JPH021529B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a novel method for manufacturing thin films of electrically conductive materials. Recently, many attempts have been made to impart electrical conductivity to organic polymers, which are originally electrically insulating, and to create unique properties that cannot be achieved with inorganic metals, semiconductors, and oxides. One important method in this effort is the formation of pyrolytic polymers. This is an attempt to obtain a polycondensed compound by thermal decomposition starting from a specific material. The product is mainly carbonaceous, but its electrical conductivity is controlled by the starting materials. Pyrolytic polymers have a long history and are a material that attracted attention in the early 1960s. For example, the thermal decomposition of polyacrylonitrile by the Russian school is known, and an electrical conductivity of about 2 Scm ^-1 has been obtained. (A, V,
Airapetjanc et al. Dokl, Akad, Nauk
SSSR Magazine, Volume 148, Page 605, 1963). Also in 1964
In 1999, Mr. S.D. Bruck of IBM Corporation discovered that polyimide (Kapton H film of DuPont) could be thermally decomposed at 800°C to produce an electrical conductor with a conductivity of 20 Scm ^-1 . The electrical conductivity of polyimide film is 10 ^-18 Scm ^-1 at room temperature, and it decreases to 10 ²⁰ Scm -1 by thermal decomposition.
Since the electrical conductivity changes over a range of 100 to 100%, this method can be said to be an excellent method for imparting electrical conductivity to organic polymeric materials. Although the types of materials that can be made highly conductive by thermal decomposition are limited, it has been discovered that some condensation polymers can also be made highly conductive by thermal decomposition. The polymer belongs to a class of heat-resistant polymers created from recent advances in polymer chemistry.
Examples include aromatic polyamide, polyamideimide, polyesteramide, polybenzimidazole, polyoxadiazole, polythiadiazole, and polybenzthiazole. These materials are heated at 400-1000℃ in vacuum or inert gas flow.
When pyrolyzed at temperatures of , it gives conductivities of up to 500 Scm ^-1 . Based on these discoveries, proposals have been made regarding methods for producing new conductive materials and conductive compositions comprising these powders and polymeric binders. Pyrolytic polymers are characterized by high conductivity and thermal and chemical stability, so in addition to conductive films for resistors and conductors, they can also be used as heaters and actuators.
Applications can be considered in a wide variety of fields, including sensors for pressure, strain, and wind speed, heat resistance, corrosive electrodes, and absorption films for solar heat collectors. However, in order to realize such various applications, it is necessary to manufacture the above-mentioned pyrolytic polymer film according to the purpose. SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a method for producing a thin film of a heat-resistant polymer imparted with electrical conductivity by thermal decomposition. The thin film manufacturing method uses physical vapor deposition (Physical Vapor Deposition).
There are two methods: physical vapor deposition (abbreviated as PVD) and chemical vapor deposition (abbreviated as CVD), but physical vapor deposition has the following drawbacks. Mass production is low. It is difficult to obtain a thin film with a large area. Requires special equipment. Therefore, if chemical vapor deposition becomes possible, this drawback will be overcome. The present invention is based on the discovery that chemical vapor deposition of certain special polymeric materials is possible. Conventionally, there are many examples of hydrocarbons such as acetylene and benzene being physically vapor deposited in a vacuum. For example, spectrally pure graphite (20 ppm) is deposited in a vacuum of 1 × 10 ^-5 torr, and the deposition is D, E
Published by Bradley. Regarding the physical properties of these deposited films, G, K,
It has been studied by Bhaganat et al. In other words, it is written about the optical and electrical properties of vapor-deposited carbon films, and the absorption in the visible field of films with different thicknesses.
A wide variety of studies have been reported, such as the conductivity at various temperatures and the semiconductor properties of films. Compared to these, the present invention is characterized in that it uses a special raw material and therefore has a higher electrical conductivity. Examples and applications will be described below to explain the effects of the present invention. Example 1 The inside of a quartz tube was filled with nitrogen air, and polyimide (trade name: DuPont, Kapton H) and 5
A mm-thick quartz plate was placed and experiments were conducted to examine the relationship between temperature and thin film formation process in the range of 700° to 1200°C. In the figure, 1 is a heat-resistant polymer, and in this example, Kapton H manufactured by DuPont is used. 2 is a heater, 3 is a 5 mm thick substrate placed inside a quartz tube 4,
5 is a cylinder for feeding nitrogen into the quartz tube 4;
6 is a nitrogen outlet. The table below shows the relationship between temperature and the formation process.

