JPH0774943B2 - Inspection method for active matrix array - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for inspecting an active matrix array in which a switching element is arranged in each picture element of a liquid crystal display device.

2. Description of the Related Art In recent years, as the number of picture elements of liquid crystal display devices has increased, the number of scanning lines has increased, and in the conventionally used simple matrix type liquid crystal display device, display contrast and response speed decrease, so An active matrix type liquid crystal display device in which a switching element is arranged in the inside is being used.
Above all, the active matrix array using amorphous silicon, which is used as a constituent element of the active matrix type liquid crystal display device, has a number of features such as the use of an inexpensive glass substrate as a substrate, and thus has attracted particular attention. However, in the active matrix array, it is necessary to arrange tens of thousands or more switching elements in a large area, and it is difficult to manufacture all the switching elements without defects. Therefore, it is necessary to inspect the active matrix array for defects and the generation position, and the inspection method is becoming more and more important.

FIG. 7 is a partial equivalent circuit diagram of the active matrix array. In FIG. 7, G _i (i = 1 to 4) is a gate signal line, S _j (j = 1 to 4) is a source signal line, and T _ij (i = 1).
˜4, j = 1 to 4) is a thin film transistor, and C _ij is a pixel electrode (i = 1 to 4, j = 1 to 4). Hereinafter, items having the same numbers and symbols have the same or similar contents or configurations.

A conventional active matrix array inspection method will be described below with reference to the drawings. 8 and 9
The figure is an explanatory view for explaining a conventional method for inspecting an active matrix array. In FIGS. 8 and 9, 1 is a resistance value measuring means, 2 and 3 are probes, 4 is a source / drain short circuit defect, and 5 is a gate / drain short circuit defect. First, an inspection method for detecting the source / drain short-circuit defect 4 will be described with reference to FIG. First source signal line
The S _{1 to} S ₄ are short-circuited as shown in FIG. 8 and the probe 2 is pressed. Next, the probe 3 is pressed against the drain electrodes of the respective thin film transistors in order, and the probe 2
Measure the resistance between 3 points. The operation is the thin film transistor T
_Go from ₁₁ to T _{44 in} order. The resistance value of a normal thin film transistor in which a short circuit defect does not occur becomes a very large value. When the probe 3 is pressed against the drain electrode of the thin film transistor T ₂₂ , the resistance value measured by the resistance value measuring means 1 becomes lower than the normal value, so that the short circuit defect 4 is detected.

Next, an inspection method for detecting a gate / drain short circuit defect will be described with reference to FIG. First, the gate signal lines G _{1 to} G ₄
Are short-circuited as shown in FIG. 9, and the probe 2 is pressed.
Next, the probe 3 is pressed against the drain electrodes of the thin film transistors in order, and the resistance value measuring means 1 measures the resistance value between the probes 2 and 3. The above operation is sequentially performed from thin film transistors T ₁₁ to T ₄₄ . When the probe 3 is pressed against the drain electrode of the thin film transistor T ₂₁ , the resistance value measured by the resistance value measuring means 1 becomes lower than the normal value, so that a short circuit defect is detected.

Problems to be Solved by the Invention However, since the probe is used in the above inspection apparatus, it is necessary to directly contact the probe with the drain terminal of the thin film transistor or the pixel electrode connected to the drain terminal, which may damage the display surface. is there. In addition, defect detection is likely to occur due to poor contact between the probe and the drain terminal. Moreover, since it is necessary to inspect while moving the probe, it takes a huge amount of time to position the probe, and when the number of picture elements exceeds tens of thousands, it is impossible to inspect all defects in reality. Was there.

In view of the above problems, it is an object of the present invention to provide a method for inspecting an active matrix array that can easily detect a defective portion of the active matrix array in a non-contact manner.

Means for Solving the Problems Conventionally, a thin film transistor using amorphous silicon has a strong photoreactivity, and the photoreactivity deteriorates the display quality of a liquid crystal display panel. Therefore, efforts are made to reduce it as much as possible.

The inventors have found that thin film transistors are regularly arranged in a matrix on an active matrix type liquid crystal display panel and are suitable for sequentially irradiating light, and a thin film transistor using amorphous silicon has high photoreactivity and short circuit defects. Paying attention to the fact that it is necessary to detect only the presence or absence of the above, and wondering whether the photoexcitation current due to the photoreactivity can be positively utilized, the inspection method of the active matrix array of the present invention was established.

The inspection method of the active matrix array of the present invention is
A signal is applied to at least one of a source signal line and a gate signal line of the array, light is applied to a thin film transistor connected to the signal line to which the signal is applied, and the source signal is generated by exciting the thin film transistor. The inspection is performed by detecting the signal output to the line or the gate signal line.

Function The present invention selectively irradiates a thin film transistor using amorphous silicon with light rays. Then, a photoexcitation current is generated in the thin film transistor. That is, even when the thin film transistor is in the off state, a current can be made to flow between the source and the drain, and a defect in the active matrix array can be detected by detecting the current.

