JP3439038B2 - Inspection method and apparatus for liquid crystal display substrate - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inspection method and an inspection apparatus for electrically inspecting a liquid crystal display substrate used for a liquid crystal display panel or the like for defects. 2. Description of the Related Art As a liquid crystal display panel with a large number of pixels used for a liquid crystal television or the like, an active matrix type liquid crystal display panel has been put to practical use. In the active matrix system, a pixel electrode corresponding to a pixel is provided on a liquid crystal display substrate, and a switch using a thin film transistor is provided for each of the pixel electrodes.
A gate electrode and a source electrode of each thin film transistor arranged in a matrix form are connected to a gate line and a source line which are arranged in rows and columns vertically and horizontally, and a voltage is applied to the source lines and the gate lines. A voltage is applied to the corresponding pixel electrode by the combination of the above, and an electric field is applied to the liquid crystal molecules. In such a liquid crystal display substrate, it is necessary to perform a defect inspection such as disconnection or short circuit of a thin film transistor, a gate wiring, and a source wiring, for example, disclosed in Japanese Patent Application Laid-Open No. 5-264461. Figure 4
As described above, there is a method of irradiating light from above the electro-optical element 10 disposed to face the liquid crystal display substrate 1 and receiving the reflected light to inspect the presence or absence of a defect. That is, the substrate 2
A liquid crystal sheet or a Pockels crystal plate 10a whose optical properties change when an electric field is applied to a liquid crystal display substrate 1 which is a test object having a pixel electrode 5 provided thereon.
An electro-optical element 10 composed of a liquid crystal display substrate 1 and a thin film transparent electrode 10 c on the surface of the electro-optical element 10 are disposed between the pixel electrode 5 on the liquid crystal display substrate 1 and the thin film transparent electrode 10 c.
Apply voltage at. By doing so, the electric field generated by each pixel electrode 5 changes in accordance with the presence or absence of a defect in the liquid crystal display substrate 1 and the situation, so that the optical properties of the electro-optical element 10 change variously. 1
By observing the state in which the irradiation light from 2 is reflected by the light reflector 10b and received by the light receiver 13, the state of the change in the optical properties of the electro-optical element can be detected by the monitor 14, and as a result, The presence or absence and the state of the defect of the liquid crystal display substrate 1 can be known. [0004] However, the inspection apparatus for a liquid crystal display substrate shown in FIG. 4 has a problem in reliability and reproducibility of the inspection. [0005] The first problem is that the non-uniformity of the light intensity distribution of the irradiation light may reduce the reliability and reproducibility of the inspection result. In general, the light intensity distribution on the screen of the illuminated light beam has a different optical path length even if it can be regarded as a point light source, even if it is a parallel light beam. Further, in the device shown in FIG. 4, the light source 12 is inclined with respect to the liquid crystal display substrate 1 for receiving the reflected light, and the distance from the light source 12 on the liquid crystal display substrate 1 varies depending on the location. Ensuring uniformity of distribution becomes even more difficult. The non-uniformity of the light intensity distribution complicates the setting of a threshold value when making a pass / fail judgment from the light receiving level of the light receiver, necessitating a complicated correction such as a shading process in image processing, and the inspection result. This will reduce reliability and reproducibility. A second problem is that the electro-optical element 10 is structurally
In this case, the sensitivity of the surface of the liquid crystal display substrate 1 to the electric field must be lowered. Even if a Pockels crystal plate is used as the electro-optical element 10, the amount of polarization of the reflected light based on the magnitude of the electric field is small due to the structure, and when this amount of polarization is received by the light receiver 13 through the polarizing plate, The change is small. Therefore, a liquid crystal sheet is practically used as the electro-optical element 10. This liquid crystal sheet also needs to enclose the liquid crystal in a transparent case, and the transparent case keeps the liquid crystal, which is the electro-optical element 10, away from the surface of the liquid crystal display substrate 1. 0.3mm practically as a transparent case
