JPH0562193A - Recording method of optical information - Google Patents

Abstract

PURPOSE:To execute a pulse-width modulation recording operation at a low linear velocity (1.2 to 1.4m/s) by means of a rewritable pulse-change optical disk and, especially, to realize a rewritable digital audio disk. CONSTITUTION:The composition of a recording film 3 is set in the limit range of a ternary system by Ge, Sb and Te, and its film thickness is set at 10nm or higher and 35nm or lower. In addition, the film thickness of a dielectric film 4 is set at 5nm or higher and 40nm or lower. The composition of a reflecting film 5 is composed of a simple substance or an alloy out of at least Au, Al, Ti, Ni and Cr, and its film thickness is limited to 35nm or higher. The recording operation of a signal is executed by using a method in which one recording mark is formed after it has been irradiated with a plurality of short pulse trains.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for recording optical information on an optical disc which records and reproduces optical information with high density using a laser beam or the like.

[0002]

2. Description of the Related Art A technique for reproducing or recording high-density information using a laser beam is well known and has been put to practical use mainly as an optical disc. As one application example of the optical disc, there is a compact disc (hereinafter referred to as CD) in which music information is recorded. This is a read-only type in which a signal is recorded in advance on an optical disc, and a user can reproduce music information, but cannot record / erase a signal. Therefore, in recent years, research and development for realizing a recordable / erasable CD by a rewritable optical disc have been actively conducted.

Rewritable optical disks can be roughly classified into magneto-optical disks and phase change disks. Among them, the phase change disk changes the laser beam irradiation condition to reversibly change the state of the recording film between amorphous and crystalline to record a signal and optically detect the difference in reflectance between amorphous and crystalline. Is to be regenerated. Therefore, compared with a magneto-optical disk, a signal can be reproduced by a change in the reflectance of laser light as in the case of a CD, and one beam overwriting can be easily realized by modulation of laser power.

As a concrete proposal of a rewritable CD using a phase change disk, a GeSbTe alloy having a composition range indicated by diagonal lines in FIG. 13 was used as a recording film material, and the recording film was sandwiched with a dielectric film as shown in FIG. There is an optical disc (Optical Memory Symposium 1988, Proceedings, P41-P4
2).

[0005]

When a CD signal was actually recorded by the conventional one-beam overwrite with the recording film composition and the optical disc structure proposed in the conventional example, the distortion of the reproduced waveform was very large and practical. I found out not.
This is because the shape of the recording mark is not symmetrical in the front-rear direction but is thin at the tip end and thick at the end end and is distorted into a teardrop shape. The cause is Figure 1
When recording is performed with a laser light modulation waveform as shown in FIG. 5A, the temperature reached by the recording film is a heat accumulation phenomenon, and as shown in FIG. It becomes a teardrop-shaped recording mark as shown in FIG. Since the heat storage phenomenon increases as the relative velocity between the laser spot and the optical disc, that is, the linear velocity becomes slower, the shape distortion of the recording mark also becomes larger when the velocity is very slow at 1.2 to 1.4 m / sec like a CD. This distortion of the recording mark leads to distortion of the reproduced waveform, which causes an increase in jitter. Particularly, the EFM signal of the CD standard is a pulse width modulated signal (PWM signal), and the length of the recording mark and the interval between the recording marks indicate information, and the distortion of the recording mark is a major cause of error occurrence. ..

[0006]

As a result of extensive studies and studies for solving the above problems, the inventors have identified the recording film composition and structure of an optical disc, and further specified the recording method. It has been found that even in a rewritable optical disc, a recording mark having a small shape distortion can be formed, a reproduction signal similar to that of a CD can be obtained, and the repetitive characteristics of recording and erasing are excellent.

