KR100876540B1 - Heat-Assisted Magnetic Recording Head Using Diffraction Grating Thin Film Pattern - Google Patents

Abstract

The present invention relates to a heat assisted magnetic recording head using a diffraction grating thin film pattern, and more particularly, to improve the transmission efficiency of near field light by using a physical phenomenon called surface plasmon by a nano slit and a diffraction grating structure. The present invention relates to a heat assisted magnetic recording head using a diffraction grating thin film pattern to overcome the limitation of the amount of light required for use as a heat source.

To this end, the present invention includes a diffraction grating thin film pattern characterized in that it comprises a diffraction grating structure installed using a micromachining process including a semiconductor process between the magnetic head substrate and the reproduction head or between the reproduction head and the recording head. Provide an auxiliary magnetic recording head.

Description

Heat Assisted Magnetic Recording Head using Grating Structure

1 is a view showing an embodiment of a magnetic recording head using a diffraction grating thin film pattern according to the present invention,

2 is a cross-sectional view of the front, top and bottom of the diffraction grating structure according to the embodiment of the dual diffraction grating and the single diffraction grating structure according to the present invention,

3 is an exploded perspective view showing a heat assisted magnetic recording head in consideration of the processing method of the embodiment according to the present invention;

4 is a view for explaining the optimization of the nano slit size and the polarization effect of the incident light according to the experimental example of the present invention,

FIG. 5 shows the optimum material and thickness of the material through the effect of light loss by applying the actual material to the nano slit optimized in FIG.

6a and 6b show the optimization of the diffraction pattern according to the incident beam for the Au thin film and the Ag thin film and the increase of the high light transmission effect and the decrease in the spot size when the diffraction grating pattern of the present invention is applied,

FIG. 7 is a table showing comparison results of light transmission effects and total results according to the present experimental example when the dual diffraction grating pattern is applied.

<Description of the symbols for the main parts of the drawings>

101: ABS substrate 102: Shield 1

103: shield 2 104: writing coil

105: sub yoke 106: play head

107: light transmission system 108: main pole

109: return yoke 110: SiO ₂ protective layer

111: light transmission path 112: incident light

113: diffraction grating pattern 202: diffraction grating structure

203: emitting light 114,204,206: nano slit

205,207 Diffraction pattern 301 Al ₂ O ₃ -TiC substrate

302: SiO ₂ 303: diffraction grating

304: optical waveguide system 305: conventional magnetic head system

401: change in peak intensity along the y direction (height)

402: change in peak intensity along the x direction (width)

403: Near field distribution and peak intensity in the optimized slit (50 nm x 300 nm)

 Spot size

501: Effect of peak intensity on the thickness of Au and Ag materials

502: Near field distribution and peak intensity and spot size at optimized thickness

601: change of peak intensity according to pitch of diffraction pattern in Au material

602: Change of peak intensity with width of diffraction pattern in Au material

603: Change of Peak Intensity with Depth of Diffraction Pattern in Au Material

604: Optimized diffraction pattern schematic and peak intensity and spot size in Au materials

605: Change of Peak Intensity with Pitch of Diffraction Pattern in Ag Material

606: Change of Peak Intensity with Width of Diffraction Pattern in Ag Material

607: Peak Intensity Variation with Depth of Diffraction Pattern in Ag Material

608: Optimized Diffraction Pattern Schematic, Peak Intensity, and Spot Size in Ag Materials

701: first exemplary structural diagram of a dual diffraction grating pattern structure

702: change in peak intensity according to the distance between both sides of Au and Ag

The present invention relates to a heat-assisted magnetic recording head using a diffraction grating thin film pattern, and more particularly, to improve the transmission efficiency of near-field light using a physical phenomenon called surface plasmon by a nano slit and a diffraction grating structure to use as a heat source. The present invention relates to a heat assisted magnetic recording head using a diffraction grating thin film pattern capable of overcoming the limitation of the amount of light required for the purpose.

In the conventional magnetic recording method, information such as voice or image is recorded on a magnetic recording medium coated with a fine magnetic material by aligning micro magnets having a length and intensity corresponding to a signal waveform, and reading a signal from the recorded medium. Refers to a technique for reproducing information such as an image.

