JPH0750656B2 - Oxide garnet single crystal - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an oxide garnet single crystal, particularly a frequency of 100 MHz.
The present invention relates to an oxide garnet single crystal that is useful as a novel magnetic film for microwave devices used in the microwave band of 10 to 10 GHz, for example, isolators and circulators.

(Prior art and its problems) Conventionally, YIG crystal grown by the flux method was used as the magnetic material for the microwave element, but the microwave element made by the flux method has a high manufacturing cost. Due to its disadvantages, it has been proposed to use a YIG crystal grown by a liquid phase epitaxial method applying a wafer process technology developed in the semiconductor industry.

However, since this YIG crystal has a large temperature dependence of saturation magnetization, there is a drawback that the temperature dependence of the resonance frequency becomes large when a microwave element is constructed.
It has been reported that a part of iron in the crystal composition is replaced with Ga, which is a non-magnetic ion.
Substitution with a increases the lattice constant mismatch between the epitaxial film and the GGG single crystal that is the substrate crystal even when the substitution amount is 0, and strain increases due to this mismatch, and in the extreme case, the epitaxial film The disadvantage of cracking occurs.

Therefore, for the purpose of matching the lattice constants of the epitaxial film and the substrate crystal, 1) La element having a large ionic radius is added to the epitaxial film, and 2) the substrate crystal is usually used for this kind of application.
A part of Gd element in GGG from the crystal is Y with a small ionic radius.
A method of using (YGd) ₃ Ga ₅ O ₁₂ crystal substituted with an element has been proposed, but in the method of 1), lanthanum substitution in the epitaxial film increases as the amount of gallium substitution in the epitaxial film increases. Although it is necessary to increase the amount, there is a problem that pits easily occur in the epitaxial film when the lanthanum substitution amount increases,
With regard to the method 2), it is necessary to increase the yttrium substitution amount in the substrate crystal as the gallium substitution amount in the epitaxial film increases. However, if the yttrium substitution amount is increased, cell growth during the growth of the substrate single crystal occurs. It turns out that there is a problem that it is easy to get up.

(Structure of the Invention) The present invention relates to a high-quality microwave device material which has solved such disadvantages, and it has a composition formula of YaGdb _- aGa _8- b.
On the garnet substrate single crystal represented by O ₁₂ (here, a and b are numbers 0.6 ≧ a> 0 and 3.1 ≧ b> 3.0), the composition formula La
xYy _- xFezGa _8- y _- zO ₁₂ (where x, y, z are 0.1>x> 0, 3.1>y> 3.0, 4.1
>Z> 3.6). The film is characterized by being epitaxially grown.

That is, the present inventors have variously studied the development of a microwave element material that does not cause pits in the grown film without mismatching of the lattice constant between the temperature dependence of the resonance frequency and the substrate crystal and the epitaxial growth layer, When the above-mentioned YaGdb _- aGa _8- bO ₁₂ (a and b are as above) is used as the substrate material, this one has a lattice constant of 12.367 to 12.383Å
Smaller is intended, it will be described later is epitaxially grown on the substrate _{(La Y Fe Ga) 8 0} 12 also lattice constant mismatch is prevented from being as small crystal lattice in the range of, the epitaxial film to be grown on the substrate _{LaxYy - xFezGa 8- y - zO 12} (x, y, z are the the street) z value that defines the amount of Tosureba this iron 4.1>
It is said that z> 3.6, and the iron ion at the (d) site in YIG is mainly replaced by a nonionic gallium element, so that the temperature dependence of the saturation magnetization due to the iron ion at the (d) site is reduced. It is also possible to grow an epitaxial film that does not cause pits and has no temperature dependence of saturation magnetization because the lanthanum substitution amount of this product is 0.1 or less when this product is epitaxially grown on the above-mentioned substrate. It was confirmed that the above can be achieved, and the present invention was completed by conducting research on the substrate single crystal used here, the composition of the epitaxial film, and the manufacturing method thereof.

Garnet substrate single crystal constituting the oxide garnet single crystal of the present invention the composition formula YaGdb as described above _- is shown in aGa _8- bO _12, this a is 0.6 ≧ a> 0, b is 3.1 ≧ b> 3.0 It is supposed to be the number shown, and this is Y in the {c} site.
And Gd, a part of Y and Ga on the [a] site, Ga on the (d) site
It is assumed that the formula Y _0.6 Gd _2.46 Ga
_4.94 O ₁₂ , Y _0.3 Gd _2.71 Ga _4.99 O ₁₂ are exemplified. This is, for example, YzO ₃ 3.5-7.5 mol%, GdzO 3
It can be obtained by charging 0 to 34 mol% and 61 to 63 mol% of GazO ₃ in a crucible, heating to 1,730 ℃ by high frequency induction to melt, and then pulling a single crystal from this solution by the Czochralski method. . In addition, it was confirmed that when this wafer was cut out from this single crystal and the lattice constant was measured after etching the wafer with hot phosphoric acid, for example, it was 12.367 to 12.383Å.

