JPH021890A - Method for testing active matrix substrate for display panel - Google Patents

Abstract

PURPOSE:To test in a short time by placing an inspected active matrix on a testing substrate, which has an electro-luminescence (EL) film, to connect by electrostatic capacity, impressing a testing voltage between an scanning electrode and electrode film, thereby detecting the light emission intensity of the EL film. CONSTITUTION:The active matrix (AM) substrate 10 is comprised by providing on an insulating substrate 11 a picture element electrode 12 and scanning electrode 3 both of which are made of a transparent conductive film and by connecting a driving element 15 between them. The testing substrate 20 is comprised by forming the electrode film 22 on the whole surface of an insulating substrate 21 and by providing the EL film 24 on that. The AM substrate 10 is placed on the testing substrate 20 with a thin spacer in-between so that the gap between the electrode 12 and EL film 24 is 10mum, thereby connecting by the electrostatic capacity. Testing is performed by impressing the AC testing voltage 40 between the scanning electrode 13 and electrode film 22 and then by detecting the light emission intensity of the EL.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a method for testing an active matrix substrate for a display panel using liquid crystal or the like as a display medium. The present invention relates to a method for testing a substrate on which a driving element associated with pixels arranged within the substrate and a scanning electrode for driving the display of the pixels via the driving element are installed for the presence or absence of display defects in each pixel.

[Prior Art] For example, a liquid crystal display panel using the above-mentioned active matrix substrate is suitable for displaying complex variable images such as television images, and has at least tens of thousands of pixels arranged in a matrix within its display surface. However, in order to prevent so-called crosstalk on the display between each pixel and obtain a clear image, a 3-terminal element such as a thin film transistor or a 2i element such as a thin film diode is installed on the active matrix substrate side. The driving elements are distributed and incorporated within the display surface as driving elements associated with each pixel. As is well known, an equivalent circuit of such an active matrix substrate is shown in FIG.

FIG. 5A shows an example in which a two-terminal element is incorporated as a driving element. Zero pixel electrodes 12 are arranged in rows and columns on the active matrix substrate 10, and in this example, the scanning electrodes are 13 are provided in common. In this example, as a two-terminal driving element 15, a pair of diodes 15P and 15n in positive and negative directions are connected to each pixel T4.
An antiparallel connection is made between the pole 12 and the scanning electrode 13. The reason why a pair of positive and negative diodes is provided as a driving element is because the scanning voltage applied to the scanning Fi 13 for so-called AC driving of the display panel is alternately switched between positive and negative at each scanning period. Yes, scanning electrode 1
When a positive scanning voltage is applied to 3, the diode 15p in the positive direction becomes conductive, and when a negative scanning voltage is applied, the diode 15n in the negative direction becomes conductive, transmitting the scanning voltage on the scanning electrode 13 to the pixel electrode 12. .

) in the same figure shows an active matrix substrate 10 in which a three-terminal element is embedded as a drive element, and in this case, data electrodes 14 are provided in a direction perpendicular to scanning electrodes 13. The three-terminal element in this example is a thin film transistor 16, which is connected between the pixel electrode 12 and the scanning electrode 13 as before, but whose gate is connected to the data voltage f! 1i
Connected to i14. Also, as before, the scan voltage applied to the scan electrode 13 is switched between positive and negative every scan period, but in the case of a single thin film transistor 16, the scan voltage in both the positive and negative directions on the scan electrode 13 is switched between the pixel type i12. can be transmitted to.

Now, since a very large number of pixels are built into the active matrix substrate 10 configured as described above, as described above, defects may occur in some of the pixels. The main defects are short-circuits and disconnections in the drive element, and the incidence of such defects is so low that it rarely exceeds 10-'. This means that a few of them are likely to occur.

The existence and number of defects can be easily determined by performing a display test after assembling the active matrix substrate with the counter substrate into a display panel, but even if a defective product is produced after assembling, the two substrates will be glued together. Since the active matrix substrate has been completely damaged, it is impossible to recycle the substrate, and all the effort required for adhering the substrates to each other and encapsulating display media such as liquid crystals is wasted.For this reason, when the active matrix substrate is completed, It is desirable to perform tests before assembling them into a display panel to eliminate defective products or correct defective pixels.

