JPH04288519A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To measure the impedance of charged liquid crystal by providing an electrode for measurement in an area where picture elements of a substrate on the opposite side from a substrate provided with a common picture element electrode are not formed. CONSTITUTION:The electrode MEL1 is provided in the area where the picture elements of the substrate on the opposite side from the substrate SUB1 provided with the common picture element electrode ITO 2 are not formed. For the purpose, a measurement voltage is applied between the electrode MEL1 for measurement and common picture element electrode ITO 2 and a current flowing through liquid crystal LC is measured to measure the impedance of the liquid crystal LC in the charged state without disassembling the liquid crystal display device. Further, when an orienting film is provided on the electrode MEL1 for measurement, the measurement voltage is applied between the electrode MEL1 for measurement and common picture element electrode ITO 2 and a brightness meter detects the brightness of the electrode part MEL1 for measurement to accurately detect the brightness characteristic, so a defect analysis of the brightness characteristic can exactly be taken.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device, and more particularly to an active matrix type liquid crystal display device using thin film transistors and the like.

0002

2. Description of the Related Art An active matrix liquid crystal display device includes a nonlinear element (switching element) corresponding to each of a plurality of pixel electrodes arranged in a matrix. Theoretically, the liquid crystal in each pixel is constantly driven (duty ratio 1.0), so the active method has better contrast than the so-called simple matrix method, which uses a time-division drive method, especially for color LCDs. It is becoming an indispensable technology for display devices. A typical switching element is a thin film transistor (TFT).

In active matrix type liquid crystal display devices, it is necessary to measure the impedance of the liquid crystal because a slight difference in the impedance of the liquid crystal greatly affects the display.

For this reason, conventionally, the impedance of the liquid crystal is measured before the liquid crystal is sealed.

[0005] An active matrix type liquid crystal display device using thin film transistors is, for example, ``12.5-inch active matrix type color liquid crystal display employing redundant configuration'', Nikkei Electronics, Inc.
Pages 193-210, December 15, 1986, published by Nikkei McGraw-Hill.

[0006]

[Problems to be Solved by the Invention] When a liquid crystal display device is operated for a long period of time, the impedance of the liquid crystal changes, causing uneven brightness and burn-in phenomenon. However, in conventional liquid crystal display devices, it is not possible to measure the impedance of the sealed liquid crystal, so in order to measure the impedance of the sealed liquid crystal, it is necessary to disassemble the liquid crystal display device. There is.

[0007] The present invention was made to solve the above-mentioned problems, and an object of the present invention is to provide a liquid crystal display device in which the impedance of sealed liquid crystal can be measured without disassembling the liquid crystal display device. do.

[0008]

[Means for Solving the Problems] In order to achieve this object, in the present invention, a measurement electrode is provided in a region of a substrate on the opposite side of the substrate where a common pixel electrode is formed, where no pixels are formed.

In this case, an alignment film may be provided on the measurement electrode.

0010

[Operation] In this liquid crystal display device, the impedance of the sealed liquid crystal can be measured by applying a measurement voltage between the measurement electrode and the common pixel electrode and measuring the current flowing through the liquid crystal. Can be done.

[0011] Furthermore, if an alignment film is provided on the measurement electrode,
Applying a measurement voltage between the measurement electrode and the common pixel electrode,
By detecting the brightness of the measuring electrode section with a brightness meter, the brightness characteristics can be detected accurately.

0012

DESCRIPTION OF THE PREFERRED EMBODIMENTS The structure of the present invention will be described below along with an embodiment in which the present invention is applied to an active matrix color liquid crystal display device.

[0013] In all the figures for explaining the embodiment, parts having the same functions are given the same reference numerals, and repeated explanations thereof will be omitted.

FIG. 2 shows an active system to which this invention is applied.
A plan view showing one pixel and its surroundings of a matrix color liquid crystal display device. FIG. 3 is a cross-sectional view taken along section line 3-3 in FIG. 2 and a cross-sectional view near the seal portion of the display panel. FIG. It is a sectional view taken along the -4 cutting line. Also, Figure 7 (
2 shows a plan view when a plurality of pixels shown in FIG. 2 are arranged.

