JP3031274B2 - How information is recorded - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an information recording method using an information recording member whose information can be rewritten by irradiation of an energy beam such as light or an atomic beam. In particular, the present invention relates to a method for recording information effective for a rewritable phase-change optical disk, which performs recording / erasing with a single laser beam. 2. Description of the Related Art A conventional recording / erasing method for a phase-change optical disk recording medium is disclosed in, for example, Japanese Patent Application Laid-Open No. Sho 59-71140. In this method, when erasing information that has already been recorded by crystallizing the recording film, it is performed by maintaining a temperature at which crystallization can be performed for a relatively long time using an oval light spot that is long in the track direction. Thereafter, new information was recorded by modulating the power of a sufficiently focused circular light spot with an information signal. More recently, however, the present inventors have improved the material used for the recording film so that a well-focused circular light spot crystallizes while passing over a point on the disk. Made it possible. For this reason, it has become possible to perform recording by first erasing with one rotation of the disk and modulating and irradiating the laser power with the next rotation by the circular light spot. Further, by modulating the laser power between the crystallization power level and the amorphization power level in accordance with the information signal, it has become possible to rewrite information in one rotation of the disk. However, in the above prior art, when the rotation speed of the disk is increased to increase the information transfer speed, the speed of the atomic arrangement change (for example, crystallization) of the recording film is reduced. Even if the crystal is melted by irradiation with an energy beam (eg, a laser beam), the atomic arrangement returns to its original state during cooling after irradiation (eg, recrystallization), and the atomic arrangement changes in the opposite direction (eg, recrystallization). (For example, amorphization) cannot be performed. Therefore, an object of the present invention is to solve the above-mentioned problems of the prior art, and to use a recording film having a high phase change speed.
An object of the present invention is to provide a method capable of reliably causing a reversible phase change. It is an object of the present invention to form a recording point with one or more pulses having a panel width shorter than the time required for the center of the energy beam spot to pass from one end of the recording point to the other. Achieved by: It is more preferable that the pulse has a pulse width smaller than 3/4 of the time required to pass from one end to the other end, and it is more preferable that the pulse has a pulse width smaller than 1/2. A pulse is particularly preferable. By narrowing the pulse width as described above, heat diffusion from the irradiated portion to the surroundings due to heat conduction is prevented,
The irradiation beam energy can be relatively reduced. Therefore, the cooling rate after irradiation can be increased. The present invention has a problem that when information is overwritten by a single laser beam (rewriting is performed by overwriting without erasing in advance), the cooling rate after laser beam irradiation tends to be low. So we will solve
Especially effective. [0008] The recording medium to which the present invention is applied may be one which causes a phase change between a crystal and an amorphous phase, or one which causes another change in the atomic arrangement. For example, one of the atomic arrangement changes is effective for a crystal-to-crystal atomic arrangement change requiring rapid cooling or an amorphous-to-amorphous atomic arrangement change. The present invention is effective irrespective of the type of energy beam, and can use light, electron beam, ion beam and the like. However, in the case of an electron beam and an ion beam, the protective film formed on the recording film of the recording medium preferably has a thickness of 1 μm or less, more preferably 1000 angstrom or less. Hereinafter, the present invention will be described by way of examples. Recording / erasing is performed reversibly by a phase change between a crystalline state and a state close to an amorphous state. Both sides of a recording film mainly composed of In and Se are sandwiched between protective films of SiO ₂ . The structure was formed on a disk-shaped glass substrate having an ultraviolet curable resin layer on the surface. Tracking grooves and bits representing addresses are transferred to the surface of the ultraviolet curable resin layer. Next, an ultraviolet curable resin was applied on the above protective film, bonded to another glass substrate, and cured by ultraviolet light. Next, this optical disk is rotated at a rotational speed of 600 rpm.
And searched for a location to record while performing tracking and autofocusing. Where to record,
After raising the power of the laser beam from the read power level to the crystallization power level, the power was varied as shown in FIG. The upper part of FIG. 1 shows an arrangement of amorphous points formed on the recording track. The other portions on the tracks are crystallized, and the space between the tracks is in an as-depo state (as deposited). Actually, the position of the light spot does not move,
