JPH0673991B2 - Optical information recording element - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical information recording element capable of optically recording / reproducing an information signal at high density and high speed using a laser beam or the like and rewriting information. Is.

2. Description of the Related Art A technique for recording and reproducing high-density information using a laser beam is already known, and at present, it is widely used for a document file system, a still image file system and the like. In addition, cases of research and development are being reported for rewritable type recording systems. These mainly utilize the state change between amorphous and crystalline of Te.For example, by irradiating relatively intense and short pulsed light, the irradiated part is rapidly cooled from the heated state to the amorphous state, and its optical Recording is erased by decreasing the constant (whitening) and by irradiating a relatively weak and long pulsed light into a crystalline state to increase the optical constant (blackening). Direction to decrease,
Erasing is to utilize the increasing direction.

Te is stable as a crystal at room temperature and does not exist in the amorphous state. Therefore, various additives have been proposed in order to stably exist in an amorphous state at room temperature, and Ge is widely known as one of the typical additives.

Ge has a function of forming a network structure in the Te-Ge thin film, and therefore, the Te-Ge thin film can exist stably in an amorphous state even at room temperature.

However, this Te-Ge thin film can also be roughly classified into two from the viewpoint of an optical recording thin film. That is, when the Te-Ge thin film is formed by the vapor deposition method, the sputtering method or the like, it is stable as amorphous in most composition ranges. However, once crystallized once, when the irradiated part is rapidly cooled by irradiating it with relatively strong and short pulsed light, when the concentration of Ge (percentage of atoms, the same applies below) is about 40% or less, amorphous However, at about 40% or more, it does not return to amorphous and becomes a crystal. Of these, it is possible to record and erase signals because Te-Ge with a Ge concentration of 40% or less, where the crystallized part becomes amorphous again by laser irradiation.
Although it is a thin film, this recording thin film is very stable as amorphous, so even if the irradiation part is irradiated with a relatively weak and long pulse light and the irradiated part is gradually heated / cooled, the crystallization speed is too slow for practical use. Is not suitable.

As a recording thin film containing Te-Ge as a main component, for example, Ge ₁₅ Te ₈₁
There are Sb ₂ S _{2 and the} like (Japanese Patent Publication No. 47-26897), but these have insufficient erasing sensitivity and insufficient writing contrast ratio.

On the other hand, it has been clarified that the crystallization rate can be greatly improved by adding Pd to a TeOx thin film which is a mixture of Te and TeO ₂ (Japanese Patent Application No. 59-192003).

However, it is difficult to blacken the TeOx-Pd recording thin film once and then whiten it again, and thus it is difficult to use it as a rewritable recording thin film.

Problems to be Solved by the Invention After all, in the conventional rewritable optical disk having the recording thin film containing Te-Ge as the main component, the erasing speed is slow and the erasing sensitivity is insufficient. Since the difference in the optical constants of the whitened portion is small, the writing contrast ratio is insufficient.

On the other hand, the conventional TeOx-Pd recording thin film cannot be used as a rewritable optical disk because the blackening speed is sufficiently high but it is difficult to whiten again.

In view of such a point, the present invention is a rewrite that has a feature that it is very stable as an amorphous of a conventional Te-Ge thin film and a feature that it is blackened (crystallized) at high speed as seen in a TeOx-Pd thin film. It is intended to provide a possible optical information recording member, and therefore these two problems must be clarified.

First, when the Te-Ge thin film is irradiated with relatively strong and short pulsed light to rapidly cool the irradiated part from a heated state, the difference in the state change of the irradiated part due to the difference in Ge concentration is considered as follows.

In other words, if the Ge concentration that becomes amorphous again after irradiation with intense short-pulse laser light is within the range of about 40% in terms of atomic percentage, Te will form hexagonal needle crystals during cooling after laser light irradiation. It is considered that the crystal growth of Te can be hindered because Ge is incorporated into the substrate to form a network structure.

