JPH03122003A - Production of alkali metal-replaced oxide thin film - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application of the Invention) The present invention relates to a method for producing an alkali metal-substituted oxide thin film, and more particularly, to a method for producing an alkali metal-substituted oxide thin film, in which alkali metal ions are substituted in a large amount (prior art and problems). Both radiuses are large.

For this reason, when attempting to produce a material in which the metals forming the lattice are substituted with alkali metal ions, special measures are required, and there is also an upper limit to the amount of substitution.

In particular, when attempting to produce oxides, alkali metal oxides tend to precipitate, and due to this property, alkali metal compounds have even been used as solvents for growing oxide single crystals. Therefore, in order to obtain an oxide containing an alkali metal, a method is used in which the alkali metal is replaced in a reducing atmosphere, and then heat treatment is performed in oxygen at a low temperature. However, in this method, the distribution of the alkali metal was uneven, oxygen defects were likely to remain, and the amount of substitution was limited by the thermal solid solubility limit, resulting in insufficient properties. Another limitation was that alkali metal oxides are chemically unstable and have many problems in handling.

By the way, introduction of carriers is important in producing oxide superconducting materials. In that case, substitution of an alkali metal with a low valence is effective, and in fact BaBiO3 is
By replacing K with K, a ceramic material with a superconducting transition temperature Tc exceeding 30K has been realized. However, with conventional ceramic production techniques, it is difficult to obtain ceramics without strict control of complicated processes, and good quality superconducting properties have not yet been obtained.Also, the amount of K substitution is 4
It was limited to 0% or less.

The present invention has been made in view of the above-mentioned problems, and its purpose is to easily produce a thin film of an oxide material containing an alkali metal.

(Means for Solving the Problems) In order to solve the above problems, the method for producing an alkali metal-substituted oxide thin film according to the present invention is to replace the main constituent metals, which are impossible or difficult to synthesize in a bulk state, with alkali metals. In the oxide substituted with , the deposited film is irradiated with oxygen ions.

The present invention will be explained in more detail.

Since the vacuum evaporation method decomposes constituent elements into atomic units and then mixes them, it is effective as a means for synthesizing material systems that are difficult to form mixed phases or non-equilibrium phases. However, in materials containing oxygen as a constituent element such as oxides, oxygen defects are likely to occur when synthesized in a vacuum, and a heat treatment process is required to compensate for this, resulting in the material returning to an equilibrium phase. Therefore, an oxide film in a non-equilibrium state can be created by simultaneously irradiating the film with oxygen ions that can perform sufficient oxidation even though the film is deposited in a vacuum.

As mentioned above, oxygen ions are simultaneously irradiated during vacuum evaporation, and the oxygen ions are preferably 40 to 6
It is preferable to irradiate with an energy of 0 eV. If the groove is not irradiated with 40 eV, the amount of oxygen ions will be small and there is a risk that a good oxide film will not be formed. On the other hand, if it exceeds 60 eV, the kinetic energy is too large and the film pressure due to the sputtering effect will decrease. This is because the disadvantage is that the decrease becomes significant.

The flow rate of this oxygen gas is preferably 3 SCCM or more; if it is less than 35 CCM, the amount of oxygen may be too small and a good oxide film quality may not be obtained. on the other hand,
The upper limit of the flow rate of oxygen depends on the degree of vacuum in the film forming system. The degree of vacuum in this film forming system is preferably a high vacuum of 10-5 Torr or more. Vacuum degree is 10”-5T
This is because if the vacuum is lower than orr, there is a risk that film formation in vacuum evaporation will not proceed well.

In the following examples, a thin film based on a material based on B aB i 03 as a host crystal will be described, but any (L a 1-xMx) 2 Cu○4, (
B at-xMx)2 (Ln+-yM'y)C
u 307, (B i t-xMx) m (S r
l-yM'y)n (CatozMNz).

Non-equilibrium thin films such as Cupo, q (where M, M', M'' are alkali metal) material systems can also be produced.

A detailed explanation will be given below based on examples.

(Example 1) A thin film of Bat-xKxB i 03 is formed on one surface of a SrTi03 substrate or a Mg○ substrate using the apparatus shown in FIG.

As is clear from FIG. 1, the oxide thin film production apparatus according to the present invention has a substrate 1 and a substrate holder 2 that supports this substrate in a shrimp growth chamber 3.
An oxygen ion source 4 consisting of a neutralization mechanism 9, a deceleration mechanism 10, a mass separator 11, and an ion source 12 is provided, and an oxygen beam 7 is provided to the substrate 1 supported by the substrate holder 2.
can be irradiated.

