JPH0549036B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a rewritable phase change optical memory medium. [Prior Art] A rewritable phase-change optical memory medium is characterized in that a glass material having a certain composition has a higher reflectance to light when it is in a crystalline state than when it is in an amorphous state, and that the optical energy Taking advantage of the fact that a phase change between an amorphous state and a crystalline state can be caused reversibly by applying a The part in the amorphous state with a low reflectance is the part where the ON information is recorded, and the part in the crystalline state with a high reflectance is the part where the ON information is recorded.
A certain amount of information can be recorded by making the part where OFF information is recorded (or a part where no information is recorded), or the recorded information can be erased and new information can be recorded. The first requirements for this type of rewritable phase-change optical memory medium are: (a) a sufficient difference between the reflectance in the amorphous (recording) state and the reflectance in the crystalline (non-recording or erasing) state; This is a big deal. That is, usually
In practical terms, contrast ratio (difference between reflectance in crystalline state and reflectance in amorphous state/
Reflectance in a crystalline state x 100%) is required to be 20% or more, particularly 25% or more. Next, in order for an optical memory medium to be put to practical use as a rewritable optical memory medium, (b) the contrast ratio will be low even if the operation of recording a certain amount of information, erasing it, and recording new information is performed repeatedly. It must be possible to maintain the initial performance in terms of properties such as, for example, for external memory of a computer, the number of repetitions is required to be 10 ⁶ times or more. Furthermore, as an optical memory medium, (c) it must be able to withstand long-term storage with a certain amount of information recorded; in practical terms, it must be able to withstand storage for more than 10 years under normal storage conditions; something is required. In other words, the amorphous state in which information is recorded is required to be stably maintained at room temperature for 10 years, for example. This is called thermal stability from the perspective of the physical properties of the glass material, but this thermal stability is determined by the crystallization temperature (Tx) and crystallization activation energy (E), and the above-mentioned level of stability is determined by the crystallization temperature (Tx) and crystallization activation energy (E). In order to have sex,
It is required that Tx = 120°C or higher and E = 2.0eV or higher. By the way, information is generally recorded on an optical memory medium by focusing a laser beam to a diameter of about 1 μm and irradiating it onto the recording film, melting the irradiated portion of the recording film, and rapidly cooling it into an amorphous state. Also,
To erase recorded information, the recording film is irradiated with a laser beam whose output is lower than that during recording, heated to a temperature lower than the melting point of the recording film and higher than the glass transition point, and This is done by making the irradiation time longer than the time of recording to create a crystalline state. In other words, in such phase-change optical memory media, the irradiation time of laser light during recording can be made sufficiently short, but the irradiation time of laser light during erasing is such that the recording film cannot effectively crystallize. Since it takes more than a certain amount of time to complete the process, a relatively long time is required. The length of time required for this recording or erasing is one of the extremely important factors that determines the performance of this type of phase change optical memory medium, and the longer the erasing time, the lower the performance. It is required to shorten the erasing time as much as possible. For example, in the conventional method, which required erasing time of several microseconds or more,
A recording-only laser device that focuses the beam on φ, and an erasing-only laser device (for example, a semiconductor laser device is used) that makes the beam elongated in order to extend the time that it irradiates one part. 2
However, if the erasing time could be reduced to, for example, 0.2 μsec or less,
These recording and erasing operations can now be performed with a single laser device, making it possible to reduce the weight and size of the optical head and shorten access time. Therefore, a rewritable phase change optical memory medium has (d) a short crystallization time and an erase time of e.g.
It is also required that it be as short as 0.2μsec or less. In order to satisfy the above conditions (a), (b), (c), and (d), attempts have been made to develop rewritable phase change optical memory media with various elements and compositions. (a) Yoshitoshi Maeda et al. discovered that the ternary compound In ₃ SbTe ₂
reported that high-speed erasing is possible in compositions that precipitate as crystals (see page 39 of Bunsho 1, Proceedings of the National Conference of Semiconductor Materials Division of the Institute of Electronics and Communication Engineers, 1988). In addition, (b) Q _x Sb _y Te _z (however, Q is In or Ga, x=34
-44 at.%, y=51-62 at.%, z=2-9 at.%) has been proposed (see JP-A-62-241145). [Problems to be Solved by the Invention] However, the above-mentioned conventional examples do not meet the conditions required for a rewritable phase change optical memory medium.
Although some of the conditions (a), (b), (c), and (d) were satisfied, it was not possible to satisfy all of these conditions. For example, in the conventional example (a), the contrast ratio is 5.0%, which is far below the practically required 20%, and even under the condition (a), the contrast ratio is 5.0%.
Does not satisfy (b). Further, in the conventional example (b), the number of repetitions is 10 ³ or less, which is far below the practically required 10 ⁶ or more, and does not satisfy the condition (b). Therefore, the problem of the present invention is to satisfy the above conditions (a), (b), and (c).
An object of the present invention is to provide a rewritable phase-change optical memory medium that satisfies all of (d). [Means for Solving the Problems] The present invention has been made to achieve the above-mentioned problems, and the rewritable phase change optical memory medium of the present invention has the following general formula: M _x N _y Te _z () [Formula In the middle, M is Ga or In, which belongs to group a of the periodic table.
, N is Sb or Bi belonging to group Va of the periodic table (however, if M is In, N is limited to Bi), x indicating the proportion of M is 10 to 20 atomic%, and N y, which represents the proportion of Te, is 23 to 34 atomic %, and z, which represents the proportion of Te, is 50 to 62 atomic %]. According to the present invention, x indicating the proportion of M (Ga or In) in the above general formula is 12 to 18 atomic %, and N
It is particularly preferable that y, which indicates the proportion of (Sb or Bi), is 25 to 32 atomic %, and z, which indicates the proportion of Te, is 52 to 60 atomic %. The present invention will be explained in detail below. In the rewritable phase change optical memory medium of the present invention, the material constituting the layer is made of M--N--Te, as is clear from the general formula (). M is limited to Ga or In belonging to group a of the periodic table. The reason for this is that among the elements of Group A of the periodic table, when Al in the 3rd period is used, the glass material composed of M _x N _y Te _z is stabilized and becomes difficult to crystallize. When Tl is used, the glass material stabilizes and becomes difficult to crystallize, although not as much as in the case of Al, and even if it crystallizes, it does not become hexagonal, and the reflectance in the crystalline state cannot be increased. On the other hand, the third period Al is
This is because Ga in the fourth period and In in the fifth period between the periods Tl do not have this problem and are suitable as material components of the recording layer. Further, N is limited to Sb or Bi belonging to group Va of the periodic table. The reason for this is that among elements in the Va group of the periodic table, when A in the 4th period is used, the glass material composed of M _x N _y Te _z is stabilized and becomes difficult to crystallize, whereas in the 5th period This is because when using Sb with the period and Bi with the sixth period, there is no such problem and it is suitable as a material component of the recording layer. In addition, in the present invention, when M is In, N is
Limited to Bi. The proportions of the metal elements M, N, and Te are limited as follows. Amount of M (Ga or In) (x) = 10 to 20 atom% Amount of N (Sb or Bi) (y) = 23 to 34 atom% Te amount (z) = 50 to 62 atom% Here, M The reason why the amount (x) is limited to 10 to 20 atomic% is because if it is less than 10 atomic%, the crystallization temperature will be lower than 120℃, and if it exceeds 20 atomic%, the crystallization temperature will be lower than 120℃ as well. It is. The amount of M is 12
Particularly preferred is ~18 at.%. Also, the reason why the amount of N (y) is limited to 23 to 34 at% is that if it is less than 23 at%, the erasing time will be longer than 0.2 μsec, and if it exceeds 34 at%, the erasing time will be longer than 0.2 μsec. Because it will be. The amount of N is
Particularly preferred is 25 to 32 atom %. Furthermore, the reason why the amount of Te (z) is limited to 50 to 62 atomic % is that if it is less than 50 atomic %, the erasure time will be longer than 0.2 μsec, and if it exceeds 62 atomic %, the erasure time will be longer than 0.2 μsec. , and the crystallization temperature is lower than 120°C. The amount of Te is 52 ~
Particularly preferred is 60 atom %. In the present invention, Ga or In is used as M, and Sb or Bi is used as N, but as mentioned above, when M is only In, N is limited to only Bi. Next, the method for manufacturing the optical memory medium of the present invention will be described. First, a glass substrate or a plastic substrate is prepared as a substrate, and a material of the general formula () is deposited thereon by a conventional sputtering method, vacuum evaporation method, etc. Form a recording layer consisting of: When using the sputtering method, a sputter target synthesized as follows, for example, is used. That is, metals M, N, and Te having a purity of 5N or more are placed in a transparent quartz glass ampoule so as to have a predetermined composition, and then the ampoule is evacuated to a vacuum of 10 ^-5 Torr and sealed.
Next, this is melted in a rocking furnace at 850° C. for 15 hours with thorough mixing, and then cooled to obtain a sputter target material. The sputter target material obtained in this way is melted in Ar gas, poured into a stainless steel mold, cooled and solidified, and then polished to form a disc-shaped target with a diameter of, for example, 75 to 100 mm and a thickness of about 5 mm. Form. As a sputtering method for forming a recording film, for example, a high-frequency magnetron sputtering method is used, in which the alloy target is attached to a high-frequency magnetron type sputtering device and the sputtering method is set to a predetermined degree of vacuum (for example, 2×10 ^-6 ~0.3×10 ^-6 Torr),
Ar gas is heated to a predetermined partial pressure (e.g. 7×10 ^-3 to 3×
10 ⁻³ Torr) and applying high frequency power (for example, 10 to 50 W). Furthermore, a protective layer made of a dielectric material such as SiO ₂ or GeO ₂ may be provided between the substrate and the recording layer and at least on one side of the recording layer. This prevents deterioration of the substrate due to moisture and deterioration of the recording film due to moisture. [Operation of the invention] In the optical memory medium of the invention, the recording layer made of a material having a composition represented by the general formula () is:
It has been confirmed by X-ray diffraction that the crystal system in the crystalline state is hexagonal, and since the reflectance in the crystalline state is high, the contrast ratio can be increased to, for example, 20% or more. Therefore, the above condition (a) is satisfied. In addition, in the recording layer, an amorphous (recording)
Even if the state and the crystalline (erased) state are repeated, for example ^, 10 ⁶ times or more, the composition of the amorphous state and the composition of the crystalline state do not change significantly from the beginning to the end, respectively. Erasing can be repeated reversibly and the above condition (b) is also satisfied. Furthermore, in the recording layer, the crystallization temperature (Tx) is high, for example, 120°C or higher, and the crystallization activation energy (E) is also high, for example, 2.0 eV or higher.
It has excellent thermal stability, allowing records to be stored for more than 10 years at room temperature. Therefore, the above condition (c) is also satisfied. Furthermore, in the recording layer made of the material having the composition represented by the general formula (), the proportion of amorphous material that remains without crystallization during crystallization is very small, so that there is no difference in the layer change during recording and erasing. No phase is involved, resulting in an erasure time of e.g. 0.2μsec.
It can be made very short as shown below. Therefore, the above condition (d) is also satisfied. [Example] Hereinafter, the present invention will be further explained with reference to Examples.
The present invention is not limited to these examples. Example 1 A glass substrate was used as the substrate, and a film with a thickness of 1000 Å was deposited on this substrate by the usual sputtering method.
A GeO ₂ film was formed. Next, an alloy target with a composition expressed by the formula Ga ₁₂ Sb ₃₀ Te ₅₈ (numbers in the formula indicate atomic percent) was used as a sputtering target, and this was attached to a predetermined position in a high-frequency magnetron type sputtering device. At a vacuum level of 2×10 ^-6 Torr or less,
By introducing Ar gas to a partial pressure of 5 x 10 ^-3 Torr and applying a high frequency power of 30 W or less, a film thickness of 600 Å made of the ternary alloy was recorded on the substrate with the GeO ₂ film. formed a layer. Next, a protective film of GaO ₂ with a thickness of 2000 Å was formed on this recording layer by the usual sputtering method.
An optical memory medium was obtained. Since the obtained optical memory medium has a recording layer in a state intermediate between an amorphous state and a crystalline state, it is necessary to bring it into a crystalline state. This is called initialization, and was performed in the following manner in this embodiment. That is, the intermediate state is eliminated by irradiating the recording layer with a semiconductor laser pulse to melt it, rapidly cool it, and make it amorphous, and then heat it with weak light (in a vacuum). (may be heated) to crystallize. For the optical memory medium after initialization, the contrast ratio, number of repetitions of recording and erasing, crystallization temperature (T _x ), crystallization activation energy (E), and erasing time of recording were determined as follows. All physical properties were satisfactory. Contrast ratio 23% Number of repetitions 10 ⁶ times Crystallization temperature (T _x ) 120°C Crystallization activation energy (E) 2.0 eV Erasing time <0.2 μsec The methods for measuring the various physical properties mentioned above are as follows. Contrast ratio: The reflectance (Ra) in the amorphous state and the reflectance (Rc) in the crystalline state were measured and determined by the following formula. Contrast ratio (%) = Rc - Ra / Rc x 100 Number of repetitions...After recording, reflectance (Ra)
After measuring and then erasing its reflectance (Rc)
Measure. Repeat this until the contrast ratio is
The number of repetitions was defined as the number of times it took for the test to drop to 15%. Crystallization temperature (Tx): Measured using a high-sensitivity differential scanning calorimeter DSC8240B manufactured by Rigaku Denki Co., Ltd. (heating rate 10° C./min). Crystallization activation energy (E)...5, 10 and 20℃/
The crystallization temperature was determined using three types of heating rates of min, and calculated using a Kissin Jar plot. (As mentioned above, _the storage stability of records is evaluated based on the crystallization temperature (T _x ) and the crystallization activation energy (E).
In this case, records are guaranteed to have a shelf life of more than 10 years at room temperature. ) Erasing time: The recording layer is irradiated with a laser beam with an output of 8 mW to melt and rapidly cool it to become amorphous, and then a crystallizing (erasing) laser pulse with a pulse width of 0.05 μsec sequentially increased is applied to the recording layer. It is irradiated to crystallize each part one after another. After the crystallization process is completed, the next step is to apply the crystallization process to the area.
A reproduction laser pulse of 0.5 mW and 1 μsec is sequentially irradiated, and the reflected light is measured. If the pulse width of the crystallization laser pulse at the portion where the intensity of the reflected light is saturated is determined (it can be determined by associating the irradiation position of the crystallization laser with the irradiation position of the reproduction laser),
That is the erasing time that should be found under these conditions. Such measurements were carried out in various ways by changing the laser output, and the erasing time under each condition was determined, and the minimum erasing time among the erasing times thus determined was taken as the erasing time of this recording layer. Examples 2 to 6 M, N, and Te within the limited range of the present invention (M10 to
20 at%, N23-34 at%, Te50-62 at%)
Five types of optical memory media were obtained in the same manner as in Example 1, except that various variations were made as shown in Table 1. The obtained optical memory media of Examples 2 to 6 had excellent performance equivalent to or better than that of the optical memory medium of Example 1, as shown in Table 1 for various physical property values. Examples 7 to 13 M, N, and Te within the desired range of the present invention (M12 to
18 atomic%, N25~32 atomic%, Te52~60 atomic%)
7 in the same manner as in Example 1 except that various changes were made in
A seed optical memory medium was obtained. As shown in Table 2, the obtained optical memory media of Examples 7 to 13 had a contrast ratio of more than 25%, a repetition rate of more than 10 ⁶ times,
The crystallization temperature exceeded 120° C., the crystallization activation energy was 2.1 eV, and the erase time was less than 0.2 μsec, which were superior to the optical memory media of Examples 1 to 6. Although not shown in Tables 1 and 2, the optical memory media of Examples 1 to 6 and Examples 7 to 13 had low melting points of the materials constituting their recording layers (for example, Example 8...570°C). , Example 10...550°C, Example 12
...545°C), and as a result, it was found that less laser power was required, the pulse width was small, and recording sensitivity was increased. Comparative Examples 1 to 6 M (Ga, In) and N (Sb, Bi) are included in the limited range of the present invention (M10 to 20 at%, N23 to 34 at%), but Te is included in the limited range of the present invention ( 50-62 atomic%)
Example 1 except that the recording layer was formed of a material of the formula Ga ₁₉ Sb ₃₄ Te ₄₇ In ₂₀ Bi ₃₃ Te ₄₇ (the numbers in the formula indicate atomic percent) which are not included in
Two types of optical memory media were obtained in the same manner as (Comparative Examples 1 and 2). In addition, M (Ga, In) is included in the range defined by the present invention, but N ₍ Sb, Bi) and Te are not included in _the range defined by the _present invention _. Example 1 except that the recording layer was formed of a material of ₃₇ Te ₄₈ (numbers in the formula indicate atomic %).
Two types of optical memory media were obtained in the same manner as (Comparative Examples 3 and 4). Furthermore, N (Sb, Bi) and Te are included in the range defined by the present invention, but M ₍ Ga, In) is not included in the range defined by _the present _{invention .} Example 1 except that the recording layer was formed of a material of ₃₄ Te ₅₈ (numbers in the formula are atomic %).
Two types of optical memory media were obtained in the same manner as (Comparative Examples 5 and 6). Various physical properties of the obtained optical memory media of Comparative Examples 1 to 6 were measured. The results are shown in Table 3. All of these optical memory media have low contrast ratios of 18% or less, and erase times of 1 to 10%.
It was as long as 3 μsec, which was far inferior to the optical memory media of Examples 1 to 17.

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[Table] [Effects of the invention] As detailed above, a predetermined proportion of M (Ga or In)
The present invention and the optical memory medium in which the recording layer is made of materials consisting of N (Sb or Bi) and Te have the following features: (a) There is a large difference in reflectance between the recorded state and the erased state; (b) An extremely large number of recording and erasing operations are possible. (c) Records can be stored stably for a long period of time; (d) Records can be erased in an extremely short time.

Claims (1)

[Claims] 1 General formula M _x N _y Te _z () [In the formula, M is Ga or In belonging to group a of the periodic table.
, N is Sb or Bi belonging to group Va of the periodic table (however, if M is In, N is limited to Bi), x indicating the proportion of M is 10 to 20 atomic%, and N y, which indicates the proportion of Te, is 23 to 34 atomic %, and z, which indicates the proportion of Te, is 50 to 62 atomic %.] Variable optical memory medium. 2 x indicating the proportion of M is 12 to 18 atomic%, and N
2. The optical memory medium according to claim 1, wherein y representing the proportion of Te is 25 to 32 atomic %, and z representing the proportion of Te is 52 to 60 atomic %.