JP2552689B2 - How to record information - Google Patents

Description

The present invention relates to an information recording method using an information recording member capable of rewriting information by irradiation with an energy beam such as light or an electron beam. In particular, the present invention relates to a method of recording information which is effective for a rewritable phase change type optical disc, in which recording / erasing is performed by a single beam spot.

[Conventional technology]

A conventional recording / erasing method for a phase change type optical disc recording medium is disclosed in Japanese Patent Laid-Open No. 59-71140, in which recording is performed by irradiating a minute circular optical spot for which a light beam spot is sufficiently converged for a short time. Then, the recording film is made completely amorphous by rapid heating and quenching, and the recording is erased by using an elliptical optical spot long in the track direction and kept at a temperature at which it can be crystallized for a relatively long time. Therefore, the recording portion which is in an amorphous state is returned to a completely crystalline state. Thus, two different beam spots are used for recording and erasing.

However, recently, the present inventors have developed a recording film capable of high-speed erasing, which can be crystallized in about the same time as the laser irradiation time required for recording information.
"Optical Memory Symposium 1986 Proceedings, pp. 81-86, Single Beam Overwrite Characteristics of Phase Change Disks," 1986, 12
Announced on March 18, by using this film, it is possible to rewrite information with a single beam spot while the optical disk substrate makes one rotation by changing the laser power.

[Problems to be solved by the invention]

In the above prior art, when rewriting information, it is obvious that the faster the crystallization speed of the recording film is, the less unerased information previously written can be reduced, but the crystallization speed is actually high. When the rewriting is performed using the recording film, the following problems occur. That is, the rate of temperature rise and cooling at a point on the recording medium irradiated with the recording energy beam is around (temporally before and after) due to heat conduction.
Depending on what kind of energy beam irradiation is performed and how it is performed, the speed of the beam increases or decreases. For example, the cooling rate is particularly low in the vicinity of the center of the portion where the energy beam is continuously irradiated while the irradiation position moves. Therefore, even if the crystal is once melted by the energy beam, it is at least partially crystallized during cooling. In the portion where the power of the energy beam is reduced, it is rapidly cooled to have a poor crystallinity or an amorphous state.
In this way, the state after irradiation of one point on the recording medium is affected by the irradiation before and after that, so the reproduction signal read using the light reflectance determined by the state of the recording film is the recorded information signal. Lose faith in. In addition, when the recording is rewritten, the unerased portion is likely to occur.

It is therefore an object of the present invention to eliminate the above-mentioned drawbacks of the prior art and provide a highly reliable information recording method.

[Means for solving problems]

The above-mentioned object is to use a thin film that can be changed in a time shorter than the time for which the recording energy beam is irradiated once on the thin film, and to use one of two or more power levels of the energy beam set during recording. For the two, when the shortest time in one level is T, the longest time is 4T or less, the shortest time in the other level is T or more, and the longest time is
This is achieved by using a laser power modulation method that is 4 T or less.

The maximum time during which the power stays at the level defined by the shortest time in one power level is preferably T or more and 3T or less, and particularly preferably 2T or less. The time for staying at the other level is preferably T or more and 4T or less, and particularly preferably T or more and 2T or less. In addition, even if the power fluctuates slightly up and down, multiple levels with slightly different power are:
They shall be regarded as the same level. Further, in the case of a recording power waveform such as a sine wave, it is considered that the level is above when the power is above the half value of the waveform and below when the power is below.

Furthermore, the maximum time 4T for keeping the power of the energy beam constant is not more than the time that the beam spot passes, that is, the half-diameter of the beam spot is r (μm),
When the relative velocity between the beam spot and the recording medium is Vm / sec, It is preferable to satisfy the relationship of It is more preferable that the relation

[Action]

The phase state of the recording film can be described by the degree of crystallization of the recording film. Crystallization proceeds while the recording film is at a temperature equal to or higher than the crystallization temperature (T _x ) and equal to or lower than the melting point (T _m ). Therefore, the degree of crystallization greatly depends on the temperature change of the recording film. First
FIG. 10 shows the result of the time variation of the recording film temperature obtained by the simulation when the power level was changed and the energy beam was irradiated. The simulation method is based on the IPSJ 34th National Congress 1987 6N-7
It is omitted here because it is detailed in "Application of DEQSOL to phase change optical disk thermal analysis simulation".