In the magnetic recording, the strength of the signal is the strength of magnetization, the polarity of the signal is recorded as the direction of the magnet, and the frequency is recorded as the length of the magnet.

The current magnetic recording apparatus has reached the physical limit of the superparamagnetic limit, and a vertical magnetic recording method has emerged as a solution.

The vertical magnetic recording technique is a technique in which magnetic information is arranged vertically on the media of a hard disk, and it is a technique that makes it possible to record more information in the same area as compared with a recording method in a horizontal plane.

Currently, Seagate Corp. has released 750GB hard disk using this technology.

However, the vertical magnetic recording method has only extended the superparamagnetism limit and is not a way to overcome it fundamentally. Therefore, new technologies are needed to overcome the superparamagnetism limitation and to produce a hard disk having a terabyte recording storage capacity.

Several technologies will be required to achieve ultra-high density recording capacity, but the fundamental technical issue is to increase the unit recording density.

For this purpose, materials with extremely high magnetic anisotropy constants (ku, which vary in the thermodynamic amount in accordance with the direction of magnetization to the crystal axis in magnetic crystals) are used as the media material. Must be available.

If only the volume of crystal grains is small, as ΔE = kuV, the energy barrier ΔE, which must be overcome in order for the particle to be reversed, becomes smaller. Therefore, thermal fluctuations overcome anisotropic energy spontaneously magnetization without an external magnetic field due to thermal energy fluctuations. The superparamagnetic limit is encountered when reversal occurs.

In other words, the ultraparamagnetic limit means that the crystal size of the storage medium should be 5 nm or less in consideration of securing the data retention stability and signal to noise ratio (SNR) of the ultra fine grain media to achieve the terabyte information storage capacity. In the small magnetic domain, the magnitude of the potential energy barrier (energy to maintain magnetism) between the north pole and the south pole is the same as the thermal energy at room temperature.

Therefore, in order to achieve an ultra-high density recording capacity, a material having a high magnetic anisotropy constant as well as a volume reduction of crystal grains is required.

At this time, the high magnetic anisotropy constant not only increases the magnetic anisotropy energy but also increases the coercive force (Hc, coercivity: the strength of the magnetic field that causes the magnetization of the magnetic body to become zero by applying an inverse magnetic field to the magnetized magnetic body). Done.

If this value exceeds the magnetic head can record (the maximum flux = 2.5T that the magnetic head can produce), the magnetic head alone cannot generate the magnetization reversal of the crystal grains, making it impossible to record on the media.

A technique that overcomes this problem is a heat assisted magnetic recording (HAMR), which is a hybrid method in which near field light and magnet are fused to be used for recording by heat assisted by light.

In other words, the head uses light as a heat source while the information is stored in the media, temporarily raising the temperature of the media sufficiently to lower the ku of the media, making the coercivity close to zero, and enabling recording.

There are several technical issues in the HAMR method, the most important of which is the partial heat transfer to a small recording area along a magnetic field having a small resolution.

In this case, for terabyte recording densities, the spot of light should not be larger than the bit size, so a high light output close to 1 mW is required at a beam size of several nanometers.

The very small sized beam below this half wavelength enters the near field region by the diffraction limit of the light. At this time, high light output cannot be obtained because the emission time is very short and the intensity of the light decreases rapidly due to the characteristics of the near field light.

One way to overcome this is surface plasmon effect. Surface plasmon is a phenomenon in which charged particles excited on a metal surface vibrate when electromagnetic waves are incident on the metal surface from the outside, and a surface plasmon wave is formed due to the collective vibration of the plasmon.

Plasmon waves have the property of propagating onto a surface without propagating from inside or outside the metal surface. Metals exhibiting this phenomenon are mainly used for metals that have a negative dielectric constant and are easy to emit electrons by external stimuli such as gold, silver, copper, aluminum, and the like. Silver with the sharpest SPR resonance peaks and gold with excellent surface stability are commonly used.

Excitation of surface plasmons is caused by the application of an electric field to two medium interfaces with different dielectric functions from the outside, that is, the interface between metal and dielectric, which induces surface charges due to the discontinuity of the electric component perpendicular to the two medium interfaces. Oscillations appear as surface plasmon waves.

