JPS6216254A - Optical recording media - Google Patents

Abstract

PURPOSE:To obtain the recording media having the high reliability, the high density recording and a simple construction by forming two optical recording media layers which have the low sensitivity to the heating beam, the sensitivity higher than it and the different material, on the substrate. CONSTITUTION:An optical recording media layer 7 of the low sensitivity to the heating beam and an optical recording media layer 8 having the sensitivity higher than it and the different material are laminated on a substrate 1, and a film thickness delta1 of the layer 7 is set to the value saturated by a reproducing output power. At the layer 7, scopes A0-A0 of the light intensity of the threshold or above of the irradiated beam are dissolved and sublimated, the pit is formed and at the layer 8, by the beam of the weak intensity consumed by the layer 7, a pit B0-B0 of the small diameter is formed. Thus, the output having the drastical rise and the large reproducing output can be obtained, the influence of the defect is decreased because of the multi-layer construction and the productivity can be improved.

Description

[Detailed Description of the Invention] <Industrial Application> The present invention relates to the improvement of optical recording media, and more specifically, the present invention relates to the improvement of optical recording media, and more specifically, the invention relates to the improvement of optical recording media. With a structure in which recording media are stacked, S
In addition to improving the N ratio and reducing the error rate, it also enables high-density recording.

<Prior art> Optical recording media can be categorized from the viewpoint of recording formats. Optical recording media are classified into so-called write-once media, which melt, sublimate, or thermally deform a part of the beam irradiation area of the recording medium by irradiating it with a heating beam such as a laser beam. ◎ Irradiation with a heating beam such as a laser beam causes state changes such as crystallographic phase transformation in the beam irradiated area of the recording medium, and also creates irregularities on the surface of the crystalline material. There is a so-called phase change type optical recording medium that utilizes changes in physical properties such as optical refractive index and reflectance caused by changes.

Regardless of the type of optical recording medium, information is recorded using heat generated on the recording medium by a heating beam. Therefore, in the following description, for the sake of simplicity, an example in which pits (holes) are formed in a write-once optical recording medium material by irradiation with a heating beam such as a laser beam will be described as a representative example.

In the case of an optical disc, for example, the optical recording medium is one in which guiding grooves 3 for focusing and tracking are provided on an optical recording medium layer 2 coated on a substrate 1, as shown in FIG. 7, and pits for recording are formed. The pits 4 are formed by laser beam irradiation with a predetermined wavelength and constant power.

When forming the pits 4, in order to increase the reflectance during reproduction and increase the reflectance contrast ratio between the recorded pit portion and other portions, that is, the reproduced signal amplitude, it is necessary to However, as the film thickness increases, the heat capacity increases, so the laser power required for recording must be increased, and the pit size becomes smaller. stiffness, the recording sensitivity of the equivalent medium decreases.

At present, since there is a limit to laser power, it is necessary to reduce the thickness of the optical recording medium layer even at the expense of reflectance. For example, the thickness of the optical recording medium layer of currently used optical recording media is selected to be as small as 150 to 200 people.

However, in this case, the pits formed on the optical recording medium layer fluctuate due to fluctuations in the intensity of the irradiated laser light.
This may cause peak shifts and reductions in the S/N ratio due to level fluctuations in the reproduced signal and interference in the reproduced waveform, and pit errors due to defects generated on the substrate and optical recording medium layer due to the thin film thickness. In other words, in conventional optical recording media,
Holes that are stable in terms of recording sensitivity, including phase change types (
It was not possible to satisfy both the improvement in the signal-to-noise ratio and the reduction in the error rate based on the recording margin that causes pits and the contrast ratio.

In order to expand the recording sensitivity and recording margin of such conventional optical recording media, for example, the Proceedings of the 41st Autumn Japan Society of Applied Physics (held in 1980), 1.
Report by Yamazaki et al. published in 7P-H-16 (1980) “Study of plasma polymerized protective film for laser recording (■)
'', it is proposed to provide an underlayer having an endothermic effect between the substrate and the optical recording medium.

The proposed configuration has a substrate 1 as shown in FIG.
For example, a C
82 polymer layers were provided.

<Problems to be Solved by the Invention> However, with the above-mentioned configuration, although the recording sensitivity is improved, the reflectance decreases due to the provision of the underlayer, and the film thickness of the optical recording layer is still 150~150 nm. Since there were only 200 members, no solution could be obtained in terms of lowering the SN ratio and error rate. In other words, in conventional single-layer optical recording media or optical recording media with a double-layer structure with an underlayer, an optical recording medium that satisfies the mutually contradictory characteristics of recording margin, improvement of S/N ratio, and reduction of error rate is used. No recording medium could be obtained.

