JP2010146638A - Information recording and reproducing device, and near field light detection method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an information recording and reproducing device capable of recording and reproducing high density record information by using near field light. <P>SOLUTION: As an antenna 1 for generating the near field light, an antenna 1 provided on a semiconductor substrate 4 across a dielectric layer 2 is used. The degree of an interaction between a material that changes by light or heat and the near field light generated from the antenna 1 is detected by a signal corresponding to an intensity change in the near field light in the semiconductor substrate 4. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an information recording / reproducing apparatus using an antenna that generates near-field light by local concentration of polarization due to polarized light and a near-field light detection method.

  An increase in recording density of an optical disk has been realized by a reduction in a condensing spot diameter by increasing the NA of a condensing lens and shortening the wavelength, but there is a limit in reducing the spot diameter due to the diffraction limit of light. Even when a so-called near-field light lens such as a solid immersion lens (SIL) is used, the spot diameter is considered to be reduced only to about 100 nm.

Around 2012, it is expected that a surface recording density of 1 Tbit / inch ² will be realized in a hard disk, but in order to realize a recording density equivalent to this on an optical disk, the spot diameter must be 20 nm or less. In order to further reduce the spot diameter, research and development using local light spot formation by the plasmon resonance phenomenon has been actively conducted (for example, see Patent Document 1). By applying this local light spot to, for example, a phase change type medium, a high density of the phase change type optical recording method is expected.

JP 2006-323989 A F. Zenhausern, et al. "Apertureless near-field optical microscope", Appl. Phys. Lett., 65 (13), 1994 Y. Martin, et al. "Optical data storage read out at 256 Gbits / inch2", Appl. Phys. Lett., 71 (1), 1997

In Patent Document 1, an antenna type prober is described, and an open type structure or the like is proposed as a prober. However, the light utilization efficiency of the aperture type is extremely small, 1 × 10 ⁻⁴ . Even in the antenna type or the like, when the scattered light detecting means is provided on the substrate supporting the prober, the near field for detecting the phase change of the medium is buried in the far field, so that the S / N ratio cannot be sufficiently obtained. Problems arise.

  Further, for example, means for comparing the observation light irradiated on the sample with the reference light irradiated on the portion outside the sample and detecting near-field light based on the phase difference has been proposed (Non-Patent Documents 1 and 2 above). reference). However, this method has a problem that the optical system becomes complicated. Further, since the detection signal is given with a slight phase difference, it is necessary to detect it with a lock-in amplifier, for example, and it is difficult to adopt it in a practical information recording / reproducing system from the viewpoint of detection speed (transfer speed). . As can be seen from these facts, a recording system that uses near-field light directly and with high efficiency and a reproducing system that detects with high efficiency have not been established, and its realization is desired.

  In view of the above problems, the present invention is capable of detecting an information recording / reproducing apparatus capable of recording and reproducing high-density recorded information by using near-field light, and a finer state of the sample surface. An object of the present invention is to provide a novel near-field light detection method that can be used.

  In order to solve the above problems, the present invention uses an antenna provided on a semiconductor substrate via a dielectric layer as an antenna that generates near-field light. The dielectric layer is made of a dielectric material having a refractive index lower than that of the semiconductor substrate with respect to light emitted from the light source. The degree of interaction between the material that changes due to light or heat and the near-field light generated from the antenna is detected by a signal corresponding to the intensity change of the near-field light inside the semiconductor substrate.

  By adopting a configuration in which the antenna serving as the near-field generating means is provided on the semiconductor substrate via the dielectric layer, a photocurrent is generated by the near-field light, thereby detecting a change in the intensity of the near-field light. This is because the strong near-field light generated at the interface between the antenna and the semiconductor substrate due to resonance forms an electron-hole pair inside the semiconductor substrate, thereby inducing current induction between the electrodes and detecting this current. Is. However, when a semiconductor substrate is used as a support substrate for an antenna, depending on the material, the refractive index in the visible light region is relatively large and the polarization is high. Concentrate near the interface.

  In contrast, by forming the antenna on the semiconductor substrate through the dielectric layer as described above, the near-field light intensity on the medium or sample side, that is, the antenna surface side, and the near-field light intensity on the inside of the semiconductor substrate side. Can be adjusted. For example, a metal that causes plasmon resonance with respect to the wavelength used is used in the surface layer facing the medium or the like. When an antenna is formed by providing a dielectric layer having a lower refractive index than the semiconductor substrate on the semiconductor substrate side, near-field light having sufficient intensity for recording can be generated on the antenna surface, for example. Furthermore, near-field light with sufficient intensity can also be generated at the interface between the semiconductor substrate and the dielectric layer on the substrate side of the antenna. Accordingly, it is possible to simultaneously include a mechanism for recording on a medium or the like and a reproducing mechanism for directly detecting near-field light.

  According to the present invention, it is possible to record and reproduce high-density recording information by using near-field light. In addition, by using this, it becomes possible to detect a finer state of the sample surface.

Hereinafter, examples of the best mode (referred to as an embodiment) for carrying out the present invention will be described, but the present invention is not limited to the following examples. This will be described in the following order.
[1] First embodiment (1) Configuration of near-field light generating unit including antenna (2) Material of antenna and electrode (3) Shape of antenna and electrode (4) Light source (5) Semiconductor substrate material (6) ) Dielectric layer material (7) Information recording material [2] Second embodiment (variation in light incident direction)
[3] Third embodiment (modification example of antenna planar shape)
[4] Fourth Embodiment (Modification of Antenna and Electrode Structure)
[5] Fifth Embodiment (Modification of Antenna and Electrode Structure)
[6] Sixth embodiment (variation example in which a light shielding portion is provided)
[7] Seventh embodiment (variation example in which a base layer is provided)
[8] Eighth Embodiment (Modified example in which a pad is provided)
[9] Ninth Embodiment (Modification in which a protective layer is provided on an electrode)
[10] Configuration of information recording medium [11] Tenth embodiment (Configuration of information recording / reproducing apparatus)
[12] Analysis example

