JPS61131253A - Optical recording medium - Google Patents

Abstract

PURPOSE:To prevent the strains of a recording body layer even when the recording body layer is thin and to improve writing and erasing characteristics by providing a strain relieving layer in the recoding body layer between a substrate and the recording body layer in the titled optical recoding medium wherein recording, reproducing, and erasing are possible. CONSTITUTION:Strains are generated in a recording body layer 2, when the film of the layer is formed. To relieve the strains, a metallic film contg. 35wt% Ag and the remainder of Zn is formed on a glass substrate 5 by sputtering as a strain relieving layer 4, and a layer of a Zn alloy contg. 37.5-40wt% Ag is formed thereon as the recording body layer 2 by sputtering. A protective layer film 1 is coated on the layer 2. The recording body layer is thus freed of strains, hence the phase transforming behavior of the recording body layer is normalized, and the writing and erasing is made possible even with a thin film. Accordingly, the writing and erasing characteristics can be improved. Besides, the instability of the phase due to aging at room temp. can be eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to an erasable and rewritable high-density optical recording medium.

[Background of the invention]

Optical recording alloys are metals or alloys that, when rapidly cooled from a high-temperature solid state, form a crystal structure different from the equilibrium phase at room temperature. can be used as a high-density optical recording medium.

However, when thinning the optical recording alloy that is the recording layer, various residual strains remain in the thin film. Optical recording alloys exhibit normal phase transformation behavior when under no load and can be used as information recording media, but if they are distorted by more than a certain amount, they do not undergo normal phase transformation and can be used as optical recording layers. I can't. For example, as an optical recording layer, Ag-40% by weight Z
When an n-alloy is used, the equilibrium phase is the ζ phase, and information is recorded by heating and rapidly cooling this with a laser to form a metastable β' phase. However, if the alloy film is 80 nm or less If this happens, distortion will occur in the recording layer, and the β' phase will become stable, making it impossible to record information. However, there is a contradiction in that the thinner the film, the smaller the amount of heat required to cause phase transformation, which improves writing and erasing characteristics, so the thinner the film, the better. -! Ag-(
When a Zn alloy (35 to 40% by weight) is processed and strained, the transformation from ζ phase to β' phase occurs at room temperature, although the difference is that it is slow with 35% Zn and fast with 40% Zn. Shima ('1rrans, Met, Soc.

AIME Vol., 242 July 1968), when used as a recording layer, changes occur over time at room temperature.

[Purpose of the invention]

The present invention provides an optical recording medium that utilizes changes in optical properties due to crystalline phase transformation, which has improved writing/erasing characteristics and excellent phase stability in the erasing section. be.

[Summary of the invention]

In the present invention, a layer is provided between the recording layer and the substrate for the purpose of alleviating the strain generated during the production of the thin film of the recording layer, thereby making it possible to make the recording layer in a strain-free state. By creating a strain-free state, the phase transformation behavior of the recording layer is normalized, and writing and erasing can be performed even with a thinner film, thereby improving the writing and erasing characteristics. It is also possible to eliminate phase instability caused by room temperature aging.

The thinning of the recording medium is done by sputtering method.
Usually, the substrate temperature is 200C to promote rearrangement or recovery of particles of the recording material deposited on the substrate. However, the recording layer formed into a thin film using a 200C substrate is subjected to thermal stress due to the difference in coefficient of thermal expansion with the substrate during the process of cooling to room temperature after sputtering. When the elastic constant of the substrate is higher than that of the recording layer, the recording layer is deformed and strain occurs when thermal stress acts between the substrate and the recording layer.

Therefore, in order to remove the strain in the recording layer due to this thermal stress, if the coefficient of thermal expansion is the same as that of the recording layer, or if it is different, a layer with a much smaller elastic constant should be used as the substrate and the recording layer. A recording layer whose transformation behavior is insensitive to the applied stress and the resulting strain must be used. When the recording layer is an alloy, suitable strain relief films include metals having similar physical properties.

However, it must be noted that when metal is used as the strain relief film, a reaction may occur due to interdiffusion with the alloy layer that is the recording layer. Therefore, if such a reaction is likely to occur, by sandwiching a very thin oxide layer between the strain relaxation layer and the recording layer, it is possible to prevent the diffusion and reaction between the two while relaxing the strain on the recording layer. .

On the other hand, the strain in the recording layer can be alleviated by using a high melting point metal that is a metal or an alloy and does not react with the recording layer as the strain relaxation film.

