JP2001266421A - Recorder and recording method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a recorder high in reliability and capable of high-density recording and a recording method. SOLUTION: This recorder is provided with a recording medium provided with a ferroelectric layer 13 and an electrode layer 12, a means 15 for irradiating the layer 13 with evanescent light and a means 14 for impressing voltage on the layer 12 through the layer 13.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a recording apparatus and a recording method.

[0002]

2. Description of the Related Art In the information-oriented society in recent years, there is a long-awaited demand for a recording method and a recording apparatus based on the recording method, which have a remarkably higher recording density than ever before, corresponding to an ever-increasing amount of information.

Techniques for realizing optical recording, which are expected as a recording method having a high recording density, include heat mode recording using light as heat and photon mode recording for recording without converting it into heat. Heat mode recording is currently in practical use for magneto-optical recording and phase transition recording.

[0004] In order to improve the recording density in heat mode recording, a near-field scanning option in which a minute spot smaller than the wavelength of light can be formed.
A technique using cal microscope (NSOM) has been proposed. For example, Betzig et al.
Co / Pt output of r ion laser by NSOM probe
By irradiating the multilayer film and trying to record and reproduce information magneto-optically,
The formation of a recording pattern having a diameter of about 60 nm has been reported (Appl. Phys. Lett. 61, 142 (19).
92)).

[0005] Hosaka et al. Used a NSOM probe to measure the output of a semiconductor laser using a Ge ₂ S film having a thickness of about 30 nm.
It has been reported that a b ₂ Te ₅ thin film was irradiated with a phase change to form a recording pattern having a diameter of about 50 nm (Thin Sol).
id Films 273, 122 (1996);
Appl. Phys. 79, 8082 (1996)).

However, in these methods, the recording spot becomes large due to the diffusion of heat, and the required energy is large, so that the spot diameter becomes about 10 nm.
It is expected that recording densities on the order of bits / cm ² cannot be accommodated.

Among the heat mode recording methods, there is a method using a ferroelectric, apart from these recording methods.

[0008] Since the ferroelectric has ferroelectricity depending on the position of atoms in the crystal lattice, a voltage is applied to the ferroelectric to generate spontaneous dielectric polarization and record information. . FIG. 5 shows a hysteresis characteristic of the polarizability of the ferroelectric substance due to the electric field. In FIG. 5, the electric field is shown on the horizontal axis and the polarizability is shown on the vertical axis, and it can be seen that spontaneous polarization can be reversed by applying an external electric field.

In this ferroelectric, when the ferroelectric material is oriented so as to generate ferroelectricity in the film thickness direction, the dipoles (dipoles) are oriented in the film thickness direction, and the dipoles are arranged in the film thickness direction. become. With this arrangement, the influence of the dipole is reduced in the direction perpendicular to the film thickness direction, that is, in the direction of the film surface. Therefore, unlike a magneto-optical medium or a phase change medium, there is no problem that a recording spot becomes large due to diffusion of heat in a minute region on a film surface, and the recording density can be increased.

As described above, the ferroelectric material is hard to record at room temperature and it is necessary to apply a high voltage. However, when the temperature is increased, the holding power of the dielectric constant is weakened. Therefore, irradiation with a laser beam has been performed in order to perform recording on a ferroelectric at a low voltage. In order to raise the temperature of the ferroelectric substance by laser light and decrease the holding power of the dielectric constant, it is possible to record information at a low voltage.

At this time, the holding force of the dielectric constant is represented by a broken line 6 in FIG.
As shown in Fig. 1, it changes rapidly with the temperature of the ferroelectric,
It is preferred that the temperature drop sharply with increasing temperature. As shown by a dashed line 61 in FIG. 6, if the coercive force of the dielectric constant has a threshold characteristic with respect to temperature, if the temperature decreases slightly after performing recording by irradiating light, recording is performed again due to a leaked electric field or the like. It is unlikely that the recording will be lost due to the data being lost.

However, in practice, as shown by the solid line 62 in FIG. 6, the holding power of the dielectric constant of the ferroelectric material changes gradually with temperature. Accordingly, even if the temperature is slightly lowered, the holding power of the dielectric constant remains reduced, so that there is a problem that the recording is likely to be lost due to a leakage electric field or the like in a cooling process after the recording.

[0013]

As described above, when performing the heat mode recording, the recording spot cannot be reduced in the magnetic medium or the phase change medium. Further, in a medium using a ferroelectric material, it is possible to reduce the recording spot, but there is a problem that the recording is easily lost due to a leakage electric field or the like in a cooling process after the recording.

[0014]

SUMMARY OF THE INVENTION Therefore, the first aspect of the present invention is as follows.
A recording medium comprising a ferroelectric layer and an electrode layer, means for irradiating near-field light to the ferroelectric layer, and means for applying a voltage to the electrode layer via the ferroelectric layer. Recording device is provided. Here, the near-field light refers to non-carrying light that permeates the surface of a substance when the substance is irradiated with light. When a substance is irradiated with light, induced dipoles are generated in the substance. Among them, near-field light is a line of electric force between the induced dipoles which are close to each other near the surface.

A second aspect of the present invention is a step of irradiating a predetermined region of a ferroelectric layer of a recording medium having a ferroelectric layer and an electrode layer with near-field light; Applying a voltage to the electrode layer through the recording method.

