JPH0627494A - Inspecting method and device for thin-film transistor active matrix substrate - Google Patents

Abstract

PURPOSE:To detect the presence or absence of the defects of picture elements inclusive of the thin-film transistors (TFTs) in a display area in a short period of time without damaging pixel electrodes. CONSTITUTION:The potential of the pixel electrode 45 connected to the source electrode of the TFT is maintained at an AC potential by applying an AC voltage to a data line 40 connected to the picture element 45 to be inspected on the TFT active matrix substrate and applying a voltage to turn on the TFT. On the other hand, a probe 44 positioned without contact with the pixel electrode 45 is used right above the pixel electrode 45 to be inspected and the AC voltage of the pixel electrode 45 to be inspected is introduced via the electrostatic capacity between this probe 44 and the pixel electrode 45 to be inspected to an amplifier 51, by which the potential is detected. This pixel electrode potential attains the state different from the normal AC potential if there are the defects, such as disconnection and shorting of the wirings, defect of the TFTs, in the pixel electrode 45 to be inspected and, therefore, the presence or absence is detected by utilizing such phenomenon.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for inspecting a thin film transistor active matrix substrate used in a liquid crystal display.

[0002]

2. Description of the Related Art A thin film transistor active matrix substrate is one in which a plurality of data lines, gate lines, thin film transistors, pixel electrodes and capacitors are formed on a glass substrate by a thin film process.

In this thin film transistor active matrix substrate, wiring short-circuits, disconnections and thin film transistors (TFT: Thin Film Transi) due to dust in the manufacturing process, defects in the photoresist process, etc.
defects such as defects occur.

Conventionally, as a defect inspection of a thin film transistor active matrix substrate, a method of measuring the electrical resistance of each gate line and data line and detecting a short circuit and a disconnection has been performed. This is checked for all gate lines and data lines in the substrate.

On the other hand, the inspection for each pixel including the defect of the TFT is performed by not measuring all the pixels but measuring the TFT provided as a measurement sample around the matrix.

As a method of inspecting all the TFTs in the display area, it is possible to apply a mechanical contact probe to each pixel electrode, but this method is
It is not practical because it damages the pixel electrode and requires a huge number of measurements (one liquid crystal display is composed of about 100,000 or more pixel electrodes). Therefore, recently, as a method of testing all pixels, a method of inspecting a pixel electrode potential using an electro-optical element (Japanese Patent Laid-Open No. 3-142498, U.S. Pat. No. 4,983,911), in which a capacitive element for each pixel is stored. A method of inspecting by detecting electric charges (Japanese Patent Laid-Open No. 3-200121), turning on a thin film transistor,
A method of inspecting a pixel defect by impedance analysis utilizing the fact that the impedance of each pixel changes when turned off has been proposed.

[0007]

However, all of these are still in the testing stage at the present time, have not yet been put into practical use, and the apparatus price is expected to be expensive.

The present invention has been made to solve the above-mentioned conventional drawbacks, and an object thereof is to detect the presence or absence of a pixel defect including a defective TFT in a display area without damaging the pixel electrode. An object of the present invention is to provide a thin film transistor active matrix substrate inspection method and device that can be detected in a short time and can be configured at low cost.

[0009]

To achieve the above object, an AC voltage is applied to a data line connected to a pixel electrode to be inspected on a thin film transistor active matrix substrate, and a thin film transistor is turned on to a gate line. By applying a voltage, the potential of the pixel electrode connected to the source electrode of the thin film transistor is set to an AC potential.

On the other hand, a probe positioned directly above the inspected electrode so as not to contact the pixel electrode is used, and the potential change of the inspected pixel electrode is measured through the capacitance between the probe and the inspected pixel electrode. Lead to the amplifier and detect. When a pixel to be inspected has a defect such as a wiring short circuit, a disconnection, or a TFT defect, the pixel electrode potential has an amplitude or a waveform different from normal, so that it can be utilized to detect the presence or absence of a defect.

The data lines include those referred to as signal lines and drain lines, and the gate lines include those referred to as scanning lines.

