FR2531798A1 - - Google Patents

Abstract

OPTICAL RECORDING MEDIUM WHICH INCLUDES A SUBSTRATE 12, A LIGHT-REFLECTING LAYER 16, OVERLOOKING A FLAT SURFACE OF THE said SUBSTRATE AND A LIGHT-SENSITIVE LAYER 18, ON THE LIGHT-REFLECTING LAYER 16, THIS RECORDING MEDIA. THAT IT INCLUDES: A TRACING LAYER 20 ARRANGED ON THE LIGHT REFLECTING LAYER 16 AND INCLUDING ONE OR MORE OPENINGS 22, AND A LIGHT ABSORBING LAYER 24, DEPOSITED ON THE TRACING LAYER 20 AND ON THE LIGHT REFLECTING LAYER 16, IN THE OPENINGS 22 OF THE TRACING LAYER 20 SO AS TO FORM A FIRST REGION 26 AND A SECOND REGION 28 IN THE LIGHT SENSITIVE LAYER 18, THESE REGIONS BEING SUCH THAT THE REFLECTIVITY OF THE FIRST REGION 26 IS LOWER THAN THE REFLECTIVITY OF THE SECOND REGION 28 FOR A CERTAIN WAVELENGTH.

Description

The present invention relates to an optical recording medium as well

  than a disc containing information, comprising a light-sensitive layer having optical properties with spatial variations, this medium

  and this disc being in particular useful for carrying out a radial grid of the information

  The invention also relates to a method for producing such a

  optical medium and an information disc produced from this medium.

  U.S. Patent No. 4,097,895 describes a two-layer optical recording medium which includes a light reflecting layer covered with a light absorbing layer U.S. Patent No. 4,216,501 describes a

  three-layer optical recording medium having a space layer-

  transparent material interposed between the reflective and absorbent layers described in US Pat. No. 4,097,895 The information is recorded in one or other of these media by locally varying the properties

  optics of this medium, for example by fusion, ablation, or by any other pro-

  assigned to modify the optical properties of the absorbent layer.

  The resulting modification of the transmission power or the reflectivity of the recording medium in the parts of this medium thus exposed during the

  processing specified above, is dete tae in order to read the recorded information.

  Such recording media have substantially uniform optical properties and structure before exposure and do not include

  therefore no means to define a track (or groove) before recording

  trement of information A recording medium which comprises a substrate provided beforehand with a groove, includes such means but it does not have the flexibility Z 5 necessary to allow modifications to the track or the

  groove or to allow identification after manufacture.

  According to a variant of the technique set out above, a part is removed.

  tie of the light absorbing layer, using a laser beam, which

  allows to make guard bands between the light absorbing tracks.

  There is thus obtained a medium which has the desired flexibility, but however being this medium has the disadvantage that the tracks can / damaged by the formation of the guard bands and the latter cannot be recorded later. It is therefore necessary to produce a medium recording with guard bands in which the tracks

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  absorbing light are not disturbed and in which the informa-

  tion can / registered at a later stage.

  This invention therefore relates to an optical recording medium per-

  in which the light-sensitive layer comprises a guide or tracing layer, comprising one or more openings passing through said layer, and an absorbent layer disposed above the layer of

  tracing and said openings, so as to form a first and a se-

  conde regions with different thicknesses so that the reflectivity of the

  first region is weaker than that of the second region.

  The invention also relates to a disc containing information which includes

  carries the optical recording medium defined above and in which the information

  mation is registered in the first region.

  Finally, the subject of the invention is a process for producing the recording medium.

  very optical defined above and which consists in sequentially depositing a reflective layer and a tracing layer on a substrate, making one or more openings in the tracing layer and depositing a layer

  absorbent on the tracing layer and on its openings.

  Other characteristics and advantages of the present invention emerge

  from the description given below with reference to the attached drawing which

  illustrates various exemplary embodiments devoid of any limiting character.

On the drawing:

  Figure 1 is a plan view of a bi-optical recording medium

  layers according to the present invention: FIG. 2 is a cross-section view of a three-layer optical recording medium according to the present invention and FIGS. 3 and 4 are cross-section views of two examples of

  production of an information disc according to the invention.

  In FIG. 1 the optical recording medium 10 - comprises: a substrate 12; a substitution layer 14 disposed on a flat surface of the substrate 12; a layer 16 reflecting the light, covering the surface of the layer 14; a layer 18 sensitive to light, disposed on the surface

  layer 16 reflecting light, this layer 18 comprising a layer

  tracking line 20 provided with one or more openings 22 and, a light-absorbing layer 24 X disposed above the layer 20 and the reflective layer 16 in the openings 22, so as to produce recording tracks 26 and guard bands 28 In Figures 2, 3 and 4 the identification of elements common to the environment

  optical recording 30 and information discs 40 and 50, respectively-

  ment, is the same as that used for the optical recording medium 10 described above with reference to FIG. 1.

  In the embodiment shown in FIG. 2, the recording medium

  optical registration 30 also includes a spacer layer 32 i, nter-

  placed between the reflective layer 16 and the light-sensitive layer 18.