[1] First Embodiment (1) Configuration of Near-Field Light Generation Unit Including Antenna FIG. 1 is a diagram of a near-field light generation unit 10 that is a main part of an information recording / reproducing apparatus according to an embodiment of the present invention. It is a schematic cross-sectional block diagram. As shown in FIG. 1, the near-field light generating unit 10 includes an antenna 1, a dielectric layer 2, a semiconductor substrate 4, and an electrode 5. The antenna 1 is formed on the semiconductor substrate 4 via the dielectric layer 2. The dielectric layer 2 is made of a material having a lower refractive index than that of the semiconductor substrate 1. An electrode 5 is provided in the vicinity of the antenna 1 on the semiconductor substrate 4. The current detector 6 is connected to the antenna 1 and the electrode 5 as a signal detector. A voltage application unit is connected between the antenna 1 and the electrode 5 (not shown). FIG. 1 shows a state in which a medium 200 such as an optical disk is disposed facing the antenna 1.

(2) Material of Antenna and Electrode As a material constituting the antenna 1, here, a metal capable of obtaining sufficient resonance with the wavelength of a light source (not shown) to be used is used. As such a material, it is desirable to use a material made of any one of Pt, Mg, Au, Al, and Ag. By using these materials and appropriately selecting the material of the semiconductor substrate 4 and the polarization direction of the incident light Li, particularly the electric field vibration direction, as will be described later, when the incident light Li is irradiated, the electrode 5 side of the antenna 1 is used. Near-field light is generated in the vicinity of the near-field light generation position 1n at the surface edge of the surface. Further, near-field light is also generated in the vicinity of the near-field light generation position 2n at the interface portion on the semiconductor substrate 4 side on the electrode 5 side of the dielectric layer 2.

  The material of the electrode 5 may be any material having conductivity such as metal, and may be the same material as the antenna 1 or a different material. The material of the semiconductor substrate 4 will be described later.

(3) Shape of Antenna and Electrode FIG. 2 is a plan view showing an example of a planar shape of the antenna 1, the dielectric layer 2 and the electrode 5. In this example, the antenna 1 and the dielectric layer 2 are formed in a substantially triangular shape, and each apex is rounded, and one apex is arranged to face the electrode 5 side. In this case, the apex on the side facing the electrode 5 is a near-field light generation position (1n, 2n), and the direction toward the opposite side is a direction (longitudinal direction) along the electric field vibration direction p of the incident light Li. The length of the antenna 1 along this direction is selected and configured in accordance with the resonance condition in which surface plasmons are generated. As an example, the electrode 5 has a rod shape, and both ends are rounded. The planar shapes of the antenna 1, the dielectric layer 2, and the electrode 5 are not limited to the example shown in FIG. 2, and may be any shape as long as the intensity of the near-field light generated in the antenna 1 is not suppressed. A shape that enhances the light intensity is more desirable. As shown in FIG. 2, when the shape is sharpened toward the position 1n (2n) where the near-field light spot is to be formed, the near-field light intensity is enhanced, which is desirable. In addition, as shown in FIG. 1, it is preferable that the electrode 5 is formed to be lower than the antenna 1 because the electrode 5 is less likely to contact the medium 200. In addition, for example, the electrode 5 is not only disposed facing the position 1n at the tip of the antenna 1, but also disposed opposite the side along the longitudinal direction of the antenna 1, that is, parallel to the longitudinal direction of the antenna 1. May be. Further, the electrode 5 may have a shape surrounding the antenna 1. Thus, the shape of the antenna 1 and the electrode 5 may be selected as appropriate so that the near-field light intensity is further enhanced. Further, the antenna 1 may be formed across a step provided on the semiconductor substrate 4. In this case, the position 1n (2n) where the near-field light spot is to be formed is disposed so as to be close to the medium 200, and conversely, the end of the antenna 1 that is not the near-field light generation position is separated from the medium 200. It is desirable to arrange. In this way, by bringing the position 1n where the near-field light spot is generated closer to the medium 200 than other parts, it is possible to efficiently irradiate only the target track position of the medium 200 with the near-field light. .

(4) Light source As a light source (not shown) for irradiating the antenna 1 with the light Li through the semiconductor substrate 4, it is assumed that light having polarized light is emitted, and the wavelength of the antenna 1 alone causes plasmon resonance. Thus, it is selected according to its shape and material. The optical system from the light source to the antenna 1 is configured so that the wavelength is appropriately selected and the electric field vibration direction is the above-described direction with respect to the antenna 1. By irradiating the antenna 1 with light from the light source through the semiconductor substrate 4, near-field light having sufficient intensity for recording or the like is generated at the position 1n on the electrode 5 side end portion on the surface of the antenna 1. Can do. At this time, near-field light is also generated at the position 2n at the end of the dielectric layer 2 on the electrode 5 side as described above. The intensity of the near-field light at these positions 1n and 2n can be adjusted by the relationship between the material of the antenna 1 and the dielectric layer 2 and the wavelength of the light emitted from the light source. It becomes possible to constitute the antenna 1 having strength. The near-field light intensity enhancement effect by an example of a specific combination of the material of the antenna 1 and the dielectric layer 2 and the wavelength will be described in detail in the item of [12] Analysis Example in the later stage.

(5) Semiconductor substrate material

Next, the material of the semiconductor substrate 4 will be described. The semiconductor substrate 4 is made of a material that is sufficiently transmissive with respect to the wavelength of the light source to be used. Further, it is desirable that the antenna 1 is made of a material having a band gap that is approximately twice the photon energy of the incident light Li irradiated to the antenna 1. That is, the photon energy of the incident light Li irradiated to the antenna 1 is selected to be approximately one half or more of the band gap energy of the material of the semiconductor substrate 4.
Furthermore, the photon energy of the incident light Li is selected so as to be equal to or lower than the band gap energy of the material of the semiconductor substrate 4. By using the semiconductor substrate 4 of such a material, the two-photon absorption phenomenon can be utilized.

