JPH04356025A - Thin film two-terminal element - Google Patents

Abstract

PURPOSE:To provide an MIM element suitable for a halftone display device having 4 or more levels of gradation. CONSTITUTION:This MIM element consists of a metal-hard carbon film-metal material and has the relation between kappa and beta in formula I=kappaexp(betaV<1/2>) within the range defined by the following four lines of lnkappa=-2.8beta-22.5...(A), lnkappa=-2.0beta-22.0...(B), lnkappa=0.5beta-27.0...(a), and lnkappa=0.5beta-41.5...(b).

Description

[Detailed description of the invention]

0001

TECHNICAL FIELD This invention relates to improved thin film two-terminal devices, or MIM devices.

0002

[Prior Art] Conventionally, a conductor-insulating film-conductor (MIM) element has a metal electrode such as Ta, Al, Ti, etc. provided as a lower electrode on an insulating substrate such as a glass plate, and an oxide of the metal Alternatively, an insulating film made of SiOx, SiNx, etc. is provided, and a metal electrode such as Al, Cr, etc. is provided thereon as an upper electrode. However, MIM elements using metal oxide as an insulating film (Japanese Patent Laid-Open No. 57-19658
No. 9, No. 61-232689, No. 62-62333, 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 (anode Even with the oxidation method, high-temperature heat treatment is required to ensure the removal of impurities, etc.), film controllability (uniformity and reproducibility of film quality and film thickness) is poor, the substrate is limited to heat-resistant materials, and insulation Since the film is made of metal oxide crystals with fixed physical properties, the device material and device characteristics cannot be freely changed, and the degree of freedom in design is limited. This means that it is impossible to design and manufacture a device incorporating an MIM element, such as a liquid crystal display device, that fully satisfies the specifications. In addition, if film controllability is poor in this way, the current (I) and voltage (V) characteristics as element characteristics, especially the symmetry of the IV characteristics and IV characteristics [current at positive bias and negative bias A problem also arises in that the variation in the ratio I(-)/I(+) becomes large. In addition, when using an MIM element for a liquid crystal display (LCD), the liquid crystal capacitance/MIM capacitance ratio needs to be 10 or more, so it is desirable that the MIM capacitance is smaller, but in the case of metal oxide films, the dielectric constant Since it is large, the element capacitance also becomes large, 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 reduction in yield in combination with microfabrication. On the other hand, MIM using SiOx or SiNx as an insulating film
In the case of the device (Japanese Unexamined Patent Publication No. 61-260219), the insulating film is formed by a gas phase method such as plasma CVD or sputtering, but since the substrate temperature usually needs to be around 300°C, low-cost substrates are not suitable. Moreover, when increasing the area, the film thickness and quality tend to become non-uniform due to the substrate temperature distribution. Further, when these insulating films are synthesized, a lot of dust is generated in the gas phase, and the film has many pinholes, which reduces the yield of devices. Alternatively, the stress on the film is so great that film peeling occurs, which also reduces the yield of the device. Further, the present inventors have previously proposed an MIM element using a hard carbon film (i-type carbon) as an insulating film, but the thickness of the insulating film is as thin as 20 to 100 Å. In the case of this insulating film,
The conduction mechanism is tunnel conduction, and it is rather suitable for applications as ultra-thin film devices such as high-speed switches and tunnel light emission. However, when applied to liquid crystal display devices and the like, it is desirable that the film be thicker in terms of breakdown voltage, yield (defect rate), uniformity of device characteristics, and threshold voltage.

0003

[Object] An object of the present invention is to provide an MIM element suitable for displaying intermediate gradations of four or more gradations. Another object of the present invention is to use a low dielectric constant insulating film (hard carbon film) that can be formed at a relatively low temperature and in a simple process and has excellent film controllability and mechanical strength, so that it can be used in a wide range of device designs. It is an object of the present invention to provide an MIM element which is capable of the above, has little variation in element characteristics, is excellent in threshold voltage and withstand voltage, and has a high yield.

0004

[Structure] In the thin film two-terminal device of the present invention, the insulating film interposed between the upper conductor and the lower conductor is a hard carbon film, and the current (I)-voltage (V) characteristics are as follows.

It is a thin film two-terminal device approximated by [Equation 2], and the relationship between κ and β is expressed by the formula ln κ=-2.8β-22.5...(A)l
nκ=-2.0β-22.0...(B)ln
κ=0.5β-27.0...(a)ln
κ=0.5β-41.5...It is characterized by being within the range surrounded by the line shown in (b).