A third aspect of the present invention is a recording medium comprising a layered structure of an electrode layer, a ferroelectric layer and a photoconductive layer containing a photoconductive compound, and irradiating the photoconductive layer with near-field light. And a means for applying a voltage to the electrode layer via the photoconductive layer and the ferroelectric layer. Here, having photoconductivity means that conductivity is increased by absorbing light.

According to a fourth aspect of the present invention, there is provided a recording medium including an electrode layer, a photoconductive layer containing a photoconductive compound, and a ferroelectric layer sequentially laminated, and a near-field light applied to the ferroelectric layer. There is provided a recording apparatus comprising: means for irradiating; and means for applying a voltage to an electrode layer via a ferroelectric layer and a photoconductive layer.

In the first, third or fourth aspect of the present invention, the ferroelectric layer may include a plurality of ferroelectric regions and a plurality of isolation regions.

In a third or fourth aspect of the present invention, the photoconductive layer comprises:
It may include a plurality of photoconductive regions and a plurality of isolation regions.

According to a fifth aspect of the present invention, a near-field is provided at a predetermined region of a photoconductive layer of a recording medium having a layered structure of an electrode layer, a ferroelectric layer, and a photoconductive layer containing a photoconductive compound. There is provided a recording method, which comprises irradiating light and applying a voltage to an electrode layer through a predetermined region of a photoconductive layer and a ferroelectric layer.

According to a sixth aspect of the present invention, there is provided a recording medium having a structure in which an electrode layer, a photoconductive layer containing a photoconductive compound, and a ferroelectric layer are sequentially laminated, the recording medium being close to a predetermined region of the ferroelectric layer. There is provided a recording method, which comprises irradiating a field light, and applying a voltage to an electrode layer through a predetermined region of the ferroelectric layer and the photoconductive layer.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below in detail with reference to the drawings, but the present invention is not limited to these embodiments.

First, the principle of the present invention will be described with reference to FIG. In the recording apparatus shown in FIG. 1, a recording medium having a substrate 11, an electrode layer 12 provided on the substrate 11, a ferroelectric layer 13 on the electrode layer 12, and an electrode 14, a near-field light comprising a light source, a lens, and the like. A recording unit having an irradiation unit 15 is provided. The ferroelectric layer 13 is divided into a hatched ferroelectric region and other isolation regions, but the entire surface may be a ferroelectric region.

From the near-field light irradiating means 15, the ferroelectric layer 1
3 is irradiated with near-field light to give a relative speed to the recording means and the recording medium (for example, the recording medium is moved in the traveling direction shown by the arrow in FIG. 1). A voltage is applied to a predetermined region of the ferroelectric layer 13.

The temperature of the ferroelectric layer 13 is increased by irradiation with near-field light, the holding power of the dielectric constant is reduced, and recording can be performed by arranging dipoles. In the present invention, near-field light is used as light. Since the near-field light is a line of electric force between induced dipoles generated on the surface of the material, the light irradiation spot can be made extremely small. The light irradiation spot can be about 10 to about 20 nm.

Further, the intensity of the near-field light rapidly decreases as the distance increases. Therefore, when near-field light is applied to the ferroelectric layer 13, the temperature rises near the surface 16 as shown in FIG. 1, but does not rise inside the ferroelectric layer 13. Therefore, the decrease in the coercive force of the dielectric constant of the ferroelectric layer 13 occurs only near the surface 16 of the region irradiated with the near-field light. After that, recording by the electrode 14
After that, the temperature of the ferroelectric layer 13 rapidly decreases, but a strong electric field is applied to the inside 17 because the dipoles are arranged near the surface 16 by recording. Therefore, recording is also performed on the interior 17 and the ferroelectric layer 1 is recorded.
3 is recorded on the whole. That is, the electrode 14
The recording in the vicinity 16 of the surface is performed, and the recording in the vicinity 16 of the surface induces the recording in the inside. In addition, since the temperature of the ferroelectric layer 13 rises at the time of irradiation with the near-field light only in the vicinity of the surface 16, the cooling is quickly performed, and it is possible to prevent the recording from being lost due to the leakage electric field or the like. Become. (First Embodiment) Next, a first embodiment of the present invention will be described. FIG. 2 shows the structure of the recording apparatus of the present embodiment.

As shown in FIG. 2, the recording apparatus of this embodiment has a recording medium 201, recording / reproducing means 202, and a motor 203 for rotating the recording medium 201. The recording medium 201 includes a substrate 204, an electrode layer 205 on the substrate 204, a ferroelectric region 206 and a separation region 207, and a recording layer (ferroelectric layer) formed on the electrode layer 205.
The recording / reproducing means 202 comprises a slider head 209, a semiconductor laser 210, a waveguide portion 211 for propagating light of the semiconductor laser 210, an electrode 212 for injecting electric charge, and a FET sensor head 213 for reading data.
Are aggregated.

Next, the recording medium 2 of the recording apparatus of the present embodiment
Each part of the 01 part will be described along the manufacturing method.

First, the substrate 204 is formed of a single crystal substrate of SrTiO ₃ and has a diameter of about 64 mm and a thickness of about 1.4 mm.
On the substrate 204, a Pt film having a (100) plane is formed on the substrate 204 so as to have a thickness of about 500 nm.