Specifically, the material of the semiconductor substrate 4 is preferably selected from any one of SiC, AlP, ZnO, ZnS, ZnSe, GaN, and TiO ₂ . The band gap of these materials is as follows.

SiC: 3.0 eV
AlP: 2.5 eV
ZnO: 3.2 eV
ZnS: 3.6 eV
ZnSe: 2.6 eV
GaN: 3.4 eV
TiO ₂ : 3.0 eV

The wavelength band of approximately ½ or more photon energy corresponding to this band gap range and less than or equal to the band gap is 344 nm to 992 nm. If the wavelength is within this range, the above-described wavelength condition is satisfied.
For example, when a light source having a central wavelength of 400 nm is used, the photon energy is converted to about 3.1 eV. Accordingly, when ZnS having the maximum band gap is used among the above materials, the photon energy is at least one half of the band gap energy and below the band gap energy. When GaN is used as the semiconductor substrate 4, the band gap energy is 3.4 eV, and the condition that the band gap energy is equal to or less than half of the band gap energy and equal to or less than the band gap energy is satisfied.
Therefore, as a light source applicable when using the material of the semiconductor substrate 4 described above, any light source that includes light in a wavelength band of 344 nm to 992 nm in the emitted light may be used. For example, in a light source having a central wavelength of emitted light of 340 nm, if light having a wavelength of 344 nm or more is included in the emitted light to some extent, for example, when ZnS (band gap 3.6 eV) is used as the material of the semiconductor substrate 4. Is available. Similarly, in a light source having a center wavelength of outgoing light of 1000 nm, if the outgoing light contains light with a wavelength of 992 nm or less to some extent, when AlP (band gap 2.5 eV) is used as the material of the semiconductor substrate 4. Be available. Therefore, it is desirable to use a light source having a center wavelength of emitted light of 340 nm to 1000 nm as the light source.

  By using the semiconductor substrate 4 made of such a material and using a light source that matches the material and shape of the antenna 1, strong near-field light is generated at a position 2n near the interface between the antenna 1 and the semiconductor substrate 4 due to resonance. A state in which the light density (energy density) is sufficiently high can be made. At this time, a two-photon absorption phenomenon occurs in a region having a strong energy density, and a photocurrent is generated with the generation of electron-hole pairs as described above. By detecting the photocurrent generated at this time in the current detector 6, it is possible to detect a signal corresponding to the near-field light intensity in this case.

  As described above, when SiC, GaN, ZnO, for example, is used as the material of the semiconductor substrate 4, these refractive indexes are approximately 2 or more in the visible light region, and further, due to the high polarization, at the time of plasmon resonance Most of the near-field light is concentrated at the position 2n near the interface. When the antenna 1 has a single layer configuration, a difference is generated in the intensity ratio between near-field light generated on the surface side and near-field light generated on the substrate interface side, and the interface side becomes strong. For this reason, during recording, for example, it is conceivable that instability of recording characteristics occurs, such as unnecessary antenna temperature increase due to near-field light intensity increase on the substrate interface side and inefficiency of recording.

  On the other hand, in this embodiment, the dielectric layer 2 is provided between the semiconductor substrate 4 below the antenna 1. Therefore, by appropriately selecting the material and shape of the antenna 1 and the dielectric layer 2 and the wavelength of the light source, the near-field light in the vicinity of the near-field light generation position 1n of the antenna 1 on the side facing the information recording medium. The strength can be made sufficiently high.

(6) Dielectric Layer Material The material of the dielectric layer 2 that can adjust the near-field light intensity as described above needs to be sufficiently transparent with respect to the wavelength of the light source to be used. Furthermore, when the refractive index of the semiconductor substrate 4 with respect to the wavelength of the light source used is n4 and the refractive index of the dielectric layer 2 is n2, it is desirable that n4> n2. As such a material, for example, when using a transparent semiconductor substrate 4 having a refractive index of approximately 2 or more, such as SiC, GaN, ZnO, a refractive index that is approximately 0.5 or more smaller than the refractive index of these semiconductor substrate materials. It is desirable to use a dielectric material exhibiting Such dielectric _materials, MgF _2, CaF 2, SiO ₂ or the like can be mentioned. In particular, it is desirable that the refractive index difference be approximately 1 or more, such as using MgF ₂ or SiO ₂ as the dielectric layer 2 for the semiconductor substrate 4 made of GaN.

  Thus, by using a material having a low refractive index as the material of the dielectric layer 2 as compared with the refractive index of the semiconductor substrate 4, the near-field light generation position 1 n of the antenna 1 made of the metal layer is obtained due to the optical confinement effect. , Stronger near-field light can be generated. That is, the near-field light intensity generated near the near-field light generation position 1n of the antenna 1 can be made stronger than the near-field light intensity generated near the near-field light generation position 2n in the dielectric layer 2. Therefore, sufficient recording power can be obtained during recording.

(7) Information recording material The information recording material of the medium 200 that is recorded and reproduced by the information recording / reproducing apparatus having the above-described configuration may be any material that can be recorded by changing the dielectric constant, such as an inorganic material such as GeSbTe. These phase change materials can be used. Although not shown, the information recording material is provided on or inside the surface of the medium 200. The planar shape of the medium 200 may be a disk shape, and various configurations such as a card shape are possible, and the shape is not limited.

  The antenna 1 having the above-described configuration is moved relative to the medium 200 on which an information recording material such as a phase change material is formed. Then, when the recording mark of the phase change material changes, the dielectric constant changes and interacts with the antenna 1, whereby the near-field light intensity in the vicinity of the position 2 n on the semiconductor substrate 4 side in the dielectric layer 2 under the antenna 1. Changes. This change also changes the photocurrent excited by the two-photon absorption described above. Therefore, by detecting the change in the photocurrent generated in the semiconductor substrate 4, it is possible to detect a signal corresponding to the recorded information recorded as a state change such as a phase change in the medium 200.

