JP2798962B2 - Liquid crystal display - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a metal-insulating film (MIM) as a non-linear resistance element.
The present invention relates to an active matrix liquid crystal display device using a (metal) element and applicable to a high-capacity flat panel display for OA, TV, and the like.

[Technology]

An active matrix type liquid crystal display device generally has a non-linear resistance element connected in series to each pixel of at least one of two insulating substrates supporting a liquid crystal layer, and a MIM element is often used as the non-linear resistance element. I have.

As a conventional MIM element, a metal electrode such as Ta, Al, or Ti is provided as a lower electrode on an insulating plate such as a glass plate, and an oxide-based transparent electrode of the metal, or an insulating film made of SiOx, SiNx, or the like is provided thereon. And a metal electrode such as Al or Cr is further provided thereon as an upper electrode.

However, a MIM device using a metal oxide for an insulating film (Japanese Unexamined Patent Publication No.
7-196589, 61-232689, 62-52333, etc.), the insulating film is formed by anodic oxidation or thermal oxidation of the lower metal electrode, so the process is complicated and requires high-temperature heat treatment. (High-temperature heat treatment is necessary even in the anodization method to ensure the removal of impurities, etc.), and film controllability (film quality and film thickness uniformity and reproducibility) is poor, and the substrate is limited to heat-resistant materials. In addition, since the insulating film is made of a metal oxide having constant physical properties, the material and device characteristics of the device cannot be freely changed, and there is a disadvantage that the degree of freedom in design is narrow. This means that it is impossible to design and manufacture a device incorporating the MIM element, for example, a device that sufficiently satisfies specifications from a liquid crystal display device or the like. If the film controllability is poor, the current (I) and voltage (V) characteristics as device characteristics, particularly the IV characteristics and the symmetry of the IV characteristics (the current ratio between the plus bias and the minus bias) I _-
/ I ₊ ) also increases. In addition, when the MIM element is used for a liquid crystal display device (LCD), the ratio of the liquid crystal part capacitance (C _LCD ) / MIM capacitance (C _MIM ) is required to be 10 or more. In the case of an object film, since the dielectric constant is large, the element capacity is also increased, and therefore, fine processing is required to reduce the element capacity and hence the element area. Further, in this case, there is also a problem that the yield is reduced due to mechanical damage to the insulating film in a rubbing step or the like at the time of sealing the liquid crystal material, in combination with fine processing.

When the capacitance is further increased (large area), pixel defects due to short-circuiting of elements, disconnection or defects on pixel electrodes, defective liquid crystal alignment due to dust, and the like are likely to occur, thereby deteriorating display quality. Will be. In order to prevent this, in Japanese Patent Application Laid-Open No. 62-59927, an image is divided into at least two parts and each is connected to a switching element such as a MIM element. is there. From this point as well, it is desirable that the MIM capacity be as small as possible.

On the other hand, MIM devices using SiOx or SiNx for the insulating film
In the case of No. 1-275819), there is no particular problem in the production of the insulating film, and the insulating film is formed by a vapor phase method such as a plasma CVD method or a sputtering method. The substrate cannot be used, and when the area is increased, there is a disadvantage that the film thickness and the film quality tend to be non-uniform due to the substrate temperature distribution. Although this insulating film is made of an amorphous material whose physical properties change significantly, the degree of freedom in device characteristic design is also narrowed due to the problems of light degradation and photoconductivity (resistance change due to light).

In addition, the insulating film used in the conventional MIM element is insufficient in withstand voltage and threshold voltage.

[Problems to be solved by the invention]

An object of the present invention is to use a hard carbon film as an insulating film of a MIM element and to divide a pixel electrode so that a low dielectric constant with excellent film controllability and mechanical strength can be obtained at a low temperature (around room temperature) and in a simple process. An inexpensive MIM device that can form an insulating film and therefore can design devices over a wide range, has little variation in device characteristics, has excellent threshold voltage and withstand voltage, and can improve mass production yield by making pixel defects inconspicuous. And a liquid crystal display device using the same.