  A barrier layer 34 is disposed above the absorbent layer 24 and

  an upper layer 36 covers the barrier layer 34.

  In FIGS. 3 and 4, the information discs 40 and 50 comprise the optical recording medium 10, represented in FIG. 1, and the optical recording medium 30, represented in FIG. 2, the information being recorded in the form of one or more zones 42 of the absorbent layer 22, in the recording tracks 26 which have optical properties

  different from those of the remaining part of the absorbent layer 24 The pro-

  optical properties different from the zones 42 of the light-sensitive layer 18 may come from an irreversible deformation of the absorbent layer 24, this ddf Drmation can for example be in the form of a well

  or of a bubble produced in this layer, or be due to: a modification

  optical constants of the absorbent layer 24, resulting for example from a modification of the degree of crystallinity of the absorbent layer, as described in particular in the American patent application No. 254-469 filed on April 16, 1981 in the name of Spong and other The presence or absence of a change in the optical properties of the light sensitive layer 18 causes a change in the reflectivity (reflectivity) of the medium

  the length of the zones 42, as well as their spacing provided

  being an indication of the information recorded.

  Information in particular in the form of ID numbers

  track specification, can also be saved in guard bands

  28, either before or after recording the information in the recording track

  record 26 Such information can be in the form of one or more zones 44 of the strip 28, these zones having properties

  optics different from the rest of this guard band.

  The substrate 12 may consist of glass, of a plastic material for example of polyvinyl chloride or of polymethylmethacrylate, or of a metal for example of aluminum The substitution layer 14 consists of a non-conforming coating of a material plastic, for example an epoxy resin or an acrylic resin having a microscopically smooth surface, this material being able to be deposited on the surface of the substrate 12 before

  deposition of the reflective layer 16.

  The reflective layer 16 reflects a relatively large fraction (preferably at least 50%) of the incident light at the wavelength of the recording light beam and this reflective layer can be made of a metal, for example d aluminum or gold or be made under

  the shape of a multi-layer dielectric reflector.

  The spacer layer 32 of the recording medium 30 is substantially transparent and non-diffusing for the wavelengths of recording and reading information. Among the materials suitable for producing this layer 32, mention may be made in particular of organic materials such as in particular fluorocarbon and hyclcarbon polymers and inorganic materials such as oxides of silicon, titanium, magnesium and aluminum These materials can be deposited on the reflective layer

  16 using known deposition techniques.

  The tracing layer 20 absorbs the light having the wavelength of the light used to form the openings. This layer 20 can be produced from an organic material or from an inorganic material.

  suitable inorganic materials include bismuth, titanium, rho-

  dium, tellurium or selenium and chalcogenide alloys containing tellurium or selenium This layer 20 can have a thickness comprised

  between 20 and 150 nanometers and preferably this thickness is chosen ma-

  negatively that the reflectivity of the combination of the reflective layer 16 and the tracing layer 20 is reduced for the wavelength used for the formation of the openings 22 These openings 22 may have the form

  of a spiral or circular groove, continuous or interrupted.

  The absorbent layer 24 is made of a material which is sensitive to the recording light beam and this layer can be made of an organic material or an inorganic material. Among the suitable inorganic materials there may be mentioned in particular bismuth, rhodium. , the

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  titanium, tellurium or selenium and chalcogenide alloys containing tellurium and selenium The thickness of the absorbent layer 24, in the recording tracks 26, is such that the reflectivity of the optical recording medium 10 or 30 is reduced and preferably minimized, corresponding to the anti-reflection conditions of the recording tracks Z 6 With regard to the recording medium 10, the optimal thickness can be determined from the optical constant S of the layer reflective 16, absorbent layer 24 and any other layer disposed above said layers for a particular wavelength using known methods. Typically, this optimum thickness is between 20 and 100 manometers. The sum of the thicknesses of the tracing layer 20 and the absorbent layer 24 in the guard strips 28 is such that the reflectivity, for the length

  particular, is larger than that of the recording tracks 26.

  With regard to the optical recording medium 30, the thickness of the absorbent layer 24 can be determined from the thickness of the spacer layer 32 and the optical constants of the reflective layer 16, of the layer d spacing 32, of the absorbent layer 24 and of any other layer surmounting said layers Typically, this thickness is

  between 3 and 100 nanometers.

  The barrier layer 34 consists of a light-transmitting material which constitutes a chemical and thermal barrier between the layer Ab B Orbante 24 and the upper layer 36 Preferably, this layer 34 consists of an aluminum oxide, of magnesium , silicon or titanium and its thickness is between 50 and 5 È O nanometers approximately The upper layer 36

  is made of a light transmitting material, for example a rubber

  silicone cauldron and its thickness is preferably between 500 and 1500 micrometers approximately A combination of barrier and upper layers

  is described in U.S. Patent No. 4,101,907.

  The invention described above provides a recording medium, the

  light-sensitive layer has thick and thin regions comprising

  both different reflectivities due to their differences in thickness.

  The example of embodiment described above corresponds to the case where the thickness

  of the absorbent layer of the recording layers is such that the reflection

  activity in this region is reduced compared to that of the guard bands.

