HK1071172A - Substrate for forming magnetic garnet single crystal film, optical device, and its production method - Google Patents

Description

Substrate for forming magnetic garnet single crystal film, optical element and method for producing the same

Technical Field

The present invention relates to a substrate for forming a magnetic garnet single crystal film, which is a magnetic garnet single crystal film such as a bismuth-substituted rare earth iron garnet (Bi-RIG) single crystal grown by liquid phase epitaxy, a method for producing a single crystal film by crystal growth using the substrate, a single crystal film produced by the production method, and an optical element.

Background

As a material used for an optical element such as a faraday rotator in the field of an optical isolator, an optical circulator, an optomagnetic sensor, or the like, a material in which a magnetic garnet single crystal film is epitaxially grown on a single crystal substrate is generally used. As a magnetic garnet single crystal film grown on a substrate, it is strongly desired to have a large faraday rotation coefficient in order to obtain a desired faraday effect. Further, in order to form a high-quality single crystal film by epitaxial growth, it is required that the difference in lattice constant between the substrate single crystal and the grown single crystal film is considerably small in a temperature range from the film formation temperature to room temperature.

It is known that the substitution of bismuth for a part of the rare earth component can significantly improve the faraday rotation coefficient of a magnetic garnet single crystal film and the increase in the substitution amount of bismuth can also increase the lattice constant of the magnetic garnet single crystal film, and therefore, a substrate material for film formation is required to have a larger lattice constant, and gadolinium-gallium garnet (GGG) having a larger lattice constant by adding Ca, Zr, Mg, or the like to the substrate material is used (japanese patent publication No. 60-4583).

However, when bismuth-substituted rare earth iron garnet single crystals are grown in a thick film (for example, a film thickness of 200 μm or more) on such a GGG single crystal substrate to which Ca, Zr, Mg, or the like is added, warpage and cracks are likely to occur during or after film formation on the substrate and the single crystal film, and this causes a reduction in the production yield during film formation and during processing.

In order to solve this problem, the present inventors have proposed a garnet single crystal substrate having a specific composition, and having a thermal expansion coefficient in a plane perpendicular to the crystal direction <111> in a temperature range of room temperature to 850 ℃ which is very close to that of a bismuth-substituted rare earth iron garnet single crystal. (Japanese patent laid-open No. Hei 10-139596). By using such a single crystal substrate, a thick film-like bismuth-substituted rare earth iron garnet single crystal film free from crystal defects, warpage, cracks and the like can be formed by liquid phase epitaxial growth.

However, the present inventors have found that a garnet single crystal substrate having such a specific composition is unstable to a lead oxide molten solution (フラツクス) used as a precipitation medium in the process of growing a bismuth-substituted rare-earth iron garnet (Bi-RIG) single crystal film by liquid phase epitaxy, and therefore, the yield of a high-quality bismuth-substituted rare-earth iron garnet single crystal is poor. In particular, it was clarified that this tendency is large in the composition of the substrate containing Nb or Ta.

Disclosure of Invention

The present invention provides a substrate for forming a magnetic garnet single crystal film, an optical element and a method for producing the same, which can stably form a thick magnetic garnet single crystal film without crystal defects, warpage, cracks, peeling and the like by liquid phase epitaxial growth.

The substrate for forming a magnetic garnet single crystal film of the present invention is a substrate for forming a magnetic garnet single crystal film for liquid phase epitaxial growth of a magnetic garnet single crystal film, and comprises a substrate (ベ -substrate) composed of a garnet-based single crystal unstable to a molten solution used for liquid phase epitaxial growth, and a first substrate and a second substrate

And a buffer layer (バツフア body frame) formed on the base substrate and made of a garnet single crystal thin film stable to the molten solution.

The molten solution is not particularly limited, and for example, a molten solution containing lead oxide as a component is used. In the present invention, the meaning of "unstable to a molten solution" is a phenomenon in which at least a part of a material constituting an object (a substrate or a buffer layer) dissolves out from the molten solution and/or at least a part of a component of the molten solution diffuses into the object to hinder liquid phase epitaxial growth of a single crystal film in a so-called supersaturated state in which crystallization starts with the object as a nucleus. Meanwhile, the meaning of "stable to a molten solution" means a phenomenon opposite to "unstable to a molten solution".

According to the present invention, if a garnet single crystal substrate having a specific composition and having a thermal expansion coefficient very close to that of a target magnetic garnet single crystal formed by liquid phase epitaxial growth, for example, a bismuth-substituted rare earth iron garnet single crystal, is selected, liquid phase epitaxial growth can be stably performed even if the substrate is unstable to a molten solution. This is because a buffer layer stable to a molten solution is formed on the base substrate.

Therefore, in the present invention, the bismuth-substituted rare earth iron garnet single crystal film which can be used for an optical device such as a faraday rotator can be grown by liquid phase epitaxy with high quality while suppressing the occurrence of crystal defects, warpage, cracks, peeling, and the like. That is, according to the present invention, a large-area (e.g., 3 inches or more in diameter) magnetic garnet single crystal film having a relatively thick film thickness (e.g., 200 μm or more) can be obtained by liquid phase epitaxial growth.

Preferably, the base substrate has a thermal expansion coefficient substantially equal to that of the magnetic garnet single crystal film. For example, the thermal expansion coefficient of the substrate is + -2X 10 relative to the thermal expansion coefficient of the magnetic garnet single crystal film in the temperature range of 0 ℃ to 1000 ℃^-6Lower range of/° c.

By making the thermal expansion coefficient of the base substrate substantially equal to that of the magnetic garnet single crystal film, peeling of the film from the base substrate after epitaxial growth, cracks, defects, and the like (hereinafter also referred to as "cracks and the like") can be effectively prevented from deteriorating. This is because, in the process of forming a magnetic garnet single crystal film by epitaxial growth, the temperature rises to about 1000 ℃ and then returns to room temperature, and if the thermal expansion coefficients are different, cracks and the like easily occur in the epitaxially grown film.

The buffer layer does not necessarily have to have a thermal expansion coefficient substantially equal to that of the magnetic garnet single crystal film. This is because the buffer layer film is very thin relative to the thickness of the base substrate, and therefore has little effect due to the difference in thermal expansion from the epitaxially grown film.

Preferably, the base substrate has a lattice constant substantially equal to that of the magnetic garnet single crystal film. For example, the lattice constant of the base substrate is within a range of ± 0.02  or less with respect to the lattice constant of the magnetic garnet single crystal film.

By making the lattice constant of the base substrate and the lattice constant of the magnetic garnet single crystal film substantially equal to each other, the magnetic garnet single crystal film can be easily grown on the buffer layer by liquid phase epitaxy.

Preferably, Nb or Ta is contained in the base substrate, and the thermal expansion coefficient and/or lattice constant of the base substrate can be easily made substantially equal to the lattice constant of the magnetic garnet single crystal film by a method of containing Nb or Ta in the base substrate. However, if Nb or Ta is contained in the base substrate, the stability to the molten solution tends to be lowered.

The buffer layer is preferably a garnet-based single crystal thin film containing substantially no Nb and Ta. Since the garnet-based single crystal thin film containing substantially no Nb and Ta is stable with respect to the molten solution.

Preferably, the buffer layer is of the formula R₃M₅O₁₂(wherein R represents at least one rare earth metal, and M represents 1 selected from Ga and Fe), or

And (2) substituting gadolinium-gallium garnet with X (wherein X is at least 1 of Ca, Mg and Zr).

The buffer layer made of such a material is relatively stable to a molten solution and has a lattice constant close to that of the magnetic garnet single crystal film, and therefore, a buffer layer made of such a material is preferable.

The thickness of the buffer layer is preferably 1 to 10000nm, more preferably 5 to 50nm, and the thickness of the substrate base is preferably 0.1 to 5mm, more preferably 0.2 to 2.0 mm. If the buffer layer is too thin, the effect of the present invention is poor, and if it is too thick, the cost increases, and the epitaxial growth film is likely to be adversely affected by the difference in thermal expansion coefficient, and cracks tend to form. Further, if the thickness of the substrate base is too thin, the mechanical strength is insufficient and the workability in use is not good; if the thickness is too large, cracks tend to be more likely to occur.

The method for producing a magnetic garnet single crystal film of the present invention has,

and a step of growing a magnetic garnet single crystal film on the buffer layer by a liquid phase epitaxial growth method using the substrate for forming a magnetic garnet single crystal film of the present invention.

With respect to the method for producing an optical element of the present invention,

after the aforementioned magnetic garnet single crystal film is formed using the method for producing a magnetic garnet single crystal film of the present invention,

the method comprises the step of removing the base substrate and the buffer layer to form an optical element formed of the magnetic garnet single crystal film.

The optical element of the present invention is obtained by the method for producing an optical element of the present invention.