At the part where the power level falls, the power level decreases while passing through the energy beam, so the heat inflow decreases, and the part melts more rapidly than the part where the high power energy beam passes, then it cools rapidly, so it solidifies while it hardly crystallizes. To do. Therefore, the amorphous state is most likely to occur in the vicinity of the fall of energy power.

On the other hand, the part where the energy power level rises is heated by the inflow of heat due to the increase of the energy power while passing through the energy beam, and is kept at the crystallizable temperature for a longer time than the part where the low power energy beam passes. Therefore, crystallization is most advanced near the point where the energy power rises.

Even if such a recording medium is used, by adopting a laser power modulation method that satisfies the above-mentioned conditions, even if the heat distribution on the recording film is averaged in a narrow range, Fluctuations are small and differences in cooling rates are unlikely to occur. Therefore, a reproduced signal that is quite faithful to the recorded signal can be obtained, and the remaining portion is reduced.

The signal modulation method of the present invention records by atomic arrangement change with almost no change in film shape, for example, crystal-amorphous phase change, crystal-crystal or amorphous-amorphous atomic arrangement change. In addition to (a phase change in a broad sense), it is also effective for magneto-optical recording and recording by hole formation, but when applied to a recording medium having a recording film capable of high-speed phase change, a great advantage is obtained.

Further, the present invention is applicable not only to digital data but also to audio signal and video signal recording.

The present invention is particularly effective in determining the linear velocity of a point on a disk.
When the repetition frequency of the pulse waveform of Xm / sec, duty 50% to be recorded is YMHz, when recording with a pulse waveform that satisfies X / Y> 10, the rising and falling edges of the recording pulse are as shown in Fig. 2. This is a case where a recording medium is used in which a reproduction signal having a spike-like shape can be obtained in some parts.

For stable and reliable overwriting, the heat distribution at the points on the recording medium irradiated with the recording energy as described above may be kept constant within a narrow range. That is, by doing so, a recording point faithful to the information signal to be recorded is recorded without the temperature rise and cooling rates on the recording medium being influenced by the preceding and following recording states.

As a method of making the heat distribution constant, there is a method of changing the irradiation energy faster than the speed of heat conduction and making the average value constant. In FIG. 3, if one of the power levels set during recording is continued for a short time t ₁ that is inversely proportional to the time constant of heat diffusion due to heat conduction, then another 1
Continue _one level for the same time t ₁ . An FM modulation method is a modulation method of such a method. At this time, a pulse having a width t ₁ and a period 2t ₁ is selected corresponding to the information signal “1”, and a pulse having a width t ₂ and a period 2t ₂ is selected corresponding to “0”. Moreover, t ₂ , t ₁
Both are selected for a short time that is inversely proportional to the time constant of thermal diffusion due to heat conduction. In this way, the heat distribution can be made uniform.

Another modulation method is an MFM modulation method which is a modification of the FM modulation method as shown in FIG.

There are three types of time (t ₁ , t ₂ , t ₃ ) that take a certain level.

Furthermore, the M ² FM method, which is a modification of this modulation method and has improved detection margin, can be selected. At this time, there are four types of time (t ₁ , t ₂ , t ₃ , t ₄ ) that take a certain level. M ² FM is suitable for the present invention because its average value is completely constant.

