JPS6140195A - Optical recording medium - Google Patents

Abstract

PURPOSE:To suppress oxidation in air, by using a thin Ge film as a recording layer to be provided with pits by a laser beam. CONSTITUTION:A disk base 1 is provided with a guide groove simultaneously with molding the base 1 by injection molding. A transparent acrylic resin or polymethyl methacrylate (PMMA) is used as a material for the base 1. By placing the base 1 in an evacuated bell-jar and while rotating it at a speed of, for example, 50rpm, a Ge source 2 is heated by resistance heating or electron ray heating to vapor-deposit Ge on the back side of the base 1, whereby a broad uniform thin Ge film is obtained. A laser beam 3 is focused on the thin Ge film 5 through the base 1 by an objective lens, thereby providing pits with a diameter of about 1mum. The power of the recording laser is preferably not lower than 12mW, such a laser output being easily obtained by, for example, a GaAlAs double-heterojunction semiconductor laser. The laser power for reproduction may be the same as in a conventional system, i.e., about 2mW.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to optical recording media, particularly for additional recording (DRAW).
This type of optical recording medium is related to ζ.

Conventional technology In DRAW type optical recording media, typically optical discs, which can be played back immediately after recording and additional recording can be made according to the required number ζ, a thin film recording layer on a transparent substrate is irradiated with a laser beam. Pit is formed by converting light energy into thermal energy. That is, the recording layer is melted by the heat generated by the laser beam irradiation, and the melted portion is pulled toward the surrounding area by surface tension, forming a hole or pit, and only a bulge is formed around the hole or pit. This type of recording layer has (a) high light absorption rate;
(b) low melting point; (c) low thermal conductivity;
) Required properties such as a well-shaped pit,
Generally, a thin film of tellurium (Te) based material is used. In a normal Te thin film, a semiconductor laser beam with a wavelength of 8301 m is focused by an objective lens with NAo of 5, and the incident power is 5.
Record in mW and read in zmw.

Problems to be solved by the invention Te satisfies the above (b) and f present conditions and has good recording sensitivity, but the drawback is that it belongs to the VIA oxygen group, is metallic and strong, and is easily oxidized in the atmosphere. be. It is known that oxidation can be suppressed by adding a small amount of 're-Se, but 're-se has another disadvantage in that it has a large crystal grain size and a high noise level.

Means for Solving the Problems As a result of extensive research into optical recording media using various elements, compounds, and oxides, the inventor found that Ge has a relatively high melting point (Gl: 936°C, Te: 450°C). ℃), but it is stable both in the air and in water.
It is not easily affected by acids such as hydrochloric acid and sulfuric acid, and with recent improvements in semiconductor lasers, high output laser light can be easily obtained.
The present invention was achieved by focusing on the fact that a high melting point, ie, a large required laser power, is not such a problem. That is, the present invention solves the above-mentioned problems by using an optical recording medium characterized in that the recording layer in which pits can be opened with a laser beam for recording information is made of a Ge thin film.

Embodiment A method of manufacturing a DRAW type optical disk according to the present invention will be explained with reference to FIG. Guide grooves are simultaneously created on the disk substrate l by injection molding, and are made of transparent acrylic resin or polymethyl methacrylate (PMMA), which is suitable for mass production.
may be used. When the substrate 1 is placed in a vacuum belt chamber and rotated at a rotation speed of, for example, 50 rpm, Ge in the evaporation source 2 is heated and evaporated by resistance heating or electron beam heating to be evaporated onto one surface of the substrate (the back surface in FIG. 1). A wide and uniform Ge thin film is obtained.

For optical discs made in this way, a second
As shown in the figure, a laser beam 3 is focused by an objective lens 4 to form pits with a diameter of about 1 μm in the Ge thin film 5 through the substrate 1. Since the Ge thin film has a relatively high melting point, it requires a higher recording laser power than a Te-based material thin film (preferably 12 mw or more, as described later). However, this level of laser output cannot be achieved using recent semiconductor lasers, such as GaAtA.
This can be easily obtained using an S double heterostructure semiconductor laser. The laser power during reproduction may be approximately 2 mW as in the conventional case. Note that 1' and H in the figure are the back side of the disc.
6 is a spacer.