Furthermore, by using a strain-relaxing layer made of the same alloy system as the recording layer and having a composition that is insensitive to strain, the strain of the recording layer can be relaxed. Especially when Ag-Zn alloy is used as the recording layer, stoichiometry
Ag-(37,5~
40% by weight) 7n alloy is more suitable as a recording medium than the composition on the j) Agrich side. First of all, the degree of color change in appearance is greater when it is closer to stoichiometry. Also, β′→ which is the phase transformation of the crystal during extinction
The rate of zeta-phase transformation is determined by the ring diffusion mechanism. Unlike ordinary diffusion mediated by holes, the ring diffusion mechanism is different from ordinary diffusion mediated by pores, and the better the crystal structure is, the faster the diffusion becomes. On the other hand, A g-Z n
In alloys, the stoichiometry composition is the most ordered crystal structure, and Ag-ri deviates from this composition.
As the channel increases, the number of Zn vacancies increases, making ring diffusion less likely to occur. Therefore, Ag-(37.5-40% by weight) Zn alloy is suitable for the recording layer, but this composition range is sensitive to stress, and the β' phase becomes stable when a certain amount of strain is applied. turn into. On the other hand, from the stoichiometric composition, Ag-r
Ag-(30-35% by weight) Zn near i ch
For the reasons mentioned above, the alloy has a slow transformation rate, and since the ζ phase is more stable, the β' phase of the recording layer returns to ζ over time. Therefore, Ag or Ag-35
An optical recording medium with excellent writing and erasing characteristics can be obtained by using a Z11 alloy as a strain relaxation layer and using an Ag-(37.5-40% by weight) Zn alloy as a recording layer thereon.

[Embodiments of the invention]

Example 1 A recording layer was prepared on a transparent glass substrate by sputtering Ag-40% by weight Zn at a basic luminescent temperature of 200 C using a 7Q nm sputtering method. After phase transformation, even if heat treatment equivalent to erasing was performed, the phase did not change to ζ phase, and erasing could not be performed. Therefore, a 200% AA or Cr layer was placed on the glass substrate.
~400 nm evaporation or sputtering. Furthermore, on top of this, At20 of about 1Qnm to 20nm
3, or a CroX layer is laminated by sputtering, and on top of this, 50 to 40% by weight of Zn is added to Ag-37, 5 to 40% by weight.
1100n was laminated, and a protective layer was further laminated. By adopting such a film configuration, it was possible to form the ζ phase in the erased state even with a film thickness of about 50 nm to 70 nm. This membrane structure is shown in FIG. In FIG. 1, numeral 1 indicates a film thickness of 200
2 is a recording layer with a thickness of 50 to 1100 nm, 3 is a reaction prevention layer with a thickness of 10 to 20 nm, 4 is a strain relaxation layer with a thickness of 200 to 5 QQ nm, and 5 is a glass substrate.

Example 2 An Ag-Zn alloy was formed as a strain relaxation layer on a glass substrate, in particular MO or W was added as a metal layer that did not react with Zn.
00~200nm sputtering and Ag-37,5 on top.
~40 wt % Zn was sputtered for 50 to 1100 nm, resulting in a ζ phase corresponding to a normal erased state, and it became possible to stably exist an erased state even in a thin recording layer due to relaxation of strain. This membrane structure is shown in FIG.

Example 3 A 20 to 3 Q nm of A, g-Zn alloy, which is insensitive to strain, was sputtered as a strain relaxation layer on a glass substrate, and then Ag-37,5 was further sputtered on top of it as a recording layer.
~40% by weight7. A film of 50 to 80 nm was formed by sputtering, and a protective film was placed thereon.

This membrane structure is shown in FIG.

By adopting such a film structure, strain in the recording layer due to thinning can be alleviated, and excellent recording and erasing characteristics can be obtained.

The optical recording medium of the present invention is an optical recording medium that can be recorded, reproduced, and erased, and a strain relaxation layer in the recording layer is provided between the recording layer and the substrate. By doing this, even if the recording layer is thin, distortion is prevented from being introduced into the recording layer, and the recording layer having a strain-sensitive composition can be made thinner than 7 Qnm, thereby making it possible to write. The embedding and erasing characteristics can be accelerated.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view showing an example in which a strain relaxation layer and a reaction prevention layer are combined, Figure 2 is a cross-sectional view showing an example in which a strain relaxation layer that does not react with the recording layer is used, and Figure 3 is a strain relaxation layer. FIG. 3 is a cross-sectional view showing an example in which a layer of the same type as the recording layer and insensitive to strain is used. DESCRIPTION OF SYMBOLS 1... Protective film layer, 2... Recording layer, 3... Reaction prevention layer, 4... Strain relaxation layer, 5... Glass substrate.

Claims (1)

[Claims] 1. In an optical recording medium whose state can be changed by light energy and information can be recorded, reproduced, and erased by using the change in optical properties based on the change, there is a structure between the recording layer and the substrate. The recording layer has a strain relaxation layer, and the recording layer is made of a metal or an alloy that forms a crystal structure different from an equilibrium phase at room temperature through phase transformation by rapid cooling from a high-temperature solid state. recoding media. 2. Claims characterized in that the strain relaxation layer has a metal layer whose elastic constant and coefficient of thermal expansion are approximately the same as those of the recording layer, or has a thin oxide layer on the metal layer. The optical recording medium according to item 1. 3. The optical recording medium according to claim 1, wherein the strain relaxation layer includes a metal layer that does not react with the metal or alloy component of the recording layer. 4. Ag or Ag-35% by weight Zn as the strain relaxation layer
It has a metal film of an alloy, and the recording layer is made of Ag-(37
．． The optical recording medium according to claim 1, characterized in that it has a Zn alloy layer (5 to 40% by weight).