JPH02303889A - Data recording medium - Google Patents

Abstract

PURPOSE:To obtain a data recording medium possible to record and erase at a high speed, reduced in deterioration due to many-time repetition of record ing and erasure and having good heat stability by mainly constituting a record ing layer of three elements of antimony, tellurium and lead and setting the composition thereof to a specific ratio. CONSTITUTION:A recording layer is mainly constituted of three elements of antimony, tellurium and lead and the composition thereof is represented by formula (SbxTe1-x)1-z(Te1-yPby)z [wherein 45<=x<=70, 30<=y<=70 and 5<=z<=30 are satisfied when x is the atomic number % of Sb in (Sb-Te) of the recording layer, y is the atomic number % of Pb in (Te-Pb) of the recording layer and z is the total atomic number % of (Te-Pb) in the recording layer]. When x or y is little outside said range, it is difficult to obtain proper crystallizing temp. and, when y is much outside said range, erasure becomes difficult. The thickness of the recording layer is selected within a range of 10-1000nm.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an information recording medium, and more particularly to an information recording medium such as an optical disk, an optical card, or an optical tape that records and reproduces information using light. It is something.

[Prior Art] Conventionally, as a rewritable information recording medium, there is one that utilizes a reversible change between two optically detectable states, an amorphous state and a crystalline state.

A typical example is Te81G, which has Te as its main component.
e□4Sb2S3 film as recording layer (JP-A-47-
26897), Te 80 whose main component is Te
8 b zos e 10 film as recording layer (Japanese Unexamined Patent Publication No. 145737/1983, 5PIEVo 1.52
9 p2), a recording layer made of a 5b-8e alloy having a composition such as 5b2Se (JP-A-60-155495, Appl, Phys, 1ett, 48 (19), 1
2 May 1986), a recording layer made of Sb2Se3 alloy (Japanese Patent Laid-Open No. 59-185048), and a recording layer made of a Te-Ge-8b alloy containing Te as a main component (Japanese Patent Laid-Open No. 61-209742). No. Publication), Te-
8b binary alloy recording film (1986 Japan Society of Applied Physics Conference Proceedings 29)
a-ZE-3,4), and one in which various elements are added to Te (Japanese Unexamined Patent Publication No. 152786/1986).

In these information recording media, generally during recording, the recording layer in a crystalline state is irradiated with light for a short period of time to partially melt the recording layer, and then rapidly cooled and solidified by thermal diffusion to form an amorphous mark. . Since the light reflectance of this amorphous mark is different from that of the crystalline state, it can be optically detected as a recording signal. When erasing, a method is used in which the amorphous mark is irradiated with light, heated to a temperature higher than the crystallization temperature, and slowly cooled to crystallize the amorphous mark and return it to its original state.

[Problems to be Solved by the Invention] However, the above-mentioned conventional technology has the following problems.

That is, TeBIGet4Sb2 Te2 film or Te[
When a 10S b IO3e to film is used as a recording layer, the crystallization speed is slow, and it is difficult to realize a real-time rewritable optical disc that requires high-speed erasing. On the other hand, Sb2Te3 film, 5b2Se film and Te
-Ge-3b film has a fast crystallization rate and an erase rate of 1
Although it is possible to make it less than μSeC, there are the following problems. That is, the 5b2Se film has drawbacks such as increased noise and decreased recorded signal quality as recording and erasing is repeated. Furthermore, in the Te-Ge-8b film, if the composition allows high-speed erasing, the recording film is likely to be deformed and open during recording, resulting in poor reliability. Also, 2 of 5b-Te
In the Sb2Te3 film using the original alloy, the crystallization temperature is 130, which is considered necessary to obtain sufficient thermal stability at room temperature.
℃~140℃ or higher, compared to the crystallization temperature of 7.
Due to the low thermal stability of 0°C or less, there was a problem with the storage stability of records.

Furthermore, in JP-A-62-152786, Te
It is claimed that a recording film with good recording properties can be obtained by adding many kinds of elements to TeGe, but what is actually cited as an example is a ternary film made by adding TI and Co to TeGe. However, there is no equivalent concrete study or disclosure regarding actual recording characteristics such as C/N and noise.

Moreover, it must be said that effective and empirical findings have not been disclosed regarding the effects of using the ternary system of 5b-Te-Pb.

In view of the current situation, the present inventors have conducted intensive studies on improvement measures, and have found that by adding PB to 5b-Te and adjusting its composition within a specific range, high-speed recording and erasing are possible, and noise is reduced. The present invention was achieved based on the finding that an information recording medium can be obtained which has a low thermal stability, shows little deterioration even after repeated recording and erasing many times, and has good thermal stability.

