JPH0429294A - Method and device fro inspecting tft picture element on lcd substrate - Google Patents

Abstract

PURPOSE:To quickly inspect a large quantity of TFT picture elements with a high precision by applying a positive or negative voltage to the drain of the FT and applying a turning-on signal to the gate to measure the drain current and changing the drain voltage to measure the drain current and comparing two measured drain currents with each other. CONSTITUTION:Picture elements are formed in a matrix on an LCD substrate 50 as the object to be inspected, and a TFT 51 is formed in each picture element and has the gate connected to a gate electrode 53 and has the drain connected to a drain electrode 52. The positive or negative voltage is applied to the drain of the TFT 51 and the turning-on signal is applied to the gate to measure the drain current, and the drain voltage of the TFT 51 is changed and the turning-on signal is applied to the gate to measure the drain current, and two measured drain currents are compared with each other to discriminate whether the TFT picture element is good or not. Thus, a large quantity of TFT picture elements are quickly and surely inspected.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a method and apparatus for testing TFT pixels on an LCD substrate.

<Prior Art> In recent years, LCD substrates have been widely used as display devices for various electronic devices. This LCD substrate usually has liquid crystal pixels and circuit patterns formed on a glass substrate. In liquid crystal televisions, especially color liquid crystal televisions, etc., in order to increase the response speed of the liquid crystal and improve its image quality, T is applied to each liquid crystal pixel.
It is common to use an LCD substrate on which FTs (thin film transistors) are formed.

In this method, a capacitance is formed on the source side of the TFT, and the voltage applied to the liquid crystal is maintained by the capacitance.

<Problem to be solved by the invention> Inspecting the quality of the LC and D substrates as described above is very important in maintaining product quality, and in particular, the quality of the LCD substrate is determined by the quality of the TFT characteristics. There is.

However, in the past, tests at the board stage were only performed by opening and shorting patterns, and the quality of pixels was checked by actually filling the board with liquid crystal and lighting it up.

However, if the quality of pixels can be determined at the board stage, there is no need to actually turn them on to check.

Furthermore, since it becomes possible to repair defective pixels, there has been a desire for a method and apparatus that can quickly and reliably test the quality of TFT pixels on an LCD substrate in large quantities.

Means for Solving the Problems> The inspection method of the present invention was developed in response to the above-mentioned demands, and involves applying a positive or negative voltage to the drain of the TFT on the LCD substrate and applying an on signal to the gate. In addition, measure the drain current at this time, then change the drain voltage of the TFT, apply an on signal to the gate, measure the drain current at this time, and compare the two measured drain currents. The basic feature is that the quality of the TFT pixel is determined by the following.

<Example> The present invention will be described below based on embodiments shown in the drawings.

In FIG. 1, pixels are formed in a matrix on an LCD substrate 50 to be inspected, and a TFT 51 is formed in each pixel. The TFT 51 has its gate side connected to a gate electrode 53 and its drain side connected to a drain electrode 52. The drain electrode 52 and gate electrode 53 are LC
They are arranged vertically and horizontally on the edge of the D board 50. Each TFT51
A capacitance C consisting of a pixel electrode 54 and an auxiliary capacitance electrode 55 is formed on the source side of the liquid crystal 56, and a voltage is applied to the liquid crystal 56 by this capacitance C.

The pulse oscillator 1 applies a pulse voltage of a predetermined period to a gate electrode 53.
and is supplied to the drain electrode 52. A phase adjuster 2 is interposed between the pulse oscillator 1 and the drain electrode 52,
The pulse is configured to be delayed by a predetermined period. That is, as shown in FIG. 2, the gate voltage is turned on when the drain voltage is a predetermined voltage, and as shown in FIG. 3, the gate voltage is turned on when the drain voltage is zero. It is designed to adjust the phase of the The pulse voltage from the phase adjuster 2 is supplied to the drain electrode 52 via a resistor R, and the drain current of the TFT 51 is detected as the voltage of this resistor R.

In this embodiment, a connector 7 and a connector 8 are attached to a drain electrode 52 and a gate electrode 53, and each electrode is scanned by a switching device 9 and a switching device 10, and the electrode is sequentially connected to a pulse oscillator 1 and a phase adjuster 2. The configuration is such that the characteristics of each TFT 51 are sequentially measured by connecting them. As the switching device 19 and the switching device 10, it is possible to use an ordinary electronic switch such as a relay switch or a multiplexer, and the device is configured to sequentially supply a pulse voltage and measure the drain current by scanning each electrode. ing. A voltage detector 3 is connected to the resistor R, and the output of the voltage detector 3 is sent to an A/D converter 4.
The signal is inputted to the determination device 5 via the device 5, where it is determined whether the TFT 51, the pixel electrode 54, and the auxiliary capacitor electrode 55 are good or bad. 6 is a memory.

From the pulse oscillator 1 to the phase adjuster 2 as shown in FIG.
Drain voltage is supplied from the drain electrode 52 via the switching device 10 and the connector 8 for a predetermined period of time. The moment a drain voltage is applied, a current 60a flows as shown in FIG. 2 due to the capacitance between the drain pattern and the common terminal. While this drain voltage is present, a gate voltage is supplied from the gate electrode 53 from the pulse oscillator 1 via the switching device 9 and the connector 7, and when the gate is turned on, the TF
A current flows between the drain and source of T51, and the capacitance C is charged. The drain current at this time is defined as a detected drain current 61a as shown in FIG. 2, and is detected as the voltage across the resistor R by the voltage detector 3. This value is converted into a digital quantity by the A/D converter 4 and stored in the memory 6 via the determination device 5.