(Pixel Arrangement) As shown in FIG. 2, each pixel is connected to two adjacent scanning signal lines (gate signal lines or horizontal signal lines) GL and two adjacent video signal lines (drain signal lines or horizontal signal lines). (vertical signal line) DL (in the area surrounded by four signal lines). Each pixel includes a thin film transistor TFT, a transparent pixel electrode ITO1, and a storage capacitor element Cadd. The scanning signal lines GL extend in the column direction, and a plurality of scanning signal lines GL are arranged in the row direction. Video signal line D
L extends in the row direction, and a plurality of L's are arranged in the column direction.

(Overall cross-sectional structure of display section) As shown in FIG. 3, a thin film transistor TFT and a transparent pixel electrode ITO1 are formed on the lower transparent glass substrate SUB1 side with respect to the liquid crystal LC, and a color electrode is formed on the upper transparent glass substrate SUB2 side. A filter FIL and a light shielding film BM forming a light shielding black matrix pattern are formed. The lower transparent glass substrate SUB1 has a thickness of, for example, about 1.1 mm. Further, silicon oxide films SIO formed by dipping treatment or the like are provided on both surfaces of the transparent glass substrates SUB1 and SUB2. Therefore, even if there are sharp scratches on the surface of the transparent glass substrates SUB1 and SUB2,
Since sharp scratches can be covered with the silicon oxide film SIO, damage to the scanning signal line GL and color filter FIL can be effectively prevented.

The center part of FIG. 3 shows a cross section of one pixel, the left side shows a cross section of the left edge of the transparent glass substrates SUB1 and SUB2 where external lead wiring is present, and the right side shows a cross section of the transparent glass substrate SUB1, SUB2. A cross section of the right edge portion of the glass substrates SUB1 and SUB2 where no external lead wiring is present is shown.

The sealing material SL shown on the left and right sides of FIG. 3 is configured to seal the liquid crystal LC, and the transparent glass substrate SUB1, excluding the liquid crystal sealing opening (not shown), is configured to seal the liquid crystal LC.
It is formed along the entire periphery of the SUB2. The sealing material SL is made of, for example, epoxy resin.

The common transparent pixel electrode ITO2 on the upper transparent glass substrate SUB2 side is connected at least in one place to an external lead wiring formed on the lower transparent glass substrate SUB1 side using a silver paste material SIL. This external lead wiring is formed in the same manufacturing process as each of the gate electrode GT, source electrode SD1, and drain electrode SD2.

Orientation films ORI1, ORI2, transparent pixel electrode ITO1, common transparent pixel electrode ITO2, protective film PSV1
, PSV2, and the insulating film GI are each made of a sealing material S.
Formed inside L. The polarizing plates POL1 and POL2 are formed on the outer surfaces of the lower transparent glass substrate SUB1 and the upper transparent glass substrate SUB2, respectively.

The liquid crystal LC is sealed between a lower alignment film ORI1 and an upper alignment film ORI2, which set the orientation of liquid crystal molecules, and is sealed by a seal portion SL.

The lower alignment film ORI1 is formed on the protective film PSV1 on the lower transparent glass substrate SUB1 side.

On the inner surface (liquid crystal LC side) of the upper transparent glass substrate SUB2, a light shielding film BM and a color filter FI are provided.
L, protective film PSV2, common transparent pixel electrode ITO2 (CO
M) and an upper alignment film ORI2 are sequentially stacked.

This liquid crystal display device has a lower transparent glass substrate S.
The layers on the UB1 side and the upper transparent glass substrate SUB2 side are formed separately, and then the upper and lower transparent glass substrates SUB1 are formed.
, SUB2 are stacked on top of each other and a liquid crystal LC is sealed between them.

(Thin Film Transistor TFT) The thin film transistor TFT operates such that when a positive bias is applied to the gate electrode GT, the channel resistance between the source and drain becomes small, and when the bias is reduced to zero, the channel resistance becomes large.

The thin film transistor TFT of each pixel is divided into two (plurality) within the pixel, and is composed of thin film transistors (divided thin film transistors) TFT1 and TFT2. Each of the thin film transistors TFT1 and TFT2 has substantially the same size (channel length and width are the same). Each of the divided thin film transistors TFT1 and TFT2 mainly has a gate electrode GT.
, gate insulating film GI, i-type (intrinsic)
, a pair of source electrodes SD1 and drain electrodes SD2. Note that the source and drain are originally determined by the bias polarity between them, and in the circuit of this liquid crystal display device, the polarity is reversed during operation, so it should be understood that the source and drain are interchanged during operation. However, in the following description, for convenience, one side is fixed as a source and the other side is fixed as a drain.

