JP2005070101A - Magnetooptical spatial light modulator and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To process a large amount of information at a high speed since an inter-pixel distance can be shortened and the amount of information per unit area can be increased. <P>SOLUTION: In the magnetooptical spatial light modulator, many pixels 14 whose magnetization direction can be set independently of one another and which rotate incident light by Faraday effect in polarization directions corresponding to the magnetization direction are arrayed and formed in a magnetic garnet film 12 through local heat treatment in two dimensions. The modulator is equipped with light reflecting films 16 and XY driving lines for controlling the magnetization directions of the respective pixels. The light reflecting films are formed individually for every area corresponding to the pixels to magnetically separate the respective pixels through the local heat treatment with stress applied by the light reflecting films, or the XY driving lines are formed in conformity with the external shape of each pixel to magnetically separate the respective pixels through the local heat treatment with stress applied by the XY driving lines. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a spatial light modulator that spatially modulates incident light using Faraday rotation of light by magneto-optical technology. More specifically, the present invention relates to a magneto-optical spatial light modulator in which pixels are magnetically separated from each other by a domain wall control technique of a magnetic garnet film using a local heat treatment and a stress application structure by an attached film, and the same. It relates to a manufacturing method.
[0002]
[Prior art]
[Patent Document 1]
US Pat. No. 5,473,466
The spatial light modulator is an element that can spatially change the intensity distribution, amplitude distribution, phase distribution, and polarization state distribution of light having a two-dimensional spread according to an external signal. A spatial light modulator in which a large number of pixels (pixels) are two-dimensionally arranged can process information in parallel at high speed. Therefore, research is being promoted as a key device for realizing optical computing, projector TV, optical volume recording, and the like. Yes.
[0004]
As a typical spatial light modulator, there are an element using liquid crystal technology, an element using MEMS (Micro-Electro Mechanical System) technology such as a membrane mirror, and an element using magneto-optical technology. However, the spatial light modulator using the liquid crystal technology has a problem that the operation speed is slow, and the spatial light modulator using the MEMS technology has a problem in terms of reliability because it has a mechanical driving portion.
[0005]
As described above, in fields such as optical information processing and computer-generated holograms, it is necessary to process a large amount of information at high speed, so a spatial light modulator requires a high operating speed and high reliability. Has been. Therefore, recently, a spatial light modulator using a magneto-optical technique which is excellent in such a point has been vigorously researched and developed.
[0006]
For example, Patent Document 1 discloses an example of a spatial light modulator using a magneto-optical technique. The magneto-optical spatial light modulator is made of a magneto-optical material and has a plurality of pixels that can independently select the direction of magnetization. Each pixel forms an oxidizable film pattern such as Si in the area corresponding to the pixel on the magnetic garnet material, and heat-treats the whole to reduce and alter the magnetic garnet material directly under the Si film. Thus, a plurality of pixels capable of magnetization reversal are formed. Then, due to the Faraday effect, the polarization direction of light passing through each pixel is rotated by a predetermined angle in opposite directions. Therefore, in such a magneto-optical spatial light modulator, spatially modulated light can be generated by arbitrarily selecting the direction of magnetization in each pixel.
[0007]
[Problems to be solved by the invention]
However, as in Patent Document 1, if the entire magnetic garnet material is heat-treated using an oxidizable film such as Si, the periphery of the Si film is also reduced due to thermal diffusion, so the outline of each pixel becomes unclear, The pixel size also varies. Therefore, a large distance between pixels must be taken. When the inter-pixel distance is increased, the amount of information per unit area is reduced, so that it is not suitable for use in processing a large amount of information at high speed.
[0008]
An object of the present invention is to provide a magneto-optical spatial light modulator that can reduce the distance between pixels, increase the amount of information per unit area, and can process a large amount of information at a high speed, and a manufacturing method thereof. Another object of the present invention is to provide a magneto-optical spatial light modulator that can achieve a reduction in device size and a reduction in current consumption because a bias magnetic field is not required and can be driven only by a pulse current.
[0009]
[Means for Solving the Problems]
In the present invention, in a magnetic garnet film, a magnetization direction can be set independently of each other, and a number of pixels that rotate the polarization direction according to the magnetization direction with respect to incident light by a Faraday effect are two-dimensionally formed by local heat treatment. In the spatial light modulator provided with the light reflecting film and the XY drive line for controlling the magnetization direction of each pixel, the light reflecting film is formed individually for each region corresponding to each pixel, The magneto-optical spatial light modulator is characterized in that each pixel is magnetically separated by heat treatment and stress applied by the light reflecting film.
