JPH02249686A - Data recording medium for optical card - Google Patents

Abstract

PURPOSE:To improve recording sensitivity and to provide an erasure characteristic having practicality by mainly constituting a recording membrane of three elements of silver, antimony and tellurium and specifying the composition thereof. CONSTITUTION:A recording membrane is mainly constituted of silver (Ag), antimony (Sb) and tellurium (Te) and the composition thereof is represented by general formula AgxSbyTez(wherein x is the atomic % of Ag in the membrane, y is the atomic % of Sb in the membrane, z is the atomic % of Te in the membrane and, when the range of x is 20<=z<=38, the ranges of x, y are respectively 5<=x<=50 and 32<=y<=60 and, when the range of z is 38<=z<=55, the ranges of x, y are respectively 5<=x<=25 and 42<=y<=60 and x+y+z is 100). A cooling layer is pref. provided so as to be adjacent to the recording membrane on the rear side thereof. When Au, Al, Hf, Ni, Cr or an alloy thereof is used as the material of the cooling layer, the formation of a film is easy and heat conductivity can be adjusted over a wide range by the selection of a material.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an information recording medium for optical cards, and is particularly suitable for optical cards that record information by irradiation with energy beams such as laser beams and electron beams. 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-8n thin film (Japanese Unexamined Patent Publication No. 61-3324, etc.), Te gos b whose main component is Te
l08e1o recording thin film (Japanese Unexamined Patent Publication No. 145737/1986, etc.), 5b-8e film with composition such as 5b2Se (Japanese Unexamined Patent Application No. 60-15549, etc.), and Te-5b binary alloy recording film (published in Applied Physics in 1986). Academic conference collection 29a-ZE-
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 the case of a recording film made of Te-Ge-8n,
It is difficult to achieve both appropriate erasing characteristics and practical recording sensitivity, and it is impractical, and Te8oSb1oSe1o
With recording thin films, such as 5b-8e alloy films with compositions such as 5b2Se, it is not easy to achieve satisfactory erasing characteristics in a practical erasing speed range, and noise increases with repeated recording and erasing. There were problems such as deterioration of signal quality. Furthermore, recording films using Sb2Te3 alloys had low crystallization temperatures and problems with storage stability of recordings, making them impractical.

Furthermore, since such recording media are required to have considerably different characteristics depending on their use, when looking at the medium characteristics for, for example, an optical card, it is difficult to say that the medium characteristics that are optimal for an optical disk are necessarily the preferable characteristics. In other words, since the medium feeding speed (recording or erasing speed) and beam diameter are different between optical cards and optical disks, the optimum conditions for amorphization and crystallization are significantly different, and it is difficult to satisfy both characteristics with the same medium composition. is not easy.

In particular, when limiting to the Ag-8b-Te ternary system, proposals can be found in JP-A-62-152786 and JP-A-64-10437, but they do not necessarily have favorable characteristics as a recording medium for optical cards. It can not be said.

That is, in JP-A-62-152786, Ag
, a combination of many elements including the three elements Sb and Te,
In other words, it is claimed that the result is a material that covers all possible combinations of almost all elements, and that good properties can be obtained.
In actual recording media, excellent properties can only be imparted by optimizing the types of elements and their composition.
Moreover, with the exception of a few examples, there has been no specific study or disclosure of what kind of excellent properties can actually be achieved. Furthermore, the purpose of this publication is to achieve a high crystallization speed, which is an important characteristic for a medium that can record and erase data at high speed, and this characteristic is not necessarily an important characteristic for an optical card medium. However, in some cases, it can be said to be an undesirable characteristic. In other words, since optical card media use an optical system that performs laser irradiation at a relatively low speed for a long time and has a relatively large beam diameter, it is difficult to remove the heat given by laser irradiation sufficiently quickly. Therefore, it is important to have the property that even under these conditions recrystallization is difficult to occur and good amorphous recording is possible. In this case, the characteristic of high-speed crystallization works in the opposite direction, and tends to promote recrystallization of the amorphous state formed by the remaining heat, which is not desirable.