On the electrode layer 205, to form the ferroelectric region 206 of the recording layer 208, Ba _0.8 Sr _0.2 TiO
₃ is epitaxially formed by an RF magnetron sputtering method so as to have a film thickness of about 30 nm. On this, polymethyl methacrylate is spin-coated as an electron beam resist so as to have a thickness of about 50 nm. And EB
An electron beam is irradiated on a region other than a circular region having a diameter of about 30 nm, the center of which is arranged at about 50 nm intervals, using a drawing apparatus. After development with ethanol, reactive ion etching (RIE) is performed to form ferroelectric regions 206.

Next, a polyimide is buried in a portion other than the circular region irradiated with the electron beam to form an isolation region 207. This polyimide is also deposited on the ferroelectric region 206,
Also serves as a protective film for the recording layer 208.

Next, information is recorded and reproduced using this recording apparatus. In the present embodiment, as the recording means,
A semiconductor laser 210 and a waveguide 211 are used, and an electrode 212 is used as a voltage applying unit. Further, an FET sensor head 213 is used as a reproducing unit. The leading end of the waveguide 211 is thin, and an opening 214 is provided.

First, information is recorded. Motor 203
, The disc-shaped recording medium 201 is about 4000 r
While rotating at pm, wavelength about 620nm, output about 5m
From the semiconductor laser 210 of W through the waveguide 211,
Near-field light is spirally applied to the recording medium 201 from an opening 214 having a diameter of about 30 nm at the narrowed end of the waveguide section 211. By irradiating the near-field light, the holding power of the dielectric constant of the ferroelectric region 206 of the recording medium 201 decreases, and a voltage is applied from the electrode 212 to the portion of the ferroelectric region 206 irradiated with the near-field light in a pulsed manner. Information is recorded by applying about 20V.

As described above, the step of irradiating the recording medium 201 with light and the step of applying a voltage to the recording medium 201 realize the recording method of the present embodiment.

Next, the recorded information is reproduced. The electric charge injected into the recording medium 201 is transferred to the FET sensor head 2.
13. Read directly at 13. The reproduced information has an error rate of about 0.01% with respect to the input information, and can be said to be a reliable signal.

In this embodiment, the recording medium 2 in the recording device
01 is irradiated with near-field light. Since the intensity of the near-field light rapidly decreases as the distance increases, when the near-field light is irradiated, the temperature rises near the surface of the ferroelectric region 206 but does not rise inside. Therefore, a decrease in the holding power of the dielectric constant of the ferroelectric region 206 occurs only near the surface of the region irradiated with the near-field light.

After recording by the electrode 212 is performed near the surface of the ferroelectric region 206,
Is rapidly reduced, but since the dipoles are arranged near the surface of the ferroelectric region 206 due to the recording, a strong electric field is applied inside, and the recording is also performed inside. The recording is performed on the entire ferroelectric region 206. That is, recording near the surface of the ferroelectric region is performed by the electrode 212, and then recording near the surface induces recording inside. In addition, at the time of irradiation with near-field light, the temperature of the ferroelectric region 206 rises only near the surface, so that the cooling is quickly performed, and it is possible to prevent the recording from being lost due to a leaked electric field or the like. .

In the recording apparatus of the present embodiment, the recording layer 208 includes the ferroelectric region 206 and the separation region 207, and the separation region 207 exists between the two ferroelectric regions 206. The separation region 207 becomes a wall and the recording layer 2
The storage state of the dipole during the step 08 is improved, and recording on minute recording pits becomes possible. If each of the ferroelectric regions 206 has a size equal to or smaller than a recording pit and is regularly arranged, the contrast-noise ratio can be further increased. Further, one recording pit may be formed in a plurality of ferroelectric regions 206.

When the recording pits are regularly arranged,
Information recording the positions of the recording pits can be provided, and position correction such as blurring of the recording head can be performed. Therefore, since blurring can be prevented, higher-density recording can be performed.

As in the present embodiment, as a method of separating the recording layer 208 into the ferroelectric region 206 and the separation region 207, a method using ordinary lithography or a phase separation from an amorphous glass component is used. Forming an isolation region by
Fine ferroelectrics are applied to the substrate together with a suitable matrix, or they are electrodeposited.Appropriate irregularities and patterns with different surface energies are formed on the substrate, and these are used as separation regions. And a method of growing a ferroelectric thereon.

Among these, a method using lithography is preferable because the crystal axis direction of the ferroelectric layer is most easily controlled. However, it is difficult to create recording pits for performing terabit-level recording using ordinary light. Therefore, in lithography in such a case, a method using nanoimprinting or a method of forming a pattern using near-field light is more preferable. (Second Embodiment) Next, a second embodiment of the present invention will be described. The present embodiment will be described focusing on the differences from the first embodiment, and will be described with reference to FIG. 2 as in the first embodiment.

This embodiment is different from the first embodiment in the method of forming the recording layer 208 of the recording apparatus. In the present embodiment, after forming the electrode layer 205 using the same material and method as in the first embodiment, the recording layer 20 is formed on the electrode layer 205.
8 to form the ferroelectric region 206 of Ba _0.8 Sr _0.2
TiO ₃ is epitaxially formed by RF magnetron sputtering so as to have a thickness of about 200 nm. On top of this, ODU manufactured by Tokyo Ohka Kogyo Co., Ltd.
R-1013 is spin-coated to a thickness of about 200 nm. And the center is about 300n using the exposure device.
Ultraviolet radiation is applied to regions other than circular regions having a diameter of about 200 nm arranged at m intervals. After developing with ethanol, RIE is performed to form a ferroelectric region 206.

After that, using the same material and method as in the first embodiment, an isolation region 207 and a protective film on the recording layer 208 are formed.

