JP2804806B2 - How information is recorded - Google Patents

Description

The present invention relates to a method for recording information using an energy beam,
In particular, the present invention relates to a so-called overwriteable information recording method for writing new information while erasing existing recorded information.

[Conventional technology]

A magneto-optical recording film or a phase-change recording film can change its state (magnetization direction, crystal structure, and the like) with a light beam, an electron beam, an ion beam, and other energy beams. Some rewritable information recording methods have already been proposed (for example, refer to JP-A-56-145530 for a phase-change recording method, and to JP-A-62-175948 for a magneto-optical recording method, for example). Gazette).

In the magneto-optical information recording method, for example, Tb-Fe-Co
A recording film composed of an exchange-coupled two-layer film of a system alloy is used.
One of the two-layer films (hereinafter referred to as “information recording layer”) is a film for recording information, and has a high coercive force at room temperature but a relatively low Curie point (magnetization reversal temperature). Has been selected. The other of the two-layer film (hereinafter, “recording auxiliary layer”) is a film specifically provided to enable overwriting (rewriting by overwriting), and has a low coercive force at room temperature but a relatively high Curie point. Its composition is chosen to have. The recording film is formed on, for example, a disk, and information writing and reading are performed using, for example, a semiconductor laser.

FIG. 7a shows a temporal change of the beam power of the semiconductor laser, and has a pulse waveform corresponding to a digital signal "1" or "0" to be recorded. In the figure, H is, exhibit high power level required to heat until the recording auxiliary layer on the Curie point T _H, M
Indicates the intermediate power level required to heat the information recording layer until it reaches its Curie point _TL . In addition,
R is a power level used when reproducing (reading) recorded information, and is set to an extremely low value for both the high level H and the intermediate level M.

In the pulse waveform of FIG. 7A, portions A and B (hereinafter abbreviated as “recording pulse” for convenience) have a high level H.
Is chosen to be an appropriate value equal to or greater than
The portions C, D, and E (hereinafter, abbreviated as “erase pulses” for convenience) are selected to have an appropriate value equal to or slightly larger than the intermediate level M.

When the power of the laser beam changes as shown in FIG. 7A, the temperature of the hottest part of the irradiated area on the recording layer changes as shown in FIG. 7B. Then, the recording auxiliary layer and the information recording layer of irradiating the receiving portion of the recording pulse A and B is a high power level, a result of both of which are heated above the Curie point of the respective (T _H or T _L), Both magnetizations once disappear.

Since the disk is rotating at a high speed, the laser beam moves on the recording film one after another. Therefore, after each portion of the recording film receives a high level of irradiation, it enters a cooling stage with the magnetizations of the recording auxiliary layer and the information recording layer being extinguished.

First the temperature of the recording auxiliary layer drops below the Curie point T _H. A fixed external magnetic field (recording magnetic field) is previously applied to the vicinity of the laser irradiation area of the disk, and the recording auxiliary layer whose temperature has decreased is magnetized again under the influence of the external magnetic field. However, since the direction of the magnetization of the recording auxiliary layer is preset so that the direction of the magnetization is reversed under the influence of the external magnetic field, the direction of the magnetization in this case is opposite to the direction of the initial setting.

Subsequently, when the temperature of the information recording layer falls below the Curie point _TL, the information recording layer is magnetized under the influence of the exchange coupling force acting between the information recording layer and the nearby recording auxiliary layer. In this case, the direction of magnetization is the same as or opposite to the direction of magnetization of the recording auxiliary layer, depending on the type of magneto-optical material used.

On the other hand, in the portion irradiated with the erase pulses C, D, and E, which are intermediate power levels, only the information recording layer is heated beyond its Curie point _TL , so that only the magnetization of the same layer disappears, The magnetization of the other recording auxiliary layer is maintained in the initially set orientation.

When the disk is rotated and the part irradiated with the intermediate level deviates from the irradiated area, the part enters a cooling stage, in which the information recording layer is exchange-coupled to a nearby recording auxiliary layer. Magnetized under the influence of force. The direction of magnetization is opposite to that of the portion that has been irradiated at a high level because the recording auxiliary layer retains the default magnetization direction.

In this way, portions having different magnetization directions are formed one after another in the information recording layer in accordance with the recording signal, and these portions correspond to “1” or “0” of the digital signal.

