JPH03147546A - Optical memory element - Google Patents

Abstract

PURPOSE:To substantially prevent the generation of ruggedness on the surface of a transparent substrate and the generation of deformation, such as curving, of the transparent material by constituting transparent dielectric films of plural layers varying in thermal conductivity and disposing the layers having the smaller thermal conductivity on the transparent substrate side. CONSTITUTION:The transparent dielectric film 2 between the transparent substrate 1 and a recording film 3 are formed as the plural layers 2a, 2b varying in the thermal conductivity and the layer 2a having the small thermal conductivity is provided on the transparent substrate 1 side. The heat from the recording film 3 is, therefore, shut off by the layer 2a of the smaller thermal conductivity of the transparent dielectric films 2 and is hardly transferred to the transparent substrate 1 even when the temp. of the recording film 3 rises at the time of recording and erasing. Thus, the generation of the ruggedness on the surface of the transparent substrate 1 and the generation of the deformation, such as curving, of the substrate 1 are obviated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical memory element that records, reproduces, and erases information by irradiating it with light such as a laser beam.

[Conventional technology]

2. Description of the Related Art In recent years, research and development of optical memory elements, in particular magneto-optical memory elements, in which information can be rewritten and erased has been actively conducted.

Among these, those using rare earth transition metal amorphous alloy thin films as recording media are attracting attention because the recording media are not affected by grain boundaries and the recording media film can be relatively easily formed over a large area. are collecting.

Magneto-optical memory devices that use the above-mentioned rare earth transition metal amorphous alloy thin films as recording media have relatively small magneto-optical effects (Kerr effect, Faraday effect) used for information reproduction, but it is important to improve the precision of the optical head. control technology,
By making full use of circuit technology, it has become possible to obtain an S/N ratio suitable for practical use.

FIG. 4 shows an example of a conventional magneto-optical memory element. In this magneto-optical memory element, a first transparent dielectric film 22 (for example, 80 nm thick) made of /1Nli is formed on a transparent substrate 21 made of a transparent resin such as polycarbonate or acrylic. GdTbFe on the body membrane 22,
A rare earth transition metal film 23 (eg, 20 nm thick) such as an alloy thin film of TbFeCo or DyFeCo is formed.

Furthermore, a second transparent dielectric film 24 (for example, film thickness 25 nm) made of an AffiN film is formed on the rare earth transition metal film 23,
A/! Reflective film 25 (for example, film thickness 50 nm)
and a protective film 26 made of resin are sequentially laminated.

In the above magneto-optical memory element, information is recorded and erased by applying an external magnetic field in a predetermined direction while irradiating the rare earth transition metal film 23 with a laser beam. By irradiating light (linearly polarized light),
Information is reproduced by detecting the rotation of the plane of polarization in the reflected light. Note that first and second transparent dielectric films 22 and 22 are disposed on both sides of the rare earth transition metal film 23 as a recording film.
24 increases the apparent rotation angle of the plane of polarization in the reflected light, thereby improving the SZN ratio during reproduction.

In the above, a magneto-optical memory element using only one side has been described, but when using both sides, it is sufficient to bond two single-sided magneto-optical memory elements together.

[Problems to be Solved by the Invention] Incidentally, in the above configuration, as the transparent substrate 21, a resin substrate that can be industrially manufactured at low cost is often used.

However, when a resin substrate is used in this way, the rare earth transition metal film 23 reaches the Curie temperature (
When the temperature is raised to around 130-200'C, the heat of the rare earth transition metal film 23 is transferred to the first transparent dielectric film 22.
The heat is transmitted to the transparent substrate 21 through the heat, and the transparent substrate 21 tends to be deformed due to this heat. Therefore, over a long period of time, unevenness may occur on the surface of the transparent substrate 21.
may be distorted and curved. If the transparent substrate 21 is deformed in this way, it will adversely affect recording and erasing sensitivity, reproduction signal quality, and the like. Incidentally, the above-mentioned problems are also discussed in Japanese Patent Laid-Open No. 114141/1983.