A glass substrate having a thickness of about a certain thickness is required. Even if the surface of the transparent case is brought close to the surface of the liquid crystal display substrate 1 up to several tens of μm, the distance of the liquid crystal, which is the important electro-optical element 10, from the surface of the liquid crystal display substrate 1 is several It reaches 100 μm. As a result, the sensitivity of the liquid crystal in the transparent case to the electric field on the surface of the liquid crystal display substrate 1 decreases. Regardless of whether the electro-optical element 10 is a Pockels crystal plate or a liquid crystal sheet, the electric field sensitivity is reduced, the change in the amount of received light is reduced, and the reliability and reproducibility of the inspection remain low. SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and to provide a method and an apparatus for inspecting a liquid crystal display substrate having high reliability and reproducibility of inspection. [0008] The present invention that achieves the above object has the following matters specifying the invention. (1) In a method for inspecting a liquid crystal display substrate connected to a source line and a gate line arranged in a lattice pattern for defects of a liquid crystal display substrate, wherein a thin film transistor is provided for each pixel electrode, and the source electrode and the gate electrode of the thin film transistor are connected. The pixel electrodes arranged on the display substrate and the switch elements arranged on the detection substrate are arranged close to and opposed to each other, and a voltage is applied between the source electrode and the drain electrode of the switch elements, and the switch elements are A voltage is applied to both or one of the source line and the gate line of the corresponding pixel electrode, and a current value flowing through the switch element is detected at this time. (2) The voltage applied to the switch element is And applying a voltage to both or one of the source line and the gate line of the pixel electrode corresponding to the switch element. Characterized in that it is carried out in the order in synchronization, and the source electrode and the gate electrode of the thin film transistor provided with a thin film transistor for each (3) pixel electrode,
In an apparatus for inspecting a defect of a liquid crystal display substrate connected to a source wiring and a gate wiring arranged in a lattice, a switch element including a source electrode, a semiconductor, and a drain electrode is arranged corresponding to a pixel electrode of the liquid crystal display substrate. Means for applying a voltage to the pixel electrode from a source line and a gate line, and applying a voltage between the source electrode and the drain electrode. Means for applying voltage, and means for synchronizing voltage application to a pixel electrode to which a voltage is applied and voltage application to a switch element corresponding to the pixel electrode. In general, an N-channel type field effect transistor comprises a source electrode, a P-type semiconductor, a drain electrode and a gate electrode, and the gate electrode is joined to the P-type semiconductor via an insulating film. When a gate voltage is applied while a voltage is applied between the source electrode and the drain electrode, electrons are emitted from the source electrode to the gate electrode by the action of an electric field generated between the gate electrode and the P-type semiconductor and the drain electrode. Attracted electrons are present between the source electrode and the drain electrode, so that a current path is formed, and a current flows between the source electrode and the drain electrode. The magnitude of this current increases in proportion to the increase of the gate voltage, but saturates when it reaches a certain value. Each part of the field effect transistor as described above is replaced as follows, the pixel electrode corresponds to the gate electrode, and the insulating film between the gate electrode and the semiconductor has a small distance between the liquid crystal display substrate and the detection substrate. The air layer corresponds to this. When there is a defect such as disconnection or short circuit of the source wiring or gate wiring on the liquid crystal display substrate side or damage of the thin film transistor, a normal voltage is not applied to the defective wiring or the pixel electrode connected to the thin film transistor. As a result, the pixel electrode does not generate a normal electric field as the gate electrode of the field-effect transistor, so that a normal current does not occur between the source electrode and the drain electrode on the detection substrate side facing the pixel electrode. Therefore, by checking the magnitude of the current between the source electrode and the drain electrode, it is possible to inspect whether the wiring or the thin film transistor related to the pixel electrode is abnormal. Although the above description has been made in accordance with the principle of the N-channel type field effect transistor, the same applies when a negative voltage is applied to the pixel electrode to form a P-channel type field effect transistor. Here, an example of an embodiment of the present invention will be described. Referring to FIG. 3, the basic configuration of the liquid crystal display substrate 1 in the active matrix system will be described first. For example, on a substrate 2 such as a glass substrate,
Pixel electrodes 5 are arranged in a matrix according to the pixels, and thin film transistors 6 are formed corresponding to the pixel electrodes 5. In this case, the pixel electrode 5 is connected to the drain electrode of the thin film transistor 6. Also, the substrate 2
Above, a gate line 4 and a source line 3 are connected to the gate electrode and the source electrode of each thin film transistor 6 so as to form a plurality of columns and a plurality of rows. Thus, the source wiring 3 and the gate wiring 4 are formed on the substrate 2 as shown in FIG.