[Configuration and operation of the invention]

The liquid crystal display device of the present invention is a liquid crystal display device comprising a non-linear resistance element connected in series to each pixel of at least one of two insulating substrates supporting a liquid crystal layer, wherein the non-linear resistance element serves as a bus line electrode. Formed between the first conductor and the second conductor as a pixel electrode, the film thickness is 100 to 8
000Å and specific resistance of 10 ⁶ to 10 ¹³ Ωcm, and further, as an impurity, a group III element, a group IV element, a group V element, an alkali metal element, an alkaline earth metal element, a nitrogen atom A MIM element comprising a hard carbon film doped with an oxygen atom, a chalcogen element or a halogen atom, and wherein the pixel electrode is divided into at least two elements each connected to the MIM element. Is what you do.

As described above, the first feature of the liquid crystal display device of the present invention is that the MIM element in which the insulating film is formed of the hard carbon film is used as the nonlinear resistance element. The insulating film used for this MIM element is a hard carbon film (i-C film, diamond-like carbon film, amorphous carbon film, etc.) containing at least one of amorphous and microcrystalline with carbon atoms and hydrogen atoms as main structure forming elements. Diamond film, also called a diamond thin film). One of the characteristics of the hard carbon film is that it is a vapor-grown film, so that its physical properties can be controlled over a wide range by film formation conditions as described later. Therefore, the resistance value of the insulating film covers the range from the semi-insulator to the insulator region, and in this sense, the MIM element of the present invention is disclosed in Japanese Patent Application Laid-Open No. 61-275.
It is also positioned as an MSI element (Metel-Semi-Insulator) shown in No. 819.

To form such a hard carbon film, an organic compound gas, particularly a hydrocarbon gas, is used. The phase state of this raw material does not necessarily need to be a gas phase at normal temperature and normal pressure, and any material that can be vaporized through melting, evaporation, sublimation, etc. by heating or decompression can be used in a liquid phase or a solid phase. is there.

For example, CH ₄ ,
Paraffin hydrocarbons such as C ₂ H ₆ , C ₃ H ₈ , C ₄ H ₁₀ , acetylene hydrocarbons such as C ₂ H ₄ , olefin hydrocarbons, diolefin hydrocarbons, and aromatic hydrocarbons Gases containing all hydrocarbons can be used.

Further, other than hydrocarbons, for example, alcohols,
Any compound containing a carbon element such as ketones, ethers, esters, and CO and CO ₂ can be used.

As a method for forming a hard carbon film from a raw material gas in the present invention, a method in which a film forming active species is formed through a plasma state generated by a plasma method using a direct current, a low frequency, a high frequency, or a micro group is used. However, a method using a magnetic field effect is more preferable because deposition is performed at a low pressure for the purpose of increasing the area, improving uniformity, and forming a film at a low temperature.

The active species can also be formed by high-temperature pyrolysis.
In addition, it may be formed through an ion state generated by an ionization evaporation method, an ion beam evaporation method, or the like, or may be formed from neutral particles generated by a vacuum evaporation method, a sputtering method, or the like. And, furthermore,
It may be formed by a combination of these.

An example of the deposition conditions of the hard carbon film thus produced is generally as follows in the case of the plasma CVD method.

RF output: 0.1 to 50 W / cm ² Pressure: 10 ^{-3 to} 10 Torr Deposition temperature: room temperature to 950 ° C. The raw material gas is decomposed into radicals and ions by this plasma state, and reacts to form carbon atoms on the substrate.
And a hydrogen atom H, a hard carbon film containing at least one of amorphous (amorphous) and microcrystalline (crystal size is several tens to several μm) is deposited. Table 1 shows various properties of the hard carbon film.