Contrary to this, in the range of Ge concentration of about 40% or more, which becomes a crystal after returning to laser light after irradiation with laser light (same as above), a large amount of TeGe crystals were broken out by Ge during cooling after laser light irradiation, and this TeGe Since the crystal is a cubic crystal, grain growth easily occurs. Therefore, it is considered that the crystal does not become amorphous at the cooling rate at the time of laser light irradiation but becomes a crystal.

However, for amorphous conversion (information recording), a Te-Ge thin film with a Ge concentration of about 40% or less, which is desirable, is irradiated with a relatively weak and sufficiently long pulse light for crystallization to gradually heat the irradiation portion, Even with slow cooling, the crystallization speed is slow because it is very stable as amorphous, and the optical constant change between amorphous and crystalline states is small due to insufficient crystal growth, and the writing contrast ratio is insufficient. Therefore, it is not suitable for practical use.

In addition, as described above, the structure in which Pd is added to the TeOx thin film, which is a mixture of Te and TeO ₂ , has been shown to significantly improve the rate of blackening, that is, crystallization.
When TeOx-Pd thin film is irradiated with laser light
Form some compound of the Te-Pd system, which is Te
It is considered to act like a kind of crystal nucleus that promotes the crystallization of. However, this TeOx-Pd recording thin film cannot be used as a rewritable recording thin film because it is difficult to whiten it once it is blackened.

Means for Solving the Problems The recording thin film according to the present invention is formed on the basis of the above facts, and improves the crystallization rate to a Te-Ge thin film which is stable as amorphous and has a Ge atom concentration of about 40% or less. For Pd
Is a recording thin film added with, and by limiting the ratio of the number of atoms of each element, while being very stable as amorphous, crystallization rate is sufficiently high during crystallization, that is, signal recording, The purpose of the present invention is to provide an optical information recording thin film which can be erased sufficiently by laser light. That is, the thin film formed on the substrate is
Including e, Ge and Pd, the atomic ratios (%) of the elements Te, Ge and Pd are respectively x = 50 to 90, y = 5 to 25 and z = 5.
To 30 and regulated by x + y + z = 100, a) In the range of Te ratio x = 50 to 65, Ge ratio y is approximately
70−x ≦ y ≦ 1/3 (x + 10), b) Te ratio x = 65 to 70, Ge ratio y = y =
5) to 25), c) Te ratio x = 70 to 90, Ge ratio is about 5
It is characterized in that it is selected from the range of ≤y≤95-x.

Action The above-described configuration of the present invention is based on the findings obtained as a result of various experimental studies by the inventor. That is, the inventors of the present invention have a very stable Ge atom content of 40% or less (25% or less in anticipation of a risk factor) as amorphous.
-When an appropriate amount (30% or less) of Pd is added to the specific composition range of the -Ge thin film, while it is very stable as amorphous,
Moreover, they have found that the recording thin film has an extremely high blackening speed and blackening sensitivity and is capable of optically rewriting signals.

The function of Ge in the Te-Ge-Pd recording thin film is that when Te or Te-Pd compound is about to crystallize in the amorphous state, it forms a network structure.
It is considered to keep the amorphous state stable.

The function of Pd is considered to be like a crystal nucleus that promotes crystal growth by forming a compound such as Te-Pd or Ge-Pd at the time of erasing, and thus a recording thin film containing Ge. However, sufficient erasing speed and erasing sensitivity can be obtained. In addition, the presence of Pd lowers the transmittance of the recording thin film, and conversely increases the light absorptivity, resulting in high sensitivity.

Description of Examples Next, the reason why the ratio of the number of atoms of each element in the recording thin film is limited in the present invention will be described according to Examples.

Fig. 1 shows that for Te atom x = 50 to 65 (%), for Ge atom y, 70-x ≤ y ≤ 1/3 (x + 10), at x = 65 to 70, y = 5 to 25, and x = In the case of 70 to 90, the same y = is attached, and triangular coordinates giving a ratio of 5 ≦ y ≦ 95−x (each vertex is
It shows a quadrilateral ABCD within 100% concentration position of any one of Te, Ge and Pd, with corresponding side 0% and equally spaced scale between them), and the above range is the lower triangle part. Corresponds to within ECD, the range of is the central quadrilateral part B
Within EDF, and the range of corresponds to within the upper triangular portion ABF.

In the region where Pd is less than the straight line AB in FIG. 1, the effect of Pd is not sufficient, that is, the crystallization speed is not improved so much, and a significant improvement in the signal erasing speed cannot be expected.

Further, a region having more Pd than the straight line CD and a region having less Ge than the straight line DA are regions that are unstable as amorphous or require a large laser irradiation power in order to make them amorphous. That is, since the addition effect of Pd is too large in the region where Pd is larger than that of the straight line CD,
In a region with less Ge than DA, the effect of adding Ge is too small, so the recording thin film easily crystallizes at room temperature, or becomes amorphous even when irradiated with heating / quenching laser light (whitening laser light). Because it is difficult to crystallize,
This is a non-practical region, which requires a larger quenching condition and thus a larger whitening laser power.

Also, rich regions Ge the straight line BC so to speak, an area with the addition of Pd to the composition close to GeTe _2, in this case GeTe ₂ Crystallization be added to Pd in any amount for a very stable as Amorufuasu The degree of speed improvement is small and not practical.

The above is the reason why the composition ratio of Te, Ge, and Pd is limited to the region surrounded by the quadrangle A, B, C, and D in FIG. The optical disk having the recording thin film in this region has practically sufficient signal recording / erasing sensitivity and high C / N.

As a precaution, the coordinates (x, y, z) of each point A, B, C, D in FIG. 1 are shown.

Next, in the preferred embodiment, A, B, and B of FIG.
It is recognized that the moisture resistance is improved by adding oxygen 0 to the recording thin film in the region surrounded by C and D.

That is, one of the deterioration mechanisms of the recording thin film is that Te and Ge are oxidized in the presence of water vapor. However, when O is added as TeO ₂ , Te and Ge in the recording thin film are It is considered to act as a barrier to prevent the promotion of oxidation. In this case, the effect of adding O can be recognized even in a small amount, but on the contrary, if added too much, the recording / erasing characteristics of the signal will be deteriorated, so the amount of O added is preferably 30% or less.

Next, embodiments of the present invention will be described in more detail with reference to the drawings.

FIG. 2 is a sectional view of the optical information recording element according to the present invention.

(1) is a substrate, and transparent resin such as PMMA, polycarbonate, vinyl chloride, polyester, or glass can be used.

(2) is a recording thin film, which is formed on the substrate (1) by vapor deposition, sputtering, etc., and the film composition is obtained by using Auger electron spectroscopy, inductively coupled high frequency plasma emission spectrometry, X-ray microanalysis, etc. You can decide.

In order to easily and accurately control the composition of the recording thin film, in the following Examples 1 to 4, an electron beam vapor deposition machine capable of three-source vapor deposition was used to add Te, Ge, and Pd from each source to a substrate (acrylic resin). It was vapor-deposited on a substrate 10 × 20 × 1.2 mm) to obtain a test piece. Deposition was performed at a vacuum degree of 1 × 10 ^-5 Torr or less, and the thickness of the thin film was set to about 1200Å. The deposition rate from each source was changed variously to adjust the ratio of the number of Te, Ge, and Pd atoms in the recording thin film. Also, for thin film formation, the substrate is 150 rpm
I rotated while rotating.

Next, a method for evaluating the blackening characteristic (erasing characteristic) and whitening characteristic (recording characteristic) of the test piece prepared by the above method will be described with reference to FIG.

In the figure, the light having a wavelength of 830 nm emitted from the semiconductor laser (3) becomes pseudo parallel light (5) by the first lens (4), is rounded by the second lens (6), and then is converted into the third light. It becomes parallel light again by the lens (7), passes through the half mirror (8), and becomes a spot (11) with a wavelength limit of about 0.8 μm on the test piece (10) by the fourth lens (9). Thus, the light is collected and recording is performed.

The signal was detected by receiving the reflected light from the test piece (10) through the half mirror (8) and making it enter the photosensitive diode (13) through the lens (12).