Embodiment An inspection method for an active matrix array according to an embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is an explanatory diagram for explaining a method of inspecting an active matrix array according to the first embodiment of the present invention. In FIG. 1, 5 is a gate-drain short-circuit defect of the thin film transistor T ₂₁ , 6 is signal applying means, 7 is signal detecting means, and 8
Is a light irradiation means, and 9 is a light beam. This ray 9 has a wavelength of 2
Those having a size of μm or less are preferable, those having a visible wavelength are suitable for the time being, and a Ne-He laser or the like is most suitable. Further, FIG. 1 shows that the gate signal lines G _{1 to} G ₄ are short-circuited and the source signal lines S _{1 to} S ₄ are short-circuited. First, the signal applying means 6 applies a non-selection voltage to the gate signal line. The non-selection voltage is a voltage for turning off the thin film transistor connected to the gate signal line to which the non-selection voltage is applied, and the selection voltage is an on state of the thin film transistor connected to the gate signal line to which the selection voltage is applied. And the voltage. Next, the thin film transistor T ₁₁ is irradiated with the light beam 9 by the light irradiation means 8. The state at this time is shown in FIG. FIG. 2 is a partially enlarged view of the active matrix array. In FIG. 2, 10 is a pixel electrode,
11 is a light spot by the light ray 9. As described above, the signal detecting means 7 detects whether or not a current flows through the source signal line in the state where the thin film transistor is irradiated with the light beam 9.

The above operation is sequentially performed for each thin film transistor. When the thin film transistor is irradiated with the light beam 9, a photoexcitation current is generated. However, when the thin film transistor is normal, the signal detecting unit 7 does not detect the current because there is no path through which the current flows. However, when the thin film transistor T ₂₁ is irradiated with a light beam, the signal detecting means 7 has a source signal line.
S ₁ → thin film transistor T ₂₁ → short circuit defect 5 → gate signal line G
_The current flowing in the ₂ direction is detected. Therefore it can be detected that the short-circuit defect 5 has occurred in the thin film transistor T _21.

A second embodiment of the present invention will be described below with reference to the drawings. FIG. 3 is an explanatory diagram for explaining the method for inspecting the active matrix array in the second embodiment of the present invention, and shows that two driving transistors are formed in each pixel of the liquid crystal display panel. . Such a liquid crystal display panel is described in JP-A-59-242876. In FIG. 3, TS _ij · TM _ij (i = 1 to 4, j = 1
4) are thin film transistors, and P _ij are pixel electrodes. Further, in FIG. 3, the gate signal lines G _{1 to} G ₅ are short-circuited and the source signal lines S _{1 to} S ₅ are short-circuited. In the defect detection method for the liquid crystal display panel described above, first, a non-selection voltage is applied to the gate signal line by the signal applying means 6. Then, the light irradiating means 8 irradiates the thin film transistor TS ₁₁ with the light beam 9, and at the same time, the signal detecting means 7 detects whether or not a current flows through the source signal line. The above operation is sequentially performed for each thin film transistor. FIG. 4 is a partially enlarged view of the active matrix array, and shows that the thin film transistor TM ₃₂ is irradiated with the light beam 9 as an example of the above. If the thin film transistors TS ₃₂ and TM ₃₂ are normal, the light detecting means 7 does not generate a current path due to the photoexcitation current even if the light beam 9 is applied only to the thin film transistor TS _{32 or} only to the thin film transistor TM _32. No current is detected. However, since the short-circuit defect 5 has occurred, when the thin film transistor TS ₃₂ is irradiated with the light beam 9, a current flows through the source signal line S ₂ → thin film transistor TS ₃₂ → short-circuit defect 5 → gate signal line G ₃ . When the thin film transistor TM ₃₂ is irradiated with the light beam 9, the source signal line S ₃ → thin film transistor TM ₃₂ → pixel electrode P ₃₂ → short circuit defect 5 → gate signal line G ₃ flowing current is detected by the signal detecting means 7. Therefore, it is detected that the thin film transistor TS ₃₂ or TM ₃₂ has a short circuit defect. In the above-mentioned configuration, the current is detected by the signal detecting means regardless of which of the thin film transistors TS ₃₂ and TM ₃₂ is irradiated with light.
It is impossible to determine whether the short-circuit defect of _{32 is} the short-circuit defect of TM _32. However, this is because the source signal lines S ₂ and S ₃ are separated and each of them is connected to the signal detection means 7 and can be switched. Obviously, it can be easily determined.