(Gate electrode GT) The gate electrode GT is shown in FIG.
As shown in detail in (a plan view depicting only the second conductive film g2 and i-type semiconductor layer AS in FIG. 2), the shape projects vertically from the scanning signal line GL (upward in FIGS. 2 and 8). (branched into a T-shape)
. Gate electrode GT is thin film transistor TFT1, TFT
It is configured to protrude to the respective formation regions of 2. The respective gate electrodes GT of the thin film transistors TFT1 and TFT2 are integrated (as a common gate electrode).
It is formed continuously with the scanning signal line GL. The gate electrode GT is composed of a single-layer second conductive film g2. The second conductive film g2 is formed using, for example, an aluminum film formed by sputtering, and has a thickness of about 1000 to 5500 Å. Furthermore, an aluminum anodic oxide film AOF is provided on the gate electrode GT.

As shown in FIGS. 2, 3 and 8, the gate electrode GT is formed larger than the i-type semiconductor layer AS so as to completely cover it (as viewed from below). Therefore, when a backlight BL such as a fluorescent lamp is attached below the lower transparent glass substrate SUB1, the gate electrode GT made of opaque aluminum forms a shadow.
The i-type semiconductor layer AS is not irradiated with backlight light, making it difficult for a conductive phenomenon due to light irradiation, that is, deterioration of the off-characteristics of the thin film transistor TFT, to occur. Note that the original size of the gate electrode GT is the same as that of the source electrode SD1 and the drain electrode SD.
2 (including the alignment margin between the gate electrode GT, source electrode SD1, and drain electrode SD2), and the depth length that determines the channel width W is the width of the source electrode SD1. It is determined by the ratio of the distance (channel length) L between the gm and the drain electrode SD2, that is, the factor W/L that determines the mutual conductance gm.

Gate electrode GT in this liquid crystal display device
Of course, the size is made larger than the original size mentioned above.

(Scanning signal line GL) The scanning signal line GL is the second
It is composed of a conductive film g2. The second conductive film g2 of the scanning signal line GL is formed in the same manufacturing process as the second conductive film g2 of the gate electrode GT, and is configured integrally. Moreover, an aluminum anodic oxide film AO is formed on the scanning signal line GL.
F is provided.

(Insulating Film GI) The insulating film GI is used as a gate insulating film for each of the thin film transistors TFT1 and TFT2. The insulating film GI is formed on the gate electrode GT and the scanning signal line GL. The insulating film GI is formed using, for example, a silicon nitride film formed by plasma CVD, and has a thickness of about 3000 Å.

(I-Type Semiconductor Layer AS) As shown in FIG. 8, the i-type semiconductor layer AS is used as a channel forming region for each of the thin film transistors TFT1 and TFT2 which are divided into a plurality of parts. The i-type semiconductor layer AS is formed of an amorphous silicon film or a polycrystalline silicon film and has a thickness of about 1800 Å.

This i-type semiconductor layer AS was formed by the same plasma CVD process following the formation of the insulating film GI to be used as a gate insulating film made of Si3N4 by changing the composition of the supplied gas.
The plasma CVD device is formed without being exposed to the outside from the plasma CVD device. In addition, an N(+) type semiconductor layer d0(
3) is similarly formed continuously to a thickness of about 400 Å. Thereafter, the lower transparent glass substrate SUB1 was taken out from the CVD apparatus, and the N(+) type semiconductor layer d0 and the i-type semiconductor layer AS were separated into independent layers as shown in FIGS. 2, 3 and 8 using photo processing technology. Patterned into islands.

As shown in detail in FIGS. 2 and 8, the i-type semiconductor layer AS is also provided between the scanning signal line GL and the video signal line DL at an intersection (crossover section). The i-type semiconductor layer AS at this intersection is configured to reduce short circuits between the scanning signal line GL and the video signal line DL at the intersection.

(Source electrode SD1, drain electrode SD2
) Thin film transistors TFT1 and TFT divided into multiple parts
2, each of the source electrode SD1 and drain electrode SD2
As shown in detail in FIGS. 2, 3, and 9 (a plan view depicting only the first to third conductive films d1 to d3 in FIG. 2),
They are provided separately on the i-type semiconductor layer AS.

Each of the source electrode SD1 and the drain electrode SD2 includes a first conductive film d1, a second conductive film d2, and a third conductive film d, from the lower layer side in contact with the N(+) type semiconductor layer d0.
3 are stacked one on top of the other in sequence. Source electrode SD
The first conductive film d1, the second conductive film d2, and the third conductive film d3 of No. 1 are formed in the same manufacturing process as the first conductive film d1, the second conductive film d2, and the third conductive film d3 of the drain electrode SD2. .