In the modulation methods described so far, when the shortest time t ₁ is determined, the period of recordable information becomes t ₁ or more. But,
Higher density, that is, the period of recordable information is t ₁
There are modulation schemes that make it shorter than. An example of this is the RLL (Run Length Limited Code) modulation method used in magnetic disks and the like. This corresponds to the data m bit to be recorded to the n bit to be actually recorded on the disk surface. When the minimum number of consecutive "0" s is d, the maximum number of consecutive "0s" is k, the input data cycle is T, and the window width for data detection is T _W , the shortest time Tmin and the longest time of the pulse actually recorded on the disk Tm
ax can expressed as Tmin = (d + 1) T W Tmax = (k + 1) T W, as a modulation scheme is defined as (d, k) RLL. This modulation method applicable to the present invention is Tmin
Let T be the maximum Tmax must be 4T. Therefore Should be satisfied. FIG. 6 shows the currently known (d, k) RLL. The above conditions are shown by the solid line in FIG. The dotted line has a Tmax / Tmin value of 2, and the values below this are not known yet. Therefore, the modulation method in the part surrounded by the dotted line and the solid line can be applied in the present invention. Regarding the specific encoding, the black circles are [IBJ Journal of Research and Development (IBM J.Ros.Develop.) P376-381, June 1970], and the white circles are [IEE E-Transaction
Of Magnetics, M.A.G. Volume 12, No. 6,
"IEEE (Trans, Magn, MAG-12,6) p740-742, November, 1976
Since it is detailed in the literature of [Year], it is omitted here. Tma above
Recording is performed as shown in FIG. 5 by a modulation method that satisfies x and Tmin.
In FIG. 5, when k becomes too large, it becomes difficult to create the clock necessary for demodulating the data from the data itself (referred to as self-clocking), and the value of k is limited to about 10. . Of these, Tmax / T is particularly suitable.
The value of min is 2. Another factor that determines the modulation method is the ratio of the allowable time width T _W for detecting data to the minimum time length Tmin of the pulse actually recorded with respect to the time T ₀ corresponding to one bit of raw data ( FIG. 7 shows the relationship with (indicating ratio). As a result, the modulation method suitable for increasing the density of the present invention is (4,9) PLL. Since it is considered that the product of the abscissa coordinate and the ordinate coordinate is large, (1,3) PLL and (3,7) PLL are preferable next to (4,9) PLL.

In the case of an optical disc, the shortest time Tmin is determined by the allowable value of the degree of signal deterioration when the recording point formed by the shortest time Tmin is read by the reproduction beam spot. For example, in the case of reading a recording point as shown in FIG. 8, at the recording point 1, the recording point length is sufficiently longer than the reproduction spot, so that the signal amplitude is sufficient and the S / N is good. In the case of recording point 2, since the recording point length is shorter than the spot, the signal amplitude decreases and the S / N deteriorates. From this, when the allowable limit value is obtained by the recording / reproducing system, the shortest recording point length, that is, the shortest time T
Can be decided. Generally, if the noise (N) is small, the recording point length is 1/2 of the spot size (diameter at which intensity is 1 / e ² ).
Is the limit. For example, when the read spot diameter is 1.6 μm, it becomes 0.8 μm.

As for the speed of heat conduction (heat diffusion), a numerical value as shown in FIG. 9 is one guide. This is the recording material InSeTlCo, InS
b and AuSn are obtained by simulating the temperature rise in the irradiated portion by changing the irradiation time in a stationary state with the irradiation power, absorption coefficient, and thermal conductivity K as parameters.

As a time constant of heat diffusion due to heat conduction, it is sufficient to take an irradiation time in FIG. 9 in which the temperature rise almost stops and the temperature becomes constant. The longer this time, the slower the heat diffusion, so T
Needs to be shortened.

In the recording material of InSeTlCo, K = 0.0025 J / sec · cm · deg optical absorptivity of 46%, irradiation power of 8.8 mW, the temperature rise stopped and the time until the temperature became constant was about 6 μsec. When this time is t ₀ μsec, the present invention is particularly effective when t ₀ > 2.

Since the specific method and model of the simulation are detailed below, they are omitted here. IPSJ 34th Showa 62
National Conference 6N-7 "Application of DEQSOL to phase change optical disc thermal analysis simulation" In the present invention, in addition to the recording film using the reflectance change accompanying the phase change between crystalline and amorphous, A recording film that can be used for recording, reading, and erasing by utilizing the reflectance change due to the atomic arrangement change that hardly accompanies the outer shape change of the film, such as crystal-crystal or amorphous-amorphous phase change It can also be applied to magnetic recording films and the like.

〔Example〕

 Hereinafter, the present invention will be described in detail with reference to examples.

Example 1 In an optical disc using a recording film containing In and Se as the main components capable of high-speed erasing, a case will be described in which information is rewritten (single beam overwrite) by a single beam spot.