[0010]
In the present invention, the magnetic direction can be set independently in the magnetic garnet film, and a large number of pixels that can rotate the polarization direction corresponding to the magnetization direction with respect to the incident light by the Faraday effect are two-dimensionally arranged by local heat treatment. In the spatial light modulator formed and provided with the light reflecting film and the XY drive line for controlling the magnetization direction of each pixel, the XY drive line matches the outer shape of each pixel and goes around the inside of the pixel. The magneto-optical spatial light modulator is characterized in that each pixel is magnetically separated by the local heat treatment and the stress applied by the XY drive line.
[0011]
Of course, by combining both of these techniques, the light reflecting film is individually formed for each region corresponding to each pixel, and the XY drive line is formed so as to match the outer shape of each pixel and go around the inside of the pixel. Each pixel may be magnetically separated by the heat treatment and the stress applied by the light reflecting film and the XY drive line.
[0012]
When a groove is formed by dry etching between each pixel of the magnetic garnet film, the stress due to the film is efficiently concentrated in the groove, and the magnetic separation effect between each pixel by applying the stress becomes clearer. Therefore, it is preferable.
[0013]
As the magnetic garnet film, a Bi-substituted rare earth iron garnet LPE (liquid phase epitaxial) film, for example, when light having a wavelength of 500 to 700 nm, particularly preferably light having a wavelength of 520 to 540 nm is incident, has a Faraday rotation angle of 5 to 5. What has the characteristic which becomes 25 degree | times and absorption loss becomes 20 dB or less is preferable.
[0014]
In the present invention, an infrared absorption film is formed on each pixel formation region of the magnetic garnet LPE film, and a plurality of pixels are two-dimensionally formed by performing local heat treatment by irradiating infrared rays from above. After removing the infrared absorbing film, a light reflecting film is formed in each region corresponding to each pixel and stress is applied, and each pixel is magnetically separated by the local heat treatment and the stress applied by the light reflecting film. A method of manufacturing a magneto-optical spatial light modulator characterized by having a structure as described above.
[0015]
Furthermore, in the present invention, an infrared absorption film is formed on each pixel formation region of the magnetic garnet LPE film, and a plurality of pixels are two-dimensionally formed by irradiating infrared rays from above to perform local heat treatment. After removing the absorbing film, a light reflecting film is formed on the entire surface, and a resist layer is patterned for each region corresponding to each pixel. Using this as a mask, the light reflecting film between the pixels is removed by a dry etching method to be independent. A magneto-optic having a structure in which each pixel is magnetically separated by a local heat treatment and a stress applied by the light reflecting film. It is a manufacturing method of a type spatial light modulator.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is an explanatory view showing an example of a magneto-optical spatial light modulator according to the present invention, in which A represents a plane and B represents a cross section. Here, the spatial light modulator 10 includes a large number of rectangular pixels in a magnetic garnet film 12 grown by an LPE method on a GGG (gadolinium gallium garnet) or SGGG (scandium gadolinium gallium garnet) substrate 11. 14 are arranged in a two-dimensional manner (regularly in length and breadth), and a rectangular light reflection film 16 having substantially the same shape as the pixel is formed at a position corresponding to each pixel 14 on the magnetic garnet film 12. Structure. Although not shown here, an XY drive line (not shown) for controlling the magnetization direction of each pixel is provided on the light reflecting film via an insulating film. In the cross-sectional view shown in B, the lower surface is the light incident / exit surface. Incident light passes through the GGG (or SGGG) substrate 11, is Faraday rotated at the pixel 14, is reflected by the light reflecting film 16, increases Faraday rotation at the pixel 14, and passes through the GGG (or SGGG) substrate 11. Then exit.
[0017]
Each pixel 14 can set the direction of magnetization independently, and applies rotation of the polarization direction corresponding to the direction of magnetization to incident light by the Faraday effect, and is formed by subjecting only the pixel formation region to local heat treatment. . The specific manufacturing process is shown in FIG. The magnetic garnet film is, for example, a Bi-substituted rare earth iron garnet film, and is formed by liquid phase epitaxial growth on a GGG substrate or SGGG substrate as described above. In the following drawings, illustration of the GGG (or SGGG) substrate is omitted.
