JPH0258028A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To uniform TFT characteristics and to improve an aperture rate by composing a lateral TFT as a picture element and providing a source electrode so that the drain electrode of the TFT is surrounded. CONSTITUTION:The thin film transistor(TR) TFT as each picture element is constituted as a lateral type and the source electrode SD1 is provided surrounding its drain electrode SD2. The drain electrode SD2 connected to the video signal line DL of the TFT is divided into plural parts. Consequently, the channel length of the TFT is prescribed by etching machining which is small in variance, so the TFT characteristics can be uniformed and the TFT is reduced in size to improve the aperture rate. Further, plural electrodes are provided, so even if one electrode is short-circuited, other parts operate and line defects are reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a technique that is effective when applied to a liquid crystal display device, particularly a liquid crystal display device configured using an active matrix method.

[Conventional technology]

An active matrix type liquid crystal display device has a plurality of pixels arranged in a matrix.

Each pixel is located within an area surrounded by a plurality of horizontally extending scanning signal lines (gate signal lines) and a plurality of vertically extending video signal lines (drain signal lines) that intersect with the horizontally extending scanning signal lines. It is located.

Each pixel is constituted by a series circuit of a vertical thin film transistor (TPT) and a pixel electrode, as described in Japanese Patent Laid-Open No. 60-261173.

A vertical thin film transistor has a semiconductor layer on the drain electrode,
Source electrodes are sequentially stacked, and a ring-shaped gate electrode is provided via a gate insulating film so as to surround the semiconductor layer. The drain electrode is connected to a video signal line. The source electrode is connected to the pixel electrode. The gate electrode is connected to a scanning signal line.

In this vertical thin film transistor, the channel region is formed along the ring-shaped gate electrode, so that the channel width can be increased and the driving ability can be improved. therefore,
Vertical thin film transistors can be made smaller, so
Liquid crystal display devices have the characteristic of being able to improve the aperture ratio.

[Problem to be solved by the invention]

The vertical thin film transistor of each pixel of the liquid crystal display device is
The thickness of the gate electrode and the thickness of the semiconductor layer, which define the channel length (gate length), tend to vary depending on the manufacturing process. For this reason, there is a problem in that vertical thin film transistors cannot obtain uniform transistor characteristics.

In addition, in the above-mentioned liquid crystal display device, short circuits easily occur between the drain electrode and the gate electrode of the vertical thin film transistor or between the video signal line and the scanning signal line, and when a short circuit occurs, a line defect occurs, resulting in a decrease in display quality. There was a problem. Furthermore, if there is a short circuit between the drain electrode and the gate electrode of the vertical thin film transistor, it is possible to disconnect this pixel from the video signal line to avoid line defects, but point defects cannot be avoided. There was still a problem that the display quality deteriorated.

An object of the present invention is to provide a technique that can uniformize the transistor characteristics of thin film transistors of pixels in a liquid crystal display device, reduce the size of the thin film transistors, and improve the aperture ratio.

Another object of the present invention is to provide, in addition to the above-mentioned object, a technique capable of reducing single-point defects and line defects and improving display quality in the liquid crystal display device.

The above and other objects and novel features of the present invention will become apparent from the description of this specification and the accompanying drawings.

[Means to solve the problem]

A brief overview of typical inventions disclosed in this application is as follows.

(1) In a liquid crystal display device, the thin film transistor is configured horizontally, and the drain electrode (
or source electrode) so as to surround the source electrode (or source electrode).
or drain electrode).

(2) The drain electrode connected to the video signal line of the lateral thin film transistor is divided into a plurality of parts.

(3) Each of the drain electrode and source electrode of the horizontal thin film transistor is formed of a conductive layer provided between a scanning signal line and a video signal line, and the drain electrode is electrically connected to the video signal line.

[For production]

According to the above-mentioned means (1), the channel length of the thin film transistor is defined by etching processing with small variations, so that the transistor characteristics can be made uniform, and the channel width of the thin film transistor can be increased to increase the driving capability. death.

Since the thin film transistor can be miniaturized, it is possible to increase the planar size of the pixel electrode and improve the aperture ratio.

According to the above-mentioned means (2), when there is a short circuit between the drain electrode or source electrode and the gate electrode of one of the plurality of thin film transistors, the connection between the drain electrode or source electrode at the short circuit point and the video signal line is Even if the gap is cut, other parts function normally, so line defects and point defects in the liquid crystal display device can be reduced and display quality can be improved.

According to the above-mentioned means (3), at least two layers of insulating film are interposed between the scanning signal line and the video signal line, and the probability of short circuit at the intersection between the two can be reduced, so that the liquid crystal Line defects in the display device can be reduced and display quality can be improved. Further, the capacitance formed between the scanning signal line and the video signal line can be reduced.

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

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

〔Example〕

(Example I) One pixel of the liquid crystal display part of the liquid crystal display device which is Example I of the present invention is shown in FIG. This is shown in Figure 1.

As shown in FIGS. 1 and 2, the liquid crystal display device includes 1.
1 [A horizontal thin film transistor TPT is provided on the inner surface (liquid crystal side) of a lower transparent glass substrate SUB 1 having a thickness of about 1 mm1. Horizontal thin film transistor T
PT mainly includes a gate electrode GT, an insulating film (JI) used as a gate insulating film, an i-type semiconductor layer AS used as a channel formation region, a source electrode (or drain electrode 1),
) SDI, and a drain electrode (or source electrode) SD2.

The goo1 to electrode GT are made of a Cr film g1.g1 deposited by sputtering, for example. It is formed with a film thickness of approximately 1,000 [people]. The gate electrode GT is formed in the same manufacturing process (same conductive layer) as the scanning signal line (gate signal line or horizontal signal line) GL, and is integrated with the scanning signal line GL.

The scanning signal line GL is A Q (A n
-S i ) It is formed of a composite film in which the film g2 is laminated. The Aff film g2 is deposited by sputtering and has a thickness of about 1000
Formed with a film thickness of about [a person]. This AI2 film g2 is configured to reduce the resistance value of the scanning signal line GL.

As shown in FIG. 1, the scanning signal lines GL extend horizontally, and although not shown in FIG. 1, a plurality of scanning signal lines GL are arranged vertically.

The insulating film GI is formed on the gate electrode GT and the scanning signal line GL. The insulating film GI may be formed by, for example, plasma CV
Approximately 3000 [people] using silicon nitride film deposited by D method
It is formed with a film thickness of approximately

The i-type semiconductor layer As is formed in a bird shape above the gate insulating film G1. The i-type semiconductor layer AS is formed of an amorphous silicon film or a polycrystalline silicon film deposited by the CVD method, and has a thickness of about 25
00[It is formed with a film thickness comparable to that of a human body. The i-type semiconductor layer AS is mainly used as a channel formation region of the lateral thin film transistor TPT.

Source electrode SD1. Each of the drain electrodes SD2 is i
They are provided separately on the type semiconductor layer As. The source electrode SDI and the drain electrode SD2 are operationally switched between source and drain when the bias polarity of the circuit changes. In other words, the lateral thin film transistor TPT is bidirectional, like the insulated gate field effect transistor FET.

Source electrode SD1. Each of the drain electrodes SD2 is
For example, the i-type semiconductor layer A
It is composed of a composite film in which a n semiconductor layer (not shown) and a Cr film are sequentially laminated from the bottom layer that contacts S. n
``The semiconductor layer is formed of an amorphous silicon film or a polycrystalline silicon film, and has a thickness of about 500 [layers]. n
It is configured to reduce the contact resistance value between the ゛-type half body layer, the i-type semiconductor layer AS, and the Cr film. The Cr film is deposited by, for example, a sputtering method, and is formed to a thickness of about 600 [layers].

As described above, each of the source electrode SDI and drain electrode SD2 is arranged in a plane on the i-type semiconductor layer As, and since the video signal flows laterally (horizontally) on the surface of the l-type semiconductor layer AS, this thin film transistor The TPT is configured horizontally. The lateral thin film transistor TPT has a source electrode S
Since the channel length (gate length) can be defined with high precision by patterning each of the DI and drain electrode SD2 by etching, the processing precision is higher than that of a vertical thin film transistor, and it is easy to obtain in manufacturing. be able to. In other words, the lateral thin film transistor TPT can have more uniform transistor characteristics than the vertical thin film transistor.

As shown in FIGS. 1 and 2, the source electrode SDI is arranged to surround the drain electrode SD2. Specifically, the source electrode SDI is spaced apart by a predetermined dimension (channel length) from the periphery of the drain electrode SD2, which has a rectangular planar shape.
It is configured along the periphery of D2. The lateral thin film transistor TPT configured in this way has a drain electrode SD
Since the channel width can be formed along the length along the periphery of 2, the channel width can be increased.

Further, the drain electrode SD2 is divided into a plurality of parts within one pixel, and each of the divided drain electrodes SD2
are each independently connected to the same video signal line DL.

The video signal line DL has a source electrode SDI and a drain electrode S
It extends above D2 with an interlayer insulating film IL interposed therebetween. The video signal line DL is above the MO film 1cA11! (An-
It is formed of a composite film in which Si) films d2 are laminated. M.O.
The film 1 is deposited by sputtering to a film thickness of about 1000 mm. The A4 film d2 is deposited by sputtering and has a thickness of about 3,500 mm. The AQ film d2 is configured to reduce the resistance value of the video signal line DL. As shown in FIG. 1, the video signal lines DL extend in the vertical direction intersecting the scanning signal lines GL, and a plurality of video signal lines DL are arranged in the horizontal direction, although not shown. The drain electrode SD2 is connected to the MO film of the video signal line DL through a connection hole TH formed in the interlayer insulating film IL. The interlayer insulating film IL may be formed by, for example, plasma CV.
A silicon nitride film deposited by the D method is used to have a film thickness of approximately 100 μm.

A transparent electrode (pixel electrode) IrO2 provided for each pixel is connected to the source electrode SDI.

The transparent electrode I'TOI constitutes one of the pixel electrodes of the liquid crystal display section. The transparent electrode IT○1 is provided on the insulating film GI, and is deposited by, for example, a sputtering method, and is formed to have a film thickness of about 1200 [layers].

The lateral thin film transistor TPT and the transparent electrode ITOI
A protective film PSVI is provided thereon.

The protective film PSVI is formed mainly to protect the horizontal thin film transistor TPT from moisture, etc., and a film having high transparency and good moisture resistance is used.

The protective film PSVI is formed of, for example, a silicon oxide film or a silicon nitride film deposited by a plasma CVD method, and has a thickness of about 8000 [layers].

A light shielding film LS is provided above the protective film PSVI on the thin film transistor TFT to prevent external light from entering the l-type semiconductor layer AS used as a channel formation region. The light shielding film LS is made of, for example, an AQ film (or A fl -
S i , A Q -Cu.

Cr film, etc.) and is deposited by sputtering.
It is formed with a film thickness of about 00 to 4000 [people].

The liquid crystal LC is defined by a lower alignment film ○RII for setting the orientation of liquid crystal molecules and an upper alignment film 11iJORI2, and is sealed in a space formed between a lower transparent glass substrate SUB1 and an upper transparent glass substrate 5UB2. There is.

The lower alignment film 0RII is formed on the protective film psvi on the lower transparent glass substrate 5UBl side.

On the inner surface (liquid crystal side) of the upper transparent glass substrate 5UB2, a color filter FIL, a protection [PSV2], a common transparent electrode (common pixel electrode) IrO2, and the upper alignment film ○R are provided.
I2 are sequentially stacked.

The retranslated common transparent electrode IT○2 is connected to the lower transparent glass substrate SU.
It faces the transparent electrode ITOI provided for each pixel on the B i side and is configured integrally with another adjacent common transparent electrode IT○2.

The color filter FIL is formed by dyeing a dyed base material made of a resin material such as acrylic resin with a dye for each pixel. Dyeing is done using photolithography technology.

The protective film PSV2 is provided to prevent the dyes used to dye the color filter FIL into different colors from leaking into the liquid crystal LC. The protective film PSV2 is made of, for example, a transparent resin material such as acrylic resin or epoxy resin.

This liquid crystal display device has a lower transparent glass substrate 5UBl side,
Each layer on the upper transparent glass substrate 5UB2 side is formed separately, and then the upper and lower transparent glass substrates SUB1 and 5UB are formed separately.
2 are stacked on top of each other and a liquid crystal LC is sealed between the two.

Lower transparent glass substrate SUB 1, upper transparent glass substrate 5
A polarizing plate P○L is formed on the outer surface of each UB2.

In this way, in the liquid crystal display device, the thin film transistor TPT is configured horizontally, and the source electrode S surrounds the drain electrode SD2 of the horizontal thin film transistor.
By configuring DI, the channel length of the lateral thin film transistor TPT is defined by etching processing with small variations, so that the transistor characteristics can be made uniform, and the channel width of the lateral thin film transistor TPT can be increased to increase the driving capability. Transparent electrode IT○
It is possible to increase the plane size of 1 and improve the aperture ratio.

Further, the video signal line D of the horizontal thin film transistor TPT
By dividing the drain electrode SD2 connected to L into a plurality of parts (three in this embodiment, but not limited to this), one of the plurality of lateral thin film transistors TPT
If there is a short circuit between two drain quasi-electrodes SD2 and the gate electrode GT, the other parts will function normally even if the short circuit between the drain electrode SD2 and the video signal line DL is disconnected (SD2-GT is (insulated and separated), line defects and point defects in the liquid crystal display device can be reduced and display quality can be improved. The drain electrode SD2 and the video signal line DL are cut by etching using photolithography, fusing using a laser beam, or the like.

Further, each of the drain electrode SD2 and source electrode SDI of the horizontal thin film transistor TPT is formed of a conductive layer provided between the scanning signal line GL and the video signal line DL, and the drain electrode SD2 is connected to the video signal line DL. By electrically connecting the scanning signal line OL and the video signal line D.
At least two layers of insulating films GT and IL are interposed between L and L.

It is possible to reduce the probability of a short circuit at the intersection (crossover section) between the scanning signal line GL and the video signal line DL, thereby reducing line defects in the liquid crystal display device.

Display quality can be improved. In addition, the scanning signal line G
The capacitance formed between L and the video signal line DL can be reduced.

(Example 2) In this example 2, the source electrode and drain electrode of the lateral thin film transistor and the video signal line were formed in the same manufacturing process in the liquid crystal display device.

This is a second embodiment of the present invention.

One pixel of the liquid crystal display part of the liquid crystal display device which is Example H of the present invention is shown in FIG. 3 (principal part plan view).
FIG. 4 shows a cross section taken along the V cutting line.

The liquid crystal display device of Example H has a source electrode SDI and a drain electrode SD2 of the lateral thin film transistor TPT of each pixel.
and the video signal line DL are formed in the same manufacturing process. In other words, the source electrode SDI, the drain electrode SD2
are each formed of an MO film d1. Video signal line DL
is formed of a composite film consisting of an MO film d1 and an AQ film d2 laminated on top of the MO film d1. Therefore, the source electrode SDI of the lateral thin film transistor TPT is configured to surround most of the drain region SD2 except for a part of its periphery.

The liquid crystal display device configured in this manner can provide the same effects as in the embodiment (2).

The effect of reducing the number of manufacturing steps can be achieved.

(Embodiment 2) Embodiment 2 is a third embodiment of the present invention in which each of the source electrode and drain electrode of the horizontal thin film transistor of the liquid crystal display device is configured in a different shape.

A source electrode and a drain electrode of a film transistor of each pixel of a liquid crystal display device according to the embodiment (2) of the present invention are shown in FIGS. 5 to 7 (schematic plan views of main parts).

The source electrode SDI and drain electrode SD2 of the lateral thin film transistor TPT shown in FIG. 5 each have a circular planar shape.

Each of the source electrode SD1 and drain electrode SD2 of the lateral thin film transistor TPT shown in FIG. 6 has a planar shape of a sea star.

Each of the source electrode SDI and drain electrode SD2 of the lateral thin film transistor TPT shown in FIG. 7 has a spiral planar shape.

In either case, the channel width of the lateral thin film transistor TPT can be increased.
The same effect can be achieved.

As above, the invention made by the present inventor has been specifically explained based on the above embodiments, but the present invention is not limited to the above embodiments, and can be modified in various ways without departing from the gist thereof. Of course.

〔Effect of the invention〕

A brief explanation of the effects obtained by typical inventions disclosed in this application is as follows.

In a liquid crystal display device, transistor characteristics of thin film transistors of pixels can be made uniform, the thin film transistors can be made smaller, and the aperture ratio can be improved.

Further, in the liquid crystal display device, point defects and line defects can be reduced and display quality can be improved.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a main part showing one pixel of a liquid crystal display part of a liquid crystal display device according to Embodiment I of the present invention, FIG. 2 is a plan view of the pixel, and FIG. 3 is an embodiment of the present invention. FIG. 4 is a plan view of a main part showing one pixel of a liquid crystal display part of a liquid crystal display device according to example (2), and FIG. 4 is a cross-sectional view of a main part of the pixel. FIG. 2 is a schematic plan view of a main part showing a source electrode and a drain electrode of a thin film transistor of each pixel of a certain liquid crystal display device. In the figure, SUB...transparent glass substrate, GL...scanning signal line, DL...video signal line, GI...insulating film, GT
...gate electrode, AS...i-type semiconductor layer, SDI
・・Source electrode, SD2 ・・Drain electrode, psv・
・・Protective film, LS・・Light shielding film, TH・・Connection hole, LC
...Liquid crystal, TPT...horizontal thin film transistor. Figure 2 Figure 3

Claims (1)

[Scope of Claims] 1. In a liquid crystal display device in which a pixel formed by a series circuit of a thin film transistor and a pixel electrode is arranged at the intersection of a scanning signal line and a video signal line, the thin film transistor is configured horizontally, A liquid crystal display device characterized in that a source electrode or a drain electrode is configured to surround the drain electrode or source electrode of the thin film transistor. 2. The liquid crystal display device according to claim 1, wherein the drain electrode or source electrode connected to the video signal line of the thin film transistor is divided into a plurality of parts. 3. Each of the drain electrode and source electrode of the thin film transistor is formed of a conductive layer provided between the scanning signal line and the video signal line, and the drain electrode or the source electrode is electrically connected to the video signal line. A liquid crystal display device according to claim 1 or 2, characterized in that: