JPH0382591A - Rewriting type optical data recording medium - Google Patents

Abstract

PURPOSE:To obtain a rewriting type optical data recording medium enhanced in recording preserving reliability by excessively adding Sb to a recording film represented by (GeTe)2{(Sb/Bi)2Te1}. CONSTITUTION:When Sb, (GeTe)2(Sb2Te3)1 and (GeTe)2(Bi2Te3) are shown by mol.%, the proper component ratio of a recording film is within a range surrounded by an A1-point (70, 30, 0), a B1-point (5, 95, 0), a C1-point (5, 0, 95) and a D1-point (70, 0, 30). Within this range, the amount of Sb in the recording film is excessively increased and crystallization temp. rises and the environmen tal temp. durability of a recording state can be improved. When the principal constitution of an optical medium is obtained by successively laminating a dielectric film, the recording film, the dielectric film and a metal film on a substrate, high speed recording and high speed erasing capacity are effectively enhanced and it is desirable that ZnS is used in the dielectric film and at least one material selected from Al, Cu, Au and Ag is used in the metal film. As a result, an optical medium excellent in the preserving reliability of recording is obtained without deteriorating high speed erasing capacity.

Description

[Detailed Description of the Invention] 5゜3゜ [Field of Industrial Application] The present invention relates to a so-called rewritable optical information recording medium that can optically record, reproduce, and erase information. , without degrading high-speed erase performance.
The present invention provides a recording film with improved recording storage reliability and a related medium configuration.

[Prior art] Reversible structural change (phase change) between an amorphous state and a crystalline state of a substance caused by light irradiation, mainly laser light irradiation
Phase-change type rewritable optical information recording media (hereinafter simply referred to as optical media), which actively utilizes information recording, have a large storage capacity in addition to high-speed information processing ability, and are expected to be used as future information storage devices. ing.

As the speed of information processing becomes more and more demanding, optical media are required to have the ability to erase information recorded at high speed even faster. The high-speed recording and high-speed erasing performance of an optical medium is not determined only by the performance of the recording film itself, but also by the characteristics surrounding the recording film, such as the protective film, anti-tJJ film, substrate, etc.
It is strongly influenced by the thermal properties of the constituent materials of the optical medium.

We have focused on a new recording film material that has four elements, Qe, 3b, 3i, and Te, as main constituent elements.
As a result of intensive study of the recording and erasing performance of optical media, including the medium structure and its constituent materials, we discovered that it has excellent high-speed recording and high-speed erasing performance, and the patented In(
Patent application No. 1-145172) has been filed.

[Problem to be Solved by the Invention] Recording on an optical medium is usually performed by forming an amorphous region on a recording film that has been crystallized in advance, but this recording region has a tendency to become crystallized due to the ambient temperature. Once the temperature is reached, it rapidly crystallizes and disappears. Therefore, it is desired that this crystallization temperature is as high as possible. However, while the recording film for which the above-mentioned patent application was applied has excellent high-speed recording and high-speed erasing performance, the practical crystallization temperature is low, and the environmental temperature reliability of the recorded state must be improved.

An object of the present invention is to provide a self-replaceable optical information recording medium that improves recording storage reliability without deteriorating high-speed erasing performance.

[Means for Solving the Problems] The present invention has been made to solve the above problems, and is made possible by the following means.

That is, (GeTe)2 ((Sb/Bi)2Te3
) + 1' A solution is sought by adding an excessive amount of Sb to the Wasarel recording film. Here, the appropriate component ratio of the recording film is Sb, (GeTe)2 (
Sb2Te3)1 and (GeTe)2 (B 12T
When e3) + is expressed as mol%, 1 point (70, 30
,O), 81 points (5,95,O), C+ point (5
, 95) and is in the range surrounded by the D1 point (70, 30).

In this range, the crystallization temperature increases as the amount of excess sb in the recording film increases, making it possible to improve the environmental temperature durability of the recorded state. A more practical recording film composition is A2 point (40,60,O) in Figure 1, 82 point < 10.90.
．． O), C2 point (10, 90) and D2 point (
40, 60).

This composition range not only increases the crystallization temperature but also effectively increases the activation energy of the amorphous state, which not only improves environmental temperature durability but also provides records with excellent storage life. It is possible to prepare a membrane.

A recording film containing more sb than on the line between point A1 and point D1 is good for increasing the crystallization temperature, but is not suitable because it slows down the erasing speed and causes deterioration in high-speed erasing performance.

Further, in a region where the amount of excess sb is smaller than the line connecting point 81 and point C1, it is not appropriate because the crystallization temperature cannot be efficiently raised.

