JP3830771B2 - Optical recording medium, processing apparatus and processing method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
Due to the explosive increase in the amount of information delivered by high-speed and wide-area communication networks such as the Internet in recent years and the dramatic increase in the size of computer software and the amount of processing data, the capacity of optical recording devices that record these information has increased. There is a strong demand. In addition, various electronic devices have been miniaturized, and the need for a small and light mass storage device that can be mounted on a satellite or a mobile (mobile, wearable) communication device is increasing. These were the background, recording capacity required is several orders of magnitude increase in the short term, 1 m ² per 1550 terabits [per square inch 1 tera (10 ^{12: T)} bit] or more (terabit) Ultra Realization of high density is eagerly desired, and the range of use and market size are very large (Reference: Optoelectronic Industry Technology Promotion Association, “Optical Industry Roadmap”).
The present invention relates to an optical recording medium, a processing apparatus, and a processing method for realizing a rewritable optical recording apparatus having a terabit-class ultrahigh recording surface density.
[0002]
[Prior art]
Conventionally, as a rewritable recording apparatus, a magnetic recording method using a difference in magnetization direction of a magnetic recording material as a recording unit has been mainly used. This includes a hard disk in which a recording medium and a signal detection mechanism are integrated, and a floppy disk that can be carried separately from the signal detection mechanism.
In recent years, the development of an optical recording system in which a recording material is focused and irradiated with a laser beam by a lens and a difference in optical characteristics of the recording material generated at that time is recorded and reproduced is a remarkable development. Examples of optical recording type rewritable recording devices include a compact disc (CD), a digital video disc (DVD), a magneto-optical disc (MO disc), and the like, which are widely used.
[0003]
[Problems to be solved by the invention]
By the way, with a terabit-class recording surface density, the size of a recording unit (pit) must be extremely small, about 25 nanometers (nanometer = 10 ⁻⁹ m) or less (hereinafter referred to as such nanometer-sized pits). Are called nanopits). There are two types of magnetic recording methods that have been used in the past: longitudinal magnetic recording and perpendicular magnetic recording. However, with the longitudinal magnetic recording currently in practical use, physical inversion cannot be maintained when the pit size reaches the nanometer level. There is a critical limit (supermagnetic limit). As a result, the upper limit of the recording surface density of the magnetic recording system is about 100 giga (10 ⁹ : G) bits, and it is difficult to put the terabit class recording apparatus using the magnetic recording system into practical use. It has been made more perpendicular magnetization scheme high surface recording density is expected for many years research, not standing still practical prospect.
[0004]
On the other hand, in the optical recording method, in the current optical disks such as DVD and CD, the surface irradiation density is 10 Gbit because the light irradiation range cannot be less than half the wavelength of light (submicron level) due to the diffraction limit of the laser light focused by the lens. The degree is limited, and it cannot be applied to a terabit class recording apparatus that still requires nanopits.
Therefore, as a method for efficiently recording and reproducing nanopits, a current is injected into the nanometer region of the medium from the tip of the conductive probe, light is excited in the medium by this current, and this light is detected (current excitation light emission). Method) was proposed. As a medium of a rewritable recording apparatus using this method, a layer (light emitting layer) that emits light by current injection is formed on a substrate, and a material on which electrical resistance and light transmittance are reversibly changed by current. A layer in which the formed layers (recording layers) are laminated is used. In this method, the probe current can be intensively injected into the nanometer-sized region in the medium with almost no loss, so that nanopits can be formed with high efficiency, and the advantage is that the S / N ratio of signal light detection can be increased because there is no excitation light. There is. However, since this conventional recording method used a phase change between crystal and amorphous for pit formation, it is necessary for a structure to suppress volume change when phase change between amorphous and crystal, and for amorphization However, there has been a problem that a structure or the like is required to prevent the substrate from being affected by heat when the temperature is increased.
[0005]
SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems in the prior art, and to detect a reproduction signal light having a sufficient intensity from nanopits and to perform a terabit-class rewritable that can repeatedly record, reproduce and erase information. An object of the present invention is to provide a (re-recordable) optical recording medium and a processing apparatus and processing method for recording / reproducing / erasing the same.
