JP2544420B2 - Liquid crystal display - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an active matrix type liquid crystal display device using a metal-insulating film-metal element (MIM element).

2. Description of the Related Art Liquid crystal display devices have been put to practical use as lightweight and thin flat panel displays, and are currently used as displays for portable computers and pocket televisions. It is also expected to be used as a high-resolution display for personal computers and word processors, and as a large display for home or high-definition television.

Here, a simple matrix system is generally used as a driving system of the liquid crystal display. However,
Considering the display performance such as the contrast ratio, the number of pixels, the response, etc. in order to increase the resolution, the display performance of the simple matrix drive system is limited, and it is not suitable for a high-resolution display. Therefore, a thin film transistor (TFT)
An active matrix method using a three-terminal element such as MIM element and a two-terminal element such as MIM element is regarded as a promising driving method. Examples of these include, for example, JP-A-57-196589.
JP-A No. 62-62333 and JP-A No. 62-62333.

6 and 7 show a liquid crystal display device according to Japanese Patent Laid-Open No. 62-62333. First, the lower electrode 2 is formed on the substrate 1 made of glass. Specifically, Ta or Al is formed into a thin film by a sputtering method or the like and patterned. Next, the lower electrode 2 is oxidized by an anodic oxidation method, a thermal oxidation method, a plasma oxidation method, or the like to form the insulating film 3 in the same pattern shape. The transparent electrode 4 to be a pixel electrode is formed on the patterned electrode, and the MIM element is formed in series with the pixel electrode (transparent electrode 4). In other words, the laminated part of the lower electrode (metal) 2-insulating film 3-transparent electrode (metal) 4 is MI.
Functions as an M element. As the insulating film in this MIM element
Ta ₂ O ₅ or Al ₂ O ₃ is used. In FIG. 6, numeral 5 is a liquid crystal layer filled with a liquid crystal material, and the other counter substrate having an upper transparent electrode of a predetermined pattern is arranged on the liquid crystal layer 5.

However, in the case of such a method of forming an oxide film on a metal surface, a heating step is required, so that the substrate is limited to one having heat resistance such as glass, for example, it should be formed on a polyfilm such as PET. It is difficult. For example, when considering the case of anodizing Ta, the oxidation itself can be processed at a relatively low temperature, but considering the fact that impurities are removed reliably, heat treatment at 300 ° C for about 30 minutes (in air) is required. Becomes Also, if the thermal oxidation method, 400 ℃ ~ 500 in oxygen atmosphere
High temperature heating of about ℃ is required.

Further, in the case of the conventional method as disclosed in the publication, the oxide film forming process is complicated, and it is difficult to obtain an oxide film having good uniformity in film quality and film thickness. Therefore, the device characteristics (IV characteristic) of the MIM element, the symmetry (IV characteristic +,
-The ratio of I when biased) is also a cause of variation.

Further, in the case of liquid crystal display, it is desired to increase the aperture ratio (that is, the ratio of the area of the pixel electrode to the area of other portions) and to reduce the capacitance of the MIM element (that is, for LCD driving, It is desirable that the ratio of capacitance / MIM element with LCD be 10 or more). In order to meet these requirements, if the insulating film is Ta ₂ O ₅ , its dielectric constant ε
Since r is as high as εr≈25, it is desirable to make the area of the MIM element as small as possible. However, in the case of the conventional simple laminated structure, the practical limit is about 15 μm × 15 μm.

The present invention has been made in view of such a point, can be produced with good reproducibility and uniformity at low temperatures, structurally achieves a small area of metal-insulating film-metal element, low cost ,
It is an object to obtain a liquid crystal display device that can contribute to high quality.

Structure In order to achieve the above object, the present invention forms a row electrode pattern on one substrate of a counter substrate and a column electrode pattern on the other substrate, and a metal-insulating film is formed on each pixel of at least one of the electrode patterns. -In a liquid crystal display device in which metal elements are connected in series and a liquid crystal material is held between the opposite substrates, the metal-insulating film-element is formed at an angle to the substrate, and the insulating film is formed. It is characterized in that it is formed by a hard carbon film containing at least one of amorphous and microcrystalline with carbon atoms and hydrogen atoms as main texture forming elements.

That is, it can be formed as an insulating film of the MIM element by vapor phase synthesis with good controllability and at a low temperature around room temperature, and the dielectric constant εr is also ε.
A hard carbon film having a size as small as r≈4 is formed in a state in which its thickness and uniformity can be easily controlled.