[0012]

1 shows an example of an inspection apparatus according to the present invention. This is the thin film transistor active matrix substrate 1,
The non-contact probe 3 is fixed on a chuck 2 capable of adsorbing a substrate, and the non-contact probe 3 is supported by a mechanism portion 4 which can be positioned and moved in the height direction Z and the X direction in the drawing so as to face the chuck 2. On the other hand, the chuck 2 is supported by a mechanism portion 7 which can be positioned and moved in a Y direction which is perpendicular to X and perpendicular to the paper surface. By using both mechanism portions 4 and 7, the non-contact probe 3 is mounted on the substrate 1. Can be positioned on any pixel electrode at any distance.

The contact type probe 8 is a probe for supplying a voltage to the data line and the gate line, and is connected to a power source (not shown). In addition, in FIG.
Reference numeral 5 is an X-direction positioning guide, and 6 is a pedestal.

FIG. 2 shows a structure of one pixel of a typical thin film transistor active matrix, and a thin film transistor (TFT) 10 has a source contact 11, a drain contact 12, and a gate contact 13. The source contact 11 is connected to the pixel electrode 16, the drain contact 12 is connected to the data line 14, and the gate contact 13 is connected to the gate line 17. The pixel electrode 16 is connected to a terminal of a capacitance element 20 that forms a storage capacitance, and the other terminal of the capacitance element 20 is connected to a storage capacitance counter electrode line 19 called a Cs line.

The thin film transistor active matrix substrate is composed of such an array of pixels. Each pixel is addressable by using specific gate and data lines. An AC voltage of frequency f (Hz) is applied to the data line that addresses the pixel to be inspected. Further, by applying an appropriate voltage to the gate line for addressing the same pixel, T
The FT can be turned on or off. On the other hand, C
The s line is grounded or kept at a constant potential. Under such a condition, the potential of the pixel electrode to be inspected has an AC component of frequency f (Hz), and the amplitude of the AC component when the TFT is turned on is greatly different from that when the TFT is turned off.

In the present invention, a non-contact type capacitive coupling type probe is used to detect the AC potential of the pixel electrode to be inspected. FIG. 3 shows a state in which the non-contact probe is positioned on the thin film transistor active matrix substrate. Figure 3
In, the non-contact probe 44 is positioned on the pixel electrode 45 to be inspected at an appropriate distance, applies an AC voltage to the data line 40 that addresses the pixel to be inspected, and applies the AC voltage to the gate line 42 that also addresses the pixel. By applying the control voltage, it is detected from the potential measurement of the probe 44 whether or not the inspected pixel 45 is operating normally. In FIG. 3, reference numeral 43 denotes a storage capacitor counter electrode line (Cs
Lines), 47 and 48 are pixel electrodes adjacent to the inspected pixel 45 (the data line addressed to the inspected pixel is common), 49 and 5
Reference numeral 0 denotes a pixel electrode adjacent to the pixel 45 to be inspected (a gate line that is addressed to the pixel to be inspected is common), 46 is a control TFT for the pixel electrode 50, and 51 is an amplifier for amplifying the voltage induced in the probe. ing.

FIG. 4 shows an equivalent electric circuit diagram of one pixel, probe and amplifier. An AC voltage of f (Hz) is supplied from the AC signal source 71 to the drain terminal of the TFT 63 via the data line 60. On the other hand, the gate voltage Vg70 is supplied to the gate terminal through the gate line 61 to turn on or off the TFT 63. The AC component voltage Vp72 generated in the pixel electrode connected to the source is greatly different when the TFT 63 is on and when it is off.

When a probe is brought close to this pixel electrode,
The voltage Vpr73 induced in the probe is Vpr = Vp · Zin, where Cp (F) 65 is the capacitance between the pixel electrode and the probe, and Zin67 is the equivalent impedance when the probe and the amplifier are viewed from the input end of the probe. /
It becomes {Zin + 1 / (j2πfCp)}. This voltage is amplified by the amplifier 68 to obtain the detection signal 69. Here, Cp is about 0.001 pF, and Cs is about 1 pF.
Since it is sufficiently small, the electrode potential can be measured without disturbing the pixel electrode potential during probing.

