JPH055901A - Active matrix liquid crystal display device - Google Patents

Abstract

PURPOSE:To correctly discriminate the characteristic of active elements by leading out a lead wire for test from the active element corresponding to at least one of many picture element electrodes to the side edge part of a substrate. CONSTITUTION:A lead wire 18 for test is branched from the connection end of an active element 15 corresponding to at least one picture element electrode 14 out of many picture element electrodes 14. An end part 18a of this lead wire 18 is led out to the side edge part of a substrate 11. The active element 15 corresponding to this picture element electrode 14 is used as the test element for characteristic measurement to measure the characteristic of the active element 15 itself. That is, a gate signal is applied to a scanning line 12 connected to the gate electrode of the active element 15 used as the test element, and a test signal is applied to a signal line 13 connected to the drain electrode of the active element 15, and the output to the lead wire 18 for test led out to the side edge part of the substrate from the source electrode of the active element 15 is measured, thereby measuring the characteristic of the active element 15.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an active matrix liquid crystal display device.

[0002]

2. Description of the Related Art In an active matrix liquid crystal display device, a large number of signal lines and a large number of pixel electrodes arranged along the respective signal lines are provided on one of a pair of transparent substrates facing each other with a liquid crystal layer in between. And an active element which is provided corresponding to each pixel electrode and supplies a data signal applied to the signal line to the pixel electrode, and a counter electrode is formed on the other substrate. .. This active matrix liquid crystal display device includes one using a thin film transistor as an active element and one using a thin film diode as an active element. FIG. 5 is a circuit diagram of a conventional active matrix liquid crystal display device, in which a thin film transistor is used as an active element.

In FIG. 5, reference numeral 1 denotes one of a pair of transparent substrates (glass substrates) facing each other across a liquid crystal layer, and a large number of scanning lines 2 are parallel to each other on the surface of the substrate 1. And a number of signal lines 3 orthogonal to the scanning line 2 are wired in parallel with each other. The scanning lines 2 and the signal lines 3 are insulated from each other by an insulating film.

A large number of pixel electrodes (transparent electrodes) 4 are arrayed on the surface of the substrate 1 along the scanning lines 2 and the signal lines 3 and correspond to the respective pixel electrodes 4. An active element 5 for supplying the data signal applied to the signal line 3 to the pixel electrode 4 is formed.

The active element 5 is a thin film transistor, the gate electrode of which is connected to the scanning line 2, the drain electrode thereof is connected to the signal line 3, and the source electrode thereof is connected to the pixel electrode 4.

Although not shown in FIG. 5, a transparent counter electrode facing the pixel electrodes 4 is formed on the other substrate, and the counter electrode is a single electrode over the entire display area. ..

In this active matrix liquid crystal display device, a sequential scanning signal (gate signal) is supplied to each scanning line 2.
Is applied and an image data signal is applied to each signal line 3 in synchronism therewith to drive the display. The active element (thin film transistor) 5 is a scanning signal applied to the gate electrode from the scanning line 2. Then, it is turned on, and the image data signal applied from the signal line 3 to the drain electrode is supplied from the source electrode to the pixel electrode 4.

By the way, in this active matrix liquid crystal display device, the display characteristics are influenced by the characteristics of the thin film transistor which is the active element 5. Therefore, in order to manufacture a liquid crystal display device with good display quality at a high yield, the manufacture thereof is required. In the process, the active element 5 formed on the surface of the substrate 1
It is necessary to judge the quality of the characteristic.

Therefore, in the conventional active matrix liquid crystal display device, as shown in FIG. 5, one or several pixels are formed in the portion of the substrate 1 on which the pixel electrode 4 and its active element 5 and the like are formed outside the display region. (Two in the figure) test elements (thin film transistors having the same configuration as the thin film transistor which is the active element 5) 5a are formed, and the characteristics of the test element 5a are measured to determine the characteristics of the active element 5. ing.

The test element 5a is formed together when the active element 5 is formed, and the characteristics of the test element 5a are measured from the gate, source and drain electrodes to the side edges of the substrate. Derived test terminals 6
Of the G, 6S, and 6D, a gate signal is applied to the gate terminal 6G, a test signal is applied to the drain terminal 6D, and the output to the source terminal 6S is measured.

Although a thin film transistor is used as the active element 5 in FIG. 5, even in an active matrix liquid crystal display device using a thin film diode as the active element, the pixel electrode and the thin film diode which is the active element have been conventionally used. Etc. on the part outside the display area of the substrate on which
One or several thin film diodes are formed for testing, and the characteristics of each test element are measured to determine the characteristics of each thin film diode that is an active element.