Furthermore, in Japanese Patent Application Laid-open No. 10437/1983, Ag-8b-
Although it is a Te ternary system, if the composition is not limited, it is difficult to say that the properties described above have been optimized sufficiently, and even if the composition is limited, optimization aimed at achieving a high crystallization rate is difficult. Therefore, in the same sense as mentioned above, it is difficult to say that it is a medium suitable for optical cards.

The present invention solves these problems and provides a highly reliable information recording medium for optical cards, which has good recording sensitivity and practical erasing characteristics, and has good characteristics as a medium for optical cards. The purpose is to provide a medium.

[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 an optical card that records information, the recording thin film is made of silver (Ag), antimony (Sb), and tellurium (T).
It mainly consists of the three elements e), and its composition is expressed by the general formula %. If the range of 2 is 20≦2≦38, then
The range of x and y is 5≦X≦50, 32≦y≦60, respectively.
, and if the range of 2 is 38〈z≦55, then X, y
This is achieved by an information recording medium for an optical card, characterized in that the ranges of 5≦X≦25.42≦y≦60 and x+y+z=100.

That is, the recording thin film used in the present invention is made of silver (
Ag), antimony (sb), and tellurium (Te), and its composition is expressed by the general formula % X: number of Ag atoms in the thin film % y: number of sb atoms in the thin film % 2: When expressed as atomic number % of Te in the thin film, if the range of 2 is 20≦2≦38,
The range of x and y is 5≦X≦50, 32≦y≦, respectively.
60 and the range of 2 is 38〈z≦55, then x
, y are in the range of 5≦X≦25.42≦y≦60, and x+y+z=100.

As a result of intensive studies by the present inventors, in the case of 20≦2≦38, the region centered on the composition on the line connecting Sb2Te and Ag2Te is good, and in the case of 38<2≦55, the region with a composition centered on the line connecting Sb2Te and Ag2Te is good. It was concluded that the region centered on the composition on the line connecting Ag and Ag has excellent properties as a medium for optical cards. Appropriate ranges for X and y differ depending on each range in 2, but there are differences in degree, and if there are many Xs outside the range, it will be difficult to erase, etc. Excellent records as described in the present invention This is undesirable because it makes it difficult to develop the characteristics, and when y is large, irreversible changes in characteristics such as excessive sb precipitation tend to occur, and the repeatability of recording and erasing decreases, which is undesirable. Further, if the amount of X or y is small, it may become impossible to obtain an appropriate crystallization temperature, which is not preferable.

In order to more preferably exhibit the effects of the present invention, the range of 2 is more preferably 25≦2≦38 and 38×≦50. If 25≦2≦38, 7≦X≦40
．． More preferably, the range is 32≦y≦55. 3
When 8<z≦50, the range of X is more preferably within the range of 7≦X≦25.

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, or mixtures of metals with any of metal oxides, carbides, nitrides, chalcogenides, etc. can be used. Especially A u , A 1 s Hf .

Ni, Cr, their alloys, etc. are easy to form into films, and their thermal conductivity can be adjusted over a wide range by material selection. It is effective in bringing out its original excellent characteristics.

The substrate used in the present invention may be a polymer resin such as polymethyl methacrylate resin, polycarbonate resin, epoxy resin, polyolefin resin, polyvinyl chloride resin, polyester resin, or styrene resin, a glass plate, or a metal plate 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 5i02, ZrC, ITO, and ZnS.

Inorganic films such as M g F 2, mixed films thereof, ultraviolet cured films, etc. are formed using methods such as vapor deposition, sputtering, and spin cord, and resins such as epoxy and polycarbonate, films, and glass are laminated together. Or you can laminate it. 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 ZnS and MgF2 has good heat resistance,
It is preferable because it has excellent durability under moist heat, and further has the effect of suppressing deterioration of the recording layer due to repeated recording and erasing and improving erasing characteristics. Also, Zr,
A film composed of at least one metal selected from Ta, Ti, and W and a component containing silicon, oxygen, and carbon has a preferable content of each component of 3 to 40 at% of the above metal and 5 to 5 at% of St. 30 at%, 0 at 5 to 70 at%.

By setting C in the range of 3 to 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] Although there are various methods for manufacturing the recording medium of the present invention, a magnetron sputtering method will be described here as an example.

The recording medium of the present invention is a 1.2 mm thick Pyrex glass or PMMA plate, a 0.4 mm thick polycarbonate (hereinafter referred to as PC) plate, or a 162 mm thick and 13 cm diameter,
A polycarbonate (PC) substrate with spiral groups of 1.6 μm pitch is rotated at 10 to 150 rpm to form, for example, a protective layer, a recording layer, a diffusion prevention layer, or a cooling layer while uniforming the composition and film thickness. Each layer is sequentially layered depending on the purpose. The sputtering conditions are, for example, using argon gas as the sputtering gas, RF output of several tens to 1 kW,
This can be carried out under a vacuum degree of 8xlO-''Pa to 1xlQ-IPa.

The protective layer and diffusion prevention layer are 5f02, ZrC, ITOlZ.
It may be formed by sputtering alone or simultaneously using a target having a composition of nS and MgF2, or a mixture thereof, while monitoring with a crystal resonator film thickness meter. Here, IT
In the case of O film, the sputtering gas is Ar:O=9:1
(molar ratio), and RF or DC sputtering was used. In the DC sputtering method, the output is 200 to 40
It was set to 0W.

Recording layer is Ag, Sb, Te and Ag-Te alloy, 5b
-Te alloy or the like is simultaneously sputtered while monitoring with a crystal film thickness meter to form a recording film of a predetermined composition. In addition, the target member was designed to have a predetermined thin film composition (Ag, S
A three-element target of b, Te) may also be used.

The cooling layer is made of Au, Sb, Sn, Bi, Pb, and Al.

Metals such as Ti, Ni, Cr, and Hf, or 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 characteristics particularly suitable as an information recording medium for optical cards. Furthermore, it is also applicable to all other uses in which differences in optical properties are used for recording, such as information recording media such as optical disks, optical tapes, optical floppies, microfiche, and laser COMs.

[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 rotation 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. The record is 1
~15mW recording power, frequency 0.2~5MHz
The signal duty was set to 10 to 90%, and the erase power was measured in the range of 1 to 15 mW. Linear speed is 0.5-12
m/sec. The CNR was determined from the RF multiplied signal by reproducing the recorded signal at 0.7 mW and 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.

■Static recording/erasing characteristics Pyrex glass, PMMA, 0, 4
A sample was prepared by forming a recording thin film on each substrate of a PC board having a thickness of mm. 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 recording or erasing pulses applied to the optical head are extracted as an RF multiplied signal to evaluate repeat durability and recording contrast. ing. The recording and erasing powers were measured in the range of 1 to 20 mW, and the reproducing power was 0.5 mW. The contrast was determined as the ratio between the level difference between the RF specific output crystal and the amorphous state and the crystalline state.

[Example] The present invention will be further described in detail based on examples.

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

A 5io2 protective layer with a thickness of about 95 nm was formed on the substrate at a vacuum degree of 5X10-'Pa, and Ag and Sb were deposited thereon.

A recording layer having a composition of Ag25sb38Te37 was formed to a thickness of about 95 nm by simultaneous sputtering while monitoring Te and its alloy with a crystal resonator film thickness meter. Then about 90 nm of 5i02
A diffusion prevention layer and an Au cooling layer of about 20 nm were sequentially formed, and finally, about 70 nm of 5i02 was formed. The crystallization temperature of this recording medium was about 130°C. The static recording and erasing characteristics described in measurement method 2 were evaluated using a Pyrex glass substrate.

15mW.

The same part of the sample was repeatedly and alternately irradiated with a 280 ns recording pulse and a 4.7 mW, 2.5 μs erasing pulse, and the RF signal change at a read power of 0.5 mW was evaluated. With contrast, we were able to stably repeat recording and erasing over 104 times. Next record is 8.6m
When similarly evaluated using W, 2 μsec, and erasing, 4 mW, 3 μsec, the contrast was about 34%, and it was possible to repeat recording and erasing 104 times or more. Next, on the PMMA board, record at 9.2 mW for 28 On seconds, and erase at 3°2 mW.
The conditions were 2.5μ seconds and the recording was 5.2mW, 1.5μ seconds.
When evaluation was made in the same manner under the conditions of 2 mW and 10 microseconds for erasing, a contrast of 25% or more was obtained in each case, and it was possible to repeat 104 times or more. As described above, the recording medium of the present invention has good recording contrast and a large reproduced signal amplitude, and even if the recording pulse width is increased, recrystallization of the amorphous mark portion is difficult to occur and stable recording is possible. The repeatability is also good.

Example 2 The substrate is a PC board with a pre-group, and the recording layer is (A)
is A g 10 S 1) soT e 40. (
b) is Ag3゜S b 33T e 37, (c) is A
A sample having the same structure and composition as in Example 1 was prepared except that g37Sb33Te3o1 was used, and the dynamic recording/erasing characteristics of measurement method (2) were evaluated.

First, initialization by crystallization was attempted at a linear velocity of 0.5 m/sec. Samples (a) and (c) are 3.6 mW.

When the sample (b) was scanned twice along the track with a power of 2.7 mW and reproduced with a power of 0.7 mW, the RF signal level clearly changed to a high reflectance, and good initialization was achieved. The increase in noise was only a few dB or less. Next, sample (a) was heated at a linear velocity of 6 m/sec, 13 mW, 2.5 MH
z, Record at 50% duty, erase at linear velocity 0.5
The measurement was performed at m/sec, 2°, and 4 mW. When reproduced at a linear velocity of 6 m/s, the recorded CNR was 50 dB and the erasure rate was 2.
More than 5 dB was obtained. Next, we set the linear velocity to 0.5 m/sec, recorded at 7 mW, o, 2 MHz, duty 10%, and erased under the conditions of 3 mW. When we performed recording and erasing, the CNR of almost the same recording was obtained by reproducing at a linear velocity of 6 m/sec. is obtained,
It was also possible to erase it. Furthermore, for samples (b) and (c), the linear velocity was set to 0.5 m/sec, and for (b), the recording was set to 5.5 mW, 0
．． Recording and erasing was performed under the conditions of 2 MHz, 20% duty, and 2.7 mW for erasing, and (c) recording was performed at 7 mW, 0.2 MHz, 10% duty, and 3 mW for erasing.

When played back at a linear velocity of 6 m/s, (b) is the recorded CN.
The R was 44 dB and the erasure rate was 32 dB or more, and (c) the recording CNR was 45 dB and the erasure rate was 26 dB or more. In all cases, the noise hardly increased and was within several dB. When we tried to repeat recording and erasing on the same track of these samples, it was possible to repeat it with the same characteristics.In this way, the recording medium of the present invention has stable amorphous recording. It has good recording and erasing properties, especially at low linear speeds used in optical card media, and has excellent recording and erasing properties that can be used as code data media. It is something.

Comparative Example 1 The same structure as in Example 2 was used except that the recording layer was 5bs9Te4t excluding Ag, using a Pyrex glass substrate and Pyrex glass substrate.
A medium was formed on each of the disk substrates of C.

When static recording and erasing characteristics were evaluated on a Pyrex glass substrate, recording was performed at 8.4 mW for 500 ns, and erasing was performed at 4.0 mW.
When the recording pulse width was increased to 7 mW and 1 μsec, the contrast decreased slightly to about 25%.
When evaluating the erasure at 4°8 mW for 11 μ seconds, the contrast decreased significantly to 14%. Further, the crystallization temperature of this medium was about 70° C., and the recording stability was also reduced.

Next, dynamic recording/erasing characteristics were evaluated using a PC board.

After initializing by scanning twice at a linear velocity of 0.5 m/sec and a power of 3.3 mW, recording was performed at a linear velocity of 0.5 m/sec and a power of 6 mW.
, 0.2 MHz, and a duty of 20%, and when reproduction was performed at a recording speed of 6 m/sec, the reproduced signal (carrier) was lowered and a sufficient recording CNR could not be obtained. Therefore, the linear velocity was set to 1 m/s, and the recording was 8 mW, 0.3 M.
When recording and erasing was performed at Hz, duty 20%, and erasure at 2.5 mW, a decrease in carriers, which was thought to be due to recrystallization of the amorphous mark, was observed even at this linear velocity, and the erasure rate was Although about 23 dB was obtained, the recording CNR was as small as 36 dB.