[2] Second Embodiment (Modification of Light Incident Direction)
As shown in FIG. 3, the incident direction of light may be incident on the antenna 1 as indicated by an arrow Li1 from the back side of the semiconductor substrate 4, and as indicated by an arrow Li2 from the other surface side on the medium side. It is also possible to enter from both. Furthermore, as indicated by an arrow Li3, the light may enter from a direction along the interface between the antenna 1 and the semiconductor substrate 4. Further, it may be incident with an angle from the back side of the semiconductor substrate 4 as indicated by an arrow Li4. Although not shown, the light may be incident on the top surface of the antenna 1 at an angle from the surface facing the medium. In addition, the utilization efficiency of the light irradiated to the interface with the board | substrate 4 of the antenna 1 can be improved by irradiating light as shown by arrow Li1 from the back surface side of the semiconductor substrate 4. FIG. Therefore, in order to sufficiently secure the near-field light intensity that affects the reproduction detection characteristics, that is, the near-field light intensity at the interface between the antenna 1 and the semiconductor substrate 4, the incident light in this direction is used, and from other directions. It is desirable that the incident light is added.

[3] Third embodiment (modification example of antenna planar shape)
Next, with reference to FIG. 4, another embodiment in which the antenna and the electrode shape are different will be described. In this case, as shown in FIG. 4, an antenna 21 and a dielectric layer 22 having different planar shapes are formed on a semiconductor substrate (not shown). In this example, the antenna 21 has a rod shape and both ends are rounded, and the dielectric layer 22 has a substantially triangular shape in the same manner as the antenna 1 in the first embodiment described above. Has a rounded shape. Thus, each layer does not need to have the same shape, and the antenna 21 disposed on the medium side only needs to be supported by the dielectric layer 22 on the semiconductor substrate 4 side. Considering that the incident light is irradiated from the semiconductor substrate 4 side, in order to efficiently propagate the light to the antenna 1 through the dielectric layer 22, the near-field light generation positions 21n and 22n are in the vicinity. It is desirable that the planar shapes are substantially matched as shown in FIG. In addition, by selecting the shape of each layer individually in this way, the near-field light generation position 21n of the antenna 21 and the near-field light generation position 22n of the dielectric layer 22 have a desired intensity, respectively. Near-field light can be generated.

[4] Fourth Embodiment (Modification of Antenna and Electrode Structure)
Next, an embodiment in which the electrode structure is the same as that of the antenna will be described. 5A is a cross-sectional view of the near-field light generating unit 30, and FIG. 5B is a plan view. As shown in FIG. 5A, the antenna 31 is formed on a semiconductor substrate 34 with a dielectric layer 32 interposed therebetween. Further, the electrode 35 is also formed through the dielectric layer 36. In this case, the current detection unit 38 is connected to the upper layer side electrode 35. As shown in FIG. 5B, the planar shapes of the antenna 31, the dielectric layer 32, the electrode 35, and the dielectric layer 36 are substantially the same shape of a substantially triangular plane, and the top portions are arranged to face each other. . When the antenna 31 and the electrode 35 are arranged in this manner, the intensity of near-field light generated in the vicinity of the positions 31n (32n) and 35a (35b) can be increased due to the interaction between the antenna 31 and the electrode 35. In order to increase the near-field light intensity by increasing the interaction, or to form a fine near-field light spot, it is desirable that the distance between the two be small. The structure of the electrode 35 may be a layer structure made of a material different from that of the antenna 31, or may be a single layer or a structure of three or more layers. Further, the planar shape may not be the same, and any shape that increases the near-field light intensity at the near-field light generation positions 31n and 32n of the antenna 31 may be used.

  Further, in the case where the near-field light intensity is increased in the vicinity of the near-field light generation positions 31n and 32n of the antenna 31 by the interaction with one end of the electrode 35, as in the example shown in FIG. It is desirable to set the height of the electrode 35 to be smaller than the height of the antenna 31. As described above, the configuration in which the electrode 35 is separated from the medium with respect to the antenna 31 can reduce the extent to which the near-field light generated on the medium-side surface of the electrode 35 reaches the medium. Therefore, it is possible to reduce the recording spot size and to reduce noise during recording and reproduction. That is, it is desirable to have a structure in which near-field light intensity generated on the antenna 31 side is enhanced by interaction, and at the same time, the influence of near-field light generated on the electrode 35 side on the medium side is suppressed as much as possible.

[5] Fifth Embodiment (Modification of Antenna and Electrode Structure)
Next, an embodiment in which an antenna and an electrode are embedded in a semiconductor substrate will be described. In this example, as shown in FIG. 6, an example in which the antenna 41, the dielectric layer 42, and the electrode 45 constituting the near-field light generating unit 40 are all embedded in the semiconductor substrate 44 is shown. A current detector 46 is connected to the electrode 45. Either one may be embedded in the semiconductor substrate 44. In order to secure the intensity of near-field light reaching the medium, it is desirable to form the antenna 41 on the semiconductor substrate 44 and embed the electrode 45 in the semiconductor substrate 44. In the illustrated example, both the antenna 41 and the dielectric layer 42 are embedded in the semiconductor substrate 44, but only the dielectric layer 42 may be embedded in the semiconductor substrate 44. Further, the entire electrode 45 may be embedded in the semiconductor substrate 44, and for example, the electrode 45 may be arranged in a shape having a portion extending closer to the near-field light generation position of the dielectric layer 42. Thus, by appropriately selecting the arrangement positions of the antenna 41, the dielectric layer 42, and the electrode 45 including the inside of the semiconductor substrate 44, the signal detection accuracy during reproduction is ensured while ensuring the near-field light intensity reaching the medium. It is possible to improve.