Next, as shown in FIG. 3, when the drain voltage from the phase adjuster 2 is set to Ov, the charges stored in the drain pattern are discharged, and this is observed as a current 60b as shown in FIG. When the gate voltage from the pulse oscillator 1 is turned on when the drain voltage is zero after the discharge is completed, the electric charge charged in the capacitance C of the TFT 51 is discharged tl, and reverses from the source to the drain of the TFT 51 and in the direction of the resistor R. A drain current flows in the direction. As shown in FIG. 3, this is detected by the voltage detector 3 as a detected drain current 61b, and is stored in the memory 6 via the determining device W5.

The detected drain current 61a and the detected drain current 61b each include leakage current between the gate and the drain and between the gate pattern and the drain pattern, and this leakage current can be removed by taking the difference between the detected drain currents 61a and 61b. I can do it.

Let the leakage current when the gate is on be ie, and actually TF
When T51 is turned on, the current flowing through the capacitance C becomes ic
Then, the detected drain current 61a=ie-ic. On the other hand, if the discharge current of the charge stored in the capacitance C due to the TFT 51 being turned on is id, then the detected drain current 61b=ie+id. Therefore, the difference between the detected drain currents 61a and 61b is ic+id, and the influence of the leakage current ie is removed. If the TFT 51, the pixel electrode 54, and the auxiliary capacitance electrode 55 are normal, charging and discharging to the capacitance C is performed normally, so the difference becomes large as shown in FIG. 4. On the other hand, if it is abnormal, the difference becomes small as shown in FIG.

In this embodiment, the determination device 5 determines the difference between the instantaneous values of the detected drain currents 61a and 61b at a predetermined time after the application of the gate-on signal, and depending on whether this difference is greater than or equal to a predetermined value, the TFT 51, the pixel electrode 54, the auxiliary capacitor The quality of the electrode 55 is determined.

Next, the measurement procedure will be explained.

First, the drain voltage is set to Ov, and an on-voltage is applied to the gate to discharge it, thereby removing any charges that may have been stored in the pixel electrode 54 and the auxiliary capacitor electrode 55. Then, a drain voltage is applied to first charge the floating eight wires of the pattern, and when this is completed, an on-voltage is applied to the gate, and the drain current is detected by the voltage detector 3 after a predetermined period of time. The predetermined time is a time during which the leakage current of the gate becomes small and the charging current does not become small, and this is determined by the characteristics of the TFT 51 or the size and pattern characteristics of the LCD substrate 50, but it is approximately 10 to 40 μsec for the switching device.
It is. The signal detected by this voltage detector 3 is held, converted into a digital quantity by an A/D converter 4, and stored in a memory 6 via a determination device 5. This value is the above-mentioned detected drain current 61a=ie-ic.

Next, the drain voltage is set to Ov to remove the charge accumulated in the drain pattern, etc., and an on-voltage is applied to the gate while keeping Ov. Then, the drain current is detected by the voltage detector 3 after the same time as the above-mentioned predetermined time. This value is similarly stored in the memory 6. This value is the above-mentioned detected drain current 61b=ie+id. Then, the determination device 5 calculates the difference between the detected drain currents 61a and 61b, and obtains the value of ic + j, d. This value is T
If the FT 51, the pixel electrode 54, and the auxiliary capacitor 1 electrode 55 are good, they are large, and if they are defective, they are small, so it is possible to determine good or bad based on the difference.

As explained above, according to the inspection method of the present invention, LCD
T is securely connected without contacting the internal pattern of the substrate 50.
It is possible to determine the quality of the FT 51, the pixel electrode 54, and the auxiliary capacitor electrode 55. Furthermore, by using the connector 7.8 and the switching device W9.10, it is possible to perform inspections at high speed.

<Effects of the Invention> As explained above, the method for inspecting TFTs on an LCD substrate of the present invention is to apply a positive or negative voltage to the drain of the TFT on the LCD substrate, apply an on signal to the gate, and test this TFT. Measure the drain current at .

Next, change the drain voltage of the TFT, apply an on signal to the gate, measure the drain current at this time, and
Since the quality of the TFT pixel is determined by comparing two measured drain currents, it is possible to perform high-accuracy inspection in large quantities and at high speed without touching the internal patterns of the LCD board. .

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of the method and apparatus of the present invention, FIGS. 2 and 3 are operation explanatory diagrams, and FIGS. 4 and 5.
The figure is an explanatory diagram of a detected current waveform. 1: Pulse oscillator, 2: Phase adjuster, 3: Voltage detector,
4: A/D converter, 5: Determination device, 6: Memory, 7
: Connector, 8: Connector, 9 Switching device, 1
0ni switching device, 50: LCD board, 51:
TFT, 52 Nidrain electrode, 53: Gate electrode, 54
: Pixel electrode, 55: Storage capacitor electrode, 56: Liquid crystal, 60:
Current, 61: Detection drain current. Diagram Drain 11 Voltage - High Gate Voltage = "-1 Diagram Drain Voltage" - m - "Gate Voltage" - 1 sec.

Claims (1)

[Claims] 1) Apply a positive or negative voltage to the drain of the TFT on the LCD substrate, apply an on signal to the gate, measure the drain current at this time, and then measure the drain voltage of the TFT. By changing the T and applying an on signal to the gate, measuring the drain current at this time and comparing the two measured drain currents, the T
A method for inspecting TFT pixels on an LCD substrate, the method comprising: determining the quality of the FT pixels. 2) means for applying a positive or negative voltage to the drain of a TFT on the LCD substrate to apply an on signal to the gate, and then applying a positive or negative voltage to the gate by changing the drain voltage of the TFT; It is characterized by comprising means for measuring the drain current when applying a negative voltage and when changing the drain voltage, and determining the quality of the TFT pixel by comparing these two measured drain currents. LC
Inspection device for TFT pixels on D substrate.