Next, a third embodiment of the present invention will be described with reference to the drawings. FIG. 5 is an explanatory view for explaining the active matrix inspection method in the third embodiment of the present invention. In FIG. 5, 12 is a source signal line voltage applying means, and 13 is a source-drain short-circuit defect of the thin film transistor TS ₂₂ . Further, in FIG. 5, gate signal lines G _{1 to} G ₅ are short-circuited and connected to the signal applying means 6, source signal lines S ₁ and S ₃ and S ₅ are short-circuited and connected to the signal detecting means 7, source signal line S ₂ and It is shown that S ₄ is short-circuited and connected to the source signal line voltage applying means 12. In the defect detecting method, first, a non-selection voltage is applied to the gate signal line by the signal applying means 6, and a predetermined voltage is applied to the source signal lines S ₂ and S ₄ by the source signal line voltage applying means 12. For example, this predetermined voltage is a positive voltage of 20V. Then, the light irradiating means 8 irradiates the thin film transistor TS ₁₁ with the light beam 9, and at the same time, the signal detecting means 7 detects whether or not a current flows through the source signal line. The above operation is sequentially performed for each thin film transistor. Now, even if the thin film transistor TM ₂₂ is irradiated with the light beam 9, if the thin film transistor TS ₂₂ is normal, a current path due to the photoexcitation current does not occur, and therefore no current is detected by the signal detection means 7. However, since the short-circuit defect 13 occurs, a current path of the source signal line S ₂ → short-circuit defect 13 → pixel electrode P ₂₂ → thin film transistor TM ₂₂ → source signal line S ₃ occurs, and the current is detected by the signal detection means 7. To be done. Therefore, it is possible to detect that the short circuit defect 13 has occurred in the thin film transistor TS ₂₂ .

In the third embodiment, in order to detect the source / drain short-circuit defect that has occurred in the thin film transistor TM ₂₂ ,
The source signal line voltage application means 12 and the signal detection means 7 are replaced with each other, a positive voltage is applied to the source signal line S ₃ , and the light irradiation means 8 is applied.
To irradiate the thin film transistor TS ₂₂ with the light beam 9. Then, the source signal line S ₃ → thin film transistor TM ₂₂ → pixel electrode
A current path of P ₂₂ → short circuit defect → source signal line S ₃ occurs.

Therefore, the short circuit defect of the thin film transistor TM ₂₂ can be detected.

Further, in the above embodiment, the signal detecting means 7 is used, but as shown in FIG. 5, the pickup resistor 14 is connected and the voltage across the pickup resistor 12 is detected by the voltage detecting means 15 to generate a current. You may judge whether it flowed.

Further, in this embodiment, one thin film transistor is selectively irradiated with a light beam, but a plurality of transistors are irradiated with a light beam at a time, and after detecting a block having a defective thin film transistor, one thin film transistor is selectively irradiated. Obviously, the thin film transistor may be irradiated with the light beam 9 to detect the defective thin film transistor.

As described above, the present invention uses the light irradiation means to selectively irradiate a thin film transistor using amorphous silicon with light to generate a photoexcitation current, and thus in a non-contact manner without using a probe as in the conventional case. Since the defect position can be detected, there is no possibility of damaging the display surface of the liquid crystal display panel.

Further, since it is only necessary to scan the thin film transistor with the light beam, it is possible to inspect the liquid crystal display panel at a very high speed without requiring the probe positioning time as in the conventional case.

From the above, the effect is great.

[Brief description of drawings]

FIG. 1 is an explanatory view of an inspection method of an active matrix array in the first embodiment of the present invention, FIG. 2 and FIG.
FIG. 7 is a partially enlarged view of the active matrix array, FIG. 3 is an explanatory view of an inspection method of the active matrix array in the second embodiment of the present invention, and FIG. 5 is an active matrix in the third embodiment of the present invention. FIG. 6 is an explanatory diagram of an array inspection method, FIG. 6 is an explanatory diagram of an active matrix array inspection method of the present invention, FIG. 7 is an equivalent circuit diagram of the active matrix array, and FIGS. 8 and 9 are conventional active matrix arrays. FIG. 6 is an explanatory diagram of the inspection method of FIG. G _{1 to} G ₄ …… Gate signal line, S _{1 to} S ₄ …… Source signal line, T
_{11 ~T 44, TS 11 ~TS 44} , TM 11 ~TM 44 ...... _{TFT, C 11 ~C 44, P 11} ~P 44 ...... picture element electrode, 1 ...... resistance measuring unit, 2,3 ...... Probe, 4,5,13 ... Short circuit defect, 6 ...
... Signal application means, 7 ... Signal detection means, 8 ... Light irradiation means, 9 ... Light rays, 10 ... Picture element electrodes, 11 ... Light spots, 12 ...
Source signal line voltage applying means, 12 ... Pickup resistance,
15: Voltage detection means.

Claims (1)

[Claims] 1. An active matrix array using amorphous silicon as a semiconductor of a thin film transistor, wherein a signal is applied to at least one of a source signal line and a gate signal line of the array, and the signal is applied. The thin film transistor connected to the signal line connected to the thin film transistor is irradiated with light, and the signal output when the thin film transistor is excited is detected by the signal detection means connected to the source signal line or the gate signal line. Matrix array inspection method.