Thus the hard carbon film to be formed is analyzed by IR absorption and Raman spectroscopy, respectively, the carbon atoms as shown in FIG. 8 and FIG. 9 is formed a hybrid orbital of the hybrid orbitals and SP ² of SP ³ It is clear that the interatomic bonds are mixed. The ratio between SP ³ and SP ² bonds can be roughly estimated by separating peaks in the IR spectrum. In the IR spectrum, spectra of many modes are overlapped and measured at 2800 to 3150 cm ^-1 , but the assignment of peaks corresponding to each wave number has been clarified, and peaks are found by Gaussian distribution as shown in Fig. 10. Separate and calculate each peak area,
It is possible to know the SP ³ / SP ² by obtaining the ratio.

According to X-ray and electron diffraction analyses, it is known that it is in an amorphous state (a-C: H) and / or an amorphous state containing fine crystal grains of about 50 ° to several μm.

In the case of plasma CVD which is generally suitable for mass production, RF
The lower the output, the higher the specific resistance and hardness of the film, and the lower the pressure, the longer the life of the active species. Therefore, the substrate temperature can be lowered, the uniformity over a large area can be achieved, and the specific resistance and hardness increase. Tend to. Furthermore, since the plasma density decreases at low pressure, the method using the magnetic field confinement effect is particularly effective for improving the film quality.

Further, this method has a feature that a high-quality hard carbon film can be similarly formed even at a relatively low temperature condition of about room temperature to about 150 ° C., so that it is most suitable for lowering the MIM element manufacturing process. Therefore, there is a feature that the degree of freedom in selecting a substrate material to be used is widened and a uniform film can be obtained over a large area in order to easily control the substrate temperature.
Also, the structure and physical properties of the hard carbon film are as shown in Table 1,
Since control is possible over a wide range, there is an advantage that device characteristics can be freely designed. Furthermore, since the dielectric constant of the film is 3-5, which is smaller than Ta ₂ O ₅ , Al ₂ O ₃ , and AlNx used for the conventional MIM element, when making an element having the same electric capacity, Since the element size can be large, fine processing is not so required, and the yield is improved.
The capacitance ratio between the LCD and the MIM element needs to be about C _LCD : C _MIM = 10: 1.

In addition, as described above, Because it steepness smaller dielectric constant ε is large, so that the ratio of the ON current Ion and off-current Io _FF, can be increased. For this reason, LCD driving at a low duty ratio becomes possible, and a high-density LCD can be realized. Further, since the hardness of the film is high, the damage due to the rubbing step at the time of enclosing the liquid crystal material is small, and the yield is improved from this point as well. From the above points, by using the hard carbon film, low cost, gradation (colorization), high-density LCD and the like can be realized.

In the hard carbon film as described above, if necessary, control of the resistance value, or stability of the film, improvement of heat resistance, and further improvement of hardness, as an impurity, an element of Group III of the periodic table, and an element of Group IV. Group elements, Group V elements, alkali metal elements, alkaline earth metal elements, nitrogen atoms, oxygen atoms, chalcogen elements or halogen atoms can be doped.
This impurity doping further increases the stability of the device and the degree of freedom in device design. The amount of these impurities is 5 atomic% or less based on all the constituent atoms, and the amount of the group IV element is 35%.
Atomic% or less, the amount of the group V element is also 5 atomic% or less, the amount of the alkali metal element is 5 atomic% or less, the amount of the alkaline earth metal element is 5 atomic% or less, and the amount of the nitrogen element is 5 atomic%. Hereinafter, the amount of oxygen atoms is 5 atom% or less, the amount of chalcogen element is 35 atom% or less, and the amount of halogen element is 35 atom% or less. The amounts of these elements or atoms can be measured by a conventional method of elemental analysis, for example, Auger analysis. Also, this amount can be adjusted by the amount of other compounds contained in the source gas, film forming conditions, and the like.

