JPH0774454B2 - Manufacturing method of oxide fine particle deposition film - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a thick film, a linear deposition film or a green compact of an oxide high temperature superconductor.

“Prior art and its problems” Conventionally, as a film forming method of an oxide high temperature superconductor, (1)
Sputtering method, (2) evaporation method, (3) ion beam method, (4) CVD method, (5) spray pyrolysis method,
Known methods include (6) thermal decomposition of coating film and (7) screen printing method.

Of these, (1) to (4) are being researched as a thin film manufacturing method, and a controlled high-performance thin film (micron order or less) is formed on a substrate at a relatively low temperature (about 500 ° C at the lowest). It has become possible to manufacture. But,
These are intended for practical use of electronic devices and have a small allowable current amount. In order to apply the superconductor in the field of flowing a relatively large amount of current in the form of wire or tape, or to give it a shape such as a magnetic shield, it should be a bulk body or a thick film or a linear deposited film. Need to be created.
(4) to (7) are currently being studied as a thick film manufacturing method. The CVD method of (4) uses a metal chloride or an organic metal gas as a raw material and deposits a superconductor on a heated substrate by a gas phase reaction. In the MOCVD method using a metalorganic gas, there are great expectations not only for thin films but also for thicker films due to the progress of high-speed deposition technology, but there are problems of raw material gas control technology and cost. In the spray pyrolysis method of (5), a metal salt solution is sprayed on a substrate heated to about 400 to 500 ° C., this is repeated several times to deposit a precursor, and this is pyrolyzed and crystallized at a higher temperature. Although it is a thick film, the film can be formed relatively easily, but there is a problem in controlling the film homogeneity and composition. The coating film pyrolysis method (6) is similar to the spray pyrolysis method, but is a method in which a solution of naphthenic acid, a metal alkoxide, or the like is applied to the substrate surface by dipping or the like and then baked.

Similar to (5), there are many problems such as the problem of composition homogeneity, the fact that the film is easily cracked and the effect of residual carbon, and only those having a low critical current density are obtained. Further, in all of these methods, the process of maintaining the substrate temperature at a high temperature of 800 ° C. to 900 ° C. is required at the time of film formation or as post-annealing, and the reaction with the substrate at that time and the deterioration of the substrate quality due to the high temperature are required. It's a problem.

[Summary of the Invention] The present invention solves these drawbacks, produces a dense thick film of a superconductor, and conducts oxidation as a film forming method capable of improving the film quality without heating the substrate or under low temperature heating conditions. It aims at the practical application as a thick film of a high-temperature superconductor.

The present inventor, in the process of researching a method for synthesizing ultrafine particles of an oxide high-temperature superconductor, decided to directly synthesize ultrafine particles that already exhibit superconducting properties in an aerosol state after pyrolysis by a spray pyrolysis method. The present invention has been achieved as a result of success, and as a result of repeated studies on the idea that this feature is effective for film formation under room temperature or low temperature heating conditions.

The present invention will be described in detail below.

The present invention has two components of (a) synthesis of superconductor ultrafine particles by spray pyrolysis method, (b) film formation by in situ deposition of ultrafine particles synthesized in (a) by aerosol collision deposition method. Consists of. (Fig. 1). First, (a) will be described. Ultrafine particles of superconductor are synthesized by spray pyrolysis method. This is described in detail in Reference 1,
A solution of nitrate, etc., prepared to have the composition of a superconductor, is made into minute droplets by an atomizer, and this is an extremely short time within the reaction zone depending on the prescribed temperature, atmosphere, and flow rate conditions (for yttrium-based systems, a few seconds). Then, dry-pyrolysis-crystallization is caused to occur to obtain superconductor ultrafine particles.

The superconducting property of the generated superconductor is greatly influenced by the generation conditions. For example, in the case of yttrium-based superconductor, 980-1
Oxygen is used as a carrier gas at a temperature of about 000 ° C.
When the reaction was carried out at a flow rate of ~ 0.8 liters per minute, the obtained fine particles were confirmed to have good crystallinity by X-ray diffraction, and superconducting properties were obtained as an aerosol by temperature-magnetization characteristics. As-is (without subsequent heat treatment at high temperature) (Fig. 2).

Next, the formation of a fine particle deposition film by the aerosol collision deposition method of (b) is proposed by Kashu et al. (Reference 2). As a method for forming a dense film by spraying
It is called the gas deposition method. In general, in the case of high-purity ultrafine metal particles, the problem was that oxidation and aggregation tended to occur during the transition from production to the next process.However, film formation by differential evacuation from a high-vacuum ultrafine particle production chamber Ultrafine particles are sent to the chamber in a floating state, ejected from a nozzle at a high speed of about the speed of sound, and the inertial force of the particles is used to strongly deposit them on the substrate. Therefore, in the case of ultrafine metal particles, handling is possible while keeping the surface clean, which is effective in producing a dense film. Kashu et al. Also produced Y, Ba, and Cu metal ultrafine particles for yttrium-based superconductors to form a dense film by the above-mentioned method, and further 850 the substrate in oxygen.
Although a superconductor film is produced by heating to ℃, it is not a superconductor at the stage of a fine particle deposition film, and requires crystallization and oxidation processes by heating at high temperature.

Therefore, the present inventor has made repeated studies in consideration of forming fine particles that have already crystallized in the desired crystal phase by the same method, and as a result, the crystallization as the superconductor already generated in (a) has been completed. By using the above ultrafine particles, it has become possible to obtain a superconductor film which has already become a dense superconductor film in a state of being deposited on the substrate (FIGS. 3 and 4). As a method for depositing particles, particles are conveyed in an aerosol state from a part for collecting particles generated in the final process of the system of (a) to a decompression chamber (several to 500 Torr or less) while controlling the pressure by differential exhaust, and a nozzle ( The tip diameter was about 0.2 to 3 mm), and it was ejected by a differential pressure to deposit it on a substrate placed at a distance of about 0.5 to 5 mm from the nozzle tip.

It should be noted that in the course of transporting fine particles, fine particles may adhere to the wall surface due to thermal deposition, and in that case, it is necessary to heat the transport pipe to about 100 to 200 ° C.
Further, the pressure difference between the process of (a) and the process of (b) needs to be controlled to an optimum condition depending on the carrier gas flow rate in (a) and the film formation state in (b). Further, the superconductor can be obtained as a linear or film-like deposit by driving or rotating the substrate in one direction or a plane direction by a low speed motor. The film thickness can be easily controlled by the amount of fine particles conveyed and the driving speed of the substrate.

According to this method, post-treatment heating of the substrate is unnecessary, but in order to improve the superconducting property of the deposited film, the substrate should be heated.
It is necessary to heat to about 400 to 500 ° C to enhance the bondability between crystal grains.

(Reference 1) M. Awano et.al: Chemistry Letters, 43 (198
9) (Reference 2) Seiichiro Kashu: Metal, January 1989, p.57 "Examples" The present invention will be described with reference to Examples.

(Example 1) With respect to an yttrium-based superconductor, a superconductor fine particle film was formed by the following method.

First, a nitrate solution was prepared in which yttrium, barium, and copper had an atomic ratio of I: 2: 3. Solution concentration
It was 0.05 mol / l. Spray pyrolysis was performed with a reaction zone temperature of 990 ° C. and a carrier gas flow rate of 0.71 per minute of oxygen. The obtained superconductor fine particles are transferred to a decompression chamber and have a diameter of 0.
A film was formed on a MgO single crystal substrate with a 5 mm nozzle. The board is 20 mm
It was driven linearly at the speed of every hour. The obtained film was a dense thick film having a density of 90% or more and an average film thickness was 0.6 mm according to cross-sectional observation. Superconducting property of Tc = 80K was shown by annealing in oxygen at 500 ℃ for 48 hours.

Example 2 With respect to the bismuth-based superconductor, a superconductor fine particle film was formed by the following method.

First, a nitrate solution was prepared in which bismuth, lead, strontium, calcium, and copper were adjusted to be 2: 0.1: 2: 1.2: 2.3. The solution concentration was 0.03 mol / l. The reaction zone temperature is 750 ° C., the carrier gas flow rate is argon 0.51 per minute,
Spray pyrolysis was performed. The obtained superconductor (low Tc phase) fine particles were transferred to a decompression chamber and formed into a film on a zirconia polycrystalline substrate with a nozzle having a diameter of 1 mm. The substrate was linearly driven at a speed of 20 mm / hr in the X direction and 100 mm / min in the Y direction. The obtained film was a dense thick film having a density of 90% or more and an average film thickness was 0.2 mm by cross-sectional observation. It showed a superconducting property of Tc = 65K.

"Effects of the Invention" As described above, the present invention makes it possible to form a dense thick film or a linear deposition film of a superconductor on a substrate under a lower temperature condition than other film forming methods. It is expected that the practical use of the superconducting material as a thick film or a wire (wiring) will be promoted by further increasing the critical current density by improving the film quality.

[Brief description of drawings]

FIG. 1 shows an apparatus configuration diagram of this method. FIG. 2 shows a grain structure photograph by a transmission electron microscope image of yttrium-based superconductor ultrafine particles synthesized by the spray pyrolysis method. FIG. 3 is a photomicrograph showing the grain structure of a cross section of a linear deposited film of a superconductor produced by the present invention. FIG. 4 shows an X-ray diffraction pattern of the yttrium-based superconducting film. (○○ in the figure
○) is the surface index and YS corresponding to each diffraction peak of the superconducting phase
Z represents a peak derived from the substrate.

Claims (1)

[Claims] 1. A metal salt solution containing barium / yttrium / copper for an yttrium-based superconductor, and bismuth / lead / strontium / calcium / copper for a bismuth-based superconductor. Then, the fine particles crystallized as a superconductor, which do not contain the impurity phase on the surface and inside, are directly synthesized, and the fine particles in the aerosol state are sprayed onto the substrate at high speed by utilizing the pressure difference due to pressure reduction or pressure, A method for forming a dense deposited film on a substrate heated at room temperature or by using the inertial force of.