JPS6363142A - Optical recording medium - Google Patents

Abstract

(57) [Abstract] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to optical recording media, and in particular DRAW type (direct read) which records and reproduces information using a light beam.
After-light; Direct ReadAft
er Write) relates to optical recording media.

[Prior Art] Various types of DRAW optical recording media have been proposed in the past for recording and reproducing information using a light beam.

For example, a low melting point metal G film recording layer is provided on the substrate, and a light beam is irradiated according to the information to be recorded on the layer.
There is an optical recording medium that utilizes a shape change in which eight thin layers of low-melting metal are melted or evaporated by local heating to form holes, that is, recording bits.

On the other hand, there have been proposals for optical recording media that utilize changes in the optical characteristics of the recording layer without using such a recording method based on shape changes.
In the medium disclosed in the publication, recording is performed by locally crystallizing an amorphous recording layer by heating with a recording light beam, and optical communication between this crystallized recording area and other amorphous areas is performed. The records are read based on the difference in physical characteristics.

Further, as another example, for example, Japanese Patent Application Laid-Open No. 60-28045
As disclosed in the above publication, a first layer having a similar high transmittance is formed on a substrate having a high transmittance to a light beam used for recording/reproducing, and the first layer is easily connected to the first layer. A two-layer recording layer consisting of a second layer mainly composed of a low-melting metal that forms an alloy is provided, and this recording layer is heated by a recording light beam to locally separate the first layer and the second layer. There is an optical recording medium that performs recording by alloying the metal and the like, and utilizes changes in the conditions of reflection of the light beam between the alloyed part and other parts.

However, in the conventional optical recording medium described above, binary information is recorded depending on the presence or absence of deformed or altered parts in the recording layer, and one recording area contains many pieces of information. There was a problem in that it was not possible to record values (three or more).

On the other hand, as disclosed in Japanese Patent Application Laid-Open No. 60-242532, in an optical recording medium that records and reproduces information depending on the presence or absence of pits, the pit depth (expressed as an optical distance) is zero. a first information bit, a second information pit whose pit depth is approximately (2n+1)in/4 (n is an integer), and an optical distance from the depth of the second information pit. a third information pit that is shallow by a length within /4, and a fourth information pit that is deeper by a length that is within /4 at an optical distance than the depth of the second information pit;
There are four types of information depending on the pit depth, and the information is divided into two types.
A four-value recording/reproducing method has been proposed in which reading is performed using two photodetectors.

However, the proposal reported in JP-A-242532 mentioned above only discloses that a photoresist is used as an optical recording medium and recording is performed by adjusting the amount of recording light and exposure.

No proposal has been made regarding a DRAW type optical recording medium that records and reproduces four-value information using a light beam.

[Problems to be Solved by the Invention] The present invention provides a DRAW type optical recording medium that has a recording density much higher than that of the conventional DRAW type optical recording medium that records and reproduces information using a light beam as described above. The purpose is to provide

[Means for Solving the Problems] That is, the present invention provides an optical recording medium in which information is recorded and reproduced using a light beam, in which the recording layer is composed of three layers having different melting points, and the intensity of the light beam during recording is changed. Possibly 4
This is an optical recording medium characterized in that value recording is performed in rotation.

Hereinafter, the present invention will be explained based on the drawings.

FIG. 1 is an explanatory diagram showing an example of the layer structure of an optical recording medium according to the present invention. In the same figure 1.

1.2.3 each indicate the recording layer, 1 is the first recording layer, 2
is the second recording layer, 3 is the third recording layer, 4 is the substrate, 5 is the reflective layer, and the first recording layer l in the figure is irradiated with a light beam 7 of the recording/reproducing beam light. Ru.

The optical recording medium of the present invention includes a first recording layer, a second recording layer,
The melting point and film thickness of the third recording layer are Tl and T2, respectively.
When 1'h, dt, dz, and dz, the melting points of each recording layer have the relationship T1 < 2 < T3, and melt or evaporate at lower temperatures starting from the light beam irradiation side.
That is, it is made of a material that does not form pits at low temperatures.

Next, a method for recording four-level information on the optical recording medium of the present invention by changing the intensity of the light beam during recording will be explained with reference to FIGS. 2(a) to 2(d). FIG. 2(a) shows the state of the optical recording medium of the present invention before irradiation with the light beam, and FIG. 2(b) shows the temperature t of the recording layer by the irradiation with the light beam, T
This shows a state in which only the first recording layer of the recording layer is locally melted or evaporated by increasing the temperature to I<t<T2 to form pits 6.

FIG. 2(C) shows that the first recording layer and the second recording layer of the recording layer are heated by irradiating a light beam with a higher intensity than that of FIG. 2(b) to a temperature of 72 < t < 73. It shows a state in which pits 6 are formed by locally melting or evaporating.