Brief description of the drawings

FIG. 1 is a sectional view showing a substrate for forming a magnetic garnet single crystal film and a bismuth-substituted rare earth iron garnet single crystal film grown using the substrate according to one embodiment of the present invention,

FIG. 2A is a surface SEM image of a substrate for forming a magnetic garnet single crystal film according to one embodiment of the present invention,

figure 2B is a cross-sectional SEM image of the substrate shown in figure 2A,

FIG. 3 is a sectional SEM image of a magnetic garnet single crystal film formed on a surface of a substrate for forming a magnetic garnet single crystal film according to an embodiment of the present invention,

FIG. 4A is a surface SEM image of a magnetic garnet single crystal film formed on the surface of a substrate for forming a magnetic garnet single crystal film according to one embodiment of the present invention,

FIG. 4B is a surface SEM image of a magnetic garnet single crystal film formed on the surface of a substrate for forming a magnetic garnet single crystal film according to a comparative example of the present invention,

fig. 5A and 5B are photographs of a magnetic garnet single crystal film formed on a surface of a substrate for forming a magnetic garnet single crystal film according to an example of the present invention and a comparative example.

Best mode for carrying out the invention

The present invention will be described in detail below with reference to embodiments shown in the drawings.

As shown in fig. 1, a substrate 2 for forming a magnetic garnet single crystal film in the present embodiment includes a substrate 10 and a buffer layer 11 formed by laminating on a surface of the substrate 10. The base substrate 10 has a lattice constant and a thermal expansion coefficient very close to those of the magnetic garnet single crystal film 12 composed of a bismuth-substituted rare earth iron garnet single crystal, but is unstable to a lead oxide molten solution. The buffer layer 11 is made of a garnet-based single crystal film stable to a molten lead oxide solution.

On the buffer layer 11 of the substrate 2, a bismuth-substituted rare earth iron garnet single crystal film 12 is liquid phase epitaxially grown. Since the magnetic garnet single crystal film 12 is grown through the buffer layer 11, the substrate 10 and the single crystal film 12 have good lattice matching properties and have a characteristic that the linear thermal expansion coefficient is close to that of the single crystal film 12.

The base substrate 10 is, for example, represented by the general formula M1_xM2_yM3_zO₁₂The non-magnetic garnet is constituted of a single crystal. In this formula, M1 is a metal selected from, for example, Ca, Sr, Cd, and Mn. M1 is stable at +2, and the coordination number is 8, and it is preferable that the ionic radius in this state is in the range of 0.096 to 0.126 nm. M2 is a metal selected from, for example, Nb, Ta and Sb. M2 is stable at +5, and the coordination number may be 6, and it is preferable that the ionic radius in this state is in the range of 0.060 to 0.064 nm. M3 is a metal selected from, for example, Ga, Al, Fe, Ge, Si and V. M3 is stably present in a +3, +4 or +5 valence state, and the coordination number may be 4, and a substance having an ionic radius in the range of 0.026 to 0.049nm in this state is preferable. These ionic radii are the values of the effective ionic radii determined by shennon (r.d. shannon). These M1, M2 and M3 may be each independently a metal or a combination of 2 or more metals.

The metal of M1 may be partially substituted with a metal M4 capable of substituting Ca or Sr in the composition, if necessary, in a range of less than 50 atomic% in order to adjust the valence and lattice constant. M4 is at least one member selected from Cd, Mn, K, Na, Li, Pb, Ba, Mg, Fe, Co, rare earth metals and Bi, for example, and is preferably a member having a coordination number of 8.

M2, like M1, may be partially substituted with a metal M5 capable of substituting Nb, Ta or Sb in its composition in the range of less than 50 atomic%. M5 is at least one member selected from Zn, Mg, Mn, Ni, Cu, Cr, Co, Ga, Fe, Al, V, Sc, In, Ti, Zr, Si and Sn, for example, and preferably has a coordination number of 6.

The thermal expansion coefficient of the single crystal substrate having such a composition is similar to that of the grown single crystal of bismuth-substituted rare-earth iron garnet, and the single crystal has good lattice matching. In particular, in the above general formula, x is preferably 2.98 to 3.02, y is preferably 1.67 to 1.72, and z is preferably 3.15 to 3.21.