A first embodiment of the present invention will be described below with reference to FIGS. 1 to 4. First, a lower electrode 12 and a hard carbon film 13 are laminated and formed on one of the opposite substrates 11 as shown in FIG. 2 (a). Here, the lower electrode 12 has a film thickness of 2500 Å or more,
Desirably, it is formed with a thickness of 5000Å or more. Further, as the material of the lower electrode 12, metals such as Al, Ni, NiCr, Cr, Pt, Ta and Mo are appropriately used, but not limited to those exemplified above, a conductive material that can be patterned by etching is used. I wish I had it. The method of forming the hard carbon film 13 and its characteristics will be described later, but the thickness of the hard carbon film 13 is 2000 Å
It should be above (preferably 4000 Å or above).

Next, as shown in FIG. 3B, the hard carbon film 13 and the lower electrode 12 are sequentially etched by the dry etching method,
Pattern into a predetermined pattern. These hard carbon films
The process of sequentially etching the lower electrode 13 and the lower electrode 12 can be continuously performed by selectively setting the gas type, pressure, discharge power, etc. in the same chamber.

At this time, when etching the lower electrode 12, etching is performed so that the step portion has a tapered cross-section. By making the taper shape with such an angle, it is easier to control the film thickness and its uniformity on the step portion of the second hard carbon film 14 formed in the next step, that is, the taper surface. Become.

Further, a second hard carbon film 14 is formed so as to cover the patterned upper surface and side surface of the hard carbon film 13 and the side surface of the lower electrode 12 as shown in FIG. This second hard carbon film
The film thickness of 14 is 300 Å or more, preferably 500 Å ~ 2000 Å. That is, the insulating film of the MIM element is constituted by these hard carbon films 13 and 14, but the film thickness becomes thicker at the surface portion of the lower electrode 12 where the hard carbon films 13 and 14 are laminated due to the sum of the two. The step portion, that is, the side surface portion of the lower electrode 12 has only the hard carbon film 14, and the film thickness is reduced.

Further, as shown in FIG. 3D, a transparent electrode 15 which will be a pixel electrode is formed by a DC or RF sputtering method, and a predetermined patterning is performed. IT as the material of the transparent electrode 15
O, SnO ₂ or the like is used, and the film thickness thereof is 300 Å or more, preferably about 500 Å to 1500 Å.

Through these manufacturing steps, the liquid crystal display device including the MIM element having the hard carbon films 13 and 14 as insulating films, which is the feature of this embodiment, is configured. The overall structure of the liquid crystal display device including the MIM element is similar to that described in the above-mentioned publication.

In such a structure, what operates as a MIM element is a thin portion of the hard carbon film 14 on the side surface of the lower electrode 12, that is, the lower electrode (metal) 12-second hard carbon film (insulating film) 14-transparent electrode (metal). ) 15 is a portion A laminated in the lateral direction. MI
The area of the M element is equal to the step (thickness) of the lower electrode 12 and the transparent electrode 1.
It is determined by the pattern of 5 and can be made extremely smaller than the conventional one. Further, since it is not formed in a plane, the aperture ratio is not lowered. Further, since the step (film thickness) of the lower electrode 12 defines the area of the MIM element, the MIM element can be formed with higher accuracy than the processing accuracy by the photolithography method, and therefore the characteristic variation due to the element area variation is small. Will be things.

By the way, an example of a method of synthesizing (forming) the hard carbon films 13 and 14 in the present embodiment will be described by a plasma CVD method.
As the apparatus, for example, a parallel plate type plasma CVD apparatus is used. First, the substrate on which the film is to be formed is attached to the RF power supply side where self-bias promotes positive ion bombardment. For example, a raw material gas obtained by mixing a hydrocarbon such as CH ₄ , C ₂ H ₆ , C ₃ H ₈ or C ₄ H ₁₀ with hydrogen is introduced into the apparatus, and a high-frequency electric field of about 13.56 MHz is applied between the parallel plate electrodes. When applied, a glow discharge occurs. The raw material gas is decomposed into radicals and ions by the glow discharge and reacts with each other. A carbon film is deposited. This hard carbon film is generally called a diamond-like carbon film, an i-C film, a diamond film or a diamond thin film. Conditions required for such reactions, RF output: 0.1~5.0W / cm ² pressure: 10 ^-3 to 10 Torr Deposition temperature: room temperature to 950 ° C.

The hard carbon film formed by such a film forming method has a specific resistance (ρ) of 10 ⁶ to 10 ¹³ Ωcm, a Vickers hardness (H) of up to 9500 kg · mm ^{-2 and a} refractive index (n) of 1.9 to 2.4. Density: has physical properties of 6 × 10 ¹⁶ to 10 ¹⁸ cm ⁻³ . However, the specific resistance was measured by the IV characteristic of a coplanar cell, the Vickers hardness was measured by a microbitusmeter, the refractive index was measured by an ellipsometer, and the defect density was measured by ESR. That is, according to X-ray and electron diffraction analysis, the amorphous state (a-C:
H) or in an amorphous state containing fine crystal grains of about 50 to 100 °. Analysis by IR absorption and Raman spectroscopy, carbon atoms as shown in FIGS. 3 and 4 is SP ³
Between hybridized and atoms to form a hybrid orbital of the SP ² bond that is clearly summer that are mixed in. Such a hard carbon film as the containing SP ² mainly of SP ^3, SP
It is as including SP ^{3 2} a mainly.

In film formation, the smaller the RF output and the lower the pressure,
As the resistivity and hardness of the film increase and the hydrogen mixture ratio increases, the refractive index increases and the defect density decreases, that is, a high-quality film can be obtained.

Furthermore, since the hard carbon film has the characteristic that the film quality does not deteriorate even when manufactured at a relatively low temperature such as from normal temperature to about 150 ° C., it is most suitable for lowering the element manufacturing process, and The material is not limited to glass or the like, and the degree of freedom in selection is increased.

In addition, a film of substantially the same quality can be formed not only by the plasma CVD method as illustrated but also by an ion beam method using the same source gas.

In this way, by forming the insulating film of the MIM element by the hard carbon films 13 and 14, variations in element characteristics are reduced and the MIM element can withstand mechanical damage. That is, the damage due to the rubbing process when the liquid crystal material is sealed is small, and the yield is improved. Further, according to this embodiment, since the MIM element can be formed on the step portion of the lower electrode 12, that is, on the side surface, the aperture ratio of the liquid crystal display device can be improved. Furthermore, since such hard carbon films 13 and 14 can be formed at a low temperature of about room temperature, the substrate is not limited to those having heat resistance, and the degree of freedom in selection increases, and Since the dielectric constants εr of 13,14 are as small as εr≈4, they can be formed with high precision without requiring fine processing to the left, and the yield is improved also from this point.

Next, a second embodiment of the present invention will be described with reference to FIG. In the present embodiment, the upper electrode 16 for the MIM element part is formed independently and is electrically connected to the transparent electrode 15.

First, the lower electrode 12 and the hard carbon film 13 are laminated and formed on the substrate 11. These materials are the same as those in the above-described embodiment, and are sequentially dry-etched to form a predetermined pattern. After forming the second hard carbon film 14 in the same manner as in the above embodiment, in this embodiment, the upper electrode 16 is formed in a predetermined pattern from a part of the hard carbon film 14 to the substrate 11. The upper electrode 16 may be formed of the same material as the lower electrode 12 and may be formed to have a film thickness of about 500Å to 3000Å. After that, a transparent electrode 15 to be a pixel electrode is formed and patterned so that a part thereof is on the upper electrode 16. As a result, according to the present embodiment, the transparent electrode 15 and the hard carbon film 14 do not directly contact with each other, the deterioration of the bonding state due to the alteration of the surface of the hard carbon film during the formation of the transparent electrode 15 does not occur, and the device characteristics are more improved. It will be stable.

Effects As described above, the present invention forms the metal-insulating film-the insulating film of the metal element by the hard carbon film having a predetermined texture-forming element structure, so that it can be formed in a state where there is little variation in element characteristics, and when the liquid crystal material is enclosed. It can be a MIM element that can withstand mechanical damage without being damaged by the rubbing process, and can also form an MIM element by utilizing the electrode step portion to improve the aperture ratio. It can be formed at a low temperature of about room temperature, the degree of freedom in selecting the substrate can be increased, and the dielectric constant is low, so microfabrication is not required so much. Since the hard carbon film is formed so as to be covered, the film thickness and the uniformity of the insulating film made of the hard carbon film can be easily controlled.

[Brief description of drawings]

FIG. 1 is a schematic perspective view showing a first embodiment of the present invention, and FIG.
FIG. 4 is a process diagram showing a manufacturing process, FIG. 3 is a waveform-absorption coefficient characteristic diagram, FIG. 4 is a wave number-intensity characteristic diagram, and FIG. 5 is a schematic perspective view showing a second embodiment of the present invention. FIG. 7 is a plan view showing a conventional example, and FIG. 7 is an enlarged sectional view of a part thereof. 11 …… Substrate, 13,14 …… Hard carbon film, 15 …… Transparent electrode

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hitoshi Kondo 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Co., Ltd. (56) References JP-A-60-241021 (JP, A) JP-A-SHO 62-174378 (JP, A) JP-A 64-40929 (JP, A)

Claims (1)

(57) [Claims] 1. A row electrode pattern is formed on one substrate of a counter electrode and a column electrode pattern is formed on the other substrate, and a metal-insulating film-metal element is connected in series to each pixel of at least one of the electrode patterns. Then, in a liquid crystal display device in which a liquid crystal material is held between the opposed substrates, the metal-insulating film-metal element is formed so that a step portion protruding from the substrate has a tapered shape, and the insulating film is made of carbon. A liquid crystal display device comprising a hard carbon film containing atoms and hydrogen atoms as main texture-forming elements and containing at least one of amorphous and microcrystalline.