[6] Sixth embodiment (variation example in which a light shielding portion is provided)
Next, with reference to FIG. 7, an embodiment in which a light shielding portion is provided on the back side of the semiconductor substrate will be described. In this example, as shown in FIG. 7A, an antenna 51 is provided on a semiconductor substrate 54 via a dielectric layer 52, an electrode 55 is provided in the vicinity of the antenna 51, and a current detection unit 56 is connected to the electrode 55 so as to be close to each other. A field light generator 50 is configured. A light shielding portion 57 having an opening 57 </ b> A is disposed on the back surface side of the semiconductor substrate 54. The light shielding portion 57 may be disposed on the back surface of the semiconductor substrate 54 at an interval or may be directly formed. It is also possible to form via an underlayer. As shown in FIG. 7B, the planar shape of the opening 57A may be a planar shape in which, for example, the entire surface of the antenna 51 having a substantially triangular shape is irradiated with incident light and the other portions are shielded. The planar shape of the opening 57A may be the same as the planar shape of the antenna 51. In this way, by avoiding the irradiation of unnecessary portions with light and irradiating only the antenna 51 with light, the light use efficiency can be increased. Note that the shape of the opening 57A does not match the shape of the beam spot of the irradiated light, and it is desirable that the position where the near-field light is generated is the light intensity peak position.

  When this embodiment is implemented in combination with the above-described fourth embodiment, the shape of the opening 57A is appropriately selected so that light is also applied to the electrode that increases the near-field light intensity by interaction. Any shape that irradiates light to necessary portions of the antenna and the electrode may be used. In addition, when a metal material is disposed around the antenna in order to increase near-field light intensity, it is desirable to provide a light-shielding portion as an opening shape that irradiates incident light to a necessary region.

[7] Seventh embodiment (variation example in which a base layer is provided)
In each of the above-described embodiments, the antenna and the dielectric layer are stacked and formed directly on the semiconductor substrate. However, in order to improve the adhesion of each layer, the antenna and the dielectric layer can be formed through a base layer. FIG. 8 shows a cross-sectional configuration of the near-field light generator 60 according to this embodiment. In this example, as shown in FIG. 8, on a semiconductor substrate 64, for example, a planar substantially triangular antenna 61 and a dielectric layer 62 and a planar bar-shaped electrode 65, for example, are formed close to each other. The planar shapes of the antenna 61, the dielectric layer 62, and the electrode 65 are not limited to this. A current detector 66 is connected to the electrode 65. For example, base layers 68 and 69 for improving adhesion are formed between the antenna 61 and the dielectric layer 62 and between the dielectric layer 62 and the semiconductor substrate 64, respectively. As a material that enhances the adhesion and has a small influence on the resonance of the antenna 61, a thin film made of, for example, Cr can be used. Thus, if the material and thickness do not affect the intensity of the near-field light generated in the antenna 61, the underlayers 68 and 69 can be interposed in order to improve the adhesion between the layers 61 and 62. It is. Of course, either one of the underlayers 68 and 69 can be formed.

[8] Eighth Embodiment (Modified example in which a pad is provided)
Next, an embodiment in which a pad portion is provided around the antenna and the electrode in order to protect the antenna and the electrode will be described. FIG. 9 is a cross-sectional configuration diagram of the near-field light generating unit 70 according to this embodiment. An antenna 71 is provided on a semiconductor substrate 74 via a dielectric layer 72, and an electrode 75 is formed in the vicinity thereof, so that the current A detection unit 76 is connected. Then, a pad portion 79 is formed in a shape surrounding the antenna 71 and the electrode 75, for example, surrounding the periphery. The material of the pad portion 79 may be, for example, a material having elasticity, and a material having a hardness that does not damage the surface or the information recording material when contacted with the information recording medium. By providing the pad portion 79 in this manner, the antenna 71 and the electrode 75 can be prevented from being damaged when contacting the information recording medium or when the information recording / reproducing apparatus receives an impact. In addition, since such damage can be suppressed, the antenna 71 can be sufficiently brought close to the medium, so that a near-field light having a sufficient intensity is irradiated to a desired position of the medium to avoid a deterioration in recording characteristics. Is possible. In addition, since the interval at which sufficient interaction with the recording material is obtained can be maintained even during reproduction, it is possible to avoid degradation of reproduction characteristics.

[9] Ninth Embodiment (Modification in which a protective layer is provided on an electrode)
This embodiment is an example in which a protective layer is provided on an electrode for the purpose of protecting the electrode. FIG. 10 is a cross-sectional configuration diagram of the near-field light generating unit 80 according to this embodiment. An antenna 81 is formed on a semiconductor substrate 84 via a dielectric layer 82, an electrode 85 is formed in the vicinity thereof, and a current detector 86 is further connected. A protective layer 89 made of a nonconductive material is formed on the electrode 85. In the example shown in the figure, the protective layer 89 is provided so as to cover the entire electrode 85, but a shape that covers a part of the electrode 85, for example, only the upper surface may be used. As described above, by providing the protective layer 89 on the electrode 85, similarly to the example shown in the eighth embodiment, damage to the electrode 85 can be suppressed without inhibiting reproduction signal detection. Even in this case, since the damage to the electrode 85 can be suppressed, the antenna 81 can be sufficiently brought close to the medium. Therefore, a near-field light having a sufficient intensity is irradiated to a desired position to suppress a decrease in recording characteristics. It becomes possible. In addition, since the interval at which sufficient interaction with the recording material is obtained can be maintained even during reproduction, it is possible to avoid degradation of reproduction characteristics.

[10] Configuration of Information Recording Medium Next, an example of the configuration of an information recording medium suitable for use in the information recording / reproducing apparatus according to the present embodiment will be described with reference to FIG.
As described above, in the information recording / reproducing apparatus according to the present embodiment, the information recording material of the information recording medium that can be suitably recorded and reproduced includes a material whose dielectric constant changes, particularly a phase change material.
In the information recording / reproducing apparatus according to the present embodiment, it is preferable to use a medium capable of recording an extremely high density recording mark of about 1 Tbit / inch ² . In order to cope with such a high recording density, as an information recording medium, as shown in FIG. 11, a medium 205 provided with fine particles 206 made of regularly arranged phase change materials is used instead of a continuous film. Is desirable. As an arrangement mode of the fine particles 206, for example, a structure in which concave portions and columnar structures (not shown) are regularly arranged on the surface of the medium 205 and the fine particles 206 are arranged in the concave portions and on the columnar structures can be considered. As described above, by adopting a configuration in which the fine particles 206 made of the phase change material are regularly arranged as the information recording medium, it is possible to perform local recording in a desired minute region. Therefore, improvement in resolution and increase in recording density can be expected.