Next, information is recorded and reproduced using this recording apparatus. In this embodiment, recording and reproduction are performed in the same manner as in the first embodiment. However, the difference from the first embodiment is that the diameter of the opening 214 at the end of the waveguide 211 is about 200 nm.

In the present embodiment, when information is recorded and reproduced, the reproduced information has an error rate of about 0.001% of the input information and is a reliable signal. Can be done. In the present embodiment, since the recording pits are enlarged, the error rate is further reduced as compared with the first embodiment, and reliable information can be obtained.

In this embodiment, since near-field light is irradiated similarly to the first embodiment, a rise in the temperature of the ferroelectric region 206, that is, a decrease in the holding power of the dielectric constant occurs only near the surface. After recording near the surface, the holding power of the dielectric constant increases immediately. Therefore, although the arrangement of dipoles near the surface of the ferroelectric region 206 induces recording inside, it is possible to prevent the recording from being lost due to a leakage electric field or the like.

The recording layer 208 is formed of the ferroelectric region 20.
6 and an isolation region 207 and two ferroelectric regions 20
6, the separation region 207 exists.
Is a wall, so that the storage state of the dipole in the recording layer 208 is improved, so that information can be recorded at a higher density, as in the first embodiment. (Comparative Example 1) Next, Comparative Example 1 will be described. In Comparative Example 1, a recording medium similar to that of the second embodiment is formed, but the method of recording information on this recording medium is the same as that of the second embodiment.
Is different from the embodiment.

In Comparative Example 1, information was recorded by rotating a disk-shaped recording medium at about 4,000 rpm using a motor while rotating a semiconductor laser having a wavelength of about 620 nm and an output of about 1.2 mW using a high refractive index lens. Is used to irradiate the recording medium in a spiral shape with a spot diameter of about 300 nm. At this time, the spot diameter is substantially set to about 200 nm by using the pen tip recording based on the intensity distribution of the laser beam.
A voltage of about 20 V is applied from the electrode to the ferroelectric region irradiated with the light in a pulsed manner. The energy density of the light applied to the recording medium is the same as in the second embodiment.

Next, the recorded information is reproduced in the same manner as in the second embodiment. The reproduced information had an error rate of about 0.6% with respect to the input information. this is,
Not only the second embodiment in which information is recorded using the same recording medium in the recording apparatus, but also the error rate is smaller than that of the first embodiment having smaller recording pits than the second embodiment, that is, having a higher recording density. Is high, indicating that there are many recording errors.

In Comparative Example 1, unlike the first and second embodiments, recording is performed using light obtained by condensing laser light using a lens. Therefore, not only the surface but also the inside of the ferroelectric region of the recording medium rises in temperature due to the light irradiation, and after the information is recorded by the electrodes, the temperature of the entire ferroelectric region gradually decreases. In this cooling process, it is considered that there are many recording errors because information recording is lost due to a leakage electric field or the like. (Third Embodiment) Next, a third embodiment of the present invention will be described. FIG. 3 shows the structure of the recording apparatus of the present embodiment.

As shown in FIG. 3, the recording apparatus of this embodiment has a recording medium 301, recording / reproducing means 302, and a motor 303 for rotating the recording medium 301. The recording medium 301 includes a substrate 304 and an electrode layer 3 on the substrate 304.
05, a photoconductive layer 308 comprising a photoconductive region 306 and an isolation region 307, formed on the electrode layer 305, and having a ferroelectric region 309 on the photoconductive region 306
Recording layer 310 separated by a separation region 307 in the same manner as
The recording / reproducing means 302 includes a slider head 3
11, a semiconductor laser 312, a semiconductor laser 312
Part 313 for propagating the light, electrode 31 for injecting electric charge
4. The FET sensor head 315 for reading out records is integrated.

Next, the recording medium 3 of the recording apparatus of the present embodiment
Each part of the 01 part will be described along the manufacturing method.

First, the substrate 304 is formed of a SiO ₂ / Si single crystal substrate, and has a diameter of about 64 mm and a thickness of about 1.4 m.
m, and an electrode layer 305 is formed on the substrate 304.
A Pt film having a (100) plane is formed so as to have a thickness of about 500 nm.

On the electrode layer 305, CdSe is spin-coated to a thickness of about 10 nm in order to form the photoconductive region 306 of the photoconductive layer 308.

On top of this, the ferroelectric region 3 of the recording layer 310
In order to form 09, a copolymer of vinylidene fluoride and trifluoroethylene is formed by a sputtering method so as to have a thickness of about 30 nm. On this, polymethyl methacrylate is spin-coated as an electron beam resist so as to have a thickness of about 50 nm. Then, using an EB lithography apparatus, electron beams are irradiated to regions other than a circular region having a diameter of about 30 nm, the center of which is arranged at intervals of about 50 nm. After developing with ethanol, RIE
Then, the recording layer 310 and the photoconductive layer 308 are removed.

Next, a polycarbonate is buried in a portion other than the circular region irradiated with the electron beam to form a separation region 307. This polycarbonate is also formed on the ferroelectric region 309 and also serves as a protective film for the recording layer 310.

Next, information is recorded and reproduced using this recording apparatus. In the present embodiment, recording and reproduction are performed in the same manner as in the first embodiment, but the difference from the first embodiment is that the light output of the semiconductor laser is about 2 mW.

