JP3826684B2 - Recording / reproducing apparatus using plasmons and manufacturing method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an information recording apparatus or recording / reproducing apparatus using light, and a manufacturing method thereof.
[0002]
[Prior art]
In optical recording, a laser beam is condensed as a small spot on a medium by a lens, and a characteristic is recorded by changing characteristics of a minute region of the medium by heat or light reaction generated thereby. When this method is used, the size of the spot diameter that can be collected is limited by the wavelength of the laser beam used for recording. Therefore, in order to write a smaller spot, a light source having a shorter wavelength has to be used.
[0003]
Further, as described in Applied Physics Letter 65 (1994), p. 388 (Appl. Phys. Lett. Vol. 65, p388 (1994)) and JP-A-5-189796, a solid immersion lens (solid An example of recording using an immersion lens) has been reported. When this lens is used, the numerical aperture of the lens can be increased in proportion to the square of the refractive index, so that light can be narrowed down to a region smaller than a normal lens.
[0004]
As another ultra-high density recording, there is a near-field optical recording method using a probe having a minute aperture. For example, as described in Journal of Applied Physics 79 (1996), page 8082 (J. Appl. Phys. Vol. 79, p8082 (1996)) There are things that change the phase by raising the temperature. When these methods are used, a light-localized region is approximately the size of the opening regardless of the wavelength of light used, and therefore, writing / reading of a minute spot exceeding the diffraction limit can be performed.
[0005]
[Problems to be solved by the invention]
In the conventional method of focusing laser light with a lens, the recording density is limited by the diffraction limit. Although it is possible to reduce the diameter of the focused spot by shortening the wavelength, there is a limit determined by the wavelength in any case. Further, when the wavelength is shortened to the ultraviolet region, an inexpensive optical system such as a lens that has been used so far absorbs ultraviolet light and cannot be used. Moreover, such a short wavelength light source itself has not been realized so far as being compact and stable. Therefore, it can be said that increasing the density by optimizing the wavelength of the light source is not practical. A solid immersion lens has a similar limitation in that it is limited in wavelength.
[0006]
In addition, in the case of recording using a probe having a minute aperture, there is a problem that the light throughput is poor due to the small aperture, a high-power laser is required for writing, and writing and reading take time. there were.
[0007]
An object of the present invention is to realize a minute light source exceeding the diffraction limit and to improve the recording speed in order to achieve ultra-high density recording / reproduction with light.
[0008]
[Means for Solving the Problems]
Even if normal laser light is condensed by a lens or the like, it can be narrowed down to only about half of the wavelength of the laser used (diffraction limit). For this reason, the size of the recording spot remains at that level. In order to concentrate the light intensity in a narrower area, there is a recording method using near-field light leaking from a minute aperture, but the weakness of the available light power is a problem.
[0009]
It is known that plasmons are excited when metal fine particles are irradiated with light. If plasmons generated in the vicinity of a metal body having a wavelength smaller than that of the wavelength are used, the intensity of the photoelectric field (electric field oscillating at the frequency of light) in the vicinity of the metal body is enhanced by plasmon excitation. Can concentrate. If this photoelectric field is used for writing or reproduction, a spot smaller than the conventional one can be written or read, and high-density recording / reproduction is possible.
[0010]
The degree of enhancement of the photoelectric field by plasmon excitation differs depending on the shape of the metal fine particles and the polarization direction of incident light. In the case of a true sphere, the incidence of p-polarized light is stronger (Optical Review 6 (1999), page 211 (Optical Review, Vol. 6, P211 (1999))). However, the degree of enhancement is larger and can be increased to several tens of times (Surface Science, Vol. 156, p678 (1985)).