[11] Tenth Embodiment (Configuration of Information Recording / Reproducing Device)
Next, a schematic configuration of the entire information recording / reproducing apparatus according to the embodiment of the present invention will be described. FIG. 12 shows a case where a disc-shaped medium 200 is mounted on the information recording / reproducing apparatus 150 as an example. The medium 200 includes a recording unit 201 made of an information recording material such as a phase change material in which a signal is recorded on the substrate 202 by the above-described change in dielectric constant. The medium 200 is fixedly supported on a mounting table on a rotating shaft 141 rotated by a driving unit 140 such as a spindle motor provided in the apparatus 150. The medium 200 is rotated about the one-dot chain line C as the central axis by the rotational drive of the drive unit 140.

  At the time of recording or reproduction, the near-field light generating unit 10 of the information recording / reproducing apparatus 150 is disposed close to the recording unit 201 of the medium 200. In this case, the semiconductor substrate 4 on which the antenna 1, the dielectric layer 2, and the electrode 5 are formed is provided on a slider (not shown), or is supported by a biaxial or triaxial actuator or the like, and the recording unit 201 of the medium 200. It is set as the structure which moves relatively, controlling the distance. When the medium 200 rotates, it is disposed so as to face a desired recording track position on the recording unit 201. A predetermined voltage is applied between the antenna 1 and the electrode 5 by an application means (not shown), and a current detection unit 6 such as an ammeter is connected, and a detection signal is output to the detection unit 7. In this example, although the case where the near-field light generation part 10 which concerns on 1st Embodiment is used is shown, various structures including the example which concerns on 2nd-9th embodiment can be employ | adopted. .

  Further, the information recording / reproducing apparatus 150 is provided with a light source 121 in which the wavelength band described above is selected. The optical system 100 is disposed between the light source 121 and the semiconductor substrate 4 so that the polarization direction (electric field vibration direction) coincides with the antenna 1 in a predetermined direction. For example, a collimator lens 122, a polarizer 124, and a condenser lens 125 are disposed on the outgoing light path of the light Li emitted from the light source 121. With such a configuration, the light Li emitted from the light source 121 is applied to the antenna 1 of the near-field light generating unit 10 with a predetermined polarization direction.

  In this configuration, as an example, an operation of recording a signal in the recording unit 201 made of a phase change material such as GeSbTe will be described. In this case, first, the drive unit 140 is driven to rotate the medium 200, while the antenna 1 formed on the semiconductor substrate 4 of the information recording / reproducing apparatus 150 is connected to a desired recording track of the recording unit 201 on the medium 200. On the top, they are arranged opposite to each other with a predetermined interval. This interval is, for example, several nm. For example, the light source 121 emits light Li having a wavelength that matches the material and shape of the antenna 1 and resonates with the antenna 1. The light Li is applied to the back surface of the semiconductor substrate 4 through the collimator lens 122, the polarizer 124, and the condenser lens 125, and further passes through the semiconductor substrate 4 and the dielectric layer 2 to be applied to the antenna 1.

  Strong near-field light is generated by resonance at the end of the antenna 1, and light having an intensity that promotes phase change is applied to a desired position of the recording unit 201 of the information recording medium 200. Thereby, information is recorded in the recording unit 201. At this time, by appropriately selecting the material and shape of the dielectric layer 2, the near-field light intensity generated at the interface of the dielectric layer 2 on the semiconductor substrate 4 side can be suppressed. Therefore, it is possible to increase the light use efficiency.

  Next, an operation for detecting a signal recorded in the recording unit 201 will be described. During reproduction, a constant voltage is applied between the antenna 1 and the electrode 5. Then, for example, the antenna 1 is opposed to the medium 200 having the recording unit 201 made of a phase change material such as GeSbTe, and disposed at a distance of, for example, several nm. In the recording unit 201 made of a phase change material, a recording area and an unrecorded area are formed in advance by the recording method described above. In this state, the light source 121 emits light Li having a wavelength suitable for the antenna 1 and resonating with the antenna 1. The light Li is applied to the back surface of the semiconductor substrate 4 through the collimator lens 122, the polarizer 124, and the condenser lens 125. Then, the antenna 1 is irradiated through the semiconductor substrate 4 and the dielectric layer 2. At this time, near-field light is generated at the interface between the semiconductor substrate 4 and the dielectric layer 2.

  As the light source 121, a light source that outputs light having a wavelength that provides photon energy that is approximately half the band gap energy of the material of the semiconductor substrate 4 is used. For example, when the semiconductor substrate 4 is used from GaN, the band gap energy is about 3.4 eV and the corresponding photon energy is 365 nm. Therefore, as the light source, a light source that outputs light with a wavelength λ≈730 nm is selected. To do. With this configuration, a two-photon absorption phenomenon occurs in a region of strong energy density inside the semiconductor substrate 4, and a photocurrent is generated with the generation of electron-hole pairs. This current fluctuates in synchronization with the change in the near-field light intensity, and changes in synchronization with the change in the signal due to the change in the dielectric constant in the recording unit 201 and the interaction with the antenna 1.

  Explaining this, since the dielectric constant is different between the recording area and the non-recording area of the recording unit 201, the relative permittivity changes over time on the surface of the recording unit 201 due to the relative movement between the information recording medium 200 and the information recording / reproducing device 150. Changes. As the dielectric constant changes, the state in which the near-field light is generated in the antenna 1 changes, so that the near-field light intensity generated in the dielectric layer 2 also changes. That is, the intensity of near-field light changes due to the interaction between the antenna 1 and the surface of the recording unit 201 whose dielectric constant changes. Therefore, the value of the photocurrent generated corresponding to the near-field light also changes, and the current value corresponding to the information recorded in the recording unit 201 of the medium 200 can be detected as an information signal in the current detection unit 6. Become.

