JP2002008235A - Recording/reproducing device using plasmon and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To quickly perform an optical recording of super high density. SOLUTION: Information is recorded in a very small area exceeding a diffraction limit by making incident light on a flat substrate in which micro metallic bodies are embedded, locally strengthening the photoelectric field in the vicinity of the micro bodies by exciting a localized plasmon and using its light. Recording is performed in parallel by using plural micro metallic bodies.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an information recording / reproducing apparatus using light and a method of manufacturing the same.

[0002]

2. Description of the Related Art In optical recording, a method is used in which a laser beam is condensed as a small spot on a medium by a lens, and the characteristics of a minute area of the medium are changed by heat or photoreaction generated thereby to perform recording. ing. When this method is used, the size of the spot diameter that can be focused 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 had to be used.

Further, Applied Physics Letter 65 (1994), p. 388 (Appl. Phys. Lett.
Vol. 65, p388 (1994)) and JP-A-5-18979.
No. 6, a solid immersion lens
On-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 to a region smaller than a normal lens.

As another ultra-high density recording, there is a near-field optical recording method using a probe having a minute aperture. For example,
Journal of Applied Physics 79 (1
996) p.8082 (J. Appl. Phys. Vol. 7)
9, p8082 (1996)), there is a method of raising the temperature of a very small region of a medium by light near a minute opening to cause a phase change. When these methods are used, a region where light is localized is about the size of the opening, regardless of the wavelength of the light to be used, so that a minute spot exceeding the diffraction limit can be written and read.

[0005]

In the conventional method of focusing a laser beam with a lens, the recording density is limited by the diffraction limit. Although it is possible to reduce the focused spot diameter 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 used so far absorbs ultraviolet light and cannot be used. Moreover, such a short wavelength light source itself,
At present, a compact and stable one has not been realized. Therefore, it can be said that increasing the density by optimizing the wavelength of the light source is not practical. Solid immersion lenses also have similar limitations in that they are subject to wavelength limitations.

Further, in the case of recording using a probe having a small aperture, a light aperture is poor due to a small aperture, a laser having a large power is required for writing, and it takes time to write and read. There was a problem.

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 and reproduction by light.

[0008]

Even if ordinary laser light is condensed by a lens or the like, it can be narrowed down to only about half the wavelength of the laser used (diffraction limit). Therefore, the size of the recording spot also 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,
The weak light power available was problematic.

It is known that irradiating light to metal fine particles excites plasmons. If a plasmon generated near a metal body smaller than the wavelength is used, the intensity of the optical electric field (electric field oscillating at the frequency of light) near the metal body is enhanced by the excitation of the plasmon. You can focus. If this photoelectric field is used for writing or reproduction, a smaller spot than before can be written or read, and high-density recording and reproduction can be performed.

The degree of enhancement of the photoelectric field by plasmon excitation differs depending on the shape of metal fine particles and the polarization direction of incident light. In the case of a true sphere, the degree of enhancement is higher when p-polarized light is incident (Optical Review 6 (1999) No. 211).
(Optical Review, Vol. 6, P211 (1999)), and the degree of enhancement is larger for elliptical spheres than for true spheres, and can be increased by several tens of times (Surface Science 156 (198)
5 years) p. 678 (Surface Science, Vol.156, p67)
8 (1985))).

As described above, the spatial spread of the electric field enhanced by the plasmon excited in the vicinity of the metal body is about the size of the metal body, and the electric field strength is increased by jumping only in the vicinity of the metal body. When the light is focused on a metal object with a lens,
The other part of the recording medium is also irradiated with light, but the threshold of the photoelectric field intensity at which recording occurs is between the photoelectric field enhanced by the plasmon and the photoelectric field intensity by the light collected by the lens. , 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 intensity of the incident light is adjusted so that the phase change occurs with the intensity of the electric field enhanced by the plasmon and the phase change does not occur only with the light condensed by the lens. Adjust it.

When a solid immersion lens is used as a focusing lens, the focusing can be performed efficiently. This lens has the shape of a part of a spherical lens cut out,
Light is condensed on the end face. 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 micro metal body such as an ellipsoidal sphere or a cylinder, it 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.