[0012]

However, the above-mentioned conventional active matrix liquid crystal display device has a problem that the characteristic of being an active element cannot be correctly determined.

This is because there is a difference in characteristics between the test element (thin film transistor 5a or thin film diode) formed outside the display area and the active element (thin film transistor 5 or thin film diode).

That is, the test element is formed together with the active element when the active element is formed. However, even if the active element and the test element are formed in the same process, the active element and The deposited film thickness of the semiconductor layer that constitutes the test element during film formation differs between the central portion (display area) of the substrate and the outer peripheral portion (portion outside the display area) of the substrate, and the deposited film is patterned. In the case of etching, the characteristics of the test elements formed are different from the characteristics of the active elements because the etching conditions of the active elements arranged at a constant pitch are different from those of the test elements formed independently.

In the conventional active matrix liquid crystal display device, since the characteristic of the active element cannot be correctly determined, this substrate is determined to be a defective product even though the characteristic of the active element is good. In some cases, a substrate with poor characteristics of active elements was judged as a good product. An object of the present invention is to provide an active matrix liquid crystal display device capable of correctly determining the characteristics of active elements.

[0016]

In the active matrix liquid crystal display device of the present invention, a test lead wire is branched from a pixel electrode connecting end of an active element corresponding to at least one pixel electrode among a large number of pixel electrodes. It is characterized in that the end portion of the test lead wire is led out to the side edge portion of the substrate.

[0017]

That is, according to the present invention, the characteristic of the active element itself is measured by using the active element corresponding to at least one pixel electrode among a large number of pixel electrodes as a test element for characteristic measurement. The characteristics of this active element can be measured by applying a test signal to the signal line connected to this active element and measuring the output to the test lead wire led to the side edge of the board. it can.

[0018]

【Example】

(First Embodiment) A first embodiment of the present invention will be described below with reference to FIGS.

The active matrix liquid crystal display device of this embodiment uses thin film transistors as active elements. FIG. 1 is a circuit diagram of the liquid crystal display device, and FIG. 2 is an active element portion also used as a test element. It is a top view.

In FIG. 1, reference numeral 11 denotes one of a pair of transparent substrates (glass substrates) facing each other across a liquid crystal layer, and a large number of scanning lines 1 are provided on the surface of the substrate 11.
2 are wired in parallel with each other, and a large number of signal lines 13 orthogonal to the scanning line 12 are wired in parallel with each other.

Each scanning line 1 is formed on the surface of the substrate 11.
2 and each of the signal lines 13, a large number of pixel electrodes (transparent electrodes) 14 are arrayed and formed, and the signal lines 13 are respectively associated with the pixel electrodes 14.
An active element 15 that supplies the data signal applied to the pixel electrode 14 is formed.

The active element 15 is a thin film transistor. The thin film transistor has, for example, an inverted stagger structure, and as shown in FIG. 2, the gate electrode G formed on the scanning line 12 wired on the surface of the substrate 11 and the substrate covering the gate electrode G and the scanning line 12 11, a transparent gate insulating film 16 formed over the entire display region, a semiconductor layer 17 formed on the gate insulating film 16 so as to face the gate electrode G, and formed on the semiconductor layer 17. And a source electrode S and a drain electrode D.

The signal line 13 and the pixel electrode 14 are formed on the gate insulating film 16, and the drain electrode D of the active element (thin film transistor) 15 is formed.
Is connected to the signal line 13, and the source electrode S is connected to the pixel electrode 14.

In the figure, reference numeral 12a is a scan line 1.
Two terminals, 13a are terminals of the signal line 13, the terminals 12a of each scanning line 12 are arranged on one edge of the substrate 11, and the terminals 13a of each signal line 13 are arranged on one edge of the substrate 11. ing.

Although not shown, a transparent counter electrode facing each of the pixel electrodes 14 is formed on the other substrate which faces the substrate 11 with the liquid crystal layer in between. One electrode is formed over the entire area.

The active element 15 corresponding to a part of the pixel electrodes 14 of the large number of pixel electrodes 14 also serves as a test element for measuring the characteristic. In this embodiment, FIG. In the above, the two active elements 15 corresponding to the two pixel electrodes 14 at both ends of each pixel electrode 14 in the uppermost row also serve as test elements.