Conventionally, this test has been carried out on a pixel-by-pixel basis using a probe 51, as shown schematically in FIG. 5(a). For this test, for example, as shown in the figure, a test circuit is used in which a probe 51, a test Ti source 52 that alternately generates positive and negative test voltages, and an automatic measuring device 53 are connected in series, and one end of the test circuit is connected in series to a predetermined scanning type 1 m 13 The test proceeds by connecting the probe 51 at the other end to the pixel types 8i12 arranged in the row direction by an automatic machine and detecting the current flowing through the test circuit with an automatic measuring device while sequentially bringing the probe 51 at the other end into contact with the pixel types 8i12 arranged in the row direction. The test for the active matrix substrate shown in FIGS. 5 and 5 is similar, except that when the drive element is a transistor, the test voltage may be fixed to either positive or negative.

[Problem to be solved by the invention] However, in the conventional test method as described above, even if the probe is moved at a fairly high speed using an automatic machine,
There is a problem in that it takes a long time to test the active matrix substrate (reverse).

For this reason, if you use a jig equipped with several hundred probes that simultaneously touch the pixel electrodes arranged in one row or column, and conduct the test while electrically switching the probes, it is possible to However, in practice, it is difficult to bring a large number of probes into contact with the pixel electrode with high reliability, and the reliability of the test results is not always sufficient. In addition, the current flowing through the test circuit is very weak, ranging from several pA to several nA, so in order to maintain test accuracy, the current detection time for each pixel cannot be shortened below a certain limit. It is difficult to complete the test within one hour only by saving time for mechanical movement of the probe.

Therefore, from the standpoint of test economics, it has conventionally been necessary to reduce the number of pixels actually tested to, for example, one-tenth of the total number of pixels in the display panel, but considering the purpose or nature of the test, This is not necessarily the most desirable solution.

It is an object of the present invention to solve these conventional problems and provide a practical and simple test method that can complete the test within a short time.

[Means to solve the problem]

According to the invention, this purpose is achieved by superimposing the active matrix substrate to be tested on a test substrate provided with an electroluminescent film in a capacitive manner, so that the scanning electrodes of the active matrix substrate and the electroluminescent film of the test substrate This is achieved by detecting the presence or absence of display defects in each pixel from the intensity of light emitted by the electroluminescent film while applying an alternating current test voltage between the electroluminescent film and the electroluminescent film.

It is advantageous to perform the above capacitive coupling through air in order to save time and effort during testing, and to achieve tighter coupling by setting the distance between the active matrix substrate and the electroluminescent film of the test substrate to be 10μ or less. However, the higher the dielectric constant of the capacitive coupling medium is, the more advantageous it is in reducing the part of the test voltage applied to the coupling capacitor and increasing the luminescence of the electroluminescent film. A dielectric film can be used as a capacitive coupling medium and can also be used to set the spacing between the active matrix substrate and the test substrate.

The electroluminescent film may be composed of an insulating base material and an electroluminescent material as usual, but in order to easily detect luminescence even if the above-mentioned capacitive coupling is weak, an electroluminescent film may be used. is Zn5e
It is desirable to lower the threshold of electroluminescence emission by using a low-energy-gamble system such as a low-energy system. It is preferable to emit bright light so that defects in pixels can be accurately detected based on the intensity of the emitted light in a dark room. As is well known, the intensity of this emission is a function of frequency and can therefore be tuned by selecting the frequency of the alternating test voltage. It is usually appropriate to use a test voltage with a frequency of several kHz. Furthermore, in order to lower the emission threshold value, it is advantageous to attach an electroluminescent film on top of the S content or GaAs. However, since such a semiconductor film has a light blocking property, when the active matrix substrate is combined with the test substrate during testing, the light emitting state is detected from the former side.

When the test substrate is commonly used for various active matrix substrates, it is advantageous to use a single electroluminescent film that is not divided into pixels.

However, depending on the structure of the active matrix substrate, the emission intensity of the electroluminescent film at the portion corresponding to the drive element portion may become too high.
For such an active matrix substrate, it is advantageous to use a test substrate exclusively for it, and to make the portion corresponding to the drive element non-emissive or light-shielding. At this time, it is advantageous to provide a light-shielding mask on the test substrate side not only for the drive element portion but also for the gaps between pixels, in order to separate and detect the light emission state of the electroluminescent film corresponding to each pixel. It is.

[Effect]

Conventionally, testing for the presence or absence of defects or determining pass/fail was carried out sequentially or in series for each pixel, but as can be seen from the above-mentioned configuration, the method of the present invention uses an electroluminescent film on a test substrate in an active matrix substrate. By emitting light for all pixels simultaneously or in parallel, it has been possible to dramatically shorten the time required to detect the presence or absence of display defects in each pixel.