The current-voltage characteristics of the MIM element of the present invention are shown in FIG. 4, and are approximately expressed by the conduction equation shown below.

[Equation 3] I: Current V: Applied voltage κ: Conductivity coefficient β: Poole-Frenkel coefficient n: Carrier density μ: Carrier mobility q:
Electron charge Φ: Trap depth ρ: Specific resistance d: Hard carbon film thickness (Å) k: Boltzmann constant T: Ambient temperature ε
1: Dielectric constant of hard carbon ε2: Vacuum dielectric constant

The thin film two-terminal element of the present invention and the liquid crystal are connected as shown in FIG. 1 in terms of an equivalent circuit. The voltage pulses applied across are shown in FIG. Vs is the scanning signal, Vd
is a data signal whose pulse width is modulated as shown in (a) to (d) corresponding to the intermediate tone (here, four gradations). When signals (A) to (D) are input to a certain pixel, the difference in transmittance due to the input signal is 10% or more, and when a halftone signal is input to all pixels in the panel, It is determined that 4-gradation display is possible when the difference in transmittance is ±10% or less (transmittance from 10% (off) to 90% (on)).
) To provide four gradations between the two, the permissible transmittance width for one halftone is 20%. ).

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 a first conductor (
After covering the hard carbon film 2 by plasma CVD, ion beam method, etc., it is 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 bus lines is coated thereon by a method such as vapor deposition or sputtering, and the second conductor (upper electrode) is patterned into a predetermined pattern to become a bus line.
6, and finally remove unnecessary portions of the lower electrode 7,
The transparent electrode pattern is exposed to serve as 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
~8000 Å, preferably 200 to 6000 Å, more preferably 300 to 4000 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 7 serving as the lower electrode includes Al, Ta, Cr, W, Mo, and Pt.
, Ni, Ti, Cu, Au, ITO, ZnO: Al, 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. Also, from this fact, in the case of this type of MIM element,
It can be seen that the upper electrode and lower electrode may be combined in any way. 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.

Next, a method for manufacturing a liquid crystal display device will be described with reference to FIG. First, a transparent conductor for the common electrode 4', such as ITO, ZnO:Al, SnO2, In2O, is placed on the insulating substrate 1'.
3 or the like is deposited to a thickness of several hundred Å to several μm by sputtering, vapor deposition, etc., and patterned into a stripe shape to form a common electrode 4'. The substrate 1' provided with this common electrode 4' and the MIM
An alignment material 8 such as polyimide is applied to the surface of each substrate 1 on which elements are arranged in a matrix, a rubbing treatment is performed, a sealing material is applied, a gap material 9 is inserted to make the gap constant, and a liquid crystal 3 is sealed. This is used as a liquid crystal display device. In this way, a liquid crystal display device is obtained. Note that a color filter may be provided inside or outside the cell to form a color liquid crystal display device.

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, acetylenic hydrocarbons such as C2H4,
Gases containing at least all hydrocarbons such as olefinic hydrocarbons, diolefinic hydrocarbons, and even aromatic hydrocarbons can be used. Furthermore, other than hydrocarbons, compounds containing at least the carbon element can be used, such as alcohols, ketones, ethers, esters, CO, and CO2.

[0011] 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 the 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 preferable. Active species can also be formed by thermal decomposition at high temperatures. In addition, it may be formed through an ionic state generated by ionization vapor deposition, ion beam vapor deposition, etc., or may be formed from neutral particles generated by vacuum vapor deposition, sputtering, etc. However, 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 as follows in the case of the plasma CVD method. RF output: 0.1~50W/cm2 Pressure: 1/103~10
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. Further, Table 1 shows various properties of the hard carbon film.

[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 of the following equation 4.

[Equation 4] Amount of hydrogen 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・dvSP3/SP
2 ratio: The infrared absorption spectrum is decomposed into Gaussian functions assigned to SP3 and SP2, respectively, and determined from the area ratio. Vickers hardness (H): Based on a micro Vickers meter. Refractive index (n): By ellipsometer. Defect density: Based on ESR.

