JPH01287836A - Rewritable phase transition type optical memory - Google Patents

Abstract

PURPOSE:To improve the characteristics of repeating recording and erasing and the long-term preservation characteristic and to shorten erasing time by providing a recording layer consisting of a material having a specific compsn. to the medium, thereby increasing the difference in reflectivity between a recording state and an erasing state. CONSTITUTION:The recording layer is constituted of the material having the compsn. expressed by formula I. In formula I, (x) indicating the ratio of Ge is 12-39atomic%; (y) indicating the ratio of (Sb+Bi) is 12-37atomic%; the atomic ratio of Bi/(Sb+Bi) is <=0.50 if x is <20atomic% and <=0.80 if x is >=20atomic%. M is Te or (Te+Se) and (z) indicating the ratio of M is 45-61atomic%. The difference in reflectivity in the recording state and the erasing state is thereby increased and the recording including erasing can be repeatedly executed extremely many times. The records can be stably preserved over a long period of time and the erasing time of the records is extremely shortened.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a rewritable phase change optical memory medium.

[Conventional technique vF1] A reversible phase-change optical memory medium has a higher reflectance to light when a glass material having a certain composition is in a crystalline state than when it is in an amorphous state. By utilizing the fact that the phase change between an amorphous state and a crystalline state can be reversibly performed by applying light energy, this material is formed as a recording film in the form of a W4 film on a base, for example. By doing this, the part in the amorphous state with low reflectance is considered to be the part where ON information is recorded, and the part in the crystalline state with high reflectance is considered to be the part in which OFF information is recorded (or no information is recorded). (parts that are missing)
By doing so, certain information is recorded, or recorded information is erased and new information is recorded.

The first requirement for this second-interchangeable phase-change optical memory medium is (a) the reflectance of the 11 items in the vJ (recording) state and the reflectance in the crystalline (non-recording or erasing) state. The difference is sufficiently large. That is, usually, in practical use, the contrast ratio (difference between reflectance in crystalline state and reflectance in 1 quality state/reflectance in crystalline state x 100%) is 20% or more, especially It is required that it be 25% or more.

Next, in order for the optical memory medium to be put to practical use as a rewritable optical memory medium, (c) the contrast ratio will be low even if the operation of recording a certain amount of information, erasing it, and recording new information is repeated. In terms of properties such as these, the initial performance must be maintained at an extremely high level, and for example, for use in external memory of a computer, the number of reversals is required to be 106 times or more.

Furthermore, as an optical memory medium, (Q) it must be able to withstand long-term storage while recording a certain amount of information; In other words, one quality state (in which the information was recorded) is required to be
For example, it is required to remain stable for 10 years at room temperature. This is called thermal stability from the viewpoint of physical properties of glass OII, but this thermal stability is due to crystallized Gp.
It is determined by x (Tx) and crystallization activation energy (E), and in order to obtain the above level of stability, Tx = 120
℃ or higher, E=2. It is required that the voltage is OeV 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 to melt the irradiated portion of the recording film and rapidly cool it into an amorphous state. Furthermore, in order to erase the recorded information, the output of the laser beam is made lower than that during the recording, and the recording film is irradiated to a temperature lower than the melting point of the recording film and higher than the glass transition point. By heating and making the irradiation time longer than the above record, crystallization! This is done by setting it to 1 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 will be. It is required to shorten this erasing time as much as possible. For example, in the conventional erasing method, which required several microseconds or more for erasing, a recording-only laser device was used to focus the beam onto a diameter of 1 micrometer, and the beam was shaped into a long circle to extend the time that one area was irradiated. However, if the erasing time can be reduced to 0.2 μsec or less, this recording/erasing can be done easily. This can now be done with a single laser device, and the lightness of the optical head is light! This also makes it possible to reduce access time. Therefore, a rewritable phase change optical memory medium has a short crystallization time and an erase time of, for example, 0°2 μs.
It is also required that it be short, less than ec.

In order to satisfy the above conditions (2), (c), (φ and , Yoshitoshi Maeda et al.
2 reported that high-speed erasing is possible in compositions that precipitate as crystals (see page 39 of Volume 1, Proceedings of the 1986 National Conference of the Semiconductor Materials Division of the Institute of Electronics and Communication Engineers).

In addition, iQ Sb Te2 (where Q is In or yGa, x = 34 to 44 atomic%, y = 51 to 62 atomic%,
Z = 2 to 9 atomic %) has been proposed (see Japanese Patent Laid-Open No. 62-241145).

Recently, in a triangular composition diagram in which the vertices of an equilateral triangle are the respective magic tricks of QsL Sb, Ge, and Te, Sb.

