JPH09223627A - Magnetostatic wave device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a device operative at a lower frequency in characteristic- stabilized surface magnetostatic mode. SOLUTION: This device 10 comprises a GGG single crystal substrate 12 having a main face at the (110)-plane on which an Fe-containing garnet YIG single crystal film 14 is formed. This film is epitaxially grown so that its (110)-plane becomes a main face. A high frequency signal input and output transducers 61a and 16b are formed on the film 14 with spaces, parallel to the [-110] axis of the film 14.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetostatic wave device, and more particularly to a magnetostatic wave device using a magnetic garnet single crystal film containing Fe.

[0002]

2. Description of the Related Art In a magnetostatic wave device, a magnetic garnet single crystal film represented by a yttrium-iron garnet (Y ₃ Fe ₅ O ₁₂ : hereinafter referred to as “YIG”) single crystal film is used as an important material. There is.

Conventionally, as a magnetic garnet single crystal film used in constructing a magnetostatic wave device, a magnetic garnet single crystal film having a (111) plane direction grown in a [111] axis direction has been used. The magnetic garnet single crystal film having the (111) plane orientation is a magnetic garnet single crystal film selected as a material for a bubble memory that positively utilizes the [111] axis orientation that is the easy axis of magnetization.

The magnetostatic wave has three types of modes depending on the direction of a DC magnetic field applied from the outside and the propagation direction of the magnetostatic wave. One is a surface magnetostatic wave (M) in which the direction of the DC magnetic field is parallel to the magnetic garnet single crystal film, and the propagation direction of the magnetostatic wave is parallel to the magnetic garnet single crystal film and is perpendicular to the DC magnetic field.
SSW). The other is the volume forward magnetostatic wave (MSF) in which the direction of the DC magnetic field is perpendicular to the magnetic garnet single crystal film and the magnetostatic wave propagation direction is parallel to the magnetic garnet single crystal film.
VW), and the other is a volume receding magnetostatic wave in which the direction of the DC magnetic field is parallel to the magnetic garnet single crystal film and the magnetostatic wave propagation direction is parallel to the magnetic garnet single crystal film and parallel to the DC magnetic field. (MSBVW).

Of these three types of modes, the magnetostatic wave device utilizing the surface magnetostatic wave is conventionally used in a frequency band of 1 GHz or higher. In this case, a magnetic garnet single crystal film having a (111) plane orientation is used. And good characteristics are obtained.

[0006]

Regarding the magnetostatic wave using the magnetic garnet single crystal film, the relationship between the normalized frequency of the magnetostatic wave and the normalized internal magnetic field as shown in FIG. S. Ishak and K-K C
hang, Hewlett-Packard Journ
al, p. 10-20, February, 1985.
It is possible to indicate the region where the magnetostatic wave exists by the reference. Upper limit f _h and lower limit f of the surface magnetostatic wave frequency band
₁ is represented by the following equations (1), (2) and (3). f _h = γ · 4πMs (hi + 0.5) ... (1) f ₁ = γ · 4πMs {hi (hi + 1)} ^0.5 ... (2) hi = Hi / 4πMs ... (3) , (1), (2) and (3), γ indicates a gyromagnetic ratio, Hi indicates an internal magnetic field in the magnetic garnet single crystal film, and 4πMs indicates saturation magnetization in the magnetic garnet single crystal film.

The internal magnetic field Hi in the magnetic garnet single crystal film is expressed by the following equation (4). Hi = Hex−N · 4πMs + Ha (4) However, in the equation (4), Hex is a DC magnetic field applied from the outside, N is a demagnetizing factor, and Ha is an anisotropic magnetic field.
Respectively.

When a magnetostatic wave device utilizing surface magnetostatic waves is produced, a DC magnetic field is applied in parallel to the magnetic garnet single crystal film, so that the demagnetizing factor N is approximated to zero. Therefore, the equation (4) can be rewritten as the following equation (5). Hi = Hex + Ha ... (5)

Here, the equations (3) and (5) are converted into the equation (1).
Substituting into the equations and the equation (2), the following equations (6) and (7) are obtained. f _h = γ (Hex + Ha + 2πMs) ... (6) f ₁ = γ {(Hex + Ha) (Hex + Ha + 4πMs)} ^1/2 ... (7)

For example, using a conventional Y ₃ Fe ₅ O ₁₂ single crystal film having a (111) plane orientation and a thickness of about 20 μm, 1 GHz is used.
For the surface magnetostatic wave device used in the above frequency band, the DC magnetic field required to propagate the magnetostatic wave is 120
It was (Oe) or more.

Recently, there is an increasing demand for magnetostatic wave devices that operate at lower frequencies. For such magnetostatic wave devices, from equations (6) and (7), a DC magnetic field Hex applied from the outside is used. Must be reduced, the saturation magnetization 4πMs should be reduced, and the anisotropic magnetic field Ha should be reduced.

