JPH0354526A - Active matrix type liquid crystal display device - Google Patents

Abstract

PURPOSE:To enhance the degree of freedom in device design and to substantially prevent mechanical damages and to decrease pinholes by an increase in film thickness by using a hard carbon film for the insulating film of MIM elements which are nonlinear resistance elements. CONSTITUTION:A conductor 2 in common use as a bus line and a conductor thin film to constitute auxiliary electrodes 4 are formed on an insulating substrate 1 formed with conductors 3 to constitute picture element electrodes and are patterned to prescribed patterns by wet or dry etching to form the conductors 2 and the auxiliary electrodes 4. After the hard carbon film 5 is coated thereon, the film is patterned to the prescribed patterns by a lift off method to form the insulating film, by which the MIM (metal-insulating film- metal) elements are obtd. The auxiliary electrodes 4 improve the joining characteristic of the conductors 3 and the hard carbon films 5.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention is applicable to high-capacity flat panel displays for OA, TV, etc., using MIM (metal-insulating film-metal) elements as nonlinear resistance elements. The present invention relates to an active matrix liquid display device capable of displaying liquids.

[Prior art]

An active matrix liquid crystal display device generally has a nonlinear resistance element connected in series to each pixel on at least one of two insulating substrates that support a liquid crystal layer, and an MIM element is used as the nonlinear resistance element. It is used a lot. Conventionally, as a MIM element, a metal electrode such as Ta, AQ, Ti, etc. is provided as a lower electrode on an insulating substrate such as a glass plate, and an oxide of the metal, SiOx, SjNx, etc. is provided on the lower electrode.
A layer of gold such as AQ, Cr, etc. is provided on top of it as an upper electrode. A device equipped with an IT electrode is known.

However, in the case of MIM elements that use metal oxide as the insulating film (Japanese Patent Application Laid-open Nos. 57-19658, 61-232689, 62-62333, etc.), the pure edge film is anodized by anodization of the lower gold GC electrode. Or, since it is formed by thermal oxidation, the process is complicated and requires high-temperature heat treatment (high-temperature heat treatment is also required to ensure the removal of impurities in anodizing), and film controllability (film quality and film thickness). uniformity and reproducibility)
In addition, the substrate is limited to heat-resistant materials, and the MA film is made of gold JHM compound with constant physical properties, so device materials and device characteristics cannot be freely changed, resulting in a limited degree of freedom in design. The disadvantage is that it is narrow. This is MI
This means that it is impossible to design and manufacture a device incorporating the M element, such as a liquid crystal display device, that fully satisfies the specifications. In addition, if film controllability is poor like this, fti current (I) voltage (V) characteristics as element characteristics, especially symmetry of IV characteristics and IV characteristics (current at positive bias and negative bias Ratio I − / I +
) will also cause the problem of increased variation. others. When using an MIM element for a liquid crystal display (LCD), the liquid crystal capacitance/MIM capacitance ratio needs to be 10 or more. Although it is desirable for MIM capacitance to be small, metal oxide films have a large dielectric constant, so the element capacitance also increases, which requires microfabrication to reduce the element capacitance and therefore the element area. In this case, there is also the problem that the insulating film is mechanically damaged during the rubbing process or the like during the filling of the liquid crystal material, resulting in a decrease in yield in combination with microfabrication.

On the other hand, in the case of an MIM element (Japanese Unexamined Patent Publication No. 61-275819) using Sjox or SiNx for the insulating film, the insulating film is
There are no particular problems with rI construction, and plasma CVD f5. The film is formed using a vapor phase method such as sputtering, but the substrate temperature is usually 300°C.
Since a temperature of about .degree. C. is required, a low-cost substrate cannot be used, and when the area is increased, the film thickness and film quality tend to become non-uniform due to the substrate temperature distribution. Furthermore, although this insulating film is made of a non-quality material whose physical properties vary greatly, there are problems with photodegradation and photoconductivity (resistance changes due to light), so the degree of freedom in designing device characteristics is still limited.

In addition, since general MIM elements are of the sandwich type,
In the case of insulating films formed by vapor phase methods such as iNx and SiOx, pinholes and voids are often generated, and such element defects reduce the yield during mass production. Furthermore, in the case of the sandwich type, the device characteristics are very sensitive to the thickness of the insulating film, so in order to obtain uniform characteristics, it is necessary to strictly control the film thickness, which poses difficult problems in terms of production technology. ing.

