JPH042009A - Manufacture of conductive thin film - Google Patents

Abstract

PURPOSE:To easily and effectively manufacture a thin film homogeneous, having a wide area, being oriented and single phased and superior in its conductivity, by allowing halogen element vapor to exist when a conductive thin film is formed on substrate. CONSTITUTION:Crucibles 2, 2', a substrate 3, a film thickness gauge 4 a halogen gas introduction tube 5, are installed within a chamber 1. And a shutter 6 is placed between the crucible 2 and the substrate 3. Necessary charge-transfer complex is placed in the crucible 2 and pressure within the chamber is reduced to required degree of vacuum via an exhaust valve 7, and then the crucible 2 is heated close to sublimation point of charge-transfer complex, after which gaseous halogen element is introduced in the chamber from the introduction tube 5. Adjustment of the while being thickness of a vapor deposition film is made by opening and closing a shutter 6, monitored by the quartz oscillator film thickness gauge 4. Thus gained charge-transfer complex film has a wide area, oriented that high electric conductivity direction becomes parallel to the substrate surface, and consists of a single phase.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to an improvement in a method for manufacturing a conductive thin film. More specifically, the present invention relates to a method for easily and efficiently manufacturing a thin film comprising a homogeneous, large-area, oriented, single-phase charge transfer complex having excellent conductivity.

[Prior Art] In recent years, charge transfer complexes, in which two types of molecules are bonded by the charge transfer force between an electron donor and an electron acceptor, have been shown to have properties such as electrical conductivity, superconductivity, and sensitivity to electron beams. It has attracted attention because it can be applied as electronic materials and resist materials, and active research is being carried out.

Various methods have been used to produce conductive charge transfer complexes, for example (1) in a solvent such as chlorobenzene,
An electrolytic crystal growth method in which an electron donor and an electron acceptor are dissolved, a platinum electrode is placed in the solution, and a current of about 1 μA is applied to grow the crystal. (2) A partition plate is provided in the container, and the electron A diffusion method in which a solution in which a donor is dissolved is placed in one chamber and a solution in which an electron acceptor is dissolved in a solvent is placed in the other chamber, the partition plate is removed, and a crystal is obtained by diffusion of both (3). ) Dissolve a small amount of electron donor and electron acceptor in a solvent,
A crystal growth method such as a slow cooling method in which the solvent is gradually evaporated to form crystals, or (4) a method in which an electron donor is reacted with a halogen element in a gas phase, liquid phase, or solid phase are known.

However, the conductive charge transfer complexes obtained by the crystal growth methods described in (1) to (3) above are all microcrystals or small needle-like crystals, and are fragile, so they cannot be used in electronic devices, etc. , do not use it as is.
＜It is desirable to use it as a thin film. Also, (4)
Conductive charge transfer complexes obtained by reacting an electron donor with a halogen element in a gas phase, liquid phase, or solid phase are usually in powder form and are mixtures of various compositions with different electrical conductivities. It cannot be used as it is in electronic devices, and requires purification to form a thin film.

As for a method for forming such a thin film, attempts have been made to form a thin film using a vacuum evaporation method using a charge transfer complex consisting of an electron donor such as tetrathiafulvalene and a norogen element (US Pat. No. 4,338, (Specification No. 392, Japanese Unexamined Patent Publication No. 56-27139). However, the thin film formed by this method has the drawback of poor orientation and low electrical conductivity of, for example, about 10 to 20 siemens/cm. This means that conductive charge transfer complexes have anisotropic electrical conductivity (e.g. σa:σb:σc-1:
100:1000), so if the microcrystals exist in various directions in the film, the electrical conductivity of the film decreases. Therefore, in order to increase the electrical conductivity of the film, it is desirable that the crystal axis exhibiting high electrical conductivity be oriented parallel to the film surface.

On the other hand, a method has been proposed in which an electron donor and an electron acceptor are alternately deposited by vacuum evaporation to form a thin film of an oriented charge transfer complex near the interface (Japanese Unexamined Patent Publication No. 61-2
02420). However, in this method, a film of oriented complexes is formed only near the interface, so it is inhomogeneous, and the electrical conductivity of the film as a whole is not high, for example, on the order of several Siemens/cm. There is.

Therefore, the present inventors have conducted repeated research on a method for manufacturing a charge transfer complex thin film consisting of an oriented single phase with high electrical conductivity, and first, the distance between the substrate and the port is 1.
It has been found that by performing vacuum deposition while maintaining the distance within 0 cm, a charge transfer complex thin film with high orientation and excellent conductivity can be obtained.

However, in this method, since the distance between the substrate and the port is too short, the substrate is affected by the heat of the port, making it difficult to control the deposition conditions, and requiring large-scale equipment to increase the film area. However, it was not always satisfactory.