FIG. 3 shows the C/N characteristic A of the DRAW type optical disk according to an embodiment of the present invention, and that of the conventional DRA using a Te thin film.
A comparison of the C/N characteristics of W-type optical discs is shown below. Characteristic A
is the thickness of the Ge thin film 5 in FIGS. 1 and 2.
0A to 500A, wavelength of laser beam 3 is 780μm, NA of objective lens is 0.55, test signal frequency is 3MHz
, reproduction laser power Pr is 2m% II (linear velocity is g, B
The C/N with respect to the recording laser power PW is shown under conditions of m/s. Characteristic B has a 'reTe thin film thickness of 40 O.
A, laser beam wavelength is g 3 Q nm1 objective lens N
The C/N with respect to the recording laser power Pw is shown under the following conditions: A is 0.5, the test signal frequency is 3MH2, the reproduction laser power Pr is 2 mW, and the linear velocity is l 3 m/s. Third
As can be seen from the figure, the DRAW type optical disc according to the present invention requires relatively high recording laser power, but the PW is 12 m.
The C/N reaches 50 dB at W, which is equivalent to a Te thin film optical disk.

Further, even when the optical disk according to this example was left in the atmosphere for 6 months, virtually no deterioration was observed. On the other hand, T
If an e-thin film optical disk is left in the atmosphere, its transmittance will change after about a month due to deterioration due to oxidation.

Note that the present inventor has developed the Ge thin film according to the present invention.

(2) It has been found that a stable recording layer can be obtained even when a group V metal, metalloid or oxide thereof is added. This is considered to be based on the property of ce to form relatively many compounds and solid solutions.

It is also possible to apply the present invention to a multilayer recording film structure as shown in FIG. In FIG. 4, substrate 1 and Ge
A transparent layer 14 (with a thickness of λ/4n) is interposed between the thin recording layer 5 and the thin recording layer 5.
n: refractive index of transparent layer, λ: wavelength of readout light), an AL light reflecting layer 15, and an organic undercoat layer 16 are provided. At the pits 10, the incident light for reading is reflected by the At reflective layer 15 and returns as it is, but at locations other than the pits 10, the light reflected by the recording layer and the light reflected from the At reflective layer cancel each other out and are reflected. A strong contrast can be obtained because a protective film is formed. Conventionally, a recording layer 15 using Te is known, but a protective layer 17 is required to prevent oxidation. However, according to the present invention, since the Ge thin film has weather resistance, the protection j-17 can be omitted.

Effects of the Invention As mentioned above, the optical recording medium of the Ge thin film according to the present invention has excellent weather resistance while providing a C/N equivalent to that of a Te thin film.
It also satisfies the requirements of high stability and high quality.

[Brief explanation of the drawing]

FIG. 1 is a partially exploded perspective view for explaining a method of manufacturing a DRAW type optical disc according to the present invention iζ. FIG. 2 is a schematic cross-sectional view for explaining recording and reproducing of a DRAW optical disc according to an embodiment of the present invention, and FIG. 3 shows the C/NnI properties of a DRAW optical disc according to an embodiment of the present invention in comparison with a conventional example. 4 and 4 are schematic cross-sectional views showing an example in which the present invention is applied to a multilayer recording film structure. 1...PMMA substrate, 5...CE thin film, 3...Laser light, 4...Objective lens. Patent Applicant NEC Home Electronics Co., Ltd. Agent Patent Attorney Takashi Sasaki Figure 1 Figure 2 Figure + Figure

Claims (2)

[Claims] (1) In an optical recording medium having a recording layer in which pits can be opened with a laser beam to record information, the recording layer is
An optical recording medium characterized by being made of e-thin film. (2) The optical recording medium according to claim 1, wherein the Ge thin film is formed on a transparent acrylic substrate to a thickness of 300 Å to 500 Å.