The substrate base plate 10 having such a composition has a thermal expansion coefficient of 1.02X 10 in a temperature range of room temperature to 850 DEG C^-5/℃～1.07×10^-5Approximately/° c, the linear thermal expansion coefficient of the single crystal film very close to that of the bismuth-substituted rare earth iron garnet in the same temperature range is 1.09 × 10^-5/℃～1.16×10^-5/℃。

The thickness of the base substrate 10 is not particularly limited, but when a thick bismuth-substituted rare earth iron garnet single crystal film having a thickness of 200 μm or more is formed, the thickness is preferably 1.5mm or less from the viewpoint of suppressing the occurrence of cracks, warpage and the like in the substrate and the single crystal film during film formation and obtaining a good quality single crystal film. If the thickness of the substrate base substrate exceeds 1.5mm, a tendency to generate cracks is seen to increase in the vicinity of the interface between the substrate and the single-crystal film as the thickness increases. Meanwhile, if the thickness of the single crystal substrate 10 is too thin, the mechanical strength is lowered and the workability is not good, so that the thickness is preferably 0.1mm or more.

The buffer layer 11 formed on the single crystal substrate 10 is made of a garnet-based single crystal film. As such a garnet-based single crystal film,

can be represented by the general formula R₃M₅O₁₂(wherein R is at least one rare earth metal, and M is 1 selected from Ga and Fe), or

And gadolinium-gallium garnet (wherein X is at least one of Ca, Mg and Zr) substituted by X.

Among these, one selected from neodymium-gallium garnet, samarium-gallium garnet, gadolinium-gallium garnet and X-substituted gadolinium-gallium garnet (where X is at least one of Ca, Mg and Zr) is preferably used, but the garnet-based material is not limited thereto if it is stable to a lead oxide molten solution.

The method for producing the substrate 10 in the substrate for forming a magnetic garnet single crystal film of the present invention is not particularly limited, and a method commonly used for producing a GGG single crystal substrate and the like can be used.

For example, first, 1 or 2 or more metals selected from the metals represented by M1, M2 and M3 in the above general formula, and 1 or 2 or more metals selected from the metals represented by M4 and M5, which are used in some cases, are mixed in a predetermined ratio to prepare a homogeneous molten mixture. Next, a polycrystal was formed by dipping a GGG seed crystal having a longitudinal direction of <111> or the like in the molten mixture perpendicularly to the liquid surface, and pulling out the seed crystal while slowly rotating the seed crystal.

The polycrystalline body had many cracks, and a single crystal portion having no cracks was selected from the polycrystalline body, and after confirming the crystal orientation, the single crystal portion was again immersed in the above molten mixture as a seed crystal, so that the crystal orientation <111> was perpendicular to the liquid surface, and the single crystal was pulled out while slowly rotating, thereby forming a single crystal having no cracks. Then, the single crystal is cut into a predetermined thickness in a direction perpendicular to the growth direction, both surfaces thereof are polished, and then, etching treatment is performed with hot phosphoric acid or the like to obtain a base substrate 10.

On the base substrate 10 thus obtained, a buffer layer 11 composed of a garnet-based single crystal film having the above-described composition is formed by a sputtering method, a CVD method, a pulse laser deposition method, a solution method, or other thin film forming techniques.

Using the thus obtained substrate 2 for forming a magnetic garnet single crystal film, a magnetic garnet single crystal film 12 composed of a bismuth-substituted rare earth iron garnet single crystal film was formed by a liquid phase epitaxial growth method. The composition of the bismuth-substituted rare earth iron garnet single crystal film thus formed can be represented by the general formula Bi_mR_3-mFe_5-nMnO₁₂(wherein R is at least one rare earth metal, M is at least one metal selected from Ga, Al, In, Sc, Si, Ti, Ge and Mg, and M and n are In the range of 0 < M < 3.0 and 0 < n < 1.5).

In the general formula, examples of the rare earth metal represented by R include Y, La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and the like, and these may contain one kind alone or two or more kinds.

Among these single crystals, it is very advantageous that a part of the rare earth metal represented by R is substituted with bismuth, and the ratio of substitution with bismuth is represented by m, and the value of m is in the range of 0 < m < 3.0, and particularly when the value of m is in the range of 0.5 to 1.5, the coefficient of thermal expansion of the single crystal is very similar to the coefficient of linear thermal expansion of the single crystal substrate. Further, M is a non-magnetic metal element which may replace iron, and examples thereof include Ga, Al, In, Sc, Si, Ti, Ge, and Mg, and these may contain one kind or two or more kinds. The ratio n of these nonmagnetic elements in place of Fe is selected in the range of 0 to 1.5.