[Problem to be solved by the invention]

In order to solve the above-mentioned problems, as a result of intensive research by the present inventors, in an active matrix type liquid crystal display device,
As a nonlinear resistance element, an MI is formed by arranging an insulating film of hard carbon film and an electrode in a coplanar structure on an insulating substrate.
By using the M element, the number of masks is reduced compared to the sandwich-inch structure, making it possible to reduce costs, making it inexpensive and suitable for mass production, and even if a bottle hole occurs in the element.
Another object of the present invention is to provide an active matrix type liquid crystal display device that is hardly affected by the inclusion of voids and is almost free from short circuits due to dielectric breakdown.

[Structure and operation of the invention]

The liquid crystal display device of the present invention is an active matrix type liquid crystal display device in which a nonlinear resistance element is connected in series to each pixel of at least one of two insulating substrates supporting a liquid crystal layer, wherein the nonlinear resistance element is It is characterized by a coplanar structure consisting of a hard carbon film formed between a first conductor as a bus line electrode and a second conductor as a pixel electrode.

As described above, the liquid crystal display device of the present invention uses an MIM element whose insulating film is a hard carbon film as a nonlinear resistance element, and has a coplanar structure.

The insulating film used in the MIM device of the present invention is a hard carbon film (i-C film, diamond-like carbon film, (Also called amorphous diamond film or diamond thin film.) One of the characteristics of hard carbon films is that, because they are vapor-grown films, their physical properties can be controlled over a wide range by changing the film-forming conditions, as will be described later. Therefore, even though it is called an Ml film, its resistance value covers the range from a simple edge to an insulator region.In this sense, the MIM device of the present invention is similar to the MSr device (Metal-S eLli-
1 nsulator).

In order 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 have to be a gas phase at room temperature and normal pressure; it can be used in either a liquid or solid phase as long as it can be vaporized through melting, evaporation, sublimation, etc. by heating or reduced pressure. be.

Regarding hydrocarbon gas as a raw material gas, for example, CH
4 r CzHs + C3H8 r All hydrocarbons such as paraffinic hydrocarbons such as C<Lo, acetylenic hydrocarbons such as C, H, olefinic hydrocarbons, diolefinic hydrocarbons, and even aromatic hydrocarbons. Containing gases can be used.

Furthermore, other than hydrocarbons, for example, alcohols, ketones, ethers, esters, co. co. Any compound containing the carbon element can be used.

In the method of forming a hard carbon film from a raw material gas in the present invention, active species for film formation are formed through a plasma state generated by a plasma method using direct current, low frequency, high frequency, microwave, etc. However, since deposition is performed under low pressure for the purpose of increasing the area, improving uniformity, and forming a film at a low temperature, a method using a magnetic field effect is more preferred.

This active species can also be formed by high temperature pyrolysis. In addition, it may be formed through an ionic state generated by an ionization vapor deposition method, an ion beam vapor deposition method, etc., or it may be formed from neutral particles produced by a vacuum vapor deposition method, a sputtering method, etc. It may also be formed by a combination of these.

An example of the deposition conditions for the hard carbon film produced in this manner is approximately as follows in the case of plasma CVD method.

RF output: 0.1~5011/(!+1) Pressure: 1.0''~lOTorr Deposition temperature: Room temperature~950
'C Due to this plasma state, the source gas is decomposed into radicals and ions and reacts, causing carbon atoms to form on the substrate.
A hard carbon film containing at least one of amorphous (non-quality) and microcrystalline (crystal size is several 10A to several centimeters) is deposited. Table 1 shows the properties of the hard carbon film. Table 1 Note) Measurement method; Specific resistance (ρ): Determined from the IV characteristics of a coplanar cell.

Optical bandgap (EgopL): Obtain the absorption coefficient (α) from the spectral characteristics, and determine θξ from the relationship (αhν)"' = B (hYEgopt).

The amount of hydrogen in the film (cJ: from the infrared absorption spectrum, 2900
It is determined by integrating the peak near cn-1 and multiplying it by the absorption cross section A.

That is, CM=A-/VSP'/SP'' ratio: the infrared absorption spectrum is s
It is decomposed into Gaussian functions assigned to p' and sp'', respectively, and determined from the area ratio thereof.

Vickers hardness (H) by two micro Vickers meter.

Refractive index (n): by ellipsometer.

Defect density: Based on ESR.

As a result of analysis by IR absorption method and Raman spectroscopy, the hard carbon film thus formed showed that the carbon atoms had sP3 hybrid orbitals and SP2 hybrid orbitals as shown in FIGS. 6 and 7, respectively. It is clear that there is a mixture of inter-connections. The ratio of SP3 bond to SP” bond is .I
It can be roughly estimated by peak-separating the R spectrum.