The shape of the recording point (recording mark) should originally be a circle or an ellipse following the shape and irradiation time of the irradiation beam, but this is not actually the case. In particular, in the case of the recording pulse B having a long duration, the shape of the recording point exhibits a so-called “tear drop shape” that spreads in a direction perpendicular to the recording track later (see the right side of FIG. 7c). When such a teardrop-shaped recording point is reproduced using a normal edge detection method, the timing between the recording signal and the reproduction signal is shifted as shown on the right side of FIG. Causes an unreadable fatal error. A similar phenomenon also occurs when the interval between recording pulses is reduced for the purpose of performing high-density recording. In this case, the diameter of the recording point becomes larger as the signal is written later, so that the individual recording points are eventually connected to each other and cannot be separated and identified.

Such a failure occurs because high heat generated by a high-level irradiation beam is conducted and accumulated in a region other than the irradiated region, and the temperature of the recording film increases over a wider area as the position is irradiated later. . However, this kind of obstacle is achieved by keeping the power of the irradiation beam at the time of information recording to the minimum necessary and making the recording point as small as possible.
Although it can be avoided to some extent, another problem arises in that the power control of the irradiation beam and the autofocus need to be performed extremely strictly.

[Problems to be solved by the invention]

A main object of the present invention is to propose an improved information recording method which can solve all of the many problems in the prior art.

Another object of the present invention is to propose an improved information recording method capable of obtaining a reproduction signal faithfully corresponding to a recording signal, and capable of recording at a higher density as compared with the conventional method. It is in.

[Means for solving the problem]

The above problem is not to change the irradiation power of the energy beam from a high level to an intermediate level immediately,
The problem can be solved by interposing a period at a level lower than the intermediate level. In other words, in the present invention, as the pulse waveform for controlling the power of the irradiation beam, as shown in FIG. 1A, an upward pulse portion from the intermediate level L to the high level H and a pulse waveform from the intermediate level L to the lower level L A waveform including at least a downward pulse portion is used.

The decrease in irradiation energy due to the downward pulse portion is desirably in the range of 0.1 to 1.0 times the increase in irradiation energy due to the upward pulse portion, and if a better result is expected, 0.2 to 0.7 times the increase. It is desirable to set the range up to.

Here, "the decrease in irradiation energy due to the downward pulse"
Is the area of the downward pulse in FIG. 1a (the duration of the low level L when the rising and falling portions of the pulse waveform are assumed to be steep) × the power difference between the low level L and the intermediate level M On the other hand, the “increase in irradiation energy due to the upward pulse” is high when it is assumed that the area (rising edge of the pulse waveform) and the falling edge of the upward pulse in FIG. 1A are steep. (Duration of level H × power difference between high level H and intermediate level M).

The ratio between the high level irradiation power and the intermediate level irradiation power is desirably in the range of 1: 0.3 to 1: 0.9, and good overwriting can be expected in this range. Note that when more favorable overwriting is expected, it is desirable to set the range from 1: 0.4 to 1: 0.8.

As a recording medium, in addition to the above-described magneto-optical recording medium, a magneto-optical recording medium of another overwrite method, a phase-change recording medium (a crystal-amorphous phase change capable of high-speed crystallization is used. Recording medium, a recording medium using an amorphous interphase change, and a crystal system such as a change in crystal system or crystal grain size.
It is possible to use a recording medium utilizing an intercrystalline phase change). Note that the recording medium is not limited to a disk shape, and may be used in any form such as a tape shape or a card shape.

As a material for the recording film, In-Se having excellent rewriting characteristics is used.
Material, In-Sb material, Ge-Sb-Te material, Sn-Sb-Te
It is desirable to appropriately select and use one or more of an In-Sb-Te-based material and a Tb-Fe-Co-based material, but it is not necessarily limited to these. In addition,
Here, “... Material” is a material containing “...” As a main component, and means that other elements may be contained within a predetermined allowable range.

As the energy beam, in addition to a light beam from a semiconductor laser or the like, other forms of energy beam, for example, an electron beam or an ion beam can be appropriately selected and used depending on the properties and type of the recording film.

It is also possible to use more than one energy beam and apply the invention to any one or all of the beams. For example, the same lens is irradiated with two energy beams onto the recording medium with a time lag, and the present invention is applied to the beam that is first irradiated on the recording medium, while the beam that is irradiated later has the same power. If the recording information is read with a low value, it can be confirmed whether or not the overwriting has been performed correctly. However, such a method of performing overwrite verification with a subsequent beam is effective even when the present invention is not applied to a beam to be irradiated first.

