JPH03192326A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To use a high polymer plate as an insulating substrate which enables film formation at a lower temperature by using a hard carbonaceous film for an insulating film as an active element. CONSTITUTION:The insulating film of the MIM element consists of the hard carbonaceous film (called i-Ci film, diamond carbonaceous film, or amorphous diamond thin film) which contains carbon atoms and hydrogen atoms as main structure forming elements and also contains at least either of amorphous crystal and fine crystal. This hard carbonaceous film can be formed at the low temperature, so a high polymer material is used for the insulating film to obtain the low cost liquid crystal panel which is thin and light in weight and has shock resistance. Further, polyester, polysulfone, polyamide, polyimide, polycarbonate, poylyacetate, etc., are used effectively as the material of the high polymer substrate (insulating substrate).

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a liquid crystal display device, and more particularly to an active matrix type liquid crystal display device using an MIM (conductor-insulator-conductor) S element as an active element. .

[Conventional technology]

The mainstream of liquid crystal display devices is now shifting from simple matrix type panels to active matrix type panels. The reason for this is that there is a demand for large-area LCD panels for office automation equipment, LCD TVs, etc. This active matrix method employs a method of providing an active element for each pixel.

By the way, HIM elements are often used as one of the active elements. This is because it exhibits nonlinear current-voltage characteristics that are good for switching. Conventionally, as an Ih element, Ta, A4. A metal electrode such as Ti is provided, an insulating film made of an oxide of the metal or 5iO1, 5iNz, etc. is provided thereon, and further, kQ, kQ, etc. are provided as an upper electrode.
A device provided with a metal electrode such as Cr is known.

However, MI technology using metal oxide as an insulator (deadline film)
No. 89, No. 62-62333, etc.), the insulating film is formed by anodic oxidation or thermal oxidation of the lower electrode, so the process is complicated and requires high-temperature heat treatment. However, high-temperature heat treatment is required to ensure removal of impurities, etc.), and film controllability (uniformity and reproducibility of film quality and film thickness) is poor.

Because the substrate is limited to heat-resistant materials and the insulating film is made of metal oxides with fixed physical properties, it is not possible to freely change device materials and device characteristics, and the degree of freedom in design is limited. There are drawbacks. This means that it is extremely difficult to design and manufacture a device that fully satisfies the specifications of a liquid crystal display device incorporating an MIM element. Furthermore, as will be explained later, there is a relationship between the relative dielectric constant εr and the steepness β of the element, which is βccl/West; when εr is high, the steepness decreases, making it unsuitable for high-density display, etc. It has the following disadvantages.

In addition, in the case of an IN element using 5iO1 or 5iNz for the insulating film (Japanese Unexamined Patent Publication No. 61-275819), the insulating film is formed by a gas phase method such as plasma CvO method or sputtering method, but the substrate temperature Since a temperature of about 300° C. is usually 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, since these insulating films are synthesized in a gas phase, a large amount of dust is generated and the film has many pinholes, which reduces the yield of devices. Furthermore, the film stress is large and film peeling occurs, which also reduces the yield of the device.

On the other hand, as described above, a glass plate is usually used as the insulating substrate. This is because the formation of insulating films in conventional active elements requires heat treatment at 300-600°C.

Therefore, if the insulating film of the NZN element can be formed at a low temperature of about room temperature, it is possible to change the insulating substrate from a glass plate to a polymer plate.

[Problem to be solved by the invention]

The present invention is a liquid crystal display in which the insulating film in the MIN element is changed from the above-mentioned metal compound, 5iO1, 5iN1, etc. to a specific film that is formed at a low temperature, and at the same time, a polymer plate is used as the insulating substrate. It provides equipment.

[Means to solve the problem]

The present invention provides an active active conductor comprising a liquid crystal material sandwiched between a pair of insulating substrates, and each of a plurality of pixel electric bridges provided on at least one of the substrates. In an active matrix liquid crystal display device in which elements are connected, at least one of the insulating substrates has a thickness of 700 mm or more and a glass transition temperature of 60 mm.
℃ or higher and visible light transmittance of 80% or higher, and the insulating film is a hard carbon film.

