JPH02147394A - Information recording medium - Google Patents

Abstract

PURPOSE:To enable overwriting by providing sequentially a first amorphous silicon layer, a recording layer, a second amorphous silicon layer and a metallic layer on a substrate, and forming the recording layer of an alloy with a specified composition. CONSTITUTION:A substrate 11 is formed from a material being transparent and showing little change with time, for example, a glass or polycarbonate. An a-Si layer 12, a recording layer 13, an a-Si layer 14, a metallic layer 15 and a protective layer 16 are provided on the substrate 11. The recording layer 13 is formed of an In-Sb-Te alloy capable of showing a phase change between a crystalline phase and an amorphous phase, the alloy having an enthalpy of mixing in liquid phase of less than -5,000J/mol. The recording layer 13 is in the crystalline phase in an initialized state, and an amorphous record mark 19 is formed upon irradiation with a laser beam 18 under predetermined conditions. The a-Si layers 12, 14 heat-insulate the recording layer 13, whereas the metallic layer 15 rapidly cools the irradiated part, and the protective layer 16 prevents generation of flaws or the like.

Description

[Detailed Description of the Invention] [Objective of the Invention] (Industrial Application Field) This invention produces a phase change between crystal and amorphous in a recording layer by irradiating it with a light beam such as a laser beam. The present invention relates to an information recording medium such as an optical disk on which information can be recorded or erased.

(Prior Art and Problems to be Solved by the Invention) Phase change type optical discs have been known as optical discs from which information can be erased. In such phase-change optical discs, information is recorded and erased by reversibly changing the irradiated portion of the recording layer between two different structural states depending on the irradiation conditions of the laser beam irradiated to the recording layer. do.

Examples of materials used for such optical discs include Te, Ge, TeGe, and InSe.

Semiconductors, semiconductor compounds, or intermetallic compounds such as 5bSe and 5bTe are known. These can take two states, a crystalline phase and an amorphous phase, depending on the laser beam irradiation conditions, and the complex refractive index N-n-1k in each state is different, so heat treatment with a laser beam can change the recording layer. Information can be recorded and erased by reversibly changing the state of the laser beam irradiated area between a crystalline phase and an amorphous phase (S, R, 0vshInsky et al, Me
tal Urgcal Transactlons
2.641 (1971)).

On the other hand, unlike this, information can be recorded by reversibly changing the phase between two crystal phases depending on the laser beam irradiation conditions.
Erasable optical discs are also known. In-5b alloy is an example of a material in which such a phase change occurs. In-S
The b-alloy thin film is melted once by irradiation with a relatively long laser beam pulse, and then slowly cooled and solidified to become fine crystals, and fine crystals are melted in a relatively short time by irradiation with a short laser beam pulse. Grows into large crystals. These two crystal structures have different complex refractive indices, and when reproducing information by irradiating with a laser beam, the crystal states are distinguished, for example, by the difference in the amount of reflected light.

Incidentally, in the above-mentioned phase change type information recording medium, active research has recently been conducted in order to enable an override function using a single laser beam. Override means that the laser beam emitted from a single laser beam is changed to two levels of power levels PE (erasure) and Pw.
(Recording) This is a method in which power is modulated between (Pw>PE) and new information is overwritten while erasing already recorded information.

However, conventionally developed phase change information recording media generally record information using a pulsed laser and erase it using a continuous laser beam.
Although good recording and erasing characteristics have been obtained using this method, the current situation is that sufficient characteristics regarding override have not yet been obtained.

This invention was made in view of such circumstances, and
The purpose of the present invention is to provide an information recording medium that can be overridden and has good characteristics.

[Structure of the Invention] (Means for Solving the Problems) An information recording medium according to the present invention includes a substrate and a recording medium whose phase changes reversibly between a crystalline phase and an amorphous phase depending on the irradiation conditions of a light beam. a first amorphous silicon layer provided between the substrate and the recording layer, a second amorphous silicon layer provided on the recording layer, and a first amorphous silicon layer provided on the second amorphous silicon layer; The recording layer has a metal layer provided with Inx Sb, Tea (however,
XrY*2 is each expressed in atomic %, x+y+z-
100), and these x, y, and z are set such that the mixing enthalpy of the liquid phase of the alloy is less than 15000 J/mol. .

