JP2010129166A - Information recording and reproducing device and near-field light intensity detection method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an information recording and reproducing device by which recording and reproducing of recording information of high density are performed by utilizing near-field light. <P>SOLUTION: An antenna 1 of a layered structure (a first layer 2 and a second layer 3) provided on a semiconductor substrate 4 is used as the antenna 1 generating near-field light. The degree of interaction between a material changed by light or heat and near-field light generated from the antenna 1 is detected by a signal corresponding to intensity change of the near-field light in the inner part of 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 a layered antenna provided on a semiconductor substrate as an antenna that generates near-field light. 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 structure in which an antenna serving as a near-field generating mechanism is provided on a semiconductor substrate, a photocurrent is generated by near-field light, and thereby a change in the intensity of near-field light can be detected. 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.

  On the other hand, as described above, the antenna formed on the semiconductor substrate has a layered structure, thereby adjusting 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. It becomes possible to do. For example, when an antenna is configured by using a metal that causes plasmon resonance with respect to the wavelength used for the surface layer facing the medium, etc., and selecting a different metal as the layer on the semiconductor substrate side, The layer can generate, for example, near-field light having a sufficient intensity for recording. Furthermore, near-field light with sufficient intensity can also be generated at the interface between the semiconductor substrate and the substrate-side layer 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) Planar shape of antenna and electrode (4) Light source (5) Semiconductor substrate material ( 6) Information recording material [2] Second embodiment (modified example of 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 (Modification of information recording material)
[7] Seventh embodiment (variation example in which a light shielding portion is provided)
[8] Eighth embodiment (variation example in which a base layer is provided)
[9] Ninth embodiment (variation example in which a pad is provided)
[10] Tenth Embodiment (Modification in which a protective layer is provided on an electrode)
[11] Eleventh Embodiment (Configuration of Information Recording Medium)
[12] Twelfth Embodiment (Configuration of Information Recording / Reproducing Device)
[13] Analysis example

1. First Embodiment (1) Configuration of Near-field Light Generation Unit Including Antenna FIG. 1 is a schematic cross-sectional configuration 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. FIG. As shown in FIG. 1, the near-field light generator 10 includes an antenna 1, a semiconductor substrate 4, and an electrode 5. The antenna 1 is configured by laminating an upper first layer 2 and a lower (semiconductor substrate 4 side) second layer 3 on a semiconductor substrate 4. An electrode 5 is provided on the semiconductor substrate 4 in the vicinity of the antenna 1. The current detector 6 is connected to the antenna 1 and the electrode 5 as a signal detector. A voltage application mechanism 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 to face the first layer 2 of the antenna 1.

(2) Material of antenna and electrode Here, as the material of each of the layers 2 and 3 constituting the antenna 1, a metal capable of obtaining sufficient resonance with respect to the wavelength of a light source (not shown) 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, the first layer 2 can be irradiated with the incident light Li. Near-field light is generated in the vicinity of the near-field light generation position 1a at the surface end on the electrode 5 side. Further, near-field light is also generated in the vicinity of the near-field light generation position 1b at the interface portion on the semiconductor substrate 4 side on the electrode 5 side of the second layer 3.