The present invention aims to eliminate the above-mentioned drawbacks of conventional optical recording media and provide an optical recording medium that is capable of high-density recording and is highly reliable.

Means for Solving Problems> In the process of conducting various experiments to achieve the above object, the inventors discovered the following fact.

(a) GaAs semiconductor laser light (wavelength 780 nm)
Optical recording medium materials with low sensitivity to, for example, C52-Te
For example, Te, which has a higher sensitivity than C52-Te, is irradiated with GaAs semiconductor laser light (wavelength 780 nm) to form pits, and the relationship between the laser light power and reproduction output is investigated by changing the film thickness. For the C52-Te film, curves 5-1, 5-2°5-3 shown in FIG. 1 are obtained,
It has been learned that for a Te film with higher sensitivity than that, a reproduction output curve 10 with a rising point of β can be obtained. The results show that the thinner the film thickness is, the lower the reproduction output is, and that once the power exceeds a certain value, the reproduction output is saturated even if the power of the irradiated laser beam is increased further.
In other words, it has been found that it is possible to determine the film thickness of an optical recording medium such that the reproduction output is saturated, depending on the value of the power of the irradiated laser beam.

(tff) Also, I learned that for a Te film with higher sensitivity than C52-Te, it is possible to form pits with the same thickness as a C3-Te film, even with a lower power, so that a sufficiently saturated reproduction output can be obtained. Ta.

(Therefore, for a GaAs semiconductor laser with a constant power, the C52-Te film 7 and the Te film 8 with the saturation value are stacked on the substrate 1 as shown in Fig. 2, and the C82-Te film surface is G
When aAs semiconductor laser light is incident, a large reproduction output can be obtained from the pits formed in these optical recording media.

This invention was able to complete an invention that can achieve the above-mentioned object based on the above-mentioned experimental facts.

That is, the optical recording medium of the present invention has heating beam 5+
! In an optical recording medium that records information in a dark blue beam irradiated area by radiation, an optical recording medium layer having low sensitivity to the heating beam is arranged on one side, and a low-sensitivity optical recording medium layer is placed on the other side. It is characterized by having a multilayer structure in which two or more optical recording medium layers, which are more sensitive to the heating beam and are made of different materials, are laminated in sequence on the side of the heating beam. .

The material of the optical recording medium of this invention is used as a so-called write-once optical recording medium in which a part of the recording medium is melted, sublimated, or thermally deformed by a heating beam, and the recording medium undergoes state changes such as crystallographic phase transformation. So-called phase change optical recording media, which cause changes in physical properties such as optical refractive index and reflectance due to changes in state, can be used.

The above-mentioned write-once optical recording medium includes C5-Te alloy, 5
n-Te-3 layer alloy, Ag-Zn alloy, Ag-AJ
Examples include materials such as -Cu alloy, and examples of phase change optical recording media include crystal-amorphous phase change materials such as Te0x (x>2), semiconductor-metal phase change materials such as Vo2 thin films, and those using styrene oligomers. , a metal-semiconductor phase transition material such as SmS film.

The heating beam irradiated onto the optical recording medium of the present invention includes all beams that enter the recording medium and heat the incident area, such as laser beams, electron beams, ion beams, and infrared beams.

Further, the optical recording medium according to the present invention may have a structure in which a transparent substrate is provided on the upper surface of the low-sensitivity optical recording medium layer, or may have a structure in which a substrate is provided on the high-sensitivity optical recording medium side.

Further, the optical recording medium layer constituting the optical recording medium of the present invention may be a laminate of two or more layers, three layers, four layers, etc., and may further improve sensitivity, reflectance, etc. Depending on the needs, the structure may include a base layer, a top layer, or a cow's layer.

The recording sensitivity of the optical recording medium layer constituting the optical recording medium of this invention is determined by light absorption rate, melting point, thermal conductivity, and cue temperature (Tc).
It is a parameter uniquely determined by optical, thermal, magnetic properties such as film thickness, physical dimensions, and recording conditions such as heating beam power and recording pulse width.

