JP2876138B2 - Thin-film two-terminal element - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin-film two-terminal element, and more specifically, a switching element, particularly a liquid crystal display, which can be suitably used for flat panel displays for OA equipment and TVs. The present invention relates to a thin-film two-terminal element useful as a switching element of a device.

[Conventional technology]

There is a strong demand for the use of large-area liquid crystal panels for OA equipment terminals and liquid crystal TVs. For this reason, in the active matrix system, a switch is provided for each pixel to maintain the voltage.

By the way, MIM (Metal Ins
(ulator metal) elements are often used. This is because the thin-film two-terminal element exhibits a good nonlinear current-voltage characteristic for switching. And the conventional thin film two-terminal element is used as a lower electrode on an insulating substrate such as a glass plate.
A metal electrode of Ta, Al, Ti, etc. was provided, an oxide film of the metal or an insulating film made of SiOx, SiNx, etc. was provided thereon, and a metal electrode of Al, Cr, etc. was provided thereon as an upper electrode. Things are known. The insulating film is generally formed by anodic oxidation or thermal oxidation of the lower electrode (Japanese Patent Application Laid-Open Nos. 62-62333 and 57-63).
-196589), or SiOx and SiNx synthesized by gas phase
Is formed.

[Problems to be solved by the invention]

However, in a thin-film two-terminal device using an anodic oxide film as an insulating film, (1) Since the insulating film is limited to the anodic oxide film of the lower electrode metal, control of the physical properties thereof and, consequently, the characteristics of the thin-film two-terminal device Control cannot be performed arbitrarily. (2) Since a heat treatment at about 300 to 600 ° C. is required, the material of the substrate to be used is limited to those having high heat resistance. (3) Since the dielectric constant is high, when used as a switching element of a liquid crystal display device, it is necessary to reduce the element area (due to the constraint of element capacitance / liquid crystal display device capacity <1/10), which requires advanced fine processing. Required.

Further, as described later, the relative permittivity ε _r and the steepness β of the element
In When the value of _εr is high, the steepness is reduced, and there are disadvantages such as high density and unsuitability for display.

Furthermore, as the insulating layer, SiO _x and SiN _x synthesized in the gas phase
In the thin film two-terminal element using the method, although the disadvantage (1) is almost eliminated, the film formation temperature is as high as about 300 ° C., and there is the same problem as the above (2). Further, (4) there is a problem that pinholes are easily generated due to dust or the like, and the yield is reduced.

According to the study of the present inventors, it has been found that the above problems (1) to (4) can be solved by using a hard carbon film as an insulating film. (5) The hard carbon film other than the element portion must be removed because the light absorption is large and the color is brown, and the number of process steps increases. Unless the hard carbon film other than the element portion is removed, the amount of light transmitted through the liquid crystal cell is reduced, and the image quality is significantly deteriorated.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances of the related art, and has as its object to provide a thin-film two-terminal element in which all of the above problems (1) to (5) have been solved.

[Means for solving the problem]

To achieve the above object, according to the present invention, in a thin-film two-terminal element having an insulating film interposed between a first conductor and a second conductor, the insulating film has an optical bandwidth of 2.4 eV.
There is provided a thin-film two-terminal element comprising the above hard carbon film.

[Action]

The insulating film of the thin film two-terminal element of the present invention has an optical bandwidth.
Since it is composed of a hard carbon film of 2.4 eV or more, it becomes colorless and transparent to visible light, and not only the above problems (1) to (4) but also without removing the hard carbon film other than the element portion. As a result, the problem (5) is also solved.

〔Example〕

 Hereinafter, the present invention will be described in more detail.

According to the present invention, a hard carbon film having an optical bandwidth of 2.4 eV or more (i-C film, diamond-like carbon film, amorphous diamond film, diamond film) is formed on an insulating film interposed between the first conductor and the second conductor. (Also referred to as a thin film).