However, when the direct-current magnetic field Hex applied from the outside is reduced, specifically, the direct-current magnetic field Hex needs to be set to a very low value of several tens (Oe). As a result, the magnetic garnet single crystal film is sufficiently formed. Not magnetizable,
Stable characteristics cannot be obtained because of the effect of low magnetic field loss. Therefore, it is difficult to operate at a lower frequency only by reducing the DC magnetic field Hex.

Therefore, a DC magnetic field Hex applied from the outside is applied.
In order not to make the value unnecessarily small, if the saturation magnetization 4πMs is made small, the operation at a lower frequency becomes possible, but the insertion loss is significantly increased due to the increase in the ferromagnetic resonance half-value width (ΔH). Seen.

Therefore, in addition to taking measures to reduce the externally applied DC magnetic field Hex and the saturation magnetization 4πMs to the extent that they do not affect the characteristics of the magnetostatic wave device, the anisotropic magnetic field Ha is further reduced. There is a need for materials for magnetostatic wave devices that can take measures to prevent this.

Therefore, a main object of the present invention is to provide a magnetostatic wave device of a surface magnetostatic wave mode which operates at a lower frequency and has stable characteristics.

[0016]

According to the present invention, in a magnetostatic wave device having a magnetic garnet single crystal film containing Fe, the crystal axis orientation of the magnetic garnet single crystal film in the direction of propagation of the surface magnetostatic wave is <100> axis. A magnetostatic wave device characterized by being azimuth.

In the magnetic garnet single crystal film, the anisotropic magnetic field changes depending on the plane orientation, and the <111> axis orientation, which is the easy axis of magnetization, has the largest anisotropic magnetic field, and conversely, the <100> axis orientation is magnetized. It is a hard axis and has the smallest anisotropic magnetic field. Therefore, in a magnetostatic wave device using surface magnetostatic waves, in order to operate at a lower frequency,
Using a magnetic garnet single crystal film having a plane orientation including the 100> axis orientation, a DC magnetic field is applied from the outside in parallel with the <100> axis orientation, and the contribution of the anisotropic magnetic field in the internal magnetic field in the equation (5) is It should be small.

However, the inventor of the present application does not use the above-described method, but applies a magnetic field from the outside in parallel with the axis direction having an angle of about 30 to 50 ° with respect to the <111> axis direction which is the easy axis of magnetization. It was found that the magnetostatic wave device in the surface magnetostatic wave mode operates to a lower frequency when applied, and when the axial direction for applying such a magnetic field is selected, the propagation direction of the magnetostatic wave is the garnet single crystal film. It was found that the orientation was <100> axis irrespective of the plane orientation.

[0019]

By using a magnetic garnet single crystal film having a <100> axis orientation parallel to the main surface within the main surface, the crystal axis orientation of the magnetic garnet single crystal film in the direction of propagation of the surface magnetostatic wave is <100. > 1GH by setting the axis direction
Stable filter characteristics can be obtained even at z or less.

[0020]

According to the present invention, it is possible to obtain a magnetostatic wave device of a surface magnetostatic wave mode having a stable characteristic which operates at a lower frequency.

The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description of embodiments of the present invention with reference to the accompanying drawings.

[0022]

FIG. 1 is an illustrative view showing one example of an embodiment of the present invention. Magnetostatic wave device 10 shown in FIG.
Includes a Gd ₃ Ga ₅ O ₁₂ (hereinafter referred to as “GGG”) single crystal substrate 12 having, for example, a 20 mm × 5 mm (110) plane as a main surface.

On the (110) plane of the GGG single crystal substrate 12, a YIG single crystal film 14 is formed as a garnet single crystal film containing Fe. The YIG single crystal film 14 is epitaxially grown so that the (110) plane becomes the main surface. In this case, the YIG single crystal film 14 is formed to have a thickness of 10 μm, for example. In addition, the YIG single crystal film 14 It is formed in a book shape.

Here, an example of a method for producing a YIG single crystal film will be described. First, solute materials Fe ₂ O ₃ and Y ₂ O ₃ and solvent materials PbO and B ₂ O ₃ are mixed and filled in a platinum crucible. The mixture filled in the platinum crucible is heated to a crystal growth temperature of 1000 ° C. or higher to be a melt. The melt is kept stable at 900 ° C., and then the GGG single crystal substrate is immersed in the melt. In this way, the YIG single crystal film is epitaxially grown in the [110] axis direction on the GGG single crystal substrate. The GGG single crystal substrate on which the YIG single crystal film has grown is
It is taken out of the melt and cooled to room temperature. And
GGG single crystal with YIG single crystal film formed A 5 mm strip is cut in parallel.