(Function) According to such a configuration, the recording layer can undergo a phase change between a crystalline phase and an amorphous phase, and such a recording layer can be connected to the first and second layers having a high heat insulating effect. Since it is sandwiched between two amorphous silicon layers, good erasing characteristics can be obtained in overwriting. Further, due to the heat dissipation effect of the metal layer, the area irradiated with the laser beam of the recording power during override can be rapidly cooled, so that good recording characteristics can be obtained. That is, overriding is possible and good overriding characteristics can be obtained.

(Example) This invention will be specifically explained below.

Phase change type information recording media, both types that undergo a phase change between crystalline and amorphous states and types that undergo a phase change between crystals, have a structure as shown in FIG. 4, for example. That is, a protective layer 2 made of a chemically and thermally stable dielectric material, a phase change type recording layer 3, a protective layer 4 made of the same material as the protective layer 2, and an ultraviolet curing layer are formed on a transparent substrate 1. A protective layer 5 made of resin (UV resin) to prevent scratches during handling is formed in this order.

Among these, the protective layer 2.4 has the following functions.

(2) A function that prevents the formation of holes due to evaporation of the irradiated portion when the recording layer 3 is irradiated with a laser beam, and also prevents deformation of the recording layer 3 due to repeated recording and erasing.

■A function that enhances the playback signal using optical interference.

(2) A function to control the temperature of the recording layer 3 so that a desired phase change occurs when the recording layer 3 is irradiated with a laser beam.

Regarding (2) above, if the recording layer 3 is of a type that undergoes a phase change between crystalline and amorphous, the heat generated by irradiation with the recording laser beam is quickly released from the recording layer 3 to rapidly cool it. It is required to facilitate crystallization. Further, in the case where the recording layer 3 is of a type that undergoes a phase change between crystals, a function of insulating the recording layer 3 and suppressing heat release from the recording layer 3 is required. That is, after the recording layer 3 is irradiated with a laser beam to melt it, it is slowly cooled to assist the phase change between the crystal phases.

However, in order to enable override, even when the recording layer 3 is of a type in which the phase changes between crystalline and amorphous, the protective layers 2.4 are required to have the above-mentioned heat insulating function. In other words, when overriding, the erasing laser beam power must be lower than the recording laser beam power, so it is more convenient to use adiabatic crystallization for erasing. It's good. That is, in order to enable overriding, it is necessary to satisfy two contradictory conditions: to insulate the recording layer and to improve heat dissipation from the recording layer.

It is difficult to satisfy the above two conditions at the same time, and in fact, when overriding is performed on a conventional crystal-amorphous layer change type information recording medium, the following problems have occurred. In other words, in the case of override, the power of the laser beam is modulated between the recording power and the erasing power. preheated by a laser beam with a power level of . Therefore, even if the power level for recording is high enough to form an amorphous recording mark, the quenching effect is inhibited by the erasing laser beam, making it difficult to form a recording mark. In order to eliminate this inconvenience, it is sufficient to increase the difference between the recording power and the erasing power. In this case, normal semiconductor lasers have a relatively low upper limit of power, so if we set the upper limit of laser power for recording accordingly, the question becomes how low can we reduce the power for erasing? . Considering that the material of the recording layer is fixed, the erasing power of the laser beam can be reduced by making the protective layer sandwiching the recording layer adiabatic, but the area irradiated with the laser beam with the recording power It is not rapidly cooled, making it difficult to make that part amorphous. When a material with good heat dissipation properties is used as the protective layer, it seems that the area irradiated with the recording laser beam becomes amorphous easily, but in reality, the erasing power must be increased (or Therefore, the difference between recording power and erasing power becomes small, and it is difficult to make the material amorphous.

However, as in the present invention, a recording layer formed of an In-3b-Te alloy that can undergo a phase change between crystalline and amorphous is sandwiched between amorphous silicon (hereinafter referred to as aSi) layers,
Furthermore, such problems can be solved by providing a metal layer. In this case, In-5b- of the recording layer
In the Te alloy, since Te is present, the mixing enthalpy of the liquid phase is low, and a phase change between crystalline and amorphous occurs easily.