In the IR spectrum, the spectra of many modes overlap between 2800 and 3150■-1, but the attribution of the peak corresponding to each wave number has been clarified.
As shown in Figure 8, if you perform peak separation using a Gaussian distribution, calculate the area of each peak, and find the ratio, S
P'/S P2 can be known. Also, according to X1iA and electron diffraction analysis, it is in an amorphous state (a-C:H). and/or about 50 people ~ 5μ
It is known that it is in an amorphous state containing microcrystalline grains of about 1.0 m in size. In the case of plasma CVD method, which is generally suitable for mass production, R
The smaller the F output, the more the specific resistance value and hardness of the membrane increase,
The lower the pressure, the longer the life of the active species, the lower the temperature of the substrate, the more uniform it can be over a large area, and the more specific resistance and hardness tend to increase. Furthermore, since the plasma density decreases at low pressures, methods using magnetic field confinement effects are more effective in increasing resistivity.

Furthermore, this method has the characteristic that a high-quality hard carbon film can be formed even under relatively low temperature conditions of about room temperature to 150° C., so it is optimal for lowering the temperature of the MUM element manufacturing process.

Therefore, the degree of freedom in selecting the substrate material to be used is increased, and a uniform film can be obtained over a large area in order to easily control the substrate temperature. In addition, as shown in Table 1, the production and physical properties of hard carbon films can be controlled over a wide range, so there is an advantage that device characteristics can be designed freely.3 Furthermore, the dielectric constant of the film is between 2 and 6, compared to conventional Ta20,, AQ,0,, SjNx used in MIM elements
Since the device size is smaller compared to that of the LCD, when manufacturing an element with the same capacitance, the element size only needs to be larger, so there is no need for much fine processing and the yield is improved (Due to the operating conditions, the difference between LCD and MIM elements is The capacity ratio is C [.CD/C
Approximately MIM=10/1 is required. ).

Furthermore, because the film is highly hard, there is less damage caused by the rubbing process when filling the liquid crystal material, which also improves yield. From the above points, by using a hard carbon film, low cost, gradation (colorization), high density LCD, etc. can be realized.

In order to control the resistance value, improve film stability, heat resistance, and improve hardness, the hard carbon film as described above may contain impurities such as elements from group Ⅰ of the periodic table and group ① of the periodic table.
It is possible to dope a group element, a group Ⅰ element, an alkali metal element, an alkaline earth metal element, a nitrogen atom, an oxygen atom, a chalcogen element, or a halogen atom. This third commandment of doping further increases the stability of the element and the degree of freedom in device design.

In particular, in coplanar MIM devices, the film thickness of the hard carbon film and the W/L ratio (W:
The width of the gap between the element parts (L: the length of the gap) and the appropriate range of specific resistance are determined, but from the viewpoint of film peeling, the film thickness should be 1μ or less,
From the length of one side of the pixel and the accuracy of photolithography, W/
It is advantageous for the L ratio to be 1/100 or more in terms of manufacturing. At this time, the appropriate range of specific resistance is 104 to 10'Ω·■ based on the driving conditions. The specific resistance of non-doped hard carbon film is 10'~10''
It is possible to obtain a specific resistance within the above range by doping an appropriate amount of a Group Ⅰ, Group V, alkali metal, alkali metal, N or O element.

In the present invention, the amount of hydrogen atoms contained as one of the constituent elements in the hard carbon film is 10% of the total constituent elements.
~50 atom%, preferably 20-45 atom%.

Further, in the present invention, the amount of carbon atoms contained as one of the constituent elements in the hard carbon film is 50 to 90 atom%, preferably 55 to 80 atom% of the total constituent elements.
m%.

Group II elements of the periodic table include B H A Q , Ga
, and In are mentioned.
The amount of group elements is within 5 atom% of the total structural elements,
It is preferably 0.001-3 atom%.

Examples of Group Ⅰ elements of the periodic table include Si, Ge, and Sn, and the amount of Group Ⅰ elements is 2% to the total structure or atoms.
Within 0ato+i%, preferably 0.01 to 17ato
m%.

Group Ⅰ elements of the periodic table include P, As, and sb, and the amount of group Ⅰ elements is 5a based on all constituent atoms.
t. Within om%, preferably 0.001 to 3 atoms
%〇 Alkali metal elements include Li, Na, and K, and the amount of the alkali metal elements is within 5 atoi+%, preferably 0.001 to 3 a to the total structure or atoms.
tom%.