The points on the disk move to the left, but the points on the disk are shown stationary and the light spot moves to the right. In the lower diagram of FIG. 1, the horizontal axis corresponds to the horizontal position of the center of the light spot in the upper diagram, and indicates the laser power applied to each point when the light spot moves to the right. I have. In a place where the film is to be made amorphous according to the information signal, the power is raised to the amorphous level for a short time. The time width during which the laser power rises to the amorphization level is about ／ of the time required for the center of the light spot to pass from end to end of the corresponding amorphization point (a region having lower crystallinity than the surroundings). ing. However, the time width during which the power rises is defined as the width of the point at half the pulse height from the crystallization level. The irradiated portion on the disk is melted by the laser light irradiation at the amorphizing power level and rapidly cooled to become amorphous. For example, when recording information including a long pulse whose length is twice or more the length of the shortest pulse, FIG.
As shown in the center of the waveform, the original recording waveform is divided into a plurality of short pulses and irradiated. In the example of FIG. 1, the irradiated portion forms a long amorphized portion in which three amorphized portions adhere to each other. When divided into such short pulses, the power between the pulses is preferably lower than the crystallization power level, and the power is preferably set to 0 or the read power level. However, depending on the composition of the recording film and the material of the protective film, the crystallization power level may be lowered to a level slightly higher than the crystallization power level. It is particularly preferable that the narrower the interval between pulses is, the greater the method of reducing the power of that portion is. FIG. 1 shows a case where the read power level is lowered to the read power level. Even if the information to be recorded has a part with a long pulse width, forming a recording pattern on a disk that gives a reproduction signal that is faithful to the original signal by irradiating it in this way by dividing it into multiple pulses Can be. When the information to be recorded has only a portion with a short pulse width, the division into a plurality of pulses as described above is not necessary. The laser power waveform of the present embodiment is a waveform that can be rewritten by overwriting that does not need to be erased in advance, that is, a waveform that can be overwritten. It is more preferable that the time width during which the laser power rises to the amorphization level be equal to or less than 1/2 of the time required for the center of the light spot to pass from one end of the corresponding amorphization point to the other. It is particularly preferable to set the number to 4 or less since the amorphous state can be completely achieved. In the case where the entire track is crystallized and erased by continuous laser beam irradiation and then erased, and then recording is performed with a laser beam power-modulated between a read power level and an amorphization power level, a pulse is similarly applied. Preferably, the width is reduced. However, in this case, the cooling rate is originally high even though the power is always reduced to the read power level between the pulses. The effect is therefore not as pronounced as in the case of single beam overwriting. In the case of single beam overwrite, the crystallization power level is set to 30 to 9 with respect to the amorphous power level.
If the adjustment is made in the range of 5%, a reproduced signal can be obtained irrespective of the width of the time width at the amorphizing power level. 5
A range of 5 to 90% is a more preferable range. In this embodiment, the recording is considered to be amorphous, but the viewpoint may be changed so that the crystallization is regarded as recording. According to the present invention, even if a recording film capable of changing the atomic arrangement at a high speed is used, the atomic arrangement can be changed in the reverse direction, so that the information transfer speed can be increased. Moreover, overwriting with a single laser beam is possible, which is extremely advantageous for recording and reading a large amount of information.

[Brief description of the drawings] FIG. 1 is a diagram showing the operation principle of one embodiment of the present invention.

──────────────────────────────────────────────────の Continued on the front page (72) Inventor Keikichi Ando 1-280 Higashi Koikekubo, Kokubunji-shi, Tokyo Inside the Central Research Laboratory, Hitachi, Ltd. (72) Norio Ohta 1-280 Higashi Koikekubo, Kokubunji-shi, Tokyo (56) References JP-A-63-266632 (JP, A) JP-A-61-216126 (JP, A) JP-A-56-145530 (JP, A) JP-A-63-113938 (JP) , A) JP-A-63-266633 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G11B ^7/ 00-7/013 G11B 7/125

Claims (1)

(57) [the claims] 1. The first state next to the first power level of the energy beam, a mark with respect to the second power of the energy beam is a second state in the medium, information having various lengths in said first state Is a method of recording information recorded by overwriting as
The medium is continuously moved with respect to the energy beam while irradiating the medium with the energy beam of the second power level at a location where the mark is to be formed. and an energy beam first power level Te, single repeat lowering the second power level or less power level, when forming the shortest mark is reaching the first power level Recording method using information pulses.