Dynamic information storage or retrieval – Storage medium structure – Optical track structure
Reexamination Certificate
1998-03-30
2001-05-08
Hindi, Nabil (Department: 2753)
Dynamic information storage or retrieval
Storage medium structure
Optical track structure
C369S288000
Reexamination Certificate
active
06229785
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an optical information recording medium that can record and reproduce information signals having a high signal quality by irradiating a high-energy beam such as a laser beam to a thin film formed on a substrate, a method for manufacturing the optical information recording medium, a method of recording/reproducing and an apparatus for recording and reproducing.
BACKGROUND OF THE INVENTION
The technique for recording and reproducing information by irradiating a laser beam that is narrowed down into a minute spot onto a thin film that has been formed on a transparent substrate is well known. Recently, various examinations have been carried out enthusiastically in order to increase the quantity of information that can be processed per optical information recording medium by utilizing a technique for recording and reproducing information signals having a high signal quality by irradiating a high-energy beam such as a laser beam to a thin film formed on a substrate. The methods can be divided into two major categories.
A first method is to increase the quantity of information per unit area. A spot diameter of a laser beam is made smaller by shortening the wavelength of a laser beam or by increasing the numerical aperture of an objective lens that gathers the laser beam, thus enabling a smaller mark to be recorded and reproduced. Consequently, the recording density in the circumferential direction and radial recording density in a disk increase and the quantity of information that can be processed per medium increases. Furthermore, in order to improve the recording density in the circumferential direction, mark edge recording in which the length of a recording mark becomes information, and in order to improve the radial recording density, land and groove recording in which information is recorded in both a groove and a land for guiding a laser beam, have been invented and applied vigorously. As such techniques for a high density recording and reproducing progress, a thin film material that is suitable for the techniques and a disk structure using the material also have been developed.
As a second method, a medium having a multilayer structure in which the quantity of information processed per recording medium is doubled by laminating a plurality of layers recording and reproducing information and a method of recording and reproducing in the medium have been proposed (for example, in Japanese Patent Application No. Hei 07-82248). Many thin film materials are also proposed as a recording material suitable for the recording medium having a multilayer structure, but a recording medium in which a favorable recording property can be obtained when only one layer is used is basically used as it is in many cases.
In an optical information recording medium (wherein the information layer is a single layer) utilizing a technique for recording and reproducing information signals having a high signal quality by irradiating a high-energy beam such as a laser beam, a thin film material whose main component is TeO
x
(o<x<2), that is a mixture of Te and TeO
2
, is provided on a substrate (Unexamined Japanese Patent Publication (Tokkai Sho) 50-46317). This kind of recording media can change a reflectance greatly in irradiating an optical beam for reproducing.
However, it takes some time in TeO
x
till a signal is saturated after recording, i.e. till a laser beam irradiated part in a recording thin film is crystallized sufficiently. This is not suitable for a recording medium in which a rapid response is required as in the case of a data file for a computer in which, for example, data are recorded in a disk and then verified after one rotation, or the like.
A recording medium in which, for example, Pd is added to TeO
x
as a third element in order to alleviate the disadvantage mentioned above is proposed in Unexamined Japanese Patent Publication (Tokkai Sho) 61-68296. The Te and the Pd act as a metal sensing a beam and the TeO
x
acts for maintaining an oxidation resistance. The TeO
x
is present as a matrix (sea) component and the Te and the Pd are present as an island component. It is conceivable that the Pd functions as a crystalline nucleus that promotes crystal growth of the Te at the time of irradiating a laser beam in a TeO
x
thin film. According to this function, crystal grains of Te or a Te—Pd alloy in which crystallization is further advanced are generated at high speed. As a result, it enables a crystallization recording at high speed, thus obtaining a rapid response as mentioned above. Furthermore, the moisture resistance of the TeO
x
thin film is not damaged, since the Pd has a high oxidation resistance.
However, a further improvement in recording density has come to be required according to the recent tendency toward mass storage of information. Consequently, a development of a recording medium that can correspond to high density recording using an optical system having a short wavelength/high NA has come to be required. That is to say, deterioration of a recording and reproducing property such as, for example, decrease of a C/N ratio and increase of jitter was found when trying to record information in a higher density recording than the experimental condition shown in the Publication mentioned above in many parts in a composition range of an optical information recording medium mentioned in the Publication in which Pd is added into TeO
x
. The C/N ratio mentioned above means a ratio of carrier
oise in a signal having a specific frequency.
The reason for the deterioration is considered to occur as follows. In the case of higher density recording and reproducing using the same optical system, a sufficient recording property cannot be obtained, if a thermal conductivity of a recording thin film does not fall in a predetermined range. That is, when the thermal conductivity of a recording thin film is too low, the heat is difficult to spread from the part heated by a laser beam and a recording mark can not be enlarged even if recording power is increased. Consequently, the sensitivity is low and the C/N ratio also tends to decrease. On the contrary, when the thermal conductivity of a recording thin film is too high, the heat is easy to spread from the part heated by a laser beam and a recording mark is enlarged by increasing the recording power a little. Consequently, the sensitivity is high and the C/N ratio also tends to increase. However, the edge of the recording mark easily becomes blurry. Adjacent marks begin to run together when increasing the recording power of a laser beam even slightly beyond the optimum power and the C/N ratio decreases. Therefore, the power margin is narrow and there is a problem in a practical use. It is conceivable that in recording and reproducing in the same optical system the problem becomes significant, as the density becomes high by narrowing the space between marks. Even if a high C/N ratio is obtained, it does not always mean that few bit errors occur. Thermal interference tends to be generated between the recording marks, for example, in the case where a recording thin film has a high thermal conductivity as mentioned above. As a result, it is conceivable that the position of the recording marks to be detected changes and many bit errors occur even in the cam of a high reflectance change and a high C/N ratio. It can be considered that this becomes more prominent in a mark edge recording method that is in wide use recently. An evaluation of a jitter is used as a means for evaluating the amount of bit errors relatively easily. The jitter means a deviation on a time base between an original signal for recording and a reproduced signal.
In the present specification, the value obtained by dividing the sum (&sgr;
sum
) of standard deviation of a jitter in each signal by a window width (T) of signal detection is indicated as a “jitter (&sgr;
sum
/T)”, and the value is determined by measurement.
For example, it is well known that a jitter of 12.8% or less is corresponding to a bit error rate of 1
Kitaura Hideki
Nagata Ken'ichi
Nishiuchi Ken'ichi
Yamada Noboru
Hindi Nabil
Matsushita Electric - Industrial Co., Ltd.
Merchant & Gould P.C.
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