An optical memory medium having a 5b-Te-Ge recording film in which GO and Te are on or near the line connecting the Sb2Te3 compound and the GeTe compound has also been reported (Showa 63
Proceedings of the 2017 Spring Applied Physics Conference, Volume 3, page 838, lecture number 28p-ZQ-1 and page 839, lecture number 28p-ZQ-2).

[Problems to be Solved by the Invention] However, in the conventional example, (9) and (9) do not meet the two conditions (2), (c), ), but it was not possible to satisfy all of these conditions.

For example, in the conventional example 0), the contrast ratio is 5.0%, which is far below the practically required 20%, and does not satisfy the condition (2) or even the condition (c). .

Furthermore, in the conventional example (c), the number of repetitions is 1.
03 times or less, far short of the 106 times or more required for practical purposes, and does not meet the above condition (b).

Further, although the conventional example 9 is improved over the conventional examples 0) and (f), 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 1.
It becomes difficult to achieve the above-mentioned regulation (c) of 06 or more times.

Therefore, the problem to be solved by the present invention is to meet the conditions (2), (c), and (
An object of the present invention is to provide a phase-change optical memory medium in which all of (b) and (b) and (b) can be replaced.

[Means for Solving the Problems] The present invention has been made to achieve the above-mentioned problems, and the replaceable phase change optical memory medium of the present invention has the following formula: Among them, X indicating the proportion of Ge is 12 to 39 at%, and y indicating the proportion of (Sb+B i ) is 12 to 37 at%.
The atomic ratio of B i / (Sb + B i ) is 0.50 or less when X is less than 20 at %, and is 0.80 or less when X is 20 at % or more, and M is Te or (T e +3 e) With Te, 2 indicating the proportion of M is 45 to 61 atomic %, and when M is (Te + Se), the atomic ratio of Se / (Te + Se) is 0.10 or less). The recording layer is made of a material having the composition shown below.

Further, the recording layer constituting the optical memory medium of the present invention includes Zr,
It can also contain at least one metal element selected from the group consisting of Mo, lr, 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 formed by the following general formula (I>): Ge − (Sb + B i ) −M (M = Te or Te + Se) It is a multi-element alloy.

That is, the recording layer in the above-mentioned conventional optical memory medium is made of a Ge-8b-Te alloy, and it is difficult to achieve the above-mentioned condition (c) of repeating 106 times or more. In the recording layer of the optical memory medium, Ge-8b-Te system or Ge-8b-Te-8e
By further adding Bi to the system alloy, the initial contrast ratio is increased, and as a result, even if the contrast ratio decreases after repeated recording and erasing, the contrast ratio will be lower than the initial contrast ratio. By maintaining a high value, the above-mentioned condition 0, which is the number of repetitions of 106 times or more, is achieved. This is because the recording layer containing 3i has a hexagonal crystal system in the crystalline state and has a high reflectance in the crystalline state.

General formula (I) forming the recording layer of the optical memory medium of the present invention
In the material, the proportion of metal elements is limited as shown in 2 below.

Ge l (x) -12~3939 atoms 3b+E3
i) suspension (y) -12 to 37 atomic% M (Te or T
e+3e) amount (z) = 45-6145-61 The reason why the amount (x) of e is limited to 12-39 at% is that if it is less than 12 at%, the crystallization temperature will be less than 120 ° C. If it exceeds 0.2μ, the erasure time will be 0.2μ.
This is because it is longer than sec.

In addition, the reason why the suspension (y) of (Sb+Bi) is limited to 12 to 37 at% is that the erasure time is 0.2μ if 12 at% is not reached.
This is because the erasing interval becomes longer than 0.2 μsec if it exceeds 37 atomic %.

Furthermore, the number (7) of M (Te or Te+Se) is 45 to 6
The reason why it is limited to 1 atomic % is that when the content is 45 atomic %, the erasing time becomes much longer than 0.2 μsec, and when it exceeds 61 atomic %, the erasing time becomes longer than 0°2 μsec.

As described above, the present invention is characterized in that a part of the Sb in the conventional Ge-8b-Te alloy is replaced with Bi to significantly improve the initial contrast ratio. B
The atomic ratio of i/(Sb+B i ) is the proportion of Ge (X
), and if X is 20 atomic% unvortexed, 0.5
0 or less, and on the other hand, when X is 20 atomic % or more, 0.
80 or less.

The reason is that as Sb is replaced with 3i, the initial contrast ratio increases as the Bi content increases, and the crystallization temperature decreases. Therefore, if X is 20 atomic% unvortexed, the atomic ratio of B i / (Sb + B i ) is 0.50.
If , B i / (Sb+B i > atomic ratio is 0
．． This is because even if the temperature is increased to 80°C, the crystallization temperature is maintained at 120°C.