The main structure of the optical medium of the present invention is a structure in which a dielectric film, a recording film, a dielectric film, and a metal film are sequentially laminated on a substrate, which is effective in improving high-speed recording and high-speed erasing performance. ZnS for the dielectric film and A1 for the metal film.
It is desirable to use at least one material selected from among Cu, Au, and Ag. The thickness of the metal film is preferably in the range of 15nl to 200rv; if it is less than 15nm or more than 200rv, the recording sensitivity and erasing speed will drop significantly, which is not desirable.

[Function] The recording film of the present invention, which is formed by adding an excessive amount of Sb, which is one of the main constituent elements of the recording film, to the (GeTe)2 ((Sb/B i )2 Te5) recording film is capable of high-speed recording and high-speed recording. The crystallization temperature can be improved without deteriorating the erasing performance, and therefore the thermal stability of the recorded state (environmental temperature reliability) can be improved.

[Example] As shown in FIG. 2, the optical medium of the present invention has a structure in which a first dielectric film 2, a recording film F13, a second dielectric film 4, and a metal film 5 are sequentially laminated on a transparent substrate 1. Become. A thoroughly cleaned glass substrate was used as the transparent substrate 1, ZnS was used for the dielectrics 1112 and 4, and He1 was used for the metal film. Record wA3 had four elements as main constituent elements: Ge, 3b, 3i, and Te. First and second dielectric films 2 and 4 and recording film 3
The film thicknesses were appropriately set in the ranges of 100-110, 190-210 and 39-41 ni, respectively. dielectric film 2,
4. The recording 113 and metal film 5 were formed mainly by high-frequency Magne-1-ron sputtering. A composite target or an alloy target was used as the recording film target.

Record 1! ! The crystallization peak temperature (hereinafter simply referred to as crystallization temperature) of (40 nl film thickness) was measured using a differential scanning calorimeter, and the activation energy of the crystallization temperature was calculated from the Kirasinger plot.The film composition was determined by photoelectron spectroscopy. Confirmed by analytical method.

The recording and erasing characteristics in a stationary state were determined by preparing the optical system shown in Fig. 3 using a laser beam with a wavelength of 830 nl as a light source, and using an objective lens with an aperture of approximately 0.52.
The investigation was conducted by focusing and irradiating the recording film with a laser beam from the transparent substrate side of the sample having the structure shown in the figure. Prior to measuring recording and erasing characteristics, the recording film was subjected to initial crystallization by laser annealing or vacuum heat treatment.

The recording sensitivity is defined as the signal contrast C: ■a: Signal intensity in the recording state IC = signal intensity in the unrecorded state, and with the recording pulse width constant, measure the recording laser output required to record a constant signal contrast. The estimate was made by The erasing time was determined as the minimum erasing pulse width required for the erasing signal output to be saturated by performing recording with a constant signal contrast and keeping the erasing laser output constant.

The appropriate composition range of the recording film of the present invention is shown in Figure 1, and the crystallization temperature (Tp), activation energy <ΔE>, frequency factor (νo), and number of recording/erasing repetitions determined for each point in the figure are shown in Figure 1. (N>), recording sensitivity and high-speed erasing performance are shown in Table 1.

The items of recording sensitivity and high-speed erasing in Table 1 qualitatively represent performance, and O marks indicate excellent performance, O marks indicate better performance, and Δ marks indicate performance. means inferior. The composition of the recording film is Sb,
(GeTe)2 (Sb2Te2)+ and (GeTe
)2 (812Te5)1 expressed in mol%, the appropriate range of recording film composition is point A1 (70, 30, O
), B+ point (5,95,O) 1 (/1 point (5,
95) and the D+ point (70, 30). In this region, as the content of excess sb in the recording film increases, the crystallization temperature of the recording film rises, for example from 147°C at point 81 to 203°C at point A1, approximately 5°C.
An improvement of 6℃ is expected. A similar tendency was observed between the 01 point and the D+ point. In this region, as the excess sb content increases, the erasing speed slows down, but (GeTe)z (Sbz Te5) contained in the recording film
+ :Y and (GeTe)z(B+2 Te5)+
:Z in mole %, the ratio, ie, Y/Z, is in the range of 0.1 to 0.9, which is desirable for high-speed erasing since there is little decrease in erasing speed. In particular, it is more preferable that Y/Z is in the range of 0.2 to 0.8, and the highest speed erasing performance can be effectively preserved in the range of 0.3 to 0.7. Ta. For example, when the excess sb is approximately 60 mol%,
Erasing time is Y/ with erasing laser output of 5.5 mW.
100ns when 2 is 0.2, 7 when 0.65
0 nS and 90 ns when 0.8. In addition, an increase in the excessive sb content in the recording film effectively works to improve the recording sensitivity. For example, when the recording laser output required to obtain a contrast of 30% has a pulse width of 60 ns, 12.7 mW when the excess sb content is 24.5 mol% and 12.7 mW when the excess sb content is 52.6 mol%, whereas it is approximately 13.5 mW when no sb is included.
1 mW, making recording more sensitive.