In other words, in order for an amorphous state to exist stably at room temperature in a certain alloy, the enthalpy of the liquid phase must be lower than the enthalpy of the solid phase. Since the crystallization is low, the amorphous state is less likely to occur, and as a result, the phase change between crystal and amorphous is less likely to occur.

Specifically, the composition of the recording layer is Inn Sb, Tea (X+)'+Z is each expressed in atomic %, and x+y+z
= 100), if X + y + z is set so that the liquid phase mixing enthalpy of the alloy is smaller than 15000 J/sol, the liquid phase mixing enthalpy becomes larger than the solid phase mixing enthalpy and becomes non-conforming. The crystalline state is stably present, a phase change between crystalline and amorphous state is possible, and good characteristics can be obtained as a recording layer.

This is based on the patent application filed in 1986-163 proposed by the inventor of the present application.
039.

Figure 2 is an isenthalpy curve of the liquid phase mixing enthalpy of the In-8b-Te ternary alloy (Source, G, Gat
her, B, Lequendre and R, Bla
ckikJournal of'Less-Comm
on Metals 77 (1981) 71).

In the case of the In-8b-Te alloy, as mentioned above, in compositions where the liquid phase mixing enthalpy is smaller than 15,000 J/mol, the liquid phase mixing enthalpy becomes smaller than the solid phase mixing enthalpy, and crystals and A phase change between the amorphous state and the amorphous state is possible, but as shown in Figure 2, these three
The liquid phase mixing enthalpy of the original alloy is 15000 J/mo.
The range in which it becomes smaller than l is extremely wide.

Next, the results of confirming the characteristics of the recording layer of an In-8b-Te alloy having a composition range in which the enthalpy of liquid phase mixing is less than 15,000 J/mol will be explained.

22 has the same layer structure as the conventional one, that is, substrate/5i
An optical disk sample having a layer structure of 02 protective layer/recording layer/5i02 protective layer/ultraviolet curing resin layer was used.

The liquid phase mixing enthalpy of the recording layer is 15000 J/mol
As an example of smaller than -10000J/a+o1, In5oSb4°Te1os is shown by the circle in Figure 2.
I n45s b45Te+os I n3+5s b
ss, sT e 10% I n +6s b baT
820 samples were prepared, and these were divided into 8 groups. Also,
As an example where the liquid phase mixing enthalpy is about -10000 J/mol, I n42sb43Te1 shown by the circle in Fig. 2
ss I n70sb15T e ,, I n 6
2S b 2. T e , 3) were used as sample group 1. Hereinafter, examples of In, 6Sb, Te2. ,I n56s bs
rTe2ts I n54s b23T'e23 is shown as a square in Figure 2 as an example of sample 0 group and about -20000 J/mol I n 5gS b +oT e
s8,I nabsb2oTea4SI n31sb
2[lTe41 was designated as sample V group.

The dynamic characteristics of these samples were evaluated in the following manner, with the rotational speed of the disk sample set to 90 Or, p, ■.

First, the output is 5. The recording layer was crystallized by continuous irradiation with a laser beam of mW. Next, recording was performed by irradiating a pulsed laser beam with an output of 10 mW, a pulse width of 100 n5ees, and a duty ratio of 50%. and,
Information was reproduced by irradiating the recording layer with a laser beam of lower power than that used for erasing and detecting the intensity of the reflected light. Erasing was performed by continuous irradiation with a 5 mW laser beam in the same manner as initialization. The first result of the characteristic evaluation
Shown in the table.

Table 1 As shown in Table 1, some residual erasure was observed in samples 0 and 7, which have a relatively high Te content, but the reproduced signal level was also low in samples S to V. It was confirmed that information can be recorded effectively. As a result of observing these samples with a transmission electron microscope, the erased portions were all crystalline, and the recorded marks were almost amorphous, although there were a few crystals in sample S group, and in groups T to 7. It was completely amorphous. In other words, it has been confirmed that in In-8b-Te alloy, if the liquid phase mixing enthalpy is smaller than 15,000 J/layer O1, a phase change between crystalline and amorphous occurs effectively and it can be applied as a phase change type recording layer. Ta.