[Means to solve the problem]

In order to solve the above problems, an optical memory element according to the present invention is an optical memory element in which a recording film is formed on a transparent substrate through a transparent dielectric film, and the transparent dielectric film is formed of a plurality of transparent dielectric films having mutually different thermal conductivities. It is characterized in that the layer with lower thermal conductivity is placed on the transparent substrate side, and the layer with higher thermal conductivity is placed on the recording film side.

[For production]

According to the above structure, the transparent dielectric film between the transparent substrate and the recording film is formed as a plurality of layers having different thermal conductivities, and the layer with low thermal conductivity is provided on the transparent substrate side, so that recording, Even if the temperature of the recording film increases during erasing, the heat from the recording film is blocked by the layer of low thermal conductivity in the transparent dielectric film, making it difficult for it to be transmitted to the transparent substrate. Therefore, deformation such as unevenness on the surface of the transparent substrate or bending of the transparent substrate is less likely to occur. Further, since a layer of a transparent dielectric film having a relatively high thermal conductivity is arranged on the recording film side, the heat of the recording film can be diffused to this layer having a high thermal conductivity.

〔Example〕

An embodiment of the present invention will be described below based on FIGS. 1 to 3.

As shown in FIG. 1, a magneto-optical memory element as an optical memory element includes a transparent substrate 1 made of a transparent resin such as polycarbonate or acrylic.

A first transparent dielectric film 2 (for example, 80 nm thick) is formed on the transparent substrate l, and a recording film of GdTbFe, TbFeCo, DyFe is formed on the first transparent dielectric 15!2.
A rare earth transition metal film 3 (eg, 20 nm thick) such as a Co alloy thin film is formed. Furthermore, a second transparent dielectric film 4 (eg, 25 nm thick) made of a /IN film or the like is laminated on the rare earth transition metal film 3.

Further, a reflective film 5 (for example, film thickness 50 nm) made of an Affi film or the like is formed on the second transparent dielectric film 4 to provide a reflection).
A protective film 6 is provided by coating 115 with silicone resin or ultraviolet curing resin and curing it. When the magneto-optical memory element is of a double-sided type, it is sufficient to bond two of the above-mentioned single-sided type magneto-optical memory elements.

The first transparent dielectric film 2 is composed of two layers 2a and 2b. Among them, the first one located on the transparent substrate l side.
The layer 2a is made of a material having a high refractive index and a relatively low thermal conductivity, for example, stabilized zirconia stabilized by Y2O3 (ZrO2.Y2Ch: Yttria 5tb).
ilized Zirconia). In that case, for example, ZrO, Y2O.

A stabilized zirconia thin film to which 10 mol % of is added is formed to have a thickness of 5 to 75 nm.

On the other hand, the second layer 2b of the three rare earth transition metal films is the same as the first layer 2b.
It is made of a material having a higher thermal conductivity than a, for example, AfN. The thickness of the second layer 2b is in the range of 5 to 75 nm, and the thickness of the first transparent dielectric film 2 as a whole is set to be about 80 nm.

Table 1 shows the refractive index and thermal conductivity of transparent dielectric films made of various materials. As is clear from the same table, the thermal conductivity of stabilized zirconia (ZrO2.y, o, Or even if the temperature of the rare earth transition metal film 3 is raised to near the Curie temperature by irradiation with laser light during erasing, the heat of the rare earth transition metal film 3 is blocked by the first layer 2a and is difficult to be transmitted to the resin transparent substrate 1. Become. As a result, deformation of the transparent substrate l becomes less likely to occur, so that deterioration in recording or erasing sensitivity or deterioration in reproduced signal quality is alleviated.

FIG. 3 shows the results of measuring the BER (bit error rate) of the magneto-optical memory element of this example and the conventional magneto-optical memory element shown in FIG. 4, where I indicates the magneto-optical memory element of this example. The initial value of BRR in the memory element BER(0
) to BER(t) after t time elapsed, that is,
The graph shows the change in the rate of increase in BER, and in the figure, ■ indicates the rate of increase in BER in the conventional example. As is clear from the figure, in the magneto-optical memory element of this example, the BER hardly increases with the passage of time, but in the magneto-optical memory element of the conventional example, the BER increases with the passage of time. This is because, in this embodiment, the heat from the rare earth transition metal film 3 is blocked by the first layer 2a, so that deformation of the transparent substrate 1 is less likely to occur, whereas in the conventional example, as described above, the heat from the rare earth transition metal film 3 is blocked by the first layer 2a. Transparent substrate 21 due to heat from 23 (Fig. 4)
This is thought to be due to deformation occurring in the .