[12] Analysis Example Hereinafter, near-field light related to recording and reproduction is generated with sufficient intensity at the near-field light generation positions on both the recording medium side and the semiconductor substrate side of the antenna mounted on the information recording / reproducing apparatus described above. A specific example of analyzing this will be described. The following analysis results are calculated by the FDTD (Finite Difference Time Domain method) method.

In this example, the analysis was performed using the near-field light generating unit configured as in the first embodiment shown in FIG. 13A is a cross-sectional configuration diagram of a near-field light generating unit according to an embodiment of the present invention, and FIG. 13B is a cross-sectional configuration diagram of a near-field light generating unit according to a comparative example. As shown in FIG. 13A, in the present embodiment, an antenna 1 made of Au is formed on a semiconductor substrate 4 made of GaN via a dielectric layer 2 made of SiO ₂ . The thickness of the antenna 1 was 20 nm, and the thickness of the dielectric layer 2 was 10 nm. The planar shape of both the antenna 1 and the dielectric layer 2 is a substantially equilateral triangle shape, and the radius of curvature at the apex corresponding to the near-field light generation positions 1n and 2n is 10 nm. The shortest distance to the opposite side is 100 nm, and incident light having polarization (electric field oscillation direction) parallel to the direction is incident from the semiconductor substrate 4 side so that the spot center position substantially coincides with the apex position.

On the other hand, in the configuration of the comparative example, as shown in FIG. 13B, an antenna 91 made of Au having a single layer structure is formed on a semiconductor substrate 92 made of SiO ₂ . The planar shape of the antenna 91 is the same as the planar shape of the antenna 1 shown in FIG. 13A. In this case, the near-field light generation positions 91n and 92n are an end portion on the surface side of the antenna 91 and an end portion on the semiconductor substrate 92 side, respectively.

FIG. 14 shows the resonance wavelength when Au is provided on the GaN substrate via SiO ₂ as a solid line a1, and the resonance wavelength when Au is provided on the SiO ₂ substrate as a solid line a2. It can be seen that in both configurations, the resonance wavelength is around 780 nm. The reason why the resonance wavelengths are almost the same in the two structures is considered to be due to the fact that both surfaces on which the antenna made of Au is in contact are only SiO ₂ .

Under such conditions, the surface of the semiconductor substrates 4 and 92 in each example was set to 0 point on the Z axis, and the near-field light intensity distribution in the Z direction was analyzed. The result is shown in FIG. In Figure 15, Z = 0 nm is interface position of the antenna and the substrate, Au _/ SiO 2 _/ GaN substrate configuration shown in FIG. 13A, in each of the Au / SiO ₂ substrate configuration shown in FIG. 14B, Z = 30nm, 20nm is This is the antenna top surface position. In FIG. 15, the solid line b1 is the Au / SiO ₂ / GaN substrate configuration according to the present embodiment, and the broken line b2 is the near-field light intensity distribution in the Au / SiO ₂ substrate configuration according to the comparative example.

  From the result of FIG. 15, it is understood that the near-field light is enhanced by providing the dielectric layer 2 between the semiconductor substrate 4 and the antenna 1. This is probably because the dielectric layer 2 has a light confinement effect because the refractive index of the dielectric layer 2 is smaller than the refractive index of the semiconductor substrate 4. In other words, since light in the vicinity of the antenna 1 does not return to the semiconductor substrate 4 side due to the light confinement effect, it is considered that the near-field light intensity is increased by increasing the utilization efficiency of the light irradiated to the antenna 1. In this case, since the near-field light intensity on the medium side is particularly enhanced, the antenna 1 is sufficient for recording, for example, a phase change material, for example, although the antenna 1 has a relatively simple configuration without being complicated. It is possible to obtain a sufficient recording power for a recording medium composed of the above.

  FIG. 16 and FIG. 17 show examples of near-field light intensity distribution generated due to the difference in refractive index between the semiconductor substrate 4 and the dielectric layer 2, the substrate internal position (Z = −0.5 nm), the dielectric layer internal position ( Z = 0.5 nm). 16 and 17, both are shown on the same scale, and the size of the circle represents the near-field light intensity. It can be seen that the intensity generated in the semiconductor substrate 4 and the dielectric layer 2 is in a nested relationship depending on the refractive index. It can be seen that near-field light enhancement always occurs when the refractive index relationship between the semiconductor substrate 4 and the dielectric layer 2 is satisfied, and that the enhancement can be further increased by increasing the refractive index difference. That is, in order to increase the near-field light intensity on the inner side of the dielectric layer 2 near the near-field light generation position 1n of the antenna 1, the refractive index of the dielectric layer 2 is made smaller than the refractive index of the semiconductor substrate 4. In particular, it can be said that it is desirable to select the material so that the refractive index difference is 1 or more.

As described above, according to the present invention, the following effects can be obtained.
1. It is possible to increase the recording density using the local light spot in the near field and stabilize the reproduction signal detection.
2. Since it is possible to adjust the near-field light intensity related to the recording and reproduction signal detection, it is advantageous for improving the light utilization efficiency.
3. Since the near-field light intensity relating to the recording / reproducing signal detection can be adjusted, the thermal damage to the semiconductor substrate can be reduced.

From these effects, it is possible to provide an optical recording / reproducing system that realizes a high recording density exceeding 1 Tbit / inch ² that has been difficult to realize by the conventional phase change optical recording system. That is, according to the present invention, there is provided an information recording / reproducing system comprising a mechanism for irradiating information recording medium with sufficient energy for recording and a mechanism for performing direct detection of near-field light under reproduction with high efficiency. It becomes possible to do.
Further, by utilizing this recording / reproducing method, it becomes possible to detect a minute change in the sample surface with high resolution.

