JPH0342276A - Information recording medium - Google Patents

Abstract

PURPOSE:To make it possible to delete recorded information at high speed and high sensitivity and besides minimize qualitative deterioration due to repeatability by providing a recording film consisting mainly of four elements such as bismuth(Bi), antimony (Sb), germanium(Ge) and tellurium(Te), with the specified composition of these elements. CONSTITUTION:A recording film consists mainly of four elements such as bismuth(Bi), antimony (Sb), germanium(Ge) and tellurium(Te). In addition, the composition of these elements is expressed by formula (TexBiySb1-x-y)1-z(Te0.5 Ge0.5)2' and the values of x,y,z satisfy 0.25<=x<=0.6, 0.5<=y<=0.4, 0.2<=z<=0.6. where x,y,z represent an atomic number ratio respectively. This satisfaction of such a composition does not allow irreversible phase separation or segregation caused by the repeated cycle of recording and deletion to occur easily in terms of crystal structure. Thus it is possible to minimize deterioration of recording and deletion properties due to repetition and at the same time, make the medium highly sensitive and amorphous easily. The crystallization speed is high so that the speed range of 500 nsec or below can easily be attained..

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an information recording medium, and in particular to an optical card or optical disk device that records information by irradiation with an energy beam such as a laser beam or an electron beam. Regarding information recording media used for.

[Prior Art] A recording method for optical information recording media that utilizes the difference in optical properties due to phase change between crystalline and amorphous media for recording.
There are no problems such as deformation of the medium itself or contamination due to evaporation, and it is possible to improve durability with a protective film.
-8e-based thin film, Te low oxide thin film, 5b-Te-based thin film,
Various materials such as Te-Ge thin films have been proposed. For example, Te-Ge-3n thin film (Appl, Ph7s,
Left, 46 (8) p15 (1985)
, JP-A No. 61-145738.5 PIE vo1529.
2 etc.), 5b-8e film with composition such as 5b2Se (JP-A-60-155495, Appl, f'Js, Let
t, , 48 (9), p12 (1986), etc.), Te-Ge-5b alloy recording films mainly composed of Te (
JP-A-62-209742, etc.), and Te-8b 2
Original alloy recording film (1986 Society of Applied Physics lectures 29a-Z
E-3, 4) etc. have been proposed.

[Problems to be Solved by the Invention] However, the recording medium according to the above-mentioned prior art has the following problems.

That is, in a recording film made of Te-Ge-3n,
It is difficult to achieve both appropriate erasing characteristics and practical recording sensitivity, and it is impractical, and Te5os b IQs
e 10 recording thin film, 5b-8e with composition such as 5b2Se
With alloy films, etc., there are problems such as it is difficult to achieve satisfactory erasing characteristics within a practical erasing speed range, and noise increases and recording signal quality deteriorates with repeated recording and erasing. Ta. Furthermore, recording films using Sb2Te3 alloys have low crystallization temperatures and problems with recording storage stability, and are therefore impractical. Furthermore, Te-
With Ge-8b films, it is possible to increase the crystallization rate and reduce the erasing rate to several hundred nanoseconds or less, but with compositions that allow high-speed erasing, amorphization during recording is not so easy, and high-speed erasing is possible. It was difficult to achieve both erasing characteristics and practical recording sensitivity and required delicate adjustment of the composition.

The present invention improves these problems and provides an optical recording medium with excellent thermal stability, which enables recording and erasing at high speed and high sensitivity, has good recording and erasing characteristics, and is highly reliable with little deterioration due to repetition. The purpose is to provide

[Means for Solving the Problems] An object of the present invention is to irradiate a recording thin film formed on a substrate with an energy beam and change the optical characteristics of the thin film by the heat generated directly or indirectly, In an information recording medium for recording information, the recording thin film is made of bismuth (Bi), antimony (sb), or germanium (Ge).
1. An information recording medium characterized in that it mainly consists of four elements: and tellurium (Te), and whose composition is represented by the following general formula.

(Te, Bt, 5bl-, -y) r--(Te
o, Geu5) z However, 0, 25≦x<0. 6 0.05≦y<Q, 4 0, 2≦z≦0. Here, XNY and 2 each represent the atomic ratio.

This is achieved by

That is, the recording thin film used in the present invention is made of bismuth (Bi), antimony (Sb), germanium (G
It mainly consists of four elements: e) and tellurium (Te),
and its composition is expressed as the general formula %), and the ranges of x, y, and z are each 0
．． 25≦x<0. 6 0.05≦y<0.4 0.2≦z≦0.6. Here, XsV and 2 each represent the atomic ratio.

By satisfying this composition, it is possible to record and record the crystal structure.
Irreversible phase separation and segregation associated with repeated erasing are less likely to occur, reducing deterioration of recording and erasing characteristics due to repeated erasing, and it can be easily amorphized with high sensitivity, and the crystallization speed is fast and easy. The time can be set to 500 ns or less. In addition, it is possible to stabilize the amorphous state, and also to improve signal contrast, which is the difference in optical properties between amorphous and crystalline materials, and to improve erasing speed.

The medium composition of the present invention can be easily obtained as a uniform structure by a thin film forming method as described below, and can be made into a structure that is unlikely to cause irreversible phase separation or segregation.

In the above general formula, if X is too small, it is unfavorable as it tends to cause precipitation of i and sb and coarsening of the crystal phase, and if it is large, the amorphous crystallization temperature decreases and recording stability deteriorates. Such things are not desirable. If y is too small, the high-speed erasing property will deteriorate, which is undesirable, and if it is too large, it will be excessive, leading to precipitation of i and deterioration of amorphous stability. Regarding 2, if the amount is too large, it will cause amorphization and high-speed erasing performance will be reduced, and if it is too small, the crystallization temperature will become low and the stability of recording will deteriorate, which is undesirable.

In order to more preferably express the effect of the present invention, X, y,
z is 0.3≦X≦0. 55. 0゜1≦y≦
The range of 0.35, 0.25≦z≦0655 is more preferable, and y is more preferably 0°15≦y≦0.35.

The thickness of the recording thin film is not particularly limited, but for example, when utilizing the film thickness interference effect on the front and back surfaces of the recording film,
It can be set in the range of 0 to 120 nm. Furthermore, when a cooling layer that also serves as a reflective layer is provided adjacent to the recording film, for example on the back side thereof, the same effect can be expected with a film thickness of about half.

A cooling layer can be provided adjacent to the recording thin film, preferably on the back side thereof.

This cooling layer facilitates the diffusion of heat generated from the recording layer,
This is effective in increasing the cooling rate of the melted portion during recording and facilitating the formation of amorphous marks. Furthermore, if materials with high optical reflectance such as metals and metal alloys are used,
It can also serve as a reflective layer, and can be expected to reduce the thickness of the recording layer by about half, increasing recording sensitivity. The thickness of the cooling layer is not particularly limited, but
10 to 80 nm is also preferable from a practical standpoint. Materials for the cooling layer include Sb, Bi, Sn, Au, and AI.

Metals such as Ti, Ni, Cr, Pb, and Hf, alloys thereof, and mixtures of metals and any of metal oxides, carbides, nitrides, chalcogenides, etc. can be used. In particular, films of Au, At, Hf, Ni, Cr, and their alloys are easy to form, and the thermal conductivity can be adjusted over a wide range by material selection. It is effective in bringing out the original excellent characteristics when designing according to the following.

Substrates used in the present invention include polymeric resins such as polymethyl methacrylate resin, polycarbonate resin, epoxy resin, polyolefin resin, polyvinyl chloride resin, polyester resin, and styrene resin, glass plates, or metal plates such as A1. can be mentioned.

In order to effectively exhibit the original characteristics of the recording medium of the present invention, a protective layer can be formed between the substrate and the recording layer or on the surface of the medium, and a diffusion prevention layer can be formed between the recording layer and the cooling layer.