(A) An infrared absorption film 18 made of Si or the like is formed only in the pixel formation region on the surface of the magnetic garnet film 12.
(B) Then, infrared (IR) irradiation is performed. As a result, the infrared absorption film 18 absorbs infrared rays, and only the region immediately below is heated, and necessary local heat treatment is performed. As a result, the magnetic anisotropy is lowered due to movement of Bi and Ga sites in the crystal, and saturation magnetization is generated. Local characteristic changes such as changes occur. A region where the characteristic change occurs is a pixel 14.
(C) Thereafter, the infrared absorbing film is removed.
(D) A light reflecting film 16 made of Al or the like is individually formed in an island shape for each region corresponding to the formed pixel.
[0018]
The light reflecting film 16 is typically made of Al or the like having a high reflectance, and is individually formed over the entire region corresponding to each pixel 14. The light reflecting film 16 also serves as a stress applying film, and applies stress to a portion (between pixels) where the light reflecting film is not attached. In the present invention, not only the pixels are formed by the local heat treatment, but also the pixels are magnetically separated from each other by the stress applied intensively between the pixels by the light reflecting film. An isolated magnetic domain structure is formed, which has one feature. With such a configuration, the inter-pixel distance can be reduced to a pixel size or less, particularly 2 μm or less.
[0019]
An example of the driving means of the spatial light modulator is shown in FIG. In the spatial light modulator 10, an X drive line is formed so as to pass in the vicinity of each pixel in the row direction (lateral direction), and a Y drive line is formed so as to pass in the vicinity of each pixel in the column direction (vertical direction). Yes. An X side drive pulse current is supplied from the X drive unit 22 to each X drive line, and a Y side drive pulse current is supplied from the Y drive unit 24 to each Y drive line. Then, the magnetization direction of the pixel located at the intersection of the selected X drive line and Y drive line is inverted and controlled by the XY composite pulse current. The operations of the X drive unit 22 and the Y drive unit 24 are controlled by the control unit 26.
[0020]
In such a spatial light modulator 10, one surface (the surface opposite to the light reflection film forming surface) is a light incident / exit surface. The light incident on the spatial light modulator 10 is spatially modulated and emitted. The light emitted from the spatial light modulator 10 may be used as it is as shown in A, or the light emitted from the spatial light modulator 10 is used after passing through the analyzer 28 as shown in B. May be.
[0021]
An example of the XY drive line is shown in FIG. Assume that pixels 14 are arranged as shown in FIG. Here, in order to simplify the drawing, only four pixels are shown. Each pixel 14 has a square shape with a vertical and horizontal dimension a = 16 μm, and is separated from adjacent pixels by a distance b = 2 μm. B shows the shape of the X drive line 30, C shows the shape of the Y drive line 32, one by one, and D shows the superimposed state. Here, both the X drive line 30 and the Y drive line 32 have a width c = 4 μm. The X drive line 30 and the Y drive line 32 are formed so as to fit inside the pixel 14 and match the outer shape of the pixel 14 so that each pixel 14 makes a 3/4 turn. It is provided to connect.
[0022]
A laminated state of the XY drive lines 30 and 32 is shown in E of FIG. After the light reflecting film 16 is formed on the magnetic garnet film 12, the first insulating film 34 is provided on the entire surface, and the X drive line 30 is provided thereon. Further, the second insulating film 36 is provided on the entire surface, and the Y drive line 32 is provided thereon. Finally, the entire surface is covered with a protective film 38.
[0023]
When the XY drive lines are formed in such a pattern, the XY drive lines 30 and 32 can function as a stress application film. By the XY drive lines 30 and 32, the stress applied between the pixels of the magnetic garnet film also contributes to the magnetic separation between the pixels, thereby further clarifying the isolated magnetic domain structure in units of pixels. Can do.
[0024]
Further, although not shown in FIG. 5, when grooves are formed between the pixels of the magnetic garnet film 12, the stress caused by the light reflecting film 16 and the XY drive lines 30 and 32 can be more efficiently concentrated between the pixels. . With such a configuration, the distance between pixels can be reduced to 1 μm or less.
[0025]
In the present invention, the magnetic domains are unified within each pixel. In the case of having a domain wall in one pixel (in the case of multi-domain), a bias magnetic field is required for magnetization reversal. As a result, the device size and current consumption increase, and there is a concern about heat generation. However, if one pixel is made into a single magnetic domain, a bias magnetic field is not required, and it can be driven only by a pulse current, thereby achieving a reduction in device size and a reduction in current consumption.