  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) Plane Shape of Antenna and Electrode FIG. 2 is a plan view showing an example of the planar shape of the antenna 1 and the electrode 5. In this example, the antenna 1 has a substantially triangular shape on the plane, and each vertex has a rounded shape, with one vertex facing the electrode 5 side. In this case, the apex on the side facing the electrode 5 is the near-field light generation position (1a, 1b), and the direction toward the opposite side is the 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 shape of the antenna 1 and the electrode 5 is not limited to the example shown in FIG. 2, and each of the planar shapes of the antenna 1 and the electrode 5 may be any shape that does not suppress the intensity of near-field light generated in the antenna 1. More desirable. As shown in FIG. 2, when the shape is sharpened toward the position 1a (1b) where the near-field light spot is to be formed, the near-field light intensity is enhanced, which is desirable. In addition, for example, not only the electrode 5 is disposed opposite to the position 1a at the tip of the antenna 1, but also the electrode 5 is disposed opposite to 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 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 1a (1b) where the near-field light spot is to be formed is arranged so as to be close to the medium 200, and conversely, the end portion 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 1a where the near-field light spot is generated closer to the medium 200 than the 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, light having polarized light is emitted, and the wavelength thereof is the first layer portion of the antenna 1. The layer 2 is selected according to its shape and material so as to cause plasmon resonance alone. 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 light from the light source to the antenna 1 through the semiconductor substrate 4, proximity to the position 1 a of the end portion on the electrode 5 side on the surface of the first layer 2 of the antenna 1 with sufficient strength for recording or the like. Field light can be generated. At this time, near-field light is also generated at the position 1 b of the end portion on the electrode 5 side in the second layer 3 of the antenna 1. The intensity of the near-field light can be adjusted by the relationship between the materials of the layers 2 and 3 of the antenna 1 and the wavelength of the light emitted from the light source. That is, by configuring the materials of the layers 2 and 3 from different materials, it is possible to configure the antenna 1 having a desired near-field light intensity by selecting the wavelength used. An example of a specific combination of the material and the wavelength of each layer 2 and 3 of the antenna 1 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 the material of the semiconductor substrate 4 is used, any light source that includes light having a wavelength in a wavelength range of 344 nm or more and 992 nm or less or a wavelength in a predetermined range in the emitted light is used. Good. 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 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 1b 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 thereof, at the time of plasmon resonance. Most of the near-field light is concentrated at the position 1b 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 antenna 1 composed of the first layer 2 and the second layer 3 is used. Accordingly, by selecting the material and shape of the first layer 2 and the wavelength of the light source appropriately, the near-field light in the vicinity of the near-field light generation position 1a of the first layer 2 on the side facing the information recording medium. The strength can be made sufficiently high.

  In addition, when a second light source that emits light of a different wavelength is used as the light source, it is possible to suppress or avoid deterioration in reproduction characteristics. That is, by appropriately selecting the material and shape of the second layer 3 and the wavelength of the second light source, the near-field light in the vicinity of the near-field light generation position 1b at the interface of the second layer 3 on the semiconductor substrate 4 side. The strength can be made sufficiently higher than the position 1a on the surface side. In this case, it is possible to avoid affecting the recording mark during reproduction. As a result, a mechanism for recording on the recording medium and a reproducing mechanism for direct detection of near-field light can be provided at the same time, and good recording / reproducing characteristics can be realized.

(6) 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, thereby changing the near-field light intensity at the position 1 b on the semiconductor substrate 4 side of the antenna 1. 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 composed of a first layer 22 and a second layer 23 having different planar shapes is formed on a semiconductor substrate (not shown). In this example, the first layer 22 has a rod shape and both ends are rounded, and the second layer 23 has a substantially triangular shape in the same manner as the antenna 1 in the first embodiment described above. Each top is rounded. As described above, the layers do not have to have the same shape, and the first layer 22 on the medium side only needs to be supported by the second layer 23 on the substrate side. Considering that the incident light is irradiated from the substrate side, in order to reduce the influence of being shielded by the second layer 23, especially near the near-field light generation positions 21a and 21b, which are the portions where the near-field light is generated. It is desirable that the planar shapes are substantially matched as shown in FIG. Further, by selecting the shape of each layer individually in this way, in the vicinity of the near-field light generation position 21a of the first layer 22 and the near-field light generation position 21b of the second layer 23, respectively. It is possible to generate near-field light having a desired intensity.

[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 has a configuration in which an upper first layer 32 and a second layer 33 are stacked on a semiconductor substrate 34. Further, the electrode 35 is also configured by an upper first layer 36 and a lower second layer 37. The current detection unit 38 is connected to the upper first layer 36, for example. As shown in FIG. 5B, the planar shapes of the antenna 31 and the electrode 35 are substantially the same shape of a substantially triangular plane, and the tops are arranged to face each other. When the antenna 31 and the electrode 35 are arranged as described above, the intensity of near-field light generated in the vicinity of the positions 31a (31b) 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 shapes may not be the same, and any shape that increases the near-field light intensity at the near-field light generation positions 31 a and 31 b of the antenna 31 may be used.