The protective layer is 5in2, ZrC, ITO, ZnS.

Inorganic films such as MgF2, mixed films thereof, UV-cured films, etc. can be formed using methods such as vapor deposition, sputtering, and spin cord, and resins such as epoxy and polycarbonate, films, glass, etc. can be laminated or laminated. You may do so. The anti-diffusion layer not only has effects such as heat-and-moisture resistance and oxidation resistance, but also has the effect of suppressing elemental diffusion between the recording layer and the reflective layer and suppressing characteristic deterioration, and can be made of the same material as the protective layer.

Such protective layers and diffusion prevention layers include, for example,
The mixed film of Z n S (! = M g F 2) has good heat resistance and excellent durability under moist heat, and furthermore, it suppresses deterioration of the recording layer due to repeated recording and erasing, and has excellent erasing characteristics. This is preferable because it has the effect of improving

In addition, a film composed of at least one metal selected from Zr, Ta, Ti, and W and a component containing silicon, oxygen, and carbon has a preferable content of each component of 3 to 3.
40 atomic%.

Si is 5-30 at%, 0 is 5-70 at%, C is 3-30 at%
By setting the content in the range of 40 atomic %, it is possible to suppress deterioration of the film quality and performance of the recording layer and to increase the adhesive force with the recording layer, which is preferable.

These protective layers and diffusion prevention layers improve durability and moisture absorption resistance, protect the recording layer, prevent deformation such as peeling or swelling from the substrate, and prevent loss of the medium due to melting, evaporation, diffusion, etc. Furthermore, effects such as improved repeatability when using reversible changes between amorphous and crystalline materials can be expected.

[Manufacturing Method 1 There are various methods for manufacturing the recording medium of the present invention, and here, a magnetron sputtering method will be described as an example.

The recording medium of the present invention is made of Pyrex glass with a thickness of 1.2 mm, or polycarbonate (PC) with a spiral group of 1.2 mm thickness, 13 cm diameter, and 1.6 μm pitch.
) is rotated at 10 to 150 rpm, and, for example, a protective layer, a recording layer, a diffusion prevention layer, or a cooling layer are sequentially laminated depending on the purpose, while making the composition and film thickness uniform.

The sputtering conditions were to use argon gas as the sputtering gas,
RF output several tens to 1kW, vacuum degree 8X10-'Pa~1X
The test was carried out under conditions of about 10-1 Pa.

The protective layer and diffusion prevention layer are 5in2, ZrC, ITo, Z
It may be formed by sputtering alone or simultaneously using nSSMgF2 or a target having a mixed composition thereof while monitoring with a crystal resonator film thickness meter.

Recording layer is Bi, Sb, Te and B1-Te alloy, 5b
-Te alloy, Te-Ge alloy, etc. can be simultaneously sputtered while monitoring with a crystal film thickness meter to form a recording film having a predetermined composition. As an example, in the case of the example described later, Sb2Te with 20 mmφ Bi2Te3 alloy pellets, sb pellets, etc.
RF target and TeGe target (1:1 composition)
Simultaneous sputtering is performed at an output of about 50 to 120 W, and the composition of the target thin film is controlled by matching the amount of sputtering obtained from a crystal oscillator film thickness gauge attached to each target with the composition ratio determined by IPC analysis. did. Target parts include
In addition, consideration was given to a predetermined thin film composition (Bi, Sb,
A four-element target of Te, Ge) may also be used.

The cooling layer is made of Au, Sb, Sn, Bi, P
b. A.I.

Metals such as Ti, Ni, Cr, Hf, and alloys thereof may be formed in the same manner as the recording thin film.

It goes without saying that these sputtering conditions are not constant depending on the equipment and may be fabricated under conditions other than those mentioned above.As for the fabrication method, for example, thin film fabrication techniques such as vacuum evaporation or electron beam evaporation may be used. Needless to say.