Are formed in a lattice shape, and the pixel electrodes 5 and the thin film transistors 6 are arranged in a matrix between them. One end of the source wiring 3 is connected to a source driver 15 having a power supply 17, and one end of the gate wiring 4 is also connected to a gate driver 16 having a power supply 27. Further, the source driver 15 and the gate driver 16
Are connected to a scanner 20 via cables 18 and 19, respectively. An arbitrary source wiring 3 and a gate wiring 4 are selected by the scanner 20, and a voltage is applied to a pixel electrode 5 at an intersection of the wiring via a thin film transistor 6 which is a switch. Is applied. In order to inspect the source wiring 3 and the gate wiring 4 for disconnection or short circuit or defect of the thin film transistor using the liquid crystal display substrate 1 as an inspection object,
The inspection device shown in FIGS. 1 and 2 is provided. In FIG. 1, 1 is a liquid crystal display substrate to be inspected, 5 is a pixel electrode, and a thin film transistor 6, a source wiring 3, a gate wiring 4, a switch 29 in the source driver 15, and a switch 28 in the gate driver 16 are simulated. Is shown.
17 and 27 are power supplies for the drivers 15 and 16. In the present inspection apparatus, the detection substrate 21 is arranged opposite to the surface side of the liquid crystal display substrate 1 to be inspected with a small interval δ of about 10 μm. This detection board 21
Is a switch element 26 comprising a P-type semiconductor 23, an N-type source electrode 24 and a drain electrode 25 on a glass substrate 22.
The pixel electrode 5 faces the central portion of the P-type semiconductor 23 via the minute interval δ. Here, a voltage is applied to the source electrode 24 by a power supply 32, and the drain electrode 25 is connected to a D / A converter 31 which is an ammeter via a switch 30. In such a structure, the switches 28, 2
When the source wiring 3 and the gate wiring 4 have no disconnection or short-circuit defect while the thin film transistors 6 do not have a defect in a state where the gate electrodes 9 and 30 are closed, a normal voltage is applied from the power supply 17 to the pixel electrode 5 and the P-type. A normal electric field acts between the semiconductor 23 and the drain electrode 25 and the pixel electrode 5. In that case, P
The semiconductor 23, the source electrode 24, the drain electrode 25, and the pixel electrode 5 constitute a field effect transistor, and the pixel electrode 5 functions as a gate electrode of the field effect transistor. As a result, holes (not shown) in the P-type semiconductor 23 are pushed to the glass substrate 22 side, and electrons flowing out of the source electrode 24 are attracted to the pixel electrode 5 side as indicated by black dots in the figure, and A current path is formed between the D / A converter and the drain electrode 25, and the D / A converter 31 detects the current. If the source line 3 and the gate line 4 are disconnected or short-circuited or the thin film transistor 6 does not operate, a normal voltage is not applied to the pixel electrode 5,
The D / A converter 31 does not detect a normal current value. When a normal voltage is applied to the pixel electrode 5 in this manner, the opposing field-effect transistors conduct and the ammeter operates. FIG. 2 is a diagram for explaining a basic configuration and an operation principle of an inspection apparatus for performing a high-speed and systematic inspection based on the above operation principle. In FIG. 2, each source electrode 24 of a plurality of switch elements 26 has a power source 3
2, a voltage is applied to each of the drain electrodes 25, and a D / A converter 31 which is an ammeter via the switch 30.
It is connected to the. The plurality of switches 30 constitute a sensor driver 34 indicated by a broken line.
In 4, control is performed by the scanner 20 via the signal line 35 so that the drain electrode 25 of one of the switch elements 26 is connected to the D / A converter 31. At the same time, the scanner 20 transmits to the main controller 38 via the signal line 36 which switch 30 is closed when the current flowing through the D / A converter 31 is closed. Therefore, the switch 30 selection signal from the signal line 35 by the scanner 20 is transmitted to the signal line 3
At 6, the controller enters the main controller 38, and the current value at this time is input to the main controller 38 via the signal line 37. For this reason, the scanner 20 selects the switch 30, and eventually selects the switch element 26. In synchronization with this, the scanner 20 is connected via the cables 18 and 19 as shown in FIG. The source wiring 3 and the gate wiring 4 to which a voltage is to be applied are selected, and the pixel electrode 5 to which the voltage is applied is selected. Therefore, scanner 2
By selecting the pixel electrode 5 at 0 and selecting the switch 30 of the switch element 26 facing the pixel electrode 5, a normal current value flows to the D / A converter 31 if there is no defect and it is normal. If it does not flow. If this is stored in the main controller 38 in order, a defective portion can be specified. The gate wiring 4 and the source wiring 3 of the pixel electrode 5