When information is recorded and reproduced in the present embodiment, the reproduced information has an error rate of about 0.01% with respect to the input information and is a reliable signal. I can do it.

In this embodiment, since the ferroelectric region 309 and the protective film thereon use a material transparent to the light to be irradiated, near-field light is irradiated to the ferroelectric region 309. The light is not absorbed and is irradiated to the photoconductive region 306. The photoconductive region 306 is irradiated with near-field light,
The electric resistance is reduced only in the region irradiated with light. Therefore, a voltage is applied from the electrode 314 only to a region of the recording layer 310 corresponding to the region irradiated with the near-field light.
Therefore, even if a relatively large electrode 314 is used, the opening 3
It is possible to apply a voltage only to the region of the ferroelectric region 309 corresponding to No. 16, and the region of the photoconductive layer 308 to which the near-field light is not irradiated has no resistance because of high resistance. The information is kept stable. In general, since the temperature of the opening 316 is high, the ferroelectric region 30
9 is heated by radiant heat, and also in this embodiment, as in the case of the first embodiment, a decrease in the holding power of the dielectric constant occurs, and the effect of easy and accurate recording is also obtained. can get.

At this time, since light is used not in the heat mode but in the photon mode, the switching speed when the conductivity of the photoconductive layer 308 is increased is high, and information can be recorded at high speed. It is possible to do. Furthermore, in photon mode recording, the light intensity can be made weaker than in heat mode recording, and energy efficiency is good.

The photoconductive layer 308 needs to have a sufficient conductivity when irradiated with light and a sufficient insulating property when not irradiated with light, so that the film thickness is preferably about 5 to about 100 nm. If the thickness is less than about 5 nm, the insulation may be insufficient, and if the thickness is greater than about 100 nm, the conductivity may be insufficient.

The recording layer 310 is formed in the ferroelectric region 30.
9 and an isolation region 307 and two ferroelectric regions 30
9, the separation region 307 exists.
Is a wall, so that the storage state of the dipoles in the recording layer 310 is improved. Therefore, as in the first embodiment, it is possible to increase the density of information recording. (Fourth Embodiment) Next, a fourth embodiment of the present invention will be described. FIG. 4 shows the structure of the recording apparatus of the present embodiment.

As shown in FIG. 4, the recording apparatus of this embodiment has a recording medium 401, a recording / reproducing means 402, and a motor 403 for rotating the recording medium 401. The recording medium 401 includes a substrate 404 and an electrode layer 4 on the substrate 404.
05, a recording layer 408 composed of a ferroelectric region 406 and an isolation region 407 and formed on the electrode layer 405, and having a photoconductive region 409 on the ferroelectric region 406 and having a separation region 407 like the recording layer 408. The recording / reproducing means 402 comprises a separated photoconductive layer 410 and the slider head 41.
1, a semiconductor laser 412, a waveguide 413 for propagating light from the semiconductor laser 412, and an electrode 41 for injecting charges.
4. The FET sensor head 415 for reading out records is integrated.

Next, the recording medium 4 of the recording apparatus of the present embodiment
Each part of the 01 part will be described along the manufacturing method.

First, the substrate 404 is formed of a SiO ₂ / Si single crystal substrate and has a diameter of about 64 mm and a thickness of about 1.4 m.
m, and an electrode layer 405 is formed on the substrate 404.
A Pt film having a (100) plane is formed so as to have a thickness of about 500 nm.

To form the ferroelectric region 406 of the recording layer 408 on the electrode layer 405, Ba _0.75 Sr _0.25 Ti
O ₃ is epitaxially formed by RF magnetron sputtering so as to have a thickness of about 30 nm.

To form a photoconductive region 409 of the photoconductive layer 410 thereon, CdSe is sputtered so as to have a thickness of about 10 nm, and a polymethyl methacrylate as a resist is formed thereon with a film of about 50 nm as a resist. Spin coat so as to be thick.

Next, it is made of SiC and has a diameter of about 30 nm,
A stamp in which concave portions having a depth of about 40 nm are formed at intervals of about 50 nm is pressed against the resist of the recording medium 401 at 100 ° C. under vacuum, and the pattern is transferred to the resist. Thereafter, RIE is performed, and the photoconductive layer 410 and the recording layer 40 are formed.
Cut 8

Next, polyimide is buried in the shaved area of the photoconductive layer 410 and the recording layer 408 to form an isolated area 407. This polyimide is also formed on the photoconductive region 409, and also serves as a protective film.

Next, information is recorded and reproduced using this recording apparatus. In the present embodiment, recording and reproduction are performed in the same manner as in the first embodiment, but the difference from the first embodiment is that the light output of the semiconductor laser is about 2 mW.

When information is recorded and reproduced in the present embodiment, the reproduced information has an error rate of about 0.01% with respect to the input information and is a reliable signal. I can do it.

In the present embodiment, similar to the third embodiment,
Since a material transparent to the light to be irradiated is used as the protective film, the near-field light is irradiated to the photoconductive layer 410. In the photoconductive layer 410, since the electric resistance is reduced only in the region irradiated with the near-field light by the irradiation of the near-field light, the voltage is applied only to the region of the recording layer 408 corresponding to the region irradiated with the near-field light. You. Therefore, even if a relatively large electrode 414 is used, it is possible to apply a voltage only to the region of the ferroelectric region 406 corresponding to the opening 416, and the photoconductive layer 4
No. 10 is exposed to the near-field light and has a high resistance, so that no voltage is applied and the recorded information is stably held.