Furthermore, among the optical recording media constituting the optical recording medium of the present invention, the film thickness of the low-sensitivity optical recording medium layer should be set to a value that saturates the reproduction output power within the range of allowable heating beam power. is preferred. If the film thickness is smaller than this value, the recording area of the low-sensitivity optical recording medium layer will become smaller, and the pits of the high-sensitivity optical recording medium layer stacked below will become too large without limit, which will reduce the playback output. Fluctuations increase.

Furthermore, if the film thickness is larger than the above value, the pits of the more sensitive optical recording medium layer laminated below will become smaller, and the reproduction output will decrease.

In the optical recording medium according to the present invention, when information is written and recorded/reproduced, a low-sensitivity optical recording medium layer is placed on the side of the irradiated thermoplastic beam or light source, and the low-sensitivity optical recording medium layer is placed on the irradiated thermoplastic beam or light source side. It is necessary to arrange the high-sensitivity optical recording medium layer on the opposite side of the sandwich, and if the arrangement is reversed, the expected effect will not be obtained.

<Function> In this way, when two or more optical recording medium layers having different sensitivities and different materials are formed into a laminated structure, for example, if the case of two layers is explained as a typical example, as shown in FIG. When point D of the low-sensitivity optical recording medium layer 7 (thickness δ) is irradiated with a heating beam (for example, a laser beam) having a light intensity distribution a shown in FIG. In the heating beam irradiation area A-A, the light intensity range gEA with a threshold value of 1 or more
O- is dissolved and sublimated (phase transformation or magnetization reversal) to form pits.

In case B, a part of the heat is diffused in the plane direction of the low-sensitivity storage layer 7 (X direction in FIG. 2), but a considerable portion of the remaining part is diffused toward the high-sensitivity optical recording medium layer 8 side.

A part of the thermal beam power irradiated at this point has already been consumed in the low-sensitivity optical recording medium layer 7, so the thermal beam power is supplied to the high-sensitivity optical recording medium layer 8 (thickness δ2). The light intensity distribution becomes the intensity shown by the broken line in FIG. The power level for melting and sublimating the high-sensitivity optical recording medium layer 8 is level L2 in the breakdown sb in FIG. 3, and the pits (Bo
-80) is formed (actually, the pit diameter may be the same as the pit diameter of the low-sensitivity optical recording medium layer 7).

). Thus, the range indicated by the shaded area: B0-80 becomes a pit.

Looking at the writing (recording) operation by the pits formed in this way from the perspective of the reproduction output of the thermal beam power pair, for the low-sensitivity optical recording medium layer 7, when the film thickness is δ1, the characteristic curve 6-2, the film Thickness (δ1 + δ2): For ζ, the curve is $6-
Although the reproduction output shown in 1 can be obtained, the low sensitivity optical recording medium layer 7
For pits formed in a laminated film of (thickness δl) and a high-sensitivity optical recording medium layer (thickness δ2), the reproduction output 10 has a steep rise and a large output, as shown by the curve 10a in FIG.
a is obtained.

The 28 rising points (critical power) of the curve 10a are shifted to the higher power side than the rising point β of the high-sensitivity optical recording medium in the case of a single layer shown in FIG.
This is because the energy obtained has already been consumed in the low-sensitivity optical recording medium layer 7 and has become small.

However, as is clear from FIG. 4, its rise is steep and is sufficiently saturated with respect to the irradiation (recording) heatable beam power indicated by point α. On the other hand, if the second high-sensitivity optical recording medium layer is also formed of a low-sensitivity optical recording medium layer made of the same material, the curve 6-1 in Figure 4 will be obtained, and the irradiation thermoplastic beam power at the α point will be playback output without saturation,
Both the pit diameter will be significantly affected by the power fluctuation of the irradiation thermoplastic beam.

When two or more layers of optical recording media having different sensitivities and made of different materials are stacked, the pit diameter is generally determined by the low-sensitivity optical recording medium layer, but the formed pits are as shown in Figures 1 and 4. As shown in the figure, since the reproduction output is determined by the power at the 0 point, which shows a tendency to saturate, the reproduction output is stable even with fluctuations in recording thermal beam power, and pits with a necessary and sufficient diameter are formed. Moreover, since the pit is the sum of the film thicknesses of the stacked optical recording medium layers, that is, the effective pit depth is (δ, +δ2+...), the reflectance and contrast ratio can be increased. Therefore, the reproduced signal output can be increased and the SN ratio can be significantly improved.

Furthermore, the film thickness of the optical recording medium can be increased.