Therefore, an object of the present invention is to provide an information recording medium that can be recorded and erased at high speed, has low noise, has little deterioration even after repeated recording and erasing many times, and has good thermal stability. There is a particular thing.

[Means for Solving the Problems] An object of the invention is to irradiate a recording layer formed on a substrate with light and change the optical characteristics of the recording layer by the heat generated directly or indirectly, thereby recording information. In an information recording medium for recording, erasing, and reproducing, the recording layer is mainly composed of three elements: antimony (sb), tellurium (Te), and lead (Pb), and its composition is expressed by the general formula (%) X: Number of atoms of sb in (Sb-Te) of the recording layer %y: Number of atoms of Pb in (Te-Pb) of the recording layer%Z: Total number of atoms of (Te-Pb) in the recording layer 96 In this case, 45≦X≦70.30≦y≦70. This is achieved by an information recording medium that satisfies 5≦2≦30.

That is, the recording layer used in the present invention mainly consists of three elements: antimony (Sb), tellurium (Te), and lead (Pb), and its composition has the general formula (Sbx Te1-x ) 1-z (Tel- F
P by ) zX: Number of atoms of sb in (S b-Te) of the recording layer %y: Number of atoms of Pb in (Te-Pb) of the recording layer %2: (Te-Pb) in the recording layer Total number of atoms%
When expressed as 45≦X≦70.30≦y≦70. It satisfies 5≦2≦30.

If X or y is small outside this range, it will be difficult to obtain an appropriate crystallization temperature, and if y is large outside this range, erasing will be difficult. is difficult to express, which is undesirable. Also, if X is large outside this range, irreversible changes in characteristics such as excessive sb precipitation tend to occur, and repeatability of recording and erasing decreases, which is undesirable. Further, if 2 is outside this range, it is not preferable because an appropriate crystallization temperature cannot be obtained or it becomes difficult to exhibit excellent recording characteristics as described in the present invention.

In order to more preferably express the effects of the present invention, XXYN
Z is 55≦X≦70, 40≦y≦60.10≦, respectively
More preferably, the range is 2≦30.

The thickness of the recording layer of the present invention is usually 10 nm to 1000 nm.
It is selected in the nm range. In particular, in order to obtain high sensitivity as an optical disc, it is preferably 10 nm or more and 150 nm or less, and in order to obtain an even better carrier-to-noise ratio of recording and reproduction signals, it is preferably 25 nm to 100 nm.

Deformation prevention layers can be provided on both sides of the recording layer of the present invention. This deformation prevention layer can be expected to play a role in preventing the substrate from being deformed by the heat of the recording layer during recording and from deteriorating the recording and erasing characteristics. As the deformation prevention layer, Zn
S, ZrC, a composite compound of indium and tin (I T O
), inorganic thin films such as M g F 2 , or Si,
Ge, Ti, Zr.

and oxides of metals such as Te, and films of mixtures thereof are preferred because they have high heat resistance.

A recording/erasing auxiliary layer may be laminated adjacent to the deformation prevention layer, preferably on the back side thereof.

This recording/erasing auxiliary layer facilitates thermal diffusion from the deformation prevention layer and increases the cooling rate of the portion melted during recording, thereby facilitating the formation of amorphous marks. In addition, when irradiating the erasing light beam, the recording auxiliary layer is heated by the light that passes through the amorphous recording mark portion with high light transmittance, which slows down the cooling rate of the recording layer, promoting crystallization and facilitating erasing. become. Furthermore, it has the effect of preventing deterioration of the deformation prevention layer due to heat caused by repeated recording and erasing.

The thickness of the recording/erasing auxiliary layer described above is approximately 10 nm to 11 nm.
It is 00n. The material for the recording/erasing auxiliary layer is a metal that has light absorption and reflection properties in the wavelength range of the recording light and has higher thermal conductivity than the deformation prevention layer, or a metal and metal oxide, metal nitride, metal carbide, or metal. Mixtures such as chalcogenides can be used.

In particular, Zr and H have low specific heat and high thermal conductivity.
Metals such as f are preferred.

The substrate used in the present invention may be the same as conventional recording media, such as plastic, glass, or aluminum. For the purpose of avoiding the influence of dust by recording from the substrate side using convergent light, it is preferable to use a transparent material as the substrate. The above materials include polyethylene terephthalate, polymethyl methacrylate, polycarbonate, epoxy resin, polyolefin resin,
Polyimide resin, glass, etc. are preferred. More preferably, polycarbonate and epoxy resin are used because they have a low birefringence and are easy to form. The thickness of the substrate is not particularly limited, but is 10 μm or more and 5 m.
m or less is practical.