[Action]

The downward pulse applied to the pulse waveform of the irradiation beam power acts to promote heating and cooling of the recording film in the irradiation area, and as a result, conduction and accumulation of high heat outside the area are effectively prevented, and the recording is performed. Prevent unwanted enlargement of points.

When the pulse width (duration) of the upward pulse is large, it is desirable to increase the pulse width or the depth (difference from the intermediate level) of the downward pulse accordingly.
The same pulse width has a certain effect. However,
Changing the width of the downward pulse rather than changing its depth makes the configuration of the device easier.

If the width of the downward pulse is fixed, and if it is different, the maximum value is selected to be the same as the minimum width of the upward pulse, the effect of inserting the downward pulse is most noticeable, but the width of the downward pulse is If (or its maximum value) is larger than this, the temperature of the recording film will be too low, causing a problem. If an overshoot occurs at the rising portion of the upward pulse, the temperature can be raised more quickly, and the shape of the recording point can be more accurately followed by the recording signal.

In general, the temperature of the recording film at the energy beam irradiation portion can hardly follow a very short-time change in beam power. Therefore, a high-speed fluctuation (for example, a zero level or a fluctuation of the readout level R for a very short time) that the temperature of the recording film can hardly follow is superimposed on the pulse waveform for power control, and the change in the average power is used as the information. Can be recorded or erased.

〔Example〕

An embodiment of the information recording method according to the present invention will be described in more detail with reference to the drawings. The embodiments described below are:
Although realized using the laser power modulation circuit illustrated in FIG. 8, the circuit for modulating the laser power is not necessarily limited to this, and a circuit having another configuration may be used as necessary. Can be. The modulation circuit shown in FIG. 8 relates to an invention which the present applicant has separately filed as a patent application as Japanese Patent Application No. 63-156779. For details, refer to the specification of the patent application.

In FIG. 8, reference numeral 81 denotes a rotating disk, on the surface of which is formed a recording film composed of, for example, an exchange-coupled two-layer film (information recording layer and recording auxiliary layer) of a Tb-Fe-Co-based material. The disk 81 is driven by an appropriate drive system 82, for example,
The optical disc is rotated at a rotation speed of 0 rpm, and a light beam (for example, a wavelength of 830 nm) from a semiconductor laser 84 is irradiated on the recording track via an optical lens system 83.
Laser power modulation circuit for driving semiconductor laser 84
85 is, for example, a modulation logic unit 86, a pulse current driver 87 to
87 and a direct current driver 88.
Direct current driver 88 is controlled by the output of the potentiometer 89, to generate a minimum level of current I _R that is required reading recorded information. Pulse current driver 87-87
Are controlled by the output of the modulation logic unit 86 to generate pulse waveform element currents I _{1 to} I ₄ . The outputs of the current drivers 87 and 88 are added by connection synthesis, and drive the semiconductor laser 84 into a desired pulse waveform.

<Example 1> The pulse waveform (recording signal waveform) of a laser beam used in this example is as shown in Fig. 1a, and includes two types of recording pulses A and B having different durations. Both pulses are composed of an upward pulse portion and a downward pulse portion, and the power level (high level H) of the upward pulse portion is 12 mW larger than the intermediate level M (the power level of the erase pulses C, D and E) by 6 mW. And
The power level (low level L) of the downward pulse portion is
It is 3 mW smaller than the intermediate level M by 3 mW.

The pulse width (duration) of the upward pulse is 180 ns for the recording pulse A and 540 ns for the recording pulse B. On the other hand, the pulse width of the downward pulse is the recording pulse A
Is 90 ns, and the recording pulse B is 180 ns. When the duration of the upward pulse is long, the duration of the downward pulse is also long. The pulse width of the upward pulse may be proportional to the pulse width of the downward pulse.

As a result of performing recording using such a recording waveform, the temperature of the recording film showed a change as shown in FIG. 1B. The shape of the recording point and the waveform of the reproduced signal in this case are shown in FIG.
And d. As is clear from the figure, the shape of the recording point shows an almost oval shape even when the recording pulse B has a long duration of the upward pulse, and the timing of the recording signal and the reproduction signal is also large. Good agreement.

