CA1095782A

CA1095782A - Method of manufacturing a data carrier which can be optically read and a data carrier obtained by said method

Info

Publication number: CA1095782A
Application number: CA275,610A
Authority: CA
Inventors: Claire Lemonon
Original assignee: Thomson-Brandt SA
Current assignee: Thomson-Brandt SA
Priority date: 1976-04-06
Filing date: 1977-04-05
Publication date: 1981-02-17
Also published as: DE2715520A1; JPS5366704A; FR2347704A1; GB1571948A; FR2347704B1

Abstract

A METHOD OF MANUFACTURING A DATA CARRIER WHICH CAN BE
OPTICALLY READ, AND A DATA CARRIER OBTAINED BY SAID METHOD

Abstract of the Disclosure The present invention relates to a method of manufacturing data carriers optically readable, which incorporates a phase during which a layer formed of decomposed oxides is produced from oxides by vaporisation under vacuum. This layer, locally heated by a recording beam modulated in on/off fashion, is locally reoxidized. The layer then has a transparency and refractive index which vary from the non-heated zones to the heated and reoxidized zones.

Description

1C~957l~Z

The present invention relates to carriers upon w~ich high-density information can be recorded, these data carrier~ being capable of optical read-out by mean~ of concen-trated radiation.
Optically readable data carriers comprise, generally speaXing, a layer in which a characteristic element, capable of modulating the read-out radiation, can v~ry between two values. This element may be the refractive index, the thickness, the transmission factor or the reflexion factor for example.
Recording of information leads to the formation of an impression constituted by domains of variable size-~ in which the characteristic element passes qucce~sively from one value to the other.
In particular, photosensitive resin layers and thin layers of diazo compound~, have been used.
The action of a recording beam on the~e layers - makes it possible either to locally diYsolve the resin (in which case thickne~s variation~ are produced) or to block the formation of a pigment in the case of diazo compound~ (in which case variations in the transmission coefficient are obtained). A data carrier covered with a layer of metal having a low melting point ha~ al~o been use : under the action of the recording beam, the metal melts or volatilises. If the metal layer has been completely pierced by the action of the recording beam, the tran~mi~ion factor i~ equal to 1 or to O in accordance with whether the success~ve domain~ have or have not been Rubjected to the beam. If, by contra~t, the layer is not~

578~

completely pierced~ then a reflective layer is produced which contains crests and troughs~
Chemical processes, local dissolving of a resin layer or the creation of a pigment, have the drawback that they require a developin~ phase and this makes it impossible to effect read-out im~ediately after recording.
The thermal method consists in volatilising a low melting point metal layer and produces a data carrier whose resolution is low. In other words, melting of the metal is accompanied by a phenomena of capillarity and later heat diffusion beyond the heated zone~ which affect the sharpness of ~he recorded domain. The information density which is capable of being recorded is thus low.
~oreover, all data carriers obtained by the aforementioned methods have the drawback of being fragile and consequently difficult to store unless they are subjected to a supplementary process consisting for example of covering them with a protec-tive transparent layer. Finally, the layer obtained in this way (photosensitive, diazo or metallic) lacks chemical stability and may kherefore change in the course of time, making it extremely difficult to store these data carriers for long periods of time, whether recorded or not.
The object of the present invention is a data carrier not subject to these drawbacks. In particular, the layer on which the domains are recorded and whose characteristic element may be the refractive index, the transmission coefficient etc., is stable before and after recording and the data carriers which have these layers can therefore be readily stored. Moreover, the recording process, which is matched to the recording of layers of this kind, does not involve the necessity of any developing operation.
According to the invention, there is provided a method of manufacturing a data carrier which can be optically read comprising a phase during which a material made up of at least one oxide, chosen from amongst the following : titanium oxide, iron oxide, chromium oxide, manganese oxide, tin oxide and zirconium oxide? is deposited by vaporisation under vacuum, upon one face of a substrate, said vaporisation being performed with a loss of oxygen atoms, the deposited layer thus being formed of a sub-oxide.
For a better understanding of the invention and to show how the same may be carried into effect, reference will be made to the following description and the attached drawings among which :
Fig. 1 illustrates explanatory graphs ;
Fig. 2 illustrates the first phase of the process of manufacturing the data carrier ;
Fig. 3 illustrates the phase of recording the data carrier ;
Fig. 4 illustrates a device for reading out thls kind of data carrier.
The invention is based llpon the optical properties of the oxides and the sub-oxides obtained from the latter.
The explanatory graphs of Fig. 1 illustrate one of these properties, which is the variation in the transmission of the radiation by more or less oxidized mixtures as a function of the wavelength of the radiation passing through them.
The mixture used is a mixture of titanium oxide Ti 2 and iron oxide Fe2 3 comprising 30 ~ of titanium oxide and 70 % of iron oxide.
The graph (a) illustrates the variations in the coeffi-cient of transmission of a layer around 500 angstrom units thick, of a decomposed mixture of this kind, that is to say a layer which has lost oxygen atoms as a consequence of a process which may for example be vaporisation under vacuum The graph (b) illustrates the variations in the coeffi-cient of transmission of the same layer, this mixture having been reoxidized by the capture of oxygen atoms from the ambient air at a temperature of around 300C.
The decomposed mixture is brown and particularly absorbent for wavelengths in the neighbourhood of and less than 4 500 angstrom units (blue and violet) and its transmission coeffi-cient increases slowly for longer wavelengths. ~he reoxidized mixture has a transmiss;on coefficient slightly greater than that of the decomposed mixture, for wavelengths around and