By the way, as shown in FIG. 3, the probe is close to other pixel electrodes adjacent to the pixel electrode to be inspected, data lines, and gate lines. Therefore, there is also capacitance between the probe and these elements. In order to detect the potential of the pixel to be inspected correctly, it is necessary to keep the coupling capacitance with other elements small. Therefore, in the present invention, the probe is electrostatically shielded while the probe surface facing the inspected pixel electrode has no electrostatic shield and is electrostatically opened, and the electrostatic opening is smaller than the inspected pixel electrode. With the structure.

FIG. 5 shows an example of the probe. In FIG. 5, the probe has a coaxial cable-like structure, and the outer conductor 9
0 is grounded and prevents the central conductor 92 from electrostatically coupling with elements other than the pixel electrode under test. A cylindrical insulator 91 is provided between the center conductor 92 and the outer conductor 90 to insulate the center conductor 92 and the outer conductor 90 and at the same time mechanically support the center conductor 90.

FIG. 6 shows a cross-sectional view when this probe is positioned on the pixel electrode to be inspected. The probe 1 is shown in FIG.
The state of electrostatic capacitance coupling between 06 and each pixel electrode or data line is shown by the electric force line 110. FIG. 6 is a diagram in the case where the pixel electrode 101 to be inspected and the data line 102 have a positive potential, and the adjacent pixel electrodes 104 and 105 and the data line 103 have a negative potential. As shown in FIG. 6, if the opening of the center conductor 107 is smaller than the pixel electrode, the coupling capacitance between the probe and the data line or between the adjacent pixel electrodes may cause a gap between the probe and the glass substrate due to the electrostatic shielding effect of the outer conductor 108. It can be seen that the capacitance can be made sufficiently smaller than the electrostatic capacitance between the probe and the pixel electrode to be inspected if properly taken. In FIG. 6, 109 is an insulator and 111 is a glass substrate.

In order to suppress the voltage induced in the probe from both the adjacent data lines, it is effective to give the adjacent data lines alternating signals that are 180 degrees out of phase with each other. This is because, in general, the pixel center is located at a position approximately equidistant from both adjacent data lines, and therefore the voltages induced from both adjacent data lines cancel each other.

In order to suppress the voltage induced in the probe from both adjacent pixels across both adjacent data lines, the pixel potential of both adjacent pixels may be made constant. For that purpose, a sine wave voltage is applied to every other data line including a data line for addressing a pixel to be inspected, and a DC voltage is applied to the other data lines.

Although this embodiment has been described as one probe, by using a probe assembly in which a plurality of probes are arranged at a pitch that is an integral multiple of the pixel pitch,
It is possible to test multiple pixels at the same time, which can reduce the inspection time.

In this embodiment, the sine wave signal is used as the time-varying signal, but the waveform signal is not limited to the sine wave, and any waveform signal can be used.

[0026]

As described above, according to the present invention, the presence or absence of a pixel defect such as a defect of the thin film transistor or a defect of the storage capacity as well as a short circuit or a disconnection of the wiring of the thin film transistor active matrix substrate is checked by a non-contact probe. It is possible to provide an inspection method and an apparatus capable of performing a defect inspection in a short time, which can be detected with high sensitivity without damaging the electrodes and without contaminating the substrate. Also, these methods and devices are extremely inexpensive as they do not require special and complex electrical or optical measuring instruments. As described above, according to the present invention, the inspection including the pixel defect of the thin film transistor active matrix substrate can be performed in a short time at a low cost, and it is effective in improving the yield and quality control of the thin film transistor active matrix display.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an example of an inspection apparatus of the present invention.

FIG. 2 is an explanatory diagram showing a structure of one pixel of a thin film transistor active matrix substrate.

FIG. 3 is a perspective view showing a state in which a non-contact probe is positioned on a substrate to be inspected.