This is because, in the case of a normal lens, the wave vector of the light condensed by the lens is oblique with respect to the end face, and the electric field strength oscillating in a direction that can excite plasmons (a direction perpendicular to the flat surface) is However, the intensity of the incident electric field is multiplied by the cosine of the incident angle, and the intensity of the incident light cannot be sufficiently utilized. When light is narrowed down by the solid immersion lens, the condensed light enters the end face at a higher angle. This means that the cosine of the incident angle increases, so that the light intensity that can contribute to excitation increases. For light incident at an angle larger than the critical angle for total reflection, it becomes an evanescent wave and has a wave number vector parallel to the end face.In other words, the light intensity can all contribute to plasmon excitation and efficiently excite plasmons. Can be.

Further, if the flat metal substrate is formed into a shape in which a minute metal body is embedded, by mounting the above-mentioned substrate on a slider, recording and reproduction can be performed without any obstacles or collisions on a disk which rotates at a high speed when the optical head is used as an optical head. It can be performed.

The conditions under which plasmons can be excited are greatly influenced by the wavelength, the dielectric constant of the surroundings, the dielectric constant of the minute metal body, and its shape. Therefore, the wavelength at which plasmon can be excited is different between the minute metal bodies having different materials and shapes. If a plurality of fine metal bodies having different materials and shapes are formed on the same head at different positions and simultaneously irradiated with light of different wavelengths, plasmons of the plurality of fine metal bodies are separately excited. According to the present invention, a multi-head can be realized by utilizing this fact, and a plurality of rows can be recorded at the same time.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a diagram showing the configuration of a basic part of an embodiment of the present invention. A light 101 having a wavelength of 533 nm of a helium / cadmium laser is narrowed down through a lens 102 and focused on a minute metal body 104 formed on a substrate 103 made of a transparent material from the back side. The laser beam 101 is perpendicularly incident on the substrate 103, and the lens 102 is positioned directly above the substrate 103, thereby achieving a compact structure.

The metal body 104 is formed so as to be embedded in the substrate 103 so as not to hinder movement on a recording medium (not shown). The method for manufacturing the substrate 103 will be described later in detail.
03, a cylindrical hole having a diameter of 50 nm and a depth of about 100 nm is formed, and gold is embedded therein.

The lens 102 has a mechanism (not shown) capable of finely moving up, down, left and right with respect to the substrate 103, and the lens 1 is positioned so that the minute metal body 104 is located exactly at the center of the focal point.
02 was adjusted and fixed. When the apparatus of this embodiment is used as a head, these may be integrated into a structure, and an automatic focusing mechanism may be added.

When the laser beam 101 is incident on this, localized plasmons are excited in the metal body 104, and the intensity of the optical electric field near the metal body 104 is increased. In this case, since the minute metal body is cylindrical and its bottom surface is on the flat surface of the head facing the medium, the spread of the enhanced electric field 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 a recording medium, and is brought close to the recording medium by a certain distance, information can be recorded with a spot diameter that is about equal to the spread of light.

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 longer in the direction perpendicular to the flat surface of the head. Is long, elliptic cylinder, spheroid,
The shape may be a cone, a prism, a pyramid, a truncated cone, a truncated pyramid, or the like.

In the present invention, as the recording medium, the same material as that conventionally used can be used in the same manner. It is necessary to take a value smaller than the light intensity enhanced by the above and larger than the light intensity of the portion focused by the other lenses. Therefore, it is necessary to adjust the sensitivity of the medium and the incident light intensity in advance. Also, since the light intensity is higher near the head, it is considered that the recording becomes more efficient without the protective layer on the medium.

The conventional method can be applied to the reproduction. The reflected or transmitted signal is detected using light whose incident light intensity is weaker than during recording. Set the detection threshold to
Set between the signal intensity from the plasmon-enhanced photoelectric field and the signal intensity from the portion focused by the other lenses so that no signal other than the signal from the plasmon-enhanced photoelectric field is taken I do. This makes it possible to reproduce information written in a minute area below the diffraction limit.

FIG. 2 is a view showing an embodiment in which a solid immersion lens is used as a lens. A laser beam 101 is narrowed down through a solid immersion lens 202 and is irradiated on a minute metal body 104 in a substrate 103 similar to that shown in FIG. The minute metal body 104 may be formed directly on the end face of the solid immersion lens 202. However, since it is difficult to manufacture the metal body at a position where light is condensed, here, the substrate 103 and the lens are separately made of the same material. It was made and a thin layer of UV-curable optical adhesive (not shown) was sandwiched between them. While measuring the light intensity, the substrate and the lens were arranged at the position where the intensity became the strongest, and the whole was irradiated with ultraviolet light to be cured and integrated, thereby forming a basic part of the head. In the figure, parallel light is illustrated as being incident, but light that has been previously focused by a lens may be incident.