In order to form a bismuth-substituted rare earth iron garnet single crystal film by the liquid phase epitaxial growth method, a homogeneous molten mixture containing (1) bismuth oxide, (2) at least one rare earth metal oxide, (3) iron oxide, and (4) at least one metal oxide selected from Ga, Al, In, Sc, Si, Ti, Ge, and Mg, which is used as the case may be, In a predetermined ratio is prepared. Lead oxide is generally used as a main component of the solute for precipitation, but other mediums for precipitation such as bismuth oxide may be used. At the same time, boron oxide or the like may be contained as a crystal growth promoter as required.

Then, by dipping the substrate 2 of the present invention in the molten mixture, a single crystal is epitaxially grown from the molten mixture on the surface of the buffer layer 11 of the substrate 2, thereby forming a magnetic garnet single crystal film. The temperature of the molten mixture in the process varies depending on the composition of the raw material mixture, etc., and is usually selected within the range of 600 to 1000 ℃. Further, the substrate 2 may be allowed to stand in the molten mixture for epitaxial growth, or the substrate 2 may be appropriately rotated for epitaxial growth. When the substrate 2 is rotated, the rotation speed is advantageously about 10 to 200 rpm. The film forming speed is usually about 0.08 to 0.8 μm/min. The immersion time varies depending on the film forming rate, the desired film thickness, and the like, and cannot be generally defined, but is usually about 10 to 100 hours.

After the epitaxial growth is completed, the substrate 2 is pulled out from the molten mixture, and the adhered molten mixture is sufficiently spun off and then cooled to room temperature. Then, the single crystal film is immersed in an aqueous solution of an inorganic acid such as dilute nitric acid to remove a solidified substance of the molten mixture adhering to the surface of the formed single crystal film, and then washed with water and dried. The thickness of the magnetic garnet single crystal film 12 formed on the substrate 2 and composed of a bismuth-substituted rare earth iron garnet single crystal is usually in the range of 100 to 1000 μm. The thermal expansion coefficient is 1.0 x 10 at the temperature of room temperature to 850 DEG C^-5/℃～1.2×10^-5Around/° c.

The crystal structure and composition of the bismuth-substituted rare earth iron garnet single crystal film formed on the substrate 2 can be determined by methods such as X-ray diffraction and composition analysis by X-ray fluorescence. Meanwhile, the performance of the single crystal film 12 can be evaluated by removing the substrate 2 from the single crystal film 12 by polishing or the like, polishing both surfaces of the film 12, and then providing non-reflective films on both surfaces thereof to obtain the faraday rotation coefficient, transmission loss, temperature characteristics, and the like.

The present invention will be described in further detail below with reference to examples and comparative examples.

Example 1

Para CaCO₃、Nb₂O₅And Ga₂O₃Weighing to make the composition of the molten liquid reach Ca₃Nb_1.7Ga_3.2O₁₂The garnet was sintered at 1350 ℃ in the atmosphere to determine a garnet single phase, and then placed in an iridium crucible, and heated to about 1450 ℃ by high frequency heating in a mixed gas atmosphere of 98% by volume of nitrogen and 2% by volume of oxygen, to be melted. Then the longitudinal direction is<111>The seed crystal of the above composition was immersed in the melt at a rate of 3 mm/hr at a speed of 20rpm in a manner of 5mm prism vertically to the liquid surface, and the crystal was pulled out, whereby a transparent single crystal completely free from cracks was obtained.

Followed by crystallization from the upper part of the crystal andthe lower part, about 1g of each sample was cut, and quantitative analysis was performed on each component metal element by an X-ray fluorescence analyzer, whereby it was confirmed that Ca was contained in both the upper and lower parts of the crystal₃Nb_1.7Ga_3.2O₁₂(CNGG) composition.

The resulting single crystal was cut into a predetermined thickness in a direction perpendicular to the growth direction, mirror-polished on both surfaces, and then etched with hot phosphoric acid to give a CNGG single crystal substrate (substrate 10). The single crystal substrate has a coefficient of thermal expansion (alpha) of 1.07 x 10 at room temperature to 850 DEG C^-5V. C. The thickness of the CNGG single crystal substrate was 0.6 mm.

Nd was formed on the CNGG single crystal substrate by sputtering₃Ga₅O₁₂(NGG) thin film (buffer layer 11). Specifically, an NGG sintered body was used as a target, and sputtering film formation was performed under the following film formation conditions, followed by annealing treatment.

(sputtering film formation conditions)

Substrate temperature: at the temperature of 600 ℃,

input power: the water-soluble organic solvent is 300W,

atmosphere gas: ar + O₂(10% by volume), 1Pa,

film forming time: the reaction time is 30 minutes and the reaction time is 30 minutes,

film thickness: the particle size of the nano-particles is 250nm,

(annealing treatment)

Atmosphere gas: o is₂、1atm，

Temperature: at a temperature of 800 c,

time: for 30 minutes.