[0026]
【Example】
A preferred embodiment of a method for manufacturing a magneto-optical spatial light modulator according to the present invention is shown in FIG. 6A (Example 1) and B (Example 2).
[0027]
(Example 1)
(1-a) As the magnetic garnet film 12, a Bi-substituted rare earth iron garnet film having a thickness of about 3 μm formed on the GGG substrate by the LPE method is used. The film composition is Bi ₁ Y ₁ Gd ₁ Fe ₄ Ga ₁ O ₁₂ . First, an infrared absorption film (Si film) 18 is formed on the surface of a magnetic garnet film that is directly above a region where a pixel is to be formed.
(1-b) Infrared rays (IR) are irradiated from above the infrared absorption film 18. The infrared absorption film 18 absorbs infrared rays and heats the region immediately below. As a result, only the magnetic garnet film region immediately below the infrared absorption film 18 is subjected to local heat treatment, and the pixel 14 capable of independently selecting the magnetization direction is formed.
(1-c) Next, dry etching (for example, ion milling) is performed using the already provided infrared absorption film (Si film) 18 as a mask. This forms a trench 40 between the pixels.
(1-d) Then, the infrared absorption film (Si film) is removed by chemical etching.
(1-e) A light reflecting film (Al film) 16 is formed in a region corresponding to the pixel on the magnetic garnet film 12 by sputtering or vapor deposition. The light reflecting film 16 also functions as a stress application film.
[0028]
Thus, a light reflecting film (Al film) 16 is formed only on the pixel region of the magnetic garnet film 12 on which the pixels 14 are formed. In the process of Example 1, since the infrared absorption film (Si film) 18 is directly used as a mask when forming a groove by ion milling, there is an advantage that the mask formation process can be omitted.
[0029]
(Example 2)
(2-a) As the magnetic garnet film 12, a Bi-substituted rare earth iron garnet film having a thickness of about 3 μm formed on the GGG substrate by the LPE method is used. First, an infrared absorption film (Si film) 18 is formed on the surface of a magnetic garnet film that is directly above a region where a pixel is to be formed.
(2-b) Infrared rays (IR) are irradiated from above the infrared absorption film 18. The infrared absorption film 18 absorbs infrared rays and heats the region immediately below. As a result, only the magnetic garnet film region immediately below the infrared absorption film 18 is subjected to local heat treatment, and the pixel 14 capable of independently selecting the magnetization direction is formed.
(2-c) Then, the infrared absorption film (Si film) is removed by chemical etching.
(2-d) Next, an Al film 42 is formed on the entire surface of the magnetic garnet film 12 by sputtering or vapor deposition, and a resist layer 44 is formed in a region corresponding to the pixel thereon.
(2-e) Ion milling is performed using the resist layer 44 as a mask, leaving a region corresponding to the pixel 14 as the light reflecting film 16, removing an unnecessary Al film portion between the pixels, and further performing ion milling to form a pixel. A groove 40 is formed between them.
(2-f) The remaining resist layer is removed. The light reflection film 16 on the magnetic garnet film 12 also functions as a stress application film.
[0030]
Thus, a light reflecting film (Al film) 16 is formed only on the pixel region of the magnetic garnet film 12 on which the pixels 14 are formed. The process of Example 2 has an advantage that the process can be simplified because the formation of the light reflection film and the groove can be performed continuously by ion milling.
[0031]
After the light reflecting film 16 is formed in the first and second embodiments, an SiO ₂ insulating film is formed on the entire surface, and an X drive line is formed on the SiO ₂ insulating film on the entire surface. As shown in FIG. 5, the X drive line is a spelled Al film that matches the outer shape of the pixel on the pixel region, and is formed by sputtering or vapor deposition. Further, a SiO ₂ insulating film is formed on the entire surface, and a Y drive line is formed thereon in the vertical direction. As shown in FIG. 5, the Y drive line is also a spell-folded Al film that matches the pixel outline on the pixel region, and is formed by a sputtering method, a vapor deposition method, or the like. These XY drive lines also function as a stress application film. Finally, a SiO ₂ insulating film is formed over the entire surface as a protective film. In this way, a magneto-optical spatial light modulator is manufactured.