Therefore, the resistance to errors caused by defects in the substrate and each layer of the optical recording medium is increased.

EXAMPLES> The contents of this study will be specifically explained below using Examples and Comparative Examples.

Example 1 In a vacuum bell jar 20 shown in FIG. 5, Te 24 is placed in a tungsten heating boat 21, and a plasma generation coil 23 is provided with a barrier 22 in between. Further, a polymethyl methacrylate (hereinafter referred to as rPMMAJ) substrate 27 is placed on a fixing table 26 with a shack 25 above these.
Place.

In addition, a DC power source 29° high frequency oscillator 301 is connected to the tungsten boat 21 and the plasma generation coil 23, respectively.
The inside of the vacuum bell jar 20 is evacuated to a degree of vacuum of 10-6 to 10-7 Torr by an exhaust system (not shown).

Further, a pipe 28 for introducing C82 monomer through a cock is attached to the vacuum belljar 20.

In the above apparatus, while rotating the substrate 27,
C82 monomer is introduced into the vacuum belljar through the tube 28, a high frequency oscillator 30 is driven, and a current is sent from the DC power supply 29 to the tungsten boat 21. Then, the shutter 25 is opened and the PMMA substrate 27 is coated. The resulting C32 polymer and Te mixed layer (hereinafter referred to as rc
s2-Te layer". ) has a thickness of 20+m (20
0 people).

In the above embodiment, the C52 polymer manufacturing method uses a vacuum bell jar 20 with an internal pressure of 10-3 Torr.

Applied voltage 100 V, C32 mono? Flow rate 20c
c/win. The film forming rate at this time was 2 to 6 people/see in the case of C82 polymer itself.

Therefore, when producing a C52-Te layer containing 90% Te, the Te deposition rate was set to 20 to 60 people/see, corresponding to the C82 polymer polymerization conditions.

Thereafter, the operation of the high frequency oscillator 30 is stopped, and the tungsten 21f! A current was then applied to form a Te film with a thickness of about 20 nm.

The sample prepared as described above is designated as No. 1.

Comparative Examples 1-1 to 1-2 A single layer of C82-Te was formed on separate PMMA substrates.
An optical recording medium was produced in the same manner as in Example 1, except that a film (thickness: 20 nm) and a Te film (thickness: 20 nm) were formed. The obtained optical recording medium was compared with a sample in the case of a C52-Te film.

1-1. The case of the Te film was designated as Comparison No. 1-2.

Comparative Example 1-3 Sample formed according to Comparative Example 1-1, Comparative No.
A C82 polymer was coated as an underlayer to a thickness of 20 nm on the back surface of Sample No. 1-1 (the surface opposite to the PMMA substrate), and the obtained sample was designated as Comparison Photo No. 1-3.

Embodiment 2 In the apparatus having the structure shown in FIG.
A tungsten boat and a DC power source similar to the tungsten boat 21 and DC power source 29 shown in the figure are provided, and the first
Put Te in the tungsten boat 21 and TeO2 in the second tungsten boat, and in the same vacuum as in Example 1, TeOx (Tat! Si,
A film having the composition x2) was obtained.

The film composition of this TeOx is as follows from the substrate 27 side: TeO□2 (
(x=1.2), TeO, (x=1.1) are laminated to a thickness of 60 nm each, forming an optical recording medium with a laminated structure. The obtained sample was designated as No. 2.

Comparative Examples 2-1 to 2-2 Optical recording media were produced in the same manner as in Example 2, except that single-layer Teal, single-layer films, and TeO12 films were formed on separate PMMA substrates. The performance of the sample prepared in this way was then compared to that of Example 1 described above. In order to investigate the performance of Example 2 and Comparison 1-2, the reproduction output and carrier-to-noise ratio (hereinafter referred to as "C/N ratio") of these samples were investigated.

The measuring device used had the configuration shown in FIG.

The apparatus shown in FIG. 6 includes an information input source 40, a recording control device 41, a GaAs semiconductor laser 42, and a condensing lens 4 on the information recording side.
3. It consists of a mirror 44, and Ga when recording on the sample.
The light output of one laser was 8 mW using an As semiconductor.