An SEM image of the surface of the NGG membrane is shown in fig. 2A. And a cross-sectional SEM image thereof is shown in fig. 2B. It was confirmed that a smooth NGG film could be obtained. When the composition of the NGG film was analyzed by X-ray fluorescence, it was confirmed that Nd, the approximate stoichiometric composition, was obtained₃Ga₅O₁₂(NGG).

Using the CNGG substrate with NGG film obtained in this way, a bismuth-substituted rare earth iron garnet single crystal film was formed by a liquid phase epitaxial growth method. Specifically, Ho is put into a platinum crucible₂O₃5.747g、Gd₂O₃6.724g、B₂O₃43.21g、Fe₂O₃126.84g、PbO989.6g、Bi₂O₃826.4g, melted at about 1000 ℃ and cooled at a rate of 120 ℃/hour after stirring uniformly, and maintained in a supersaturated state at 832 ℃. Next, a substrate having a 250nm thick NGG thin film formed on a CNGG substrate having a thickness of 0.6mm was immersed in the molten solution, and a single crystal film was grown by a liquid phase epitaxial growth method while rotating the substrate at 100rpm for 10 minutes to form a bismuth-substituted rare earth iron garnet single crystal film having a thickness of about 4 μm on the substrate.

The composition of the single crystal film was analyzed by X-ray fluorescence, and it was confirmed that the composition was Bi_1.1Gd_1.1Ho_0.8Fe_5.0O₁₂(Bi-RIG). The cross-sectional SEM image of the single crystal film is shown in fig. 3, and the surface SEM image thereof is shown in fig. 4A. It was confirmed that a Bi-RIG film having a smooth and dense surface, a good quality and a substantially stoichiometric composition could be obtained by epitaxial growth. It was also determined that the difference between the lattice constant of the single crystal film and the lattice constant of the substrate CNGG substrate was 0.009  within ± 0.02 . The lattice constant of the single crystal film was also determined to be 0.007  different from the lattice constant of the buffer NGG film. The determination of the lattice constant is carried out by X-ray diffraction.

Then, another sample was subjected to liquid phase epitaxial growth under the same conditions as described above for 30 hours to form a film of a single crystal of bismuth-substituted rare earth iron garnet having a thickness of about 470 μm on the substrate. A photograph of the single crystal film formed on the substrate is shown in fig. 5A.

No cracks were observed in either of the obtained single crystal film and the single crystal substrate, and the composition of the single crystal film was analyzed by X-ray fluorescence, whereby it was confirmed that Bi was present_1.1Gd_1.1Ho_0.8Fe_5.0O₁₂

Removing the substrate from the single crystal film by polishing, polishing both surfaces of the single crystal film, and providing SiO on both surfaces₂Or Ta₂O₅The non-reflective film was evaluated for the transmission loss and temperature characteristics of the single crystal film at a Faraday rotation angle of 45deg and a Faraday rotation angle of 1.55 μm, and the film had a Faraday rotation coefficient of 0.119deg/μm, a transmission loss of 0.03dB and a temperature characteristic of 0.065 deg/deg.C. Can satisfy the requirements of optical characteristics as an optical isolator.

The Faraday rotation angle was determined by measuring the angle of the plane of polarization of the emitted light by causing a polarized laser beam having a wavelength of 1.55 μm to be incident on the single crystal film. The transmission loss was determined by the difference between the intensity of a laser beam having a wavelength of 1.55 μm and transmitted through the single crystal film and the intensity of the laser beam in the absence of the single crystal film. The temperature characteristic is calculated by measuring the rotation angle of a sample at a temperature varying from-40 ℃ to 85 ℃.

The single crystal film has a coefficient of thermal expansion (alpha) of 1.10 x 10 at room temperature to 850 DEG C^-5V. C. The difference between the thermal expansion coefficients of the base substrate and the single crystal film is 0.03X 10^-5V. C. And no cracks were found in the obtained single crystal film.

Example 2

A CNGG single crystal substrate was produced in the same manner as in example 1.