At this time, since the light is used in the photon mode, as in the third embodiment, the switching speed when the conductivity of the photoconductive layer 410 is increased is high, and information is recorded at high speed. It becomes possible. Furthermore, in photon mode recording, the light intensity can be made weaker than in heat mode recording, and energy efficiency is good.

Further, the temperature of the photoconductive layer 410 rises to absorb light. Accordingly, the temperature of the surface of the recording layer 408 also increases, and also in this embodiment, a decrease in the coercive force of the dielectric constant of the recording layer 408 occurs, which is similar to that described in the first embodiment. In addition, the effect that the operation is performed accurately can be obtained.

The recording layer 408 is formed of the ferroelectric region 40
6 and an isolation region 407 and two ferroelectric regions 40
6, there is a separation region 407, and this separation region 407
Is a wall, so that the storage state of the dipoles in the recording layer 408 is improved. Therefore, as in the first embodiment, it is possible to increase the density of information recording.

Further, in this embodiment, the photoconductive layer 410
However, since it is above the recording layer 408, the photoconductive layer 410 can also serve as a protective film for the recording layer 408. (Fifth Embodiment) Next, a fifth embodiment of the present invention will be described. This embodiment will be described with a focus on portions different from the fourth embodiment, and will be described with reference to FIG. 4 as in the fourth embodiment.

This embodiment is different from the fourth embodiment in the method of forming the recording layer 408 and the photoconductive layer 410 of the recording apparatus. In the present embodiment, the same material as the fourth embodiment, after forming the electrode layer 405 by using a method, on the electrode layer 405, to form a ferroelectric region 406 of the recording layer 408, Ba _0.75 Sr _0.25 TiO ₃ is epitaxially formed by RF magnetron sputtering so as to have a thickness of about 200 nm. In order to form a photoconductive region 409 of the photoconductive layer 410 thereon, a film in which molecules represented by the following formula (1) are dispersed in polymethyl methacrylate is spin-coated so as to have a thickness of about 50 nm. And the center is about 3
Electron beams are irradiated to regions other than the circular region having a diameter of about 200 nm arranged at intervals of 00 nm. After developing with ethanol, RIE is performed to remove the ferroelectric region 406 and the photoconductive region 409.

[0078]

Embedded image

After that, using the same material and method as in the fourth embodiment, an isolation region 407 and a protective film on the photoconductive layer 410 are formed.

Next, information is recorded and reproduced using this recording device. In this embodiment, recording and reproduction are performed in the same manner as in the fourth embodiment. However, the diameter of the opening 416 at the tip of the waveguide 413 is set to about 200 nm, and the semiconductor laser 4 is used.
The fourth embodiment differs from the fourth embodiment in that the output of No. 12 is about 3 mW and the wavelength is about 400 nm.

In this embodiment, when information is recorded and reproduced, the reproduced information is different from the input information.
The error rate is about 0.001%, which means that the signal is reliable. In the present embodiment, since the recording pit is enlarged, the error rate is further reduced as compared with the fourth embodiment, and reliable information can be obtained.

In the present embodiment, similar to the third embodiment,
Since a material transparent to the light to be irradiated is used as the protective film, the near-field light is irradiated to the photoconductive layer 410. In the photoconductive layer 410, since the electric resistance is reduced only in the region irradiated with the near-field light by the irradiation of the near-field light, the voltage is applied only to the region of the recording layer 408 corresponding to the region irradiated with the near-field light. You. Therefore, even if a relatively large electrode 414 is used, it is possible to apply a voltage only to the region of the ferroelectric region 406 corresponding to the opening 416, and the photoconductive layer 4
No. 10 is exposed to the near-field light and has a high resistance, so that no voltage is applied and the recorded information is stably held.

At this time, since the light is used in the photon mode, the switching speed when the conductivity of the photoconductive layer 410 is increased is high and the information is recorded at high speed as in the third embodiment. It becomes possible. Furthermore, in photon mode recording, the light intensity can be made weaker than in heat mode recording, and energy efficiency is good.

Further, the recording layer 408 is formed in the ferroelectric region 40.
6 and an isolation region 407 and two ferroelectric regions 40
6, there is a separation region 407, and this separation region 407
Is a wall, so that the storage state of the dipoles in the recording layer 408 is improved. Therefore, as in the first embodiment, it is possible to increase the density of information recording.

Further, in the present embodiment, the photoconductive layer 410
However, since it is above the recording layer 408, the photoconductive layer 410 can also serve as a protective film for the recording layer 408. (Comparative Example 2) Next, Comparative Example 2 will be described. In Comparative Example 2, a recording medium similar to that of the fifth embodiment is formed, but the method of recording information on this recording medium is the same as that of the fifth embodiment.
Is different from the embodiment.

In Comparative Example 2, information was recorded by rotating a disc-shaped recording medium at about 4000 rpm using a motor while using a semiconductor laser having a wavelength of about 400 nm and an output of about 0.8 mW as a high refractive index lens. Is used to irradiate the recording medium in a spiral shape with a spot diameter of about 200 nm. A voltage of about 20 V is applied from the electrode to the ferroelectric region irradiated with the light in a pulsed manner. The energy density of the light applied to the recording medium is the same as in the fifth embodiment.

