JP2742537B2 - Magneto-optical thin film and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field of the Invention) The present invention relates to a magneto-optical thin film and a method for producing the same, and more specifically, a large Faraday rotation index for light,
The present invention relates to a magneto-optical thin film that can be easily formed and a method for manufacturing the same.

(Conventional technology and problems) In order to obtain a non-reciprocal effect, Faraday rotation of light, which is a kind of magneto-optical effect, is used for the configuration of a non-reciprocal optical element such as an optical isolator or an optical circulator. Conventionally, single crystals of yttrium iron garnet (Y ₃ Fe ₅ O ₁₂ , hereinafter referred to as YIG) have been often used as optical materials. These, for compactness and high performance of the device, the Faraday rotation angle per unit length, i.e. Faraday constant theta _F is large and requires magneto-optical material small propagation loss of light, Therefore A so-called bismuth-substituted iron garnet in which yttrium of YIG is replaced by bismuth (chemical formula Bi _x Y _3-x Fe ₅ O ₁₂ ) has been developed.

Recently, with the goal of integrating optical devices into integrated circuits,
There has been an increasing demand for thinner magneto-optical materials.

Characteristics required for magneto-optic material, the Faraday constant theta _F is large, it the propagation loss is small, but is particularly important, including the bismuth-substituted iron garnet above,
Attempts have been made to reduce the thickness of various materials.

The present invention has been made in view of the above problems, and has as its object to provide a high-performance magneto-optical thin film and a method for manufacturing the same.

(Means for Solving the Problems) In order to solve the above problems, the magneto-optical thin film according to the present invention has a chemical formula Ce _x Gd _3-x Fe ₅ O where _{x is} a value of 0.5 to 1.5.
_It has a composition of _{12 and} is formed by sputtering on an optical substrate.

In the method of manufacturing a magneto-optical thin film according to the present invention, x is set to 0.
As a value of 5 to 1.5, a sintered body having a chemical formula of Ce _x Gd _3-x Fe ₅ O ₁₂ is used as a target material, the substrate temperature during formation is set to 520 ° C. to 540 ° C., and an inert gas atmosphere is used. Deposited on the substrate by sputtering at 650 ° C
The heat treatment is performed at a temperature between 850 ° C. and 850 ° C.

The present invention is characterized in that yttrium of yttrium iron garnet is replaced by cerium and gadolinium. This realizes a small, high-performance magneto-optical film.

In the present invention, a sintered body having a composition of Ce _x Gd _3-x Fe ₅ O ₁₂ is used as a target material, and a substrate temperature of 520 ° C.
From 540 ° C. to 540 ° C. by sputtering in an inert gas atmosphere.

In the sintered body, x is 0.5 to 1.5. If it is less than 0.5, it is difficult to obtain a large Faraday constant, while if it exceeds 1.5, it becomes difficult to form a crystal film.

The substrate temperature during the deposition is 520 to 540 ° C. As is clear from the examples described below, when the temperature is lower than 520 ° C,
Crystallization does not proceed sufficiently during sputtering formation, 540 ° C
This is because, when the ratio exceeds, grain boundaries tend to be formed in the formed film.

Such deposition on the substrate can be performed in an inert gas atmosphere, for example, an argon gas atmosphere.

After forming the optical thin film as described above, in the present invention, heat treatment is performed at a temperature of 650 ° C. to 850 ° C. If the temperature of the heat treatment is lower than 650 ° C., the Faraday constant does not increase, and transmission loss may increase.
This is because, if it exceeds, the crystal state may change.

The heat treatment may be performed in a non-oxidizing atmosphere, for example, an atmosphere of argon, nitrogen gas, or the like, or a reducing atmosphere.