Gd was formed on the CNGG single crystal substrate by pulse laser deposition_2.65Ca_0.35Ga_4.05Mg_0.3Zr_0.65O₁₂(GCGMZG) film. Specifically, a KrF excimer laser is used at a rate of 2.0J/cm²Irradiating the GCGMZG single crystal target with the irradiation laser density of (1), maintaining the substrate temperature at 800 ℃ on a CNGG substrate, and applying the oxygen partial pressure: 1Pa, irradiation time: the film thickness of the GCGMZG thin film was about 10nm under the condition of 5 minutes. The GCGMZG thin film was analyzed by X-ray fluorescence, and it was confirmed that it was GCGMZG having the same composition as the target.

Using the thus obtained CNGG single crystal substrate with the GCGMZG thin film, a bismuth-substituted rare earth iron garnet single crystal film was formed by the same liquid phase epitaxial growth method as in example 1. No cracks were found in the obtained single crystal film.

Comparative example 1

A CNGG single crystal substrate was produced in the same manner as in example 1, and a bismuth-substituted rare earth iron garnet single crystal film was formed by the same liquid phase epitaxial growth method as in example 1 without forming a buffer layer made of a single crystal film stable to lead oxide on the CNGG single crystal substrate.

Fig. 4B is a SEM image of the surface of the substrate after the experiment, and it was confirmed that the surface was corroded. Also, it was found that a bismuth-substituted rare earth iron garnet single crystal film was not formed by X-ray fluorescence analysis.

Fig. 5B is a photograph of the entire bismuth-substituted rare earth iron garnet single crystal film grown in comparative example 1, and it was confirmed that a non-uniform film was formed on the substrate surface and a part of the film was peeled.

Example 3

A CNGG single crystal substrate with an NGG thin film was produced in the same manner as in example 1. Using the CNGG single crystal substrate with the NGG thin film, a bismuth-substituted rare earth iron garnet single crystal film was formed by a liquid phase epitaxial growth method.

Concretely, Tb is put into a platinum crucible₄O₇12.431g、Yb₂O₃1.464g、B₂O₃43.21g、Fe₂O₃121.56g、PbO989.6g、Bi₂O₃826.4g, melting at about 1000 deg.C, stirring, cooling at 120 deg.C/hr, and keeping at 840 deg.C supersaturation state. Next, a single crystal substrate material having a 250nmNGG thin film formed on a CNGG substrate having a thickness of 0.6mm was immersed in the molten solution, and the substrate was grown by liquid phase epitaxy while rotating the substrate at 100rpmThe method was carried out for 43 hours to form a single crystal film of bismuth-substituted rare earth iron garnet with a thickness of 560 μm on the substrate.

No cracks were observed in either of the obtained single crystal film and the single crystal substrate, and it was confirmed that the composition of the single crystal film was Bi by analyzing the composition by X-ray fluorescence_1.0Tb_1.9Yb_0.1Fe_5.0O₁₂。

The difference between the lattice constant of the single crystal film and the lattice constant of the substrate CNGG substrate was measured to be 0.005 , and the difference between the lattice constant of the single crystal film and the lattice constant of the buffer layer NGG thin film was measured to be 0.004  within ± 0.02 .

The single crystal film was evaluated for its Faraday rotation angle at a wavelength of 1.55 μm, its transmission loss at a Faraday rotation angle of 45 degrees, and its temperature characteristics in the same manner as in example 1. The Faraday rotation coefficient was 0.102deg/μm, the transmission loss was 0.09dB, and the temperature characteristic was 0.051 deg/deg.C. The single crystal film has a thermal expansion coefficient of 1.09X 10^-5V. C. The difference between the thermal expansion coefficients of the base substrate and the single crystal film was 0.02X 10^-5V. C. And no cracks occurred in the obtained single crystal film.

Example 4

A CNGG single crystal substrate with an NGG thin film was prepared in the same manner as in the foregoing example 1. Using the CNGG single crystal substrate with the NGG thin film, a bismuth-substituted rare earth iron garnet single crystal film was formed by a liquid phase epitaxial growth method.

Specifically, Gd is put into a platinum crucible₂O₃7.653g、Yb₂O₃6.778g、B₂O₃43.21g、Fe₂O₃113.2g、Ga₂O₃19.02g、Al₂O₃3.35g、PbO869.7g、Bi₂O₃946.3g, melting at about 1000 deg.C, stirring, cooling at 120 deg.C/hr, and keeping supersaturation state at 829 deg.C. Then, a CNGG substrate with a thickness of 0.6mm is formed thereonA single crystal substrate material of 250 nNGG thin film was immersed in the melt, and a single crystal film was formed by liquid phase epitaxial growth for 43 hours while rotating the substrate at 100rpm, to form a bismuth-substituted rare earth iron garnet single crystal film having a film thickness of about 520 μm on the substrate.