In the 5b-Ge-Te ternary material, sb toward the eutectic point
It is known that as sb becomes excessive, the melting point decreases. Based on this, it can be inferred that the improvement in recording sensitivity of a recording film containing an excessive amount of sb is closely related to the decrease in the melting point of the recording film. Seem. When the content of sb increases more roughly than on the line connecting A1 and 01, the crystallization temperature increases in a direction approaching the crystallization temperature of sb, but the erasing time becomes longer than 100 nS under the same conditions as above. , it was unsuitable for performing high-speed erasing operations, and the number of repetitions of recording and erasing was only about 103 (0
point).

Next, A2 and B2 have practically preferable characteristics.

The area surrounded by points C2 and D2 will be explained. The composition ratio (mol%) at each point is A2 point (40,60°0), 8
2 points (10,90,O), 02 points (1G, 0゜9
0) and 02 points (40, 60). In this region, as shown in Table 2, the practical crystallization temperature ranges from 166°C to 1°C.
It is as high as 92℃ and has an activation energy of 2.2 eV.
Since the above-mentioned high value is obtained, not only the environmental temperature durability of the recorded state is excellent, but also the recording retention life is excellent. In particular, when the content of excess sb is set between 15 and 30 (mol%), the activation energy of the amorphous state further increases and shows a high level of 2.8 e■ to 3.Oe■.Here, JhOnSOnmHehl -AVrali equation and reaction rate constant) The frequency factor calculated using the relational equation and the activation energy is 10 S to 10338-1
This is a high value.

2-1 These numbers are JhonsonmHehl-Avram.
By applying the equation of i to the relational expression of the reaction rate constant, we calculated and estimated the storage life of the record, and found that more than 90% of the recorded state was preserved for 30 years in an 8-temperature environment of 50°C, indicating an excellent effect on the storage life of the record. It was found that the recording film had the following characteristics.

The area where recording and erasing operations are possible was investigated based on the relationship between laser output and pulse width. As an example, FIG. 4 shows the results obtained for a recording film having the composition of point Q in Table 2.

Recording operation occurs in the area between curve I and curve ■, and curve ■
Erasing operation was possible in the region between curve 2 and curve ■. In addition,
When erasing, the signal contrast during recording is 30
It was assumed that the percentage was constant. Pulse width for both recording and erasing operations is 50n
It was confirmed that even a speed of about 100 s is possible, and that it has excellent high-speed recording and high-speed erasing performance. The pulse width required for erasure does not change much as the excess sb content increases up to about 40 mol%, and after that it tends to gradually become longer, but at 70 mol% it reaches 100 mol%.
It was good, staying at about ns. Similar effects were observed in recording films having other composition ratios within the appropriate composition range.

If the content of excess sb is high, the crystallization temperature will also be high and it will exhibit an excellent effect on environmental temperature durability, but if faster erasing is required, the content of excess sb will be lower. It is preferable to set

The recording and erasing performance is strongly influenced by the thermal properties of the constituent materials of the optical medium, but in the structure of the optical medium of the present invention, the performance varies greatly depending on the type of metal film material used and its film thickness. A metal film material and its film thickness range that are effective for improving performance have been discovered.

Figure 5 shows the recording laser output and gold m1ll (All
This shows the relationship between film thickness. Aj film thickness is 15
When the range is from nm to 20 onm, high-speed recording can be performed effectively with high sensitivity, and from 20 nm to 18 o
It is more effective if it is in the nm range.

Similarly, similar effects were observed for recording films with other composition ratios. Furthermore, the same effect as Aj was obtained when ALJ, Cu1, and Ao were used instead of Aj for the metal film. As in the case of the recording sensitivity characteristics described above, using a recording film having the composition ratio of the Q point in Table 2, the erase time was measured with the erase laser output constant at 5.5 g + W for recording with a constant signal contrast of 30%. FIG. 6 shows the film thickness dependence of Fan (Aj'). A range of AJll film thickness is recognized to be effective for high-speed erasing, and is often in the range of 15nl to 200ni+, preferably in the range of 20nl to 180nw.

Within the appropriate composition range (A+ -8t -C+ -D+), almost the same effect was observed in recording films with other composition ratios having high-speed erasing performance. Also, the metal film is Au in addition to A1, similar to the recording performance described above.

Similar good effects were observed when using CU and Ag.

When T+ was used for the metal film, the recording and erasing performance was significantly reduced, making it unsuitable for high-speed recording and high-speed erasing. When Taz Os or 5iOz is used instead of ZnS for the dielectric film, the recording sensitivity is greatly reduced compared to when ZnS is used. In case, 25
It was not possible to record even at a laser power of -W.

In addition, the erasing speed also deteriorates, making it unsuitable for high-speed recording and high-speed erasing.