A cell 5 is provided in the lower part of the shrimp growth chamber 3, and emits a metal element beam 7 to form a vapor deposited film of the metal element on the substrate 1. Note that 8 is a preliminary exhaust chamber.

First, the substrate l is attached to the substrate holder 2 in the apparatus shown in FIG.

The degree of vacuum in the shrimp growth chamber 3 is set to 1O-5 Torr or less,
With the substrate temperature at 500°C, from K cell 5, K, Ba
, Bi metals are evaporated to form a deposited film on the substrate 1.

When forming this deposited film, oxygen ions generated with high energy by the ion source 12 are purified by the mass separator 11, and then the oxygen beam 7 is decelerated by the deceleration mechanism 10, and the oxygen beam 7 is applied to the deposited film. B implanted at 50 eV, thus having a perovskite structure.
An at-xK x B i○3 thin film was epitaxially grown.

The composition ratio of Ba and K can be varied from X=0 to x=0 by controlling the evaporation rate by varying the cell temperature.
I got up to 8.

Note that the neutralization device 9 of the oxygen ion source 4 is for preventing the deposited film formed on the substrate from being charged.

From the 0 diffraction peak showing the X-ray diffraction pattern of the thin film obtained in Figure 2, B a
It can be seen that the t-xK x B i○3 thin film is grown epitaxially.

Figure 3 shows the lattice constant and EP obtained from the X-ray diffraction pattern.
The relationship between Ni/Bi ratio determined from MA is shown.

Conventionally, only the region where X is 0.4 or less has been clarified, but with the oxide thin film of the present invention, the relationship between the lattice constant and the amount of substitution can be seen over almost the entire region.

As described above, by the vapor deposition method described in the present invention, it is possible to fabricate a thin film in the region of x 0.8.

Figure 4 shows the alkali metal substituted oxide thin film (Bao
, 7KO, 3Bi03).

Even in the asdevo non-equilibrium state (indicated by ○), diamagnetic properties are observed at temperatures below 20°C, indicating that it is a superconductor. In addition, if heat treatment is performed to bring it to an equilibrium state (
), the Meissner effect is observed like in ceramic materials, but as shown in Figure 4, it is reduced compared to the non-equilibrium state, and the superconductivity is weaker. As described above, according to the present invention, a thin film material having excellent superconducting properties can be realized without going through a high-temperature substitution reaction process.

(Example 2) As in Example 1, using the apparatus shown in FIG.
An oxygen beam is irradiated onto the iO3 or MgO substrate while evaporating the metals Rb, Ba, and Bi from the cell.
o, 7Rbo, 3) BiO2 was deposited to a thickness of 6000 to obtain a superconducting thin film with the characteristics shown in FIG.

(Effects of the Invention) As explained above, since an oxide thin film in which an alkali metal is substituted can be produced at a low temperature, carriers can be easily injected into an oxide superconductor and the crystal structure can be distorted.

Therefore, a novel alkali metal substituted oxide thin film material having a non-equilibrium composition region can be obtained. Therefore, there are great advantages not only in the realization of high Tc materials and superconducting devices, but also in the development of oxide thin film materials.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of the apparatus for producing the oxide thin film of the present invention;
Figure 2 shows the X-ray diffraction pattern of the obtained thin film, and (a) shows M
on the gO substrate, (b) on the 5rTi03 substrate (B a
o, 7Ko, 3) Characteristics of B i ○3 thin film, Figure 3 shows the relationship between the lattice constant and the amount of substitution, and Figure 4 shows the relationship between (B ao, 7 to 0.3) B i 03 thin film as-deposited and after heat treatment. Figure 5 shows the temperature change in magnetic susceptibility of (Baa, 7Rbo,
3) Temperature change in magnetic susceptibility of the Bio3 thin film. DESCRIPTION OF SYMBOLS 1...Substrate, 2...Substrate holder, 3...Shrimp growth chamber, 4...Oxygen ion source, 5...K cell, 6...
・Metal element beam, 7...Oxygen beam, 8...Preliminary exhaust chamber, 9...Neutralization mechanism, 1o...Deceleration mechanism, 11
...Mass separator, 12...Ion source.

Claims (2)

[Claims] (1) An alkali metal-substituted oxide, which is produced by irradiating a deposited film with oxygen ions, in an oxide in which the main constituent metal is replaced with an alkali metal, which is impossible or difficult to synthesize in a bulk state. Method for manufacturing thin films. (2) As the alkali metal, Ba is used as a constituent metal.
2. The method for producing an alkali metal-substituted oxide thin film according to claim 1, characterized in that and Bi are used.