JPS6314344A - Information recording medium - Google Patents

Abstract

PURPOSE:To maintain a large difference in analyzer transmission components by confining the effective double refractions when a substrate and intermediate layer are considered together to <=20nm (forward and backward) at a reading- out wavelength of recording information. CONSTITUTION:A magneto-optical recording layer 8 is formed of an amorphous alloy such as, for example, Tb-Fe, Gd-Co, Gd-Fe, Dy-Fe or GdTbFe and dielectric films 15, 16 are formed of AlN or Si3N4. The effective double refractions when the transparent substrate 12 and at least one layer of the dielectric film 16 are joined together is confined to <=20nm (forward and backward) at the reading-out wavelength of the recording information. The difference in the analyzer transmission component is thereby maintained relatively large.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to information recording media, and in particular to magnetic recording and reproducing devices that write information thermally using light or the like and read this information using magneto-optical effects. The present invention relates to magneto-optical recording media.

Conventional technology Optical disks as information recording media have high density, large capacity,
It has the feature of high-speed access, and various research and development efforts are being conducted on it. Among these, optical disc recording media that can be additionally recorded only once are TeOx, TeC, Te-3n-3.
e, etc. are known, and some have been commercialized. On the other hand, as a type of rewritable optical recording, magneto-optical recording is attracting attention.

As a magneto-optical recording medium, MnB1% MnCuB1
Polycrystalline thin films such as TbFe, GdFe, GdCo, D
Amorphous thin films such as yFe, GdTbFe, and TbDyFe are known. For example, JP-A-59-17105
No. 5 discloses a rare earth-transition metal amorphous alloy thin film (e.g. GdTbFe) and an oxygen-free A/N.
or Si3N, and a transparent dielectric film made of Ti or T.
A magneto-optical memory element is shown in which a reflective film made of tN is laminated on a substrate in this order.

These magneto-optical recording media, such as magneto-optical disks, have high recording density, are rewritable, and are highly reliable because there is no contact between the recording medium and the head (lens) during recording or playback. It has the following features.

FIG. 3 shows the main part of a magneto-optical recording device rotatably incorporating an information recording medium 1 configured as a magneto-optical disk. In this recording device, a laser beam 9 emitted from a laser light source 11 such as a semiconductor laser passes through a polarizing plate 10 and then a half mirror 5, and is then transmitted through a lens 6 to a transparent substrate I2 of a disk 1 for magneto-optical recording. It enters layer 8 and connects the spots. The reflected light 3 from the recording layer 8 returns in the opposite direction, is reflected by the half mirror 5, further passes through the analyzer 4, and enters the photodetector 2. Here, writing and reading of information can be performed in common using the above-mentioned optical system, but in this case, the laser power for writing may be made larger than that for reading.

FIG. 4 shows an enlarged view of the main part of the medium 1, in which 13 is a guide groove for tracking, 14 is a recording bit, and dielectric It! +5.16 is formed, and an organic protective layer 17 is formed on the top surface.

During recording, information is written on the magneto-optical recording layer 8, which has an axis of easy magnetization in the direction perpendicular to the surface, by selectively forming uniform magnetization scratching properties and reversed magnetic domains with a laser beam 9. It's crowded. In FIG. 5, the written portion of the recording layer 8 is indicated by "1", the non-written section is indicated by "0", and the arrow indicates the magnetization direction. In order to read the written information, the polarization plane of the irradiated laser beam 9 changes depending on the direction of magnetization (i.e., based on the magneto-optical effect called the Kerr effect). , in the 6th section of inversion, the deflection surface rotates by θ in the written part "1" and rotates -0 in the non-written part "0" compared to the incident light.
The reflected light 3 can be detected by the photodetector 2.

In the medium 1 as described above, a resin substrate is often used as the optically transparent substrate 12, but among these, it is difficult to suppress birefringence, which greatly affects the characteristics, especially in those manufactured by injection molding. That is, the sixth
The figure shows the component transmitted through the analyzer (analyzer 4 in front of photodetector 2), and this transmitted component is the vector difference ΔP between the non-written part "0" and the written part "1",
This difference will be read by the photodetector 2. However, when the laser beam travels back and forth across the substrate 12, the birefringence of the substrate 12 is a cause of an elliptically polarized component, especially in magneto-optical disks that use linearly polarized light for reading, so the C/N
This is a major factor in the decline.

That is, in FIG. 6, birefringence changes linearly polarized light into elliptically polarized light shown by a broken line, and as a result, the difference ΔP' in the components transmitted by the analyzer becomes considerably small. For this reason,
Noise increases and C/N deteriorates.