In this case, the use of the diffraction grating may exhibit stronger surface plasmon excitation, which has been studied in various fields. Among them, in particular, it has been studied as an important method to solve the problem of low light efficiency characteristic of near field light, which is the only method that can simultaneously obtain various optical information with high resolution that overcomes the diffraction limit.

One means of utilizing the surface plasmon effect is a light transmission system of a heat assisted magnetic recording apparatus that can overcome the superparamagnetic limit and obtain high near field light output at a small beam size of several nanometers.

The heat-assisted magnetic recording head requires a light transmission system and a magnetic recording head, and a representative problem in the implementation of the heat-assisted magnetic recording method is that a high amount of light close to 1 mW in a nano-sized beam as a heat source is required. The coupling system of the head and the light transmission is difficult.

In order to form the beam size below the diffraction limit (λ / 2), many researches have been conducted on the optical element of the aperture type through which small holes are made in the metal probe to transmit light and the transmission efficiency according to the shape of the aperture.

However, the optical element of such a structure is difficult to manufacture as a heat assisted magnetic recording head when the transmission efficiency, i.e. the amount of transmitted light is so small, that it is difficult to obtain the amount of energy required for actual recording or high transmission efficiency according to the shape of the opening.

The present invention has been made in view of the above, and minimizes the size of the exit beam using the nano slit, and optimizes the width and height of the nano slit primarily by using the polarization effect with the incident beam By improving the output light efficiency of near-field light and improving the transmission efficiency of near-field light emitted through the nanoslit by using the surface plasmon effect by the diffraction grating, ultra-sized light having high light transmission efficiency can be realized and air It is manufactured in the vertical direction on the lubricating surface (hereinafter referred to as ABS), and can be applied to both the horizontal magnetic recording method and the vertical magnetic recording method, and it is easy to manufacture by using the existing semiconductor process, and to the current magnetic head structure. It is an object of the present invention to provide a heat assisted magnetic recording head using an applicable diffraction grating thin film pattern.

The present invention for achieving the above object is a heat assisted magnetic recording head,

And a diffraction grating structure fabricated using a micromachining process including a semiconductor process between the magnetic head substrate and the reproduction head or between the reproduction head and the recording head.

In a preferred embodiment, the depth, width, distance between gratings, the number and length of gratings (patterns) of the diffraction gratings are expressed as a function of the conditions of the incident light, and are interpreted by the finite difference element method to determine the optimal diffraction pattern for each condition. Characterized in that implements.

In a more preferred embodiment, the diffraction grating is formed on one surface to increase the surface plasmon effect at the incident surface.

In addition, the diffraction grating is formed on both sides to increase the surface plasmon effect on the incident surface.

In addition, the nano slit is formed through the diffraction grating in the advancing direction of the incident light or processed in the form of a hole in the center portion of the pattern, the slit shape is designed and manufactured in consideration of the polarization effect of the incident light and the characteristics of the incident light do.

In addition, the nano slit is designed with an optimal structure for maximum light efficiency, and has any one of rectangular, non-rectangular polygonal, circular, oval, and non-circular shape, and penetrates the entire thickness or the central portion of the thin film pattern. It is characterized by being formed.

In addition, the diffraction grating structure material is characterized by being deposited with a precious metal containing gold or silver in the metal for the excitation of the surface plasmon.

In addition, in order to eliminate the light loss from the incident light to the diffraction grating on the top of the diffraction grating is characterized in that the light transmission path is laminated.

In addition, the optical transmission path is characterized in that the low refractive index material is installed on both sides of the material having a high refractive index, and the total reflection effect due to the difference in the refractive index is used.

In addition, the material of the diffraction grating structure is characterized in that the optimum thickness is determined according to the incident wavelength.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a view showing an embodiment of a magnetic recording head using a diffraction grating thin film pattern according to the present invention.

The upper figure shows the present invention applied to the existing magnetic recording head, and the lower figure shows the structure of the present invention.

The existing magnetic recording head receives the current from the write coil 104 by the return yoke 109 and the main pole 108 to form the N pole and the S pole, and records the subpole. The sub yoke 105 induces a magnetic field by metal. To be used.

Shield 1 102 and shield 2 103 are manufactured for protection in consideration of external influences during regeneration, and use magnetoresistance due to electromagnetic induction.