The present inventors have conducted a lot of research and consideration on liquid crystal display devices, and found that if an MIM element whose insulating film is a hard carbon film is used as an active element, and such a MIX element is formed, an insulating substrate It was confirmed that certain polymer plates can be used instead of glass plates. The present invention has been made based on this.

〔Example〕

In the following, the invention will be explained in more detail with reference to the accompanying drawings.

As described above, the liquid crystal display device of the present invention has an active element (M
The insulating film of the IM element) is formed with a hard carbon film that can be formed at a deposition temperature of about room temperature, and at least one of the insulating substrates is made of a polymer plate (thickness of 7001 Js or more, glass transition temperature (
Tg) 60° C. or higher, visible light transmittance 80% or higher).

The insulating film in the -IM element of the present invention is a hard carbon film (i-cBg, diamond-like carbon film, amorphous diamond film) containing carbon atoms and hydrogen atoms as main structure-forming elements and at least one of amorphous and microcrystalline materials. (also called diamond film).

One of the features of the hard carbon film is that it is a vapor-phase grown film.
As will be described later, the various physical properties can be controlled over a wide range by controlling the film forming conditions. Therefore, even though it is an insulating film, its resistance value is half 11! The MIM element used in the present invention covers the range from forest body to absolute body area, and in this sense, the MIM element used in the present invention is
The MSI element (Metal-3emi-Insula) described in JP-A-61-275819
tor) and SIS elements (an element consisting of a semiconductor-insulator-semiconductor, where the semiconductor is doped with impurities at a high concentration).

In addition, a polymer material is used for the insulating substrate in the present invention,
A liquid crystal panel that is lower cost, thinner, lighter, and more impact resistant can be obtained. However, on the other hand, due to the characteristics of polymer materials, rigidity is weak and if the substrate is too thin, the substrate may bend, or it may be difficult to handle, resulting in poor dimensional accuracy during microfabrication (when making HIM or common line). There are problems such as an increase in processing (etching) defects.

FIG. 1 shows the relationship between the thickness of the polymer substrate, dimensional accuracy, and failure rate. From this, the thickness of the polymer substrate is 700μ
It can be seen that if it is above -, no particular problem arises in practical use.

Furthermore, in order to perform heat treatment at 80°C for about 20 minutes during the process, at least the glass transition temperature (Tg) of the polymer substrate is required.
), unless the temperature is 60° C. or higher, the substrate will be significantly deformed and it will be almost impossible to form a fine pattern. In addition, in order to achieve a display contrast ratio of 20:1 or more as a liquid crystal panel, the transmittance of the polymer substrate must be at least 80% (total visible (light area) is desirable.

From these viewpoints, it is advantageous to use polyester (PET), polysulfone (PES), polyamide, polyimide, polycarbonate, polyacetate, etc. as specific materials for the polymer substrate (insulating substrate).

Next, the production of an active element (HIM element) and a liquid crystal display device using the same will be described with reference to FIGS. 2 and 3.

FIG. 2 shows how the four image electrodes are connected to the element. First, a transparent electrode material for one pixel electrode is deposited on a polymer substrate (not shown) by vapor deposition, sputtering, etc., and then patterned into a predetermined pattern to form the pixel electrode 4. A conductor thin film for the lower electrode is formed by a method such as vapor deposition or sputtering, and patterned into a predetermined pattern by wet or dry etching to form a first conductor 7 that will become the lower electrode,
A hard carbon film 2 is coated thereon by a plasma CVD method, an ion beam method, etc., and then patterned into a predetermined pattern by dry etching, wet etching, or a lift-off method using a resist to form an insulating film. A conductor thin film for a pass line is coated by a method such as sputtering, and patterned into a predetermined pattern to form a second conductor 6 that will become a pass line.Finally, an unnecessary portion of the lower electrode 7 is removed to form a transparent electrode pattern. The pixel electrode 4 is exposed. In this case, the MIM element (active element) 5
The structure of is not limited to this, but after the creation of the MIM element, a transparent electrode is provided on the top layer, a structure in which the transparent electrode also serves as the upper or lower electrode, and a structure in which MIM is provided on the side of the lower electrode.
Various modifications are possible, such as one in which an IX element is formed.