FIG. 4 is a circuit diagram showing an equivalent electric circuit of one pixel, a probe, and an amplifier.

FIG. 5 is a perspective view showing the structure of a probe.

FIG. 6 is a cross-sectional view showing a state in which a probe is positioned on a pixel electrode.

[Explanation of symbols]

 3 probe 10 TFT 14 data line 16 pixel electrode 17 gate line

Claims (8)

[Claims] 1. A thin film transistor active matrix substrate comprising a plurality of pixels arranged in a matrix, a plurality of data lines and a plurality of gate lines, each pixel comprising a switching transistor and a capacitive element. The potential of the pixel electrode is temporally changed by applying a voltage to the line, and the probe is positioned on the inspected pixel electrode on the substrate in a non-contact manner or moved on the inspected pixel electrode to inspect the inspected pixel electrode. A method of inspecting a thin film transistor active matrix substrate, characterized in that a potential change of a pixel electrode to be inspected is guided to an amplifier via an electrostatic capacitance between an upper portion and a probe and detected. 2. In the probe, a portion facing the pixel electrode to be inspected is composed of a central conductor portion and an electrostatic shield portion around the central conductor portion which is kept at a ground potential, and the central conductor portion and the electrostatic shield portion. Is electrically insulated, the surface of the central conductor portion facing the inspected pixel electrode has no electrostatic shield, and is electrostatically opened, and the electrostatic opening is smaller than the inspected pixel electrode. The thin film transistor active matrix substrate inspection method according to claim 1. 3. As a method of changing the potential of the pixel electrode, adjacent data lines are alternately arranged into a plurality of data lines so as to have sinusoidal wave voltages having mutually inverted phases.
3. A method for inspecting a thin film transistor active matrix substrate according to claim 1, wherein sinusoidal voltages having a phase shift are applied, and a voltage for turning on the thin film transistor is applied to the gate line. 4. As a method of changing the potential of the pixel electrode, a sine wave voltage is applied to every other one of the plurality of data lines, a DC voltage is applied to the other data lines, and a gate line is applied. A voltage for turning on a thin film transistor is applied to the thin film transistor active matrix substrate inspection method according to claim 1, 2 or 3. 5. A thin film transistor active matrix substrate comprising a plurality of pixels arranged in a matrix, a plurality of data lines and a plurality of gate lines, each pixel comprising a switching transistor and a capacitive element, and a potential of a pixel electrode. For applying a voltage to the data line for temporally changing the voltage, a means for applying a control voltage of the thin film transistor to the gate line, and a probe are positioned in a non-contact manner on the pixel electrode to be inspected on the substrate. Means or means for moving on the inspected pixel electrode, and detection means for detecting a potential change of the inspected pixel electrode via the capacitance between the inspected pixel electrode and the probe. Matrix substrate inspection device. 6. In the probe, a portion facing the pixel electrode to be inspected is composed of a central conductor portion and an electrostatic shield portion around the central conductor portion, which is kept at a ground potential, and the central conductor portion and the electrostatic shield portion. Is electrically insulated, the surface of the central conductor portion facing the inspected pixel electrode has no electrostatic shield, and is electrostatically opened, and the electrostatic opening is smaller than the inspected pixel electrode. The thin-film transistor active matrix substrate inspection device according to claim 5. 7. As a method of changing the potential of the pixel electrode, adjacent data lines are alternately arranged into a plurality of data lines so as to have sinusoidal wave voltages having mutually inverted phases.
7. An apparatus for inspecting a thin film transistor active matrix substrate according to claim 5 or 6, wherein sinusoidal voltages whose phases are shifted from each other are applied, and a voltage for turning on the thin film transistor is applied to the gate line. 8. As a method of changing the potential of the pixel electrode, a sine wave voltage is applied to every other one of the plurality of data lines, and a DC voltage is applied to the other data lines, and a gate line is applied. A voltage for turning on a thin film transistor is applied to the thin film transistor active matrix substrate inspection device according to claim 5, 6, or 7.