JPH0440648A - Optical information recording medium - Google Patents

Abstract

PURPOSE:To suppress the deformation of a substrate by providing two layers of a ZrO2 or SiO2 film and Si3N4 film on the rear surface side of the substrate. CONSTITUTION:The transparent resin substrate 1 is provided with guide grooves for tracking at the time of reading out recording in the upper part and is provided with the thin film 2 essentially consisting of the ZrO2 which is the 1st dielectric film and the thin film 3 essentially consisting of the Si3N4 which is the 2nd dielectric film in the lower part. The 1st dielectric film 2 is provided on the side nearer the substrate 1 than the 2nd dielectric film 3. The 1st dielectric film essentially consisting of the ZrO2 or SiO2 and the 2nd dielectric film essentially consisting of the Si3N4 which are two layers of the dielectric films are provided on the rear surface of the substrate, by which the differences in moisture absorption resistance, coefft. of thermal expansion, etc., on both front and rear surfaces of the transparent resin substrate 1 of the optical information recording medium are eliminated and, therefore, the deformation of the substrate is sufficiently suppressed.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to an optical information recording medium such as an optical disk on which information is written and read optically.

[Conventional technology]

Conventionally, optical discs of this type have used transparent resin (plastic) substrates, but such substrates are susceptible to mechanical deformation due to environmental changes such as temperature and humidity, and this is especially true when two substrates are pasted together. This phenomenon becomes more noticeable when the plate is made of a single plate rather than a combination of plates. This is because such optical discs have a recording film and a protective film on only one side of the substrate, so that one side has a different surface condition from the other side, and has significantly different properties mainly in terms of moisture absorption. It is believed that. Specifically, when such optical discs with different front and back surfaces (hereinafter the side on which a recording film is formed is defined as the front surface) are exposed from a low-humidity environment to a high-temperature environment, the substrate absorbs moisture and expands. , it is known that the recording surface side is deformed so that the recording surface side is concave. Materials Research Institute, Chuo America, etc.). In addition, such an optical disk deforms due to the difference in coefficient of thermal expansion between the front and back surfaces due to temperature changes. in general,
It is known that optical discs that use a plastic substrate and have a protective layer made of a ceramic thin film and a recording film made of a thin metal film formed on one side of the substrate deform as the temperature rises, causing the recording film side to become concave. There is. In order to solve the above-mentioned problems, various efforts and improvements have been made in the past. As an example, as described in Japanese Patent Publication No. 63-69046, a portion of an optical information recording medium such as an optical disk similar to that mentioned above that comes into contact with the outside world has a refractive index n in the range of 1.35. Disclosed is a means for preventing expansion and deformation of a transparent resin substrate due to humidity and temperature rise by coating it with a dielectric film satisfying n≦1.75.

[Problem to be solved by the invention]

However, in the above-disclosed means, an 8-electrode film is provided on the back side of an optical disc made of a single substrate, and there are no problems with concave deformation of the optical disc and protection of the recording film against changes in temperature and humidity. It is not intended to fundamentally improve the situation. Incidentally, the above-mentioned deformation of the optical disc usually causes surface warping of the disc, which adversely affects the mechanical properties of the disc and, by extension, the recording/reproduction signal characteristics, etc. during actual use. In order to solve the above-mentioned problems of the prior art, the present invention provides an optical disk, etc., that uses a transparent resin substrate that suppresses deformation due to humidity and humidity changes during actual use and improves the durability of the recording film itself. The purpose is to provide information recording media.

[Means to solve the problem]

The structure of the present invention is such that at least a recording film is provided on one surface of a transparent resin substrate, and a transparent two-layer dielectric film is provided on the other surface, and among the two-layer dielectric film, the substrate is The main component of the layer closer to is ZrO. or 5in2, and the main component of the other layer is Si3N
It is characterized by consisting of 4. Here, as the transparent resin substrate, for example, PC (polycarbonate resin), PMMA (polymethyl methacrylate resin), polyolefin, epoxy resin, etc. can be used. Further, as the recording film, for example, TbFeCo, G
Amorphous magnetic alloys such as dDyFeCo and TbDyFeCo are used, and the film thickness is numerically 0.01 to 0.1 μm.
is suitable. Furthermore, an 8-electrode film (hereinafter referred to as a first
(referred to as dielectric film), the main component of which is Zr01 or 5i02 is used, and the film thickness is 11.
The thickness is preferably 00n or less, more preferably 20nm or less. As the dielectric film of the other layer (hereinafter referred to as the dielectric film of 's2), a film whose main component is 5lsN4 is used, and its film thickness is preferably not more than 300 nm. The means for forming the recording film and both dielectric layers is not particularly limited as long as it can ensure uniform thickness, and for example, film forming means such as vacuum evaporation, sputtering, and ion blasting can be applied. .