Next, the reason why override is possible according to the present invention will be explained.

As described in Japanese Patent Application No. 62-10342 proposed by the inventor of this application, the thermal diffusivity of an a-Si film can be significantly reduced depending on the manufacturing conditions. rate is 0.005cm
Since it is extremely small at 2/sec, the effect of insulating the recording layer is extremely large. Therefore, by focusing only on erasing information, information can be erased even if the erasing power of the irradiated laser beam is small. Since the erasing power can be reduced in this way, the difference between the recording power and the erasing power of the laser beam in override can be increased. Also, when focusing on recording information, the heat of the area irradiated with the high-power recording laser beam is quickly released by the metal layer, and this area is rapidly cooled, making it possible to reliably turn this area into an amorphous state. be able to. Therefore, the above problems can be solved and good override characteristics can be obtained.

Next, the structure of the information recording medium of the present invention will be explained in detail. FIG. 1 is a sectional view showing an information recording medium according to an embodiment of the invention. The substrate 11 is made of a transparent material that does not change much over time, such as glass or resin such as polycarbonate.

On the substrate 11 are an a-3i layer 12, a recording layer 13, and an a-SL.
Layer 14, metal layer 15, and protective layer 16 are formed in this order.

The recording layer 13 is made of In-5 whose phase can change between crystalline and amorphous states.
It is made of b-Te alloy. Specifically, when the alloy composition is expressed as Inn Sb, Te+ (where x, y, and z are each expressed in atomic %, and x+y+zm100), the liquid phase mixing enthalpy of the alloy is 15000 J.
When it is smaller than /sol, the amorphous state is stable, phase change between crystal and amorphous occurs effectively, and the properties as a recording layer are good.

This recording layer 13 is in a crystalline phase in the initialized state, and by irradiation with the laser beam 18 under predetermined conditions,
Amorphous recording marks 19 are formed. This recording layer 13
can be suitably formed by sputtering.

As described above, the a-SL layers 12 and 14 mainly have the function of insulating the recording layer 13. This a-8i layer 12
．． 14 is preferably formed by sputtering. As a result, the thermal diffusion coefficient can be made extremely small to 0.005 cm2/sec, and the effect of insulating the recording layer 13 can be made even thicker.
2.14 also has a protective function such as preventing the irradiated portion of the recording layer 13 from being evaporated and forming holes due to laser beam irradiation.

The metal layer 15 is a layer that has a function of rapidly cooling the portion irradiated with the recording laser beam, and is
It is preferable to use a metal having particularly good heat dissipation properties, such as 1 % Cu s P .

The protective layer 16 is made of, for example, an ultraviolet curing resin, like the protective layer 5 described above, and has a function of preventing scratches and the like from occurring. Note that although it is preferable to provide this protective layer 16, it is not always necessary.

Next, an example of a method for manufacturing an information recording medium configured as described above will be described. First, the substrate 11 is placed in a vacuum chamber of a sputtering apparatus, and the inside of the chamber is brought to a high vacuum. Then, introduce argon gas into the chamber,
Argon sputtering is performed by supplying power to the Si target.

As a result, an a-3i layer 12 is formed on the substrate 11.

While maintaining the same atmosphere in the chamber, the recording layer 1 is sputtered by three-dimensional simultaneous sputtering using a target made of each constituent element of the recording layer, or by sputtering using an alloy target adjusted in advance to have the composition of the recording layer to be obtained.
form 3.

Thereafter, sputtering is performed again using a Si target to form an a-8i layer. Furthermore, a metal layer 15 is formed by sputtering using a desired metal target.

After that, if it is necessary to form the protective layer 16, the substrate is removed from the sputtering apparatus, and an ultraviolet curing resin is applied on the metal layer 15 by a spin code method, and then ultraviolet rays are irradiated to form the protective layer 16. form.

Next, initialization, overriding and reproduction of information in the information recording medium configured as described above will be explained.

The initialization recording layer 13 is normally amorphous immediately after film formation, so in order to form amorphous recording marks, the recording layer 13 is continuously irradiated with a laser beam to form the recording layer. After melting, it is slowly cooled and the phase changes to a crystalline phase.