The pulse width of the downward pulse with respect to the recording pulse B is
As shown in FIG. 2, even when the pulse width (90 ns) of the downward pulse with respect to the recording pulse A was the same, the same effect was recognized. In addition, the same effect as the low power level L of 1 mW, which is the same as the read power level R, was recognized. The laser power modulation circuit shown in FIG. 8 is simpler in this case. This is because if the low power level L and the read power level R are the same, the laser power modulation can be reduced to three levels of H, M, and R (= L).

Further, as shown in FIG. 3, the time point at which the recording pulse B ends is the falling time point a corresponding to the given information signal.
When the time point is earlier (for example, point b), the recording point spreads less in the direction perpendicular to the recording track, and a more faithful reproduction signal can be obtained. Further, as shown in FIG. 4, when an overshoot portion (level H ') of 2 mW was provided at the head of the upward pulse, the shape of the recording point could be made a predetermined width from the first portion. .

Next, the relationship between the ratio (Z = Y / X) and the edge shift was examined by assuming that the increase in the laser energy due to the upward pulse is X and the decrease Y of the laser energy due to the downward pulse. The results shown were obtained. Here, the edge shift refers to a value in which the edge after the recording point is shifted from the target value, and whether the value is large or small causes an error. As is apparent from Table 1, the edge shift value significantly decreases when the value of Z is set in the range of 0.1 to 1.0, and decreases significantly when the value of Z is set in the range of 0.2 to 0.7.

Table 1 Edge Shift Z = 0 + 25ns Z = 0.1 + 15ns Z = 0.2 + 10ns Z = 0.3 + 5ns Z = 0.4 + 5ns Z = 0.5-5ns Z = 0.6-5ns Z = 0.7-10ns Z = 0.8-15ns Z = 0.9-15ns Z = 1.0 −15 ns Z = 1.1 −20 ns Z = 1.2 −25 ns Furthermore, the effect of the ratio of the high level laser power H to the intermediate level laser power M on the erase ratio was examined. The results shown in Table 2 were obtained. Could be obtained. As is clear from the table, the erasure ratio is considerably improved when the value of H: M is in the range of 1: 0.3 to 1: 0.9, and further improved in the range of 1: 0.4 to 1: 0.8. Therefore, if the value of H: M is set in this range, good overwriting can be performed.

Table 2 H: M Erasure ratio 1: 0.1 0dB 1: 0.2 5dB 1: 0.3 35dB 1: 0.4 44dB 1: 0.5 44dB 1: 0.6 44dB 1: 0.7 44dB 1: 0.8 44dB 1: 0.9 35dB Up-pulse and down-pulse A similar effect can be obtained even if a power portion of the intermediate level M is interposed therebetween. However, in the case of the present embodiment, there was no problem even if the power level of the intermediate level M was interposed up to 100 ns, but above this, the effect of providing the downward pulse was reduced.

In the case where the phase change recording film is used, similarly to the case where the magneto-optical recording film is used, when recording is performed with the waveform shown in FIG. 7A, the shape of the recording point becomes as shown in FIG. It becomes a teardrop type (however, in this case, _TH is a melting point and _TL is a crystallization temperature). The degree of the teardrop type is slight because the phase change type disk has lower thermal conductivity, but by using the pulse waveform of the present invention, it is possible to obtain a reproduction signal corresponding to the recording signal. confirmed. In addition, it was possible to reduce the remaining defect of the existing recording, which is the biggest defect of the phase change type recording film.

When two semiconductor lasers are used as an optical head and two laser beams are condensed on the disk with the same lens from these semiconductor lasers, the power waveform of the beam irradiated first on the disk By including the above-mentioned downward pulse, the effect of the present invention could be obtained. Therefore, by maintaining the power at a constant value of 1 mW, the beam that is later irradiated on the disk
It was possible to confirm that it was correctly overwritten by the previous beam.

<Embodiment 2> FIGS. 5 and 6 show the case where the present invention is applied to a recording signal in which a high level H portion has a high frequency (a recording signal in which the duration of the high level H is short and the interval between them is small). This is one embodiment of the case. As shown in FIG. 5a, each individual recording pulse includes a downward pulse portion after an upward pulse portion.

The effect of providing the downward pulse is more remarkable as the density between the recording pulses is higher, and it is recognized that the separation between the peaks of the reproduced waveform is good even at a higher density. Further, when a large number of recording pulses are consecutive, the recording pulse that comes later has the energy reduction Y of the downward pulse.
By increasing the number, a greater effect could be obtained. Note that the effect of the downward pulse is not remarkable in a portion where the interval between the recording pulses is wide, and the pulse can be omitted.