That is, a dielectric film, a recording film, a dielectric film, and a reflective film are laminated in this order on a substrate, and the recording film has a composition of Ge.
_x Sb _y Te _z (45 ≤ z ≤ 53 at%, 0.5 ≤ y / (x + y) ≤ 0.72, x + y + z =
100 at%), and the film thickness is 10 nm or more and 35 nm or less, the thickness of the dielectric film on the reflective film side is 5 nm or more and 40 nm or less, and the reflective film is at least Au, Al, Ti, Ni In a method of recording optical information, a pulse width modulated digital signal is overwritten using a single laser spot on an optical disc that is composed of a single substance of Cr, Cr or an alloy and has a film thickness of 35 nm or more. Converting each pulse included in the digital signal into a pulse train composed of a plurality of pulses; modulating laser power between an erasing level and a recording level by the pulse train, and recording one pulse in each pulse train. Forming a mark on the optical disc and recording the digital signal, wherein the pulse train comprises a leading pulse and a trailing pulse train, Is always constant regardless of the length of the recording mark and is larger than the width of each pulse in the subsequent pulse train, the width and interval of each pulse in the subsequent pulse train are equal, and the n-th recording mark is long. In this case, the number of pulses in the subsequent pulse for forming the optical disc is n-1.

[0008]

The optical information recording method of the present invention can significantly reduce the heat storage phenomenon and at the same time realize good erasing speed, recording sensitivity and repetitive characteristics.

In the optical disk used in the present invention, the thin recording film is provided very close to the metal reflection film, so that the heat dissipation effect is great, and the recording film is quickly cooled after being heated. Therefore, the heat storage phenomenon is reduced and the temperature of the end portion of the recording mark is prevented from rising more than necessary.

Further, the laser irradiation to the optical disk is
Since the head pulse having a wide pulse width is irradiated to sufficiently raise the temperature of the recording film and the subsequent pulse having a narrow pulse width is irradiated intermittently, the heat accumulation phenomenon at the end portion of the recording mark can be reduced.

[0011]

The present invention will be described in detail below with reference to the drawings.

As described above, in order to realize PWM recording at a low linear velocity, it is necessary to suppress the heat accumulation phenomenon during recording and reduce the shape distortion of the recording mark. The inventors studied the optical disc structure and the recording film composition and the recording method in order to reduce the shape distortion of the recording mark. As a result, it has been found that by recording a signal with a limited recording laser waveform on an optical disc having a limited recording film composition and structure, the shape distortion of the recording mark can be reduced.

By adopting this optical disk and laser beam irradiation method at the same time, the shape distortion is drastically reduced, and it is a very effective means when recording / reproducing an EFM (8-14 modulation) signal of the CD standard. I knew it was.

FIG. 1 shows the structure of the optical disk of the present invention.
A dielectric film 2, a recording film 3, a dielectric film 4, and a reflective film 5 are laminated on a substrate 1 in this order. As the substrate 1, metal, glass,
A resin or the like can be used, but since a laser beam is generally incident from the substrate side, transparent glass, quartz, polycarbonate, polymethylmethacrylate or the like is used.
The optical disk according to the present invention is characterized in that the recording film composition is specified in a region surrounded by points A, B, C and D in FIG. 2, the recording film thickness is 10 nm or more and 35 nm or less, and the dielectric film is used. The thickness of 4 is 5 nm or more and 40 nm or less, and the reflective film 5 is at least Au, A
It consists of l, Ti, Ni, Cr alone or alloy and has a film thickness of 35
It has been specified as nm or more. The coordinates of the points A, B, C and D are shown below.

(Ge, Sb, Te) at% A (23.5, 23.5, 53) B (13, 34, 53) C (15.5, 39.5, 45) D (27.5, 27.5, 45) Since the recording film is provided very close to the metal reflection film, the heat dissipation effect is large,
The recording film is cooled rapidly after the temperature is raised, so that the heat storage phenomenon is reduced, the shape distortion of the recording mark is suppressed even at a low linear velocity, and at the same time, the composition of the recording film is limited, thereby achieving a good erasing speed. It is possible to realize recording sensitivity and repeatability.

Here, the reason why each component of the optical disk is limited as described above will be explained.

The composition of the recording film is limited to the area surrounded by each point of ABCD in FIG. 2, for the following reason. When the composition is changed while maintaining the above optical disc structure, the crystallization speed is too fast in the region where Te is larger than the straight line AB, so that the recording film is easily crystallized even after melting, and the shape of the amorphous recording mark is distorted and reverse. In the region with less Te than the linear CD, the crystallization speed was too slow and the amorphous portion was not sufficiently crystallized, resulting in a large unerased portion, and the jitter was increased. It was also found that the recording / erasing repetitive characteristic is low in the region where Ge is smaller than that of the straight line BC and in the region where Ge is larger than that of the straight line DA. Therefore, in the optical disc structure in which the heat storage phenomenon is suppressed to a small level, the recording film composition is preferably a region surrounded by points A, B, C and D in FIG.