Example 3 The substrate was a PC board with a thickness Q of 4 mm, the protective layer and the diffusion prevention layer were 5i02 film for sample (d), and D for sample (e).
The ITO film was made by C sputtering method, and the sample was made of M on ZnS.
Except for the film containing 10mol1% of gF2.
A recording medium was formed with the same configuration as in Example 1. after that,
A PET film with a thickness of 0.3 mm was attached to the medium side using an adhesive and punched out to a size of 85° 5 mm x 54 mm to produce a card medium. Using a static recording/erasing characteristic evaluation device, the X-Y stage was scanned in the X direction, and recording/erasing from the PC board side was attempted. First, at a linear velocity of about 5 to 10 cm/sec and an erasing power of 3 to 4 mW, a large area was initialized by repeatedly scanning in the X direction while performing minute feeding in the Y direction. As a result, crystallization resulting in high reflectance was confirmed from the RF output of all samples. While scanning this initialized area at a linear velocity of about 5 to 10 cm/sec,
5-7mW.

When recording under the conditions of 1 kHz and pulse width of 1 μs, the sample (
Clear amorphous marks were observed under a microscope in all of (d) to (f), confirming that good and stable recording was possible. Next, return to the X direction and increase the erase power to 2.0 at the same linear velocity.
When the recording marks were scanned while being continuously irradiated at 5 to 3.5 mW, the amorphous marks in the overlapped areas were observed under a microscope to be crystallized (sample (d)).
~(to) I was able to confirm everything. This shows that the recording medium of the present invention is capable of good and stable recording and erasing as a card medium.

Example 4 A recording layer was formed using a Pyrex glass substrate.
b33Te32, and the cooling layer (g) is approximately 20n of Au.
m, (ch) is Hf about 40 nm, (su) is AI about 40 nm
nm, (nu) is about 40 Nl 80 Cr 20 alloy
A sample having the same configuration as in Example 1 was prepared except that the thickness was changed to nm. The crystallization temperature of this sample was about 143°C, which was sufficient for storage stability of the record. The static recording and erasing characteristics described in measurement method
．． When evaluated at 5 to 4.5 mW and 1 μsec, a contrast of 25% or more was obtained in all cases, and recording/erasing could be repeated 104 times or more.

Example 5 The recording layer was made of Ag238 on a Pyrex glass substrate.
544Te33”o) ’t Ag 15s b 52
A sample having the same structure as in Example 1 was prepared except that T e 33-(wa) was Ag15Sb43Te42. The static recording/erasing characteristics described in measurement method
W.

When evaluation was performed using 3.5 to 4.5 mW for 1 .mu.sec and erasing for 1 .mu.sec, a contrast of 25% or more was obtained in all cases, and recording and erasing could be repeated 104 times or more.

[Effects of the Invention] The information recording medium for optical cards according to the present invention has excellent effects as described below.

(2) Even at low linear speeds, a recording medium for optical cards with good recording CNR characteristics and erasure rate and low medium noise can be obtained.

(2) A recording medium for optical cards with good recording/erasing repetition characteristics and good recording contrast even when the recording pulse width is increased can be obtained.

(2) By providing a cooling layer, the stability of recording mark formation is increased, and a recording medium for an optical card with good mark edge sharpness and excellent CNR can be obtained.

(2) A recording medium for optical cards having an appropriate crystallization transition temperature and excellent long-term preservation of recorded information can be obtained.

Claims (1)

[Claims] 1. Information for an optical card 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. In the recording medium, the recording thin film mainly consists of three elements, silver (Ag), antimony (Sb), and tellurium (Te), and its composition has the general formula Ag_xSb_yTe_z x: number of Ag atoms in the thin film % y: thin film % of Sb atoms in the thin film: % of Te atoms in the thin film When the range of z is 20≦z≦38,
The range of x and y is 5≦x≦50, 32≦y≦60, respectively.
and when the range of z is 38<z≦55, x, y
An information recording medium for an optical card, wherein the ranges are 5≦x≦25, 42≦y≦60, and x+y+z=100. 2. The information recording medium for an optical card according to claim 1, further comprising a cooling layer adjacent to the recording thin film. 3. The information recording medium for an optical card according to claim 2, further comprising a diffusion prevention layer between the recording thin film and the cooling layer. 4. The information recording medium for an optical card according to claim 2 or 3, wherein the cooling layer is mainly composed of at least one of Au, Hf, Al, Ni, and Cr.