JPH0959093A - Production of magnetic garnet single crystal by lpe method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To grow an NdBi-based magnetic garnet single crystal on a nonmagnetic garnet substrate in high yield by LPE method. SOLUTION: An NdBi-based magnetic garnet single crystal is grown on a nonmagnetic garnet substrate having thickness (t) in the range of 200μm<=t<=450μm by CPE method. For example, Gd3-y Ndy Sc2 Ga3 O12 (1.0<=y<=1.4) is used as the nonmagnetic garnet substrate. The magnetic garnet single crystal to be grown has preferably a composition represend by the formula Nd3-x Bix Fe5 O12 (0.5<=x<=1.9).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a magnetic garnet single crystal by the LPE method (liquid phase epitaxial method). The present invention relates to a technique for preventing cracking of a single crystal by growing a garnet single crystal. This technique is useful for manufacturing Faraday elements such as optical isolators.

[0002]

2. Description of the Related Art A magnetic garnet single crystal has a Faraday effect and is a central material of an optical isolator. In recent years, a bismuth-substituted rare earth iron garnet grown on a non-magnetic garnet substrate by the LPE method has been mainly used as a magnetic garnet single crystal of this type. This is part of the rare earth element in the rare earth iron garnet single crystal.
It is replaced with (bismuth) and is a thick film having a thickness of several hundreds of μm. The reason why the LPE method is adopted is that the LPE method is excellent in mass productivity and a high quality single crystal film can be manufactured at a low price.

Conventionally, when growing a magnetic garnet single crystal on a non-magnetic garnet substrate by the LPE method, a thick substrate is used, the raw material is completely melted first, and then the liquid phase temperature thereof is supercooled (crystal The temperature of the melt is lowered to a temperature state in which precipitation is possible), and in the supercooled state, the condition of constant temperature is maintained for growth. Such L
In the growth of a single crystal by the PE method, a phenomenon that the growth becomes difficult due to the occurrence of cracks often occurs. It is said that this is due to a mismatch (mismatch) between the lattice constants of the substrate and the single crystal. Therefore, when growing a single crystal, the composition of the single crystal and the substrate is selected so that the lattice constants of the single crystal and the substrate are the same.

However, since the substrate and the single crystal have different coefficients of thermal expansion, it is impossible to match the lattice constants of both with each other in the entire temperature range from room temperature to the crystal growth temperature (eg, about 800 ° C.). In particular, in the case of a bismuth-substituted rare earth iron garnet single crystal, the Faraday rotation coefficient of the single crystal increases in proportion to the bismuth content, which is preferable because the film thickness for obtaining the necessary Faraday rotation angle can be reduced. On the other hand, since the coefficient of thermal expansion of the single crystal increases in proportion to it, cracks easily occur during the growth.

Therefore, the lattice constants do not match (mismatch).
In order to relieve the stress caused by, the technique of changing the lattice constant in the growing direction has been developed (for example, JP-A-6-
92796). Specifically, a method of changing the bismuth substitution amount by changing the temperature during the growth of the single crystal is adopted.

[0006]

By the way, among bismuth-substituted rare earth iron garnet single crystals, NdBi-based magnetic garnet single crystals are known to exhibit excellent performance as a Faraday rotation element in the 950 to 1070 nm band. However, in this NdBi-based magnetic garnet single crystal, since the ionic radii of Bi (bismuth) and Nd (neodymium) are very close to each other, the lattice constant of the crystal hardly changes even if the substitution amount of bismuth is changed. . Therefore, the stress cannot be relaxed by the conventional method of changing the bismuth substitution amount by changing the temperature during the growth of the single crystal, and cracks frequently occur.

An object of the present invention is to provide a method capable of growing NdBi-based magnetic garnet single crystals by the LPE method with a high yield.

