Dynamic information storage or retrieval – Specific detail of information handling portion of system – Radiation beam modification of or by storage medium
Reexamination Certificate
1998-02-17
2001-07-03
Tran, Thang V. (Department: 2651)
Dynamic information storage or retrieval
Specific detail of information handling portion of system
Radiation beam modification of or by storage medium
Reexamination Certificate
active
06256286
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for initializing a phase change recording medium, and more specifically to a method for initializing a phase change recording medium whereby laser light is radiated onto an information recording surface to cause crystallization thereof.
2. Description of Related Art
A phase change recording medium is an optical recording medium which uses a material capable of supporting reversible crystalline and amorphous (non-crystalline) states as a recording film, the difference in reflectivity between the crystalline and amorphous states being detected as a signal.
In general, a chalcogenide material such as GeSbTe, InSbTe, InSe, InTe, AsTeGe, TeOx-GeSn, TeSeSn, SbSeBi, BiSeGe, AgInSbTe, or the like is used as the phase change recording material, and when these materials are formed as a film over a substrate, immediately after formation they are entirely amorphous.
The state immediately after film formation is generally an unstable amorphous state having a low reflectivity that makes servo pull-in difficult. Because of this, a process known as initialization must be performed to convert the entire recording film to the crystalline state. This initialization process is extremely important in establishing the phase change recording characteristics, the subsequent phase change recording characteristics greatly changing depending upon the method of initialization.
Initialization in the past has used the fusion method, which is disclosed in the Japanese Unexamined Patent Publication H4-366424 and Japanese Unexamined Patent Application Publication H4-209317. This initialization method is that of raising the temperature until the phase change recording film melts, causing it to crystallize. In the case of this method, because the recording film is formed at one time, in the same manner as occurs in the actual recording and erasing processes, the recording and playback characteristics are stable after the initialization. This initialization process uses an optical head that is very similar to the normal optical head, and is performed with a laser beam of a size on the order of several micrometers.
One problem with the above-noted initialization process is the time that it requires. In the case of the initialization of an overwritable magneto-optical disk, since a strong magnetic field is merely applied over the entire surface, the time required is approximately 5 seconds. In the case of a phase changed disk, however, the above-noted method requires several hours.
Because of the above-noted problem, approaches to shortening the initialization time are disclosed in the Japanese Unexamined Patent Publication H8-221814 and Japanese Unexamined Patent Publication H8-153343, although these are not necessarily successful in achieving good initialization.
In contrast to the above, in the Japanese Unexamined Patent Publication H7-192266, there is disclosure of an attempt to perform high-speed initialization using a laser beam having an elliptical beam with its major axis in the radial direction of the disk. In the case of this high-speed initialization, initialization is done by the fusing method.
FIG. 8
is a flowchart showing the fusion method of initialization.
First, the phase change disk is mounted to the spindle (step S81), and the rotation of the spindle is started (step S82). Then, the focus servo is set to on (step S83), and the initialization of the disk is started from the innermost circumference (step S84). During the initialization, the laser power is set to a power which is considerably larger than the power at which crystallization begins, that is, to a power sufficient to fuse the recording film (S85). The initialization operation is stopped at the outermost circumference of the disk (step S86) at which point the initialization ends (step S87).
However, while initialization using a laser beam that is elliptical with the major axis thereof aligned in the radial direction of the disk is suited for high-speed initialization, the laser beam power distribution in the radial direction is not uniform, this leading to the problem of unevenness in initialization. That is, it was not possible to discover a method capable of both good initialization and high-speed initialization.
FIG. 9
shows the reflected light intensity signal (RF signal) from a phase change disk that has been initialized by the above initialization method. In the above-described method, the RF signal level is not at constant level, as shown in FIG.
9
. This is a result of using laser light that is elliptically elongated in the radial direction of the disk to perform a high-speed initialization, this variation in level manifesting itself as variation in initialization. As described above, the power distribution of light from a laser which has been elliptically elongated in the radial direction of disk is not uniform, this manifesting itself as initialization unevenness.
While
FIG. 9
shows the example of high-speed initialization using a laser light that has been elliptically elongated in the radial direction of the disk, in the case of fusion initialization, even if a small light spot, having a radius of several micrometers, is used, this type of situation can occur if the servo is unstable.
In view of the above-described drawbacks in the prior art, an object of the present invention is to provide a method for initializing a phase change recording medium at high speed and with good initialization quality, and in doing so alleviate the above-described problems.
SUMMARY OF THE INVENTION
To achieve the above-noted object, the present invention of the first embodiment is a method of initializing a phase change recording medium by radiating laser light of a prescribed power onto the information recording surface to initialize the information recording surface, wherein the power of the laser light is set to a first power which is in the condition of power around at which crystallization is about to occur in the information recording surface, the above-noted laser light being repeatedly radiated onto the part to be initialized.
The present invention of the second embodiment is a method of initializing an information recording surface of a phase change recording medium by radiating laser light of a prescribed power onto the information recording surface to initialize the information recording surface, this method having a first step of setting the power of the laser light to a first power which is in the condition of power around at which crystallization is about to occur in the information recording surface, the radiating of the laser light onto the part to be initialized being done repeatedly, and a second step of setting the power of the laser light to a second power that is greater than the first power, the laser light set to this second power being radiated onto the part to be initialized at least one time.
In the present invention of the first or the second embodiment, the first power is set to a power that is between 1 and 1.3 times the power around at which crystallization is about to occur in the information recording surface.
In the present invention of the second embodiment, the second power is set with a range over which the part to be initialized does not fuse.
In the present invention, when radiating the laser light a plurality of times onto the part to be initialized in the second step, each time the light is radiated the laser light power is gradually made stronger.
FIG. 1
is a flowchart which corresponds to the initialization method of the present invention of the first embodiment. Specifically, initialization is performed a plurality of times using a laser power that is extremely close to the power around at which the crystallization (initialization) is about to occur. In this case, the phase change recording film is not raised to a temperature at which it begins to melt, and crystallization proceeds with this layer remaining in as a solid.
FIG. 4
shows the reflected light intensity signal (RF signal) in the case of usi
McGuireWoods LLP
NEC Corporation
Tran Thang V.
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