As a result of analysis by Raman spectroscopy and IR absorption method, the hard carbon film thus formed shows that the carbon atoms have SP3 hybrid orbitals and SP2 hybrid orbitals, as shown in FIGS. 7 and 6, respectively.
It has become clear that there are interatomic bonds that form a hybrid orbital. The ratio of SP3 bonds to SP2 bonds can be approximately estimated by peak-separating the IR spectrum. 2800-3150/cm for IR spectrum
Although the spectra of many modes overlap and are measured,
The attribution of peaks corresponding to each wave number is clear, and if we perform peak separation using a Gaussian distribution as shown in Figure 5, calculate the area of each peak, and find the ratio, we can obtain SP.
3/SP2 can be known. Moreover, 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 2 to 6, which is Ta2O, which is used in conventional MIM devices.
5.Since it is smaller than Al2O3 and SiNx, 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 (because of the driving conditions, LCD The capacitance ratio of C(LCD)/C(MIM) = approximately 10:1 is required between C(LCD) and MIM element. Also, since the element steepness is β∝1/√ε・√d, the smaller the dielectric constant ε, the greater the steepness.
The ratio between the on-current Ion and the off-current Ioff can be increased. Therefore, LCD with lower duty ratio
This makes it possible to drive a high-density LCD. Furthermore, since the film has high hardness, there is less damage caused by the rubbing process during encapsulation of the liquid crystal material, which also improves the yield. Considering the above points, by using a hard carbon film, a low-cost, gradation (color), and high-density LCD can be realized.