[0008]

The present invention has a thickness of 200 to
This is a method in which a nonmagnetic garnet substrate of 450 μm is used and an NdBi-based magnetic garnet single crystal is grown on the substrate by the LPE method. The present inventor has found that the yield is significantly improved when an NdBi-based magnetic garnet single crystal is produced by the LPE method by thinning the non-magnetic garnet substrate used to a certain extent or less.
The present invention has been completed based on the knowledge of such a phenomenon.

The thickness t of the non-magnetic garnet substrate used
Is set to 200 μm ≦ t ≦ 450 μm for the following reason. When the thickness of the substrate exceeds 450 μm, the rapidly growing single crystal is cracked and the yield is extremely deteriorated. If the substrate thickness is less than 200 μm,
When such a thin substrate is cut out from an ingot, a crack occurs in the substrate itself, resulting in a significant reduction in the yield of manufacturing the substrate. According to the result of the experiment, the thickness of the substrate is 2
The thickness is preferably about 00 to 320 μm, and most preferably about 300 μm from the viewpoint of workability.

In the present invention, Gd _3-y Nd _y Sc ₂ Ga ₃ O ₁₂ (provided that 1.0≤y
≦ 1.4) using a magnetic garnet single crystal _{Nd 3-x Bi x Fe 5} O 12 for growing in LPE method on it (provided that
Those having a composition of 0.5 ≦ x ≦ 1.9) are desirable.

In the present invention, Nd (neodymium) is used as the rare earth element in the magnetic garnet single crystal because Nd causes the same negative Faraday rotation as Bi (bismuth) and the Faraday rotation coefficient θ _F can be increased. Is. Nd has absorption in the 1500 nm band and is therefore unsuitable as a Faraday element material in the 1550 nm wavelength band, but there is no such inconvenience on the shorter wavelength side. Then, the replacement amount x of bismuth is 0.5
The reason why it is preferable to be ˜1.9 is that if it is less than 0.5, the Faraday rotation coefficient θ _F is small, so that the 45 ° -rotation film thickness necessary for the optical isolator becomes thicker, and the absorption especially on the short wavelength side becomes large. That is, when the bismuth substitution exceeds 1.9, the grown magnetic garnet single crystal film is likely to be cracked.

A magnetic garnet single crystal having a composition of (NdBi) ₃ Fe ₅ O ₁₂ has a lattice constant a of a = 12.62Å. When a crystal is grown by the LPE method, naturally, there is a constraint that the lattice constants of the substrate and the LPE film should be matched. Compositional formula Gd _3-y Nd used in the present invention
_The nonmagnetic garnet substrate represented by _y Sc ₂ Ga ₃ O ₁₂ (where 1.0 ≦ y ≦ 1.4) has a lattice constant a of 12.
It is 61 to 12.63Å, which is optimal for film formation of the above magnetic garnet single crystal by the LPE method.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION A thin non-magnetic garnet substrate is used, otherwise NdB is obtained by a conventional general LPE method.
An i-based magnetic garnet single crystal is grown. The growth temperature is
The temperature is usually about 800 ° C., and the temperature at which the grown single crystal is taken out is about 100 ° C. to room temperature. At the growth temperature, the lattice constants of the substrate and the single crystal are almost the same (the composition of the substrate used is selected with respect to the composition of the single crystal grown in that way), and the film is grown to a predetermined film thickness. . actually,
Several kinds of test chips each having a single crystal thin film with a film thickness of 1 to 2 μm are formed by changing the growth temperature and measured with an X-ray diffractometer to determine whether or not the peaks overlap (match). Then, the product is manufactured according to the manufacturing conditions of the test chip in which it is confirmed that the peaks are overlapped, that is, the mismatch of the lattice constant is almost zero.

Thereafter, when the temperature is lowered to take out the single crystal, stress is generated because the substrate and the single crystal have different coefficients of thermal expansion. However, in the present invention, since the substrate is very thin, the entire stress (both the substrate and the single crystal) is deformed by the generated stress. This relieves the stress and prevents cracks from entering the single crystal. That is, in the present invention, by making the substrate thin, it is easy to deform and the durability against deformation is improved.