The present inventors have conducted intensive research on the method of forming a hard carbon film, and as a result, by intermittently generating plasma, specifically, by setting the plasma frequency to 100 KHz or less, or by using a square wave pulsed plasma, It has been found that the electron temperature can be increased without causing a decrease in plasma density, and as a result, even at a relatively low temperature, a hard carbon film having a closer optical structure to a diamond structure can be formed.

1 and 2 show an apparatus for forming a hard carbon film used in the thin-film two-terminal element of the present invention. In these figures, 101 is an upper electrode, 102 is a lower electrode, 103 is a substrate, 104 is a plasma power supply, 105 is a DC power supply (for bias application), 106
Is a magnetic field coil, 107 is a susceptor, 108 is a waveguide, 109 is a matching unit, 110 is a power monitor, 111 is a microwave oscillator,
112 is a plunger. Tables 1 and 2 show typical film forming conditions.

Table 1 Plasma output; 0.1~50W / cm ² Frequency; 100 KHz or less pressure; 10 ^-3 to 10 Torr deposition temperature: room temperature to 900 ° C. Table 2 plasma power; 20~400W t _OFF (interval time); 2 × 10 ^{- 5} sec or more t _ON / to _OFF ; 10 or more Pressure; 10 ^{-3 to} 100 Torr Deposition temperature; Room temperature to 950 ° C. The thing shown in FIG. 1 is a parallel plate type plasma CVD apparatus, but the frequency of the plasma power supply 104 is 100 KHz. As shown in FIG. 3, it can be seen that the electron temperature is about two to three times higher than that of normal 13.5 MHz high frequency plasma.

As the reaction gas, an organic compound gas, particularly, a hydrocarbon gas is used. The phase state of these raw materials does not necessarily need to be a gaseous phase at normal temperature and normal pressure, but may be used in a liquid phase or a solid phase as long as it can be vaporized through melting, evaporation, sublimation, etc. by heating or decompression. is there.

For hydrocarbon gas as a source gas, for example, CH
₄ , C ₂ H ₆ , C ₃ H ₈ , C ₄ H _10, etc., paraffinic hydrocarbons, C ₂ H ₄
Gases containing at least all hydrocarbons such as acetylene-based hydrocarbons, olefin-based hydrocarbons, acetylene-based hydrocarbons, diolefin-based hydrocarbons, and aromatic hydrocarbons can be used. In addition, other than hydrocarbons,
For example, compounds containing at least a carbon element, such as alcohols, ketones, ethers, esters, CO, and CO ₂ can be used. These source gases are decomposed into film-forming active species (radicals and ions) in plasma, and a hard carbon film is deposited on the substrate 103. Further, a method utilizing a magnetic field effect is more preferable because deposition is performed under a low pressure for the purpose of increasing the area, improving uniformity, and forming a film at a low temperature.

Next, a method for manufacturing a falling film two-terminal element according to the present invention will be described.

FIG. 4 is a diagram showing a configuration example of a thin-film two-terminal device of the present invention, and FIG. 5 is a diagram showing a configuration of a conventional device. 4th
In FIG. 5 and FIG. 5, reference numerals 1 and 11 denote insulating substrates, 2 and 12 denote first conductors (bus lines), 3 and 13 denote second conductors (pixel electrodes),
Reference numerals 4 and 14 are insulating films (hard carbon films). In the conventional device shown in FIG. 5, the insulating film 14 is made of a normal hard carbon film, has a relatively small optical bandwidth and is brown, so that the insulating film under the second conductor (pixel electrode) 13 is formed. Had to be removed. On the other hand, in the device of the present invention, as shown in FIG. 4, the optical band width of the hard carbon film constituting the insulating film 4 is as large as 2.4 eV or more and is transparent to visible light.
There is no need to remove the insulating film under the second conductor (pixel electrode) 3, and the etching process can be omitted.