Next, stabilized zirconia (ZrO2/Y
The procedure for forming the first layer 2a of the first transparent dielectric film 2 made of ZOl will be described.

The first layer 2a is formed, for example, by a sputtering method using a sputtering apparatus IO as shown in FIG. The sputtering apparatus 10 includes a transparent substrate 1 held in a Pel jar 11 by a substrate holder 12, and a target 13 made of Zr at a position facing the transparent substrate 1.
is placed on a support stand 14 and protected by a shield 15. Further, a plurality of pellets 16 made of metal yttrium (Y) are arranged on the target 13 made of Zr, and a shutter 17 that can be opened and closed is provided between the target 13 and the transparent substrate 1.

Using the above sputtering apparatus 10, Ar and 0□
Sputtering was performed in a mixed atmosphere. As a result, the first layer 2a formed on the transparent substrate 1 is made of ZrO with 3.9 to 20.0 male% of Y2O3 added thereto, and the crystal becomes a cubic crystal, with a refractive index of 2.0 to 2.0. 2.2
values were obtained and were found to be equivalent to the properties obtained by bulk crystal and calcination.

In addition, although stabilized zirconia in which Y2O3 was added to ZrO□ was shown above, Yb20:
l , Smz Ot , MgO1CaO1Gd203
, Tbz O, etc. can be added to ZrO to obtain the same effect, and is not limited to Y2O3. Furthermore, zirconia may be used as the first layer 2a.

Further, as the second layer 2b in the first transparent dielectric film 2, AIN is illustrated as an example, but in addition to AIN, S iz Na, S iC, etc. whose characteristics are shown in Table 1 above can also be used. can.

Although the first transparent dielectric film 2 is made up of two layers in the above example, the first transparent dielectric film 2 may be made up of three or more layers.

Further, the second transparent dielectric film 4 may be omitted and only the first transparent dielectric film 2 may be provided. Further, in the above embodiment, information is reproduced based on reflected light.
It may also be configured to perform reproduction based on transmitted light.

〔Effect of the invention〕

As described above, the optical memory element according to the present invention is an optical memory element in which a recording film is formed on a transparent substrate via a transparent dielectric film, and the transparent dielectric film is composed of a plurality of layers having mutually different thermal conductivities. , and a layer with low thermal conductivity is arranged on the transparent substrate side.

As a result, the transparent dielectric film between the transparent substrate and the recording film is formed as multiple layers with different thermal conductivities, and a layer with low thermal conductivity is provided on the transparent substrate side, so that the recording film can be heated during recording and erasing. Even if the temperature rises, heat from the recording film is blocked by a layer of low thermal conductivity in the transparent dielectric film, making it difficult for it to be transmitted to the transparent substrate. As a result, deformations such as unevenness on the surface of the transparent substrate and bending of the transparent substrate are less likely to occur.

[Brief explanation of the drawing]

1 to 3 show one embodiment of the present invention. FIG. 1 is a schematic longitudinal sectional view showing a magneto-optical memory element. FIG. 2 is an explanatory diagram of the sputtering apparatus. FIG. 3 is a graph showing the relationship between the elapsed time and the rate of increase in the bit error rate. FIG. 4 is a schematic longitudinal sectional view showing a conventional magneto-optical memory element. 1 is a transparent substrate, 2 is a first transparent dielectric film, 2a is a first layer (layer with low thermal conductivity), 2b is a second layer (layer with high thermal conductivity), 3 is a rare earth transition metal film ( recording film). ] 1 Figure

Claims (1)

[Claims] 1. In an optical memory element in which a recording film is formed on a transparent substrate via a transparent dielectric film, the transparent dielectric film is composed of a plurality of layers having mutually different thermal conductivities, and The layer with the smaller ratio is on the transparent substrate side,
An optical memory element characterized in that a layer with higher thermal conductivity is arranged on the recording film side.