[0011]
Thus, the spatial expansion of the photoelectric field enhanced by the plasmons excited in the vicinity of the metal body is about the size of the metal body, and only the vicinity of the space expands and the intensity of the photoelectric field increases. When the light is focused on the metal body by the lens, the other part of the recording medium is also irradiated with the light, but the photoelectric field intensity and the lens in which the threshold of the photoelectric field intensity for recording is enhanced by plasmons By using a medium that is between the photoelectric field intensities of the light condensed in step 1, the photoelectric field enhanced by the plasmon can be used for optical recording. For example, in the case of a phase change disk, the relationship between the material of the recording medium and the incident light intensity is set so that the phase change occurs with the intensity of the photoelectric field enhanced by the plasmon and the phase change does not occur only with the light collected by the lens. Adjust it.
[0012]
Further, when a solid immersion lens is used as a condensing lens, the light can be collected efficiently. This lens has a shape obtained by cutting off a part of a spherical lens, and light is condensed on the end face thereof. Since the numerical aperture is very high, the light collection efficiency is higher than that of a normal lens. Furthermore, when this lens is combined with an elongated fine metal body such as an elliptical sphere or cylinder, the lens is arranged so that the longitudinal direction of the micro metal body is perpendicular to the flat surface of the head, that is, the flat surface of the solid immersion lens. By doing so, further enhancement of the photoelectric field can be expected.
[0013]
This is because, in the case of a normal lens, the wave vector of light collected by the lens is oblique with respect to the end face, and the electric field intensity oscillating in the direction in which plasmons can be excited (direction perpendicular to the flat surface) The intensity of the electric field is multiplied by the cosine of the incident angle, and the incident light intensity cannot be fully utilized. When light is narrowed down by the solid immersion lens, the condensed light is incident on the end face at a higher angle. In other words, the cosine of the incident angle increases, and the light intensity that can contribute to excitation increases. For light incident at an angle greater than the total reflection critical angle, it becomes an evanescent wave and has a wave vector parallel to the end face, that is, its light intensity can all contribute to plasmon excitation and efficiently excite plasmons. Can do.
[0014]
If a flat metal substrate is embedded in a minute metal body, the above substrate is mounted on a slider, and when this is used as an optical head, recording and reproduction can be performed on a disk that rotates at high speed without any obstacles or collisions. Can do.
[0015]
The conditions for exciting plasmons greatly depend on the wavelength, the dielectric constant of the surroundings, the dielectric constant of the minute metal body, and the shape thereof. Therefore, in the fine metal bodies having different materials and shapes, the wavelengths at which plasmons can be excited are different. If a plurality of minute metal bodies having different materials and shapes are created on the same head, and different wavelengths of light are simultaneously irradiated on the same head, plasmons of the plurality of minute metal bodies are separately excited. According to the present invention, this can be utilized to make a multi-head, and a plurality of columns can be recorded at the same time, so that the time required for recording can be shortened accordingly.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a diagram showing the basic configuration of an embodiment of the present invention. A helium-cadmium laser beam 101 having a wavelength of 533 nm is narrowed through a lens 102, and condensed from a back side onto a minute metal body 104 formed on a substrate 103 made of a transparent material. The laser beam 101 is incident on the substrate 103 perpendicularly, and the lens 102 is positioned directly above the substrate 103, so that a compact structure is obtained.
[0017]
The metal body 104 is formed so as to be embedded in the substrate 103 so as not to be an obstacle when moving on a recording medium (not shown). Although a method for manufacturing the substrate 103 will be described in detail later, the minute metal body 104 of this embodiment has a structure in which a cylindrical hole having a diameter of about 50 nm and a depth of about 100 nm is formed in the substrate 103 and gold is embedded therein.
[0018]
The lens 102 has a mechanism (not shown) that can be finely moved vertically and horizontally with respect to the substrate 103. The position of the lens 102 is adjusted and fixed so that the minute metal body 104 comes to the center of the focal point. When the apparatus of the present embodiment is used as a head, these may be integrated and an autofocus mechanism may be added.