By thus modulating the semiconductor laser and irradiating the test piece with various pulsed laser beams having different irradiation power and irradiation time, it is possible to know the blackening characteristic and the coloring characteristic.

To evaluate the blackening characteristics, the irradiation power is relatively small, for example
Applying a method of fixing the power density to about 1 mw / μm ² and measuring the irradiation time of the blackening start by changing the irradiation time, blackening the recording member in advance to evaluate the whitening characteristics,
A method of fixing the irradiation time to, for example, about 50 nsec and measuring the irradiation light power required for whitening was applied.

The results of evaluating the prepared test pieces using the above evaluation method are shown below.

Example 1 As an evaluation material composition, composition control was performed so that the atomic ratio of Te and Ge was 85:15, and at the same time, the ratio of Te ₈₅ Ge ₁₅ and Pd was variously changed to obtain a plurality of test recording members. Created.

Fig. 4 (a) shows the change in irradiation time required to start blackening when the amount of Pd added was increased as a parameter while maintaining the composition of Te ₈₅ Ge ₁₅ and irradiation was performed with a power of 1 mw / μm ^2. It is a thing. From this figure, by adding Pd, the irradiation time at the start of blackening was greatly shortened and the reflectance change
It can be seen that R / Ro also increases. If Pd is not added,
Te ₈₅ Ge ₁₅ was not blackened at all when irradiated with 1 mw / μm ² for 10 μsec, but a sufficient effect was already obtained when the amount of Pd added (atomic percentage) was about 5%.

Fig. 4 (b) shows the start of whitening when, for example, irradiation is performed with a power of 1 mw / μm ² for 15 μs and the surface is sufficiently blackened, and the irradiation power is variously changed for a fixed irradiation time of 50 μs. Shows the difference in irradiation power required for. from now on,
Although the irradiation power required for the start of whitening is increased by adding Pd to Te ₈₅ Ge ₁₅ , it is clear that the irradiation power required for whitening does not pose a practical problem if the amount of Pd added is 30% or less.

From these two figures, it is understood that the addition of 5% to 30% of Pd to Te ₈₅ Ge ₁₅ can significantly improve the erasing speed without impairing the recording characteristics.

Example 2 As an evaluation material composition, composition control was performed so that the atomic ratio of Te and Ge was 67:33, and at the same time, the ratio of Te ₆₇ Ge ₃₃ and Pd was variously changed to obtain a plurality of test recording members. Created. FIG. 5 shows the change in irradiation time required to start blackening when the Pd additive was increased while maintaining Te ₆₇ Ge ₃₃ and irradiation was performed with a power of 1 mw / μm ² . From this figure, by adding Pd, no blackening occurs at 10 μs irradiation.
It can be seen that Te ₆₇ Ge ₃₃ becomes blackened and that the irradiation time required to start blackening is shortened, but the extent is small and not practical.

This means Te ₆₇ Ge ₃₃ is very stable Te ₂ G as amorphous
It is considered that the composition is e, and since it is too stable as amorphous, the addition effect of Pd cannot be sufficiently obtained even if Pd is added.

Example 3 As a material composition to be evaluated, composition control was performed so that the atomic ratio of Te and Pd was 90:10, and at the same time, the ratio of Te ₁₀ Pd ₁₀ and Ge was variously changed to obtain a plurality of test recording members. Created. Te
₉₀ Ge ₁₀ was crystalline at room temperature at the time of preparation, but when Ge was added at 3%, it became stable amorphous at room temperature.

Figure 6 (a) shows the change in irradiation time required to start blackening when the amount of Ge added was increased while maintaining Te ₉₀ Pd ₁₀ and irradiation was performed with a power of 1 mw / μm ^2. . From this figure, the irradiation time at the start of blackening gradually increased as the amount of Ge added to Te ₉₀ Pd ₁₀ was increased, and the amount of Ge atoms added exceeded 23%. The erasing speed becomes slow, that is, the erasing speed becomes impractical.