Further, when only the recording film thickness was changed while maintaining the above structure, when the recording film thickness was less than 10 nm, the recording film had a poor absorption of laser light and a large heat dissipation effect, and the recording sensitivity was deteriorated. When the value exceeds the range, the heat capacity of the recording film increases, and the shape distortion of the recording mark due to the heat storage phenomenon increases. Therefore, the recording film thickness is preferably 10 nm or more and 35 nm or less.

Similarly, when the thickness of the dielectric film 4 on the reflective film side was examined, if the thickness was less than 5 nm, the recording film was too close to the reflective film, the heat dissipation effect was too large, and the recording sensitivity was deteriorated.
When the temperature exceeds the range, the heat radiation to the reflective film becomes small and the shape distortion of the recording mark due to the heat storage phenomenon becomes large. Therefore, the film thickness of the dielectric film 4 is preferably 5 nm or more and 40 nm or less. The materials for the dielectrics 2 and 4 are, for example, SiO2, SiO, Al2O3, G
eO2, TeO2, MoO3, WO3, Si3N4, AlN, BN, TiN, ZnS, ZnSe, ZnTe, S
Although iC can be used alone or a mixture of these, it is preferable that it has excellent thermal stability and easy film formation, especially ZnS, SiO2, S
A mixture of i3N4, AlN, TiN, ZnS and SiO2, and a mixture of ZnSe and SiO2 are good.

Further, when the film thickness of the reflection film 5 was examined, when the thickness was less than 35 nm, the heat dissipation effect of the reflection film was reduced and the shape distortion of the recording mark due to the heat storage phenomenon was increased. Therefore, the thickness of the reflective film 5 is preferably 35 nm or more. Considering that the composition of the reflective film has high reflectance, high thermal conductivity, and easy film formation, at least Au, Al, Ti, Ni,
It is preferable to use Cr alone or an alloy.

Next, a method of irradiating the recording laser light will be described. The CD standard EFM signal is composed of 9 types of pulses with different pulse widths of 3T to 11T (T is a clock period), and the conventional 1-beam overwrite recording method uses the laser power as the erasing level and the recording level. In the meantime, the signal was directly modulated by the EFM signal and recorded on the optical disk. However, in this recording method, the recording mark is greatly distorted into a teardrop shape, and the inventors have devised a method of reducing this (for example, Japanese Patent Application No. 1-32336).
9). This is a method for recording a signal by converting a recording pulse forming one recording mark at the time of one-beam overwriting into a pulse train consisting of a plurality of short pulses of a specific shape (this recording method is hereinafter referred to as multi-pulse recording. Method or MP recording method). The recording method of the present invention extracts and limits elements particularly effective for the optical disk of the present invention among MP recording methods.

That is, after converting each pulse included in the digital signal into a pulse train consisting of a plurality of pulses, the laser power is modulated between the erasing level and the recording level by the pulse train, and one recording is performed for each pulse train. When the mark is formed on the optical disc and the digital signal is recorded, the pulse train is composed of a leading pulse and a trailing pulse train, and the width of the leading pulse is always constant regardless of the length of the recording mark, and each pulse in the trailing pulse train is The pulse width is larger than the pulse width, the width and interval of each pulse in the subsequent pulse train are equal, and the number of pulses in the subsequent pulse when forming the n-th recording mark is n-1. ..

As shown in FIG. 3, 3T ~ included in the EFM signal.
Of the 9 types of pulses with different widths of 11T, 3T pulse is converted to a wide leading pulse, 4T pulse has one narrow trailing pulse added to the leading pulse, and then the pulse width becomes wider. As a result, pulses having the same width are converted into a pulse train in which pulses are added one by one. The pulse train modulates the laser power between the recording level and the erasing level to record a signal. Therefore, for example, an input waveform as shown in FIG. 4A is recorded on the optical disk by the laser output as shown in FIG. 4B. A new signal is recorded while being illuminated and the previously recorded signal is erased. As a method of modulating the laser power, the modulation may be performed between the recording level Pp and the reproduction level Pr or the off level only during the pulse train period as shown in FIG.