[Effect]

'In the configuration of the present invention, a two-layer dielectric 111 (a first dielectric film containing ZrOz or 5iOz as a main component, and a first dielectric film containing ZrOz or 5iOz as a main component;
sN4 principal component'! By providing a dielectric film (J2) on the back side of the substrate, the transparent resin substrate 1 of the optical information recording medium
Since differences in moisture absorption resistance, thermal expansion coefficient, etc. between the front and back surfaces of the substrate can be eliminated, it is possible to sufficiently suppress the deformation of the substrate as described above. In addition, in the optical information recording medium, a protective film is provided to sandwich the recording film provided on the front side in order to protect the recording film. For this reason, it is desirable that the second dielectric film on the back side has approximately the same thermal expansion as that of the protective film or the like. This makes it possible to reduce any deformation of the optical information recording medium due to the effects of temperature and humidity. On the other hand, the first dielectric film is provided to strengthen the adhesion between the second dielectric film and the substrate. Generally, a nitride-based film is often used as a film that imparts moisture permeation resistance, but it is difficult to obtain sufficient adhesion with the resin substrate with this film, so the first dielectric film is The film is formed of an oxide-based material to easily obtain the desired adhesion with the transparent resin substrate. In this way, 3i on the side closer to the transparent resin substrate! The dielectric film of No. 1 is an oxide-based film to increase adhesion to the substrate, and
The second dielectric film is provided to have a predetermined thickness to increase moisture permeability and also to reduce deformation due to temperature rise (deformation due to difference in thermal expansion).

【Example】

FIG. 341 shows a schematic cross section of a magneto-optical disk as an optical information recording medium according to the present invention. Example 1, Comparative Example 1.2 1 is a transparent resin substrate, and a guide groove for tracking during recording and reading is provided in the upper part of the figure. 2 is the first dielectric film, which is a thin film mainly composed of ZrO2. 3 is a second dielectric film, which is a thin film mainly composed of Si and N4. Note that the first dielectric film is provided closer to the substrate 1 than the second dielectric film. 5 is a recording film, and 4 and 6 are thin films such as ceramics for protecting the recording film 5. 7 is a reflective film, and 8 is an overcoat layer made of ultraviolet curing resin or the like. A magneto-optical disk having the structure shown in FIG. 1 was manufactured by the following procedure. First, a polycarbonate material having a diameter of 130 mm was used as the substrate 1, and a protective film 4, a recording film 5, and a protective film 6 were sequentially formed on the front side, that is, the surface on the guide groove side, by sputtering. The protective film 4.6 is a silicon nitride film formed to a thickness of 8 nm, and the recording film 5 is a TbFeCo alloy film formed to a thickness of 30%.
Next, a reflective film 7 was formed to a thickness of . A CrAu alloy film with a thickness of 1100 nm was formed on the reflective film. Note that an overcoat layer 8 of ultraviolet curing resin or the like is normally provided, but it was omitted in the samples produced in the tests described later. On the other hand, a two-layer dielectric M2.3 was provided on the back side of the substrate 1. Here, the first dielectric film 2 was made of ZrO2 with a thickness of Ionm, and the dielectric film 3 of 342 was made of Si and N4 with a thickness of 200 nm, both of which were formed using a sputtering method. A sample having such a configuration, that is, a sample according to an example of the present invention is referred to as sample A (Example 1). Next, a sample as a comparative example was prepared as below, and a film similar to that of the sample A was placed on the surface side of the film 4.
7 and only the second dielectric film 3 was formed on the back side, in other words, a sample was fabricated as a sample having a configuration in which the dielectric film 341 was not formed. This sample is referred to as Sample B as Comparative Example 1. Furthermore, each film on the surface side was fixed to the samples A and B.
We prototyped a sample with the same configuration, but without any film on the back side. This sample is designated as Sample C as Comparative Example 2. The following tests were conducted on samples A and B%C prepared as described above. (Warp deformation test) Using the above three samples A, B, and C; Mechanical change (deformation) of the disk in an environment where temperature and humidity change
I looked into it. First, put the three samples A%B%C into a constant temperature and humidity chamber.
Next, the amount of change in the disk surface warpage was measured in real time by changing the temperature and humidity using a warp measuring device using laser light. Figure 2 shows the changes in the disk when the temperature is changed.
! Diagram J3 shows changes when humidity is changed. Note that the amount of deformation of the disk is determined by the radial warping angle (
Ti 1 t [mrad] ). In addition, the amount of concavity on the surface side is assumed to be positive, and the initial surface warpage angle is O (zero).
In FIG. 2, the line marked ``■'' represents that of Sample A, the line ``■'' represents that of Sample B, and the line ``■'' represents that of Sample C, respectively. In experiments where the temperature was varied, the humidity was set at 50% relative humidity at each temperature. As can be understood from Figure 2, in sample C, which does not have any film on the back side,
The warp angle of the disk surface changed as the humidity rose and fell. This is considered to be due to a difference in the coefficient of thermal expansion between the resin substrate 1 and the films 4 to 7 provided on the surface on the guide groove side. On the other hand, in Sample A1 and Sample B, almost no change in the warp angle was observed. In subsequent experiments in which humidity was varied, the temperature was fixed at 60°C. As can be understood from the N3 diagram, only sample C shows a large change in its warp angle over time, whereas
In Sample A and Sample B, there was almost no change. The change in Sample C is thought to be due to the fact that water absorption and dehydration occur in the resin substrate 1 as the humidity changes, and the resulting increase and decrease in deposition occurs at different rates on the front and back surfaces. (Temperature and Humidity Cycle Test) The following experiments were conducted on the samples A and B described above. Two samples A and B were placed in an automatically controllable thermostatic chamber and subjected to a temperature/humidity cycle test. Specifically, 20℃
After maintaining the temperature and humidity environment at 20% for 2 hours, the temperature was changed to 60℃ and 80% in 1 hour, this environment was maintained for 2 hours, and then the original temperature and humidity was changed to 20℃ and 20% within 1 hour. The idea is to return it to . This series of environmental changes was treated as one cycle and repeated while visually inspecting the appearance of the back surface of the disk, and in sample B, minute peeling and cracks were observed in the film after approximately 2,500 cycles were repeated. In contrast, sample A has at least 1000
No change occurred up to 0 cycles. In other words, this example demonstrated that not only does it not warp due to environmental changes in temperature and humidity, but it also does not peel or crack in the thin film even after repeated temperature and humidity cycle tests many times. . In addition, the first dielectric film 2 has a thickness of 1
It has also been shown that when the thickness is about 5 nm or less, the optical transmission loss becomes small. Example 2 Next, as samples for Example 2, we prepared several samples that had the same film structure as Sample A produced in Example 1, but had different film thickness ratios between the two dielectric films on the back side. I made a prototype. Specifically, the film thickness of 21 dielectric films 2 on the side closer to the substrate 1 was set to 15% m b 30 nm s and 50 nm s.
Prototypes were made with three different types: %m. The samples are named A-1, A-2, and A-3 in order of film thickness. (Light Transmission Measurement) For each of Samples A-1 to A-3 and Sample A, the light transmittance required for an optical disk substrate was measured. In this measurement, a constant amount of light flux was irradiated from the back side of the disk, and the reflected light from the recording film 5 and reflective film 7 on the front side was measured using a light meter on the back side. The results are shown in Table 1 below. Table 1 In the above table, the amount of reflected light is 1
．． It was set as 00. As can be understood from the values in Table 1 above, sample A-2
, A-3 caused a loss of light quantity. It is thought that this loss in light amount occurred because as the film thickness increased, the multiple reflection condition approached and the light transmission efficiency in the film decreased. In addition, when each sample A-1 to A-3 of this Example 2 was subjected to the warpage deformation test and temperature/humidity cycle test performed in Example 1, the same results as in Example 1 were obtained for each of them. Ta. As shown in Table 1, it was also shown that when the first dielectric film 2 had a thickness of about 15 nm or less, the optical transmission loss was reduced. Example 3 In this example, the first dielectric @2 is made of 5i02, and as in Example 1, its film thickness is 10%.
A film was formed using a sputtering method so that the thickness of the film was m. Since the other configurations are the same as those of the first embodiment, redundant explanation will be omitted. In this example, as in Example 1 above, a warp deformation test, a temperature/humidity cycle test, and a light transmission measurement were conducted under the same conditions, but the results were similar to those in Example 1 above. It was exactly the same as the case. That is, it was understood that in the optical information recording medium of the present invention, similar characteristics can be obtained whether the first dielectric film 2 is formed of Sin or ZrO2.