A test lead wire 18 is branched from the pixel electrode connecting end of the active element 15 which also serves as the test element, and the end portion 18a of the test lead wire 18 is
It is led out to one side edge portion of the substrate 11, that is, the arrangement edge portion of the signal line terminals 13a. The test lead wire 18 is formed integrally with the source electrode S of the active element 15, as shown in FIG.

That is, in the active matrix liquid crystal display device of this embodiment, the active elements 15 corresponding to a part of the pixel electrodes 14 of the large number of pixel electrodes 14 are also used as test elements for measuring the characteristics. The characteristic of the active element 15 itself is measured.

To measure the characteristics of the active element 15, a gate signal is applied to the scanning line 12 to which the gate electrode G of the active element 15 which also functions as a test element is connected, and the drain electrode D of this active element 15 is connected. This can be performed by applying a test signal to the signal line 13 present and measuring the output from the source electrode S of the active element 15 to the test lead wire 18 led to the side edge of the substrate. In addition, the measurement of this characteristic also serves as a test element.
It may be performed for both of the one active elements 15 or for only one of them.

In this liquid crystal display device, the active element 15 corresponding to some of the pixel electrodes 14 is also used as a test element to measure the characteristics of the active element 15 itself. The characteristics of the thin film transistor, which is the element 15, can be correctly determined.

In this case, the active element 15 capable of directly measuring the characteristics is only one or both of the two active elements 15 which also serve as the test element, but the active element 15 which also serves as the test element and the other active element 15 All of them are arranged and arranged at a constant pitch in the display region in the central portion of the substrate. Therefore, the deposited film thickness and the semiconductor layer 17 at the time of forming the gate insulating film 16 and the semiconductor layer 17 which constitute each active element 15 are formed.
Since the etching conditions when patterning etc. are almost uniform in all thin film transistors 15, the characteristics of the active element 15 whose direct characteristics cannot be measured are the same as the characteristics of the active element 15 which also functions as a test element. By measuring the characteristics of the active element 15 that also serves as the test element, the characteristics of all the active elements 15 can be determined.

In the above embodiment, the two pixel electrodes 1
Although the two active elements 15 corresponding to 4 are used as the test elements, the number of active elements 15 used as the test elements may be at least one.

Further, although the liquid crystal display device of the above embodiment uses the thin film transistor as the active element, the present invention can be applied to the active matrix liquid crystal display device using the thin film diode as the active element. .. (Second Embodiment) FIGS. 3 and 4 show a second embodiment of the present invention.

The active matrix liquid crystal display device of this embodiment uses a thin film diode as an active element, and FIG. 3 is a partial circuit diagram of the liquid crystal display device.
[FIG. 3] is a plan view of an active element portion that is also used as a test element.

In FIG. 3, reference numerals 20 and 21 denote a pair of transparent substrates (glass substrates) which face each other with a liquid crystal layer in between, and a striped counter electrode is provided on the surface of the first substrate 20 shown by a chain line in the figure. A large number of (transparent electrodes) 22 are formed in parallel with each other at a minute interval, and the second substrate 21 shown by a solid line in the figure.
On the surface, a large number of signal lines 23 orthogonal to the length direction of the counter electrode 22 are wired in parallel with each other.

On the surface of the second substrate 21, a large number of pixel electrodes (transparent electrodes) are arranged along the signal lines 3 and face the respective counter electrodes 22 on the surface of the first substrate 20.
24 are arranged in an array, and active elements 25 corresponding to the respective pixel electrodes 24 are formed.

The active element 25 is a thin film diode. In this embodiment, the active element 25 is a back-to-back (TBT) in which two thin film diodes 25a and 25b are connected in series in opposite directions. It has a structure.

Two thin film diodes 25a and 25b which constitute the active element 25 of this back-to-back structure.
Are the base electrodes 26 formed on the surface of the substrate 21, respectively.
And a semiconductor layer 27 having a P-I-N junction or P-N junction structure formed on the base electrode 26, and an upper electrode 28 formed on the semiconductor layer 27.

Then, these two thin film diodes 25
Of the base electrode 26 and the upper electrode 28 of a and 25b,
One electrode (base electrode in this embodiment) 26 is an electrode common to both thin film diodes 25a and 25b, and the other electrode (upper electrode in this embodiment) 28 is separated for each thin film diode 25a, 25b. The two thin film diodes 25a and 25b are connected in series in a state where their polarities are opposite to each other via the base electrode 26 which is a common electrode.