Next, more specific examples of the present invention will be shown. (Embodiment 1) First, an example in which the effectiveness of the optical disc and the method for recording optical information according to the present invention is compared with a conventional example will be shown.
Here, two kinds of optical disks according to the present invention and an optical disk according to a conventional example are prepared, and an EFM signal is recorded on each optical disk by the irradiation method of the recording laser light according to the present invention and the irradiation method of the recording laser light according to the conventional example. , And reproduced and compared the magnitude of the signal jitter.

The optical disk A according to the present invention has the same structure as that of FIG. 1, and the substrate 1 is 120 mm in which signal tracks are provided in advance.
The composition of φ polycarbonate substrate and recording film 3 is Ge20Sb30
Te50: at% film thickness is 20 nm, dielectric film composition is 20 mol% SiO2
Is a mixture of ZnS and SiO2 containing
The dielectric film 4 had a thickness of 12 nm, and the reflective film 5 had a composition of Au and a thickness of 50 nm. A protective cover made of polycarbonate was further adhered to protect these thin film layers. Relative velocity between optical disc and laser spot, that is, linear velocity is 1.25m /
Fixed at sec.

The optical disk B of the conventional example has the same structure as that of FIG. 14, and the composition of the substrate, the recording film and the dielectric is the optical disk A.
Same as Regarding the film thickness, the dielectric film on the substrate side is 100 nm, the opposite side is 200 nm, and the recording film thickness is 100 nm. For the optical disc B, a polycarbonate protective cover was further adhered to protect the thin film layer.

The irradiation method of the recording laser light is the conventional method in which the power of the laser light is directly modulated between the recording level and the erasing level by the EFM signal, and the laser light is modulated after converting the EFM signal into the pulse train according to the present invention. The MP recording method is adopted. Since the input pulse of 3T to 11T in the MP recording method is converted into a pulse train according to a certain rule, all pulse trains can be known by designating the width t1 of the leading pulse and the width t2 of the subsequent pulse. That is, FIG.
When the waveform of 11T in (a) is converted into a pulse train as shown in FIG. 5 (b), all pulse trains for 3T to 11T can be found by specifying the width t1 of the leading pulse and the width t2 of the subsequent pulse (t3 = T- t2).

FIG. 6 shows a recording apparatus used in this embodiment to obtain the waveform of FIG. 4 (b). First, the relative velocity of the laser spot from the optical head 8 and the optical disc 6 by the spindle motor 7 of the optical disc 6, that is, the linear velocity is 1.25.
Rotate to be constant at m / sec.

When recording a signal, the EFM signal s1 from the signal generator 9 is converted into a pulse train signal s4 by the MP circuit 10. The MP circuit 10 detects a pulse width in s1 and a pattern setter 11 which presets a pattern of a pulse train corresponding to a pulse of 11T having the longest pulse width, and the pattern setter 11 detects the pulse width according to the length. The modulator 12 is constructed by cutting out a required length from the beginning of the set pattern and generating and outputting a pulse train. To prevent fluctuations in the edge position of the input signal from the signal generator due to modulation in the pulse train, synchronize the input signal generator, modulator, and pattern setter with the same clock C1 to reduce jitter in the recording signal. Suppressed.

The semiconductor laser in the optical head 8 has a current Ir flowing to obtain a reproduction level Pr at the time of signal reproduction, but during the signal recording period, that is, a recording gate signal.
When Wg is input, the bias current Ib for obtaining the erase level Pb flows, and the switch 1 receives the pulse train signal of s4.
When 3 operates, the current Ia for obtaining the recording level Pp is further superimposed. Therefore, at the time of signal recording, the laser power is the erase level Pb and the recording level as shown in FIG.
Between Pp, it is modulated based on the pulse train waveform. The reference voltage setting circuit 14 generates the voltages necessary to obtain the currents Ir, Ia, Ib. The wavelength of the semiconductor laser in the optical head 8 is 830 nm, and the numerical aperture of the objective lens is
al aperture; NA) is 0.5.

The configuration of the pulse train in this embodiment is t1 = 348nsec, t2 = 116nsec, T = 232nsec in FIG.

In the case of the conventional recording method, the switch 13 is directly operated by the EFM signal s1 to modulate the laser power.

With the combination of the optical disk and the recording method as described above, a signal overwritten 10 times on the same track was reproduced and the magnitude of the jitter was measured. A CD jitter meter MJM-631 manufactured by Meguro Denki Co., Ltd. was used for the jitter measurement.

The measurement results are shown in (Table 1). The jitter values shown here are obtained by changing the laser powers Pb and Pp in each combination to obtain the minimum jitter. At that time, Pb and Pp are also noted. The laser power is a value on the surface of the optical disc. As can be seen from Table 1, the combination of the conventional optical disc B and the conventional recording method has a very large jitter, but the combination of the conventional optical disc B and the MP recording method, or the optical disc A according to the present invention and the conventional recording method. The combination greatly improves the jitter. Further, the effect of reducing the jitter by the combination of the optical disk A and the MP recording method according to the present invention is very large. Therefore, in order to reduce the jitter, it is of great significance to simultaneously adopt the MP recording method limited by the present invention for the optical disc A according to the present invention.

[0035]

[Table 1]

A detailed example in which the constituent factors of the optical disk are limited will be described below. As can be seen from Example 1, the recording laser beam irradiation method has a smaller jitter in the MP recording method. In 2 to 8, the MP recording method with the same waveform as in Example 1 was used.

Further, although the linear velocity was constant at 1.25 m / sec in this example, similar results were obtained even when the linear velocity was changed within the range of 1.2 to 1.4 m / sec.

First, the composition of the recording film is set to A, B, C, D in FIG.
An example limited to the area surrounded by is shown.

Example 2 The inventors of the present invention, JJAP, Vol.26 (198)
7) In Suppl.26-4, P61-P66, GeTe of GeSbTe alloy
On the line connecting Sb2Te3 and Sb2Te3, three kinds of compounds that crystallize from amorphous at high speed GeSb4Te7, GeSb2Te4, Ge2Sb2Te5
It was shown that these compounds had excellent recording and erasing properties and excellent repetitive properties, and that the crystallization rate slowed down as the distance from the GeTe-Sb2Te3 line increased.
With the linear velocity of CD, the crystallization rate on the GeTe-Sb2Te3 line is too fast, and it is difficult to amorphize. Therefore, the compound Ge2Sb2
An attempt was made to slow down the crystallization rate by adding Sb to Te5. The optical disc structure was changed in the same manner as the optical disc A in Example 1 except that only the recording film composition was changed on the line connecting Ge2Sb2Te5 and Sb. The jitter of the produced optical disk was measured in the same manner as in Example 1. Further, a characteristic required for the phase change optical disk is a repeated recording / erasing characteristic. The repetition characteristics were evaluated by repeatedly recording the EFM signal at the recording level Pp and the erasing level Pb that minimize the jitter, measuring the jitter, and determining the number of repetitions at which the jitter is twice the initial value.

The measurement results are shown in FIG. Jitter J0 indicates the minimum value obtained by changing the recording level Pp and the erasing level Pb. The reproduction signal jitter J0 has an Sb amount of 30 at%
A minimum value was shown near (point E in FIG. 2). E
If the Sb amount decreases from the point, the crystallization speed becomes faster and the recording mark shape is distorted, and if the Sb amount increases, the crystallization speed becomes slower and the erasing rate becomes worse, and the signal recorded before is affected. Is expected to increase. The size of the jitter is 30nsec considering the CD standard.
The following is good. This is in the range of Sb amount of 25 at% to 37 at%.

The repetition test was carried out up to 100,000 times for an optical disc having an initial jitter J0 of 30 nsec or less, and the number of repetitions C2 at which the jitter was twice the initial value was obtained. Ge2Sb2Te5 and S
On the line connecting b, the jitter did not increase to twice the initial value even after 100,000 repetitions.

As described above, the composition on the Ge2Sb2Te5-Sb line suitable for the heat dissipation structure and the recording method according to the present invention has an Sb content of 25 at%.
The range is from ~ 37 at%.

(Example 3) Next, a recording film was formed by changing the ratio of Ge and Sb while keeping the Te amount constant at 50 at%.
The composition on the line connecting F and G) was prepared, an optical disc was prepared, and a signal was recorded in the same manner as in Example 2 to measure jitter and repetitive characteristics. The optical disc structure is the same as that of the second embodiment. The results are shown in Fig. 8. Initial jitter J0 is Ge
Even when was changed, it was 30 nsec or less, and a good value was obtained.