Next, the recorded information is reproduced in the same manner as in the fifth embodiment. The reproduced information had an error rate of about 0.5% with respect to the input information. this is,
Not only the fifth embodiment in which information is recorded using the same recording medium in the recording apparatus, but also an error rate smaller than that of the fourth embodiment having smaller recording pits than the fifth embodiment, that is, a higher recording density. Is high, indicating that there are many recording errors.

In Comparative Example 2, unlike the fifth embodiment,
Recording is performed using light obtained by condensing laser light using a lens. Therefore, not only the surface of the ferroelectric region of the recording medium but also the inside thereof rises in temperature due to light irradiation, and after information is recorded by the electrodes, the temperature of the entire ferroelectric region gradually decreases. In this cooling process, it is considered that there are many recording errors because information recording is lost due to a leakage electric field or the like.

In the fourth and fifth embodiments, the light is used in the photon mode, and the electric resistance of the photoconductive layer only in the region irradiated with the near-field light is reduced. Therefore, a voltage is applied only to a region of the ferroelectric layer corresponding to the region, and a voltage is not applied to a region where the near-field light is not irradiated because the resistance is high, and recorded information is stably held. . (Other Embodiments) According to the present invention described in detail above, it is possible to obtain a recording apparatus and a recording method capable of high-density recording with high reliability. However, the present invention is not limited to this.

For example, as the material of the present invention, which absorbs light and increases conductivity, there are various materials such as organic substances and inorganic substances. In general, under non-light irradiation, the insulating property is high, and the conductivity sharply rises by light irradiation. Are preferred. It is preferable that the response be as fast as possible.
GHz or higher is preferred. Further, the conductivity of the photoconductive layer preferably changes non-linearly with respect to the light intensity. When the conductivity of the photoconductive layer changes nonlinearly with respect to the light intensity, it becomes possible to reduce the size of the spot where the resistivity of the photoconductive layer changes, rather than the size of the light irradiation spot. Super-resolution recording becomes possible.

Specifically, in the case of organic substances, the following (A1)
To (A6), but not limited thereto.

[0092]

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[0093]

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[0094]

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[0095]

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[0096]

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Further, among inorganic substances, Si, Se, Ge, Z
oxides such as nO, TiO ₂ , SnO ₂ , AlGaAs,
GaAs, AlInAs, GaInAs, GaIn
P ₂ , InP, PbS, ZnS, ZnSSe, ZnT
e, As ₂ SeTe ₂ , As ₂ Te ₃ , CdS, CdTe,
ZnCdTe, CdSSe, CdSe, CuInS
Alloys or compounds such as, but not limited to, e ₂ , CuS.

These materials may be used alone as they are, or they may be mixed or used by being dispersed in various matrices.

As the ferroelectric that can be used in the ferroelectric layer of the present invention, various substances such as organic substances and inorganic substances can be used.

Specifically, as the organic substance, a trifluoroethylene-vinylidene fluoride copolymer or the like can be used, but is not limited thereto.

In the case of inorganic substances, for example, Pb (Zr, T
i) O_Three(PZT) or (Pb, La) (Zr, Ti) O_Three
(PLZT) and other perovskite oxides, SrBi
_TwoTa _TwoO₉Sr-Bi-Ta-O-based oxides such as
Bi_FourTi_ThreeO₁₂Or a Bi-Ti-O-based oxide such as
There is an i-Sr-Ti-O-based oxide and the like. In addition, Ba
Ba_1-XSr_XTiO_ThreeAnd BaTiO_ThreeSuch as perov
Lattice mismatch with lower substrate using skyte type oxide
Of ferroelectric layer using strain-induced ferroelectricity caused by
However, the present invention is not limited to these.

The thickness of the ferroelectric layer is about 5 to about 10
It is preferably 0 nm. If it is less than about 5 nm, the stability of the recorded charge may be lost and the signal will be weak. On the other hand, if the thickness is larger than about 100 nm, the effect of surface heating by near-field light does not reach the deep part of the ferroelectric layer, and the recording density may be reduced. Further, the thickness of the ferroelectric layer is more preferably from about 10 to about 30 nm.

It is preferable that the ferroelectric layer is formed such that the dipoles are uniformly arranged in the film thickness direction and the number of crystal grain boundaries is as small as possible. For example, in the case of using a trifluoroethylene-vinylidene fluoride copolymer, it is preferable to apply a voltage at a temperature equal to or higher than the glass transition temperature of a film formed by coating from a solution to perform alignment.

As a film forming method using an inorganic ferroelectric, for example, a sputtering method such as an ion beam sputtering method, an RF magnetron sputtering method, or a MOCVD method is used.
Method, a sol-gel method, a metal organic deposition (MOD) method, a laser ablation method, or the like may be used, and the method is not limited. After film formation by these methods, heat treatment may be performed in order to perform crystallization.

As a substrate on which a ferroelectric layer is formed, glass, an organic polymer such as polycarbonate, a semiconductor substrate such as a Si substrate having a SiO ₂ film formed thereon, or a MgO single crystal substrate or SrTiO ₃ single crystal is used. And is not limited to these. Further, in order to reduce the crystal grain boundaries, a MgO single crystal substrate or a SrTiO ₃ single crystal substrate is preferable.

An electrode layer is formed between the ferroelectric layer and the substrate. Examples of the material of the electrode layer include noble metal materials such as Pt and Ru, conductive Ru oxide, and SrRuO 2.
A conductive perovskite-type oxide such as ₃ can be used, but is not limited thereto. It is also preferable to interpose a compound layer such as TiN or (Ti, Al) N between the substrate and the electrode layer.