The first conductive film d1 is a chromium film formed by sputtering, and is formed with a thickness of 500 to 1000 Å (in this liquid crystal display device, the thickness is about 600 Å). The thicker the chromium film is, the greater the stress will be.
The film thickness is formed within a range of approximately 000 Å. The chromium film has good contact with the N(+) type semiconductor layer d0. In the chromium film, the aluminum of the second conductive film d2, which will be described later, is N(
It constitutes a so-called barrier layer that prevents diffusion into the +) type semiconductor layer d0. As the first conductive film d1, in addition to a chromium film, a high melting point metal (Mo, Ti, Ta, W) film, a high melting point metal silicide (MoSi2, TiSi2, TaSi
2. It may be formed using a WSi2) film.

After patterning the first conductive film d1 by photo processing, using the same photo processing mask or patterning the first conductive film d1,
Using the conductive film d1 as a mask, the N(+) type semiconductor layer d0 is removed. That is, the portions of the N(+) type semiconductor layer d0 remaining on the i-type semiconductor layer AS other than the first conductive film d1 are removed by self-alignment. At this time, since the N(+) type semiconductor layer d0 is etched so that its entire thickness is removed, the i-type semiconductor layer AS is also slightly etched on its surface, but the extent is controlled by the etching time. do it.

Thereafter, the second conductive film d2 is formed by aluminum sputtering to a thickness of 3000 to 5500 Å (in this liquid crystal display device, the thickness is about 3500 Å). The aluminum film has less stress than the chromium film, and can be formed to a thick film thickness, so that the source electrode SD
1. It is configured to reduce the resistance values of the drain electrode SD2 and the video signal line DL. The second conductive film d2 may be formed of an aluminum film containing silicon or copper (Cu) as an additive in addition to the aluminum film.

After patterning the second conductive film d2 using a photoprocessing technique, a third conductive film d3 is formed. This third conductive film d3 is a transparent conductive film (I) formed by sputtering.
ndium-Tin-Oxide ITO: Nesa film)
It is formed with a film thickness of 1000 to 2000 Å (in this liquid crystal display device, the film thickness is about 1200 Å). This third conductive film d3 includes a source electrode SD1 and a drain electrode SD.
2 and the video signal line DL, and also constitutes the transparent pixel electrode ITO1.

Each of the first conductive film d1 of the source electrode SD1 and the first conductive film d1 of the drain electrode SD2 is located inwardly (
(into the channel region). That is, the first conductive film d1 in these parts is the second conductive film d2,
The structure is such that the channel length L of the thin film transistor TFT can be defined independently of the third conductive film d3.

Source electrode SD1 is transparent pixel electrode ITO1
It is connected to the. The source electrode SD1 has a stepped shape of the i-type semiconductor layer AS (corresponds to the sum of the thickness of the first conductive film g1, the thickness of the N(+)-type semiconductor layer d0, and the thickness of the i-type semiconductor layer AS). It is constructed along the steps (steps). Specifically, the source electrode SD1 includes a first conductive film d1 formed along the step shape of the i-type semiconductor layer AS, and a first conductive film d1 formed along the step shape of the i-type semiconductor layer AS.
In contrast, a transparent pixel electrode ITO1 is formed on the upper part of the conductive film d1.
a second conductive film d formed with a smaller size on the side connected to
2, and the first conductive film d1 exposed from the second conductive film d2.
and a third conductive film d3 connected to the third conductive film d3. The second conductive film d2 of the source electrode SD1 cannot overcome the step shape of the i-type semiconductor layer AS because the chromium film of the first conductive film d1 cannot be formed thickly due to increased stress, so the second conductive film d2 can overcome the step shape of the i-type semiconductor layer AS. is configured for. In other words, step coverage is improved by forming the second conductive film d2 thickly. Since the second conductive film d2 can be formed thickly, the resistance value of the source electrode SD1 (drain electrode SD2
(The same applies to the video signal line DL). Since the third conductive film d3 cannot overcome the step shape caused by the i-type semiconductor layer AS of the second conductive film d2, by reducing the size of the second conductive film d2,
It is configured to be connected to the exposed first conductive film d1. The first conductive film d1 and the third conductive film d3 not only have good adhesion, but also have a small step shape at the connection between them, so it is possible to reliably connect the source electrode SD1 and the transparent pixel electrode ITO1. can.