Further, when M is Te+Se, the atomic ratio of Se/(Te+Se) is limited to 0.10 or less. The reason is 0.
This is because when it exceeds 10, the contrast ratio becomes less than 25%.

Further, as described above, according to a preferred embodiment of the present invention, Zr9M00lr and Pt are added to the recording layer material of the general formula (I).
At least one metal element selected from 8T consisting of:

These metal elements act as nucleating agents, not only increasing the crystallization speed but also reducing the grain size of the crystals that precipitate during crystallization, which eliminates the problem of unerased records. , it is possible to prevent a decrease in contrast ratio.

The preferable addition amount of these metal elements varies depending on the type, and in the case of 7r, it is 1 for the alloy of general formula (I).
~8 atom%, especially 2-7 atom%, and in the case of MO, 0
．． 5 to 10 atom %, especially 2 to 8 atom %, and in the case of 1r or Pt, 0.3 to 5 atom %, especially 0.5 to 4 atom %
It is. The reason is that Zr is less than 1 atomic % and MO is 0.
If 5 atomic% is unvortexed and lr or Pt is 0.3 atomic% vortex, the amount is too small to work effectively as a nucleating agent, and Zr exceeds 8 atomic% and Mo is 10 atomic%. beyond l
This is because if r or Pt exceeds 5 at %, the crystallization rate becomes too high and amorphousization (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 the material of the general formula (I) is deposited on this by ordinary sputtering method, vacuum evaporation method, etc. A recording layer is formed.

When using sputtering, a sputter target synthesized as follows, for example, is used. In other words, germanium (Ge) with a purity of 5N or higher
, antisodium (Sb), bismuth (Bi), tellurium (Te), and if necessary selenium (Se) are placed in an ampoule made of transparent quartz glass so as to have a predetermined composition, and then This is evacuated to a vacuum of 10' Torr and sealed.

Next, this is melted in a swinging door at 850° C. for 15 hours with thorough mixing, and then cooled to obtain a sputter target material. The sputter target I thus obtained is melted in Ar gas, poured into a stainless steel mold, cooled and solidified, and then polished to a diameter of, for example, 75 to 100 mm and a thickness of 5 ami! i! Forms a disc-shaped target.

As a sputtering method for forming the 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 unit and the target is heated to a predetermined degree of vacuum (for example, 2×10').
~0.3 x 10-6 Torr), △r gas is introduced at a predetermined partial pressure (e.g. 7 x 10 to 3 x 1 O-31 Torr), and high frequency power (e.g. 10 to 50 W) is applied. be exposed.

Also, Si is formed between the substrate and the recording layer and/or on the recording layer.
A protection layer made of a vAm substance such as O or GeO2 may be provided, and this protection layer prevents deterioration of the substrate due to repeated recording and erasing of the recording layer and deterioration of the recording film due to moisture6. [Credit to the Invention] In the optical memory medium of the present invention, it has been confirmed by X-ray diffraction that the recording layer made of the material having the composition represented by the general formula (I) has a hexagonal crystal system in the crystalline state. Since the reflectance in the crystalline state is low, the initial contrast ratio is set to 38, for example, as is clear from the examples below.
It can be as high as ~40%. Therefore, the above condition (2) is satisfied.

In addition, in the recording layer, the initial contrast ratio is 1:) as described above, so
(11) A nucleating agent consisting of Zr, Mo, Ir, or Pt can be contained as needed. , the grain size of the crystals that precipitate during crystallization can be made small, the problem of unerased recording can be solved, and the decrease in contrast ratio can be prevented. becomes possible, and the above condition (2) is also satisfied.

Additionally, the &! In the recording layer, the crystallization temperature (Tx> is high, for example, 120 to 160 degrees Celsius, and the activation energy (E) for crystallization is also high, for example, 2.0 to 2.213 V. When a nucleating agent is added to Zara, crystallization occurs. The temperature rises to 165° C. Therefore, it has excellent thermal stability, and records can be stored for more than 10 years at room temperature. Therefore, the above condition (b) is also satisfied.

Furthermore, in a recording layer made of a material having a composition represented by the above general formula <I), the proportion of amorphous material that remains without crystallization during crystallization is extremely small, so that phase changes during recording and erasing occur. As a result, the interval between erased portions can be made extremely short, for example, 0.2 μsec or less.

Especially when using a nucleating agent, for example, 0.06μsec
can be made extremely short. Therefore, the above-mentioned condition 4 is also satisfied.

[Examples] Hereinafter, the present invention will be further explained with reference to Examples, but the present invention is not limited to these Examples.

Example 1 A glass base was used as a substrate, and a 1,000-layer GeO□ film was formed on this base by a normal sputtering method.

Next, as a sputtering target, an alloy target with a composition expressed by the formula % (the numbers in the formula indicate atomic %, and the atomic ratio of Bi/(Sb+3i) is 0.25) was used, and this was Attach the number plate to a predetermined position within the magnetron type sputter RFf, with a vacuum level of 2 x 10' Torr or less,
By introducing r gas to a partial pressure of 5 x 10' Torr and applying a high frequency power of 20 W or less, the alloy made of the alloy [1
A record layer of 600 people was formed.

Next, a protective film of GeO2 having a thickness of 2000 nm was formed on this recording layer by ordinary sputtering to obtain an optical memory medium.

Since the recording layer of a damaged optical memory medium is in a state intermediate between a "quality 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 (heat it in a vacuum). crystallized by

For this first 111 (Is I) optical memory medium, the contrast ratio, number of recording and erasing repetitions, crystallization temperature (Tx), crystallization activation energy (E), and amateur recording time were determined as follows. All physical properties were satisfactory.

Contrast ratio 39% Number of repetitions 106 times Crystallization temperature (TX) 130°C Crystallization activation energy (E) 2.1 eV erasure time
0.1 μsec The methods for measuring the various physical properties mentioned above are as follows.

Contrast ratio...Reflectance in an amorphous state (Ra
) and the anti-9A ratio (Rc) in the crystalline state were measured and calculated using the following formula.

Number of repetitions...After recording, its i*ji'(Ra
) and then after erasing, its inverse 11) J rate (Rc
). Repeat this until the contrast ratio is 1
The number of repetitions was defined as the number of times until it decreased to 5%.

Crystallized '4A melon ('rX)...Measured using a high-sensitivity differential scanning calorimeter DSC8240B manufactured by Rigaku Denki Co., Ltd. (
heating rate 10°C/1n).

Crystallization activation energy (E)...5, 10 and 2
The crystallization temperature was determined using three types of heating rates of 0° C./min, and calculated by Kirasinger plot.

(As mentioned above, the storage stability of records is evaluated based on the crystallization temperature (TX) and crystallization activation energy (E). ) Erasing time: The recording layer is irradiated with a laser beam with an output of 8 IllW to melt and rapidly cool it to become amorphous, and then the pulse width is A crystallizing (erasing) laser pulse in which the time is increased sequentially by 0.05 μsec is irradiated to successively crystallize each part. After the crystallization process is completed, the crystallized area is sequentially irradiated with a reproduction laser pulse of 0.51.1 μsec, and the reflected light can be 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 Example 1 except that Ge, Sb, Bi, Te, and Se were varied within the limited range of the present invention as shown in Table 1.
An optical memory medium was obtained in the same manner as above.

The obtained optical memory media of Examples 2 to 12 had excellent performance such as n or better than the optical memory medium of Example 1, as shown in Table 1 for various physical property values.

Examples 13 to 16 Four weighing optical memory media were prepared in the same manner as in Example 11 except that predetermined amounts of Zr, Mo, Ir, and Pt were added as nucleating agents.

The obtained optical memory media of Examples 13 to 16 have various physical properties as shown in Table 2 (as shown in Table 2), they all have a contrast ratio of 40%, a repetition rate of far more than 106 times, and a crystallization temperature of 40%. is 160℃, the activation energy of crystallization is 2.2ev, and the erasing time is 0.06μse.
c, which was superior to the optical memory media of Examples 1 to 12.

Table-2 Umbrella 1: In Examples 13 to 16, the number of repetitions was 106
Although the experiment was stopped at 106 times, the contrast ratio at 106 repetitions was approximately 25%, and it is estimated that repetitions far exceeding 106 times are possible.

[Effects of the Invention] As detailed above, the optical memory medium of the present invention, in which the recording layer is made of a material consisting of Ge, (3b+Bi), and M (Te or Te+Se) in a given proportion, has (2) recording state. (c) Recording and erasing can be repeated an extremely large number of times (); records can be stored stably for a long period of time; It has various advantages such as extremely short distance between erased sections.

Further, 7r and MO may be added to the recording layer as necessary.

When gold is used as the nucleating agent selected from lr and Pt, the advantages of (2), (c), and (0, lJ) become even more remarkable.

Claims (1)

[Claims] 1. General formula Ge_x(Sb+Bi)_yM_z(I) (wherein, x indicating the proportion of Ge is 12 to 39 atomic %, and y indicating the proportion of (Sb+Bi) is 12 to 37 atoms %, and the atomic ratio of Bi/(Sb+Bi) is 0.50 or less when x is less than 20 atom%, and is 0.80 or less when x is 20 atom% or more, and 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 0.10 or less). A rewritable phase change optical memory medium comprising a layer. 2. Zr is added to the material having the composition represented by the general formula (I).
2. The optical memory medium according to claim 1, further comprising at least one metal element selected from the group consisting of , Mo, Ir, and Pt.