In the method of the present invention, the electroluminescent film emits light instantaneously at the same time as the test voltage is applied, and by appropriately setting the test voltage value and frequency, it is possible to determine whether the number of defective pixels is above the allowable limit or not. In other words, the quality of the active matrix substrate can be visually determined within a few seconds. Also for testing active matrix substrates)! Since the coupling to the E plate is capacitive coupling, it has higher reliability than the conventional coupling by contact with the probe, and therefore there is much less risk of misjudgment. However, in the method of the present invention, the drive element attached to the pixel In principle, it is impossible to accurately measure the characteristics of a pixel or an active matrix substrate, but in most cases it is sufficient to simply determine the quality of each pixel or active matrix substrate.

As described above, the present invention solves the above-mentioned problem by providing a practical method capable of detecting the presence or absence of display defects in each pixel of an active matrix substrate within a short period of time. .

〔Example〕

Embodiments of the present invention will be specifically described below with reference to the drawings. FIG. 1 illustrates the method for testing active matrix substrates for display panels according to the present invention in a form close to its principle, and FIG. 2 shows its equivalent circuit.

The active matrix substrate 10 as the test object shown in FIG. 1 is placed on an insulating substrate Fill, such as a transparent glass plate, as usual! A very thin transparent conductive film such as TO (indium tin oxide) is used to form the pixel electrode 12 and the scanning type fli1.
3, and a driving element 15, which is a two-terminal element or a three-terminal element, is connected between them.

A specific example of this structure will be explained later with reference to FIG. The test substrate 20 shown on the lower side has, for example, an electrode WA22 made of a transparent conductive film or a metal thin film on the entire surface of an insulating substrate 21 as in the above, and an electroluminescent film 24 is provided on top of the electrode WA22. There is. This electroluminescent film is made of, for example, Y2O2, BaTiOs.
, doped Z with an insulating base material such as PbTiOs
lO made of electroluminescent material such as n5e
I! It is 1111 with a thickness of about m. In this example, since the electroluminescent film 24 is a --like film as shown, the test substrate 20 can be used in common regardless of the type of active matrix substrate.

During the test, the active matrix substrate 10 is placed on the test substrate 20 via a thin spacer (not shown) so that the distance δ between the pixel electrode 12 and the electroluminescent film 24 is less than Ion, preferably several microns. As a result, the pixel electrode 12 of the active matrix substrate IO and the electroluminescence 11124 of the test substrate 20 are capacitively coupled with air in between in this example. The alternating current test voltage 40 is applied to the commonly connected scanning electrodes 1 on the active matrix substrate lO side.
3 and the electrode film 22 on the test substrate 20 side,
As mentioned above, the frequency is approximately several kHz, and the voltage value is several tens of V or less, preferably around IOV, and these values are adjusted as appropriate depending on the type of active matrix substrate and test conditions.

FIG. 2(a) equivalently shows the above test circuit when the drive element is a two-terminal element 15 such as a thin film diode, and as can be seen from the figure, the drive element 15, pixel electrode 12 and The capacitance 1c of the coupling between the luminescence M24 and the electroluminescence membrane 22 will be in series with respect to the test voltage 40. Since the electroluminescent film 24 has an equivalent capacitance Ce, the light emission drive voltage applied to it is the value obtained by dividing the test voltage by both capacitances.As can be easily seen, in order to increase this light emission drive voltage, The larger the capacitance 1c of the coupling, the more advantageous it is, so as mentioned above, it is desirable to make the distance between the pixel electrode 12 and the electroluminescent film 24 as small as possible to make the capacitive coupling dense.

When testing an active matrix substrate with such a test circuit, if there is a short-circuit defect in the drive element 15 of a certain pixel, the emission intensity of the electroluminescence [24] of the corresponding part becomes abnormally high, and if there is a disconnection defect, no light emission occurs. Therefore, the presence or absence and type of defects can be easily detected or determined by visual inspection. Of course, instead of visual inspection, it is also possible to automate the detection and output using a highly sensitive image sensor such as a television camera, and to automatically record the test results in combination with a data processing device.

At this time, the light emitting state of the electroluminescent film can normally be observed or detected from the upper side of FIG. 1, that is, from the active matrix substrate side. When using , it is also possible to do it from the test board side.