[0006]
[Means for Solving the Problems]
In order to achieve the above object, the present invention is configured as described in the claims. That is,
The phase in which the electric conductivity is reversibly changed by the energy that is light-transmitting on the upper part of the light emitting medium that generates light by the energy injected from the outside and the energy injected from the outside. An optical recording medium configured by laminating a change recording medium, wherein the phase change recording medium is made of a phase change recording material having at least two kinds of crystal states having different electric resistances depending on a difference in maximum temperature reached. The optical recording medium is used.
[0007]
Further, as described in claim 2, in the optical recording medium according to claim 1 , the light emitting medium is a direct transition type semiconductor that emits light by current injection or has a well structure including these materials. It is what.
[0008]
Further, as described in claim 3, in the optical recording medium according to claim 1 or 2 , the phase change recording material is an optical recording medium made of a compound containing germanium, antimony and tellurium. .
[0009]
Further, the phase change recording of the current is made in contact with the surface of the optical recording medium or facing the surface of the optical recording medium at a minute interval in a range where a tunnel current flows. Having a sharpened conductive probe so that the injection region into the medium is limited to a nanometer-sized region, and the crystalline state of the phase change recording medium between the conductive probe and the optical recording medium A probe current that can be heated to a temperature that changes the crystal state of the phase change recording medium from a low resistance crystal to a high resistance crystal, and a probe current that can be heated to a temperature that changes the crystal state of the phase change recording medium from a low resistance crystal to a high resistance crystal. in the processing apparatus for an optical recording medium having a pulse power source capable of pulsed manner applying a bias voltage that can be, means that allowed to produce light by exciting the luminescent medium in the optical recording medium The light emitted from the light emitting medium is means for focusing light, it is an apparatus of an optical recording medium characterized by having a coated transparent electrode film on the end face of the optical fiber or optical waveguide structure.
[0012]
In addition, as described in claim 5 , the phase change recording medium that is in contact with the surface of the optical recording medium or is opposed to the surface of the optical recording medium at a minute interval in a range in which a tunnel current flows, Using a processing device for an optical recording medium having a sharpened conductive probe so that the injection region into the nanometer-sized region is limited to a nanometer-sized region, a low-resistance crystal nanopit corresponding to the recording signal is used for the phase change recording medium. A power within a range in which the low resistance crystal of the phase change recording medium does not change is injected from the probe into the recording area of the phase change recording medium from the surface portion of the optical recording medium in which the recording pits are formed. The processing method of the optical recording medium for reproducing the recording by detecting the light emission from the light emitting medium provided in the lower part of the recording medium.
[0014]
The present invention includes a means for supplying a current to a minute region of an optical recording medium, and a phase change recording medium in which electric conductivity is reversibly changed by current injection on a light emitting medium that generates light by injection of the current. In the optical recording apparatus provided with the optical recording medium and the means for detecting light emission from the light emitting medium, the phase change recording medium has at least two types of crystals having different electric resistances at two highest temperatures lower than the melting temperature. Terabit class that uses a material that causes phase change between the two, and makes the two crystal states correspond to the presence or absence of pits, so that there is no problem of volume change or heat resistance without using high temperatures required for amorphization. The rewritable optical recording apparatus is realized.
The present invention realizes terabit-class rewritable optical recording / reproducing / erasing that enables optical recording / reproducing / erasing of information data with less current injection by adopting the above-described materials and configurations. There is an effect that can be done.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
As a phase change recording material used in the optical recording medium of the present invention, for example, the relationship between the temperature history and electrical resistance of Ge ₂ Sb ₂ Te ₅ (hereinafter simply abbreviated as GeSbTe) is schematically shown in FIG.
Initially, the GeSbTe film immediately after being sputtered on the substrate is in an amorphous state, and before being used, it is once in a temperature range (referred to as temperature region A) between T1 (about 150 ° C.) and T2 (about 350 ° C.). After heating, when the temperature is returned to room temperature, a state of crystal A is obtained (this process is omitted in FIG. 1).