The method for inspecting defects such as disconnection and short circuit is as follows. First, when there is a disconnection in one of the gate wiring 4 and the source wiring 3 or in the thin film transistor 6, no voltage is applied to the pixel electrode 5 associated with the wiring. Therefore, by sequentially switching the pixel electrodes 5 to which a voltage is to be applied by the scanner 20 and sequentially switching and measuring the current value of the switch element 30 facing the pixel electrode 5, the switch element corresponding to any pixel electrode 5 is determined. It is possible to determine whether a normal current has not flowed through 30 and to inspect which pixel electrode 5 related wiring or thin film transistor 6 is disconnected. When a short circuit occurs in the gate line 4 or the source line 3, the pixel electrode corresponding to the short-circuited voltage is applied to one of the source lines 3 and the gate line 4, even though the selection of the voltage application is not specified in both of the source line 3 and the gate line 4. Is applied. Therefore, the current value of the switch element corresponding to each pixel electrode is measured by selecting the voltage application to one of the source or gate wirings of the pixel electrode and not selecting the voltage application to the other gate or source wiring. If it goes on, it can be inspected for short circuits. This can be applied to the short circuit of the thin film transistor 6. The power supply 17 may be not only a DC power supply but also an AC power supply or a power supply that generates positive and negative pulse voltages. As described above, the inspection apparatus of the present invention is similar to the conventional inspection apparatus in that it uses the change in the electric field generated by the voltage applied to the pixel electrode. The change in the electric field is directly and electrically detected by applying the principle of the field effect transistor without replacing the change in the electric field with the change in the light reflected by the electro-optical element. Therefore, while solving the problems caused by the non-uniformity of the light intensity distribution and the detection sensitivity of the electro-optical element, the defect associated with each pixel electrode is detected by the current value of the switch element corresponding to each pixel electrode on a one-to-one basis. Since the inspection is performed, there is an effect that the inspection can be performed with high reliability and reproducibility and in which the defect correction portion can be easily specified.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic configuration diagram of an inspection device for a liquid crystal display substrate. FIG. 2 is a schematic diagram of the inspection device of FIG. FIG. 3 is a plan view of an example of a liquid crystal display substrate. FIG. 4 is a configuration diagram of a conventional inspection device. [Description of Signs] 1 Liquid crystal display substrate 3 Source wiring 4 Gate wiring 5 Pixel electrode 6 Thin film transistor 24 Source electrode 23 Semiconductor 25 Drain electrode 26 Switch element 21 Detection substrates 17, 27, 32 Power supply 31 D / A converter (current detector) )

──────────────────────────────────────────────────続 き Continuation of the front page (51) Int.Cl. ⁷ Identification symbol FI G02F 1/1368 G02F 1/136 500 (56) References JP-A-64-35597 (JP, A) JP-A-4-34491 ( JP, A) JP-A 1-167795 (JP, A) JP-A 8-110365 (JP, A) JP-A 4-324980 (JP, A) JP-A 4-164264 (JP, A) (58) ) Fields investigated (Int.Cl. ⁷ , DB name) G01R 31/00 G01M 11/00 G01R 19/00 G01R 29/12 G01R 31/02 G02F 1/1368

Claims (1)

(57) [Claim 1] A liquid crystal display in which a thin film transistor is provided for each pixel electrode, and a source electrode and a gate electrode of the thin film transistor are connected to a source line and a gate line arranged in a grid. In the method of inspecting a substrate for defects, a pixel electrode arranged on the liquid crystal display substrate and a switch element arranged on a detection substrate are arranged close to and opposed to each other, and a source electrode and a drain electrode of the switch element And applying a voltage to both or one of a source line and a gate line of a pixel electrode corresponding to the switch element, and detecting a current value flowing through the switch element at this time. Inspection method for liquid crystal display substrates. 2. A liquid crystal display according to claim 1.
In the inspection method of the substrate, the application of the voltage to the switch element and the application of the voltage to the source wiring and / or the gate wiring of the pixel electrode corresponding to the switch element are sequentially performed in synchronization with each other. A method for inspecting a liquid crystal display substrate, comprising: 3. An apparatus for inspecting a liquid crystal display substrate connected to a source line and a gate line arranged in a lattice pattern for defects of a liquid crystal display substrate, wherein a thin film transistor is provided for each pixel electrode, and the thin film transistor has a source electrode and a gate electrode. A source electrode, a semiconductor, and a test substrate on which a switch element composed of a drain electrode is arranged corresponding to the pixel electrode of the liquid crystal display substrate. The test substrate and the liquid crystal display substrate are brought close to each other and opposed to each other. Means for applying a voltage from a wiring and a gate wiring, and means for applying a voltage between the source electrode and the drain electrode, and applying a voltage to a pixel electrode to which a voltage is applied and a switch element corresponding to the pixel electrode And a means for synchronizing with the above, and a liquid crystal display substrate inspection apparatus.