In order to control the resistance value, improve the stability and heat resistance of the film, and further improve the hardness, the hard carbon film as described above may contain impurities containing compounds from periodic table II.
Group I elements, Group IV elements, Group V elements, alkali metal elements, alkaline earth metal elements, nitrogen atoms, oxygen atoms,
A chalcogen element or a halogen atom can be doped therein. Doping with this third component further increases the stability of the element and the degree of freedom in device design. In particular, in coplanar MIM elements, appropriate ranges for the film thickness of the hard carbon film, W/L ratio (W: width of the element gap, L: length of the gap), and specific resistance are determined from the element characteristics suitable for liquid crystal driving. However, from the viewpoint of film peeling, it is advantageous for the film thickness to be 1 μm or less, and for the W/L ratio to be 1/100 or more from the side length of the pixel and the precision of photolithography. At this time, the appropriate range of specific resistance is 10 4 to 10 8 Ω·cm based on the driving conditions. The specific resistance of non-doped hard carbon film is 106 to 1013
Ω·cm, and by doping an appropriate amount of Group III, Group V, alkali metal, alkaline earth metal, N, or O element, it is possible to obtain a specific resistance within the above range. 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%, based on the total constituent elements.
It is atom%. Group III elements of the periodic table include:
Examples include B, Al, Ga, and In, and in the present invention, the amount of Group III elements of the periodic table contained as one of the constituent atoms in the hard carbon film is 5 atoms with respect to all constituent elements. % or less, preferably 0.001 to 3 atoms
% is preferable. Examples of Group IV elements of the periodic table include Si, Ge, and Sn, and the amount of Group IV elements is within 20 atom %, preferably 0.01 to 17 atom % based on the total constituent atoms. periodic table V
Examples of group elements include P, As, and Sb, and the amount of group V elements is within 5 atom %, preferably 0.001 to 3 atom % based on all constituent atoms. Examples of the alkali metal elements include Li, Na, and K, and the amount of the alkali metal elements is 5at based on all constituent atoms.
om% or less, preferably 0.001 to 3 atom%. Examples of alkaline earth metal elements include Ca and Mg, and the amount of alkaline earth metal atoms is within 5 atom%, preferably 0.001 to 3 at.
om%. The amount of nitrogen atoms is 5 for all constituent atoms.
Within atom%, preferably 0.001 to 3 atom%
It is. The amount of oxygen atoms is 5ato to all constituent atoms.
m% or less, preferably 0.001 to 3 atom%. Chalcogen elements include S, Se, and Te, and the amount of chalcogen elements is as follows with respect to all constituent atoms:
Within 20 atom%, preferably 0.01 to 17 atom
m%. Examples of the halogen element include F, Cl, Br, and I, and the amount of the halogen element is within 35 atom%, preferably 0.1 to 3
5 atom% is preferable. Incidentally, the amount of the above-mentioned elements or atoms can be measured by a conventional method of elemental analysis, for example, 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. The thickness of a hard carbon film doped with impurities can be made approximately 2 to 3 times thicker than that of a non-doped film, and this prevents the occurrence of pinholes during device fabrication and improves the mechanical properties of the device. Strength can be dramatically improved. 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 raw material 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, forming a C-X bond. This is because it enters the film and increases the bond energy (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 as raw material gases, elements from group III of the periodic table and elements from group I of the periodic table are added to the film as dopants.
In order to contain group V elements, group V elements, alkali metal elements, alkaline earth metal elements, nitrogen atoms, oxygen atoms, chalcogen elements, or halogen elements, compounds (or molecules) containing these elements or atoms. (Hereinafter, these may be referred to as "other compounds") gases are used. Examples of compounds containing Group III elements of the periodic table include B(OC2H5)3, B2H6, BCl3, BBr
3, BF3, Al(O-i-C3H7)3, (CH3)
3Al, (C2H5)3Al, (i-C4H9)3Al
, AlCl3, Ga(O-i-C3H7)3, (CH3
)3Ga, (C2H5)3Ga, GaCl3, GaBr
3, (O-i-C3H7)3In, (C2H5)3In
etc. Examples of compounds containing Group IV elements of the periodic table include Si3H8, (C2H5)3SiH, SiF4
, SiH2Cl2, SiCl4, Si(OCH3)4,
Si(OC2H5)4, Si(OC3H7)4, GeC
l4,GeH4,Ge(OC2H5)4,Ge(C2H
5) 4, (CH3)4Sn, (C2H5)4Sn, Sn
There are Cl4 etc. Examples of compounds containing Group V elements of the periodic table include PH3, PF3, PF5, PCl2F3,
PCl3, PCl2F, PBr3, PO(OCH3)3
, P(C2H5)3, POCl3, AsH3, AsCl
3, AsBr3, AsF3, AsF5, AsCl3,S
bH3, SbF3, SbCl3, Sb(OC2H5)3
etc. Examples of compounds containing alkali metal atoms include LiO-i-C3H7, NaO-i-C3H7, K
There are O-i-C3H7 and the like. Examples of compounds containing alkaline earth metal atoms include C
a(OC2H5)3, Mg(OC2H5)2, (C2H
5) There are 2Mg, etc. Compounds containing nitrogen atoms include:
Examples 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 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. Examples of compounds containing chalcogen elements include H2S, (CH3)(CH2)4S
(CH2)4CH3,CH2=CHCH2SCH2CH
=CH2, C2H5SC2H5, C2H5SCH3, thiophene, H2Se, (C2H5)2Se, H2Te, etc. Examples of compounds containing halogen elements include fluorine, chlorine, bromine, iodine, hydrogen fluoride, carbon fluoride, chlorine fluoride, bromine fluoride, iodine fluoride, hydrogen chloride, bromine chloride, iodine chloride, and hydrogen bromide. , inorganic compounds such as iodine bromide and hydrogen iodide,
Organic compounds such as halogenated alkyl, halogenated aryl, halogenated styrene, halogenated polymethylene, and haloform are used. A hard carbon film suitable as a liquid crystal driving MIM element has a film thickness of 100 to 8000 mm depending on the driving conditions.
Å, the specific resistance is advantageously in the range from 10 6 to 10 13 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%). Therefore, it is more desirable that the film thickness is 300 Å or more. . In addition, in order to make it difficult for the hard carbon film to peel off due to stress, and to lower the duty ratio (preferably 1/10
00 or less), the film thickness is more desirably 4000 Å or less. Taking all of these into consideration, it is more preferable that the hard carbon film has a thickness of 300 to 4000 Å and a specific resistivity of 10 7 to 10 11 Ω·cm.

[0015]

[Examples] Examples will be shown next, but the present invention is not limited thereto. Example 1 A pixel electrode and a thin film two-terminal element were fabricated on a (Pyrex) transparent insulating substrate as shown in FIG. 2 in the following manner. First, ITO was deposited to a thickness of 500 Å by sputtering, and then patterned to form the pixel electrode 4. Next, Al was deposited to a thickness of 600 Å by vapor deposition, and then patterned to form the lower conductor 7. A hard carbon film was deposited thereon by plasma CVD, and then patterned by dry etching to form an insulating film 2. moreover,
Ni was deposited on this to a thickness of 1000 Å by EB evaporation, and then patterned to form an upper conductor (also serving as a scanning electrode) 6 to obtain a thin film two-terminal element. The film-forming conditions and film thickness of the hard carbon film at this time are as follows. Pressure: 0.035TorrCH4 Flow rate:
20 SCCM H2 Flow rate: 0 SCCM RF power: 0.30 W/cm2 Film thickness: 1100 Å The average values of the device characteristics were β = 4.5, ln κ = -33.5, and 4-gradation display was possible. .