[0032]
Next, the result of observing the magnetic domain structure in the pixel will be described. Pixels of various sizes (4 to 50 μm) in which the pixels are magnetically separated from each other by the local heat treatment and the stress applied by the light reflection film were prepared on the magnetic garnet film. Then, the direction of magnetization of each pixel is arbitrarily reversed, and the difference in light transmission (ON, OFF) due to the difference in Faraday rotation of light is observed with a polarization microscope to determine whether or not the pixel has a single magnetic domain. Was judged.
[0033]
As a result, almost all the pixels were made into a single domain (single domain). That is, each pixel has a coercive force and has a single domain. Therefore, in such a state, a bias magnetic field is unnecessary, and magnetization can be reversed only by a pulse current, and it was confirmed that it is preferable as a spatial light modulator.
[0034]
【The invention's effect】
In the present invention, as described above, a magneto-optical type in which a light reflecting film is individually formed for each region corresponding to each pixel, and each pixel is magnetically separated by a local heat treatment and a stress applied by the light reflecting film. An XY drive line is formed to match the spatial light modulator or the outer shape of each pixel, and each pixel is magnetically separated by local heat treatment and stress applied by the XY drive line. Since it is a spatial light modulator, it is possible to reduce the distance between pixels to less than the pixel size, especially about 2 μm or less, increase the amount of information per unit area, and process a large amount of information at high speed. It becomes.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram showing an example of a spatial light modulator according to the present invention.
FIG. 2 is an explanatory view showing an example of the manufacturing process.
FIG. 3 is an explanatory diagram showing an example of a spatial light modulator and peripheral circuits.
FIG. 4 is a conceptual diagram showing an example of a usage state of a spatial light modulator.
FIG. 5 is an explanatory diagram showing an example of an XY drive line according to the present invention.
FIG. 6 is an explanatory view showing one embodiment of a manufacturing process of the spatial light modulator according to the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Spatial light modulator 11 GGG or SGGG board | substrate 12 Magnetic garnet film | membrane 14 Pixel 16 Light reflection film

Claims (6)

In the magnetic garnet film, a number of pixels that can independently set the magnetization direction and give rotation of the polarization direction according to the magnetization direction to the incident light by the Faraday effect are two-dimensionally arrayed by local heat treatment, In a spatial light modulator provided with a light reflecting film and an XY drive line for controlling the magnetization direction of each pixel,
The light reflecting film is formed separately for each region corresponding to each pixel, and each pixel is magnetically separated by the local heat treatment and the stress applied by the light reflecting film. Optical spatial light modulator. In the magnetic garnet film, a number of pixels that can independently set the magnetization direction and give rotation of the polarization direction according to the magnetization direction to the incident light by the Faraday effect are two-dimensionally arrayed by local heat treatment, In a spatial light modulator provided with a light reflecting film and an XY drive line for controlling the magnetization direction of each pixel,
The XY driving line is formed to match the outer shape of each pixel and go inside the pixel, and each pixel is magnetically separated by the local heat treatment and the stress applied by the XY driving line. A magneto-optical spatial light modulator. 2. The magnetism according to claim 1, wherein the XY drive line is formed so as to coincide with an outer shape of each pixel and go inside the pixel, and a stress applied by the XY drive line also contributes to magnetic separation between the pixels. Optical spatial light modulator. 4. The magneto-optical spatial light modulator according to claim 1, wherein a groove by dry etching is formed between each pixel of the magnetic garnet film. An infrared absorbing film is formed on each pixel formation region of the magnetic garnet LPE film, and a plurality of pixels are two-dimensionally arrayed by irradiating infrared rays from above to perform a local heat treatment, and the infrared absorbing film is removed. After that, a light reflecting film is formed for each region corresponding to each pixel and stress is applied, and each pixel is magnetically separated by the local heat treatment and the stress applied by the light reflecting film. A method of manufacturing a magneto-optical spatial light modulator. An infrared absorbing film is formed on each pixel formation region of the magnetic garnet LPE film, and a plurality of pixels are two-dimensionally arrayed by irradiating infrared rays from above to perform a local heat treatment, and the infrared absorbing film is removed. After that, a light reflecting film is formed on the entire surface, and a resist layer is patterned for each region corresponding to each pixel. Using this as a mask, the light reflecting film between the pixels is removed by dry etching to form an independent light reflecting film. A magneto-optical spatial light modulator having a structure in which a pixel is formed and a groove is formed between pixels, and each pixel is magnetically separated by a local heat treatment and a stress applied by a light reflecting film. Manufacturing method.

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