JPH04283724A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To reduce the generation of a DC bias and to eliminate a flicker and liquid crystal separation by setting a difference in film thickness between orienting films, provided on respective substrate sides, within a specific range. CONSTITUTION:After a transparent electrode is patterned, active elements (switching element) 5 for respective picture element electrodes 4 and a common electrode 6 are provided to manufacture a liquid crystal display substrate 1. Then an orienting material 8 of polyimide, etc., is fitted onto the surface of the transparent substrate 1 and a rubbing process is performed; and a sealant is provided, a gap material 9 is charged to make a gap constant, and liquid crystal 3 is charged to form the liquid crystal display device. Then the difference in film thickness between the orienting film 8 on the side of one substrate 1 and the orienting film 8 on the side of the other substrate 1' is set to 20% of the film thickness of one orienting film. Further, the film thickness of one orienting film is 300-8000Angstrom .

Description

[Detailed description of the invention]

0001

TECHNICAL FIELD The present invention relates to a liquid crystal display device.

0002

2. Description of the Related Art When a liquid crystal display device is driven, a direct current bias is generated, resulting in flicker and decomposition of the liquid crystal. According to the research conducted by the present inventors, the DC bias has a negative effect on the symmetry of active elements for active driving when there is a large difference in the film thickness of the alignment film, when the interface state between the alignment film and the substrate is different. It was found that this occurred in some cases.

0003

[Objective] An object of the present invention is to provide a high-quality liquid crystal display device that generates less DC bias and does not cause flicker or liquid crystal decomposition.

0004

[Structure] In a liquid crystal display device having a liquid crystal layer between a pair of substrates, the difference in film thickness between an alignment film on one substrate side and an alignment film on the other substrate side is the thickness of one alignment film ( The present invention relates to a liquid crystal display device characterized in that the film thickness is within 20% of the thickness of the thicker film.

[0005] The thickness of one alignment film is usually 300 to 80 mm.
00 Å, preferably 500 to 4000 Å, particularly preferably 600 to 3000 Å.

The alignment film is an inorganic vapor deposited film such as SiO, an oblique vapor deposited film, or a film obtained by rubbing a polymer film such as polyimide. An organic polymer alignment film such as is desirable. In order to uniformly produce this polyimide polymer and alignment film over a large area, there are methods such as dip coating, roll coating, spin coating, and printing. Roll coating, rotation coating,
The printing method is good. In addition, there are contact methods (stylus method) and non-contact methods using an ellipsometer to measure the film thickness, but measurement using a non-destructive, non-contact ellipsometer is preferable. After measuring the thickness of the alignment film, it is attached to the substrate, but at this time,
It is desirable that the alignment films have the same thickness. However, even if there is a difference in film thickness between facing alignment films, if the difference is 20% or less, the flicker caused by the DC voltage is hardly perceptible to the eye and a good display is obtained. The difference in film thickness is 20% or less, preferably 10% or less, more preferably 5%.
The following shall be done. Note that the present invention is not affected by the type of substrate.

Next, a method for manufacturing the LCD of the present invention will be described. FIG. 1 is a partially cutaway perspective view of the liquid crystal display device of the present invention. First, as the insulating transparent substrate 1, a glass plate, a plastic plate, a flexible plastic film, or the like is used. I as a transparent electrode material for liquid crystal display on the substrate
A transparent electrode material such as TO, ZnO:Al, ZnO:Si, or SnO2:Sb is deposited to a thickness of several hundred Å to several μm by sputtering deposition, CVD, or the like, and then patterned into a predetermined pattern. At this time, if the substrate is for a simple matrix, transparent electrodes are patterned into stripes to form a substrate for liquid crystal display. To make a substrate for an active matrix, after patterning the transparent electrode, an active element (switching element) 5 and a common electrode 6 are formed for each pixel electrode 4.
will be established. As the active element 5, a-Si, Poly-
TFT elements using Si etc. and hard carbon films as insulating layers,
MIM elements and MSI elements using SiNx, SiC, Ta2O5, Al2O3, etc., PIN diodes, back-to-back diodes, varistors, etc. are used. The common electrode wiring is made of the previously used transparent electrode material, Al, Ni, C.
r, Ni-Cr, Mo, Ta, Ti, Au, Ag, Pt
sputtering method, vapor deposition method, C
It is deposited to a thickness of several hundred Å to several μm by a method such as a VD method, and then patterned. In this way, an active matrix substrate was obtained. A transparent substrate 1 made in the same manner was used as the opposite substrate to these substrates, an alignment material 8 such as polyimide was applied to the surface, a rubbing treatment was performed, a sealing material was applied, and a gap material 9 was put in to close the gap. Keep it constant;
The liquid crystal 3 is sealed to form a liquid crystal display device. Regarding the above-mentioned active elements, there are three-terminal elements such as TFTs and two-terminal elements such as conductor-insulator-conductor (MIM) elements, but MIM elements are preferred due to their structure and ease of manufacturing method. It's advantageous. In particular, when a hard carbon film is used as an insulating layer of an MIM element, it is particularly desirable because it enables the production of a high-quality liquid crystal display device with a larger area and fewer defects than the method and quality of the hard carbon film.