Crystal A has a high electrical resistance of several tens of kΩ or more. Next, when the A crystal is reheated to a temperature range (referred to as a temperature region B) between T2 and Tm (melting temperature: about 600 ° C.) and then cooled, it becomes a crystal B. Crystal B has an electrical resistance as low as several tens of ohms. When the crystal B is again heated to the temperature range A and cooled, it becomes the crystal A again. Thus, GeSbTe undergoes a phase change between crystals A and B according to the experienced temperature history, and the electrical resistance changes by about three orders of magnitude or more accordingly. If the temperature is not higher than Tm, it will not return to amorphous. That is, the GeSbTe film has a high-resistance crystal A and a low-resistance crystal B, and shows a phase change between the crystal A and the crystal B due to the history of the maximum temperature.
[0016]
A basic embodiment of the present invention using the characteristics shown in FIG. 1 will be described with reference to FIG. Here, 1 is a conductive condensing probe, 2 is a probe current (electron), 3 is a surface protective layer, 4 is a phase change recording medium (GeSbTe), 4a is a region of crystal A in the phase change recording medium (initial state) 4b is a region of the crystal B in the phase change recording medium (referred to as nanopits), 5 is a light emitting medium, 6 is an electrode (when the substrate is insulating), 6 'is an electrode (when the substrate is conductive), 7 Is a substrate, 8 is light, 9 is a hole, 10 is a pulse power supply, and 11 is an optical recording medium.
[0017]
The conductive condensing probe 1 has a structure in which, for example, the surface of an optical fiber whose tip is sharpened to about the pit size is covered with a transparent conductive film. The probe tip has both conductivity and transparency, and injects a tunnel current into the phase change recording medium 4 and simultaneously collects light from the light emitting medium 5. In this embodiment, current injection and light collection are performed using the same probe. However, current injection is performed using a conductive probe, and light collection is performed separately from a probe (for example, a lens or a reflecting mirror). ) Is also possible. An electrode 6 (only in the case of an insulating substrate) and a light emitting medium 5 are laminated on a substrate 7. The light emitting medium 5 is a material or a structure that emits light by current injection. For example, AlGaAs, GaN, InP, etc., which are direct transition semiconductors, or a light emitting medium 5 made of a well structure containing these materials. The phase change recording medium 4 is laminated.
Here, an example in which GeSbTe is used as the phase change recording material is shown. The GeSbTe immediately after being deposited by sputtering is in an amorphous state. When this is heated together with the substrate to the temperature region A and returned to room temperature, it becomes a crystal A. High electrical resistance of several tens of kΩ or more. This is the initial state.
[0018]
FIG. 2 is a schematic diagram showing an example of the configuration of the terabit-class ultrahigh-density optical recording apparatus of the present invention. Although an embodiment in which light is collected from the probe using a transparent and conductive probe as the light collecting means is shown here, the light collecting probe and the concave mirror are provided separately from the current injection probe. Is applicable.
[0019]
(1) The probe is scanned on the medium surface of the recording crystal A film. When the probe comes to a position where a pit is to be formed, a probe current is pulse-injected between the probe and the medium surface so that the GeSbTe film is heated to the temperature region B. Once this temperature is experienced, GeSbTe becomes crystal B and returns to room temperature. GeSbTe that has become crystal B has an electrical resistance that is significantly reduced to several tens of ohms. On the other hand, the light transmittance is almost the same as that of the crystal A. This crystal B region is defined as a pit. The size can be controlled by the probe current and can be reduced to about 10 nm in diameter. By repeating this operation while moving the probe, nanopits corresponding to the recording signal are sequentially formed on the GeSbTe film. Since the temperature region B is lower than the melting temperature (about 600 ° C.) of GeSbTe, recording can be performed with less probe current than the optical recording method using amorphous. Furthermore, there is an advantage that the medium structure for heat resistance can be reduced.
[0020]
(2) Playback,
Next, a probe current that does not allow GeSbTe to reach the temperature region A is injected into the medium. Since the electric resistance is high on the crystal A where no pit is formed, the probe current is small and no light emission is detected. On the other hand, a large probe current flows through the GeSbTe layer because the electric resistance is small on the crystal B in which the pits are formed. This current flows into the light emitting medium under the GeSbTe layer, and light is strongly emitted. This light is collected and detected. The emission intensity is proportional to the probe current. Since the resistance ratio between the crystal A and the crystal B is remarkably large, at least three orders of magnitude, the emission intensity varies greatly depending on the presence or absence of pits. The recording can be reproduced by reading the change in the emission intensity. It is possible to collect light with a lens or concave mirror installed separately from the probe, but it is better to use a means that collects light at the probe tip using a transparent and conductive probe. Light can be detected with higher sensitivity. Note that by making the luminescent medium an electron confinement structure, the injected current is localized in a narrow space of the luminescent medium immediately below the probe, so that the light collection efficiency by the probe can be increased.