2~ less than ~ 500 angstrom units, but increases quite rapidly with wavelength to reach o.8 at 6 300 angstrom units. The mixture then has an orange colour. There is at this point an increase o around 30 % in the light intensity transmitted by the reoxidized layer, in relation to that transmitted by the decomposed la~er.
To this variation in the transmission coe~ficient (and absorption) of the oxide mixture~ there is added a property of 1~9578Z

variation in the refractive index of the mixture depending upon whether or not i~ is decomposed or reoxidized. Thus, in the case of the aforesa1d mixture a the refracti~e index of the decomposed mixture is equal to 2 whilst that of the reoxidized mixture is equal to 2.4. One or the other or again both of these ~ptical properti~es can be used for the optical read-out of a data carrier comprising domains which are alternately formed by decomposed oxides or sub-oxides, and oxides.
To obtain this kind of data carrier, the manufacturing method described below can be used. In a first phase, illus-trated in F'ig. 2, an appropriate substrate 1 constituted for example b~ a perfectly flat polished glass disc~ is arranged in an evacuated enc:lose 2 containing a high vacuum, for example 10 6 mm of mercur~. If it is required tc produce a data carrier which can be read by a reflexion, then a reflec-tive substrate must be used~ for example a previously metalli-sed substrate. A vaporisation source 3 containing the mixture of oxides to be deposited upon one face of the substrate, emits a stream of particles towards the latter. This vaporisation gives rise to a loss of ox~gen akoms and the mi~ture deposited on the substrate is oxygen deficient. If the source comprises a rnixture of rl`i 2 and Fe203, the mixture deposited contains molecules of Ti O and molecules of Fe304, and more oxidized molecules are ]ef~. The composition of the mixture is non-stoichio-metric. The thickness of the deposited layer 4 should be appropriately selected if the thickness is too large the radiation will be totally absorbed even at the reoxidized zones 1~5782 whilst if it is too smallg the variation in the luminous inten-sity transmitted, from the sub-oxidized zones to the reoxidized zones, will be too weak to be detected at the time of read-out-The thickness is therefore chosen so that t~e absolute varia-tion is maximal at the time of read-out.
At completion of this first phase, the substrate upon which the layer of decomposed oxides (or sub-oxidesj has been deposited, can be stored for a very long time under normal temperature conditions.
The recording of this kind of data carrier is performed by means o a device of the kind shown schematically in Fig. 3 It comprises a radiation source of LASER type, 5, emitting the radiation beam 6. The source should have a sufficient power for the radiation which it emits to locally raise the layer of sub-oxides to an adequate temperature and bring about the oxidation of the layer. The temperature will typically be of the order of 200-300C. The LASER source used for recording thus has a power of some tens of milliwatts. Its wavelength is a matter of arbitrary choice. The radiation is modulated by means of an optical modulator 7 which is additionally supplied with the electrical signal S which is to be optically recorded on the data carrier. This recording radiation, modu-lated in on/off fashion, is reflected by a mirror 8 and concen-trated by an ob,jective lens ~ on the sub-oxide layer 4 carried by a substrate 1 rotating about its axis at angular speed ~
The domains which receive the radiation heat up and the oxygen atoms present in the ambient air are captured by the molecules l~9S782 of the layer. The layer locally changes colour and, as descri-bed before3 its opkical properties are modified.
The thus recorded data carrier is highly stable at ordinary temperatures since the chemical reaction can only take place within a fairly high temperature range. ~iloreover, the oxide layer is extremely hard both in the highly oxidized zones and in the sub-oxidized ~ones. Consequently, it is highly resistant to abrasion by dust and can readily be cleaned. The optical power required for this recording, some tens of milllwatts, is substantially smaller than that required in ablation techniques. Finally, ~s indicated earlier, the wavelength of the L~SER source used for recording, is not critical.
This kind of data carrier is particularly suitable for professional equipment since the recorded information can be read out immediately after recording.
Fig. 4 illustrates a device for reading out a recorded disc, the disc being assumed to be readable by reflexion. It comprises a read~out LASER source 10 of low power, typically 0.7 milliwatts, operating at a wavelength of around 6 300 angstrom units, emitting radiation which is reflected by a mirror 11 on to the recorded face 4 of the data carrier. The radiation passes through a partially reflective plate 12, a read-out objective lens 13 and is ~ocused at point 0. The data carrier rotates about its axis at the angular speed ~. The radiation passes through or is partially absorbed by the thin layer and is reflected , it passes through the objective lens 13 again, lt~7~32 is reflected by the partially reflective plate 12 on to a read-out cell 15 and the latter furnishes an amplitude-modula-ted signal L which translates the impression recorded on the disc in the situation where the disc is read out by variation in amplitude of the radiation emerging from the oxide layer.
In fact, the variation in refractive index of the oxide means that the emergent beam is modulated in amplitude and phase.
The read-out of data carriers of this kind can therefore be performed either by reflexion or by transmission depending upon the type of substrate (reflectïve or otherwise) upon which the oxide layer has been deposited~ and in each case read-out can be performed in amplitude or in phase. The sub-oxide layer which has been locally reoxidized cannot be returned to its initial state. Consequently~ discs of this kind can only be used as dead stores.
Data carriers of this kind are perfectly suitable for the production of special recordings in small numbers of copies, that is to say particularly suitable for the profes-sional field but are not very well suited to the reproduction of a large number of copies. In other words, a disc comprising an oxide layer carrying information, cannot be reproduced by a conventional photographic technique since the known oxides are too absorptive at the actinic wave]engths located in the violet range of the spectrum.
This kind of duplication is possible, however, but requires the use of layers formed of diazo compounds sensitive to higher wavelengths (red~ which do not belong to the current techniques.

~95782 The invention is not limited to the embodiment and manu-facturing process described. In particular~ a glass substrate has been described but the substrate used could be of any kind, rigid or flexible. ~loreover, the indicated mixture of oxides is not the only one which can be used. