JP2003090994A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the rise of driving voltage. SOLUTION: A liquid crystal display device is provided with a pixel electrode and a counter electrode which are formed in different layers with an insulation film therebetween on each pixel area of the surface of one substrate at the side of the liquid crystal out of substrates which are disposed oppositely through the liquid crystal therebetween. High dielectric constant is imparted to the surface of the portion of the insulation film exposed from the electrode formed above the insulation film between the pixel electrode and counter electrode.

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 a so-called lateral electric field type liquid crystal display device.

[0002]

2. Description of the Related Art A so-called horizontal electric field type liquid crystal display device is
A pixel electrode and a counter electrode, which are spaced apart from each other, are provided in each pixel region on the liquid crystal side surface of one of the substrates that are opposed to each other with the liquid crystal interposed therebetween, and occur between these electrodes. The liquid crystal is configured to behave by a component of the electric field that is substantially parallel to the substrate.

A liquid crystal display device of this type applied to a so-called active matrix type has gates extending in the x direction and arranged in parallel in the y direction on the liquid crystal side surface of the one substrate. Each region surrounded by the signal line and the drain signal line extending in the y direction and juxtaposed in the x direction is defined as a pixel region.

In these pixel regions, a thin film transistor driven by a scanning signal from one side gate signal line, and the pixel electrode to which a video signal from one side drain signal line is supplied via the thin film transistor,
The counter electrode is provided with a counter voltage serving as a reference for the video signal.

The pixel electrode and the counter electrode are composed of at least one of them, and they are alternately arranged, for example, substantially in parallel with the drain signal line, and the counter electrodes are positioned on both sides of the electrode group. It is usually placed.

The electric force line from the drain signal line terminates at the counter electrode arranged in the vicinity of the drain signal line and does not terminate at the pixel electrode arranged adjacent to the counter electrode. is there. This is because the line of electric force from the drain signal line that terminates in the pixel electrode becomes noise with respect to the video signal.

[0007]

However, in recent years, in order to improve the aperture ratio of the pixel region, the inventors of the present invention have formed an insulating film between the drain signal line and the counter electrode arranged in the vicinity thereof. It has been proposed to have a structure in which they are superposed via a (protective film), and to make the insulating film an organic material layer made of, for example, a resin material in order to reduce its dielectric constant.

However, in this case, the pixel electrode is formed in the lower layer of the organic material layer, and the electric field lines of the electric field between the pixel electrode and the counter electrode pass through the organic material layer, It was found to reduce the voltage applied to the liquid crystal.

This raises the driving voltage for driving the liquid crystal, and a countermeasure against it has been desired.

The present invention has been made under these circumstances, and an object thereof is to provide a liquid crystal display device capable of suppressing an increase in drive voltage.

[0011]

Among the inventions disclosed in the present application, a brief description will be given to the outline of typical ones.
It is as follows.

Means 1. The liquid crystal display device according to the present invention includes, for example, a pixel electrode formed in a different layer with an insulating film in each pixel region on the liquid crystal side surface of one of the substrates opposed to each other through the liquid crystal. A counter electrode is provided, and at least the surface of the portion of the insulating film exposed from the electrode formed on the insulating film of the pixel electrode and the counter electrode is subjected to a high dielectric constant treatment. It is characterized by.

Means 2. A liquid crystal display device according to the present invention includes, for example, a switching element operated by a scanning signal from a gate signal line in each pixel region on the liquid crystal side surface of one of the substrates opposed to each other with a liquid crystal interposed therebetween. A pixel electrode to which a video signal from the drain signal line is supplied via the switching element, and a counter electrode for generating an electric field between the pixel electrode and the pixel electrode, the counter electrode being the switching element and the pixel. Formed on the upper surface of the insulating film made of an organic material layer that also covers the electrodes,
At least the surface of the insulating film exposed from the counter electrode is subjected to a high dielectric constant treatment.

Means 3. The liquid crystal display device according to the present invention includes, for example, a pixel electrode formed in a different layer with an insulating film in each pixel region on the liquid crystal side surface of one of the substrates opposed to each other through the liquid crystal. Fine particles for improving the dielectric constant of the insulating film at least on the surface of the portion of the insulating film exposed from the electrode formed in the upper layer of the insulating film of the pixel electrode and the counter electrode. Is diffused.

Means 4. A liquid crystal display device according to the present invention includes, for example, a switching element operated by a scanning signal from a gate signal line in each pixel region on the liquid crystal side surface of one of the substrates opposed to each other with a liquid crystal interposed therebetween. A pixel electrode to which a video signal from the drain signal line is supplied via the switching element, and a counter electrode for generating an electric field between the pixel electrode and the pixel electrode, the counter electrode being the switching element and the pixel. Formed on the upper surface of the insulating film made of an organic material layer that also covers the electrodes,
Fine particles for improving the dielectric constant of the insulating film are diffused at least on the surface of the part of the insulating film exposed from the counter electrode.

Means 5. The liquid crystal display device according to the present invention includes, for example, a pixel electrode formed in a different layer with an insulating film in each pixel region on the liquid crystal side surface of one of the substrates opposed to each other through the liquid crystal. A counter electrode, wherein fine particles of titanium oxide are diffused at least on the surface of the insulating film exposed from the electrode formed on the insulating film of the pixel electrode and the counter electrode. It is characterized by.

Means 6. A liquid crystal display device according to the present invention includes, for example, a switching element operated by a scanning signal from a gate signal line in each pixel region on the liquid crystal side surface of one of the substrates opposed to each other with a liquid crystal interposed therebetween. A pixel electrode to which a video signal from the drain signal line is supplied via the switching element, and a counter electrode for generating an electric field between the pixel electrode and the pixel electrode, the counter electrode being the switching element and the pixel. Formed on the upper surface of the insulating film made of an organic material layer that also covers the electrodes,
It is characterized in that fine particles of titanium oxide are diffused at least on the surface of the portion of the insulating film exposed from the counter electrode.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of a liquid crystal display device according to the present invention will be described below with reference to the drawings.

FIG. 2 is an equivalent circuit diagram showing an embodiment of the liquid crystal display device according to the present invention. Although this figure is an equivalent circuit diagram, it is drawn corresponding to the actual geometrical arrangement.

First, there is a pair of transparent substrates SUB1 and SUB2 arranged to face each other with a liquid crystal in between, and the liquid crystal has one transparent substrate SUB1 and the other transparent substrate SUB2.
It is enclosed by a sealing material SL which also serves as a fixing.

On the liquid crystal side surface of the one transparent substrate SUB1 surrounded by the seal material SL, the gate signal lines GL extending in the x direction and juxtaposed in the y direction and the y direction extending in the y direction. A drain signal line DL is formed side by side in the direction.

Each gate signal line GL and each drain signal line D
The region surrounded by L and L constitutes a pixel region, and the matrix-shaped aggregate of these pixel regions is the liquid crystal display unit A.
It constitutes R.

Further, a common counter voltage signal line CL running in each of the pixel regions is formed in each of the pixel regions arranged in parallel in the x direction. The counter voltage signal line CL serves as a signal line for supplying a reference voltage for a video signal to a counter electrode CT described later in each pixel region.

In each pixel region, a thin film transistor TFT operated by a scanning signal from the gate signal line GL on one side thereof and a pixel electrode to which a video signal from the drain signal line DL on one side is supplied via the thin film transistor TFT. PX is formed.

The pixel electrode PX generates an electric field between the counter voltage signal line and the counter electrode CT connected thereto, and the electric field controls the light transmittance of the liquid crystal.

One end of each of the gate signal lines GL extends beyond the seal material SL, and the extended end constitutes a terminal to which the output terminal of the vertical scanning drive circuit V is connected. . Further, a signal from a printed circuit board arranged outside the liquid crystal display panel is inputted to an input terminal of the vertical scanning drive circuit V.

The vertical scanning drive circuit V comprises a plurality of semiconductor devices, a plurality of gate signal lines adjacent to each other are grouped, and one semiconductor device is applied to each of these groups.

Similarly, one end of each of the drain signal lines DL extends beyond the sealing material SL, and the extended end constitutes a terminal to which the output terminal of the video signal drive circuit He is connected. Has become. Further, a signal from a printed circuit board arranged outside the liquid crystal display panel is input to the input terminal of the video signal drive circuit He.

The video signal driving circuit He is also composed of a plurality of semiconductor devices, and a plurality of drain signal lines adjacent to each other are grouped, and one semiconductor device is assigned to each group. Further, the counter voltage signal lines CL common to the respective pixel regions arranged in the x direction are commonly connected at the end portion on the right side in the drawing, and the connection line extends beyond the sealing material SL and extends therethrough. The terminal CTM is formed at the end. From this terminal CTM, a reference voltage for the video signal is supplied.

One of the gate signal lines GL is sequentially selected by a scanning signal from the vertical scanning circuit V.

A video signal is supplied to each of the drain signal lines DL by a video signal drive circuit He at the timing of selecting the gate signal line GL.

FIG. 1 is a plan view showing the structure of the pixel region, and FIG. 3 is a sectional view taken along line III-III in FIG.
A sectional view taken along line -IV is shown in FIG.

First, on the liquid crystal side surface of the transparent substrate SUB1,
A pair of gate signal lines GL extending in the x direction and juxtaposed in the y direction are formed.

These gate signal lines GL surround a rectangular region together with a pair of drain signal lines DL which will be described later, and this region is configured as a pixel region.

An insulating film GI made of, for example, SiN is formed on the surface of the transparent substrate SUB1 on which the gate signal lines GL have been formed as described above so as to cover the gate signal lines GL as well.

The insulating film GI functions as an interlayer insulating film for the gate signal line GL in the formation region of the drain signal line DL described later, and functions as a gate insulation film in the formation region of the thin film transistor TFT described later. In the formation region of the capacitive element Cstg, which will be described later, the film has a function as a dielectric film.

On the surface of this insulating film GI,
A semiconductor layer AS made of, for example, amorphous Si is formed so as to overlap a part of the gate signal line GL.

This semiconductor layer AS is a thin film transistor T.
By forming the drain electrode SD1 and the source electrode SD2 on the upper surface of the FT, the MI of the inverted stagger structure in which a part of the gate signal line GL is used as the gate electrode.
An S-type transistor can be constructed.

Here, the drain electrode SD1 and the source electrode SD2 are formed at the same time when the drain signal line DL is formed.

That is, the drain signal line DL extending in the y direction and arranged in parallel in the x direction is formed, and a part of the drain signal line DL extends to the upper surface of the semiconductor layer AS to form the drain electrode SD.
1 is formed, and the source electrode SD2 is formed apart from the drain electrode SD1 by the channel length of the thin film transistor TFT.

The source electrode SD2 extends from the surface of the semiconductor layer AS to the pixel region side, in other words, the source electrode S2.
The pixel electrode PX is formed integrally with D2.

The pixel electrode PX is composed of, for example, two electrode groups which extend in the y direction in the drawing and are arranged in parallel in the x direction, and are connected in the central portion, for example, in order to electrically connect them to each other. It is formed as a "H" -shaped pattern.

The material of the pixel electrode PX may be a non-translucent conductive layer such as a metal layer, or may be ITO (Indium Tin Oxide) or ITZO (Indium Tin Z).
It may be formed of a transparent conductive layer such as incOxide) or IZO (Indium Zinc Oxide).

Incidentally, the semiconductor layer AS and the drain electrode SD1
A thin layer doped with a high concentration of impurities is formed at the interface with the source electrode SD2, and this layer functions as a contact layer.

This contact layer is, for example, the semiconductor layer A.
When S is formed, a high-concentration impurity layer is already formed on the surface thereof, and the drain electrode SD1 formed on the upper surface of the impurity layer is formed.
And the impurity layer exposed from the pattern of the source electrode SD2 as a mask may be etched.

On the surface of the transparent substrate SUB1 on which the thin film transistor TFT, the drain signal line DL, the drain electrode SD1 and the source electrode SD2 are thus formed, a protective film PSV1 made of, for example, SiN and a protective film made of an organic material layer made of resin are formed. PSV2 is formed by being sequentially laminated.

The protective films PSV1 and PSV2 are films for avoiding direct contact with the liquid crystal of the thin film transistor TFT and prevent deterioration of characteristics of the thin film transistor TFT. Of these, the protective film PSV2 can be formed by coating. Therefore, the surface can be flattened, and the dielectric constant of the protective film PSV1 or PSV2 can be reduced because the dielectric constant of the protective film PSV1 or PSV2 is small.

The counter voltage signal line CL and the counter electrode CT are formed on the surface of the protective film PSV2.

Here, the counter voltage signal line CL and the counter electrode CT are integrally formed. The counter voltage signal line CL is superposed on the gate signal line GL and formed along the traveling direction of the gate signal line GL, and the counter electrode CT is connected to the adjacent counter voltage signal line CL and extends in the y direction in the drawing. It is composed of, for example, three electrode groups arranged in parallel in the x direction.

One of the counter electrodes CT formed of the electrode group is the center of the pixel region, that is, the two pixel electrodes PX.
Are formed on the drain signal line DL side so that the pixel electrodes PX and the counter electrode CT are disposed between the other two electrodes.

The counter electrode CT on the drain signal line DL side is x
It is formed in common with the counter electrode CT on the drain signal line DL side of the other pixel region adjacent to the direction side, whereby the counter electrodes CT are superimposed on the drain signal line DL with their central axes substantially aligned with each other. The drain signal line DL has a width larger than that of the drain signal line DL.

Thus, the electric field from the drain signal line DL can be easily terminated to the counter electrode CT arranged so as to be superposed on the electric field, and it is possible to avoid terminating the pixel electrode PX arranged adjacent to the counter electrode CT. Can be made. Therefore, when the electric field terminates at the pixel electrode PX, it can be prevented from becoming noise.

In this case, the protective films PSV1 and PSV2 interposed between the drain signal line DL and the counter electrode CT.
Of these, the protective film PSV2 is composed of an organic material layer having a low dielectric constant, so that the above-described effects can be more ensured.

The material of the counter voltage signal line CL and the counter electrode PT may be formed of a non-translucent conductive layer such as a metal layer, or may be ITO (Indium Tin Oxid).
e), ITZO (Indium Tin Zinc Oxide) or IZ
It may be formed of a transparent conductive layer such as O (Indium Zinc Oxide).

Further, on the surface of the protective film PSV2 exposed from the counter voltage signal line CL and the counter electrode CT thus formed, for example, titanium oxide is used with the counter voltage signal line CL and the counter electrode CT as a mask. The diffusion layer DFL is formed in which the fine particles are selectively diffused.

Such a diffusion layer DFL is formed for the purpose of forming that portion as a region having a high dielectric constant. From this, if the portion where the diffusion layer DFL is formed has a high dielectric constant, the diffusing fine particles are not necessarily titanium oxide, and are higher than zinc oxide, alumina, barium sulfate, zirconia, or the like, or an organic film. It goes without saying that other materials having a dielectric constant may be used.

In the liquid crystal display device thus configured, the protective film PSV2 made of an organic material layer interposed between the pixel electrode PX and the counter electrode CT is arranged particularly adjacent to the pixel electrode PX. The dielectric constant is increased between the other pixel electrodes PX.

This means that the organic material layer between the pixel electrode PX and the counter electrode CT which causes an electric field is made to have a high dielectric constant, and the decrease in the voltage applied to the liquid crystal is suppressed. can do. Therefore, when driving the liquid crystal display device, it is possible to suppress an increase in the drive voltage thereof.

Since the protective film PSV2 interposed between the drain signal line DL and the counter electrode CT formed overlying the drain signal line DL is not made to have a high dielectric constant, an organic material is used as the protective film PSV2. The significance of selecting layers is not impaired.

Further, the protective film PSV2 made of an organic material layer
The increase in the dielectric constant is performed by using the counter electrode CT formed on the upper surface of the protective film PSV2 as a mask to diffuse ultrafine particles made of, for example, titanium oxide. Diffusion can be easily performed by using a solution in which fine particles are diffused.

Therefore, the object of the present invention can be achieved by a simple method without going through complicated steps. Of course, a method may be used in which after forming the counter electrode CT, the lower protective film PSV2 is etched using the counter electrode CT as a mask to form a recess, and a material having a high dielectric constant is embedded in the recess.

[0062]

As is apparent from the above description,
According to the liquid crystal display device of the present invention, it is possible to suppress an increase in the drive voltage thereof.

[Brief description of drawings]

FIG. 1 is a plan view showing an embodiment of a pixel of a liquid crystal display device according to the present invention.

FIG. 2 is an equivalent circuit diagram showing an embodiment of a liquid crystal display device according to the present invention.

FIG. 3 is a sectional view taken along line III-III in FIG.

FIG. 4 is a sectional view taken along line IV-IV in FIG.

[Explanation of symbols]

SUB1, SUB2 ... Transparent substrate, GL ... Gate signal line,
GI ... Insulating film, AS ... Semiconductor layer, DL ... Drain signal line, SD1 ... Drain electrode, SD2 ... Source electrode, PX
... Pixel electrode, PSV1 ... Protective film (inorganic material layer), PSV
2 ... Protective film (organic material layer), CL ... Opposing voltage signal line, C
T ... Counter electrode, DFL ... Diffusion layer.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ Identification symbol FI theme code (reference) G09F 9/30 330 G09F 9/30 330Z 338 338 348 348A 9/35 9/35 (72) Inventor Yoshiaki Nakayoshi 3300 Hayano, Mobara-shi, Chiba Hitachi, Ltd. Display Group F-term (reference) 2H090 HA03 HB07X HB19X HC10 HD01 KA04 LA01 LA04 2H092 GA14 HA01 JA24 JB56 KB21 NA25 PA06 QA06 5C094 AA24 BA03 BA43 CA19 DA15 EA04 A16 GA10 FB15G435 BB12 CC09 KK05 KK09 KK10

Claims (6)

[Claims] 1. A pixel electrode and a counter electrode formed in different layers with an insulating film provided in each pixel region on the liquid crystal side surface of one of the substrates opposed to each other with a liquid crystal interposed therebetween. A part of the insulating film exposed from the electrode formed on the insulating film of the pixel electrode and the counter electrode, at least the surface of which has a region subjected to a high dielectric constant treatment. Liquid crystal display device. 2. A switching element operated by a scanning signal from a gate signal line and a switching element in each pixel region on a liquid crystal side surface of one of the substrates opposed to each other with a liquid crystal interposed therebetween. A pixel electrode to which a video signal from the drain signal line is supplied through and a counter electrode for generating an electric field are formed between the pixel electrode and the pixel electrode, and the counter electrode also covers the switching element and the pixel electrode. It is characterized in that it is formed on the upper surface of an insulating film made of an organic material layer to be formed, and has a region exposed to the counter electrode of the insulating film, at least the surface of which has been subjected to a high dielectric constant treatment. Liquid crystal display device. 3. A pixel electrode and a counter electrode formed of different layers with an insulating film provided in each pixel region on the liquid crystal side surface of one of the substrates opposed to each other with the liquid crystal interposed therebetween. Fine particles for improving the dielectric constant of the insulating film are diffused at least on the surface of the insulating film exposed from the electrode formed on the insulating film of the pixel electrode and the counter electrode. A liquid crystal display device characterized by the above. 4. A switching element operated by a scanning signal from a gate signal line and a switching element in each pixel region on a liquid crystal side surface of one of the substrates opposed to each other with a liquid crystal interposed therebetween. A pixel electrode to which a video signal from the drain signal line is supplied through and a counter electrode for generating an electric field are formed between the pixel electrode and the pixel electrode, and the counter electrode also covers the switching element and the pixel electrode. A region formed on the upper surface of the insulating film formed of the organic material layer, in which fine particles for improving the dielectric constant of the insulating film are diffused at least on the surface of the insulating film exposed from the counter electrode. A liquid crystal display device comprising: 5. A pixel electrode and a counter electrode formed of different layers with an insulating film provided in each pixel region on the liquid crystal side surface of one of the substrates opposed to each other with the liquid crystal interposed therebetween. Characterized in that at least the surface of the insulating film exposed from the electrode formed on the insulating film of the pixel electrode and the counter electrode has a region in which fine particles of titanium oxide are diffused. Liquid crystal display device. 6. A switching element operated by a scanning signal from a gate signal line and a switching element in each pixel region on the liquid crystal side surface of one of the substrates opposed to each other with a liquid crystal interposed therebetween. A pixel electrode to which a video signal from the drain signal line is supplied through and a counter electrode for generating an electric field are formed between the pixel electrode and the pixel electrode, and the counter electrode also covers the switching element and the pixel electrode. It is formed on the upper surface of an insulating film made of an organic material layer to be formed, and has a region in which fine particles of titanium oxide are diffused on at least the surface of the portion of the insulating film exposed from the counter electrode. Liquid crystal display device.