Example 2 A pixel electrode and a thin film two-terminal element were fabricated on a (plastic) transparent insulating substrate 1 as shown in FIG. 9 in the following manner. First, Al was deposited to a thickness of 1000 Å by vapor deposition, and then patterned to form a lower conductor (also serving as a scanning electrode) 7. A hard carbon film was deposited thereon by plasma CVD, and then patterned by dry etching to form an insulating film 2. Further, an ITO film having a thickness of 1000 Å was coated thereon by EB evaporation, and patterned by etching to form an upper conductor (also serving as a pixel electrode) 6 to obtain a thin film two-terminal element. The film-forming conditions and film thickness of the hard carbon film at this time are as follows. Pressure: 0.035 TorrCH4 Flow rate: 20 SCCM H2 Flow rate: 0 SCCM RF power: 0.90 W/cm2 Film thickness: 1100 Å The average value of the device characteristics is β = 4.5, ln κ = -31.5. , 4-gradation display was possible.

Example 3 A thin film two-terminal device similar to Example 1 was produced. However, the film forming conditions and film thickness of the hard carbon film are as follows. Pressure: 0.035 TorrCH4 Flow rate: 20 SCCM H2 Flow rate: 0 SCCM RF power: 0.25 W/cm2 Film thickness: 1100 Å The average value of the device characteristics is β = 4.5, ln κ = -35.0. , 4-gradation display was possible. Comparative Examples 1 to 4 Thin film two-terminal devices similar to those in Example 1 were produced. However, the average value (β,
lnκ) were as shown in Table 2. 4-gradation display was not possible. Example 4 A thin film two-terminal device similar to Example 2 was produced. However, the film forming conditions and film thickness of the hard carbon film are as follows. Pressure: 0.035 TorrCH4 Flow rate: 20 SCCM H2 Flow rate: 0 SCCM RF power: 0.23 W/cm2 Film thickness: 650 Å The average value of the device characteristics is β = 6.0, ln κ = -34.5. ,
Four-gradation display was possible. Example 5 A thin film two-terminal device similar to Example 1 was produced. However, the film forming conditions and film thickness of the hard carbon film are as follows. Pressure: 0.035 TorrCH4 Flow rate: 5 SCCM H2 Flow rate: 15 SCCM RF power: 0.13 W/cm2 Film thickness: 650 Å The average values of the device characteristics are β = 6.0, ln κ = -38.0. ,
Four-gradation display was possible.

Comparative Examples 5 and 6 Thin film two-terminal devices similar to those in Example 1 were produced. However, the average value (β,
lnκ) were as shown in Table 3. 4-gradation display was not possible. Example 6 A thin film two-terminal device similar to Example 1 was produced. However, the film forming conditions and film thickness of the hard carbon film are as follows. Pressure: 0.035 TorrCH4 Flow rate: 5 SCCM H2 Flow rate: 15 SCCM RF power: 0.13 W/cm2 Film thickness: 500 Å The average value of the device characteristics is β = 7.0, ln κ = -37.5. ,
Four-gradation display was possible. Comparative Example 7 A thin film two-terminal device similar to Example 1 was produced. However, the film forming conditions and film thickness of the hard carbon film are as follows. Pressure: 0.035 TorrCH4 Flow rate: 5 SCCM H2 Flow rate: 15 SCCM RF power: 0.10 W/cm2 Film thickness: 500 Å The average value of the device characteristics is β = 7.0, ln κ = -38.5. ,
4-gradation display was not possible. Example 7 A thin film two-terminal device similar to Example 1 was produced. However, the film forming conditions and film thickness of the hard carbon film are as follows. Pressure: 0.035 TorrCH4 Flow rate: 20 SCCM H2 Flow rate: 0 SCCM RF power: 2.4 W/cm2 Film thickness: 5900 Å The average value of the device characteristics is β = 2.0, ln κ = -26.5. , 4-gradation display was possible. Example 8 A thin film two-terminal device similar to Example 1 was produced. However, the film forming conditions and film thickness of the hard carbon film are as follows. Pressure: 0.035 TorrCH4 Flow rate: 20 SCCM H2 Flow rate: 0 SCCM RF power: 1.8 W/cm2 Film thickness: 5900 Å The average value of the device characteristics is β = 2.0, ln κ = -28.0. , 4-gradation display was possible. Comparative Examples 8 to 9 Thin film two-terminal devices similar to those in Example 1 were produced. However, the average value (β,
lnκ) were as shown in Table 3. 4-gradation display was not possible. Example 9 A thin film two-terminal device similar to Example 1 was produced. However, the film forming conditions and film thickness of the hard carbon film are as follows. Pressure: 0.035 TorrCH4 Flow rate: 20 SCCM H2 Flow rate: 0 SCCM RF power: 2.4 W/cm2 Film thickness: 8000 Å The average value of the device characteristics is β = 1.7, ln κ = -26.5. , 4-gradation display was possible. Comparative Example 10 A thin film two-terminal device similar to Example 1 was produced. However, the film forming conditions and film thickness of the hard carbon film are as follows. Pressure: 0.035 TorrCH4 Flow rate: 20 SCCM H2 Flow rate: 0 SCCM RF power: 3.0 W/cm2 Film thickness: 8000 Å The average value of the device characteristics is β = 1.7, ln κ = -26.0. , 4-gradation display was not possible.