FIG. 6 (b) shows, for example, whitening when a portion that has been sufficiently blackened by irradiating with a power of 1 mw / μm ² for 15 ns is irradiated by changing the irradiating power for a fixed irradiation time of 50 ns. It shows the change in power required to start. From this, it is found that the irradiation power required for the initiation of whitening is reduced by adding Ge to Te ₉₀ Pd ₁₀ , and it is understood that sufficient recording sensitivity can be obtained if the addition amount of Ge is 5% or more. After all, from these two figures, for Te ₉₀ Pd _10, there are 5 Ge atoms.
It is understood that by adding up to 23%, a recording thin film having good recording characteristics and erasing characteristics can be obtained.

Example 4 As an evaluation material composition, composition control was performed so that the atomic ratio of Te and Pd was 70:30, and at the same time, the ratio of Te ₇₀ Pd ₃₀ and Ge was variously changed to obtain a plurality of test recording members. Created.

Te ₇₀ Pd ₃₀ is crystalline at room temperature at the time of preparation, while Ge ₇₀
Only by adding 3% of atoms, a stable morphus was obtained even at room temperature.

FIG. 7 (a) shows the change in irradiation time required to start blackening when the amount of Ge added was increased while maintaining Te ₇₀ Pd ₃₀ and irradiation was performed with a power of 1 mw / μm ^2. .

From this figure, by increasing the Ge addition amount to Te ₇₀ Pd ₃₀ , the irradiation time at the start of blackening gradually becomes longer, and when the addition amount of Ge atoms exceeds 20%, the blackening rapidly occurs. The speed becomes slow, that is, the erase speed becomes impractical.

FIG. 7 (b) shows that it is necessary to start whitening when irradiation is performed for 15 μsec with a power of 1 mw / μm ² for a sufficient blackening, and the irradiation power is changed for a constant irradiation time of 50 nsec. The change in irradiation power is shown. From now on Te ₇₀ Pd ₃₀
It can be seen that the irradiation power required for the initiation of whitening is reduced by adding Ge to the alloy, and sufficient recording sensitivity can be obtained if the amount of Ge atoms added is 5% or more.

From these two figures, it is understood that by adding 5 to 20% of Ge atoms to Te ₇₀ Pd ₃₀ , a recording thin film having good recording characteristics and erasing characteristics can be obtained.

According to the above Examples 1 to 4, Te, Ge, and Pd are essential elements, and the ratio of the number of atoms of each element is A, B, C in FIG.
It can be seen that the recording thin film satisfying the range surrounded by D can provide an optical information recording member having excellent recording characteristics and erasing characteristics.

Example 5 As an evaluation material composition, composition control was performed so that the atomic ratio of Te, Ge, and Pd was 75:15:10, and at the same time, Te ₇₅ Ge ₁₅ Pd ₁₀
A plurality of test recording members were prepared by variously changing the ratio of O and O. In this case, the method of forming the recording thin film is to use an electron beam evaporation machine capable of four-source evaporation and evaporate Te, TeO ₂ , Ge, and Pd from each source, and O is TeO ₂ in the thin film. Was added. Other vapor deposition conditions are the same as in Example 1.

The recording member thus obtained was allowed to stand in a warm and humid bath at 50 ° C. and 90% RH, and the humidity resistance was determined by the change in transmittance with 830 nm light. The results are shown in Fig. 8 (a). From this figure, it can be seen that the addition of O into Te ₇₅ Ge ₁₅ Pd ₁₀ reduces the amount of change in transmittance and improves the moisture resistance. This is because TeO ₂ is considered to act as a barrier that prevents Te and Ge from being oxidized in the presence of water vapor. This effect is observed even if the amount of O atom added is less than 3%, and it can be seen that the greater the amount added, the more the moisture resistance improves.

Next, the blackening characteristics and the whitening characteristics of the recording member are shown in FIGS. 8 (b) and 8 (c), respectively.

FIG. 8 (b) shows the change in the time required to start blackening when the amount of O added was increased while maintaining Te ₇₅ Ge ₁₅ Pd ₁₀ and irradiation was performed at 1 mw / μm ^2. . From this figure, it can be seen that by increasing the amount of O added, the irradiation time at the start of blackening is gradually lengthened and the reflectance change R / Ro is also slightly reduced. It is considered that this is because the TeO ₂ barrier makes it difficult to crystallize Te, and the increase in TeO ₂ reduces the relative amount of Te. However, if the amount of addition of O atoms is 30% or less, it is considered that a sufficient blackening rate can be obtained, which is not a practical problem.