Further, the structure to be epitaxially grown on the substrate single crystal composition formula as described above LaxYy _- xFezGa _8- y _- indicated by zO _12, the x, y, z is 0.1>x>0,3.1> y > 3.
0, 4.1>z> 3.6, which means La and Y at {c} site, Fe and Y and a part of Ga at [a] site, and Fe and Ga at (d) site. In the formula La _0.02 Y _3.04 Fe _3.79 Ga _1.15 O ₁₂ , La _0.1 Y _2.97 Fe _3.78 Ga
_1.15 O ₁₂ is exemplified. This one has a lattice constant of 12.36
3 to 12.372Å, but the lattice constant of the substrate single crystal on which this is epitaxially grown is 12.3 as described above.
67 to 12.383Å and the lattice constant of both is ± 0.003Å
Since they match within the range, there is no mismatch, epitaxial growth can be easily performed, and the obtained epitaxial growth layer does not crack.

Assuming that this epitaxial film is a conventionally known YIG, the YIG has about 2.0 formula weight iron ions at the [a] site and about 3.0 formula weight iron ions at the [d] site. ], Since the [d] site is mostly occupied by iron ions, a saturation magnetization value of 1.760 G, which corresponds to about 1.0 formula weight, is generated. Although it has a strong temperature dependence, the composition represented by the above-mentioned compositional formula used in the present invention is obtained by substituting the gallium element for the iron ion mainly at the [d] site of this YIG. Set quantity Z value to 4.
Since 1>Z> 3.6, it is considered that the saturation magnetization has no temperature dependence.

Regarding the iron ion substituted with gallium element, it is known that the lanthanum substitution amount x value is 0.24>x> 0.13 by further adding the lanthanum element. (La Y Fe Ga) _Since it was found that many pits were generated in the epitaxial film when the lanthanum value in the crystal of ₈ O ₁₂ was set as described above, the x value of the present invention was 0.
Since 1>x> 0, no pits are generated.

This epitaxial growth may be carried out by the liquid phase method, and therefore, it contains LazO ₃ , YzO ₃ , FezO ₃ , GazO ₃ and flux components PbO and BzO ₃ in a platinum crucible, and 950-1,10
It suffices to heat it to 0 ° C. to melt it, and immerse the above-mentioned substrate single crystal in this melt. The thickness of the epitaxial layer formed by this epitaxial growth method varies depending on the frequency used in the target microwave element, but normally it is 5 μm to 40 μm.
The range may be m.

The oxide garnet single crystal of the present invention obtained by the method as described above does not have temperature dependence of the resonance frequency, there is no mismatch in lattice constant between the substrate single crystal and the epitaxial growth layer, and further, in the grown epitaxial film. Since it does not cause pits, it has excellent physical properties as a material for microwave devices.
In addition to being useful as a microwave element used in the microwave band of 100 MHz to several tens of GHz, it is also useful as a magnetic film for isolators and circulators.

Next, examples of the present invention will be described. In the examples, the measurement of the resonance magnetic field value, the calculation of the saturation magnetization, and the calculation of the temperature coefficient quantitatively showing the temperature dependence of the saturation magnetization are carried out as follows.

[Measurement of resonance magnetic field value]

A small piece of 2.6 x 2.6 mm was cut out from the sample and a ferromagnetic resonance device with a temperature varying device was used to change the resonance magnetic field value when the direction of the epitaxial film and the applied magnetic field was horizontal and vertical when the sample temperature was changed. While measuring.

[Calculation of saturation magnetization]

It is calculated from the resonance magnetic field value measured above using the following formula.

Here, 4πMs… saturation magnetization, Ha… anisotropic magnetic field H ₁ … resonance magnetic field value when the epitaxial film is placed perpendicular to the applied magnetic field, H ₁₁ … resonance magnetic field when the epitaxial film is placed parallel to the applied magnetic field. value.

[Calculation of temperature coefficient]

From the graph of the temperature dependence of the saturation magnetization for each sample −
The temperature coefficient showing the temperature dependence of the saturation magnetization in the range of 30 ° C to 80 ° C is calculated from the following formula.