[Problems to be Solved by the Invention] Under these circumstances, the present invention provides a thin film consisting of a homogeneous, large-area, and oriented single-phase charge transfer complex having excellent conductivity. This was done for the purpose of providing a method for extremely easy and efficient manufacturing.

[Means for Solving the Problems] As a result of extensive research to achieve the above object, the present inventors vacuum-deposited a charge transfer complex having a halogen element as an anion in a halogen element vapor to form a substrate. It was discovered that the objective could be achieved by forming a thin film thereon, and the present invention was completed based on this knowledge.

That is, the present invention provides a conductive thin film characterized in that when forming a conductive thin film by vacuum depositing a charge transfer complex having a halogen element as an anion on a substrate, the vacuum deposition is performed in a halogen element vapor. The present invention provides a method for manufacturing.

The present invention will be explained in detail below.

The charge transfer complex having a halogen element as an anion used in the method of the present invention can be obtained by reacting an electron donor with an electron acceptor made of a halogen element. As the electron donor, for example, the general formula %% () (in the formula, M 1 , M !, M 3 and M 6 are each a sulfur atom or a chalcogen element such as selenium or tellurium, and they are the same) R1, R2, R3 and R4 are each a hydrogen atom, a thioalkyl group, an ethylenedithio group, a methylenedithio group, an alkyl group, etc., and they may be the same. However, they may be different from each other, and R1
and R2 and R3 and R6 may be bonded to each other,
) A compound having a fullvalene skeleton represented by the following can be used. Examples of such substances include tetrathiafulvalene (TTF), dimethyltetrathiafulvalene (DMTTF), tetramethyltetrathiafulvalene (TMTTF), hexamethylenetetrathiafulvalene (HMTTF), and bisethylene dithiotetrathiafulvalene ( tetrathiafulvalenes such as BEDT-TTF), diselenadithiafulvalene (DSDTF)
, dimethyldiselenadithiafulvalene (DMDSDTF)
), tetramethyldiselenadithiafulvalene (TMDS
DTF), diselena dithiafulvalenes such as hexamethylene diselenadithiafulvalene (HMDSDTF), tetraselenadithiafulvalene (TSF), dimethyltetraselenaflu/querene (DMTSF), tetramethyltetraselenadithiafulvalene (TMTSF) , and tetraselenafulvalenes such as hexamethylenetetraselenafulvalene (HMTSF).

In addition, examples of electron donors other than these compounds having a fulvalene skeleton include tetrathianaphthalene, tetrathiatetracene, and tetraselenatetracene (TST).
, perylene, dithiobilane, tetramethylphenylenediamine, and the like.

On the other hand, as an electron acceptor made of a halogen element, for example! , Br, CU, and mixtures thereof.

There is no particular restriction on the method of reaction between the electron donor and electron acceptor, and conventionally known methods such as crystal growth methods such as electrolytic crystal growth method, diffusion method, and slow cooling method, or the reaction between the electron donor and the electron acceptor in a gas phase or a liquid phase are used. A method of reacting a halogen element in a phase or solid phase can be used.

A specific example of the conductive charge transfer complex thus obtained is (T T F ) IO-7! , (TTF)
Brooo, (TTF)CI! , (TTF) 1
．． , (TMTTF), I, (TMTTF), Br.

(TMTTF) aCl 1 (BEDT-TTF) 21
, BEDT-TTF)zBr, (BEDT-TTF)
2CL (BEDT TTF)z I s, (B
EDT-TTF)zBr3, (B E D T -T
T F ) 3C! Examples include s.

There are no particular limitations on the substrate used in the present invention, and substrates that have been conventionally used for forming thin films, such as glass, sodium chloride, potassium chloride, magnesium oxide, potassium iodide, quartz, bulk materials, ceramics, Any substrate can be selected from among plastics and metals such as gold, silver, aluminum, and copper.

In the present invention, the above-mentioned conductive charge transfer complex is vacuum-deposited on these substrates to form a thin film thereof, and at that time, it is necessary to have a halogen element vapor present. If this /10 gen element vapor is not present, the effects of the present invention will not be fully exhibited. The degree of vacuum is 10'Pa (
Pascal) or less, preferably 10-''Pa or less. If the degree of vacuum exceeds 102 Pa, the charge transfer complex may be oxidized or decomposed, which is not preferable. Heating is usually carried out to reach near the sublimation point, but the heating temperature is selected appropriately depending on the type of the complex.The temperature of the substrate is usually -270 to 300°C.
range, preferably 0-200'C! selected within the range.

Next, one example of a preferred method for manufacturing the conductive thin film of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a schematic diagram of an example of a vacuum evaporation apparatus for producing a thin film composed of a charge transfer complex, in which a chamber 1 includes a crucible 2.2', a substrate 3, a film thickness gauge 4, and a halogen gas introduction tube. A shutter 6 is further provided between the crucible 2 and the substrate 3.