(Embodiment) FIG. 1 shows an example of characteristics of a magneto-optical film of a cerium-gadolinium-substituted iron garnet having a chemical composition of CeGd ₂ Fe ₅ O ₁₂ according to the present invention. The horizontal axis is the wavelength of light, and the vertical axis is the Faraday rotation angle per 1 cm length, that is, the Faraday constant Θ
_F , the broken line corresponds to the sample after the sputter formation by the method described later, and the solid line corresponds to the sample subjected to the heat treatment. Where Θ _F
The sign is positive for clockwise rotation. As shown, wavelength 1
The sign of _ＦF is reversed between the short wavelength side and the long wavelength side around the boundary of about μm. On the long wavelength side, _ＦF tends to decrease gradually with wavelength, but at a wavelength of 1.55 μm,
Having a value of 0 deg / cm or more, the value of BiY ₂ Fe ₅ O ₁₂ which is a typical bismuth-substituted yttrium iron garnet 1,200 deg / cm
It is 2.5 times or more compared to.

FIG. 2 shows the relationship between the composition ratio of cerium and gadolinium and the absolute value of the Faraday constant. Here, the horizontal axis represents the chemical formula of cerium-gadolinium-substituted iron garnet as CeGd ₂ F
The value of x when expressed as e ₅ O ₁₂ , the horizontal axis is the Faraday constant Θ
The absolute value of _F , and the wavelength is 1.55 μm. x is 0.5
, A Faraday constant value of 1,500 deg / cm or more is obtained, and increases in proportion to the cerium substitution amount. On the other hand, when x is 0.5 or less, the effect of cerium substitution is small.
When x exceeds 1.5, it is extremely difficult to form a crystal film.

Next, a method for forming the magneto-optical film in this embodiment will be described. The magneto-optical film of the present invention can be easily formed by a sputtering method. As a target material in sputtering, a sintered body having substantially the same chemical composition as a target film was used, and as a sputtering method, it could be formed by a general method such as high frequency sputtering. An argon gas was used as a gas atmosphere for sputtering, and a (111) substrate of a garnet crystal such as gadolinium gallium garnet (GGG) or niobium gallium garnet (NGG) was used as a formation substrate. In order to obtain magneto-optical characteristics, it is necessary to perform epitaxial growth on a substrate.
It has been found that a film exhibiting magneto-optical properties can be obtained in the range of 540540 ° C.

Propagation loss among the light propagation characteristics is the state as it is formed,
In other words, in the as-grown state, it is more than 100 dB / cm and cannot be used as a waveguide. It was found to be less than 25 dB / cm. On the other hand, the Faraday constant has a sufficient value even in the as-grown state as shown in FIG. 1, and the effect of the improvement by the heat treatment is not recognized, but rather tends to decrease. , The ratio of the Faraday constant to the propagation loss per unit length, ie, the figure of merit, is greatly improved by the heat treatment.

The table shows typical characteristics of the magneto-optical thin film according to the present invention.

The thin film is produced by high frequency bipolar sputtering, and the heat treatment temperature is 800 ° C. As shown in the table, the magneto-optical thin film according to the present invention can realize a magneto-optical performance index of 130 deg / dB or more in a long wavelength band around a wavelength of 1.55 μm, and has a very large Faraday constant.

(Effect of the Invention) As described above, the magneto-optical thin film according to the present invention
Since high-frequency two-pole sputtering can be used to form a film by a simple method and can obtain an extremely large Faraday constant and a high magneto-optical performance index with respect to light in a long wavelength band around 1.5 μm, Applicable to high performance non-reciprocal light devices.

[Brief description of the drawings]

FIG. 1 is a diagram showing the wavelength dependence of the Faraday rotation angle of the magneto-optical thin film according to the present invention, and FIG. 2 is a diagram showing the relationship between the cerium substitution amount and the Faraday constant.

Claims (2)

(57) [Claims] 1. The chemical formula Ce _x Gd, where x is a value of 0.5 to 1.5.
A magneto-optical thin film having a composition of _3-x Fe ₅ O ₁₂ and being formed by sputtering on an optical substrate. 2. The chemical formula Ce _x Gd where _{x is} a value from 0.5 to 1.5.
_Using a sintered body having a composition of _3-x Fe ₅ O ₁₂ as the target material, the substrate temperature during formation was set between 520 ° C. and 540 ° C., and deposited on the substrate by sputtering in an inert gas atmosphere. Thereafter, a heat treatment is performed at a temperature between 650 ° C. and 850 ° C. to produce a magneto-optical thin film.