FIG. 3 is a graph showing the light intensity near the optical head shown in FIG. The flat surface of the lower part of the head with respect to the medium was scanned by a near-field optical microscope so as to pass over the minute metal body, and the generated light was picked up by a probe and its intensity was measured. Micro metal body 10 created
A place where the light intensity was amplified, having a width almost equal to the size of No. 4, was observed.

FIG. 4 is a view showing another embodiment using the solid immersion lens 202. In FIG. A light shielding portion 401 is provided at the center of the solid immersion lens 202 irradiated with the laser beam 101.
Is provided. The light-shielding portion 401 was formed by evaporating metal chromium. Such a light blocking mechanism is
It does not necessarily have to be provided directly on the lens. For example, a lens such as a pupil filter may be inserted into the optical path of the incident laser 101 to irradiate the lens with ring-shaped light. The range in which light is blocked is determined so that the angle θ at which the light blocked by the light enters the substrate is smaller than the critical angle for total reflection.

With such a structure, the minute metal body 10
The light irradiated to 4 mainly has an incident angle larger than the critical angle for total reflection. 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, its polarization plane is perpendicular to the interface. Therefore, it is possible to efficiently excite localized plasmons of a minute metal body elongated in a direction perpendicular to the interface.

When the 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. The contrast with the electric field intensity of the portion focused by the lens increases. Therefore,
It is possible to suppress an error that a spot having a large diameter is erroneously recorded in a portion focused by the lens other than the optical electric field enhanced by plasmon excitation. Further, there is an advantage that the range of possible values of the threshold value of the light intensity required for recording is widened, and the design becomes easy.

FIG. 5 shows still another embodiment. Substrate 1 provided with micro metal body 104, prepared by the above method
The laser beam 101 is incident on the laser beam 03 through the prism 502 so as to be totally reflected at the lower portion of the substrate. At this time, the polarization direction of the incident laser light was p-polarization, that is, the direction in which the polarization direction was included in the incident plane. Also in this case, the plasmon can be efficiently excited because it is excited by an evanescent wave generated by total reflection. In the figure, parallel light is illustrated as being incident, but light focused by a lens may be incident.

FIG. 6 is a view of a parallel recording head by wavelength multiplexing, as viewed from a surface facing a medium. The diameter of each of the gold column 601 and the silver column 602 formed on the substrate 603 is about 50 nm, and both heights are about 100 nm.
The fabrication method will be described later in detail.

Although the number of the fine metal members included in the head is two here for simplicity, it may be increased if the conditions are met. Also, although the shape was a cylinder, as described above, when placed on the head, it has a dimension that is longer 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, Elliptic cylinder, spheroid, cone, prism,
Various shapes such as pyramids are possible, and they may be arranged such that the longitudinal direction is perpendicular to the flat surface of the head.

In this embodiment, the distance between the minute metal bodies 601 and 602 is set to about 200 so that the electric field excited near the metal body does not affect the electric field around the other metal body.
nm apart. In order to narrow the interval between marks on the medium recorded by the minute metal bodies 601 and 602, 601 and 6
02 is arranged so as to be oblique to the head traveling direction. Here, since it is desired to record at intervals of about 100 nm, the line connecting 601 and 602 is shifted by 30 degrees from the head traveling direction. 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.

FIG. 7 is a diagram simply showing the configuration of a recording apparatus using the head described in FIG. Gold and silver are embedded in the head 703 as described above. Gold and silver have different plasmon resonance wavelengths.
Even when a laser beam of a color is incident, an intense photoelectric field is observed only on one side. Here, an argon laser having a wavelength of 514.5 nm was used to excite gold plasmon, and a 363.8 nm argon laser was used to excite silver. The two lasers are turned on / off by AO modulators 701 and 70
By performing the control in step 2 and controlling each, recording can be performed independently and simultaneously without affecting the other.

The 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 stopped down through the lens 102 and is focused on the head 703 from the back side. The laser beam is perpendicularly incident on the substrate, and the lens 102 is positioned right above the substrate to achieve a compact structure.

The lens 102 has a structure (not shown) capable of finely moving up, down, 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, they may be integrated into a structure, and an automatic focusing mechanism may be added. When laser light is incident on this, localized plasmons are excited by the metal body, and the intensity of the optical electric field near the metal body is increased. In this case, since the minute metal body is cylindrical and its bottom surface is on the flat surface of the head facing the medium, the spread of the enhanced electric 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 a recording medium, and is brought close to the recording medium by a certain distance, information can be recorded with a spot diameter that is about equal to the spread of light.