[0021]
(3) When the erasing crystal B is again heated to the temperature region A and then cooled to room temperature, the phase changes to the crystal A and the crystal B disappears. Thereby, nanopits, that is, recorded data can be erased.
Since both the crystal A and the crystal B are stable at room temperature, nanopit recording, reading (reproducing), and erasing operations necessary for the terabit optical recording apparatus can be realized.
[0022]
【The invention's effect】
According to the optical recording medium, the processing apparatus, and the processing method of the present invention, a terabit-class ultra-high-density rewritable optical recording apparatus that operates stably with a smaller probe current than an optical recording apparatus that uses an amorphous state is provided. It can be realized.
[Brief description of the drawings]
FIG. 1 is a graph showing the relationship between temperature history and electrical resistance of Ge ₂ Sb ₂ Te ₅ which is a phase change recording material exemplified in an embodiment of the present invention.
FIG. 2 is a schematic diagram illustrating a configuration of a terabit-class ultrahigh-density optical recording apparatus exemplified in an embodiment of the present invention.
[Explanation of symbols]
1 ... Conductive condensing probe 2 ... Probe current (electron)
3 ... Surface protective layer 4 ... Phase change recording medium 4a ... Crystal A region (initial state)
4b ... Crystal B region (nanopit)
5 ... Luminescent medium 6 ... Electrode (when substrate is insulative)
6 '... Electrode (when the substrate is conductive)
7 ... Substrate 8 ... Light 9 ... Hole 10 ... Pulse power supply 11 ... Optical recording medium

Claims (5)

  It is constructed by laminating a phase change recording medium that is light transmissive and reversibly changes its electric conductivity by energy injected from the outside, above the light emitting medium that generates light by energy injected from the outside. An optical recording medium, wherein the phase change recording medium is made of a phase change recording material having at least two kinds of crystal states having different electric resistances depending on a difference in maximum temperature reached. 2. The optical recording medium according to claim 1 , wherein the light- emitting medium has a direct transition type semiconductor that emits light by current injection or a well structure including these materials. 3. The optical recording medium according to claim 1 , wherein the phase change recording material comprises a compound containing germanium, antimony and tellurium. It is in contact with the surface of the optical recording medium, or is opposed to the surface of the optical recording medium at a minute interval in the range where the tunnel current flows, and the injection region of the current into the phase change recording medium is within a nanometer size region. The phase change recording medium is changed from a high resistance crystal to a low resistance crystal between the conductive probe and the optical recording medium. A bias voltage capable of flowing a probe current that can be heated to a temperature and a probe current that can be heated to a temperature that changes the crystal state of the phase change recording medium from a low-resistance crystal to a high-resistance crystal can be applied in pulses. collecting the processing apparatus for an optical recording medium with the possible pulse power supply, and means allowed to rise to emission by exciting the luminescent medium in the optical recording medium, the light emitted from the light emitting medium Means processing apparatus for an optical recording medium characterized by having a coated transparent electrode film on the end face of the optical fiber or optical waveguide structure. It is in contact with the surface of the optical recording medium or opposed to the surface of the optical recording medium at a minute interval in the range where the tunnel current flows, and the injection region of the current into the phase change recording medium is within a nanometer size region. As described above, an optical recording medium processing apparatus having a sharpened conductive probe is used to form an optical recording medium in which recording pits made of nano-pits of low resistance crystals corresponding to a recording signal are formed on the phase change recording medium. From the surface portion, power within a range in which the low-resistance crystal of the phase change recording medium does not change is injected from the probe into the recording area of the phase change recording medium, and from the light emitting medium provided below the recording area. A method of processing an optical recording medium, wherein recording reproduction is performed by detecting light emission .

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