In addition, the voltage value and frequency of the AC test voltage applied during the above tests are selected to be advantageous in detecting short circuits or disconnections in pixels, and in practice, the light emitting state of the electroluminescent film is checked at the start of the test. These values are adjusted optimally while checking.

Figure 2 0)) is a three-terminal element 1 as a thin film as a drive element.
This is the equivalent circuit of the test when using 6, AC test voltage 40
The connection between the capacitance lc of the coupling between the drive element 16 and the substrate and the equivalent capacitance ice of the electroluminescent film is the same as before, but the third terminal of the drive element 16, for example, the gate of a thin film transistor is connected. Another DC test voltage 41 is connected between the data electrode 14 and the scan electrode 13. The test procedure is the same as that shown in Figure (a), but as can be easily seen, the above test voltage 41
By turning on the drive element 16, it is possible to test whether there is an open circuit defect in the drive element 16, and by turning it off, it is possible to test whether there is a short circuit defect in the drive element 16.

FIG. 3 shows a different embodiment of the invention in the same manner as FIG. The structure of the active matrix substrate IO is the same as before, but since the details of the structure are shown in a plan view in FIG. 4 for an example in which the driving elements are diodes, this will be briefly explained first.

As shown in FIG. 4, the pixel electrode 12 is formed in a substantially rectangular shape, and the pixel electrode 13 is formed in an elongated shape that is common to the pixel electrodes arranged in the left-right direction in the figure. 1 constituting the drive element 15
Of the pair of diodes 15p and 15n, the former is formed on the scanning electrode 13 and the latter on the pixel electrode 12, and a thin insulator 11i15a made of silicon nitride or the like is provided to commonly cover both. The connecting film 15b made of aluminum or the like is scanned by scanning i! Diode 15P on tffila
is connected to the pixel electrode 12, and the Vi contact film 15c is connected to the pixel electrode 12.
The diode 15n on the top 2 is connected to the scanning electrode 13. In this example, the latter extends from the connection of the diode so as to substantially cover the scanning electrode 13 as well, as shown.

The active matrix substrate shown in FIG. 3 is used for a liquid crystal display panel, and an alignment film 17 for aligning liquid crystal molecules in a predetermined direction is deposited so as to cover almost the entire surface thereof. This alignment film is made of polyimide resin, for example, and has a third
When superimposed on the test substrate 20 as shown in the figure, it is interposed as a dielectric film between the pixel electrode 12 and the electroluminescent film 24, and serves to increase the coupling capacitance value between the two. In the example, the drive element 15 protrudes considerably from the pixel electrode 12, and although this height difference is alleviated by the deposition of the alignment film 17, the electroluminescence 1112 facing the drive element 15 during the test
The luminescence intensity in the part 4 may become high and interfere with the test.

For this reason, in this embodiment, a mask 23 is provided in a portion corresponding to the drive element 15 on the test substrate 20 side. This mask 23 is made of, for example, a metal film, and is therefore placed at the same potential as the electrode film 21 during testing, and has a light shielding property against light emitted from the electroluminescent film 24. Utilizing this light-shielding property, the mask 23 is formed in a frame shape surrounding the pixel electrode 112 in addition to the locations corresponding to the diodes 15P and 15n in FIG. can be separated into When the mask 23 is formed into a frame shape in this manner, the electroluminescent film 24 is provided only inside the frame, that is, at a location facing the pixel electrode 12. However, the test substrate 2o in this embodiment is dedicated to one type of active matrix substrate.

In this embodiment, a very thin dielectric film 25 is applied or applied to the test substrate 20 so as to cover the mask 23 and the electroluminescent material 24.

This dielectric film 25 also serves as a kind of spacer, and during testing, the active matrix substrate 10 is set so as to be in contact with this dielectric film 25 as shown. This dielectric film 25 is used together with the alignment film 17 to form a conductive mask 23.
It is also useful for insulating the drive element 15 from the drive element 15 during testing.

This test board 20 is housed in a recess in a main body 31 of a test jig 30, which is shown in the dark by a thin line in the figure, and is preferably made of a transparent material at the bottom, and a bottle 3 is placed therein.
132 is fitted to 1a. The active matrix substrate 10 to be tested is this! 32
By loading the test board 20 onto the test board 20 through the window, the test board 20 is positioned in the front, rear, left, and right directions in the figure, and at the same time is capacitively coupled to the test board. If necessary, a light-shielding lid is placed over it.