[0019]
When the laser beam 101 is incident on this, localized plasmons are excited by the metal body 104 and the photoelectric field intensity in the vicinity of the metal body 104 is enhanced. In this case, since the minute metal body has a cylindrical shape and its bottom surface is on the flat surface of the head facing the medium, the enhanced photoelectric field spread is about the diameter of the bottom metal body cylinder, that is, about 50 nm. When this head is mounted on a recording / reproducing apparatus having a function of controlling the distance to the recording medium and is brought close to the recording medium by a certain distance, information can be recorded with a spot diameter of the extent of light spread.
[0020]
Here, in the above embodiment, the shape of the minute metal body is a cylinder, but when it is arranged on the head, it has a dimension that is long in the direction perpendicular to the flat surface of the head, that is, a shape whose height is longer than the width of the bottom surface. If so, an elliptical cylinder, a spheroid, a cone, a prism, a pyramid, a truncated cone, a truncated pyramid shape, or the like may be used.
[0021]
In the present invention, the recording medium can be used in the same manner as long as it is the same material as conventionally used. However, the threshold value that exerts a physical property change on the recording medium is enhanced in the vicinity of the minute metal body. It is necessary to take a value that is smaller than the light intensity and greater than the light intensity of the portion condensed by the other lens. Therefore, it is necessary to adjust the sensitivity and incident light intensity of the medium in advance. Also, since the light intensity is closer to the head, it is considered that recording is more efficient when there is no protective layer on the top of the medium.
[0022]
Conventional methods can also be applied to reproduction. The reflected or transmitted signal is detected using light whose incident light intensity is weaker than that during recording. The detection threshold is set between the signal intensity from the plasmon-enhanced photoelectric field and the signal intensity from the part collected by the other lens, and the detection threshold from the plasmon-enhanced photoelectric field is set. Do not take anything other than signals. As a result, information written in a minute region below the diffraction limit can be reproduced.
[0023]
FIG. 2 is a view showing an embodiment in which a solid immersion lens is used as a lens.
The laser beam 101 is narrowed down through the solid immersion lens 202 and irradiated to the minute metal body 104 in the substrate 103 similar to that shown in FIG. The minute metal body 104 may be created directly on the end surface of the solid immersion lens 202, but it is difficult to produce the metal body at the position where the light is focused, so here the substrate 103 and the lens are separately made of the same material. Created and sandwiched between UV light curable optical adhesive (not shown). While measuring the light intensity, the substrate and the lens were placed at the position where they became the strongest, and the whole was irradiated with ultraviolet light to be cured and integrated to form the basic part of the head. In the figure, it is drawn so that parallel light is incident, but light that has been previously narrowed by a lens may be incident.
[0024]
FIG. 3 is a graph showing the light intensity in the vicinity of the optical head shown in FIG. The flat surface with respect to the medium at the bottom of the head was scanned with a near-field optical microscope so as to pass over the fine metal body, and the generated light was picked up with a probe and the intensity thereof was measured. A place where the light intensity was amplified having a width substantially the same as the size of the produced minute metal body 104 was observed.
[0025]
FIG. 4 is a view showing another embodiment using the solid immersion lens 202. A light shielding portion 401 is provided at the center of the solid immersion lens 202 irradiated with the laser beam 101. The light shielding portion 401 was formed by vapor-depositing metallic chromium. Such a light shielding mechanism is not necessarily provided directly on the lens. For example, a lens such as a pupil filter may be inserted in the optical path of the incident laser 101 to irradiate the lens with ring-shaped light. The light shielding range is determined so that the angle θ at which the light to be shielded is incident on the substrate is smaller than the total reflection critical angle.
[0026]
With such a structure, the light irradiated to the minute metal body 104 mainly has an incident angle larger than the total reflection critical angle. Such light causes total reflection at the lower part of the head and generates an evanescent wave near the interface. Since the evanescent wave near the interface has a wave vector in a direction parallel to the interface, the plane of polarization is perpendicular to the interface. Therefore, it is possible to efficiently excite localized plasmons of a minute metal body that is elongated in the direction perpendicular to the interface.
[0027]
When light that does not cause total reflection is blocked as in this embodiment, the intensity of the entire incident light is reduced, but the excitation efficiency of the plasmon is increased, so that the photoelectric field intensity enhanced by the plasmon and the other lens are collected. Contrast with the photoelectric field intensity of the illuminated portion is increased. Therefore, it is possible to suppress an error that a spot having a wide diameter is erroneously recorded in a portion condensed by the lens other than the photoelectric field enhanced by plasmon excitation. Further, there is an advantage that the range of values that can be taken by the threshold value of the light intensity required for recording is widened and the design becomes easy.
[0028]
FIG. 5 shows still another embodiment. The laser beam 101 is incident on the substrate 103 formed by the above method and including the minute metal body 104 so as to be totally reflected through the prism 502 at the lower portion of the substrate. At this time, the polarization direction of the incident laser light was p-polarized light, that is, the direction in which the polarization direction was included in the incident surface. Also in this case, since the excitation is performed by the evanescent wave generated by the total reflection, the plasmon can be excited efficiently. In the drawing, it is drawn so that parallel light is incident, but light that is narrowed by a lens may be incident.
[0029]
FIG. 6 is a view of a parallel recording head using wavelength multiplexing as viewed from the surface facing the medium. Both the gold cylinder 601 and the silver cylinder 602 formed on the substrate 603 have a diameter of about 50 nm and a height of about 100 nm. The manufacturing method will be described in detail later.
[0030]
Here, the number of minute metal bodies included in the head is two for simplicity, but may be increased if the conditions are met. Also, although the shape is a cylinder, as described above, when it is placed on the head, it has a dimension that is long in the direction perpendicular to the flat surface of the head, that is, if the height is longer than the width of the bottom surface, Various shapes such as an elliptic cylinder, a spheroid, a cone, a prism, and a pyramid are possible, and these may be arranged so that the longitudinal direction is perpendicular to the head flat surface.
[0031]
In this embodiment, the distance between the minute metal bodies 601 and 602 is approximately 200 nm so that the photoelectric field excited in the vicinity of the metal body does not affect the photoelectric field around the other metal body. In order to narrow the interval between the marks on the medium recorded by the minute metal bodies 601 and 602, the line connecting 601 and 602 is arranged so as to be oblique to the traveling direction of the head. Here, since recording is desired at intervals of about 100 nm, the line segment connecting 601 and 602 is shifted by 30 degrees from the traveling direction of the head. The minute metal bodies 601 and 602 are formed so as to be embedded in the substrate so as not to be an obstacle when moving on the recording medium.
[0032]
FIG. 7 is a diagram simply showing the configuration of a recording apparatus using the head described in FIG. As described above, gold and silver are embedded in the head 703. Since gold and silver have different plasmon resonance wavelengths, even if two colors of laser light are incident at the same time, a strong enhancement of the photoelectric field is observed only on one side. Here, an argon laser with a wavelength of 514.5 nm was used to excite gold plasmon, and an argon laser with 363.8 nm was used to excite silver. By turning on and off the two lasers with the AO modulators 701 and 702 and controlling them respectively, recording can be performed independently and independently without affecting the other.
[0033]
Light emitted from the argon lasers 711 and 712 is adjusted to have the same optical axis by using a mirror 721 and a half mirror 722. The light is squeezed through the lens 102 and condensed on the head 703 from the back side. The laser light is perpendicularly incident on the substrate, and the lens 102 is positioned directly above the substrate, thereby forming a compact structure.
[0034]
The lens 102 has a structure (not shown) that can be finely moved up and down and left and right with respect to the head 703, and the position of the lens is adjusted and fixed so that the minute metal body comes to the center of the focal point. When used as a head, these may be integrated and an autofocus mechanism may be added. When laser light is incident on this, localized plasmons are excited by the metal body, and the intensity of the photoelectric field near the metal body is enhanced. In this case, since the minute metal body has a cylindrical shape and its bottom surface is on the flat surface of the head facing the medium, the enhanced spread of the photoelectric field is about the diameter of the circle on the bottom surface, that is, about 50 nm. When this head is mounted on a recording / reproducing apparatus having a function of controlling the distance to the recording medium and is brought close to the recording medium by a certain distance, information can be recorded with a spot diameter of the extent of light spread.
