.

3) Inspection of Point Defects Due to Short Circuit between Pixel Electrode 7 and Additional Capacitance Line 10 Since the voltage applied to the liquid crystal layer 4 becomes large, the pixels turn black quickly.

4) Inspection of Point Defect Due to Short Circuit between Pixel Electrode 7 and Common Electrode 3 The pixel does not become black because no voltage is applied to the liquid crystal layer 4.

5) Inspection of Point Defect Due to Defect of Thin Film Transistor 6 When a point defect which is not due to any of the above point defects 1) to 4) occurs, it is judged as a point defect due to a defect of the thin film transistor 6.

As described above, according to the inspection method of this embodiment, it becomes possible to inspect the liquid crystal characteristics of the liquid crystal display element with a thin film transistor itself, and it is possible to inspect point defects without mounting a drive circuit. Like Further, since the inspection of the point defect can be performed without raising the probe, it becomes possible to easily inspect the high-definition liquid crystal display element. Although the drive method according to the present embodiment can only perform raster display as described above, when the drive circuit is finally driven, the same signal is input to the common electrode 3 and the additional capacitance electrode 8a as in the conventional case.

Although the above-described embodiment is an inspection method for a liquid crystal display element with a thin film transistor, which has a structure in which an additional capacitance is provided independently, which is generally used, the present invention is not limited to this. In addition, the liquid crystal display element with a thin film transistor of the type in which the additional capacitance line is omitted and the additional capacitance is formed by using the gate wiring of the previous pixel can be used as the inspection target. The (additional capacitance signal) and the source signal can be inspected by inputting them by 180 ° out of phase with the common signal.

[0023]

As described above, according to the present invention, the common electrode line and the additional capacitance line are separated from each other, and the common electrode line and the additional capacitance line are applied with a voltage with a phase difference of 180 °. Since the voltage determined based on the capacitance ratio between the liquid crystal capacitance and the additional capacitance is directly applied to the liquid crystal layer, it is possible to inspect the liquid crystal characteristics of the liquid crystal display element with a thin film transistor itself and before mounting the drive circuit. Point defects can be inspected.

[Brief description of drawings]

FIG. 1 is a configuration diagram and an equivalent circuit diagram of each pixel of a liquid crystal display element with a thin film transistor for explaining an inspection method of a liquid crystal display element with a thin film transistor according to an embodiment.

FIG. 2 is a plan view of the entire liquid crystal display element with the thin film transistor.

FIG. 3 is a configuration and an equivalent circuit of each pixel of a liquid crystal display device with a thin film transistor for explaining a conventional method for inspecting a liquid crystal display device with a thin film transistor.

FIG. 4 is also a configuration and an equivalent circuit of each pixel of a liquid crystal display element for quality control, for explaining a conventional method.

[Explanation of symbols]

4 liquid crystal layer 6 thin film transistor 9 common electrode line 10 additional capacitance line C _LC liquid crystal capacitance C _S additional capacitance

Claims (1)

[Claims] 1. A capacitance ratio between a liquid crystal capacitance and an additional capacitance is obtained by forming the common electrode line and the additional capacitance line as separate wirings, and applying a voltage with a 180 ° phase shift to the common electrode line and the additional capacitance line. A method for inspecting a liquid crystal display device with a thin film transistor, characterized in that a voltage determined based on the liquid crystal layer is directly applied to the liquid crystal layer.