Examples of alkaline earth metal elements include Ca and Mg, and the amount of alkali earth metal Hl atoms is within 5 atom%, preferably 0.001 to 3 at.
om%.

The amount of nitrogen atoms is within 5 atom%, preferably 0.001 to 3 atom%, based on the total atoms in the structure.

The amount of oxygen atoms is within 5 atom%, preferably 0.001 to 3 atom%, based on all the constituent atoms.

As a chalcogen element. S, Se, and Te are mentioned, and the amount of chalcogen element is 2 for the total structure or atoms.
0atoI within 1%, preferably 0. Ol~17ato
m%.

Examples of the halogen element include F, CQ, Br, and Br, and the amount of the halogen element is 3% relative to all constituent atoms.
Within 5 atom%, preferably 0.1 to 35 atom%
is preferred.

The amounts of the above-mentioned elements or atoms are determined by the method of elemental analysis,
For example, it can be measured by Auger analysis. Further, the amounts of these elements or atoms can be measured by conventional methods of elemental analysis, such as Auger analysis. This amount can be adjusted by adjusting the amount of other compounds contained in the source gas, film forming conditions, etc.

In the MIM element of the present invention, the insulating film is made of the hard carbon film as described above and has a coplanar structure with respect to the insulating substrate. Examples of this coplanar type MIM element will be described below in comparison with a conventional sandwich type MIM element.

FIG. 5 shows an ellipse of a conventional sandwich type MIM element. An oxide film (Ta, O, AQ, 0, etc.) formed by anodic oxidation or a vapor phase film is formed on the first conductor 2, which becomes the bus line@pole. SiNx, SiO
It is covered with an insulating film 6 such as x, and a second conductor 3 serving as a pixel electrode is further laminated thereon. It is the laminated portion of the first conductor 2, the pure film 6, and the second conductor 3 that functions as a switching element. The thickness of the insulating film 6 is usually about several hundred to several thousand, and the dynamic voltage is around 20V, so the electric field strength applied to the film is 10V/e.
Higher than ll, li! If there are voids, pinholes, etc. in the membrane 6, it will be destroyed immediately. Further, if there is dust, foreign matter, etc. in or on the surface of the first conductor 2, a hole will be formed in the insulating film, and as a result, the second conductor 3 will be easily exposed to the show 1 when it is laminated. 1 to 4 show examples of the MIM device of the present invention. As shown in Figure 1, first the second conductor 3 which becomes the pixel electrode
are formed on the insulating substrate 1, which also serves as a bus line.
The first conductor 2 and the auxiliary electrode 4 are formed by forming the conductor a film, which will become the conductor 2 and the auxiliary electrode 4, by a method such as vapor deposition or sputtering, or by patterning it into a predetermined pattern by wet or tri-etching. On top of that, plasma CVD
After covering the hard carbon film 5 by a method such as a method, an ion beam method, or the like, the insulating film is patterned into a predetermined pattern by dry etching, wet etching, or a lift-off method using a resist, thereby completing the MIM element.

The auxiliary electrode 4 improves the bonding characteristics between the second conductor 3 and the hard carbon film 5, and is inserted as necessary. Furthermore, many configurations are possible for the shapes of the first conductor 2 and the second conductor 3 (which can also be called the shape of the gap between the first conductor and the second conductor) and the pattern of the hard carbon film. These structures are shown in plan views in FIGS. 2(a) to 2(d). Note that FIG. 2(a) corresponds to the perspective view of FIG. 1. Figure 2(b)
The hard carbon film 5 is vertically continuous, and if the hard carbon film has a large resistivity value, there will be no interference with adjacent bits, and this shape is acceptable. FIG. 2(c) shows a shape in which only the gap between the element parts is narrowed to reduce short circuits due to pattern defects between the first conductor 2 and the second conductor 3.

In Fig. 2(d), the first conductor 2 and the second conductor 3 have an interdigital shape, and the specific resistance value of the hard carbon film is very large, so in order to keep the element resistance within the appropriate range, the W/L ratio is (W
: Width of element gap, L: Length of silent gap) (Figure 2 (a)
)Reference} can be made smaller. As described above, various types of element formation are possible depending on the specific resistance of the hard carbon film, and are not limited to the above embodiments. In FIG. 3, the first conductor 2 and the second conductor 3 are formed on the hard carbon film 5. With this shape, if the specific resistance value of the hard carbon film 5 is appropriate, the hard carbon film 5 There is no problem even if patterning is not performed. Rather, it is a desirable shape in the sense that it reduces the number of masks.