Further, one end of the active element 25, that is, the upper electrode 28 of the thin film diode 25a on the signal line 23 side.
Is connected to the signal line 23, and the other end of the active element 25, that is, the upper electrode 28 of the thin film diode 25b on the pixel electrode 24 side is connected to the pixel electrode 24.

The active element 25 having the back-to-back structure transmits the image data signal applied to each signal line 23 in synchronization with the scanning signal sequentially applied to each counter electrode 22 on the surface of the first substrate 20. Which is supplied to the pixel electrode 24,
This active element 25 has a voltage value exceeding its threshold voltage (a voltage at which one of the two thin film diodes 25a and 25b, which is opposite to the direction of current, becomes conductive to the opposite direction current). When this data signal is applied, it is turned on and this data signal is supplied to the pixel electrode 24.

In the figure, 22a is a terminal of the counter electrode, 23a is a terminal of the signal line 23, and the terminals 22a of the counter electrodes 22 are arranged at one edge of the first substrate 20 and the signal lines 23 are arranged. 23a are arranged on one side edge of the second substrate 21.

The active circuit 25 corresponding to a part of the pixel electrodes 24 out of the large number of pixel electrodes 24 is also used as a test element for characteristic measurement, and the active circuit 25 also functions as a test element. A test lead wire 29 is branched from the pixel electrode connection end of the circuit 25.

As shown in FIG. 4, the test lead wire 29 is formed integrally with the upper electrode 28 of the thin film diode 25b on the pixel electrode 24 side, and the end portion 29a of the test lead wire 29 is It is led out to one side edge portion of the substrate 21, that is, the arrangement edge portion of the signal line terminals 23a.

That is, also in the active matrix liquid crystal display device of this embodiment, the active elements 25 corresponding to some of the pixel electrodes 24 among the many pixel electrodes 24 are also used as test elements for measuring the characteristics. The characteristic of the active element 25 itself is measured.

The characteristic of the active element 25 is measured by
A test signal is applied to the signal line 23 connected to the active element 25 which also functions as a test element, and the active element 25
This can be done by measuring the output from the pixel electrode connecting end to the test lead wire 29 led to the side edge of the substrate.

Also in this liquid crystal display device, the active elements 25 corresponding to some of the pixel electrodes 24 are also used as test elements to measure the characteristics of the active elements 25 themselves. The characteristics of the element 25 can be correctly determined.

In the above embodiment, the active element 25 composed of the thin film diode has a back-to-back structure. However, in the active matrix liquid crystal display device having the thin film diode as the active element, one or the same direction is used. An active circuit composed of a plurality of thin film diodes connected in series, or two locations of a pixel electrode are connected to a signal line via a pair of active elements, and the direction of the thin film diode of one active circuit and the other active circuit There is also a diode ring structure in which the directions of the thin film diodes are reversed, and the present invention can be applied to these liquid crystal display devices.

[0049]

According to the active matrix liquid crystal display device of the present invention, a test lead wire is led out from the active element corresponding to at least one pixel electrode among a large number of pixel electrodes to the side edge of the substrate, and this active element is Since the characteristics of the active element itself are measured by using it as a test element for measuring characteristics, the characteristics of the active element can be correctly determined.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a liquid crystal display device showing a first embodiment of the present invention.

FIG. 2 is a plan view of an active element portion that is also used as a test element.

FIG. 3 is a circuit diagram of a liquid crystal display device showing a second embodiment of the present invention.

FIG. 4 is a plan view of an active element portion that is also used as a test element.

FIG. 5 is a circuit diagram of a conventional liquid crystal display device.

[Explanation of symbols]

11 ... Substrate, 12 ... Scan line, 13 ... Signal line, 1
4 ... Pixel electrode, 15 ... Active element (thin film transistor),
18 ... Test lead wire, 20, 21 ... Substrate, 22 ... Counter electrode, 23 ... Signal line, 24 ... Pixel electrode, 25 ... Active element, 25a, 25b ... Thin film diode, 29 ... Test lead wire.

Claims (1)

1. A large number of signal lines and a large number of pixel electrodes arranged along each of the signal lines on one of a pair of transparent substrates facing each other with a liquid crystal layer in between. An active matrix liquid crystal display device in which an active element which is provided corresponding to each pixel electrode and which supplies a data signal applied to the signal line to the pixel electrode is formed, and an opposite electrode is formed on the other substrate. The test lead wire is branched from the pixel electrode connection end of the active element corresponding to at least one pixel electrode of the plurality of pixel electrodes, and the end portion of the test lead wire is led to the substrate side edge portion. Characteristic active matrix liquid crystal display device.