In the case of the vertical magnetic recording method, since the head shape after the playhead is deformed to fit the vertical media, the present invention can be applied to both the horizontal magnetic recording and the vertical magnetic recording methods.

The diffraction grating of the present invention is fabricated by coating an SiO ₂ protective layer 110 in an oxidation process in a direction perpendicular to the ABS substrate 101 of the magnetic recording head, and patterning the diffraction grating pattern using the semiconductor process thereon. do.

The diffraction grating 113 has a resonance structure different according to incident conditions such as the wavelength and the size of the incident light 112, and thus the depth, width, spacing between patterns, the number and length of the patterns vary depending on the incident conditions. Is optimized.

That is, since the Gaussian beam (laser beam) is incident not only when the incident light is performed as parallel light but also in actual application, the diffraction gap pattern optimized according to the incident angle of the Gaussian beam and the degree of focusing focus may vary.

The material of the diffraction grating is preferably made of gold and silver for effective excitation of the surface plasmon, and it has been experimentally found that the material showing the highest peak is silver. A diffraction grating 113 is fabricated and a light transmission path 111 of incident light 112 is fabricated thereon.

The optical transmission path 111 is to eliminate the light loss until the incident light 112 reaches the diffraction grating structure. The method uses the total reflection effect due to the difference in refractive index. Materials having a low refractive index on both sides of the material having a high refractive index are manufactured in consideration of the thickness of the thin film. The SiO ₂ layer is again applied thereon, and the planarization operation is performed through the CMP process.

The conventional magnetic head process is performed on the structure of the present invention thus fabricated to insert a light transmission system into the existing magnetic head structure.

In the recording method, the beam passing through the nano slit 114 first heats the recording area to temporarily increase the temperature of the media sufficiently to reduce the Ku of the media, and then the magnetic field of the magnetic head and the beam are perpendicular to minimize the recording area. Information is recorded on a magnetic region corresponding to a portion intersecting with and the reproduction head reproduces the information.

2 is a cross-sectional view of the diffraction grating 202. As described above, the width and height of the diffraction grating and the distance between the gratings can be expressed as a function according to the conditions of the incident light 201. The optimal diffraction pattern for each wavelength is analyzed by the finite difference element method. ) Can be implemented.

The diffraction grating 202 of the present invention may have a diffraction grating pattern on both the front and the back, or only on the front side, in particular by placing the rotating grating pattern on the front and back, as well as the surface plasmon effect at the incident surface as well as the light in the interior. Efficiency by tunneling and diffraction gratings was maximized.
Here, the front of the light reaches the front side, the side through which the light is transmitted is defined as the rear with respect to the traveling direction of the incident light.

Although the shape of the diffraction grating pattern of the diffraction grating is shown as a rectangular cross section of irregularities, the shape of the upper and lower surfaces, the symmetry or asymmetry of the diffraction grating pattern, the gap between both sides, and the shape of the lower pattern according to the incident light conditions It may include.

The nano slits 204 and 206 are manufactured perpendicular to the polarization direction of the incident light 201 in consideration of the incident wavelength and the polarization direction of the incident light 201, and may reduce light loss in the square and circular openings.

3 is an exploded perspective view of a dual diffraction grating and a single diffraction grating. The SiO ₂ 302 layer is placed on the Al ₂ O ₃ -TiC substrate 301 and the double diffraction grating 303 which is the structure of the present invention is patterned thereon.

Thereafter, the optical waveguide system 304, which is a thin film stack structure, is manufactured to effectively transmit incident light, thereby fabricating a simple structure and easy control of the spot diameter. After the CMP process, the existing magnetic head process is finally performed.

Experimental Example

4, 5, and 6 are experimental examples of the present invention, in the case of a single nanoslit without a diffraction grating in order, the effect of the actual material, including the diffraction grating. 4 and 5 proceeded to be comparable with the result of FIG. 6.

The experiment used Remcom's XFDTD program, a commercialization program of the finite-difference time element method (FDTD), which has been proven reliable in many papers.