However, the repetitive characteristic is that the Ge amount is 14 at% to 25 at%.
In the range of, the jitter did not increase up to twice the initial value even after 100,000 repetitions, but in the region where the Ge amount was smaller or larger than this range, the repetition number C2 was 100,000 times or less, and the jitter was 10 times. It was twice the initial number with less than 10,000 times.

From the above, the recording film composition suitable for the optical disk structure and the recording laser beam irradiation method according to the present invention is as follows:
If the Te amount is kept constant at 50 at%, the Ge amount is 14 at% to 25 at%
The range is.

(Example 4) Next, a recording film was formed by changing the ratio of Ge and Te while keeping the Sb amount constant at 30 at%.
The composition on the line connecting H and I), an optical disc was prepared, and a signal was recorded in the same manner as in Example 2 to measure jitter and repetitive characteristics. The optical disc structure is the same as that of the second embodiment.

The results are shown in FIG. The initial jitter J0 of the reproduced signal showed a minimum value when the Ge amount was around 20 at% (point E in FIG. 2). If the amount of Ge decreases from the point E, the crystallization speed becomes faster and the recording mark shape is distorted, and if it increases, the crystallization speed becomes slower and the erasing rate deteriorates, and the signals recorded before are affected. Jitter is expected to increase. In the region where the jitter size is 30 nsec or less, the Sb amount is constant: When the Sb amount is kept at 30 at%, the Ge amount is 1
It is in the range of 7 at% to 25 at%.

The repetition test was carried out up to 100,000 times for an optical disk having an initial jitter J0 of 30 nsec or less, and the number of repetitions C2 at which the jitter was twice the initial value was obtained. Sb constant (30a
In an optical disc having a recording film in which the Ge amount was changed in the range of 17 at% to 25 at% at (%), the jitter did not increase to twice the initial value even after 100,000 repetitions.

From the above, a recording film composition suitable for the optical disc structure and the recording laser beam irradiation method according to the present invention is
When the Sb amount is kept constant at 30 at%, the Ge amount is 17 at% to 25 at%.
The range is.

The above composition range of GeSbTe alloy suitable for heat dissipation structure and a recording method according to the invention from Examples 2-4 in FIG. 2 A, B, C, range surrounded by D, ie Ge _x Sb _y Te _z (45
≦ z ≦ 53 at%, 0.5 ≦ y / (x + y) ≦ 0.72, x + y + z = 100 at%). The coordinates of A, B, C and D are shown below.

(Ge, Sb, Te) at% A (23.5, 23.5, 53) B (13, 34, 53) C (15.5, 39.5, 45) D (27.5, 27.5, 45) (Example 5) An example for determining the film thickness range of the recording film is shown in FIG. The optical disc structure and the recording film composition were prepared by changing only the film thickness of the recording film in the same manner as the optical disc A in Example 1, and the signal was recorded by the same recording method as in Example 2, and the jitter and recording sensitivity were measured. did. The result is shown in FIG.
Shown in. The initial jitter J0 is 20 nsec when the film thickness is 25 nm or less.
Although it is very small and constant, it becomes large when it exceeds 25 nm and exceeds 30 nsec when it is 35 nm or more. It is considered that this is because the heat capacity of the recording film is increased and a heat storage phenomenon appears, and the shape distortion of the recording mark is increased. Therefore, from the viewpoint of jitter, the recording film thickness should be 35 nm or less, especially
25nm or less is good.

However, when the recording film thickness is thin, the recording film is poorly absorbed by the recording film and has a large heat radiation effect, so that the recording sensitivity is lowered. Currently available semiconductor lasers for optical disk light sources have an output of 40-50 mw
It is about 20 mW or less on the surface of the optical disk, considering the transmission efficiency of the optical system. Therefore, the recording level Pp of laser light is preferably 20 mW or less. In the structure according to this example, when the recording film thickness became thinner than 10 nm, the recording level exceeded 20 mW due to the deterioration of the recording sensitivity. That is, from the viewpoint of recording sensitivity, the recording film thickness is preferably 10 nm or more.

That is, the film thickness of the GeSbTe recording film suitable for the heat dissipation structure and the recording method according to the present invention is preferably 10 nm or more and 35 nm or less, particularly 10 nm or more 25 nm from the viewpoint of both jitter and recording sensitivity.
Below nm is excellent.