(Transparent pixel electrode ITO1) Transparent pixel electrode I
TO1 constitutes one of the pixel electrodes of the liquid crystal display section.

The transparent pixel electrode ITO1 is connected to the source electrode SD1 of the thin film transistor TFT1 and the thin film transistor T
It is connected to the source electrode SD1 of FT2. Therefore, when a defect occurs in one of the thin film transistors TFT1 and TFT2, for example, the thin film transistor TFT1, the thin film transistor TFT1 and the video signal line DL are separated by laser light or the like during the manufacturing process, and the thin film transistor TFT1 and the transparent pixel electrode ITO1 are separated from each other by laser light or the like during the manufacturing process.
If you separate them, there will be no point defects or line defects, and 2
Since defects rarely occur in the two thin film transistors TFT1 and TFT2 at the same time, the probability of point defects occurring can be extremely reduced.

(Protective film PSV1) Thin film transistor TF
A protective film PSV1 is provided on the T and transparent pixel electrode ITO1. The protective film PSV1 is formed mainly to protect the thin film transistor TFT from moisture etc.
Use a material that is highly transparent and has good moisture resistance. The protective film PSV1 is formed of, for example, a silicon oxide film or a silicon nitride film formed by a plasma CVD apparatus, and has a film thickness of 80%.
The film thickness is approximately 00 Å.

(Gate terminal GTM, drain terminal DTM
) As shown in FIG. 5, the gate terminal GTM is connected to the first conductive film g.
1 and a third conductive film d3.

Furthermore, as shown in FIG. 6, the drain terminal D
TM is composed of a first conductive film g1 and a third conductive film d3.

The first conductive film g1 is formed using, for example, a chromium (Cr) film formed by sputtering, and has a thickness of about 1000 Å.

(Light-shielding film BM) Upper transparent glass substrate SUB
A light shielding film BM is provided on the 2 side to prevent external light (light from above in FIG. 3) from entering the i-type semiconductor layer AS used as a channel formation region.
The pattern is as shown by the zero hatching. Note that FIG. 10 is a plan view depicting only the third conductive film d3 made of an ITO film, the color filter FIL, and the light shielding film BM in FIG. The light shielding film BM is formed of, for example, an aluminum film or a chromium film having a high light shielding property, and in this liquid crystal display device, the chromium film is formed by sputtering to a thickness of about 1300 Å.

Therefore, the thin film transistors TFT1,
The i-type semiconductor layer AS of the TFT2 is sandwiched between the upper and lower light-shielding films BM and the large gate electrode GT, and that portion is not exposed to external natural light or backlight light. The light shielding film BM is formed around the pixel as shown by the hatched area in FIG.
The effective display area of pixels is partitioned. Therefore, the outline of each pixel becomes clear due to the light shielding film BM, and the contrast is improved. In other words, the light shielding film BM has two functions: shielding the i-type semiconductor layer AS and serving as a black matrix.

[0051] Also, a portion opposite to the edge portion on the root side in the rubbing direction of the transparent pixel electrode ITO1 (lower right portion in FIG. 2)
is shielded from light by the light-shielding film BM, so even if a domain occurs in the above-mentioned portion, the domain will not be visible and the display characteristics will not deteriorate.

It is also possible to attach the backlight to the upper transparent glass substrate SUB2 side and make the lower transparent glass substrate SUB1 the observation side (externally exposed side).

(Common Transparent Pixel Electrode ITO2) The common transparent pixel electrode ITO2 faces the transparent pixel electrode ITO1 provided for each pixel on the lower transparent glass substrate SUB1 side, and the optical state of the liquid crystal LC is determined by each pixel electrode ITO1. It changes in response to the potential difference (electric field) between the ITO2 and the common transparent pixel electrode ITO2. The configuration is such that a common voltage Vcom is applied to this common transparent pixel electrode ITO2. The common voltage Vcom is a low-level drive voltage Vdmin and a high-level drive voltage Vdmax applied to the video signal line DL.
It is the intermediate potential between

(Color Filter FIL) The color filter FIL is constructed by coloring a dyed base material made of a resin material such as acrylic resin with a dye. Color filter F
The IL is formed in a stripe shape at a position facing the pixel (
(Fig. 11) shows only the third conductive film layer d3, light shielding film BM, and color filter FIL in Fig. 7, and each of the B, R, and G color filters F
ILs are 45°, 135°, and cross hatched, respectively). As shown in FIG. 10, the color filter FIL is formed in a large size so as to cover the entire transparent pixel electrode ITO1, and the light shielding film BM is formed on the periphery of the transparent pixel electrode ITO1 so as to overlap with the edge portions of the color filter FIL and the transparent pixel electrode ITO1. It is formed more inward.

Color filter FIL can be formed as follows. First, a dyed base material is formed on the surface of the upper transparent glass substrate SUB2, and the dyed base material other than the red filter forming area is removed using photolithography technology. Thereafter, the dyed base material is dyed with a red dye and subjected to a fixing treatment to form a red filter R. Next, a green filter G and a blue filter B are sequentially formed by performing similar steps.

(Protective film PSV2) The protective film PSV2 is made of dyes that dye the color filter FIL in different colors.
This is provided to prevent leakage to C. The protective film PSV2 is made of a transparent resin material such as acrylic resin or epoxy resin.

(Equivalent circuit of entire display device) FIG. 12 shows a wiring diagram of the equivalent circuit of the display matrix section and its peripheral circuits. Although this figure is a circuit diagram, it is drawn to correspond to the actual geometrical arrangement. AR is a matrix array in which a plurality of pixels are arranged two-dimensionally.

In the figure, X means a video signal line DL, and subscripts G, B, and R are added corresponding to green, blue, and red pixels, respectively. Y means the scanning signal line GL, and the subscripts 1, 2, 3, . . . , end are added according to the order of scanning timing.

Video signal lines X (subscript omitted) are arranged alternately on the upper side (
(or odd number) video signal drive circuit He, and is connected to the lower (or even number) video signal drive circuit Ho.

[0060] The SUP uses a power supply circuit to obtain a plurality of divided and stabilized voltage sources from one voltage source and information for a CRT (cathode ray tube) from a host (upper processing unit) to a TFT liquid crystal display device. This is a circuit that includes a circuit that exchanges information for use.

(Structure of Storage Capacitor Element Cadd) The transparent pixel electrode ITO1 is formed so as to overlap the adjacent scanning signal line GL at the end opposite to the end connected to the thin film transistor TFT. This superposition is shown in Figure 4.
As is clear from the above, the transparent pixel electrode ITO1 is used as one electrode PL2, and the adjacent scanning signal line GL is used as the other electrode P.
A storage capacitance element (electrostatic capacitance element) Cadd designated as L1 is configured. The dielectric film of this storage capacitor element Cadd is composed of an insulating film GI used as a gate insulating film of the thin film transistor TFT and an anodic oxide film AOF.

As is clear from FIG. 8, the storage capacitor element Cadd is formed in the widened portion of the second conductive film g2 of the scanning signal line GL. Note that the second conductive film g2 at the portion intersecting with the video signal line DL is made thin in order to reduce the probability of short circuit with the video signal line DL.

Similar to the source electrode SD1, the transparent pixel electrode ITO1 is disconnected when going over the step shape in a part between the transparent pixel electrode ITO1 and the electrode PL1 which are overlapped to form the storage capacitor element Cadd. An island region made up of the first conductive film d1 and the second conductive film d2 is provided to prevent this. This island area is the transparent pixel electrode I
The structure is made as small as possible so as not to reduce the area (aperture ratio) of TO1. (Equivalent circuit of storage capacitor element Cadd and its operation) An equivalent circuit of the pixel shown in FIG. 2 is shown in FIG. In FIG. 13, Cgs is a thin film transistor TF
This is a parasitic capacitance formed between the gate electrode GT and source electrode SD1 of T. The dielectric film of the parasitic capacitance Cgs is an insulating film GI. Cpix is the transparent pixel electrode ITO1 (PI
This is a liquid crystal capacitor formed between the common transparent pixel electrode ITO2 (COM) and the common transparent pixel electrode ITO2 (COM). The dielectric film of the liquid crystal capacitor Cpix includes the liquid crystal LC, the protective film PSV1, and the alignment films ORI1 and O.
It is RI2. Vlc is a midpoint potential.

The storage capacitor element Cadd functions to reduce the influence of the gate potential change ΔVg on the midpoint potential (pixel electrode potential) Vlc when the thin film transistor TFT switches. This situation can be expressed as the following formula.

ΔVlc={Cgs/(Cgs+Cadd+Cpix)
}×ΔVg Here, ΔVlc represents a change in the midpoint potential due to ΔVg. This variation ΔVlc causes a direct current component applied to the liquid crystal LC, but the larger the holding capacitance Cadd is, the smaller its value can be. Furthermore, the storage capacitor element Cadd also has the effect of lengthening the discharge time, so that image information is stored for a long time after the thin film transistor TFT is turned off. Reducing the DC component applied to the liquid crystal LC can improve the life of the liquid crystal LC and reduce so-called burn-in, in which the previous image remains when switching between liquid crystal display screens.

As described above, since the gate electrode GT is made large enough to completely cover the i-type semiconductor layer AS, the overlapping area with the source electrode SD1 and drain electrode SD2 increases, and therefore the parasitic capacitance Cgs increases. , the opposite effect occurs that the midpoint potential Vlc becomes more susceptible to the influence of the gate (scanning) signal Vg. However, the storage capacitor C
By providing add, this disadvantage can also be eliminated.

The storage capacitance of the storage capacitor element Cadd is 4 to 8 times (
4・Cpix<Cadd<8・Cpix), parasitic capacitance C
8 to 32 times that of gs (8・Cgs<Cadd<32
・Set to a value of about Cgs).

(Connection method of storage capacitor element Cadd electrode line) The first-stage scanning signal line GL (Y0), which is used only as a storage capacitor electrode line, is connected to the common transparent pixel electrode ITO2 (Vcom) as shown in FIG. Connecting. As shown in FIG. 3, the common transparent pixel electrode ITO2 is connected to an external wiring at the peripheral edge of the liquid crystal display device by a silver paste material SL. Furthermore, a part of the conductive film (g1 and g2) of this external wiring is formed in the same manufacturing process as the scanning signal line GL. As a result, the storage capacitor electrode line GL at the final stage can be easily connected to the common transparent pixel electrode ITO2.

The holding capacitor electrode line Y0 of the first stage is connected to the scanning signal line Yend of the final stage, or connected to a DC potential point (AC grounding point) other than Vcom, or one extra scanning pulse Y0 is applied from the vertical scanning path circuit V. You may also connect it so that it is received.

(Measurement electrode MEL1) As shown in FIGS. 1 and 14, a measurement electrode MEL1 made of a third conductive film d3 is placed on the insulating film GI in the region of the lower transparent glass substrate SUB1 where no pixels are formed. It is provided. The measurement electrode MEL1 has a width of about 0.5 mm, a length of about 70 mm, and an area of 35 mm2. Then, a measurement voltage VM is applied between the measurement electrode terminal MTM1 connected to the measurement electrode MEL1 and the common pixel electrode terminal CTM connected to the common transparent pixel electrode ITO2 via the silver paste material SIL,
By measuring the current IM flowing through the liquid crystal LC,
By finding the relationship between the side constant voltage VM and the current IM as shown in 5, it is possible to measure the impedance of the sealed liquid crystal LC. Therefore, the impedance of the liquid crystal LC can be measured without disassembling the liquid crystal display device. Failure analysis can be performed.

(Measurement electrode MEL2) As shown in FIGS. 14 and 16, a measurement electrode MEL2 made of a third conductive film d3 is placed on the insulating film GI in the region of the lower transparent glass substrate SUB1 where no pixels are formed. It is provided. The width of this measurement electrode MEL2 is approximately 0.5 mm, the length is approximately 70 mm,
The area is 35mm2. An alignment film ORI1 is provided on this measurement electrode MEL2, and an alignment film ORI2 is provided on a portion of the common transparent pixel electrode ITO2 facing the measurement electrode MEL2. Further, a through hole THR having a diameter of 0.5 mm or more is provided in a portion of the light shielding film BM facing the measurement electrode MEL2. Also, Figure 1
7 is an equivalent circuit diagram of the second part of the measurement electrode MEL. Figure 17
, R1 to R3 and C1 to C3 are alignment films O, respectively.
These are the resistance and capacitance of RI2, liquid crystal LC, and alignment film ORI1.If the thickness of alignment films ORI1 and ORI2 is 0.1 μm, the resistivity is about 1014 Ωcm, and the dielectric constant is 3.0, the resistances R1 and R3 are about 3×109Ω, capacitance C1 and C3 are 93
0 pF, and assuming that the thickness of the liquid crystal LC is 7.0 μm, the resistivity is approximately 1014 Ωcm, and the relative dielectric constant is 3.0 to 6.0, the resistance R2 is approximately 2×1011 Ω, and the capacitance C2 is 130 to 2.
It is 60 pF. The measurement electrode terminal MTM2 and the common pixel electrode terminal CTM are connected to the measurement electrode MEL2.
A measurement voltage VM is applied between the measurement electrode M and the luminance meter
By detecting the brightness of the EL2 section and finding the relationship between the side constant voltage VM and brightness as shown in FIG. 18, the brightness characteristics can be detected accurately, so failure analysis of the brightness characteristics can be performed accurately. be able to.