【Effect of the invention】

As described above, according to the present invention, at least a recording film is provided on one surface of a transparent resin substrate, and a transparent two-layer dielectric film is provided on the other surface, and the two-layer 8-electric material The main component of the layer closer to the substrate in the film is ZrO or 5i02
The main components of the other layer are Si and N4, so two layers of llj (Z r'-02 or Sin, film, and Si 3 Na l1l) are formed on the back side of the substrate. By providing this, it is possible to eliminate differences in moisture absorption resistance, coefficient of thermal expansion, etc. between the front and back surfaces of the optical information recording medium, in other words, the transparent resin substrate, so that deformation of the substrate can be sufficiently suppressed. Furthermore, even if severe environmental changes occur, the thin film will not peel or crack.

[Brief explanation of drawings]

Figure 's1 is a cross-sectional view showing the configuration of each embodiment 1.2.3 of the present invention, and Figure 2 is a graph showing changes in the amount of warpage of optical disk samples A, B, and C due to temperature changes. Figure 3 shows optical disc samples A, B, and C as humidity changes.
3 is a graph showing changes in the amount of warpage. (Explanation of symbols) 1... Transparent resin substrate, 2... Dielectric film, 3... Dielectric film, 5... Recording film.

Claims (1)

[Claims] (1) At least a recording film is provided on one surface of a transparent resin substrate, and a transparent two-layer dielectric film is provided on the other surface, and the side of the two-layer dielectric film that is closer to the substrate An optical information recording medium characterized in that the main component of one layer is composed of ZrO_2 or SiO_2, and the main component of the other layer is composed of Si_3N_4.