The dependency of the repeating characteristics on the recording film thickness was not observed in the recording film thickness range of 10 to 35 nm, and the jitter did not increase to twice the initial value even after 100,000 repetitions.

Example 6 Further, the dielectric film 4 on the reflection film side
An example for determining the film thickness range of is shown. An optical disc structure and a recording film composition were prepared by changing only the film thickness of the dielectric film 4 in the same manner as the optical disc A in Example 1, and a signal was recorded by the same recording method as in Example 2, and its jitter and recording sensitivity were recorded. Was measured. The results are shown in Fig. 11. Jitter J0
When the film thickness of the dielectric 4 is 25 nm or less, it is about 20 nsec, which is extremely small and constant, but when it exceeds 25 nm, it becomes large, and when it is thicker than 40 nm, it exceeds 30 nsec. It is considered that this is because the heat radiation from the recording film to the reflective film is reduced and a heat storage phenomenon appears, and the shape distortion of the recording mark is increased. Therefore, from the viewpoint of jitter, the film thickness of the dielectric film on the reflective film side is 40
nm or less is preferable, and 25 nm or less is particularly preferable.

However, when the film thickness of the dielectric film on the reflective film side becomes thin, the recording film becomes too close to the reflective film and the heat dissipation effect becomes too large, so that the recording sensitivity is lowered. In this example, when the thickness was less than 5 nm, the recording sensitivity decreased and the recording level Pp exceeded 20 mW. In other words, from the viewpoint of recording sensitivity,
The thickness of the dielectric film on the reflective film side is preferably 5 nm or more.

That is, the film thickness of the dielectric film 4 suitable for the heat dissipation structure and the recording method according to the present invention is preferably 5 nm or more and 40 nm or less, and particularly preferably 5 nm or more and 25 nm or less from the viewpoint of both jitter and recording sensitivity.

The film thickness dependence of the dielectric properties of the dielectric film 4 was not observed in the film thickness range of 5 to 40 nm, and the jitter did not increase to twice the initial value even after 100,000 cycles. It was

(Embodiment 7) An embodiment for determining the film thickness range of the reflective film 5 will be shown. The optical disc structure and the recording film composition are the same as those of the optical disc A in the first embodiment.
The film was prepared by changing only the film thickness of the reflective film 5 of No. 3, a signal was recorded by the same recording method as in Example 2, and its jitter and recording sensitivity were measured. Results are shown in FIG. The jitter J0 is very small and constant at about 20 nsec when the thickness of the reflective film 5 is 45 nm or more, but becomes large when it becomes thinner than 45 nm and becomes less than 35 nm when it is less than 35 nm.
It exceeds 30nsec. It is considered that this is because the heat dissipation effect of the reflective film was reduced, the heat storage phenomenon appeared, and the shape distortion of the recording mark increased.

Although the recording sensitivity decreases as the reflection film thickness increases because the heat dissipation effect increases, the recording power is almost saturated at the reflection film thickness of 45 nm or more, and the recording level Pp
Was less than 20mW.

That is, the film thickness of the reflective film 5 suitable for the heat dissipation structure and the recording method according to the present invention is preferably 35 nm or more, and particularly preferably 45 nm or more from the viewpoint of both jitter and recording sensitivity.

The dependency of the repeatability on the reflection film thickness is 35
It was not observed above nm, and the jitter did not increase up to twice the initial value even after 100,000 repetitions.

Further, although Au was used as the reflective film in this example, similar results were obtained by using Al, Ti, Ni, Cr alone or an alloy containing them.

[0064]

As is apparent from the above embodiments, the optical information recording method of the present invention is an optical disc in which the composition and film thickness of the recording film, the film thickness of the dielectric film, the film thickness of the reflective film, etc. are limited. In addition, by limiting the waveform of the recording laser light and recording the signal,
Even at a low linear velocity, it is possible to realize a reproduction signal quality similar to that of a CD, and it is possible to provide a rewritable digital audio disc, for example.

[Brief description of drawings]

FIG. 1 is a sectional view of an optical disc of the present invention.

FIG. 2 is a composition range diagram of a recording film of an optical disc according to the present invention.

FIG. 3 is a diagram showing an example of signal waveform conversion in the optical information recording method according to the present invention.

4A is a diagram showing an input signal waveform of optical information. FIG. 4B is a diagram showing an example of a laser modulation method for the input signal of FIG. 4A. FIG. 4C is a diagram of FIG. 4A. The figure which shows an example of the modulation method of the laser with respect to an input signal.