However, in conventional disks, the value of the birefringence of the substrate often changes in sign or negative in the radial direction and circumferential direction, or the value fluctuates greatly. In this case, although the absolute value of birefringence is small, the signal level and noise level fluctuate greatly, and therefore stable dynamic characteristics cannot be obtained.

C9 Process leading to the invention As a result of investigation, the present inventor has found that the actual birefringence expressed in the recording layer is not the same as the birefringence between the substrate and the intermediate layer, such as the dielectric film 16 described above. I discovered that this is birefringence when considered together with the layers. However, especially with resin substrates, dehydration, temperature rise, and
The value of birefringence changes significantly when stress is applied. Conventionally, when manufacturing a substrate, consideration has been given to keeping the birefringence of a single substrate low, but this is insufficient.

20. OBJECTS OF THE INVENTION An object of the present invention is to provide an information recording medium with good dynamic characteristics by effectively reducing the value of birefringence that affects the recording layer.

Structure of the Invention That is, the present invention provides an information recording medium in which an information recording layer is provided on a base and recorded information is read through the base, in which at least one layer is provided between the information recording layer and the base. This patented medium has an intermediate layer, and has an effective birefringence of 20 nm or less round trip at the information reading wavelength when considering the base body and the intermediate layer together. be.

Here, the above-mentioned "birefringence" means 2・Δn Off・d−tt (unit: n
m). This can be measured using common birefringence measuring devices, including a conventional ellipsometer.

To, Example Examples of the present invention will be described in detail below.

First, a magneto-optical disk, which is an information recording medium according to this embodiment, has a structure as shown in FIG. The magneto-optical recording layer 8 is made of, for example, Tb-Fe.

Gd-Co, Gd-Fe, Dy-Fe, GdTbFe
It may be formed to a thickness of, for example, 1,000 mm using an amorphous alloy such as, but it can also be formed by a sputtering method or a vacuum evaporation method. The dielectric films 15 and 16 are also A I N , S i:+
The upper and lower layers may be formed of Na, and their types may be the same or different for the upper and lower layers, and each layer may have one or more layers. Furthermore, A
7! A reflective film such as the above may be provided.

The noteworthy structure here is the effective birefringence (2・Δn eft・d, ff mentioned above) of the transparent substrate 12 and at least one dielectric layer 16 when they are combined.
The reading wavelength of the recorded information (round trip) is set to 20 nm or less. In this case, in order to obtain such an effective birefringence range, the molding conditions are controlled in advance when the substrate is manufactured, for example, by injection molding of resin. Usable resins for the substrate include polycarbonate, epoxy resin, polymethyl methacrylate, polysulfone, polyethersulfone, and the like.

As mentioned above, by setting the combined effective birefringence of the substrate 12 and dielectric film 16 to 20 nm or less, preferably lonm or less, the difference in the analyzer transmission components described in FIG. 6 can be maintained relatively large. . This was confirmed for the first time by the present inventor, as will be described later.
This is extremely significant for improving media performance. In addition, keeping the effective birefringence variation to 10 nm or less over the entire surface, and further to 5 layer meters or less, stabilizes the electrical properties and satisfies the demands for higher density and larger capacity. This is desirable because it allows a highly accurate medium to be obtained.

To set this effective birefringence within the above range,
It is important to control the molding conditions for the substrate 12. In particular, the resin temperature and mold temperature during molding are important, and if these are set relatively high, good results can be obtained regarding the above-mentioned effective birefringence after the formation of the next dielectric film. . For example, the resin temperature is preferably 330 to 350°C when polycarbonate is used, and the mold temperature is preferably 105 to 115°C.

Next, the present invention will be explained in detail using specific experimental examples.

Made of polycarbonate resin, diameter 130mm, thickness 1.2
The first transparent substrate was injection molded under different molding conditions, and the first transparent substrate was injection molded under different molding conditions.
Two types of substrates having the birefringence distributions shown in Figure (al) and Figure 2 (a) were obtained.

〔Molding condition〕

Resin temperature ('C) Mold temperature (''C) A (Figure 1)
320 100B (Figure 2) 340
110 birefringence is the round trip value measured perpendicular to the substrate surface at a wavelength of 830 nm.

In this state, the substrate under molding condition A has a birefringence of 20 nm.
2 at the inner periphery under molding condition B.
Exceeds 0 nm.