(Note) 4πMs (80 ° C) ... Saturation magnetization at 80 ° C 4πMs (-30 ° C) ... Saturation magnetization at -30 ° C Example 1 La ₂ O ₃ , Y ₂ O as components for forming an epitaxial film
₃ , Fe ₂ O ₃ and Ga ₂ O ₃ were charged into a platinum crucible in an amount such that eight kinds of epitaxial film compositions having different ratios of Fe ₂ O ₃ and Ga ₂ O ₃ shown in Table 1 were obtained. Further, PbO and B ₂ O ₃ as a flux component were charged, and then the mixture was heated to 1,100 ° C. to melt it, and then in this melt, the formula Y _0.5 Gd _2.55 Ga
A garnet substrate single-bonded wafer represented by _4.95 O ₁₂ was dipped to grow an epitaxial film represented by the formula (La Y Fe Ga) ₈ O ₁₂ in the (111) orientation to a thickness of about 2 μm.

Next, when the lattice constant of the oxide garnet single crystal thus obtained, the mismatch degree (Å) between the substrate single crystal and the epitaxial film, and this temperature coefficient were examined, the results shown in Table 1 were obtained. All of them have a mismatch of 0.003Å or less and are practically no problem.Since the lanthanum substitution amount of this epitaxial film is 0.1 formula amount or less, the number of pits is small and the temperature coefficient is high. It was confirmed to be less than YIG's 3.2 G / ° C.

Incidentally, the attached FIG. 1 is a graph showing the temperature dependence of the saturation magnetization of Sample No. 5 and the temperature dependence of the saturation magnetization of YIG as a comparative example. It was confirmed that it was excellent.

Example 2 La ₂ O ₃ and Y ₂ O as components for forming an epitaxial film
₃ , Fe ₂ O ₃ and Ga ₂ O ₃ were charged into a platinum crucible in such amounts that eight kinds of epitaxial film compositions with different ratios of Fe ₂ O ₃ and Ga ₂ O ₃ shown in Table 2 were obtained. Then, PbO and B ₂ O ₃ as flux components were charged, and the mixture was heated to 1,000 ° C. to be melted, and then a garnet substrate single crystal wafer represented by the formula Y _0.6 Gd _2.46 Ga _4.94 O ₁₂ was added to the melt. By dipping, an epitaxial film represented by the formula (La Y Fe Ga) ₈ O ₁₂ was grown in the (111) orientation so as to have a thickness of about 2 μm.

Next, the lattice constant of the oxide garnet single crystal thus obtained, the degree of mismatch (Å) between the substrate single crystal and the epitaxial film, and the temperature coefficient were examined, and the results shown in Table 2 were obtained. From this, it can be seen that all of them have a mismatch of 0.003Å or less and are practically no problem, and the lanthanum substitution amount of this epitaxial film is 0.
It was confirmed that the 02 formula weight was less than 0.1 formula weight, that it was a good quality product with a small number of pits, and that the temperature coefficient was 0.7 G / ° C or less.

Example 3 La ₂ O ₃ and Y ₂ O as components for forming an epitaxial film
₃ , Fe ₂ O ₃ and Ga ₂ O ₃ were charged in a platinum crucible in the amounts to obtain eight kinds of epitaxial film compositions in which the ratios of Fe ₂ O ₃ and Ga ₂ O ₃ shown in Table ₃ were changed. Furthermore, after charging PbO and B ₂ O ₃ which are flux components, they are heated to 950 ° C. to melt them, and a garnet substrate single crystal wafer represented by the formula Y _0.3 Gd _2.71 Ga _4.99 O ₁₂ is immersed in this melt. And then (11
1) Orient the epitaxial film shown in Table 3 to a thickness of about 2
Epitaxially grown to μm.

Next, the lattice constant of the oxide garnet single crystal thus obtained, the degree of mismatch (Å) between the substrate single crystal and the epitaxial film, and the temperature coefficient of this were investigated, and the results shown in Table 3 were obtained. In each case, there is no problem in practice because the mismatch is 0.003Å or less, and this epitaxial film is a good quality one with a lanthanum substitution degree of 0.1 formula weight and a small number of pits.
Furthermore, the temperature coefficient was 0.7 G / ° C or less, confirming that it has excellent physical properties.