Override As shown in FIG. 3, during override, the power is modulated between the recording puff PW, which has a high level, and the erasing power PE, which has a lower level, to erase previously recorded information. while overwriting new information.

In the case of an optical disc, while rotating the disc at a predetermined speed, PE is irradiated on the area of the disc that is desired to be erased, and Pw is irradiated on the area that is desired to be overwritten. As a result, P
In the part irradiated with E, the amorphous recording mark 19 changes to a crystalline phase and the information is erased, and in the part irradiated with P, the phase changes to amorphous and the recording mark 19 is formed. .

Note that even in the case of simply recording and erasing information rather than overwriting, information can be recorded and erased by irradiating a predetermined portion with a laser beam of power PW or PE while rotating the disk.

Reproduction of the reproduced information is performed by irradiating the recording layer 13 with a laser beam having a power even lower than that of PE, and detecting the difference in reflected light intensity between the recording mark 19 and the non-recorded portion using a photoelectric conversion element.

Next, the results of actually producing an optical disc and evaluating its characteristics based on this example will be described. Here, the composition of the recording layer is 1 n 7 as shown by the triangle mark in FIG.
6S b (, T e 23, I n 36S b 3
? Te27 and In54Sb23Te23 were used, and Au was used as the metal layer.

Ternary sputtering equipment (target is Si.

A disk-shaped substrate made of polycarbonate with groups was set in a vacuum chamber of three alloys (Au, and In76SbllTe23 alloy), and film formation was performed in the following procedure.

First, after drawing a high vacuum of 10-6 Torr in the chamber, the disk substrate was rotated at 60 r, p, m,
Argon gas was introduced into the chamber, and the exhaust valve was adjusted so that the argon gas pressure within the chamber was 5 mTorr.

Next, 200 W of 13.56 MHz radio frequency power (hereinafter abbreviated as R, F, power) was applied to the Si target, and sputtering was performed for about 3 minutes. This results in approximately 800 A-6s on the disk board.
An i-layer was deposited.

Next, 300W of R, F power was applied to the In76Sbt+Te23 alloy target and sputtering was performed for about 2 minutes, and 500 In76Sbz
T e 2. An alloy recording layer was formed.

Using the Si target again, 800 A-3i layers were formed on the recording layer under the same conditions as described above.

Thereafter, R, F and power of 100 W were applied to the Au target and sputtering was performed for 1 minute to form a 300-layer Au layer on the a-3i layer.

The thickness of each layer was determined by the optical enhancement calculation described above so as to maximize the reproduced signal.

The optical disc sample manufactured as described above was designated as Sample A.

I n yts b t, T e□1 alloy targets were
n5. Sb2. Te2) The recording layers were formed in exactly the same manner as sample A except that the alloy target was replaced, and the recording layer compositions were In36S b 3yT e 27% and In 5, respectively.
4S b 23T e 23 samples were prepared and designated as sample B and sample C, respectively.

Replace Si target with 5i02 target, a-S
Samples A, B, and
Three samples were manufactured under exactly the same conditions as C, and these were named samples D and E, respectively.

It was set as F.

Next, while rotating these samples at 1800 r, p, m, dynamic characteristics were evaluated according to the following procedure.

(a) First, the amorphous In-3b-Te recording layer immediately after film formation was crystallized for one track using a continuous laser beam of 10 mW. In this case, the same track was traced several times with a laser beam until this part was completely crystallized.

(b) Information was then recorded on the above-mentioned crystallized track by a pulsed laser of 20 mW, frequency of 4 MHz, and Denity ratio of 50%. After recording, there will be 0 on the recording layer.
．． A 5mW reproduction laser beam is irradiated, and the reproduction signal from the amorphous recording mark is analyzed by a spectroanalyzer.
It was measured as an N value.

(C) The recording marks formed as described above were irradiated with a continuous laser beam for one track while changing the power level, and the lowest power level at which the signal could be erased was measured.

(d) After performing the operation in (a) on another track, an override experiment was conducted by irradiating the power-modulated laser beam shown in FIG. 2 onto that track. The override was performed using the following steps.