A method for manufacturing the MIM device of the present invention will be explained. First, a transparent electrode material for a pixel electrode is deposited on a transparent insulating substrate 1 such as glass, a plastic plate, or a plastic film by a method such as vapor deposition or sputtering, and patterned into a predetermined pattern to form a pixel electrode 4. Next, a conductor thin film for the lower electrode is formed by a method such as vapor deposition or sputtering, and is patterned into a predetermined pattern by wet or dry etching to form the 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 the bus line is coated by a method such as vapor deposition or sputtering, and patterned into a predetermined pattern to form the second conductor 6 that will become the bus line.Finally, unnecessary portions of the lower electrode 7 are removed and a transparent electrode is formed. The pattern is exposed and becomes the pixel electrode 4. In this case, the configuration of the MIM element is not limited to this, and after the MIM element is created, a transparent electrode is provided on the top layer, a transparent electrode also serves as an upper or lower electrode, and a side surface of the lower electrode. Various modifications are possible, such as one in which an MIM element is formed on the top. Here, the thickness of the lower electrode, the upper electrode, and the transparent electrode is usually in the range of several hundred to several thousand Å, several hundred to several thousand Å, and several hundred to several thousand Å, respectively. The thickness of the hard carbon film is 100 to 8000 Å, preferably 200 to 6000 Å, and more preferably 300 to 400 Å.
It is in the range of 0 Å. Furthermore, in the case of plastic substrates, it has been extremely difficult to fabricate active matrix devices using active elements due to their heat resistance. However, a hard carbon film can be produced at a substrate temperature of about room temperature, and can also be produced on a plastic substrate, making it a very effective means for improving image quality.

Next, the material of the MIM element used in the present invention will be explained in more detail. The material of the first conductor 1 serving as the lower electrode includes Al, Ta, Cr, W, Mo, and Pt.
, Ni, Ti, Cu, Au, ITO, ZnO: A1, I
Various conductors such as n2O3 and SnO2 are used. Next, the material of the second conductor 6 which becomes the bus line is Al, C.
r, Ni, Mo, Pt, Ag, Ti, Cu, Au, W,
Various conductors can be used, such as Ta, ITO, ZnO:Al, In2O3, SnO2, etc., but Ni, Pt, and Ag are preferred because of their particularly excellent stability and reliability of IV characteristics. In the MIM device using the hard carbon film 2 as an insulating film, the symmetry does not change even if the type of electrode is changed, and lnI∝
From the relationship √v, it can be seen that Poole-Frenkel type conduction is occurring. Furthermore, it can be seen from this that in the case of this type of MIM element, the upper electrode and the lower electrode may be combined in any manner. However, the device characteristics (IV characteristics) deteriorate and change depending on the adhesion between the hard carbon film and the electrode and the state of the interface. Considering these, it was found that Ni, Pt, and Ag are good.

The current-voltage characteristics of the MIM element of the present invention are shown in FIG. 6, and are approximately expressed by the conduction equation shown below.

[Equation 1] I: Current V: Applied voltage α: Conductivity coefficient β: Poole-Frenkel coefficient n: Carrier density μ: Carrier mobility q:
Electron charge Φ: Trap depth ρ: Specific resistance d: Film thickness of hard carbon (Å) k: Boltzmann constant T: Ambient temperature ε1: Dielectric constant of hard carbon ε2:
vacuum permittivity

The hard carbon film in the present invention will be explained in detail. An organic compound gas, especially a hydrocarbon gas, is used to form a 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 the hydrocarbon gas as the raw material gas, for example, paraffinic hydrocarbons such as CH4, C2H6, C3H8, C4H10, olefinic hydrocarbons such as C2H4,
Gases containing at least all hydrocarbons such as acetylenic hydrocarbons, diolefinic hydrocarbons, and even aromatic hydrocarbons can be used. Furthermore, other than hydrocarbons, compounds containing at least carbon element, such as alcohols, ketones, ethers, esters, CO, and CO2, can be used. In the method of forming a hard carbon film from a raw material gas in the present invention, the film-forming active species is
It is preferable to use a plasma state generated by a plasma method using direct current, low frequency, high frequency, microwave, etc., but 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 preferable. Active species can also be formed by thermal decomposition at high temperatures. In addition, it may be formed through an ion state generated by an ionization vapor deposition method, an ion beam vapor deposition method, etc., or a vacuum vapor deposition method,
Alternatively, it may be formed from neutral particles produced by a sputtering method or the like, or may be formed from a combination of these.

An example of the deposition conditions for the hard carbon film produced in this manner is as follows in the case of the plasma CVD method. RF output: 0.1 to 50 W/cm2 Pressure: 1/103 to 10 Torr Deposition temperature: Room temperature to 950°C Due to this plasma state, the raw material gas is decomposed into radicals and ions and reacts, thereby forming carbon atoms C on the substrate.
A hard carbon film containing at least one of amorphous (amorphous) and microcrystalline (crystal size is several tens of angstroms to several μm) is deposited. The properties of the hard carbon film are shown in Table 1.

[Table 1] Note) Measurement method; Specific resistance (ρ): Determined from IV characteristics using a coplanar cell. Optical bandgap (Egopt): Obtain the absorption coefficient (α) from the spectral characteristics and determine from the relationship shown in Equation 2.

[Equation 2] Hydrogen dormancy in the film [C(H)]: 29 from the infrared absorption spectrum
It is determined by integrating the peak around 00/cm and multiplying it by the absorption cross section A. That is, C(H)=A・∫α(v)/v・dv SP3/SP2 ratio: The infrared absorption spectrum is
It is decomposed into Gaussian functions respectively attributed to P2, and determined from the area ratio thereof. Vickers hardness (H): Based on a micro Vickers meter. Refractive index (n): By ellipsometer. Defect density: Based on ESR. The hard carbon film thus formed was measured using Raman spectroscopy and IR spectroscopy.
As a result of analysis by an absorption method, it has been revealed that interatomic bonds forming SP3 hybrid orbitals and SP2 hybrid orbitals coexist in the carbon atoms, as shown in FIGS. 3 and 4, respectively. The ratio of SP3 bonds to SP2 bonds can be approximately estimated by peak-separating the IR spectrum. IR
The spectrum is measured with many mode spectra overlapping between 2800 and 3150/cm, but the attribution of the peak corresponding to each wave number has been clarified, and peak separation can be performed using a Gaussian distribution as shown in Figure 5. If you do this, calculate the area of each peak, and find the ratio, SP3/SP
You can know 2. Further, according to X-ray and electron diffraction analysis, it has been found that it is in an amorphous state (a-C:H) and/or an amorphous state containing microcrystalline grains of about 50 Å to several μm. In the case of the plasma CVD method, which is generally suitable for mass production, the lower the RF output, the higher the specific resistance and hardness of the film, and the lower the pressure, the longer the life of active species, so lowering the substrate temperature and increasing the The area can be made uniform, and the specific resistance and hardness tend 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 characteristic that it can form a hard carbon film of good quality even under relatively low temperature conditions of about room temperature to 150° C., so it is optimal for lowering the temperature of the MIM element 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 and physical properties 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 also 3.
~5 and Ta2O5,A, which was conventionally used in MIM elements.
Since it is smaller than l2O3 and SiNx, when making an element with the same capacitance, the element size only needs to be larger, so microfabrication is not required and the yield is improved (Due to the driving conditions, LCD and MIM The capacitance ratio of the elements needs to be about C(LCD):C(MIM)=10:1). Furthermore, since the element steepness is β∝1/√ε·√d, the smaller the dielectric constant ε, the greater the steepness, and the ratio of the on-current Ion to the off-current Ioff can be increased. Therefore, it becomes possible to drive the LCD at a lower duty ratio, and a high-density LCD can be realized. Furthermore, since the film has high hardness, there is little damage caused by the rubbing process during encapsulation of the liquid crystal material, which also improves yield. In view of the above points, by using a hard carbon film, low cost, gradation (colorization), high density LCD, etc. can be realized.

Furthermore, this hard carbon film contains, in addition to carbon atoms and hydrogen atoms, Group III elements, Group IV elements, Group V elements of the periodic table, alkali metal elements, alkaline earth metal elements, and nitrogen atoms. , an oxygen atom, a chalcogen-based element, or a halogen atom as a constituent element. 1 of the constituent elements
Group III elements of the periodic table, as well as group V elements,
Those into which alkali metal elements, alkaline earth metal elements, nitrogen atoms, or oxygen atoms are introduced can make the hard carbon film about 2 to 3 times thicker than non-doped ones.
Moreover, this can prevent the occurrence of pinholes during device fabrication and dramatically improve the mechanical strength of the device. Further, in the case of a nitrogen atom or an oxygen atom, the same effect as in the case of a group IV element of the periodic table as described below can be obtained. Similarly, devices incorporating Group IV elements of the periodic table, chalcogen elements, or halogen elements dramatically improve the stability of the hard carbon film and improve the hardness of the film, resulting in highly reliable elements. can be made. These effects can be obtained because Group IV elements and chalcogen elements reduce the active double bonds present in the hard carbon film, and in the case of halogen elements, 1) abstraction for hydrogen The reaction promotes the decomposition of the source gas and reduces dangling bonds in the film, and 2) during the film formation process, the halogen element X pulls out hydrogen in the C-H bond and replaces it,
This is because it enters the film as a -X bond and the bond energy increases (the bond energy between C-H and between C-X is larger for C-X). In order to use these elements as constituent elements of the film, in addition to hydrocarbon gas and hydrogen, the film must contain elements from Group III, IV, V, and alkalis of the periodic table. In order to contain metal elements, alkaline earth metal elements, nitrogen atoms, oxygen atoms, chalcogen elements, or halogen elements, compounds (or molecules) containing these elements or atoms (hereinafter referred to as "other compounds") (sometimes) gases are used. Here, as a compound containing a group III element of the periodic table, for example, B
(OC2H5)3,B2H6,BCl3,BBr3,B
F3, Al(O-i-C3H7)3, (CH3)3Al
, (C2H5)3Al, (i-C4H9)3Al, Al
Cl3, Ga(O-i-C3H7)3, (CH3)3G
a, (C2H5)3Ga, GaCl3, GaBr3, (
Examples include O-i-C3H7)3In and (C2H5)3In. Examples of compounds containing Group IV elements of the periodic table include Si3H8, (C2H5)3SiH, SiF4, Si
H2Cl2, SiCl4, Si(OCH3)4, Si(
OC2H5)4, Si(OC3H7)4, GeCl4,
GeH4, Ge(OC2H5)4, Ge(C2H5)4
, (CH3)4Sn, (C2H5)4Sn, SnCl4
etc. Examples of compounds containing Group V elements of the periodic table include PH
3, PF3, PF5, PCl2F3, PCl3, PCl
2F, PBr3, PO(OCH3)3, P(C2H5)
3, POCl3, AsH3, AsCl3, AsBr3,
AsF3, AsF5, AsCl3, SbH3, SbF3
, SbCl3, Sb(OC2H5)3, etc. As a compound containing an alkali metal atom, for example, LiO-i-
C3H7, NaO-i-C3H7, KO-i-C3H7
etc. Examples of compounds containing alkaline earth metal atoms include Ca(OC2H5)3, Mg(OC2H5)2
, (C2H5)2Mg, etc. Examples of compounds containing nitrogen atoms include nitrogen gas, inorganic compounds such as ammonia,
Examples include 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 monoxide, carbon dioxide, suboxide, nitrogen monoxide, 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. Compounds containing chalcogen elements include, for example, H2S, (CH3) (CH
2) 4S(CH2)4CH3, CH2=CHCH2SC
H2CH=CH2, C2H5SC2H5, C2H5SC
H3, thiophene, H2Se, (C2H5)2Se, H
There are 2Te, etc. Examples of compounds containing halogen elements include fluorine, chlorine, bromine, iodine, hydrogen fluoride, chlorine fluoride, bromine fluoride, iodine fluoride, hydrogen chloride, bromine chloride, iodine chloride, hydrogen bromide, and iodine bromide. , inorganic compounds such as hydrogen iodide, and organic compounds such as halogenated alkyl, halogenated aryl, halogenated styrene, halogenated polymethylene, and haloform. A hard carbon film suitable as an MIM element for driving a liquid crystal has a film thickness of 100 to 8000 Å and a specific resistance of 10 to 8000 Å depending on the driving conditions.
Advantageously, it is in the range of 1013 Ω·cm. In addition, considering the margin between drive voltage and withstand voltage (dielectric breakdown voltage), it is desirable that the film thickness is 200 Å or more, and the difference in level (cell gap) between the pixel part and the thin film two-terminal element part
In order to prevent color unevenness caused by carbon from becoming a practical problem, it is desirable that the film thickness be 6000 Å or less, so the hard carbon film should have a thickness of 200 to 6000 Å and a specific resistance of 5.
It is more preferable that it is ×10 6 to 10 12 Ω·cm. The number of device defects due to pinholes in hard carbon films increases as the film thickness decreases, and becomes especially noticeable below 300 Å (defect rate exceeds 1%), and the uniformity of the in-plane distribution of film thickness (The accuracy of film thickness control is limited to about 30 Å, and the variation in film thickness exceeds 10%).
More preferably, it is Å or more. Further, in order to prevent the hard carbon film from peeling off due to stress and to drive at a lower duty ratio (preferably 1/1000 or less), the film thickness is more preferably 4000 Å or less. Taking these into account, the thickness of the hard carbon film is 300 to 4000 Å, and the specific resistance is 107 to 1011.
More preferably, it is Ω·cm.