  The present invention is not limited to the configuration described in the above-described embodiment, and various modifications and changes can be made without departing from the configuration of the present invention.

It is a schematic sectional block diagram of the principal part of the information recording / reproducing apparatus which concerns on embodiment of this invention. It is a plane block diagram of an example of the antenna and electrode of the information recording / reproducing apparatus shown in FIG. It is a schematic sectional block diagram of the principal part of the information recording / reproducing apparatus which concerns on embodiment of this invention. It is a schematic block diagram of the principal part of the information recording / reproducing apparatus which concerns on other embodiment of this invention. A and B are a schematic cross-sectional configuration diagram and a plan configuration diagram of a main part of an information recording / reproducing apparatus according to another embodiment of the present invention. It is a schematic sectional block diagram of the principal part of the information recording / reproducing apparatus which concerns on other embodiment of this invention. FIG. 3A is a schematic cross-sectional configuration diagram of a main part of an information recording / reproducing apparatus according to another embodiment of the present invention. B is a plan view of the main part. It is a schematic sectional block diagram of the principal part of the information recording / reproducing apparatus which concerns on other embodiment of this invention. It is a schematic sectional block diagram of the principal part of the information recording / reproducing apparatus which concerns on other embodiment of this invention. It is a schematic sectional block diagram of the principal part of the information recording / reproducing apparatus which concerns on other embodiment of this invention. It is explanatory drawing of the information recording medium suitable for using for the information recording / reproducing apparatus which concerns on embodiment of this invention. 1 is a schematic configuration diagram of an information recording / reproducing apparatus according to an embodiment of the present invention. 1A is a schematic cross-sectional configuration diagram of a main part of an information recording / reproducing apparatus according to an embodiment of the present invention. B is a schematic cross-sectional configuration diagram of an antenna according to a comparative example. It is a diagram showing the wavelength dependence of the near-field light intensity in Au _/ SiO 2 _/ GaN substrate structure and au / SiO ₂ substrate structure. It is a figure which shows the near field light intensity distribution in the example shown to FIG. 13A and B. FIG. It is a figure which shows typically the near field light intensity in the inside of a board | substrate at the time of changing a dielectric material layer refractive index and a board | substrate refractive index by the magnitude | size of a circle | round | yen. It is a figure which shows typically the near field light intensity inside a dielectric material layer at the time of changing a dielectric material layer refractive index and a board | substrate refractive index by the magnitude | size of a circle | round | yen.

Explanation of symbols

  1, 21, 31, 41, 51, 61, 71, 81. Antennas 2, 22, 32, 42, 52, 62, 72, 82. Dielectric layers 4, 34, 44, 54, 64, 74, 84. Semiconductor substrate, 5, 35, 45, 55, 65, 75, 85. Electrodes, 6, 38, 46, 56, 66, 76, 86. Current detection unit 10, 30, 40, 50, 60, 70, 80. Near-field light generating section, 100. Optical system, 121. Light source, 122. Collimating lens, 124. Polarizer, 125. Condensing lens, 140. Driving unit, 141. Rotation axis, 150. Information recording / reproducing apparatus, 200, 205. Medium, 206. Information recording material

Claims (13)

A light source;
A semiconductor substrate having transparency to the light emitted from the light source;
A dielectric layer made of a dielectric material having a refractive index lower than the refractive index of the semiconductor substrate provided on the semiconductor substrate and corresponding to the light emitted from the light source;
An antenna that is provided on the semiconductor substrate via the dielectric layer and is irradiated with light emitted from the light source to generate near-field light;
A signal detection unit that detects the degree of interaction between the information recording material that changes due to light or heat and the near-field light generated from the antenna, based on a change in the intensity of the near-field light inside the semiconductor substrate. Playback device.   The information recording / reproducing apparatus according to claim 1, wherein the antenna includes a layer made of a metal that resonates with a wavelength of light emitted from the light source.   The information recording / reproducing apparatus according to claim 1, wherein the antenna includes a layer made of any one of Pt, Mg, Au, Al, and Ag.   2. The information recording / reproducing apparatus according to claim 1, wherein the wavelength of the light emitted from the light source is a wavelength corresponding to a photon energy of approximately one half or more of a band gap energy of a material of the semiconductor substrate.   The information recording / reproducing apparatus according to claim 1, wherein the signal detection unit is a current detection unit that detects a photocurrent generated in the semiconductor substrate when the near-field light is generated. _2. The information recording / reproducing apparatus according to claim 1, wherein the semiconductor substrate is made of any one of SiC, AlP, ZnO, ZnS, ZnSe, GaN, and TiO2. The information recording / reproducing apparatus according to claim 1, wherein the dielectric layer is made of any one of MgF ₂ , CaF ₂ , and SiO ₂ .   The information recording / reproducing apparatus according to claim 1, wherein the light source is a light source that emits light having a wavelength band of 344 nm to 992 nm.   The information recording / reproducing apparatus according to claim 5, wherein a height of the current detection unit is formed smaller than a height of the antenna.   The information recording / reproducing apparatus according to claim 1, wherein a light shielding portion having an opening corresponding to the shape of the antenna is provided on a surface of the semiconductor substrate on which light from the light source is irradiated. An antenna formed on a semiconductor substrate via a dielectric layer is irradiated with light from a light source to cause local concentration of polarization, and near-field light is generated on the surface side of the antenna and the inside of the semiconductor substrate side. Occur and
Opposing the antenna, a medium having a material that changes by light or heat is disposed,
A near-field light detection method, wherein a degree of interaction between the material and near-field light generated from the antenna is detected by a signal corresponding to an intensity change of near-field light inside the semiconductor substrate.   The near-field light detection method according to claim 11, wherein the material of the medium is made of inorganic fine particles.   The near-field light detection method according to claim 12, wherein the inorganic fine particles are made of a phase change material.

Images