  In the case where the near-field light intensity in the vicinity of the near-field light generation positions 31a and 31b of the antenna 31 is increased by the interaction with one end of the electrode 35 as described above, as in the example shown in FIG. It is desirable to set the height of the electrode smaller than the height of the antenna. As described above, the configuration in which the electrode is separated from the medium rather than the antenna can reduce the degree of the near-field light generated on the medium-side surface of the electrode reaching 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 both the antenna 41 and the electrode 45 constituting the near-field light generating unit 40 are 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, the first layer 42 and the second layer 43 constituting the antenna 41 are both embedded in the semiconductor substrate 44, but only the second layer 43 is included in the semiconductor substrate 44. It may be embedded. Further, the entire electrode 45 may be embedded in the semiconductor substrate 44, and for example, it may be arranged at a position closer to the near-field light generation position of the second layer 43. Thus, by appropriately selecting the positions of the layers 42 and 43 and the electrode 45 including the inside of the semiconductor substrate 44, it is possible to improve the signal detection accuracy during reproduction while ensuring the near-field light intensity reaching the medium. It is possible to plan.

[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 including a first layer 52 and a second layer 53 is provided on a semiconductor substrate 54, an electrode 55 is provided in the vicinity of the antenna 51, and a current detection unit is provided on the electrode 55. 56 is connected to form the near-field light generator 50. 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 plane formation in which incident light is irradiated on the entire surface of the antenna 51 having a substantially triangular shape, for example, and 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.

[7] Seventh embodiment (variation example in which a base layer is provided)
In each of the above-described embodiments, the layers constituting the antenna are directly stacked and formed. However, in order to improve the adhesion of each layer, the layers can be formed through a base layer. FIG. 8 shows a cross-sectional configuration of the near-field light generating device 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, for example, a planar bar-shaped electrode 65 are formed in proximity to each other. The planar shapes of the antenna 61 and the electrode 65 are not limited to this. A current detector 66 is connected to the electrode 65. The antenna 61 has a configuration in which an upper first layer 62 and a second layer 63 on the semiconductor substrate 64 side are laminated, and a base layer 68 for improving adhesion, for example, is formed between the layers 62 and 63. May be. Further, an underlayer 69 may be interposed between the second layer 63 and the semiconductor substrate 64. 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 the 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 62 and 63. 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 device 70 according to this embodiment. An antenna 71 composed of a first layer 72 and a second layer 73 is provided on a semiconductor substrate 74, and an electrode 75 is provided in the vicinity thereof. Is formed, and the current 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 a material having elasticity, for example, as long as it has a hardness that does not damage the surface or the information recording material when it comes into contact 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 a near-field light generating device 80 according to this embodiment. An antenna 81 composed of a first layer 81 and a second layer 82 is formed on a semiconductor substrate 84, 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 electrode can be prevented from being damaged, 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 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.

[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 (not shown) are regularly arranged on the surface of the medium 205 and incorporated therein is conceivable. 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 reproducing, the antenna 1 of the information recording / reproducing apparatus 150 is disposed close to the recording unit 201 of the medium 200. The semiconductor substrate 4 on which the antenna 1 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 is controlled relative to the recording portion 201 of the medium 200 while controlling the distance. It is set as the structure which moves automatically. 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 generator which concerns on 1st Embodiment is used is shown, various structures including the example which concerns on the 2nd-9th embodiment can be employ | adopted.

  In this example, an example in which a first light source 121 and a second light source 131 that emit light of different wavelengths are provided is shown. The optical system 100 is arranged between the light sources 121 and 131 and the semiconductor substrate 4 so that the polarization direction (electric field vibration direction) coincides with the antenna 1 in a predetermined direction. On the outgoing optical path of the light Lia emitted from the first light source 121, for example, a collimator lens 122, an optical path synthesis element 123 such as a prism, a polarizer 124, and a condenser lens 125 are arranged. Also, for example, a collimator lens 132 and an optical path synthesis element 123 are disposed on the outgoing optical path of the light Lib emitted from the second light source 131. Then, the light Lib emitted from the second light source 131 in the optical path synthesizing element 123 is changed in the traveling direction by 90 degrees and is directed toward the semiconductor substrate 4. With such a configuration, light Lia and Lib having different wavelengths are incident on the antenna 1 through the semiconductor substrate 4. In addition, it is set as the structure by which incident light Lia and Lib are switched by the controller (not shown) connected to the light sources 121 and 131. FIG. By making such switching possible, light of different wavelengths from the first light source 121 and the second light source 131 to the antenna 1 from the back side through the semiconductor substrate 4 during recording and during reproduction. Lia and Lib are irradiated.