On the YIG single crystal film 14, a transducer 16a for inputting a high frequency signal and a transducer 16b for outputting are arranged at a distance of 5 mm, for example.
YI An input terminal (not shown) is connected to one end of the
An output terminal is connected to one end of the transducer 16b. Also, these transducers 16a and 16
The other end of b is grounded.

Next, the filter characteristics of the magnetostatic wave device 10 will be described. First, this magnetostatic wave device 10
Is parallel to the (110) plane which is the main surface of the YIG single crystal film 14. Is applied. Next, the high frequency signal is input to the input transducer 16a via the input terminal. At this time, the frequency of the input signal is 0.5 to 5 GHz,
The electric power is set to 1 μW. As a result, filter characteristics are obtained according to the strength of the DC magnetic field applied from the outside. At this time, the surface magnetostatic wave MSSW is a YIG single crystal film.

Further, in order to compare the characteristics of the magnetostatic wave device 10 and the magnetostatic wave device in which the direction in which the surface magnetostatic wave is propagated is changed, in the low index azimuth direction parallel to the (110) plane. Similarly, three types of magnetostatic wave devices that propagate waves were manufactured. That is, ( Three types of magnetostatic wave devices were produced by cutting out.

Then, with respect to these four types of magnetostatic wave devices, changes in the center frequency f of the filter characteristics with respect to changes in the DC magnetic field Hex applied from the outside were examined. The result Regarding the magnetostatic wave device, the filter characteristic was not obtained at 1 GHz or less, As a result, it was confirmed to operate up to 500 MHz.

For comparison with the conventional example, (11
1) A YIG single crystal film whose main surface is The graph of FIG. 2 also shows the filter characteristics of the magnetostatic wave device. This magnetostatic wave device is also 1 GH
The operation below z could not be confirmed.

Next, the reason why the magnetostatic wave device 10, which is an example of the embodiment of the present invention, operates at a lower frequency will be theoretically explained.

A magnetic single crystal film having a garnet structure, that is, a magnetic garnet single crystal film is in a state where the anisotropic energy becomes the smallest along the <111> axis of the cubic crystal according to the notation on crystal symmetry, and the When no magnetic field is applied, spontaneous magnetization is likely to occur in the direction of this axis. Therefore, the <111> axis is referred to as the easy magnetization axis.

When the surface magnetostatic wave mode is used to operate at a lower frequency of 1 GHz or less, it is necessary to make the DC magnetic field applied from the outside smaller. Under a situation where the magnitude of the DC magnetic field applied from the outside is very small, the relationship between the direction of the DC magnetic field applied from the outside and the easy axis cannot be ignored.

[0033] It exists at an angle of about 35 ° from the x direction. Then, the inventor of the present application considered that the direction in which the magnetization vector by the spontaneous magnetization was synthesized was equivalent to the easy axis of magnetization of the magnetic single crystal film having the garnet structure. That is,
It is the axis of easy magnetization 0] Axis azimuth matches.

[0034] Nevertheless, the anisotropic energy is in a state lower than the easy axis of magnetization, which is considered to be the cause of operation at a lower frequency of 1 GHz or less.

Although the magnetic garnet single crystal film having the (110) plane as the main surface is used in the example of the embodiment of the invention described above, the invention is not limited to the (110) plane but the (001) plane. A magnetic garnet single crystal film whose main surface is may be used. Again, When a magnetostatic wave device in which a surface magnetostatic wave propagates in the [010] axis azimuth by applying a DC magnetic field from the outside in parallel to the azimuth direction, operation at 1 GHz or less has been confirmed.

[Brief description of drawings]

FIG. 1 is an illustrative view showing one example of an embodiment of the present invention;

FIG. 2 is a center frequency f of a filter characteristic of a magnetostatic wave device with respect to a change in a DC magnetic field Hex applied from the outside.
6 is a graph showing a change in the graph.

FIG. 3 shows a direct current applied from the outside in a magnetic garnet single crystal film having a (110) plane orientation. ] It is a figure which shows the relationship with an axis direction.

FIG. 4 is a graph showing a relationship between a standardized frequency of a magnetostatic wave and a standardized internal magnetic field and a region where the magnetostatic wave exists.

[Explanation of symbols]

 10 Magnetostatic Wave Device 12 GGG Single Crystal Substrate 14 YIG Single Crystal Film 16a, 16b Transducer Hex DC Magnetic Field MSSW Surface Magnetostatic Wave

Claims (1)

[Claims] 1. A magnetostatic wave device having a magnetic garnet single crystal film containing Fe, wherein a crystal axis direction of the magnetic garnet single crystal film in a direction of propagating a surface magnetostatic wave is a <100> axis direction. A magnetostatic wave device.