5A is a waveform diagram of an input pulse of 11T, and FIG. 5B is a diagram showing an example in which the input pulse of FIG.

FIG. 6 is a block diagram showing an example of a recording apparatus that realizes an optical information recording method according to the present invention.

FIG. 7 is a characteristic diagram showing the relationship between recording film composition (Sb amount as a parameter) and recording characteristics.

FIG. 8 is a characteristic diagram showing a relationship between a recording film composition (a constant Te amount) and recording characteristics.

FIG. 9 is a characteristic diagram showing the relationship between recording film composition (constant Sb amount) and recording characteristics.

FIG. 10 is a characteristic diagram showing the relationship between recording film thickness and recording characteristics.

FIG. 11 is a characteristic diagram showing the relationship between the film thickness of the dielectric 4 on the reflective film side and the recording characteristics.

FIG. 12 is a characteristic diagram showing a relationship between a reflective film thickness and recording characteristics.

FIG. 13 is a diagram showing a composition of a recording film of a conventional optical disc.

FIG. 14 is a cross-sectional view showing the structure of a conventional optical disc.

15A is a waveform diagram showing the laser power level. FIG. 15B is a diagram showing the temperature reached by the recording film at the laser power shown in FIG. 15A. FIG. 15C is a recording at the laser power shown in FIG. 15A. Diagram showing the shape of the mark

[Explanation of symbols]

 1 substrate 2 dielectric film 3 recording film 4 dielectric film 5 reflective film 6 optical disk 7 spindle motor 8 optical head 10 multi-pulse circuit

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Nobuo Akabira 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (10)

[Claims] 1. A dielectric film, a recording film, a dielectric film, and a reflective film are laminated in this order on a substrate, and the composition of the recording film is Ge _x Sb _y Te _z (4
5 ≦ z ≦ 53 at%, 0.5 ≦ y / (x + y) ≦ 0.72, x + y + z = 100 at%)
And the film thickness is 10 nm or more and 35 nm or less, the film thickness of the dielectric film laminated on the reflective film side is 5 nm or more and 40 nm or less, and the reflective film is at least Au, Al, Ti, A method of recording optical information by overwriting a pulse-width modulated digital signal on a single optical disc on an optical disc that is composed of Ni or Cr alone or an alloy and has a film thickness of 35 nm or more. In the step of converting each pulse included in the digital signal into a pulse train consisting of a plurality of pulses, laser power is modulated between the erasing level and the recording level by the pulse train, and each pulse train has one pulse Forming a recording mark on the optical disc to record the digital signal, wherein the pulse train comprises a leading pulse and a succeeding pulse train. The width of the leading pulse is always constant irrespective of the length of the recording mark and is larger than the width of each pulse in the subsequent pulse train, the width and interval of each pulse in the subsequent pulse train are equal, and the length is n-th. 2. The method for recording optical information, wherein the number of pulses in the subsequent pulse when forming the recording mark is n-1. 2. The optical information recording method according to claim 1, wherein the relative speed between the optical disk and the laser spot is 1.2 to 1.4 m / sec. 3. The optical information according to claim 1, wherein the modulation of the laser power is performed between the recording level and the reproduction level or the off level only during a period of the corresponding pulse width before conversion of the pulse train. Recording method. 4. The method for recording optical information according to claim 1, wherein the digital signal is an EFM signal of CD standard. 5. The method for recording optical information according to claim 1, wherein the composition of the recording film is a composition on a line connecting the compounds Ge2Sb2Te5 and Sb. 6. The method for recording optical information according to claim 5, wherein the composition of the recording film is represented by Ge20Sb30Te50 (at%). 7. The method for recording optical information according to claim 1, wherein the recording film has a thickness of 25 nm or less. 8. The dielectric film comprises ZnS, SiO2, Si3N4, AlN, TiN, ZnS.
2. The method for recording optical information according to claim 1, wherein the method comprises at least one of a mixture of SiO2 and a mixture of ZnSe and SiO2. 9. The film thickness of the dielectric film laminated on the reflective film side is 25.
The method for recording optical information according to claim 1, wherein the optical information is not more than nm. 10. The method for recording optical information according to claim 1, wherein the thickness of the reflective film is 45 nm or more.