On the reproduction side, a GaAs semiconductor laser 45 and a condensing lens 46
, a beam splitter 47, a tracking mirror 48, a photodetector 49, a reproduction output control device 50, and a motor 51, and records written by the above-mentioned GaAs semiconductor laser 45, and adjusts the optical output from the GaAs semiconductor laser to 0.
When the power was set to 8 mW, the output reproduction signal obtained by the photodetector 49 was transmitted through the reproduction device 50 and was measured by the cyclic noise ratio (hereinafter referred to as rC/N ratio). However, the frequency of the carrier wave at this time was measured with IW(z) and a bandwidth of 30 yen.

The measurement results are shown in Table 1 below. However, in Table 1, Example No. 1 Comparison No. 1 1 p Comparison N
o, 1-2 reproduction output (dB) and C/N ratio (dB
) are based on the measured values of playback output (dB) and C/N ratio (dB) of Comparison No. 1-3, respectively, and the difference from this reference value is indicated as "+" for larger ones and "+" for smaller ones. "
−” is added. In addition, the reproduction output (dB) and C/N ratio (dB) of Example tooth No. 2 and Comparison point 2 are based on the measured value of Comparison No. 2-1, respectively, and are similar depending on the magnitude of deviation from this reference value. It was expressed in

Table 1 From the results in Table 1, although the optical recording medium with the laminated structure according to this example has a slightly lower reproduction output than the conventional single layer optical recording medium, the C/N ratio is sufficiently improved. I understand that. This seems to be the result of the recording area being stabilized and output fluctuations and noise being considerably suppressed.

Further, in this embodiment, an optical recording medium having a two-layer structure has been described, but similar results can be obtained with an optical recording medium having a multilayer structure of three or more layers.

Further, in the above embodiment, an example was shown in which the reflectance was high when unrecorded and the reflectance after recording was low, but the relationship between the reflectance before and after recording may be reversed.

Further, the optical recording medium is not limited to the so-called write-once type, but may be a phase-transformable type.

<Effects of the Invention> As is clear from the above description, the optical recording medium of the present invention has two or three layers of optical recording media with different sensitivities and materials laminated, so it is different from the conventional single-layer optical recording medium. Compared to media, ■ The effective film thickness can be thicker, resulting in higher reproduction output. Moreover, by irradiating light with a power at the saturation point for the film thickness of the low-sensitivity optical recording medium layer, it is possible to obtain a reproduction output with a rapid rise and a large reproduction output.

(2) Furthermore, because of the multilayer structure, it is possible to reduce the effects of defects, etc. in the optical recording medium layer, so it is possible to reduce the error rate and improve the S/N ratio.

■ Since the influence of defects can be reduced, reflectance can be improved.

Therefore, the high density potential of the optical recording medium can be utilized.

■ Since the structure is relatively simple, it is easy to manufacture.

(2) Due to the multi-layer structure, the influence of defects can be reduced compared to optical recording media with a single-layer structure, improving accumulation and increasing productivity.

[Brief explanation of drawings]

Figure 1 is a characteristic diagram showing the relationship between recording laser power and reproduction output in optical recording media with different film thicknesses, and Figure 2 is a longitudinal cross-sectional view showing the relationship between thermal beam irradiation and pit-shaped areas in a two-layer optical recording medium. , FIG. 3 is a light intensity distribution diagram of the thermoplastic beam irradiated onto the optical recording medium, and FIG. 4 is an explanatory diagram showing the relationship between the recording laser power pair and the reproduction output of the optical recording medium of the example.
FIG. 5 is a schematic diagram of the vacuum apparatus used to produce the optical recording medium of the example, FIG. 6 is a schematic diagram of the performance measuring device of the optical recording medium of the example, and FIGS. 7 and 8 are conventional examples, respectively. 1 is a perspective view and a sectional view of main parts showing the schematic structure of an optical recording medium of FIG. In the drawings: 1...Substrate, 7.Low-sensitivity recording medium layer, 8.High-sensitivity recording medium layer

Claims (3)

[Claims] (1) In an optical recording medium in which information is recorded in a heating beam irradiation area by heating beam irradiation, the optical recording medium has an optical recording medium layer that has low sensitivity to the heating beam, and this low-sensitivity optical recording medium layer. An optical recording medium characterized by having a multilayer structure in which optical recording medium layers having higher sensitivity and different materials are laminated. (2) The optical recording medium according to claim (1), wherein each layer of the optical recording medium forming the multilayered optical recording medium is entirely made of a write-once optical recording medium material. (3) The optical recording medium according to claim (1), wherein each layer of the optical recording medium forming the multilayered optical recording medium is entirely made of a phase change type optical recording medium material.