JPH11286774A - Ferromagnetic and ferroelectric thin film and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a thin film having ferromagnetism and ferroelectricity and useful for a memory device high in recording density by forming a crystallized thin film of oxide with a perovskite type crystal structure composed of bivalent or trivalent metallic elements and trivalent or quadrivalent metallic elements. SOLUTION: The crystallized thin film has a perovskite type crystal structure expressed by ABO3 . A denotes a bivalent or trivalent metallic element, and B denotes a trivalent or quadrivalent metallic element. As the metallic element of A, Bi, Ba and Pb are cited, and as the metallic element of B, Fe, Mn, Cr, Ti, Zr and Hf are cited. The ABO3 thin film is formed suitably by a method using a low temp. laser beam. For example, in a feeding atmosphere of gaseous oxygen, the oxide of Bi, Fe, Mn or the like is used as a target, and a laser beam is applied to form a crystallized thin film. Moreover, it is effective that <=15% ozone is incorporated into the gaseous oxygen.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ferromagnetic ferroelectric thin film and a method for producing the same. More specifically, the invention of this application relates to an oxide thin film that is a ferromagnetic material and a strong derivative, which is useful as a memory device having a large recording density.

[0002]

2. Description of the Related Art Conventionally, as a memory medium for recording information, there are a memory medium for recording information with electric charges, that is, + and-, a method applied as a DRAM or FRAM, and a spin medium, that is, a method for applying information. There is known a type applied as an MO disk, a hard disk, or the like for recording information by N and S.

Various attempts have been made to improve the recording density of each of these memory media. However, in each case, since each type of information is either kind of charge or spin, n pieces of information are used. There is a restriction that the allowable amount of information when a cell is used is 2 ⁿ . Therefore, for the purpose of increasing the recording density, research has conventionally been focused on improving the degree of integration of cells.

However, the essential restriction that the allowable information amount is 2 ⁿ has not been solved. Therefore, it has been considered to enable recording with a different mechanism, for example, charge and spin. This is because if the charge and the spin can be used as information, the allowable information amount when using n cells is 4 ⁿ , and overwhelmingly much information can be recorded.

[0005] Unfortunately, recording by such a heterogeneous mechanism has not been realized so far. This is because no clue has been obtained for a memory medium that enables such recording. The invention of this application has been made with the aim of exceeding the limitations of the prior art as described above, and has been known to pioneer its application as a new memory medium that enables recording by a heterogeneous mechanism. The challenge is to provide no technical means.

[0006]

In order to solve the above-mentioned problems, the invention of the present application is based on the following formula: ABO ₃ (A is a divalent or trivalent metal element, B is a trivalent or tetravalent metal element) A ferromagnetic ferroelectric thin film, which is a crystallized thin film having a perovskite crystal structure and having a compound composition represented by:

The invention of this application is based on the above formula AB
In O ₃ , A is Bi, Ba or Pb;
, Fe, Mn, Cr, Ti, or Zr, and a ferromagnetic ferroelectric thin film in which A is Bi and B is Fe or Mn. The invention of this application also provides a memory medium characterized by comprising the thin film.

Further, the invention of the present application provides a method for producing a ferromagnetic ferroelectric thin film, wherein the method is for producing the thin film by vapor deposition or coating. As described above, in order to solve the above-described problems, the inventors of the present application have focused on ferroelectrics and have studied and have completed the invention based on the knowledge obtained as a result. That is, for example, Bi-based ferroelectrics are expected to be applied to FRAM because of their good fatigue resistance characteristics.
Research on thin films has been actively conducted, and perovskite analogs containing Bi have been converted from dielectric materials to magnetic materials and superconductors in a wide range of electric and Because of its magnetic properties, the inventor of the present application has invented a compound thin film that enables the coexistence of ferromagnetism and ferroelectricity, and that can exhibit different mechanisms of dipolar polarization and spin polarization in the same region. It was completed as.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The invention of this application has the features as described above, and embodiments thereof will be described below. In the present invention, having a compound composition represented by ABO _3, a crystallized thin film having a perovskite crystal structure, the ferromagnetic strong derivatives is provided, the composition of ABO ₃ in this case, A is B represents a divalent or trivalent metal element, and B represents a trivalent or tetravalent metal element. When the metal elements of A and B are illustrated, as A, Bi, Ba, and Pb are representative examples;
Examples of B include Fe, Mn, Cr, Ti, Zr, and Hf. A and B may each be a single element or two or more elements.

[0010] In particular, in the present invention, a compound thin film of BiFeO ₃ and BiMnO ₃ is exemplified more specifically. Note that, in the present invention, substantially AB
Needless to say, as long as it is a crystallized thin film having a perovskite-type crystal structure of O _{3 and} a strong ferromagnetic derivative, slight differences in its composition and crystal structure are allowed.