Tables 2 and 3 summarize the film forming conditions, characteristics, and whether four-gradation display is possible for the above examples. Also, element characteristics (
FIG. 10 shows the relationship between β, lnκ) and whether four-gradation display is possible. From this figure, the possible range of four-gradation display is four straight lines lnκ=-2.8β-22.5...(A) lnκ=-2.
0β-22.0...(B)lnκ=0.5β-27.
It can be seen that the area is surrounded by 0...(a) lnκ=0.5β-41.0...(b).

[Table 2]

[Table 3]

[0020]

[Effects] The hard carbon film used in the MIM device of the present invention is 1) manufactured by a vapor phase synthesis method such as plasma CVD, so its physical properties can be controlled over a wide range by changing the film formation conditions, and therefore there is greater freedom in device design. 2) It is hard and can be made into a thick film, so it is less susceptible to mechanical damage, and the thicker the film can be expected to reduce the number of pinholes, 3) It is possible to form a high-quality film even at low temperatures near room temperature. 4) Excellent uniformity in film thickness and film quality, making it suitable for thin film devices; 5) Low dielectric constant, so advanced microfabrication technology is not required; It has advantages such as being advantageous in increasing the area of the display, and is therefore particularly suitable as a highly reliable switching element for liquid crystal display. Furthermore, the thin film two-terminal device of the present invention is particularly indispensable as a device for displaying intermediate tones of four or more gradations.

[Brief explanation of drawings]

FIG. 1 shows an equivalent circuit of a thin film two-terminal element of the present invention and a liquid crystal.

FIG. 2 shows a thin film two-terminal device according to Example 1 of the present invention.

FIG. 3: 1 of a liquid crystal display device using the MIM element of the present invention
Give an example.

FIGS. 4(a) and 4(b) show typical IV characteristics and lnI-√V characteristics of the MIM device of the present invention.

FIG. 5 shows the Gaussian distribution of the IR spectrum of the hard carbon film-based insulating film used in the MIM device of the present invention.

FIG. 6 shows an IR spectrum of the insulating film.

FIG. 7 shows a Raman spectrum of the insulating film.

FIG. 8 shows (A) to (D) how the voltage pulse width applied to both ends of the MIM element of the present invention changes in four gradations.

FIG. 9 shows a cross-sectional view of an MIM element according to Example 2 of the present invention.

FIG. 10 shows the relationship between element characteristics and four-gradation display.

[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 (MIM element) 6 Second conductor (bus line) (upper conductor) 7 First
Conductor (lower conductor) 8 Orientation film 9 Gap material

Claims (1)

[Claims] Claim 1: The insulating film interposed between the upper conductor and the lower conductor is a hard carbon film, and the current (I) - voltage (
V) A thin film two-terminal device whose characteristics are approximated by [Equation 1], and the relationship between κ and β is expressed by the formula ln κ=-2.8β-22.5...(A)l
nκ=-2.0β-22.0...(B)ln
κ=0.5β-27.0...(a)ln
A thin film two-terminal device characterized in that κ=0.5β−41.5 falls within the range surrounded by the line shown in (b).