ZnS1 was placed on a glass substrate (N5 substrate made by HOYA ■) with a direct pregroove with an outer diameter of 130rvφ formed on one main surface.
An optical memory disk was prepared in which a recording film (composition at point P in Table 2), ZnS, AU, ultraviolet curable resin, adhesive, and a protective plate were sequentially laminated, and the dynamic characteristics were evaluated. As a result, the optical medium of the present invention was found. was confirmed to have excellent high-speed recording and high-speed erasing performance.

The explanation will be given below. Prior to measuring dynamic characteristics, the recording film was subjected to initial crystallization. Linear speed 22m/s.

Under carrier frequency 7 HI3, resolution bandwidth is 3
◇The C/N determined as KH7 showed a high value of 58 dB or more at a recording laser output of about 19- or more, indicating that the recording film of the present invention had excellent characteristics in high-speed recording performance. Furthermore, when we investigated the single beam overwrite characteristics using a recording laser output of 21 mW, an erasing bias laser output of 13-W, and two carrier frequencies of 2 MHz and 5.338 H2, we found that the erasure rate was 35 d.
Good override performance of B or higher was obtained, and sufficient erasing performance was obtained even at high speeds. Similar good dynamic properties were obtained with other compositions within the appropriate composition range, and the recording film of the present invention was excellent in high-speed recording and high-speed erasing performance.

Next, the environmental durability of the recorded state will be explained.

The prepared optical memory disk has the same dynamic characteristics as described above. Linear speed 1t1111/S, recording laser output 17
Recording was performed under the conditions of mW and carrier frequency 5ht+z, and the result was left in a constant temperature and humidity environment at 85°C and 90% R for 30 days. As a result, the C/M changed from the initial 58.2 dB to 0.
The decrease was limited to 5 dB1f1fi. Similar good results were obtained when recording films having other composition ratios within the appropriate composition range were used, and the recording film of the present invention was recognized to have excellent environmental durability in the recorded state.

[Effects of the Invention] The recording film of the present invention, which has four elements of Ge, Sb, Bi, and Te as main constituent elements, does not deteriorate high-speed recording and high-speed erasing performance, and has excellent durability at record storage environmental temperatures and record storage life. The effect of increasing the In other words, it is possible to provide an optical medium that is capable of high-speed information processing and has excellent storage reliability for recorded information.

[Brief explanation of drawings]

FIG. 1 is a composition diagram showing the appropriate composition range of the recording film of the optical medium of the present invention, FIG. 2 is a cross-sectional view of the structure of the optical medium according to the embodiment of the present invention, and FIG. 3 is a recording film in a stationary state. A side view showing the measurement system for erasing characteristics. Figure 4 shows the recording and erasing operation area determined as the relationship between laser output and pulse width. Figure 5 shows the dependence of the laser output required for recording on the metal film (Aj) film thickness and Figure 6 shows the pulse width (erasing time) required for erasing the metal film (A1).
It is a graph showing each film thickness dependence. Non-Oxide Glass Research and Development Co., Ltd.

Claims (1)

[Claims] 1. A rewritable optical information recording medium that causes a reversible phase transition between an amorphous state and a crystalline state of a recording film by light irradiation, thereby making it possible to record and erase information. The main constituent elements of the recording film are Ge, Sb, Bi and Te.
element, and the composition of the recording film is Sb, (GeTe)_2(Sb_2Te_3)_ in the composition diagram of FIG.
When the composition ratios of 1 and (GeTe)_2(Bi_2Te_3)_1 are each expressed in mol%, A_1(7
0, 30, 0), B_1 (5, 95, 0), C_1 (5
, 0, 95) and D_1 (70, 0, 30). 2. In a rewritable optical information recording medium that causes a reversible phase transition between the amorphous state and the crystalline state of the recording film by light irradiation, thereby making it possible to record and erase information, the main component of the recording film is 4 whose constituent elements are Ge, Sb, Bi and Te
element, and the composition of the recording film is Sb, (GeTe)_2(Sb_2Te_3)_ in the composition diagram of FIG.
When the composition ratios of 1 and (GeTe)_2(Bi_2Te_3)_1 are each expressed in mol%,
0, 60, 0), B_2 (10, 90, 0), C_2(
10, 0, 90) and D_2 (40, 0, 60). 3. The rewritable optical information recording medium according to claim 1 or 2, wherein the main film structure of the rewritable optical information recording medium is formed by sequentially laminating a dielectric film, a recording film, a dielectric film, and a metal film on a substrate. Information recording medium. 4. Zn is added to the main dielectric film of the rewritable optical information recording medium.
4. The rewritable optical information recording medium according to claim 3, wherein at least one material selected from among Al, Cu, Au, and Ag is used for the S and metal film. 5. The rewritable optical information recording medium according to claim 4, wherein the metal film has a thickness in the range of 15 nm to 200 nm.