  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 4 formed on the semiconductor substrate 4 of the information recording / reproducing apparatus 150 is placed on a desired recording track of the recording unit 201 on the medium 200. And facing each other at a predetermined interval. This interval is, for example, several nm. For example, the first light source 121 emits light Lia having a wavelength that matches the material and shape of the first layer 2 of the antenna 1 and resonates with the first layer 2. The light Lia is applied to the back surface of the semiconductor substrate 4 through the collimator lens 122, the optical path combining element 123, the polarizer 124, and the condenser lens 125, and further passes through the semiconductor substrate 4 and is applied to the antenna 1.

  Strong near-field light is generated by resonance at the end of the first layer 2 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, the intensity of the near-field light generated at the interface of the second layer 3 on the semiconductor substrate 4 side can be suppressed by appropriately selecting the material and shape of the second layer 3. 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 second light source 131 emits light Lib having a wavelength that matches the material and shape of the second layer 3 of the antenna 1 and that causes the second layer 3 to resonate. The light Lib is incident on the optical path synthesizing element 123 via the collimator lens 132, the optical path is converted, and the rear surface of the semiconductor substrate 4 is irradiated via the polarizer 124 and the condenser lens 125. Then, the light passes through the semiconductor substrate 4 and is applied to the second layer 3 of the antenna 1. At this time, near-field light is generated at the interface between the semiconductor substrate 4 and the second layer 3 of the antenna 1. Note that near-field light is also generated on the surface side of the first layer 2 of the antenna 1, that is, the end of the medium 200 facing the recording unit 201, but the material and shape of the first layer 2 are appropriately set. By selecting, it is possible to appropriately suppress the near-field light intensity at this time.

  Then, as the light source 131, 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 second layer 3 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.

  FIG. 13 shows the wavelength dependence of near-field light intensity when using an antenna composed of an Au single layer. When Au is used as the antenna, it is understood that light having a wavelength of around 700 nm, which is near the resonance condition, is preferable.

  In this example, the analysis was performed using the near-field light generating unit configured as in the first embodiment shown in FIG. FIG. 14A is a cross-sectional configuration diagram of the near-field light generating unit according to the embodiment of the present invention, and FIG. 14B is a cross-sectional configuration diagram of the near-field light generating unit according to the comparative example. As shown in FIG. 14A, in the present embodiment, the antenna 1 is formed in a two-layer configuration so as to be in contact with the semiconductor substrate 4 made of GaN. The thickness of both the first layer 2 and the second layer was 30 nm, the upper first layer 2 was made of Au, and the second layer 3 on the semiconductor substrate 4 side was made of Al. The planar shape of each layer was almost a regular triangle. The curvature in the vicinity of the near-field light generation position 1a on the surface side of the first layer 2 and the near-field light generation position 1b of the second layer 3 was 10 nm. The shortest distance to the opposite side is 100 nm, and incident light having polarization (electric field oscillation direction) parallel to that direction is incident from the substrate 4 side so that the spot center position substantially coincides with the apex position. The wavelength used was 700 nm suitable for the Au resonance condition as described above.

  On the other hand, in the configuration of the comparative example, as shown in FIG. 14B, an antenna 91 made of Au having a single layer structure is formed on a semiconductor substrate 92 made of GaN. The planar shape of the antenna 91 is the same as the planar shape of the antenna 1 shown in FIG. 14A. In this case, the near-field light generation positions 91a and 91b are an end portion on the surface side of the antenna 91 and an end portion on the semiconductor substrate 92 side, respectively.

  In each example, the near-field light intensity distribution in the Z direction was analyzed with the surface of the semiconductor substrates 4 and 92 as 0 point on the Z axis. The result is shown in FIG. 15, Z = 0 nm is the interface position between the antenna and the substrate. In the Au / Al / GaN substrate configuration shown in FIG. 14A and the Au / GaN substrate configuration shown in FIG. 14B, Z = 60 nm and 30 nm are the top surface of the antenna. Position. In FIG. 15, the solid line a1 is the Au / Al / GaN substrate configuration according to the present embodiment, and the solid line a2 is the near-field light intensity distribution in the Au / GaN substrate configuration according to the comparative example.