The test was conducted with the active matrix substrate 1 in the condition shown in Figure 3.
The test is performed in the same manner as before by applying a predetermined test voltage between the scanning electrode 13 of 0 examples and the electrode film 22 of 20 test substrates. The luminescence state of the electroluminescent film 24 can be measured visually or with a television camera, etc., from the upper side of the diagram, but it is better to measure the luminescence state of the electroluminescent film from that direction by using the lower side of the test jig as a dark room. In this embodiment, the capacitance of the connection between the active matrix substrate and the test substrate, which is desirable for sharp observation, is the same as that of the dielectric film 25 and the alignment film 17.
is larger than that in the previous embodiment, and therefore the emission intensity of the electroluminescent film can be improved.

[Effects of the Invention] As explained above, in the method of the present invention, an active device incorporating a driving element attached to pixels arranged in a display surface and a scanning electrode for driving display of the pixels via the driving element is provided. In testing the presence or absence of display defects in each pixel of the matrix substrate, the active matrix substrate to be tested is superimposed on the test substrate provided with the electroluminescent film so as to be capacitively coupled. With an alternating current test voltage applied between the scanning electrode and the electroluminescent film of the test substrate, the presence or absence of display defects in each pixel was detected from the brightness of the light emitted by the electroluminescent film. Unlike the conventional method of sequentially testing each pixel for defects, this method allows the electroluminescence/sensing film on the test substrate to emit light corresponding to all pixels on the active matrix substrate at the same time. As a result, the time required to detect the presence or absence of display defects in each pixel and to determine the quality of the active matrix substrate can be significantly shortened compared to the conventional method.

Since the electroluminescent film described above emits light simultaneously and in parallel without being restricted by the number of pixels in the display panel, the method of the present invention makes it possible to detect defects in all pixels in the display panel without any difficulty. Become. In the past, it was often necessary to test only some pixels due to economic reasons, but with the present invention, it is possible to conduct a complete test and accurately determine whether the active matrix board is good or bad, and it is also possible to conduct tests based on the test results for all pixels. By correcting the detected defective pixels, it is also possible to regenerate the active matrix substrate.

In addition, the capacitive coupling of the active matrix substrate to the test substrate in the method of the present invention has much higher reliability of coupling than the conventional contact coupling using a probe, which prevents false detection of defects and Misjudgments are almost completely eliminated, and the reliability of test results is greatly improved.

[Brief explanation of the drawing]

The figures all relate to the present invention; Figure 1 is a sectional view of an active matrix substrate and a test substrate showing an embodiment of the method for testing active matrix substrates for display panels according to the present invention, and Figure 2 is an equivalent circuit diagram during this test. , FIG. 3 is a sectional view of both boards showing different embodiments of the present invention, FIG. 4 is a partially enlarged plan view of an active matrix board as a test object, and FIG. 5 is an equivalent circuit diagram of this active matrix board. In addition, in Figure 0, which is a diagram briefly showing the gist of the conventional test method, 1O: active matrix group (anti, 11: active matrix group),
Substrate, 12: pixel electrode, 13: scanning electrode, 14: data electrode, 15: two-terminal element as driving element, 15p,
15n: diode as a driving element, 16: 3-terminal element as a driving element, 17: alignment film, 20: test substrate, 21: insulating substrate, 22: electrode film, 23; mask, 24
: Electroluminescent film, 25'm electric film, 30
: Test jig, 31: Jig body, 31a: Bottle, 32:
Jig lid, 40: AC test voltage, 41: DC test voltage,
51: Probe, 52: Test power supply, 53: Automatic measurement device,
C: Capacitive coupling or its capacitance, Ce: Capacitance of the electroluminescent film, Figure 2 between the 68 pixel electrode and the electroluminescent film and the coupling.

Claims (1)

[Claims] An active matrix substrate incorporating a driving element attached to pixels arranged in a display surface and a scanning electrode for displaying the pixels via the driving element is tested for the presence or absence of display defects in each pixel. A method, comprising: superimposing an active matrix substrate to be tested on a test substrate having an electroluminescent film in a capacitive manner, and comprising: a scanning electrode of the active matrix substrate and an electroluminescent film of the test substrate; A method for testing an active matrix substrate for a display panel, which comprises applying an alternating current test voltage and detecting the presence or absence of a display defect in each pixel based on the intensity of light emission from an electroluminescent film.