■Set the PW to 20 mW, set the PE to the lowest power determined in (c) above, and first set the frequency to 4 MH.
Recording is performed at a duty ratio of 50%, and the frequency is 4MHz.
The C/N value of was measured using a spectroanalyzer.

■Next, change the frequency to 3 without changing the Pw and PE settings.
MHz, and the part previously recorded at 4 MHz was overridden with 3 MHz.

Thereafter, the reduction in C/N at 4 MHz was measured as the erasure rate, and the C/N at 3 MHz was further measured using a spectroanalyzer.

The results of these series of tests are shown below.

First, regarding the above-mentioned (a) to (C), the results shown in Table 2 were obtained.

Table 2 As shown in Table 2, there is no big difference in the C/N value between the group of samples A, B, and C and the group of samples D, E, and F, but the minimum power required for erasure is Sample B
was found to be 1.5 times larger than that of sample A. That is, it was confirmed that by sandwiching both sides of the recording layer between a-3i layers, the erasing laser power can be made extremely small.

Next, regarding the above-mentioned (d), the results shown in Table 3 were obtained.

Table 3 As is clear from this Table 3, sample D.

For groups E and F, even in the first 4 MHz recording, the C/N value was extremely low at 10 to 12 dB, and it was confirmed that they were hardly recorded.

As is clear from Table 1 above, this is true for sample D,
Groups E and F have a PW of 15-17mW and a Pw of 20mW.
This is because there is only a difference of 3 to 5 mW from mW.

On the other hand, in the groups of samples A, B, and C, the Pw is 20 mW and the PE is 10 to 12 mW, so the power contrast is sufficient, so as shown in this table, in the first 4 MHz recording, the C /N value is 45-47dB
, 46-48. in the second 3MHz recording. A sufficient reproduction signal of dB was obtained.

Furthermore, the erasure rate was -26 to -28 dB, which was a sufficient value. In this way, Samples A, B, and C were able to obtain good override characteristics.

As is clear from these experimental results, if the erasing characteristics of continuous laser beam irradiation are good, if a single beam override experiment using only power modulation is performed,
It has been found that even if the composition of the recording layer is the same, large differences in characteristics occur depending on the composition of the protective layers that sandwich the recording layer.

Note that in this test example, Au was used as the metal layer, but as mentioned above, AI and Cu were used.

Of course, similar effects can be obtained by using pt or the like. Furthermore, tests were conducted with the recording layer having the composition shown by the triangle in Figure 2, but it goes without saying that exactly the same results could be obtained if the recording layer alloy had a composition with a liquid phase mixing enthalpy of less than 15,000 J/sol. .

[Effects of the Invention] According to the present invention, the recording layer is formed of an In-5b-Te alloy whose liquid phase mixing enthalpy is less than 15,000 J/sol, and this recording layer is formed of an In-5b-Te alloy having a high heat insulating effect. Since a metal layer with high heat dissipation effect is provided between the amorphous silicon layers, it is possible to obtain a crystalline-amorphous phase change type information recording medium with excellent characteristics, and also to obtain good override characteristics. .

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view showing an information recording medium according to an embodiment of the present invention, Figure 2 is a diagram showing isenthalpy curves of liquid phase mixing enthalpy in In-8b-Te alloy, and Figure 3 is a diagram showing a single beam FIG. 4 is a cross-sectional view showing a general phase change type information recording medium. 11; Substrate, 12.14; a-3L layer, 13; Recording layer, 15; Metal layer, 16; Protective layer. Applicant's representative Patent attorney Takehiko Suzue 1; Figure 3 Figure 4 Figure 2

Claims (1)

[Claims] (1) A substrate, a recording layer whose phase changes reversibly between a crystalline phase and an amorphous phase depending on the irradiation conditions of the light beam, and a first amorphous layer provided between the substrate and the recording layer. It has a silicon layer, a second amorphous silicon layer provided on the recording layer, and a metal layer provided on the second amorphous silicon layer, and the recording layer is made of In_xS.
b_yTe_z (where x, y, and z are each expressed in atomic percent, and x+y+z=100), and these x, y, and z are the mixture of liquid phases of the alloy. An information recording medium characterized in that the enthalpy is set to be smaller than -5000 J/mol.