  From the results of FIG. 15, when the refractive index of the substrate that directly supports the antenna as in the Au / GaN substrate configuration is high, the near-field light intensity on the substrate interface side is higher than the near-field light intensity generated at the top of the antenna. It turns out that it becomes much higher. This is probably because most of the polarization related to the generation of near-field light inside the antenna is biased toward the substrate due to the high refractive index and the high polarizability of the substrate. For this reason, in the case of the comparative example, the recording becomes unstable and inefficient, and the antenna itself unnecessarily rises in temperature due to near-field light at the antenna / substrate interface that does not contribute to recording. Bad effects occur.

  On the other hand, as in the Al / Au / GaN substrate configuration, the antenna is made into two layers, and the wavelength near the resonance condition of the antenna layer on the recording medium side is used. Can be generated with sufficient strength. At the same time, it is possible to maintain the near field intensity at the antenna / substrate interface related to the reproduction signal detection to some extent. In this way, even on a substrate with a high refractive index, the near-field light with the intensity required for recording and reproduction signal detection can be formed into a layer structure on the antenna so that both the antenna top and the antenna / substrate interface It becomes possible to make it the structure which generate | occur | produces.

  Further, by adjusting the thickness and shape of each layer, it is possible to adjust the near-field light intensity at each of the antenna upper portion and the antenna / substrate interface to a ratio suitable for recording and reproduction signal detection.

Next, the effect which appears by using two wavelengths with respect to the two-layer structure of an antenna is shown.
FIG. 16 shows the wavelength dependence of the near-field light intensity generated at the antenna / substrate interface and the upper part of the antenna in the near-field light generating section having the structure shown in FIG. 14A. It can be seen from FIG. 16 that the resonance wavelengths are different between the two layers of Al and Au. Using this property, it is possible to adjust the near-field light intensity generated at the top of the antenna or at the interface between the antenna and the semiconductor substrate. For this reason, as described above, a light source having two wavelengths is prepared, and the wavelength at which the recording medium side layer of the antenna resonates is used during recording, and the wavelength at which the substrate side layer resonates when a reproduction signal is detected. . By adopting a configuration including such a two-wavelength light source, it is possible to provide an information recording / reproducing apparatus that generates near-field light suitable for recording / reproducing. In this case, since the near-field light intensity generated on the recording medium side can be suppressed at the time when the reproduction signal is detected, the recording phase can be prevented from being rewritten due to the temperature rise, and the recording / reproduction characteristics are deteriorated. It can be expected to suppress.

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.
4. By using two wavelengths, it is possible to use near-field light intensity suitable for optical recording and reproduction.

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. It is a figure which shows the wavelength dependence of the near-field light intensity with respect to the antenna of Au single layer. 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 figure which shows the near field light intensity distribution in the example shown to FIG. 14A and B. FIG. It is a figure which shows the wavelength dependence of the near-field light intensity in each antenna position.

Explanation of symbols

  1, 21, 31, 41, 51, 61, 71, 81. Antennas 2, 22, 32, 42, 52, 62, 72, 82. 1st layer, 3, 23, 33, 43, 53, 63, 73, 83. Second layer, 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. First light source, 122. Collimating lens, 123. Optical path synthesis element, 124. Polarizer, 125. Condensing lens, 131. Second light source, 132. Collimating lens, 140. Driving unit, 141. Rotation axis, 150. Information recording / reproducing apparatus, 200, 205. Medium, 206. Information recording material

Claims (15)

A light source;
A semiconductor substrate having transparency to the light emitted from the light source;
An antenna having a layer structure that is provided on the semiconductor substrate and generates near-field light when irradiated with light emitted from the light source;
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 has a layer structure made of two or more metals.   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.   2. The information recording / reproducing apparatus according to claim 1, wherein each layer of the antenna is made of two kinds of metals that cause respective resonance states corresponding to different wavelengths.   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.   6. The information recording / reproducing apparatus according to claim 5, wherein the antenna is constituted by a layer structure of Au and Al.   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 light source is a light source that includes light of any wavelength in a wavelength band of 344 nm or more and 992 nm or less in emitted light.   The information recording / reproducing apparatus according to claim 8, wherein a height of the current detection unit is 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. Irradiation of light from a light source to a layered antenna formed on a semiconductor substrate causes local concentration of polarization, generating near-field light on the surface side of the antenna and inside the semiconductor substrate side 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 13, wherein the medium material is made of inorganic fine particles.   The near-field light detection method according to claim 14, wherein the inorganic fine particles are made of a phase change material.

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