If it is less than 10 μm, it will be easily affected by dust even when recording with convergent light from the substrate side, and if it exceeds 5 mm, it will not be possible to increase the numerical aperture of the objective lens when recording with convergent light, and the pit size will increase. becomes large, making it difficult to increase the recording density.

The substrate may be flexible or rigid. The flexible substrate can be used in the form of a tape or a sheet. The rigid substrate can be used in the form of a card or a circular disk. Furthermore, if necessary, two substrates may be used to form an air sandwich structure, an air incident structure, a closely laminated structure, or the like.

The light used for recording on the information recording medium of the present invention is light such as a laser beam or a strobe light. In particular, a semiconductor laser is used because the light source is small, consumes low power, and is easy to modulate. preferable.

Recording can be performed by irradiating the crystalline recording layer with laser light to form amorphous marks. Alternatively, crystallization marks can be formed on the recording layer in an amorphous state by laser beam irradiation. Also, erasing can be performed by irradiating a laser beam to crystallize an amorphous mark, or by amorphizing a crystallized mark, in the same way as recording.

[Manufacturing Method] Although there are various methods for manufacturing the recording thin film of the present invention, the sputtering method described below is effective as a simple and easy method.

For example, it may be produced by a three-wet sputtering method of Sb, Te, and Pb, or 5bTe, Pb or Sb, T
It may also be manufactured by ePb two-moisture sputtering method. Furthermore, a three-element target of Sb, Te, and Pb adjusted so that the recording thin film after sputtering has a predetermined composition ratio may be used, or small pieces of an alloy of Pb may be set in advance on a 5bTe target. They may be arranged so that the composition ratio is as follows.

Next, regarding the sputtering method, a method for producing a recording film using the magnetron sputtering method illustrated in the figure will be described. The basic structure consists of a sputter target 10, a substrate mounting part 3 and a film thickness monitor 5 arranged opposite to the sputter target 10. When the shutter 2 is opened after the start of sputter discharge, film formation on the substrate 7 is started, and the amount of film deposited on the substrate 7 is monitored by the film thickness monitor 5. A sufficiently homogeneous recording film can be produced by rotating the substrate mounting part at 10 to 3 QQ rpm. With such a device, for example, a 5bTe target (composition ratio 2:1) and a TePb target (composition ratio 1:1) can be used.
). Note that an inert gas such as argon is used as the sputtering gas, and the sputtering can be carried out under conditions of an RF output of 10 to 500 W, and a degree of vacuum during sputtering of about 5 to IXIQ-'Pa.

Naturally, appropriate sputtering conditions are not constant depending on the apparatus, and it goes without saying that recording media may be produced under conditions other than these conditions.

Furthermore, other methods for producing the recording thin film include thin film producing techniques such as vacuum evaporation and electron beam evaporation.

[Applications] The recording medium of the present invention thus obtained has properties particularly suitable for information recording media such as optical discs, optical tapes, and optical cards.

However, it goes without saying that the present invention is not limited to such uses, and can be applied to any use that utilizes differences in optical properties for recording.

[Measurement method] The evaluation method used in the examples of the present invention will be explained.

■Transition temperature recording A thin film was prepared on a glass substrate (1.2 mm thick), and a heating furnace was used to uniformly heat the entire substrate, and a temperature controller was used to raise the temperature at a rate of approximately 15°C/min. while measuring the resistance. The resistance value of the thin film at this time can be determined by installing a pair of electrodes on the recording thin film, connecting a 30Ω resistor and a 5V constant voltage power source in series to both ends, and measuring the voltage across the resistor with a voltmeter. It is calculated by finding the voltage and current applied to the thin film from this. The point where the resistance suddenly changes from high resistance to low resistance is defined as the transition point where the resistance changes from amorphous to crystalline.
The temperature at this time was defined as the transition temperature.

■ Dynamic recording/erasing characteristics Signal recording/reading characteristics were evaluated using the following method and equipment. In this case, the disk-shaped recording medium used was one in which a recording thin film was formed on a polycarbonate substrate with spiral groups.

The evaluation device mainly consists of a semiconductor laser beam with a wavelength of 830 nm, a disk rotation device, and their control circuits.