The incident light was assumed to travel in the z direction as x-polarized parallel light having a wavelength of 632.8 nm, which is the wavelength of the He-Ne laser, and the calculation area size was Δx = Δy = Δz = 5nm. The measurement surface was measured at 50 nm away from the emission surface. Since the actual metal film cannot be assumed to be a PEC (Perfect Magnetic Conductor) whose conductivity is infinite, a modified Debye model is used.

4 is an experiment to examine the polarization effect of the incident beam according to the width (width) and length (height) length of the nanoslit. The ideal material, PEC, was used to exclude the effect of the material and only consider the effect of nano slit size.

In the experiment, first, the width (width) was fixed to 100 nm, and then the peak value was found by changing the height (height) (401). The width (width) was finally changed based on the height (height) value at this time, and finally the nano slit. The horizontal (width) and vertical (height) sizes of were optimized (402).

Peak intensity (E2) showed the highest peak at 50 nm in width and 300 nm in length, and the shape of the spot can be known from the near field distribution, and the spot size in the x and y directions is determined by FWHM calculation. 110 nm x 135 nm can be obtained (403).

As can be seen from the graph, it can be seen that the influence of the incident light on the vertical direction is much greater than the size of the polarization direction and the horizontal direction, thereby confirming the polarization effect by the nanoslit.

5 is a simulation of applying the gold (Au) and silver (Ag) film to the slit size optimized in Figure 4 to see the effect of the thickness and material of the actual metal. Au was optimized at 190nm thickness and Ag at 210nm (501).

In the case of the Au film, the peak intensity was 3.83, and the spot size was 130 nm in the x direction and 195 nm in the y direction. In the case of Ag film, the peak intensity was 4.49, and the spot size was 130 nm in the x direction and 185 nm in the y direction (502).

Through this experiment, it can be seen that when the actual metal is used, the amount of emitted light is very small due to the loss of the metal itself, and Ag has a better surface plasmon effect.

6A and 6B apply a diffraction grating pattern to the models tested in FIGS. 4 and 5.

FIG. 6A shows a result of optimizing a diffraction pattern using a single diffraction grating for an Au film, and the diffraction pattern was optimized at a pitch of 450 nm (601), a width of 190 nm, and a depth of 80 nm. As a result, the peak intensity was 18.24 and the spot size was 105 nm in the x direction and 135 nm in the y direction.

Figure 6b is the result of optimizing the diffraction pattern of the Ag film, the diffraction pattern is optimized at a pitch of 450nm, 210nm width, 90nm height, the resulting value is 20.26 peak intensity, 105nm spot size, 120 nm of y-directions were obtained.

In both cases, an increase in light quantity of about 5 times and beam spot size reduction of 30% were obtained when a diffraction grating was present.

7 is an example when a dual diffraction grating is applied. This experiment is the first experimental example, but the pattern shape of both sides is kept the same but intersected and only the distance between the two sides is changed. In the case of the dual diffraction grating, the diffraction pattern is not yet optimized, but it is not an optimal result. However, the results of this experiment show the possibility of the influence of the dual diffraction pattern.

While the invention has been shown and described with respect to certain preferred embodiments thereof, the invention is not limited to these embodiments, and has been claimed by those of ordinary skill in the art to which the invention pertains. It includes all the various forms of embodiments that can be carried out without departing from the spirit.

As described above, according to the heat-assisted magnetic recording head using the diffraction grating thin film pattern according to the present invention, the heat-assisted magnetism is obtained by using a diffraction grating pattern which has high light transmission efficiency and can realize fine focus below the diffraction limit. It is possible to provide a sufficient heat source of the recording method, and to achieve a heat assisted magnetic recording apparatus that is easy to manufacture and apply.

Claims (10)

delete delete delete delete A heat assisted magnetic recording head, A diffraction grating manufactured by patterning a diffraction grating pattern by using a semiconductor process between the magnetic head substrate and the playhead or between the playhead and the recording head, wherein a diffraction grating pattern is formed on the front surface of the diffraction grating to be incident A heat-assisted magnetic recording head using a diffraction grating thin film pattern, which enhances the surface plasmon effect on the surface, and wherein the diffraction grating is formed with nano slits penetrating in the direction of incident light. The method according to claim 5, The nano-slit has a heat-assisted magnetic recording head using a diffraction grating thin film pattern, characterized in that having a shape of any one of rectangular, polygonal, circular, oval. delete delete delete delete

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