[Applications] The recording medium of the present invention thus obtained has properties particularly suitable for information recording media such as optical disks, optical cards, optical tapes, optical floppies, microfiche, laser COM, etc. In addition, the present invention can be applied to all other uses in which differences in optical properties are utilized for recording.

[Measurement method] (1) A pair of electrodes is provided on a recording thin film prepared on a transition temperature glass substrate, and a resistor of 30Ω is connected in series to one end of the electrode. A constant voltage of 5 V is applied across the remaining electrode and the resistor, and the voltage across the resistor is measured with a voltmeter. From this, the applied voltage and current of the thin film are determined to calculate the resistance value. Next, using a heating furnace, measure the resistance while uniformly heating the entire substrate at a rate of about 0°C/min with a temperature controller, and find the temperature at which the resistance changes from high resistance to low resistance, which is determined as the transition temperature. .

(2) Composition The recording thin film prepared on the glass substrate was dissolved with aqua regia, nitric acid, etc. and separated from the substrate. This solution was analyzed using high-frequency inductively coupled plasma (ICP) emission spectrometry (Seiko Electronics Co., Ltd.).
SPS-1100 model) to determine the content of each element,
The composition ratio was calculated.

■ Dynamic recording/erasing characteristics The sample was a recording thin film formed on a PC grouped substrate. The evaluation device mainly consists of an optical head incorporating a semiconductor laser with a wavelength of 830 nm, a disk rotating device, and their control circuits. The optical head is controlled to focus a laser beam onto a recording film through a rotating disk substrate using an objective lens with a numerical aperture of 0.5, and to track the laser beam along a group carved on the substrate. Record is 1-1
With a recording power of 5 mW, a frequency of 0.2 to 6 MH2, a signal duty of 10 to 90%, and an erasing power of 1 to 6 MH2.
It was measured in a range of 15 mW. Linear speed is 0.5-20m/
Seconds. CNR reproduces the recorded signal at 0.7mW,
The RF multiplied signal was obtained 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. In addition, the noise at the carrier frequency position was determined by interpolation from the noise values before and after that position.

■ Activation energy After forming a recording film on a "Teflon" (polytetrafluoroethylene manufactured by DuPont) substrate, the film was peeled off with a knife to prepare a powder sample. The crystallization peak temperature of this powder was measured using a differential thermal analyzer (DSC-50 manufactured by Shimadzu) while changing the heating rate. This data was plotted on a Kirasinger plot, and the activation energy Ea was calculated from the slope.

The heating rate was varied in the range of 5-80°C/min.

From the report No. 3 (page 21) of the Optical Memory Symposium '85 Proceedings, etc., it is found that when left at 60°C at Ea ~ 1.8 eV, the
Estimated to have a shelf life of over 20 years.

[Example] The present invention will be further explained based on examples.

Example 1 A protective layer was formed on each of the Pyrex glass substrate and the PC board with pregroups by the sputtering method described in the manufacturing method.
A recording layer, a diffusion prevention layer, and a cooling layer were formed in this order. The substrate was rotated at 40 revolutions per minute to ensure uniform composition and film thickness.

20m of SiO2 was deposited on the substrate at a vacuum level of 5X10-'Pa.
A ZnS protective layer containing 1% O was formed to a thickness of about 170 nm.

On top of this, two pieces of Bi, Te3 alloy paper of 20 mmφ are placed.
A recording layer having a thickness of about 73 nm was formed by simultaneously sputtering individual Sb and Te targets and a TeGe target (1:1 composition) at a ratio of about 2:1 as measured by a crystal resonator film thickness meter. The composition ratio determined by IPC analysis of this recording layer is (T e
0.32B 1 +.

26Sb11.42) 0.64 (Tea, s Ge
05) It was 0.36. Then 5 at about 230 nm
An in2 diffusion prevention layer and an approximately 41 nm thick Hf cooling layer were sequentially formed. When the crystallization temperature of this recording medium was measured using measurement method (2), it was approximately 150° C., and it can be estimated that the thermal stability of the recording medium at room temperature is sufficient. Furthermore, the activation energy was measured to be 1.82 eV or more, and the storage stability of the medium can be estimated to be 10 years or more at 60°C.