The optical head passes through the rotating disk substrate onto the recording film with a numerical aperture of 0. The laser beam is focused by the objective lens No. 5 and is controlled to track along the groups carved on the substrate. Recording is performed with a recording power of 1 to 15 mW, a frequency of 0.2 to 5 MHz, and a signal duty of 10 to 90%.
The erasing power was measured in the range of 1 to 15 mW.

The linear velocity was 0.5 to 12 m/sec.

After recording/erasing, reduce the intensity of the semiconductor laser beam to 0. The recorded portion was scanned with a power of 7 mW, and the carrier-to-noise (C/N ratio) of the recorded signal was measured as an RF multiplied signal using a spectrum analyzer with a bandwidth of 30 kHz. The erasure rate was determined from the difference between the recorded and erased carrier signals.

■ Static recording/erasing characteristics The sample was a recording thin film formed on a Pyrex glass substrate. The evaluation device mainly consists of an optical head incorporating a semiconductor laser with a wavelength of 830 nm and its control circuit. The optical head is controlled to focus laser light onto the recording film through a substrate held on an XY stage using an objective lens with a numerical aperture of 0.5. Changes in the amount of reflected light due to the reversible phase transition between amorphous and crystal caused by a recording or erasing pulse applied to the optical head are extracted as an RF signal and repeated durability is evaluated. The recording and erasing power was measured in the range of 1 to 20 mW, and the reproducing power was 0.
It was set to 6mW. The contrast was determined as the ratio of the level difference between the RF specific output crystal and the amorphous state to the crystalline state.

■ Composition analysis A recording thin film prepared on a glass substrate is dissolved in aqua regia, nitric acid, etc., separated from the substrate, and this solution is used to perform high-frequency inductively coupled plasma (ICP) emission spectroscopy (Seiko Electronics Co., Ltd. SPS-1100). The content of each element was determined according to the type (type), and the composition ratio (number of atoms %) was calculated.

[Example] Hereinafter, the present invention will be explained in detail based on examples.

Example 1 A recording layer, a deformation prevention layer, and a recording layer were formed using the sputtering method described in the manufacturing method while rotating a polycarbonate substrate with spiral groups having a thickness of 1.2 mm, a diameter of 13 cm, and a pitch of 1.6 μm at 70 revolutions per minute. An erasing auxiliary layer was formed.

First, after exhausting to 1.5X10-3Pa, 6XIO
In an Ar gas atmosphere of -'Pa, 2 SiO2 was added to ZnS.
Using a ZnS-8in2 target mixed with 0 mol%, a 140 nm ZnS-8in2 deformation prevention layer was formed on the substrate by sputtering, and Te5Sb and Pb were simultaneously sputtered while monitoring with a quartz crystal film thickness meter. ,(
Sb6. Te37) 75 (Te 50P b 50
) A recording layer with a thickness of 50 nm was formed with an elemental composition ratio of 25. Further, on the recording layer, a 200 nm layer of the above-mentioned Zn
A deformation prevention layer of S-5iO□ was formed, and a 45 nm Hf layer was formed as a recording/erasing auxiliary layer on this deformation prevention layer to construct an information recording medium of the present invention.

This information recording medium was rotated at a linear velocity of 1.5 m/sec, and the track was scanned once while being continuously irradiated with semiconductor laser light at a film surface intensity of 4 mW to perform initialization to crystallize the recording layer. At this time, due to crystallization, the reflectance of the recording layer is
It rose from 13.3% to 26.6%. After that, the frequency was 3.5 MHz and the duty was set at a linear velocity of 9 m/s.
Recording was performed using a 12 mW semiconductor laser beam modulated to a ratio of 50%.

After recording, the recorded area was scanned with the intensity of the semiconductor laser beam at 0.7 mW and the recorded area was reproduced. When the reflectance of the recorded mark area decreased due to amorphization, it was confirmed that recording was being performed. . When the C/N ratio of this reproduced signal was measured, the carrier strength of the recording frequency was -19.5 dBm.
, the noise level is sufficiently low at 69.4 dBm, and C
A /N ratio of 49.9 dB, which enables good digital recording, was obtained.

Furthermore, when the recorded portion was irradiated once with 8 mW semiconductor laser light at a linear velocity of 4 m/sec, it was confirmed that the recorded signal could be erased. When recording and erasing were repeated 30 times under the above recording and erasing conditions, the C/N ratio improved to 53.8 dB and the erasure rate was stably obtained at about 43.2 dB. Furthermore, even after 500 recording and erasing cycles, the laser power required for recording and erasing remains unchanged, there is no increase in the noise level of the reproduced signal, and the C/N ratio is 53.7 dB, so there is almost no deterioration in recording characteristics. I couldn't see it.