Here, the thickness of the lower electrode, upper electrode and transparent electrode is usually
They range from several hundred to several thousand people, several hundred to several thousand people, and several hundred to several thousand people, respectively. The thickness of the hard carbon film is 100 to 8,000, preferably 200 to 5,000, more preferably 300 to 5,000.
The number is in the range of 4,000 people.

The use of MIM elements using hard carbon films not only improves display quality and enables production at low temperatures;
Up until now, it had been considered difficult to use plastic materials for insulating substrates due to heat resistance considerations, but this has now been resolved, albeit with some conditions.

Next, the material of the MIM element used in the present invention will be explained.

The material of the first conductor 7, which becomes the lower electrode, is AQ, Ta.
, Cr, 'i, Mo, Pt, Ni, transparent conductors, etc. are used.

The material of the second conductor 6 which becomes the pass line is AQ, C.
A variety of conductors can be used, including Ni, Mo, Pt, Ag, and transparent conductors, but Ni, Pt, and Ag are preferred because they have particularly excellent stability and reliability of IV characteristics.

In the MIM device using the hardened carbon film 2 as an insulating film, the symmetry does not change even if the type of electrode is changed, and the QnIccf
From the relationship 7, it can be seen that Poole-Frenkel type conduction is occurring. Also, from this fact, in the case of this type of MI element,
It can be seen that the upper electrode and lower electrode may be combined in any way. However, depending on the adhesion between the hard carbon film and the electrical bridge and the state of the interface, deterioration and changes in device characteristics (low (2) characteristics) occur. Considering these, it was found that Ni, r't, and Ag are good. The current-voltage characteristics of the MIM element in the present invention are shown as shown in Fig. 4, and can be approximated by the conduction formula shown below. It is expressed as

1=Kexp(βV”) −(1) I: Current ■: Applied voltage N: Conductivity coefficient β: Poole-Frenkel coefficient n: Carrier density μ: Carrier mobility q
; Electron charge Φ Nidrap depth ρ: Specific resistance d: Thickness of hard carbon film: Boltzmann constant T: Ambient temperature
Cr: dielectric constant ε of hard carbon film. : An organic compound gas, especially a hydrocarbon gas, is used to form a vacuum dielectric hard carbon film. The phase state of these raw materials does not necessarily have to be a gas phase at normal temperature and pressure; they can be used in either a liquid or solid phase as long as they can be vaporized through melting, evaporation, sublimation, etc. by heating or reduced pressure. be.

Regarding hydrocarbon gas as a raw material gas, for example, C
H4, C□H C, H,, C, H,. A gas containing at least all hydrocarbons such as paraffinic hydrocarbons such as C, IH, acetylenic hydrocarbons, olefinic hydrocarbons, acetinic hydrocarbons, diolefinic hydrocarbons, and even aromatic hydrocarbons. Available for use.

Furthermore, in addition to hydrocarbons, any compound containing at least a carbon element can be used, such as alcohols, ketones, ethers, esters, Co, and CO2.

As a method for forming a hard carbon film from a raw material gas in the present invention, there is a method in which 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. Although this is preferable, a method using a magnetic field effect is more preferable since the deposition is performed under low pressure for the purpose of increasing the area, improving uniformity, and forming a film at a low temperature.

However, active species can also be formed by thermal decomposition at high temperatures.

In addition, a hard carbon film may be formed through an ionic state generated by an ionization vapor deposition method or an ion beam vapor deposition method, or a hard carbon film may be formed from neutral particles generated by a vacuum vapor deposition method, a sputtering method, etc. Alternatively, a combination of these may be used to form a film.

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 to 50 W/cm'' pressure Crab 10-3 to 10 TOrr Deposition temperature: Room temperature to 950°C (such a wide range can be adopted, but preferably room temperature to 300°C, more preferably room temperature to 300°C) (150°C) Due to this plasma state, the raw material gas is decomposed into radicals and ions and reacts, resulting in amorphous (amorphous) and microcrystalline (crystalline) consisting of carbon atoms C and hydrogen atoms H. A hard carbon film is deposited containing at least one of the following: (with a size of several tens of micrometers to several micrometers).The properties of the hard carbon film are shown in Table 1.

Table-1 Note) 81! Standard method: Specific resistance (ρ): Determined from the knee characteristics of a coplanar cell.

Optical band gap (Egopt): Obtain the absorption coefficient (α) from the spectral characteristics and determine from the relationship (αh v )”J(h v −Elopt).

Amount of hydrogen in the film (CH): 290 from infrared absorption spectrum
Integrate the peak around 0o-1 and multiply by the absorption cross section A to find 6Co=AIfα(su)7w・dw SP3/SP" ratio: Infrared absorption spectrum, sp".

Galas belonging to SP2 and its area ratio Seek more.

Vickers hardness (H): Based on microbisocurs 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 shows that carbon atoms form SP3 hybrid orbitals and SP2 hybrid orbitals, as shown in FIGS. 5 and 6, respectively. It is clear that there is a mixture of inter-connections. The ratio of sp3 bonds to SP2 bonds is I
It can be roughly estimated by peak-separating the R spectrum.

In the IR spectrum, many mode spectra from 2800 to 3150a++-'' are measured to overlap, but the attribution of the peak corresponding to each wave number is clear, and the peaks can be separated by Gaussian distribution as shown in Figure 7. If you calculate the area of each peak and find the ratio, SP
You can know the "/SP" ratio.

Further, according to X-ray and electron diffraction analysis, it has been found that it is in an amorphous state (a-C: H) or an amorphous state containing microcrystalline grains of several tens to several micrometers in size.

In the case of plasma CVD method, which is generally suitable for mass production,
The lower the RF output, the higher the resistivity and hardness of the film, and the lower the pressure, the longer the life of the active species. There is a tendency for the number to increase. Furthermore, since the plasma density decreases at low pressures, methods using magnetic field confinement effects are particularly effective in increasing resistivity.

Furthermore, this method has the feature of being able to form a high-quality hard carbon film even under relatively low temperature conditions of room temperature to 150°C, making it ideal for lowering the temperature of the M I MiA child manufacturing process. . Therefore, the degree of freedom in selecting the substrate material to be used is increased, and the substrate temperature can be easily controlled, so that a uniform film can be obtained over a large area. Furthermore, as shown in Table 1, the structure, physical properties, etc. of the hard carbon film can be controlled over a wide range, so there is an advantage that device characteristics can be designed freely. Furthermore, the dielectric constant of the film is 2 to 6, which is Ta20ssA, which is conventionally used in MIM.
Q20. , is smaller than SiNx, so when making an element with the same capacitance, the element size only needs to be larger, so it does not require much fine processing and the yield improves (due to the driving conditions, LCD and MIM elements The capacitance ratio between CLcD and CNIM is required to be approximately 10:1).

Therefore, the smaller the dielectric constant, the greater the steepness,
The ratio between the on-current Ion and the off-current Ioff can be increased. Therefore, L at lower duty ratio
This makes it possible to move CDs and realize high-density CDs.

Furthermore, since the hard carbon film has high hardness, there is little damage caused by the rubbing process when filling the liquid crystal material, and from this point of view as well, the yield is improved.

In view of the above points, by using a hard carbon film, a low-cost, gradation (color), and high-density LCD can be realized.

Furthermore, in addition to carbon atoms and hydrogen atoms, this hard carbon film contains
It may also contain as a constituent element an element of Group 1 of the Periodic Table, an element of Group 2 of the Periodic Table, an element of Group 2 of the Periodic Table, an alkali metal element, an alkaline earth metal element, a nitrogen atom, an oxygen element, a chalcogen element, or a halogen atom.