An optical recording medium formed on a PC board was heated at a linear velocity of 10.5 mW at a linear velocity of 15 m/sec, a linear velocity of 15 mW at a linear velocity of 11 m/sec, and a linear velocity of 1
The recording layer is crystallized (initialized) by scanning the track three times while continuously irradiating the laser beam at 5 m/sec with a power of 10.5 mW.
did. This initialization increased the reflectance of the recording medium, and uniform crystallization with little noise was confirmed.

After that, when the signal was recorded under the conditions of 5.5 MHz, 50% duty, and 15 mW at a linear velocity of 15 m/s, 0.
At a reproduction light intensity of 7 mW, a CNR of 51 dB was obtained, a value that allows good digital recording. Noise is also -66dBm
The results were as follows, and no increase in noise due to recording was observed. Further, when the recorded portion was scanned at a linear velocity of 15 m/sec and a power of 10.5 mW, the recording was erased, and the erasure rate was good at -30 dB. When the above recording/erasing conditions were repeated 2000 times, the CNR of recording was 49 dB at the 800th time, and the erasure rate was 30 dB, and even at the 2000th time, the CNR was 49 dB.
The erasure rate was 30 dB, which was good with almost no deterioration.

As described above, since recording and erasing can be performed at high speed at the same linear velocity, it can be estimated that one-beam override is possible in which the recording pulse is superimposed on the erasing level power and the signal is rewritten in one scan.

Example 2 The composition of the recording layer was (T e O, 35B 10.22S
b Q, 43) o, 74 (Tea5Geo5) 0.2
6, the film thickness was 50 nm, the film thickness of the protective layer and the diffusion prevention layer were 160 nm and 210 nm, respectively, and the cooling layer was made of Ni-
A medium with a different layer structure was formed in the same manner as in Example 1, except that the thickness was about 45 nm using a Cr alloy (80:20), and the medium was used as the medium of this example.

When the crystallization temperature of this recording medium was measured, it was found to be approximately 140
℃, and as in Example 1, it can be estimated that the thermal stability of the recording medium at room temperature is sufficient.

When the track was scanned twice under initialization conditions of 15 m/sec and 10.5 mW, good initialization similar to Example 1 was achieved.

On this initialized track, the recording conditions were set to 5.5 MHz, duty 50%, 1
Recording and erasing were repeated 160 times with an erase power of 5 mW and an erase power of 1 mW. As a result, with a reproduction light intensity of 0.7 mW, the CNR after recording was as good as 50 dB, and the erasure rate after erasing was 31 dB, and the same characteristics could be stably reproduced even after further repetition.

Example 3 Recording layer (A) is (Teo4+B io2tsbo3g
)0.5g (Teg, +s Geo,s) 0.4
1% (0) is (TeO, 33B 1o, i+5bo
36) A sample having the same structure and composition as in Example 2 except that o6 (Tea, s Geo,) was 0.4X was prepared, and the dynamic recording/erasing characteristics of measurement method (2) were evaluated.

After scanning twice along the track at a linear velocity of 9 m/s and a power of 9 mW as initialization, playback was performed at 0.7 mW.
In both samples (a) and (b), the RF signal level clearly changed to a high reflectance, and good crystallization (initialization) was achieved.

The increase in noise was only a few dB or less. Next, recording was performed at a linear velocity of 9 m/s at 13 mW, 4 MHz, duty 50%, and erasing was performed at 9 mW. The CNR of the recording was 51 dB for sample (a) and 49 dB for sample (b).
The results were excellent, and erasure rates of 25 dB or higher were obtained in all cases. Furthermore, when recording and erasing were repeated on the same track, it was confirmed that stable repetition was possible.