The reproduction output waveform of the old information before rewriting is shown in FIG.
FIG. 1B shows an example of a temporal change of the laser power at the time of rewriting the recording information, and FIG. 1C shows an example of the change of the reflectance of the recording film (change of the reproduction output voltage) accompanying the change. The state of the recording film before recording may be crystalline or amorphous. First, as shown in FIG. 3B, the power is raised from a low (reproduction) level to a high (amorphization) level all at once, and the power is maintained as it is. If there is any information during this time, it will be deleted. And when I come to a new information recording place,
The power is pulsed down to a medium (crystallization) level laser power. When the recording is completed, the laser power is increased again to a high level, and the existing information is erased. The operation was repeated as described above and predetermined information was recorded. At this time, the recording film is in an amorphous state where the laser power is at a high level and is in a crystalline state where the laser power is at a medium level. The power may be changed between the middle level and the high level after increasing the power from the low level to the middle level. Further, it is arbitrary whether the crystalline state or the amorphous state corresponds to the recording state or the erasing state, the information 1 or 0, or the high level or the low level. The medium level of laser power is preferably 55% or more and 90% or less of the high level, and 65% or more
A range of 85% or less is particularly preferred. Even if the medium level power was too high or too low, the phase could not be sufficiently changed during irradiation.

Examples recorded by the signal modulation method of the present invention are shown in FIGS. In both cases, the signal unit time T is only 2 to
If the average value within the time of 4 times is taken, it can be seen that the average laser power is constant no matter where it is averaged, and variations in the heating / cooling time at each point hardly occur. Therefore, as can be seen from the figure, the reproduced signal waveform was almost faithful to the recorded waveform. Moreover, the error rate due to the disappearance of the previously written information was 1 × 10 ⁻⁵ or less.

On the other hand, when a similar digital signal is recorded by the conventional signal modulation method, a reproduced waveform faithful to the recorded waveform cannot be obtained,
The error rate was 1 × 10 ^-3 even when recorded for the first time in a place where nothing was written, and 5 × 10 ^-3 or more when overwritten at the already recorded place. When the code information is recorded, the recording is performed for each sector indicating a data delimiter. Therefore, at the start of data recording, the temperature distribution is not constant, and if data is immediately recorded, a faithful reproduced waveform cannot be obtained. Therefore, signals other than data are recorded so that the temperature distribution is constant. As such a signal, for example, there is a synchronization signal provided for pulling in a PLL (Phase Locked Loop) that generates a clock signal.

〔The invention's effect〕

According to the present invention, a sufficiently low value of the error rate of the reproduction signal is obtained, and since overwriting is possible and the remaining portion is less likely to remain, a high transfer rate and high reliability of recording / reproduction can be obtained. Further, the present invention is effective not only when using a disk-shaped recording medium, but also when using another recording medium such as a card-shaped or tape-shaped recording medium.

[Brief description of drawings]

FIG. 1 is a diagram showing a recording laser power waveform and a reproduction output waveform in one embodiment of the present invention, FIG. 2 is a diagram showing a reproduction output waveform in a conventional example, and FIGS. 3 to 5 are embodiments of the present invention. Explanatory drawing which shows the modulation system of the recording signal in an example, 6th
7 and 8 are explanatory views showing various modulation methods included in the present invention, FIG. 8 is a plan view showing the relationship between recording points and optical spots in the embodiment of the present invention, and FIG. 9 is various materials. FIG. 10 is a temperature rise characteristic diagram when the laser beam is irradiated, and FIG. 10 is a diagram showing a laser power and a temperature change at a point where the laser beam is irradiated.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tetsuya Nishida 1-280, Higashi Koikeku, Kokubunji, Tokyo Inside Central Research Laboratory, Hitachi, Ltd. (72) Inventor, Yasushi Miyauchi 1-280, Higashi Koikeku, Kokubunji, Tokyo Hitachi, Ltd. Central Research Laboratory (72) Inventor Keikichi Ando 1-280, Higashi Koikekubo, Kokubunji City, Tokyo Metropolitan Research Laboratory, Hitachi, Ltd. (56) Reference JP-A-62-185250 (JP, A) JP-A-57-125543 (JP-A-57-125543 JP, A) JP 62-188025 (JP, A)

Claims (2)

(57) [Claims] 1. A method of recording information using an information recording medium capable of recording information by utilizing heat generated by irradiation of an energy beam, wherein a recording energy beam is irradiated once onto the thin film as an information recording thin film. A thin film that can be changed in a time shorter than the specified time is used, and T is the shortest time at which one of the two or more power levels of the energy beam is set during recording. An information recording method characterized by recording by a laser power modulation method such that the maximum time is 4T or less, the shortest time at the other level is T or more, and the maximum time is 4T or less. 2. The energy beam spot diameter (half-value width) is γ (μm), and the relative velocity between the beam spot and the information recording medium is V (m / sec). And the maximum time of 4T (seconds) A method of recording information, characterized by: