JPH053983B2 - - 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, the contrast ratio (the difference between the reflectance in the crystalline state and the reflectance in the specific crystalline 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, and this thermal stability is determined by the crystallization temperature (Tx) and crystallization activation energy (E).
In order to obtain the above-mentioned stability, it is necessary that Tx = 120° C. or higher and E = 2.0 eV 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. Furthermore, to erase the recorded information, the recording film is irradiated with a laser beam whose output is lower than that during the recording, and
This is carried out by heating the recording film to a temperature lower than its melting point and higher than its glass transition point, and making the irradiation time longer than that during recording to bring it into 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, 1μmφ
There are two types of laser devices: a recording-only laser device that focuses the beam on a single area, 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 area. Although two laser devices were required, the erasing time was
For example, if it can be reduced to 0.2μsec 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 Proceedings of the National Conference of the Semiconductor Materials Division of the Institute of Electronics and Communication Engineers in 1988, Volume 1, page 39). 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). Recently, (c) In a triangular composition diagram in which Sb, Ge, and Te are the vertices of an equilateral triangle, Sb, Ge, and Te are located on the line connecting the Sb ₂ Te ₃ compound and the GeTe compound or in the vicinity of this line. An optical memory medium with an Sb-Te-Ge recording film has also been reported (Proceedings of the 1985 Spring Conference of the Japan Society of Applied Physics, Volume 3, page 838, lecture numbers 28p-ZQ-1 and 839).
page, lecture number 28p-ZQ-2). [Problems to be Solved by the Invention] However, the conventional examples (a), (b), and (c) do not meet the conditions (a), (b), and (c) required for a rewritable phase-change optical memory medium. Although some of the conditions in ) 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 the contrast ratio is far below the practically required 20%.
does not satisfy. 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 (c). Further, although the conventional example (c) is improved compared to the conventional examples (a) and (b), there is a problem in that the contrast ratio gradually decreases when recording and erasing are repeated. This decrease in contrast ratio is due to the fact that crystal grains precipitated during crystallization (erasing) are larger than surrounding crystal grains. Due to this decrease in contrast due to repeated recording and erasing, the number of repetitions is 10 ⁶
It becomes difficult to achieve the above-mentioned condition (b) of more than 10 times. 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: Ge _x (Sb+Bi) _y M _z ( ) (In the formula, x indicating the proportion of Ge is 12 to 39 atomic %, and y indicating the proportion of (Sb + Bi) is 12 to 37
atomic%, and the atomic ratio of Bi/(Sb+Bi) is when x is 12
atomic% to less than 20 atomic%, it is 0.50 or less (however, 0 is not included), and x is 20
At % to 39 atomic %, it is 0.80 or less (however, 0 is not included), M is Te or (Te + Se), z indicating the proportion of M is 45 to 61 atomic %, and M is (Te + Se). If Se/(Te+
The atomic ratio of Se) is 0 to 0.10). Further, the recording layer constituting the optical memory medium of the present invention can also contain at least one metal element selected from the group consisting of Zr, Mo, Ir, and Pt. 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 recording layer is a multi-component material consisting of Ge-(Sb+Bi)-M (M=Te or Te+Se), as is clear from the above general formula (). It is an alloy. That is, the recording layer in the optical memory medium of the conventional example (c) described above is made of a Ge-Sb-Te alloy, and it is difficult to achieve the above-mentioned condition (b) of repeating ¹⁰⁶ times or more. In the recording layer of the optical memory medium of the present invention, Ge-Sb-Te system or Ge-
By further adding Bi to the Sb-Te-Se alloy, the initial contrast ratio is increased, and the crystal grains that precipitate during crystallization (erasing) are suppressed from becoming larger than the surrounding crystal grains. As a result, a high contrast ratio can be maintained for a long time, and the above-mentioned condition (b) of 10 ⁶ or more repetitions is achieved. this is,
This is because the recording layer containing Bi has a hexagonal crystal system in the crystalline state, and the reflectance in the crystalline state becomes high. In the material of the general formula () constituting the recording layer of the optical memory medium of the present invention, the proportion of the metal element is limited as follows. Amount of Ge (x) = 12 to 39 at% Amount of (Sb + Bi) (y) = 12 to 37 at% Amount of M (Te or Te + Se) (z) = 45 to 61 at% Here is the amount of Ge (x ) is limited to 12 to 39 at%, because if it is less than 12 at%, the crystallization temperature will be 120℃.
If it becomes less than 39 atomic%, and if it exceeds 39 atomic%, the erasure time will be reduced.
This is because it is longer than 0.2 μsec. Also, the reason why the amount (y) of (Sb + Bi) was limited to 12 to 37 at% is that if it is less than 12 at%, the erasure time will be longer.
This is because the erasing time becomes longer than 0.2 μsec, and if it exceeds 37 atomic %, the erasing time also becomes longer than 0.2 μsec. Furthermore, the amount (z) of M (Te or Te + Se) is 45 ~
The reason why it is limited to 61 atomic % is that if it is less than 45 atomic %, the erasing time will be longer than 0.2 μsec, and if it exceeds 61 atomic %, the erasing time will also be longer than 0.2 μsec. As mentioned above, the present invention is based on the conventional example (c) of Ge-Sb-Te.
It is characterized by replacing part of the Sb with Bi in the alloy, significantly increasing the initial contrast ratio. The atomic ratio of Bi/(Sb+Bi) varies depending on the Ge ratio (x), where x is 12 at% to 20 at%
If x is less than 0.50 (excluding 0), and if x is 20 atomic % to 39 atomic %, it is 0.80 or less (excluding 0). The reason is,
As Sb is replaced with Bi, as the amount of Bi increases, the initial contrast ratio increases and the crystallization temperature decreases, but the degree of decrease in the crystallization temperature is more significant as x decreases. x is 12 atomic% ~
When x is less than 20 atom%, it is necessary to keep the atomic ratio of Bi/(Sb+Bi) below 0.50 and maintain the crystallization temperature of 120℃ or higher, whereas when x is between 20 atom% and 39 atom% , even if the amount of Bi increases, the degree of decrease in crystallization temperature is small, so Bi/(Sb+Bi)