  In an arrangement corresponding to a variant, the optical constants

  and the thicknesses of the tracing and absorbent layers are such that the reflection

  guard strip activity is lower than that of recording tracks

  the roles of the recording tracks and the guard bands then being reversed.

  sés Such a variant may be useful for certain applications However

  the first embodiment is preferred since the amount of rna-

  material of the recording tracks, which must be modified, by fusion, ablation

  or any other process for recording information is reduced to a minimum.

  Likewise, the information is recorded in a layer of material which has not been disturbed after the deposition, while damage to the tracing layer may result from the implementation of the groove formation process. When a C recording, playback, or recording erase system is in operation, a recording, playback, or erasure light beam is centered on a track or groove since the t

  reflectivities of the two regions of the optical recording media and of the

  ques of information according to the invention differ from each other, the radial displacement of this beam, or of a track or groove detection beam, can

  be detected as a change in the reflected intensity of the beam.

  This modification can be transformed into a proportional electrical signal

  when the beam moves relative to the track or the train path, this electric signal

  stick being in turn used to correct the position of the recording, reading or erasing light beam,

  The method of manufacturing the optical recording medium according to the pre-

  sente invention comprises the following steps: depositing a substitution layer on the surface of a substrate; deposit of a light reflecting layer on the surface of the substitution layer; deposition of a tracing layer of 4 bant material on the light-reflecting layer formation of one or more openings through the tracing layer deposit of an absorbent layer on the tracing layer and in the openings made in the latter, and

  deposition of barrier and upper layers on the absorbent layer.

  According to an embodiment of this method, the openings made in the tracing layer can be formed by ablation or by fusion and

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  removal of the molten material, using a laser beam whose length

  waveform may be the same or different from that used during the last recording

  / be a registrar of information; Alternatively, these openings can / made

  using well known techniques of chemical attack and photolithography

  phie. It remains to be understood that the present invention is not limited to the various embodiments and implementations described and represented.

  here, but that it includes all variations.

REV ENDICAT IONS

  1 Optical recording medium which comprises a substrate (12), a

  light reflecting layer (16), surmounting a flat surface of said substrate

  trat and a light-sensitive layer (18) on the light-reflecting layer 6), this recording medium being characterized in that it comprises a tracing layer (20) disposed on the light-reflecting layer ( 16) and o mportant one or more openings (2), and an abs layer orbiting the

  light (24), deposited on the tracing layer (20) and on the reflective layer

  sant light (16), in the openings (22) of the tracing layer (20) so as to form a first region (26) and a second region (28) in the light sensitive layer (18), these regions being such that the reflectivity of the first region (26) is less than the reflectivity of the second region

  (28) for a certain wavelength.

  2. An information disc comprising a substrate (12), a light reflecting layer (16), disposed on a flat surface of the substrate (12) and a light sensitive layer (18), having a track or information groove, surmounting the light reflecting layer (16), this disc being characterized in that it comprises a tracing layer (20) deposited on

  the light reflecting layer (16) and comprising one or more openings

  tures (22), and a light absorbing layer (24), deposited on the tracing layer (20) and on the light reflecting layer (16), in the openings (22) of the layer (20), so producing a first region (26) and a second region (28) in the light-sensitive layer (_ 8), these regions being such that the reflectivity of the first region (26) is less than the reflectivity of the second region (28) for a certain wavelength and, in that the information track comprises one or more zones (42) of the first region (26)

  which have different optical properties from those of the rest of the first

first region (26).

  3. Optical recording medium according to claim 1, characterized in that it comprises a spacer layer (32) interposed between the layer

  reflecting light (16) and the tracing layer (20).

  4. Information disc according to claim 2, characterized in that it comprises a spacer layer (32) interposed between the reflective layer

  the lumen (16) and the tracing layer (20).

  Recording medium and information disc according to one of the res

  indications 3 or 4, characterized in that the spacer layer (3 Z) is

  consisting of a material which is chosen from the group which comprises the oxides of

  silicon, magnesium, aluminum, and titanium.

  6 recording medium and information disc according to one of claims 1 or 2, characterized in that the tracing layer (20) and the absorbent layer (24) each consist of a material chosen from the group which

  includes bismuth, titanium, rhodium, tellurium, selenium and

  chalcogenide alloys containing tellurium or selenium.

  7 Recording medium and information disc according to any one

  claims 1 to 4, characterized in that the second region (28) is

  provided with an information track or groove (44) which is constituted by one or more zones of the second region (28) which have optical properties

  different from the rest of the second region (28).

  8 A method of producing an improved optical recording medium which consists in depositing a light reflecting layer on the surface of a substrate; to deposit a light absorbing layer on the

  surface of a tracing layer and in openings made therein

  tracing layer, this process being characterized in that it consists in depositing a tracing layer on the light-reflecting layer and in forming a

  or several openings through this tracing layer.

  9 Method according to claim 8, characterized in that the openings made in the tracing layer are obtained by fusion or ablation of

  this layer by a process of exposure to a light beam.