Comparative Example 1 Recording layer (c) (Teo, 3 B to5Sbo2)
o, 71 (Teo5Geo5)0.29, (d) is (
Tea, b B 1o4) 0.27 (Tea5Geo
, )0.73 except that the medium was formed on a Pyrex glass substrate and a PC disk substrate, respectively, with the same configuration as in Example 1. The crystallization temperature of this medium measured on a Pyrex glass substrate was 110 for both samples (c) and (d).
It is estimated that the thermal stability of the recording medium has decreased significantly.

Next, when recording was repeated at a linear velocity of 9 m/s, 13 mW, 4 MHz, and duty 50%, and erasing was repeated at 9 mW, recording became extremely difficult, and the CNR of both samples (c) and (d) was Less than 35dB, erasure rate is 20d
The score was B or below, and no improvement was observed through repetition.

Example 4 10 mo of MgF2 in the protective layer, anti-diffusion layer and intermediate layer
Using a 1% mixed ZnS inorganic film, the composition of the recording layer was (T
eg3□Bio26sbo4゜) 0.65 (Te.,
5Geo,). 3. The protective layer, the recording layer, and the anti-diffusion layer each have a thickness of about 170 nm in that order.

The layers were stacked to a thickness of 51 nm and 216 nm.

Next, a Ni-Cr alloy (80:20) of about 26 nm, an intermediate layer of about 21 nm, and a Ni-Cr alloy of about 26 nm were formed to form the medium of this example.

When the track was scanned under initialization conditions of 8 m/sec and 8.5 mW, good initialization similar to Example 1 was achieved.

Linear speed was 8 m/s, recording was 4 MHz, duty was 40%, 14 mW, and erasing was 120 mW at 8.5 mW.
As a result of repeating several times, the CNR was 49 at a reproduction light intensity of 1 mW.
dB and an erasing rate of 27 dB were obtained, and good repeating of recording and erasing was possible. Furthermore, in order to see the dependence of the erasure rate on the erasure speed, recording was performed at 12 m/s, 3.69 MHz,
Duty 50%, 15mW, erasure 15m/sec, 1
After repeating 120 times under the condition of 0.5 mW, the erasing rate was measured while keeping the recording conditions constant and changing the erasing linear velocity in the range of 5 to 20 m/sec. The erasing power was optimized to give the best erasing rate at each linear velocity. As a result, for example, at a linear velocity of 18 m/sec and an erasing power of 13 mW, an erasure rate of 27 dB was obtained, and similarly, at any linear velocity of 5 to 20 m/sec, an erasure rate of 26 to 30 dB was achieved. in this case,
The reproduction light intensity is 0. At 7 mW, a recording CNR of about 48 dB was obtained regardless of the erase linear velocity.

[Effects of the Invention] The recording medium according to the present invention exhibits excellent effects as described below.

■ An optical recording medium with high erasing speed and capable of high-speed recording and erasing can be obtained.

■ Recording CNR from low linear velocity to high linear velocity.

A stable optical recording medium with a good erasing rate can be obtained.

(2) An optical recording medium with good transition temperature, high activation energy, and excellent thermal and storage stability can be obtained.

■ Recording and erasing is possible with a practical semiconductor laser output, and an optical recording medium with good sensitivity can be obtained.

(2) Operation is stable even after repeated recording/erasing many times, and a good optical recording medium with little deterioration in recording sensitivity, recording/erasing characteristics, increase in noise, etc. can be obtained.

Claims (1)

[Scope of Claims] An information recording medium in which information is recorded by irradiating a recording thin film formed on a substrate with an energy beam and changing the optical characteristics of the thin film by the heat generated directly or indirectly, The recording thin film is made of bismuth (Bi), antimony (
1. An information recording medium mainly consisting of four elements: Sb), germanium (Ge), and tellurium (Te), and whose composition is represented by the following general formula. (Te_xBi_ySb_1_-_x_-_y)_1_
−_z(Te_0_._5Ge_0_._5)_x where 0.25≦x<0.6 0.05≦y<0.4 0.2≦z≦0.6 Here, x, y, and z are the number of atoms, respectively. represents the ratio.