[0072] As described above, the invention made by the present inventor is as follows.
Although this invention has been specifically explained based on the above embodiments,
It goes without saying that the invention is not limited to the embodiments described above, and that various changes can be made without departing from the spirit thereof.

For example, in the above embodiment, the steps are as follows: gate electrode formation→gate insulating film formation→semiconductor layer formation→source/
Although an inverted staggered structure in which the drain electrode is formed is shown, the present invention is also effective in a staggered structure in which the vertical relationship or the order of formation is reversed. Further, in the above embodiment, the measurement electrodes MEL1 and MEL2 are provided on the insulating film GI, but the measurement electrodes may be provided on the protective film PSV1.

[0074]

As explained above, in the liquid crystal display device according to the present invention, the impedance of the liquid crystal in the sealed state can be measured, so the impedance of the liquid crystal can be measured without disassembling the liquid crystal display device. Failure analysis can be performed.

[0075] Furthermore, if an alignment film is provided on the measurement electrode,
Since the brightness characteristics can be detected accurately, failure analysis of the brightness characteristics can be performed accurately.

[0076] As described above, the effects of the present invention are remarkable.

[Brief explanation of the drawing]

FIG. 1 is a partial cross-sectional view of the liquid crystal display device shown in FIG. 2;

FIG. 2 is a plan view of a main part showing one pixel of a liquid crystal display section of an active matrix color liquid crystal display device to which the present invention is applied.

FIG. 3 is a cross-sectional view of a portion taken along section line 3-3 in FIG. 2 and a peripheral portion of a seal portion.

FIG. 4 is a sectional view taken along section line 4-4 in FIG. 2;

FIG. 5 is a cross-sectional view showing a gate terminal portion of the liquid crystal display device shown in FIG. 2;

6 is a sectional view showing a drain terminal portion of the liquid crystal display device shown in FIG. 2. FIG.

7 is a plan view of a main part of a liquid crystal display section in which a plurality of pixels shown in FIG. 2 are arranged; FIG.

FIG. 8 is a plan view depicting only a predetermined layer of the pixel shown in FIG. 2;

9 is a plan view depicting only a predetermined layer of the pixel shown in FIG. 2; FIG.

FIG. 10 is a plan view depicting only a predetermined layer of the pixel shown in FIG. 2;

11 is a plan view of main parts depicting only a pixel electrode layer, a light shielding film, and a color filter layer shown in FIG. 7; FIG.

FIG. 12 is an equivalent circuit diagram showing a liquid crystal display section of an active matrix color liquid crystal display device.

13 is an equivalent circuit diagram of the pixel shown in FIG. 2. FIG.

14 is a schematic plan view showing a lower transparent glass substrate of the liquid crystal display device shown in FIG. 2. FIG.

15 is a graph showing the relationship between side constant voltage VM and current IM of the liquid crystal display device shown in FIG. 2. FIG.

16 is a partial cross-sectional view of the liquid crystal display device shown in FIG. 2. FIG.

17 is an equivalent circuit diagram of a measurement electrode section of the liquid crystal display device shown in FIG. 2. FIG.

18 is a graph showing the relationship between side constant voltage VM and brightness of the liquid crystal display device shown in FIG. 2. FIG.

[Explanation of symbols]

SUB…Transparent glass substrate GL...Scanning signal line DL...Video signal line GI...Insulating film GT...gate electrode AS...i-type semiconductor layer SD...source electrode or drain electrode PSV…Protective film BM...shading film LC…Liquid crystal TFT...Thin film transistor ITO...transparent pixel electrode g, d...conductive film Cadd...Holding capacitor element Cgs...parasitic capacitance Cpix…Liquid crystal capacity AOF…anodized film MEL...Measurement electrode

Claims (2)

[Claims] 1. A liquid crystal display device characterized in that a measurement electrode is provided in a region of a substrate opposite to a substrate provided with a common pixel electrode where no pixels are formed. 2. The liquid crystal display device according to claim 1, further comprising an alignment film provided on the measurement electrode.