However, these two types of substrates were sputtered with Al in an ArNz mixture gas, and ANNi was deposited to a thickness of 800 mm.
After the molding process, they were taken out and the birefringence was measured again, resulting in the distribution shown in Figure 1 (bl) and Figure 2 (b).For molding condition A, the birefringence greatly exceeded 20 nm. On the other hand, B was improved to within 20 nm.

Further, on these substrates on which the AIN layer was formed, 1000 T b Fe Co N as a magnetic layer and Af
A magneto-optical disk was fabricated by sequentially forming 800 fN layers and an organic protective layer.

The C/N of this magneto-optical disk was measured at a linear velocity of 4 m/s and a recording frequency of IMIIz. Here, C/N(Ca
The noise level is the relative intensity ratio between the signal output at the recording frequency and the noise level, which is obtained when the reproduced output when a signal at a certain frequency is recorded is passed through a spectrum analyzer.

As a result, compared to the disk using the substrate made under molding condition A (Fig. 1(b)), the disk under molding condition B (Fig. 2(b)) was 4.5 dB (lower). In other words, it was found that when considering birefringence, it is necessary to take into account the effective value that affects the recording layer (the value when considering the substrate and intermediate layer together).And, If this effective birefringence exceeds 20 nm, the performance as a disk deteriorates and the reliability decreases significantly.In addition, in the disk shown in Figure 2 (bl), the amount of variation in effective birefringence is suppressed to 10 nm or less, which is also preferable for stabilizing the characteristics.

Although the present invention has been illustrated above, the above-mentioned example can be further modified based on the technical idea of the present invention.

For example, the material, shape, manufacturing method, etc. of the substrate and intermediate layer may be changed in various ways, and the reading wavelength may also be changed. Furthermore, the present invention is applicable not only to magneto-optical disks but also to other optical readout media.

(1) Functions and Effects of the Invention As described above, in the present invention, the effective birefringence when considering both the base and the intermediate layer is set to 20 nm or less at the reading wavelength of recorded information (round trip), so that the analyzer transmits the light. It is possible to maintain a relatively large difference in components and provide an excellent medium from a practical point of view.

[Brief explanation of drawings]

1 and 2 show examples of the present invention. Figure 2(a) is a graph showing the change in effective birefringence when an intermediate layer is formed on the substrate obtained under the first molding condition. Graph showing changes in refraction. FIG. 2(b) is a graph showing changes in effective birefringence when an intermediate layer is formed on a substrate obtained under the second molding condition. Fig. 6 shows a conventional example, Fig. 3 is a schematic diagram of main parts of a magneto-optical recording device, Fig. 4 is a partially cutaway perspective view of a magneto-optical disk and a partially enlarged view thereof, and Fig. 5 6 is a schematic diagram explaining the principle of information reading, and FIG. 6 is a vector diagram showing components passing through the analyzer. In addition, in the symbols shown in the drawings, 1. Recording medium 2---
------1.- Photodetector (detector) 3, S -
−−−−−−−− Laser light 8−−−−−−−−
光磁気記録層（磁性膜）１１−・−−一−−−・・−レーザー光源＋ ２−−−−−−−・−・一基板＋ ３−−−−−−一一一一一・-Guide groove 14---
・-recording bit 15, + 6−−−−−−−−dielectric film 17−・−−
--1 --- It is a protective layer. Agent Patent Attorney Hiroshi Aisaka Figure 1 (a) Melo (Nanatakumei kl A) Figure 2 (a) G To (Shape 4 Miigyu B; Figure 5 Figure 6 (Volunteer) Procedural Amendments Showa January 1962 tIA date 1986 Patent Order No. 157573 2, Name of the invention Information recording medium 3, Relationship with the case of the person making the amendment Patent applicant address 1-26-2 Nishi-Shinjuku, Shinjuku-ku, Tokyo Name name
(127) Konishiroku Photo Industry Co., Ltd. 4, Agent address: 2-4-11F, Shibasaki-cho, Tachikawa-shi, Tokyo! NE Bill 6, Number of inventions increased by amendment 7, Figure 1 (al), Figure 1 (b), Figure 2 ial and Figure 2 (b'88, Contents of amendment ``1st Figure (a) He-shaped strip now A: Figure 2 (a) A, wo (ta 1 mii 5 [B:

Claims (1)

[Claims] 1. In an information recording medium configured such that an information recording layer is provided on a base and recorded information is read through the base, at least one intermediate layer is provided between the information recording layer and the base, and An information recording medium characterized in that effective birefringence when considered together with the intermediate layer is 20 nm or less in a round trip at the information reading wavelength.