One of the constituent elements is the Group ■ element of the periodic table, which is also Group ■.
By introducing elements, alkali metal elements, alkaline earth metal elements, nitrogen atoms, or oxygen atoms, the thickness of the hard carbon film can be made about 2 to 3 times thicker than that of non-doped ones. The occurrence of pinholes during device fabrication can be prevented, and the mechanical strength of the device can be dramatically improved. Further, in the case of a nitrogen atom or an oxygen atom, the same effect as in the case of an element of group Ⅰ of the periodic table as described below can be obtained.

Similarly, devices that incorporate elements from group Ⅰ of the periodic table, chalcogen elements, or halogen elements dramatically improve the stability of the hard carbon film and also improve the hardness of the film, resulting in highly reliable elements. can be made. These effects can be obtained because Group (I) elements and chalcogen elements reduce active double bonds present in the hard carbon film. In addition, in the case of halogen elements, 1) the decomposition of the source gas is promoted by an abstraction reaction with hydrogen to reduce dangling bonds in the film, and 2) the halogen element
extracts the hydrogen in the C-H bond and replaces it, C-x
It enters the membrane as a bond and increases the bond energy (
This is because the bond energy between C-0 and between C-x is larger between C-x.

In order to use these elements as the constituent elements of the film, in addition to hydrocarbon gas and hydrogen, the raw material gases include elements from group Ⅰ, elements from group Ⅰ, elements from group Ⅰ of the Periodic System Table, and alkali metals. element,
Compounds (or molecules) containing alkaline earth metal elements, nitrogen atoms, oxygen atoms, chalcogen elements, or halogen elements (
Hereinafter, these gases may also be referred to as "other compounds").

Examples of compounds containing Group I elements of the periodic table include B(OClHS)3, B2O, BCl2. ,BBr
,,BF,,AQ (0-i-Callt)3,(
CHI)3AQ, (C, I(S), Al11, (i-
C4I(,), AΩ, AQCQ3. Ga(0-i-C
,)l,),,(CH3),Ga,(CaH2)3Ga
, GaCQ, , GaBr, , (0-i-C,H7)3,
Examples include In, (CzHs)aIn, and the like.

Examples of compounds containing Group Ⅰ elements of the periodic table include Si.
H,,Si,H5i3H,,(C2H,),SiH,
SiF4.5ill□C et al., Sl (OCH3)
(QC,H,)Si (QC,H7)4, GaCQ
4. GeH,, Ga(OCJ,)4, Go(C,)I
,)I(CI(3)4Sn,(C,H,),Sn%5n
There are CQ4 etc.

As a compound containing an element of group Ⅰ of the periodic table, for example, P
H,,PF,,PFPCQ,F,,PC712F,
PCQ,,PBr,,pococH3)3,p(c,
Hs)! ,POCQ3,AsH3,AsCQ,,AsB
r,, AsF,, AsF,, AsCQ3.5bH4,
There are SbF, 5bcQ, sb (QC, Hs )a, etc.

As a compound containing an alkali metal atom, for example, Li0
-i-C,H,,Na0-i-C,H,,KO-i-C
, H7, etc.

Examples of compounds containing alkaline earth metal atoms include C
a (oc, )I, ):l, Mg (QC2Hs
)a, (CiH=)aMg, etc.

Examples of compounds containing nitrogen atoms include nitrogen gas, inorganic compounds such as ammonia, organic compounds having functional groups such as amino groups and cyano groups, and nitrogen-containing heterocycles.

Examples of compounds containing oxygen atoms include oxygen gas, ozone, water (steam), hydrogen peroxide, -carbon oxide, carbon dioxide, carbon suboxide, -nitrogen oxide, nitrogen dioxide, dinitrogen trioxide, and dinitrogen pentoxide. , inorganic compounds such as nitrogen trioxide, hydroxyl groups, aldehyde groups, acyl groups, ketone groups, nitro groups, nitroso groups, sulfone groups, ether bonds, ester bonds, peptide bonds, and functional groups or bonds such as heterocycles containing oxygen. Further, examples thereof include organic compounds having a metal alkoxide, metal alkoxides, and the like.

Examples of compounds containing chalcogen elements include H2S
, (cl(c14s(co,),cH,,C)I, =
CHCH, 5CII□C+1 = CH2, C, H, S
C,H,,C,H,5C)l,,thiophene,)I2S
s, (C, Hs)2Se, H2Te, etc.

Compounds containing halogen elements include, for example, fluorine,
Inorganic compounds such as chlorine, bromine, iodine, hydrogen fluoride, chlorine fluoride, bromine fluoride, iodine fluoride, hydrogen chloride, bromine chloride, iodine chloride, hydrogen bromide, iodine bromide, hydrogen iodide, alkyl halides Organic compounds such as halogenated aryl, halogenated styrene, halogenated polymethylene, and haloform are used.

Actually, in order to manufacture the liquid crystal display device of the present invention, first, a transparent conductor for the common electrode 4', such as ITO, is placed on the insulating substrate 1'.
, ZnO:10, ZnO:Si, SnO,, In, 0
3rd grade by sputtering, vapor deposition, etc. from several hundred to several -
It is deposited thickly and patterned into stripes to form the common electrode 4'. Insulating substrate 1' provided with this common electrode 4'
An alignment material 8 such as polyimide is applied to each surface of the polymer substrate 1 on which HIM elements are previously provided in a matrix.
A rubbing process is performed, a sealing material is attached, a gap material 9 is inserted to make the gap constant, and a liquid crystal 3 is sealed to form a liquid crystal display device (FIG. 3).

〔Effect of the invention〕

The liquid crystal display device according to the present invention provides the following effects.

By using a hard carbon film as the insulating film, 1) Since it is created using a vapor phase synthesis method such as plasma CVD, the physical properties can be controlled over a wide range depending on the film formation 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 pinholes can be expected to be reduced by thickening the film. 3) A high-quality film can be formed even at low temperatures near room temperature, so it can be used on substrates. There are no restrictions on materials.

4) Excellent uniformity in film thickness and film quality, making it suitable for thin-film devices. 5) Low dielectric constant, requiring no advanced microfabrication technology, and therefore advantageous for increasing the area of devices. can be.

Furthermore, since the dielectric constant is low, the steepness of the element is high and Ion/
Since the Ioff ratio can be maintained, it is possible to drive at a low duty ratio.Also, by using a specific polymer material as the insulating substrate, the above 1) to 5) are not impaired, and 6) It is lighter than a glass substrate. 7) It has impact resistance and a thinner display, and 8) It has a small refractive index difference with the liquid crystal material and has good image quality with less aberration.

[Brief explanation of drawings]

FIG. 1 is a graph showing the relationship between the thickness of a polymer substrate, dimensional accuracy, and failure rate. FIG. 2 is a diagram showing a state in which the IM element and the image electrode are continuous. FIG. 3 is a partially cutaway perspective view of the liquid crystal display device. FIG. 4 is a current-voltage characteristic diagram of the HIM element in the present invention. FIG. 5, FIG. 6, and FIG. 7 are diagrams for explaining the properties of the hard carbon film in the present invention. l...Polymer substrate 1'...Insulating substrate 2...Hard carbon film 3...Liquid crystal 4...Pixel electrode 4'
...Common electrode 5...Active element 6...Second conductor (pass line) 7...First conductor (base electrode) 8
...Alignment film 9...Gap material No. 1 Figure 0.2 0.4 0.6 0. B1. Oj, 2
(S) Number 4 of Meishin Senmu Handling Figure 5

Claims (1)

[Claims] (1) A liquid crystal material is sandwiched between a pair of insulating substrates, and each of the plurality of pixel electrodes provided on at least one substrate has at least one active element consisting of a conductor-insulating film-conductor. In the connected active matrix liquid crystal display device, at least one of the insulating substrates is a polymer plate having a thickness of 700 μm or more, a glass transition temperature of 60° C. or more, and a visible light transmittance of 80% or more, and A liquid crystal display device, wherein the insulating film is a hard carbon film.