[0014]

[Example] Examples are shown below, but the invention is not limited thereto. Example 1 A Pyrex substrate was used as the transparent substrate, and ITO was coated with 800
It was deposited using the Å magnetron sputtering method. Next, it was patterned to form a pixel electrode. Next, an MIM element using a hard carbon film as an active element was provided as follows. First, Al was deposited to a thickness of 800 Å on the pixel electrode of the substrate by vapor deposition, and then patterned to form a lower electrode. On top of that, a hard carbon film is applied as an insulating film by plasma CVD method.
After depositing to a thickness of 0.00 Å, it was patterned by dry etching. Furthermore, Ni is deposited on each hard carbon insulating film by vapor deposition.
After depositing to a thickness of 0.000 Å, it was patterned to form an upper electrode. A color filter and an interlayer insulating layer were provided on Pyrex as a counter substrate, and then ITO was deposited to a thickness of 1000 Å by sputtering and patterned into stripes to form a common pixel electrode. Next, a soluble polyimide solution was applied to each substrate using a printing method, and then baked to form an alignment film. At this time, the film thickness of the alignment film is 1000 Å on the active element side and 900 Å on the color filter side.
It was set as Å. Next, these substrates were placed facing each other with each pixel electrode side facing inside, and were bonded together with a gap material interposed therebetween, and a liquid crystal material was further sealed in the thus formed cells to produce a color liquid crystal display device. The hard carbon film formation conditions used for the MIM element at this time were as follows: Pressure: 0.03 Torr CH4 Flow rate: 10 SCCM RF power: 0.2 W/cm2 Temperature: Room temperature.

[0015]

[Effects] According to the present invention, the generation of DC bias is suppressed to a low level, so that flicker does not occur and the quality of liquid crystal does not deteriorate.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing an example of a liquid crystal display device of the present invention using an MIM type element.

FIG. 2 is a perspective view of an MIM type element used in the present invention.

FIG. 3 is a spectrum diagram showing the results of an IR absorption analysis of the hard carbon film used for the insulating layer of the MIM type element used in the present invention.

FIG. 4 is a spectrum diagram showing the results of Raman spectroscopy analysis of the hard carbon film used as the insulating layer of the MIM type element used in the present invention.

FIG. 5 is a Gaussian distribution diagram of the IR spectrum of the hard carbon film.

FIG. 6 (a) and (b) are MIMs used in the present invention.
The typical IV characteristic and lnI-√V characteristic diagram of the device are shown.

[Explanation of symbols]

1 Insulating substrate 1' Insulating substrate 2 Hard carbon film 3 Liquid crystal 4 Pixel electrode 4' Common electrode 5 Active element 6 Second conductor (bus line) (upper electrode) 7 First
Conductor (lower electrode) 8 Alignment film 9 Gap material

Claims (2)

[Claims] Claim 1: In a liquid crystal display device having a liquid crystal layer between a pair of substrates, the difference in film thickness between the alignment film on one substrate side and the alignment film on the other substrate side is larger than the film thickness of one alignment film. 20
% or less. Claim 2: The thickness of one alignment film is 300 to 800.
2. The liquid crystal display device according to claim 1, wherein the thickness is 0 Å.