As a method of reading out the electric field by the dipole accumulated in the recording layer, other than the method of the above-described embodiment, for example, a method of measuring an electrostatic force using an atomic force microscope (AFM), a method of measuring an electric force, A method for measuring changes in capacity, a method for measuring changes in intensity and wavelength of absorbed light, reflected light, and fluorescence by irradiating light with an intensity and wavelength that does not destroy the recording, and detecting the electrical resistance of the recording layer The method may be used, and the method is not limited. Further, an electric field sensor having a field-effect transistor structure described in each embodiment of the present invention is also preferably used. If a single-electron transistor is used as the field-effect transistor, detection with higher sensitivity can be performed.

Also, as in the embodiments of the present invention, it is possible to integrate the recording means and the reproducing means to form a slider head structure, whereby the recording medium is rotated at a high speed to record information. And the speed of reproduction can be increased. As described above, when the recording means and the reproducing means are integrated, the head is levitated by generating an air flow with the slider, the near-field light irradiating means irradiates the near-field light, and the voltage applying means applies the voltage. However, if information is recorded in the order of checking whether or not the recording has been correctly performed by the reproducing means, it is efficient and the speed can be increased.

The voltage applying means may be provided so as to surround the near-field light irradiating means. When the light is used in the photon mode, the recording medium responds at a high speed, so that the irradiation of the near-field light and the application of the voltage can be performed at the same time, and in this case, the voltage application unit surrounds the near-field light irradiation unit. It is preferable that it is installed. At this time, since the holding power of the dielectric constant is reduced only in the portion irradiated with the near-field light, the voltage applying unit may be larger than the near-field light irradiating unit.

Further, as a method of integrating the recording means and the reproducing means, a multi-array is formed by utilizing a semiconductor integration technique, a plurality of recording means and reproducing means are formed in one head, and a plurality of information are simultaneously formed. It can be said that recording and playing back is also effective in increasing the speed.

[0111]

As described above, according to the present invention, it is possible to provide a recording apparatus and a recording method capable of performing high-density recording with high reliability.

[Brief description of the drawings]

FIG. 1 illustrates the principle of a recording apparatus according to the present invention.

FIG. 2 is a diagram showing a configuration of a recording apparatus according to the first embodiment of the present invention.

FIG. 3 is a diagram illustrating a configuration of a recording apparatus according to a third embodiment of the present invention.

FIG. 4 is a diagram showing a configuration of a recording apparatus according to a fourth embodiment of the present invention.

FIG. 5 illustrates a hysteresis characteristic of a ferroelectric.

FIG. 6 is a diagram illustrating a temperature of a ferroelectric substance and a holding force of a dielectric constant.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 ... Substrate 12 ... Electrode layer 13 ... Ferroelectric layer 14 ... Electrode 15 ... Near-field light irradiation means 16 ... Near surface 17 ... Inside 61 ... Broken line 62 ... Solid line 201, 301, 401 ... Recording medium 202, 302, 402 ... Recording / reproducing means 203, 303, 403 Motors 204, 304, 404 Substrates 205, 305, 405 Electrode layers 206, 309, 406 Ferroelectric regions 207, 307, 407 Separation regions 208, 310, 408 Recording Layers 209, 311, 411: Slider heads 210, 312, 412: Semiconductor lasers 211, 313, 413: Wave guides 212, 314, 414: Electrodes 213, 315, 415: FET sensor heads 214, 316, 416: Openings 306, 409 photoconductive region 308, 410 photoconductive layer

Claims (8)

[Claims] 1. A recording medium having a ferroelectric layer and an electrode layer, means for irradiating near-field light to the ferroelectric layer, and applying a voltage to the electrode layer via the ferroelectric layer. And a recording device. Irradiating a predetermined area of the ferroelectric layer of the recording medium having a ferroelectric layer and an electrode layer with near-field light, and via the predetermined area of the ferroelectric layer. Applying a voltage to the electrode layer. 3. A recording medium comprising an electrode layer, a ferroelectric layer, and a photoconductive layer containing a photoconductive compound sequentially laminated, a means for irradiating the photoconductive layer with near-field light,
Means for applying a voltage to the electrode layer via the photoconductive layer and the ferroelectric layer. 4. A recording medium comprising an electrode layer, a photoconductive layer containing a photoconductive compound and a ferroelectric layer sequentially laminated, and means for irradiating the ferroelectric layer with near-field light A means for applying a voltage to the electrode layer via the ferroelectric layer and the photoconductive layer. 5. The photoconductive layer according to claim 3, wherein the photoconductive layer includes a plurality of photoconductive regions and a plurality of separation regions.
Or the recording device according to 4. 6. The recording apparatus according to claim 1, wherein the ferroelectric layer includes a plurality of ferroelectric regions and a plurality of separation regions. 7. A near-field light is applied to a predetermined region of the photoconductive layer of a recording medium having a layered structure of an electrode layer, a ferroelectric layer, and a photoconductive layer containing a photoconductive compound. Recording a voltage to the electrode layer via the predetermined region of the photoconductive layer and the ferroelectric layer. 8. A predetermined area of the ferroelectric layer of a recording medium comprising a layered structure of an electrode layer, a photoconductive layer containing a photoconductive compound, and a ferroelectric layer is irradiated with near-field light. And applying a voltage to the electrode layer via the predetermined region of the ferroelectric layer and the photoconductive layer.