Furthermore, an erasure rate of 50.1 dB was obtained.

Similar measurements were made without changing the recording conditions, but with the linear velocity of the erasing conditions being increased to 6 m/s and erasing laser power of 11 mW.
When recording and erasing was repeated 30 times, the C/N ratio was 4.
9.6 dB was obtained, and the erasure rate was also good at 29.4 dB.

Furthermore, when the crystallization temperature of this recording layer was measured, it was found that 1
The temperature was 140°C under the temperature increasing condition of 5°C/min.

Therefore, it can be estimated that the thermal stability at room temperature is good.

As described above, the recording medium of the present invention can be easily initialized, can be recorded and erased at high speed, and has good thermal stability. Further, it does not deteriorate even after repeated recording and erasing many times, has excellent characteristics such as high C/N and high erasing rate, and low noise.

Example 2 An information recording medium was produced in the same manner as in Example 1, except that the substrate in Example 1 was changed to a 32 mm square 1.2 mm thick Pyrex glass. This recording medium was used to evaluate static recording and erasing characteristics as described in measurement method ①. Recording was performed with a laser power of 15 mW and a pulse width of 100 nsec, and erasing was possible at high speed with a laser power of 8 mW and a pulse width of 100 nsec. Moreover, reproduction was performed at 0.6 mW. Under these conditions, recording and erasing is possible even after 100,000 recording and erasing cycles, and the contrast of the recorded signal is 2.
5% or more was obtained, and there was no deterioration in characteristics.

Comparative Example 2 An information recording medium was produced in the same manner as in Example 2, except that the composition of the recording layer was as follows.

5b66Te34 A sample with the above composition was first diluted with 700n, which corresponds to a low erasing rate.
When recording and erasing was performed with a wide erasing pulse width of sec, it was possible to repeat the recording. Next, when the erase pulse width is narrowed to correspond to high-speed erasing, erasing gradually becomes difficult, and finally the erase pulse width is 10, which is the same as in Example 2.
When I erased the record in about 0 nsec, it became impossible to repeat it at all. As described above, it can be seen that erasing with a narrow pulse width corresponding to high-speed erasing cannot be performed when pb is not added.

Example 3 Two types of information recording media were produced in the same manner as in Example 2, except that the composition of the recording layer was as follows.

(a) (S bb3T e 37) 75 (T
e 38P b62) 25(b) (S b63T
e3t) 89 (T e5oP b5o) 11 Recording and erasing were performed on these information recording media in the same manner as in Example 2. In (a), the recording pulse is 12°6mW,
100 ns, erase pulse 6. 2mW.

At 100 ns, (o) the recording pulse was 12.3 mW, 1
The erase pulse was 6.3 mW and 100 ns. Reproduction was performed at Q and 5 mW. Under these conditions, stable recording and erasing was possible for both (a) and (b) even after repeating the recording and erasing cycle 100,000 times.

[Effects of the Invention] Since the recording layer of the information recording medium of the present invention has a specific composition of Sb, Te, and Pb, the following effects were obtained.

(1) By using the ternary system of Sb-Te-Pb, the erasing speed could be increased.

(2) High erasure rate and C/N ratio.

(3) Operation is stable even after repeated recording and erasing many times, and there is no deterioration in the reproduction signal strength.

(4) High transition temperature and excellent thermal stability.

(5) Recording and erasing can be performed using a semiconductor laser with a practical output range of about 15 mW.

[Brief explanation of the drawing]

The figure is a schematic explanatory diagram showing an example of an apparatus used when manufacturing an information recording medium according to the present invention. 2: Shutter 3 temporary attachment parts, 5: Film thickness monitor, 6: Drive device, 7: Substrate material, 10 Varnish spatter target

Claims (1)

[Claims] Information recording that records, erases, and reproduces information by irradiating a recording layer formed on a substrate with light and changing the optical characteristics of the recording layer by directly or indirectly generating heat. In the medium, the recording layer is made of antimony (Sb) tellurium (Te).
) and lead (Pb), and its composition has the general formula (Sb_xTe_1_-_x)_1_-_z(Te_1
_-_yPb_y)_zx: Number of atoms of Sb in (Sb-Te) of the recording layer %y: Pb in (Te-Pb) of the recording layer
Number of atoms %z: When expressed as % of the total number of atoms of (Te-Pb) in the recording layer, the following conditions are satisfied: 45≦x≦70, 30≦y≦70, 5≦z≦30 Information recording medium.