[Table] Film thickness was measured using a Talystep, and electrical conductivity was measured using a four-probe method after applying silver paste (DuPont 4922). As a result, since the growth rate of the film differs depending on the temperature, 800°C to 1100°C is considered to be the optimum range. The higher the temperature, the better the conductivity becomes. Further, the conductivity of this vapor-deposited film is 1/2 to 1/3 that of a film obtained by directly thermally decomposing Kapton H. This is because the products are different. The film density is different. The above is thought to be the cause. Example 2 Polyoxadiazole (POD film, 50 microns) manufactured by Furukawa Electric Co., Ltd. was kept at a temperature of 900°C in a nitrogen stream (flow rate of 50 ml/min) for 10 minutes to 2 hours to form a porous alumina ceramic film. Chemical vapor deposition is performed using the substrate as a substrate. As a result, both sides of the alumina become completely black and conductive. Microscopic observation revealed that it was evenly deposited even inside the porous pores. The time and resistance values are shown in the table below. The resistance value was measured with an electrode width of 2 cm and an electrode spacing of 4 cm, with a stainless steel scale pressed against the electrodes.

[Table] Next, the properties of the obtained film as a heater were tested. When AC 100V was applied to a substrate with a resistance of 6.0KΩ, the temperature of the substrate surface rose to 200℃. When this heater was subjected to a load (100V) durability test in air, it showed only a 1% increase in resistance and a drop in temperature of about 2°C over 1000 hours. An example of its use as a heater is shown below. An alumina ceramic having a glass layer of 30 to 100 μm on its surface, deposited to a thickness of approximately 1000 Å, and a protective film provided thereon can be used as a thermal head for thermosensitive recording. Tubular (e.g. inner diameter 8mm, outer diameter 10mm, length 100mm)
A quartz tube (mm) in which the conductive thin film of the present invention is chemically deposited on the inner wall can be used as a space heater. Example 3 Aromatic polyamide resin was heated in a nitrogen stream (20ml/
At the same time, a 0.5 mm thick stainless steel substrate was placed in the same air flow and chemical vapor deposition was performed at 800° C. for 1 hour. As a result, stainless steel with excellent heat and chemical resistance is produced. For example, it has a heat resistance of 500 hours or more at 300℃ in air. Also, the stainless steel did not suffer any corrosion after being immersed in sulfuric acid and nitric acid for three months. Applications include ceramic heater electrodes and other corrosion-resistant electrodes. As described above, chemical vapor deposition has advantages over physical vapor deposition in that it is highly mass-producible and can produce thin films with a large area without the need for special equipment. or aromatic polyamide at 800°C in an inert gas.
The present invention provides an extremely useful method for producing conductive thin films by vapor deposition on other substrates at a temperature range of 1100°C. The thin film obtained by the method of the present invention can be expected to have wide applications such as thermal head heaters for heat-sensitive recording, electrodes for ceramic heaters, and corrosion-resistant electrodes.

[Brief explanation of drawings]

The figure is a schematic configuration diagram showing an example of an apparatus for carrying out the method of the present invention. 1...Heat-resistant polymer, 2...Heating heater, 3
...Substrate, 4...Quartz tube.

Claims (1)

[Claims] 1. Either a condensed polymer having a nitrogen-containing heterocycle or an aromatic polyamide is prepared in an inert gas.
A method for producing a conductive thin film, characterized by chemical vapor deposition on another substrate at a temperature range of 800°C to 1100°C. 2. Claims characterized in that the condensed polymer having a nitrogen-containing heterocycle is any one of polyimide, polyamideimide, polyesteramide, polybenzimidazole, polyoxadiazole, polybenzthiazole, and polythiadiazole 2. A method for producing a conductive thin film according to item 1. 3. Claim 1, wherein the aromatic polyamide is obtained by a condensation reaction of m-phenylenediamine and isophthalic acid, or p-phenylenediamine and terephthalic acid. A method for producing a conductive thin film as described in .