No cracks were found in both the obtained single crystal film and the single crystal substrate. The composition of the single crystal film was analyzed by X-ray fluorescence, and it was confirmed that the composition was Bi_1.3Gd_1.2Yb_0.5Fe_4.2Ga_0.6Al_0.2O₁₂。

The difference between the lattice constant of the single crystal film and the lattice constant of the substrate CNGG substrate was measured to be 0.014  within ± 0.02 . The difference between the lattice constant of the single crystal film and the lattice constant of the buffer NGG film was also measured to be 0.013 .

The single crystal film was evaluated for its Faraday rotation angle at a wavelength of 1.55 μm, its transmission loss at a Faraday rotation angle of 45 degrees, and its temperature characteristics, namely, its Faraday rotation coefficient was 0.113deg/μm, its transmission loss was 0.02dB, and its temperature characteristics were 0.096 deg/deg.C, in the same manner as in example 1. The single crystal film has a thermal expansion coefficient of 1.05X 10^-5V. C. The difference between the thermal expansion coefficients of the base substrate and the single crystal film was 0.02X 10^-5V. C. And no cracks occurred in the obtained single crystal film.

Evaluation of

According to examples 1 to 4, as shown in fig. 5A, the single crystal film was uniformly grown, the crystal surface was smooth and glossy, and on the contrary, if the reaction occurred at the interface between the grown film and the substrate according to comparative example 1, the single crystal film could not be uniformly grown, and partial exfoliation was observed.

The embodiments and examples described above are all illustrative of the present invention, and are not intended to limit the present invention, and the present invention may be implemented by various other embodiments and modifications.

Claims (13)

1. A substrate for forming a magnetic garnet single crystal film for the purpose of liquid phase epitaxial growth of a magnetic garnet single crystal film, comprising,

substrate comprising garnet-based single crystal unstable to molten solution used for liquid phase epitaxial growth, and method for producing the same

A buffer layer formed on the substrate and formed of a garnet-based single crystal film stable to the molten solution.

2. The substrate for forming a magnetic garnet single crystal film according to claim 1, wherein the molten solution contains lead oxide and/or bismuth oxide as a main component.

3. The substrate for forming a magnetic garnet single crystal film according to claim 1 or 2, wherein the substrate has a thermal expansion coefficient substantially equal to that of the magnetic garnet single crystal film.

4. The substrate for forming a magnetic garnet single crystal film as set forth in claim 3, wherein the coefficient of thermal expansion of the substrate is within the range of. + -. 2X 10 relative to the coefficient of thermal expansion of the magnetic garnet single crystal film in the temperature range of 0 ℃ to 1000 ℃^-6Lower range of/° c.

5. The substrate for forming a magnetic garnet single crystal film according to any one of claims 1 to 4, wherein the substrate has a lattice constant substantially equal to that of the magnetic garnet single crystal film.

6. The substrate for forming a magnetic garnet single crystal film according to claim 5, wherein the lattice constant of the substrate is within a range of ± 0.02  or less with respect to the lattice constant of the magnetic garnet single crystal film.

7. The substrate for forming a magnetic garnet single crystal film according to any one of claims 1 to 6, wherein the substrate base plate contains Nb or Ta.

8. The substrate for forming a magnetic garnet single crystal film according to any one of claims 1 to 7, wherein the buffer layer is a magnetic garnet single crystal film substantially free of Nb and Ta.

9. The substrate for forming a magnetic garnet single crystal film according to any one of claims 1 to 8, wherein the buffer layer is formed of the general formula R₃M₅O₁₂(wherein R is at least one rare earth metal, and M is 1 selected from Ga and Fe), or

And X replaces gadolinium-gallium garnet (wherein X is at least 1 of Ca, Mg and Zr).

10. The substrate for forming a magnetic garnet single crystal film according to any one of claims 1 to 9, wherein the buffer layer has a thickness of 1 to 10000nm, and the substrate base has a thickness of 0.1 to 5 mm.

11. A method for producing a magnetic garnet single crystal film, comprising the step of growing a magnetic garnet single crystal film on the buffer layer by a liquid phase epitaxial growth method using the substrate for forming a magnetic garnet single crystal film according to any one of claims 1 to 10.

12. A method for producing an optical element, comprising the step of forming an optical element made of the magnetic garnet single crystal film by forming the magnetic garnet single crystal film by the method for producing a magnetic garnet single crystal film according to claim 11 and then removing the base substrate and the buffer layer.

13. An optical element obtained by the method for producing an optical element according to claim 12.