This is because the crystallization temperature of 120°C is maintained even if the atomic ratio of is increased to 0.80. Further, when M is Te+Se, the atomic ratio of Se/(Te+Se) is limited to 0 to 0.10. The reason is 0.10
This is because if the contrast ratio exceeds 25%, the contrast ratio becomes less than 25%. Further, as described above, according to a preferred embodiment of the present invention, Zr,
At least one metal element selected from the group consisting of Mo, Ir, and Pt can be added. These metal elements act as nucleating agents, not only increasing the crystallization rate but also reducing the grain size of the crystals that precipitate during crystallization.
This solves the problem of unerased recordings and prevents a decrease in contrast ratio. The preferable addition amount of these metal elements varies depending on the type, and in the case of Zr, it is 1 to 8 atomic %, especially 2 to 7 atomic %, based on the alloy of general formula (), and in the case of Mo, it is 0.5 atomic %. ~10 atom%, especially 2 to 8 atom%, in the case of Ir or Pt, 0.3 to 5 atom%,
In particular, it is 0.5 to 4 at%. The reason is that Zr is 1
Less than atomic%, Mo less than 0.5 atomic%, Ir or Pt 0.3
If the Zr content is less than 8 atomic %, the amount is too small to work effectively as a nucleating agent, and if the Zr content exceeds 8 atomic %,
This is because if Mo exceeds 10 atomic % and Ir or Pt exceeds 5 atomic %, the crystallization rate becomes too fast and amorphization (recording) becomes impossible. 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. In other words, germanium (Ge), antimony (Sb), bismuth (Bi), and tellurium (Te) with a purity of 5N or higher, and selenium (Se) if necessary, are placed in a transparent quartz glass ampoule to a specified composition. Then, it is evacuated to 10 ^-5 Torr and sealed. Then,
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, e.g.
A disk-shaped target with a diameter of 100 mm and a thickness of about 5 mm is formed. 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). Further, 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/or on the recording layer, and this protective layer can be used to protect the recording layer from repeated recording and erasing. This prevents deterioration of the substrate and 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 the reflectance in the crystalline state is high, so the initial contrast ratio is set to 38 to 40%, for example, as is clear from the examples below. It can be made as high as Therefore, the above condition (a) is satisfied. In addition, in the recording layer, () the initial contrast ratio is high as described above, and the crystal grains precipitated during crystallization (erasing) are suppressed from becoming larger than the surrounding crystal grains, and the contrast ratio is high. () If necessary, a nucleating agent consisting of Zr, Mo, Ir, and Pt can be included, so the grain size of the crystals precipitated during crystallization can be made small, and records can be easily erased. Because the remaining problems are resolved and a decrease in contrast ratio can be prevented, it is possible to repeat the process far more than 10 ⁶ times, and the above condition (b) is also satisfied. Further, in the recording layer, the crystallization temperature (Tx) is high, for example, 120 to 160° C., and the crystallization activation energy (E) is also high, for example, 2.0 to 2.2 eV. Further addition of nucleating agent increases the crystallization temperature to 165
The temperature rises to ℃. Therefore, it has excellent thermal stability, and records can be stored for more than 10 years at room temperature.
Therefore, the above condition (c) is also satisfied. Furthermore, in a recording layer made of a material having the composition represented by the general formula (), the proportion of amorphous material that remains without crystallization during crystallization is extremely small, so phase separation occurs during phase changes during recording and erasing. As a result, the erasing time is reduced to 0.2μsec, for example.
It can be made very short as shown below. In particular, when a nucleating agent is used, the time can be extremely shortened to, for example, 0.06 μsec. 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, as a sputter target, use the formula Ge _22.2 (Sb + Bi) _22.3 Te _55.5 (the numbers in the formula indicate atomic %, Bi/(Sb + Bi)
(The atomic ratio ^of
By introducing Ar gas to a partial pressure of 5×10 ^-3 Torr and applying a high frequency power of 20 W or less, a recording layer of 600 Å thick made of the alloy was formed on the substrate with the GeO ₂ film. Formed. Next, a GeO ₂ protective film 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 in this embodiment, it was performed as follows. 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. Regarding the optical memory medium after this initialization, the contrast ratio, number of repetitions of recording and erasing, crystallization temperature (Tx), and crystallization activation energy (E)
In addition, the recording erasing time was determined as shown below, and all physical properties were satisfactory. Contrast ratio 39% Number of repetitions 10 ⁶ times Crystallization temperature (Tx) 130°C Crystallization activation energy (E) 2.1 eV Erasing time 0.1 μsec The methods for measuring the above-mentioned various physical properties 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
The crystallization temperature was determined using three types of heating rates of 20° C./min, and calculated by Kitsinjar plot. (As mentioned above, the storage stability of records is evaluated based on the crystallization temperature (Tx) and crystallization activation energy (E). Tx = 120℃ or higher, E = 2.0eV
In the above cases, the preservation of records for more than 10 years at room temperature is guaranteed. ) 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 increasing is applied to the recording layer. It is irradiated to crystallize each part one after another. After the crystallization process is completed, apply 0.5mW to the crystallized area.
Sequentially irradiate with 1μsec reproduction laser pulses,
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), then In other words, is the erasing time to be found under this condition. 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 12 Optical memory media were obtained in the same manner as in Example 1, except that Ge, Sb, Bi, Te, and Se were varied as shown in Table 1 within the limited range of the present invention. The obtained optical memory media of Examples 2 to 12 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 properties. Examples 13 to 16 Four types of optical memory media were obtained in the same manner as in Example 11, except that predetermined amounts of Zr, Mo, Ir, and Pt were added as nucleating agents. As shown in Table 2, the obtained optical memory media of Examples 13 to 16 had a contrast ratio of 40%, a repetition rate far exceeding 10 ⁶ times, and a crystallization temperature of 40%. was 160° C., the activation energy for crystallization was 2.2 eV, and the erasing time was 0.06 μsec, which were superior to the optical memory media of Examples 1 to 12.

【table】

[Table] Defined.

[Table] [Effects of the invention] As detailed above, when a predetermined proportion of Ge and (Sb+
The optical memory medium of the present invention, in which the recording layer is made of a material consisting of Bi) and M (Te or Te+Se), has (a) a large difference in reflectance between the recorded state and the erased state, and (b) an extremely large number of recording and erasing operations. (c) Records can be stored stably for a long period of time; (d) Records can be erased in an extremely short time. Further, if the recording layer contains a nucleating agent selected from Zr, Mo, Ir and Pt as necessary, the above-mentioned
The advantages of (a), (b), (c), and (d) become even more pronounced.

Claims (1)

[Claims] 1 General formula Ge _x (Sb+Bi) _y Mz () (wherein, x indicating the proportion of Ge is 12 to 39 atom%, and y indicating the proportion of (Sb+Bi) is 12 to 37 atoms %, and the atomic ratio of Bi/(Sb+Bi) is 12 atomic % to x
Less than 20 atomic% is 0.50 or less (excluding 0)
and when x is 20 to 39 atom%, it is less than 0.80 (however, 0
), M is Te or (Te + Se), z indicating the proportion of M is 45 to 61 atomic %, and when M is (Te + Se), the atomic ratio of Se / (Te + Se) is 0 1. A rewritable phase change optical memory medium, comprising a recording layer made of a material having a composition represented by (~0.10). 2 In the material having the composition represented by the general formula (),
The optical memory medium according to claim 1, further comprising at least one metal element selected from the group consisting of Zr, Mo, Ir and Pt.