ABO ₃ , for example, B as a specific example
iFeO ₃ and BiMnO ₃ are produced as thin films by various methods in the present invention.
For example, by a vapor deposition method as a vapor phase film forming method, a sputtering method, a laser ablation method, or
A film is formed by a sol-gel method or a MOD method as a coating film forming method.

Among them, a suitable method is a method using a laser beam capable of producing a crystallized thin film at a low temperature.
This is a method of forming a film under irradiation of a laser beam, for example, in an oxygen gas supply atmosphere. For example, Bi, Fe, M
A crystallized thin film is formed by irradiating a laser beam with an oxide such as n as a target material. In this case, it is appropriate to use an oxygen gas atmosphere.

More specifically, oxygen gas contains
It is effective to contain O ₃ (ozone) up to 15% for forming the thin film of the present invention having excellent characteristics.
More preferably, the content is 3 to 10%. For laser beams, excimer lasers are indicated as suitable. The substrate is not particularly limited, and may be, for example, Si (silicon) or a composite oxide such as strontium titanate.

Hereinafter, the present invention will be described in more detail with reference to Examples.

[0015]

EXAMPLE BiF ₂ O ₃ and Fe ₂ O ₃ were used as target materials, respectively, and an ArF excimer laser (wavelength 1) was used in an atmosphere of 5 × 10 ⁻³ Torr oxygen gas (containing 8% O ₃ ).
Laser ablation at about 93 ° / mi on an opposing strontium titanate substrate.
The film was formed at a speed of n. The substrate temperature was 500 ° C. Bi
A crystallized thin film of FeO ₃ was obtained. Similarly, MnO ₂ was used as a target instead of Fe ₂ O ₃ , and BiMnO ₃
Was obtained.

FIG. 1 shows BiFeO_ThreeX-ray diffraction of thin film crystals
It shows a pattern. FIG. 2 shows that BiFe
O_ThreeFIG. 3 is a diagram showing dielectric properties of a thin film, and FIG.
eO _ThreeIt is the figure which showed the DE curve of the thin film. BiMnO
_ThreeIn the case of the thin film, a curve similar to FIG. 3 was obtained. On the other hand, SQ
By measuring the magnetic susceptibility by UID, BiFeO_ThreeThin film and
And BiMnO_ThreeIn either case, the applied magnetic field
About 2 × 10 at 1T^-Fiveshows ferromagnetic properties of about emu
Was.

FIG. 4 shows a magnetization curve of the BiFeO ₃ thin film. Both of the thin films of BiFeO ₃ and BiMnO ₃ were crystallized thin films having a perovskite-type crystal structure, and were confirmed to be ferromagnetic and strong derivatives. Recording by the mechanism of charge and spin is possible,
A thin film useful as a new memory medium was obtained.

[0018]

As described in detail above, according to the present invention, a crystallized thin film having a perovskite type crystal structure specifically exemplified as BiFeO ₃ or BiMnO ₃ , which is acceptable when n cells are used. Possible information 4
^A ferromagnetic ferroelectric thin film is provided which is useful as a new memory medium capable of recording by a heterogeneous mechanism of electric charge and spin, which is dramatically increased as ⁿ .

[Brief description of the drawings]

FIG. 1 is a diagram showing an X-ray diffraction pattern of a BiFeO ₃ thin film as an example.

FIG. 2 is a diagram showing dielectric properties of a BiFeO ₃ thin film as an example.

FIG. 3 is a DE curve diagram of a BiFeO ₃ thin film as an example.

FIG. 4 is a magnetization curve diagram of a BiFeO ₃ thin film as an example.

Claims (6)

[Claims] A perovskite crystal structure having a compound composition represented by the following formula: ABO ₃ (A represents a divalent or trivalent metal element, and B represents a trivalent or tetravalent metal element) 1. A ferromagnetic ferroelectric thin film, characterized in that it is a crystallized thin film having a ferromagnetic ferroelectric. 2. In ABO ₃ , A is Bi, Ba or Pb, and B is Fe, Mn, Cr, Ti or Z.
2. The ferromagnetic ferroelectric thin film according to claim 1, wherein r is r. 3. The ferromagnetic ferroelectric thin film according to claim 2, wherein A is Bi and B is Fe or Mn. 4. A memory medium comprising the thin film according to claim 1. 5. The method for producing a ferromagnetic thin film according to claim 1, wherein the film is formed by vapor deposition or coating. 6. The method according to claim 5, wherein the film is formed by a vapor phase using a laser beam.