Figure 2(d) shows that by irradiating a light beam with a higher intensity than that of Figure 2(c), the recording layer is heated to 13 or more and all three layers, the first to third recording layers, are locally melted. A state in which pits 6 are formed by evaporation is shown.

As described above, by irradiating the optical recording medium of the present invention with light beams having three different intensities during information recording, the temperature rise of the recording layer is controlled and the temperature rise in the recording layer is controlled.
), (c), and (d) can be recorded in one pit.

The depth of the pit recorded as described above (the optical distance) is the second In the case of Fig. 2(a), it is zero, in Fig. 2(c), it is approximately (2n+1)λ/2, and in Fig. 2(b), the length is shallower than that in Fig. 2(c) by within 1/4. In addition, in FIG. 2(d), the depth is within 1/4 of that in FIG.
It is possible to read out the information using a reproduction method using two photodetectors as disclosed in Japanese Patent No. 32, and it is possible to reproduce four-value information.

In the present invention, the materials forming the three Q layers need only have different melting points and satisfy the conditions of melting point T+ < Tt < Tx, and are not used as the recording layer of a normal base material R medium. A specific example of the material for the first, second and third recording layers is Se-Pb.
-Dinge, 5e-Bi-Pb, and the like.

[Function] Since the optical recording medium of the present invention is composed of three recording layers having different melting points, when the light beam is irradiated with varying intensities during recording, the recording pits formed in the three recording layers are Since pits are formed with predetermined depths that vary depending on the intensity of the irradiated light, 4-value information can be recorded in one pit, and 4-value recording can be recorded and played back. becomes.

[Example] Next, the present invention will be explained in more detail with reference to Examples.

Example 1 Polycarbonate (P) with dimensions of 4 cm x 6 cm
C) On the substrate, a 100 OA thick Aj) thin film reflective layer is formed by resistance heating using a vacuum evaporation film forming apparatus, and a 500 Å thick Te1J film that becomes the third recording layer is laminated thereon. Then, a pb film with a thickness of 500 A is made to become the second recording layer.
G film is laminated, and the thickness is 145O, which finally becomes the first recording layer.
4 of the media configuration shown in Figure 1 was obtained by laminating the Se thin film of A.
An optical recording medium capable of recording values was created.

Table 1 shows the melting point, film thickness, etc. of each layer.

When an optical recording medium prepared as shown in Table 1 L was irradiated with laser light using a semiconductor laser with a wave i of 780 QA and a spot diameter of 21, the intensity of the laser light was 5+.
Only 5el-NU, which is the first recording layer, was melted and evaporated with W, and pits were formed. Similarly, when the intensity of the laser beam is set to 7mW and the laser beam is irradiated, 7IS
The Se thin film of the first recording layer and the Pb thin film of the second recording layer were melted and evaporated to form pits. Furthermore, when the intensity of the laser beam was set to 9 mW, the recording layer from the first to the third recording layer was
All three recording layers up to the recording layer were melted and evaporated to form pits.

Regarding the four types of pits formed as described above, the wavelength is 780.
When reproduction was performed using a laser beam of 0 A, an output of only 4 could be obtained, and it was confirmed that 4-value information could be recorded and reproduced in one pit.

[Effects of the Invention] As explained above, the optical recording medium of the present invention is a DRAIII
By using three recording layers with different melting points as the recording layers of the DRAw type optical recording medium, four-value information can be recorded in one pit, resulting in a higher recording density than the conventional DRAw type optical recording medium. It can be much improved.

For example, when 10 pits are used, the amount of information that can be represented by binarization is 210 pieces, but in the case of quaternary conversion, it is 410 pieces, and it is recognized that the recording density is much improved.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing an example of the layer structure of the optical recording medium of the present invention, and FIGS. 2(a) to 2(d) are sectional views showing pits of four-value recording information. 1... First recording layer, 2... Second recording layer, 3
...Third recording layer, 4...Substrate. 5... Reflective layer, 6... Pit, 7...
light beam

Claims (2)

[Claims] (1) An optical recording medium that records and reproduces information using a light beam, characterized in that the recording layer consists of three layers with different melting points, and that four-value recording is possible by changing the intensity of the light beam during recording. optical recording medium. (2) In the recording layer, the melting point and film thickness of the three recording layers are T_1 and T_, respectively, in order from the information recording side.
2. When T_3 and d_1, d_2, d_3, T
A patent where _1<T_2<T_3 and d_1+d_2=(2n+1)λ/4 0<d_2<λ/4 0<d_3<λ/4 (where λ is the wavelength of the reproduction light beam and n is an integer) An optical recording medium according to claim 1.