The hard carbon film has a thickness range of 100 to 8000 mm and a specific resistance of 10 ⁶ to 10 ¹³ Ωcm from the relationship between the driving voltage and the breakdown voltage.
Is desirably within the range. In consideration of the margin between the drive voltage and the withstand voltage (dielectric breakdown voltage), the film thickness is desirably 200 mm or more, and color unevenness due to a step (cell gap) between the pixel portion and the MIM element portion is practically impossible. The thickness of the hard carbon film is preferably 200 to 6000
Å, the specific resistance is more preferably 5 × 10 ⁶ to 10 ¹² Ωcm. In addition, the number of defects in the element due to pinholes in the hard carbon film increases as the film thickness decreases, and becomes particularly remarkable at 300 ° or less (the defect rate exceeds 1%), and the in-plane distribution of the film thickness is uniform. (The accuracy of film thickness control is limited to about 30 mm, and the variation in film thickness exceeds 10%), so that the film thickness is 300 mm.
More desirably. Further, in order to make the hard carbon film hardly exfoliated due to stress and to drive at a low duty ratio (preferably 1/1000 or less), the film thickness is more preferably 4000 ° or less. Therefore, the thickness of the hard carbon film is 300 to 4000 mm, and the specific resistance is 1
More preferably, it is in the range of 0 ⁷ to 10 ¹¹ Ωcm.

The MIM element used in the present invention has an insulating film made of a hard carbon film as described above. In this MIM element, a pixel electrode is divided into at least two elements and connected to the respective elements. I have. The configuration of such a MIM element of the present invention will be described with reference to the drawings with reference to a conventional product.

FIG. 1 is a plan view of a conventional example, and FIGS. 2 to 5 are embodiments of the present invention. In the conventional example shown in FIG. 1, the pixel electrode 5 is single, and one element portion is connected thereto. If this element does not function due to disconnection, short circuit, etc., the pixel (corresponding to the pixel electrode 5 portion) ) The whole is not displayed and becomes a defect.

FIG. 2 shows an embodiment of the present invention. The pixel electrode 5 is divided into two elements 5 ', and a switching element 6 composed of a MIM element is connected to each element. Pixel electrode 5
Is divided in the horizontal direction in this example, the invention is not limited to this, and a configuration as shown in FIGS. 3 to 5 may be used. In short, any shape may be used as long as the display state in a normal operation can be expressed by being averaged over the entire pixel electrode 5. As a result, it is possible to reduce the apparent decrease in the yield for accidental pixel defects. FIG. 3 and FIG. 4 show another embodiment of the present invention having different division modes.

The number of divisions of the pixel electrode is not limited to two as in the above example, but may be three or more as shown in FIG.

Next, a method of forming the switching element used in the present invention will be described.

In order to fabricate the MIM device of the present invention, for example, as shown in FIG. 6, first, a conductive thin film for the auxiliary electrode 4 is formed on the insulating substrate 1 on which the transparent electrode pattern to be the pixel electrode 5 is formed by a method such as vapor deposition and sputtering. It is formed and patterned into a predetermined pattern by wet or dry etching to form an auxiliary electrode 4. After coating the hard carbon film 3 thereon by a plasma CVD method, an ion beam method, or the like, lift-off using dry etching, wet etching or a resist An insulating film is formed by patterning into a predetermined pattern by a method, and then a conductive thin film serving as a bus line 2 also serving as an upper electrode is coated thereon by a method such as evaporation or sputtering, and is patterned into a predetermined pattern to form an upper electrode. 2, and an unnecessary portion of the auxiliary electrode 4 is finally removed to expose the pixel electrode 5 '. Alternatively, as shown in FIG. 7, a bus line 2 also serving as a lower electrode, an insulating film 3 and an auxiliary electrode 4 serving as an upper electrode are formed on the substrate 1 in the same manner as in FIG. After the formation, a thin film for a transparent electrode is formed by a method such as evaporation or sputtering, and a part of the thin film is
May be connected to the pixel electrode.