[0015]

EXAMPLE A substrate obtained by thinly cutting a single crystal ingot of Gd _1.8 Nd _1.2 Sc ₂ Ga ₃ O ₁₂ (lattice constant a = 12.62Å) with a diameter of 1 inch (about 25 mm) was used.
A single crystal of Nd _1.7 Bi _1.3 Fe ₅ O ₁₂ was grown by the PE method. As a raw material for crystal growth, Nd ₂ O ₃ , Fe ₂ O
₃ , Bi ₂ O ₃ , PbO and B ₂ O ₃ were used. First 95
It was melted at 0 ° C. for 10 hours and then stirred at the same 950 ° C. for 3 hours. After that, the temperature was lowered to 735 ° C., and a single crystal was grown by the LPE method. Five experiments of sample numbers 1 to 5 were performed by changing the thickness of the substrate. Table 1 shows the results. At the same time, FIG. 1 shows the relationship between the substrate thickness and the yield.

[0016]

[Table 1]

During the crystal growth, as a result of the test chip, the mismatch is almost zero. Therefore, as shown in FIG. 2A, the substrate and the single crystal film under growth are considered to be flat. When the single crystal is taken out, (b) of FIG.
As shown in, all of them were deformed so as to be spherically warped.
Therefore, for the deformation, the curvature radius r (mm) of the warp was calculated, and the reciprocal thereof was evaluated as the deformation degree. Therefore, the larger 1 / r is, the larger the deformation is.

The yield was used for the evaluation of cracks. Yield (%) is the ratio of the obtained crack-free (no crack) 3mm square chips to the total number of 3mm square chips obtained by cutting a single crystal with a substrate into 3mm squares after growing the single crystal. I asked for. That is, yield (%) = (number of crack-free 3 mm square chips) /
(Total number of 3mm square chips obtained) x 100

From this result, it is understood that it is appropriate that the thickness of the substrate is 450 μm or less. In this experiment, the experiment was performed only when the thickness of the substrate was 200 μm. The reason is that when the thickness of the substrate is less than 200 μm, the substrate is easily cracked when it is cut out from the ingot, and the yield of manufacturing the substrate is extremely deteriorated. From the results of Table 1, it is understood that the thickness t of the substrate needs to be in the range of 200 μm ≦ t ≦ 450 μm, and is preferably 200 to 320 μm. Generally, the thicker the substrate is, the easier it is to handle. Therefore, the thickness of the substrate is most preferably about 300 μm.

[0020]

INDUSTRIAL APPLICABILITY The present invention, as described above, uses the LPE method for Nd
By reducing the thickness of the non-magnetic garnet substrate when growing the Bi-based magnetic garnet single crystal, it is possible to suppress the occurrence of cracks, thereby significantly improving the manufacturing yield.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between substrate thickness and yield.

FIG. 2 is an explanatory view showing the cross-sectional shapes of the substrate and the single crystal during and after the single crystal growth.

[Explanation of symbols]

 10 Non-magnetic garnet substrate 12 Magnetic garnet single crystal

Claims (2)

[Claims] 1. A method for growing an NdBi-based magnetic garnet single crystal on a non-magnetic garnet substrate by the LPE method, wherein the thickness t of the substrate used is 200 μm ≦ t ≦ 450.
A method for producing a magnetic garnet single crystal by the LPE method, characterized in that the thickness is μm. 2. The composition of the non-magnetic garnet substrate is Gd _3-y
Nd _y Sc ₂ Ga ₃ O ₁₂ (however, 1.0 ≦ y ≦ 1.4)
And the composition of the growing magnetic garnet single crystal is Nd.
_{3-x Bi x Fe 5 O} 12 ( where, 0.5 ≦ x ≦ 1.9) the method of manufacturing a magnetic garnet single crystal by the LPE method according to claim 1, wherein a.