According to this embodiment, the temperature distribution on the recording film is shown in FIG.
As a result, a recording point having the shape shown in FIG. 5c could be formed. The size of the recording point was substantially the same for every recording pulse, and as shown in FIG. 5d, a reproduced signal waveform faithful to the recording signal could be obtained. This reduces errors due to edge shift,
The recording points can be easily separated, and information can be recorded at a higher density as compared with the conventional method. In addition, when a phase change type recording film is used, the erasure of existing recording information is reduced.

In the present embodiment, the depth (power level L) of the downward pulse is different from the read level R. However, if the pulse width of the downward pulse is appropriately selected, the power level L is changed to the read level R. Alternatively, it is possible to make the laser power modulation circuit coincide with the zero level, and the configuration of the laser power modulation circuit becomes relatively easy. Further, as shown in FIG. 6, a certain effect was recognized even when the pulse width of the downward pulse was the same for all recording pulses. In this case, the configuration of the laser power modulation circuit is easiest.

〔The invention's effect〕

According to the present invention, even in the case of a recording pulse having a high level and a long duration, or even when a large number of recording pulses with a narrow pulse interval are continuous, a faithful reproduction signal corresponding to the recording signal can be obtained. It is possible to perform high-density recording with few errors in the reproduction signal. Further, in the case of a phase-change optical recording film, the unerased portion due to rewriting can be reduced.

Incidentally, a magneto-optical recording medium having a multilayer recording film, which has recently been receiving attention, tends to easily cause an undesirable heat storage effect because the total thickness of the recording film is large. It works particularly effectively when such a recording medium is used.

[Brief description of the drawings]

FIGS. 1 to 4 are waveform diagrams for explaining one embodiment of the information recording method of the present invention, and FIGS. 5 and 6 are waveform diagrams for explaining another embodiment of the present invention. FIG. 7 is a waveform diagram for explaining a conventional information recording method, and FIG. 8 is a system diagram showing an example of a laser power modulation circuit used in carrying out the method of the present invention. <Explanation of Codes> A, B... Recording pulse, C, D, E.
…… Upward pulse part …… Downward pulse part…
... overshoot portion, H ... high level, M ... intermediate level, L ... low level, R ... read level, 81 ...
... Disk, 84 ... Semiconductor laser, 85 ... Laser power modulation circuit, 86 ... Modulation logic section, 87 ... Pulse current driver, 88 ... DC current driver

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Toshio Niihara 1-280 Higashi Koikebo, Kokubunji-shi, Tokyo Inside the Central Research Laboratory, Hitachi, Ltd. (72) Inventor Masaaki INABAYASHI 292 Yoshidacho, Totsuka-ku, Yokohama-shi, Kanagawa Within Hitachi, Ltd., Home Appliance Research Laboratory (72) Inventor, Jichiichi Miyamoto 1-280, Higashi-Koikekubo, Kokubunji-shi, Tokyo Inside, Hitachi, Ltd. Central Research Laboratory (72) Inventor, Norio 1-280, Higashi-Koikekubo, Kokubunji, Tokyo, Japan (56) References JP-A-62-259229 (JP, A) JP-A-63-113938 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G11B 7/00 G11B 7/125 G11B 11/10

Claims (2)

(57) [Claims] 1. A method according to claim 1, wherein the power of the irradiation energy beam to the recording medium is temporally controlled with a predetermined pulse waveform, and one state corresponding to the irradiation beam having a high power level and another state corresponding to a lower intermediate power level. In the method of recording information by causing the states to occur on a recording medium, the power control of the irradiation beam comprises an upward pulse portion from an intermediate level to a high level followed by a downward pulse portion to a lower level than the intermediate level. The irradiation energy reduction due to the downward pulse portion of the pulse waveform (the reduction in the irradiation energy assuming that the intermediate power level is continued) is performed by the upward pulse portion of the same waveform. Energy increase (assuming intermediate power levels continued) To increase) with respect to the irradiation energy of the case, the recording method of information which is a range from the 0.1-fold to 1.0-fold. 2. An irradiation energy decrease due to a downward pulse portion is an irradiation energy increase due to an upward pulse portion.
2. The information recording method according to claim 1, wherein the range is from 0.2 times to 0.7 times.