Furthermore, the configuration of the MIMS element is not limited to this,
After the MIM element is created, various configurations are possible, such as a configuration in which a transparent electrode is provided on the uppermost layer, a configuration in which the transparent electrode also serves as the upper or lower electrode, and a configuration in which the MIM device is formed on the side surface of the lower electrode. .

The thickness of each of the lower electrode, the upper electrode, and the pixel electrode is in the range of several hundreds to several thousand square meters. The thickness of the hard carbon film is
It is in the range of 100 to 8000, preferably 200 to 6000, more preferably 300 to 4000.

In order to make the liquid crystal display device of the present invention using the substrate having the MIM element as described above, a second substrate on which this substrate and a stripe-shaped common electrode are formed is prepared, and a liquid crystal is formed between the two substrates by an ordinary method. A layer may be formed.

[Function and effect of the invention]

As described above, according to the present invention, it is a nonlinear resistance element.
By using a hard carbon film as the insulating film of the MIM element, the following effects 1) to 5) can be obtained.

1) Since it is manufactured by a gas phase synthesis method such as a plasma CVD method, the physical properties can be controlled in a wide range depending on the film formation conditions, and thus the degree of freedom in device design is large.

2) Since it is hard and can be formed into a thick film, it is hard to be damaged mechanically, and a reduction in pinholes due to the thick film can be expected.

3) Since a high-quality film can be formed even at a low temperature near room temperature, there is no restriction on the substrate material and it is suitable for increasing the area.

4) It is suitable for thin film devices because of its excellent uniformity of film thickness and film quality.

5) Since the dielectric constant is low, a high level of fine processing technology is not required, and the sharpness of the MIM can be increased, which is advantageous for increasing the area of the panel.

Further, by dividing the pixel of the MIM element substrate into at least two elements, the following effect 6) can be obtained.

6) Since the pixel defect can be made inconspicuous, the mass production yield is improved, so that an inexpensive liquid crystal display device can be provided.

[Brief description of the drawings]

FIG. 1 is a plan view of a substrate having a MIM element as a nonlinear resistance element used in a conventional liquid crystal display device, and FIGS. 2 to 5 are plan views of a substrate having a MIM element used in the liquid crystal display device of the present invention. FIGS. 6 and 7 are explanatory views of a method of manufacturing a substrate having the MIM element of the present invention. FIGS. 8 and 9 are IR spectra and graphs of a hard carbon film-based insulating film used in the MIM element of the present invention, respectively. Raman spectrum
FIG. 10 shows a Gaussian distribution of the hard carbon film. DESCRIPTION OF SYMBOLS 1 ... Insulating substrate, 2 ... Bus line electrode 3 ... Hard carbon film insulating film 4, ... Auxiliary electrode 5 ... Pixel electrode, 5 '... One element of pixel electrode 6 ... MIM element

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-62-59927 (JP, A) JP-A-64-40929 (JP, A) JP-A-64-7577 (JP, A) JP-A-1- 217326 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G02F 1/136 G02F 1/1343 G09F 9/30 H01L 49/02

Claims (1)

(57) [Claims] 1. A liquid crystal display device comprising a non-linear resistive element connected in series to each pixel of at least one of two insulating substrates supporting a liquid crystal layer, wherein said non-linear resistive element serves as a bus line electrode. A film formed between one conductor and a second conductor as a pixel electrode has a film thickness of 100 to 8000 mm and a specific resistance of 10 ⁶ to 10 ¹³ Ωcm, and further, as an impurity, a Group III element of the periodic table. A MIM element comprising a hard carbon film doped with a group IV element, a group V element, an alkali metal element, an alkaline earth metal element, a nitrogen atom, an oxygen atom, a chalcogen element or a halogen atom, and the pixel The liquid crystal display device, wherein the electrode is divided into at least two elements each connected to the MIM element.