Referring to FIG. 4, the method of manufacturing the thin-film two-terminal element of the present invention will be described. First, a conductive film is formed on an insulating substrate 1 (made of a glass plate, a plastic plate, a flexible plastic film, or the like). IT is the material
Transparent conductors such as O, In ₂ O ₃ , ZnO, SnO ₂ or Al, Ni, Cr, N
A metal such as iCr, Pt, Ag, Au, Cu, Mo, Ti, Ta, or a highly doped semiconductor is used, and is deposited by a film forming method such as evaporation or sputtering. Next, the conductor film is patterned into a predetermined pattern by wet or tri-etching to obtain a first conductor 2 serving as a bus line. And
A hard carbon film 4 having an optical bandwidth of 2.4 eV or more is deposited on the entire surface by plasma CVD (intermittent plasma).
Further, a second conductor 3 serving as a pixel electrode is formed thereon. The specific material and forming method used for this formation are the same as those for forming the first conductor 2. In this way, a thin-film two-terminal element comprising the first conductor, the hard carbon film, and the second conductor is obtained.

6 to 9 are views showing another configuration example of the thin film two-terminal element according to the present invention. The element in FIG. 6 has a sandwich type structure, and the element in FIGS. 7 to 9 has a coplanar type structure. It is. The difference between these configurations is that either the first conductor 2 serving as a bus line or the second conductor 3 serving as a pixel electrode is formed on the insulating film 4.
In other respects, the material and the manufacturing method are almost the same as those of the element shown in FIG.

First electrode (lower electrode) of the thin-film two-terminal element of the present invention
2. The thickness of the second electrode (upper electrode) 4 is usually in the range of several hundred to several thousand Å. Insulating film (hard carbon film)
The thickness of 3 ranges from 100 to 8000, preferably 200 to 6000, more preferably 30 to 4000.

To make a liquid crystal display device using a substrate having a thin film two-terminal element as described above, prepare a substrate and a second substrate on which a stripe-shaped common electrode is formed, and use a conventional method between the two substrates. What is necessary is just to form a liquid crystal layer.

〔The invention's effect〕

In the thin-film two-terminal device of the present invention, the insulating film interposed between the first conductor and the second conductor is made of a hard carbon film having an optical bandwidth of 2.4 eV or more. Since it is produced by a gas phase synthesis method such as
The physical properties can be controlled over a wide range depending on the film formation conditions, and therefore the degree of freedom in device design is large. 3) Since a good quality film can be formed even at a low temperature near room temperature, there is no restriction on the material of the substrate. 4) Because of excellent uniformity of film thickness and film quality, it is suitable for thin film devices. 5) Dielectric Since the rate is low, it does not require advanced microfabrication technology and is therefore advantageous for increasing the area of the element. 6) Since it is colorless and transparent to visible light, it is necessary to remove the hard carbon film other than the element part The thin film two-terminal element using such an insulating film is suitable as a switching element for a liquid crystal display.

[Brief description of the drawings]

1 and 2 are views showing an apparatus for forming a hard carbon film used as an insulating film of a thin-film two-terminal element of the present invention, FIG. 3 is a graph showing the relationship between plasma power supply frequency and electron temperature,
FIG. 4 is a perspective view showing an example of the structure of a thin-film two-terminal element according to the present invention, FIG. 5 is a perspective view showing the structure of a conventional thin-film two-terminal element, and FIGS. It is sectional drawing which shows another structural example of an element. DESCRIPTION OF SYMBOLS 1 ... Substrate, 2 ... First conductor 3 ... Insulating film, 4 ... Second conductor

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-64-40929 (JP, A) JP-A-64-40930 (JP, A) JP-A-1-164925 (JP, A) (58) Field (Int.Cl. ⁶ , DB name) G02F 1/136 510

Claims (1)

(57) [Claims] 1. A thin-film two-terminal element having an insulating film interposed between a first conductor and a second conductor, wherein the insulating film is made of a hard carbon film having an optical bandwidth of 2.4 eV or more. A thin-film two-terminal element characterized by the above-mentioned.