Hereinafter, a method of manufacturing a substrate having a structure like an optical head in which a minute metal body is embedded as shown in FIGS. 1, 2, 4, 6, and 7 will be described. A flat dielectric substrate that is transparent at the wavelength to be used is processed with a focused ion beam, and
Drill a hole with a diameter of about 0 nm and a depth of about 100 nm. A metal is deposited here, and then the surface is polished so that the whole surface has the same height. As a result, a structure in which a part of the minute region on the surface of the dielectric is replaced with metal can be obtained. The hole may be formed not by a focused ion beam but by lithography or a stamp method of transferring a microstructure to a substrate.

The type of metal is a trade-off between the wavelength used and the optical characteristics of the substrate to be embedded, but gold is preferred in terms of stability and plasmon excitation efficiency. When this is used and high refractive index glass is used for the substrate, localized plasmons can be excited at a wavelength around 500 nm. Accordingly, green light such as a second harmonic of a helium-neon laser or a neodymium-yag laser, or a semiconductor laser can be used. In the case of localized plasmons, the excitation conditions are relatively mild compared to surface plasmons, and thus there is an advantage that there is no strict restriction on the incident angle, wavelength, and the like.

[0037]

According to the present invention, in optical recording, a spot smaller than the spot diameter limited to about half a wavelength at the diffraction limit can be written, and a plurality of recordings can be performed simultaneously. The time required for recording can be reduced.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a basic configuration of a main part of a recording head according to an embodiment of the present 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 present invention.

FIG. 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 present invention.

FIG. 5 is a sectional view showing a basic configuration of a main part of a recording head according to another embodiment of the present 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]

101 laser light, 102 lens, 103 substrate, 1
04 ... minute metal body, 202 ... solid immersion lens, 401 ...
Shielding section, 502: prism, 601: minute metal body (gold), 602: minute metal body (silver), 603: substrate, 7
01 and 702: AO modulator, 703: head, 711 and 712: argon laser, 721: mirror, 722: half mirror.

Claims (10)

[Claims] In a recording / reproducing apparatus for recording / reproducing a medium by light, a head portion has a portion which is transparent to light used for recording / reproduction and has a flat surface with respect to a medium, and the flat surface is used for recording / reproduction. A recording / reproducing apparatus in which a minute metal body having a size equal to or smaller than the wavelength of light is embedded, and recording or reproduction is performed using a photoelectric field enhanced by plasmons generated near the minute metal body. 2. A recording apparatus for recording on a medium or the like by light, wherein a head portion is provided with a plurality of fine metal bodies having a size equal to or smaller than the wavelength of the light used for recording, and enhanced by plasmons excited in the vicinity thereof. A recording device using an electric field for recording. 3. The recording apparatus according to claim 2, wherein the plurality of minute metal bodies have different plasmon resonance wavelengths. 4. A recording apparatus according to claim 2, wherein the plurality of minute metal bodies are arranged obliquely to a relative traveling direction of the head and the medium. apparatus. 5. The apparatus according to claim 1, wherein the shape of the minute metal body has a dimension longer in a direction perpendicular to the flat surface of the head, that is, the height of the fine metal body is larger than the width of the bottom surface. A recording device or a recording / reproducing device having a long shape. 6. An apparatus according to claim 1, further comprising a lens on an upper portion of the recording head for condensing light perpendicularly incident on a flat surface of the head on a minute metal body. Characteristic recording device or recording / reproducing device. 7. A recording apparatus or a recording / reproducing apparatus according to claim 6, wherein the lens that focuses on the minute metal body is a solid immersion lens. 8. A recording apparatus according to claim 7, wherein said recording apparatus has a structure for shielding at least a part of light having an incident angle on a surface in which a minute metal body is embedded, smaller than a critical angle for total reflection. Device or recording / reproducing device. 9. A recording apparatus or a recording / reproducing apparatus according to claim 1, wherein the polarization direction of the incident light is a direction included in the incident surface. 10. A method of manufacturing a head portion of a recording apparatus or a recording / reproducing apparatus according to any one of claims 1 to 9, wherein a fine hole is dug in a substrate by using a focused ion beam or a lithography technique to deposit metal. A method of manufacturing a recording device or a recording / reproducing device, characterized in that a hole is filled, and the whole is polished to make a flat surface.