FIG. 8 (c) shows a constant irradiation time of 50 for a sufficiently blackened portion by irradiation with a power of 1 mw / μm ² for 15 μsec.
It shows the change in the irradiation power required for the start of whitening when the irradiation power is changed in n seconds for irradiation. From this, it is understood that even if O is added to Te ₇₅ Ge ₁₅ Pd ₁₀ , the irradiation power required for the initiation of whitening hardly changes and the whitening characteristics are hardly affected.

From the above, the addition of O is effective for improving the moisture resistance of the Te-Ge-Pd recording thin film, and particularly when the amount of O added is 30% or less, the moisture resistance is improved while maintaining good blackening characteristics and whitening characteristics. It can be seen that

Example 6 A 1.2 t × 200 φ acrylic resin base material was used as a base material, and a Te ₈₀ Ge ₂₀ thin film and a Te ₈₀ Ge ₂₀ thin film, ie, a Te ₇₂ Ge ₁₈ Pd ₁₀ thin film, were formed as a recording thin film and 10% Pd. Two types of optical disks were prototyped, and signals were recorded and erased by the method described in Japanese Patent Application No. 58-58158.

The method of forming each recording thin film is the same as in the first embodiment.

Using these two types of optical disc, 8 mW recording power, the erasing power, respectively, and 15 mw, where erasing laser beam length whitening recorded as approximately 1 × 15 [mu] m in the half width was rows summer blackening erase, Te ₇₂ Ge _With a disk with ₁₈ Pd ₁₀ thin film, C / N 55 dB was obtained at a single frequency of 2 MHz and disk peripheral speed of 7 m / s.
Moreover, even after recording and erasing 100,000 times, almost no deterioration of C / N was observed.

On the other hand, in the disk having the Te ₈₀ Ge ₂₀ thin film, even when the erase beam was irradiated, it was not blackened at all, and it was impossible to record the signal at all.

EFFECTS OF THE INVENTION As described above, the optical information recording member having the Te-Ge-Pd recording thin film according to the present invention has a signal recording portion which is very stable as amorphous, but is crystallized at high speed during erasing. Moreover, since the erasing sensitivity is very good, it is possible to provide an extremely practical optical disk capable of recording and erasing signals.

[Brief description of drawings]

FIG. 1 is a composition diagram in which the composition of a recording thin film included in the optical information recording member according to the present invention is limited, FIG. 2 is a sectional view of an embodiment of the optical information recording member according to the present invention, and FIG. Schematic diagram of the optical system of the information recording member evaluation device,
Figures (a), (b), Figure 5, Figure 6 (a), (b), Figure 7 (a), (b), Figure 8 (b) and (c) are optical information recording members. 8 is a graph showing the evaluation result of the blackening characteristic or whitening characteristic, and FIG. 8 (a) is a graph showing the change with time of the transmittance of the optical information recording member. (1) …… Substrate (2) …… Recording thin film

Claims (3)

[Claims] 1. A thin film formed on a substrate contains Te, Ge and Pd as essential elements, and the atomic ratios (%) of the elements Te, Ge and Pd are x = 50 to 90 and y =, respectively. 5-25 and z =
5 to 30 is regulated by x + y + z = 100, and a) In the range of Te ratio x = 50 to 65, the Ge ratio y is approximately
70−x ≦ y ≦ 1/3 (x + 10), b) Te ratio x = 65 to 70, Ge ratio y = y =
5) to 25), c) Te ratio x = 70 to 90, Ge ratio is about 5
An optical information recording element comprising an amorphous and crystallizable thin film selected from the range of ≤y≤95-x. 2. The optical information recording element according to claim 1, further comprising oxygen O as an additive substance. 3. The optical information recording element according to claim 2, wherein the amount of added oxygen (percentage of atoms) is 30% or less.