Next, in FIG. 4, a hard carbon film 5 is deposited on the first conductor 2, and then a second conductor 3 is formed adjacent to the stepped portion (side surface) of the first conductor 2. By doing so, there is no short circuit between the first conductor and the second conductor, and the gap therebetween can be minimized (up to the thickness of the hard carbon film). Also, although the hard carbon film is patterned in this figure, there is no particular need to do so. Next, the materials used in the present invention will be explained in more detail.

First, the insulating substrate 1 is a glass plate. A plastic plate or flexible plastic film is used. The materials of the first conductor 2, which becomes the bus line electrode, and the auxiliary electrode 4, which is provided as necessary, include AQ, Ni, Cr,
Various 4-electric materials are used, such as metals such as Pt, Ag, Au, Cu, Mo, Ta, and W, and transparent conductors, but these become the lower layer of the hard carbon film as shown in Figures 1 and 4. In this case, A Q , C
r, Ni, and Cu are preferred. In addition, as shown in Figure 3, when the film is placed on top of the hard carbon film, from the viewpoint of preventing property deterioration and stability. Ni, Pt, Ag and Au are preferred. It is desirable that the second conductor 3 serving as the pixel electrode be transparent, and a transparent conductor such as ITO, SnO2, ZnO, etc. is used. Here, the thickness of the first conductor 2 and the second conductor is usually in the range of several hundred to several thousand liters, respectively.

Further, the thickness of the hard carbon film and the W/L ratio mentioned above are usually suitably 1 μm or less and 1/100 or less, respectively.

In order to manufacture a liquid crystal display device of the present invention using a substrate having a coplanar MIM element as described above, this substrate and an insulating substrate on which a striped transparent common electrode pattern is formed are prepared, and a conventional method is used between the two substrates. The liquid crystal layer may be shaped accordingly.

[Function and effect of the invention]

As described above, according to the present invention, the nonlinear resistance element M
In addition to the effects 1) to 4) below by using a hard carbon film as the insulating film of the IM element, the coplanar structure of the MIM element provides the effects 5) to 8) below. It will be done.

1) Since it is produced by a simple gas phase method such as plasma CVD, the physical properties can be controlled over a wide range depending on the conditions, and therefore there is a large degree of freedom in device design.

2) Since it is hard and can be made into a thick film, it is less susceptible to mechanical damage, and it is also expected that pinholes will be reduced by making the film thicker.

3) Since a high-quality film can be formed even at low temperatures near room temperature, there are no restrictions on the substrate material.

4) It has excellent uniformity in film thickness and film quality, making it suitable for thin film devices.

5) Uniformity of device characteristics and defect rate due to pinholes etc. are further improved, and an inexpensive active matrix liquid crystal display device suitable for mass production can be provided.

6) Even if there are pinholes, voids, etc. in the element, it is not easily affected by them and will not cause short circuits due to damage to the seam.

7) Since the device characteristics depend more on the gap between the first conductor and the second conductor than on the thickness of the hard carbon film, the film thickness may be controlled relatively roughly.

8) Compared to the sandwich type, the number of masks is reduced (possibly one mask for the entire process), making it possible to reduce costs.

[Brief explanation of drawings]

FIG. 1, FIG. 3, and FIG. 4 are perspective views of an example of a coplanar MIM element used in the liquid crystal display element of the present invention, respectively.
Figure 2(a) is a plan view of the M element in Figure 1;
b) to (d) are modified views of the example in Fig. 2(a) and Fig. 5, respectively.
The figure is a perspective view of an example of a conventional sandwich-inch MIM element.
6 and 7 show the IR spectrum and Raman spectrum of the hard carbon insulating film used in the MIM device of the present invention, and FIG. 8 shows the Gaussian distribution of the IR spectrum. 1... vA Hayashi substrate 2... First conductor (becomes a bus line electrode) 3... Second conductor (becomes a pixel electrode) 4... Auxiliary electrode 5... Hard carbon film-based pure film 6... Conventional slip-on film

Claims (1)

[Claims] 1. In an active matrix liquid crystal display device in which a nonlinear resistance element is connected in series to each pixel on at least one of two insulating substrates supporting a liquid crystal layer, the nonlinear resistance element is used as a bus line electrode. An active matrix liquid crystal display device characterized by having a coplanar structure consisting of a hard carbon film formed between a first conductor and a second conductor serving as a pixel electrode.