The distance between the crucible 2 and the substrate 3 is not particularly limited, but is preferably 40 crn or less. First, a required charge transfer complex is put into the crucible 2, and the pressure inside the chamber is reduced to a vacuum level of 10'Pa or less, preferably 1O-3Pa or less via the exhaust valve 7, and then the crucible 2 is filled with the charge transfer complex. It is heated to near the sublimation point, and at the same time as the complex begins to sublimate, a gaseous halogen element is introduced into the chamber from the gas introduction pipe 5. In addition, when iodine is used as the element, iodine may be placed in the crucible 2' and iodine gas may be present in the chamber in the form of binary vapor deposition. Further, the pressure inside the chamber 1 may be reduced after replacing the chamber with an inert gas such as argon in advance. The thickness of the deposited film is adjusted by opening and closing the shutter 6 while monitoring with a crystal resonator film thickness gauge 4. According to this method, the film thickness can be increased to about several tens of micrometers. Further, the size of the film can be controlled by the distance between the substrate and the crucible, and by moving the substrate laterally with a roller or the like, a film having an even larger area can be formed.

The charge transfer complex thin film thus obtained has a large area, is oriented so that the direction of high electrical conductivity is parallel to the substrate surface, and is composed of a single phase. is usually extremely high, 20 siemens/cm or more.

[Example] Next, the present invention will be explained in more detail with reference to Examples.
The present invention is not limited in any way by these examples.

In addition, the electrical resistance of the thin film is 2 mm in width and 5 m in length from the membrane.
Cut out part m and measure it using the DC 4-terminal method.

Example I BEDT-TTF25I++9 was placed in a beaker, 25 mg of iodine was added thereto as a solid, the mixture was sealed, and the beaker was heated at room temperature for 1 hour.
The mixture was left to react for several days to produce a BEDT-TTF iodine complex.

Using the apparatus shown in FIG. 1, 50 mg of the BEDT-TTF iodine complex was placed in crucible 2, and 5
Place 0mg in crucible 2' and place 20cm above each crucible.
A glass substrate of lOcmXlocm was held at a separate position. After evacuating the chamber to a vacuum level of 1O-3Pi, the substrate temperature was maintained at 70°C, and the crucible 2
was heated to 200° C. and the crucible 2' was heated to 100° C. to simultaneously sublimate both raw materials and form a film on a glass substrate. The size of this film is 7 cm x 7 cm in the homogeneous area, and the film thickness was measured with a film thickness meter (nanoscope) and was found to be 2.
00 nm.

X-ray diffraction was performed on this film. FIG. 2 shows the X-ray diffraction chart. As a result, the crystalline structure of the wire film was determined by Bender et al.

Cryst, Liq, crystal, 107 ('84
)45” reported by σfi(BEDT-T T
From the fact that it matched the (ooB reflection of F')21s, it was found that it was a single-phase film in which the a-b plane of the crystal was oriented parallel to the substrate.

The in-plane electrical conductivity of this film at room temperature is 20S/C
It was m.

Example 2 (TMTTF) 2110 produced by electrolytic crystal growth method
A conductive thin film was formed on the substrate in the same manner as in Example 1 by placing m9 in crucible 2 and iodine 9 in crucible 2''.

The results of X-ray diffraction showed that this film was a single-phase, highly oriented, homogeneous film. Also, the size is 10 cm
The thickness was 500 nm and the electrical conductivity was 505/cm at room temperature.

Comparative Example 1 When vacuum deposition was performed in the same manner as in Example 2, except that iodine was not used during vacuum deposition, the raw material complex decomposed in the deposited film, resulting in a film consisting only of TMTTF. Therefore, the electrical conductivity of this film is 10-'S/
cm or less.

[Effects of the Invention] According to the present invention, when a charge transfer complex having a halogen element as an anion is vacuum-deposited to form a conductive thin film on a substrate, by allowing a halogen element vapor to be present,
A homogeneous, large-area, oriented, single-phase, highly conductive thin film can be easily and efficiently produced. The conductive thin film is suitably used for devices in the electronic field.

[Brief explanation of drawings]

Figure 1 shows one of the vacuum evaporator apparatuses for carrying out the method of the present invention.
2. It is a schematic diagram of an example, and the code|symbol 1 in a figure is a chamber.
2'' crucible, 3 a substrate, 4 a membrane pressure needle, 5 a halogen gas introduction tube, 6 a shutter, and 7 an exhaust valve.
) is an X-ray diffraction chart of an example of a conductive thin film made of 2I3. Agent: Patent Attorney Fujibe Kubota 1/a r b

Claims (1)

[Claims] 1. A method for producing a conductive thin film, which comprises vacuum-depositing a charge transfer complex having a halogen element as an anion onto a substrate to form a conductive thin film, the vacuum deposition being carried out in a halogen element vapor.