Comparative Example 1 La ₂ O ₃ , Y ₂ O ₃ , Fe ₂ O ₃ and Ga ₂ O ₃ which form an epitaxial film were used, and the formula weights of Fe and Ga in the epitaxial film crystal were F.
Fe3.86 where e and Ga are within the range where the saturation magnetism does not depend on temperature
Formula amount, Ga1.10 formula amount, and for La, the formula amount is added to the platinum crucible as the amount changing within the range shown in Fig. 2, and PbO and B ₂ O as flux components are added to this. ₃ was charged, and this was heated to 1,100 ° C. to be melted, and then the GGG single crystal wafer represented by the formula (Ga _3.03 Ga _4.97 O ₁₂ ) was dipped into this melt to form the (111) system with the formula (La Y Fe G
a) The epitaxial film of ₈ O ₁₂ was epitaxially grown to a thickness of about 2 μm, and the lattice constant of the obtained oxide garnet single crystal and the number of pits present in this epitaxial film were examined. In order to prevent the mismatch between the GGG single crystal and the epitaxial film, the formula constant of La must be 0.19 in order to match the lattice constant of the epitaxial film with the lattice constant of the GGG single crystal. In this case, the number of pits in the epitaxial film is large, which causes a problem in practical use.
Epitaxial growth of the epitaxial film represented by Y Fe Ga) ₈ O ₁₂ cannot eliminate the temperature dependence of the saturation magnetization and the mismatch of the lattice constants, and that the epitaxial film with a small number of pits cannot be grown. Was confirmed.

Comparative Example 2 The formula weights of Fe and Ga in the epitaxial film crystal are Fe, and the formula weight of Fe3.86 is such that Ga has a range in which the saturation magnetic field does not have temperature dependence, and Ga1.10.
Y ₂ O ₃ , Fe ₂ O ₃ and Ga ₂ O ₃ and PbO and B ₂ O ₃ as flux components were prepared in a platinum crucible and heated to 1,000 ° C. This is melted, and a garnet single crystal substrate represented by the formula (Y Gd Ga) ₈ O _{12 in} which the lattice constant is changed by changing the Y substitution amount in the range shown in FIG. 3 is immersed in this melt. When an epitaxial film represented by the formula Y _3.04 Fe _3.86 Ga _1.10 O ₁₂ was epitaxially grown in the (111) orientation, this formula (Y Gd G
a) Relationship between the Y-type amount of the substrate material represented by ₈ O ₁₂ and the lattice constant, and the relationship with the dislocation density of the epitaxial film.
In order to obtain the results shown in the figure and to make the epitaxial film in a practical range in which the dislocation density is 10 / cm ² or less, the Y-type amount of the substrate material needs to be 0.5 or less. This substrate material is 12.36 even if the lattice constant is 0.5
Since it is 0, it becomes 0.004Å larger than the lattice constant of the epitaxial film having a desirable temperature characteristic, and therefore the formula on the garnet single crystal defined by the formula (Y Gd Ga) ₈ O ₁₂ with the Y formula weight being 0.5 The line width of the absorption spectrum of ferromagnetic resonance of the oxide garnet single crystal on which the epitaxial film represented by Y _3.04 Fe _3.86 Ga _1.10 O ₁₂ was grown was 5.00 e, which was a value at which no lattice constant mismatch was observed.
Since it is twice as large as 50e, a mismatch occurs, and in this case there is no temperature dependence of the saturation magnetization,
Furthermore, it was confirmed that an epitaxial film with a small number of pits could not be obtained.

[Brief description of drawings]

FIG. 1 shows the saturation of the oxide garnet single crystal of the present invention produced by epitaxially growing the epitaxial film represented by the formula (La Y Fe Ga) ₈ O ₁₂ on the garnet single crystal substrate produced in Example 1. A graph showing the temperature characteristics of the magnetization and the temperature characteristics of the saturation magnetization of YIG as a comparative example. FIG. 2 shows the epitaxial film of the formula (La Y Fe Ga) ₈ O ₁₂ on the GGG single crystal in Comparative Example 1. FIG. 3 is a diagram showing the relationship between the La formula weight and the lattice constant of an oxide garnet single crystal obtained by epitaxially growing the GaN on the garnet single crystal substrate represented by the formula (Y Gd Ga) ₈ O ₁₂ in Comparative Example 2. Relationship between the Y formula content and the lattice constant of the substrate material of the oxide garnet single crystal obtained by epitaxially growing the epitaxial film represented by the formula Y _3.04 Fe _3.86 Ga _1.10 O ₁₂ and the relationship diagram with the dislocation density of the epitaxial film. Is shown.

Claims (1)

[Claims] 1. A composition formula on a garnet substrate single crystal represented by a composition formula YaGdb _- aGa _8- bO ₁₂ (where a and b are numbers 0.6 ≧ a> 0 and 3.1 ≧ b> 3.0). LaxYy _- xFezGa _8- y _- zO ₁₂ (where x, y, z are 0.1>x> 0, 3.1>y> 3.0, 4.1
An oxide garnet single crystal obtained by epitaxially growing a film of z>3.6>.