[0035]
Hereinafter, a method for manufacturing a substrate having a structure like an optical head in which a minute metal body as shown in FIGS. 1, 2, 4, 6, and 7 is embedded will be described. A flat dielectric substrate that is transparent at the wavelength to be used is processed with a focused ion beam, and a hole with a diameter of about 50 nm and a depth of about 100 nm is formed. A metal is vapor-deposited here, and then the surface is polished so that the whole becomes the same height. As a result, a part of a minute region on the surface of the dielectric is replaced with metal. The hole may be formed by lithography or a stamp method in which a microstructure is copied onto a substrate, instead of using a focused ion beam.
[0036]
The type of metal is a balance between the wavelength to be used and the optical characteristics of the substrate to be embedded, but gold is preferable in terms of stability and plasmon excitation efficiency. When this is used and a high refractive index glass is used for the substrate, it is possible to excite localized plasmons at a wavelength near 500 nm. Accordingly, the second harmonic wave of a helium-neon laser or neodymium-yag laser, or green light such as a semiconductor laser can be used. In the case of localized plasmons, the excitation conditions are relatively gentle compared to surface plasmons, and there is an advantage that there are no strict restrictions on the incident angle and wavelength.
[0037]
【The invention's effect】
By using the present invention, in optical recording, it is possible to write a spot smaller than the spot diameter that is limited to a diffraction limit of about a half wavelength, and simultaneously perform a plurality of recordings. It can be shortened.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a basic configuration of a main part of a recording head according to an embodiment of the invention.
FIG. 2 is a cross-sectional view showing a basic configuration of a main part of a recording head according to another embodiment of the invention.
3 is a graph showing a spatial distribution of light intensity emitted from the head shown in FIG.
FIG. 4 is a cross-sectional view showing a basic configuration of a main part of a recording head according to another embodiment of the invention.
FIG. 5 is a cross-sectional view showing a basic configuration of a main part of a recording head according to another embodiment of the invention.
FIG. 6 is a plan view of a main part of a head according to another embodiment of the present invention.
FIG. 7 is a block diagram showing a basic configuration of a recording apparatus according to another embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 101 ... Laser beam, 102 ... Lens, 103 ... Board | substrate, 104 ... Micro metal body, 202 ... Solid immersion lens, 401 ... Light-shielding part, 502 ... Prism, 601 ... Micro metal body (gold), 602 ... Micro metal body ( Silver), 603... Substrate, 701 and 702... AO modulator, 703... Head, 711 and 712... Argon laser, 721.

Claims (5)

  In a recording apparatus for recording on a medium or the like with light, the head portion has a plurality of minute metal bodies having a size equal to or smaller than the wavelength of light used for recording, and a photoelectric field enhanced by plasmons excited in the vicinity is recorded. A recording apparatus characterized by being used. The recording apparatus according to claim 1 , wherein the plasmon resonance wavelengths of the plurality of minute metal bodies are different from each other. The recording apparatus according to claim 1 or 2, a recording apparatus in which a plurality of micro metal members being provided, characterized in that are arranged oblique to the relative moving direction of the head and the medium. The apparatus according to any one of claims 1 to 3, the shape of the minute metallic body, having a long dimension in the direction perpendicular to the head flat surface, i.e., that the direction of higher than the width of the bottom of having a long shape A recording apparatus or a recording / reproducing apparatus. In the preparation method of the head portion of the recording apparatus or a recording and reproducing apparatus according to any one of claims 1 to 4, digging a small hole in the substrate using a focused ion beam or lithographic techniques, to fill the hole by depositing a metal A method for producing a recording apparatus or recording / reproducing apparatus, characterized in that the whole is polished to form a flat surface.

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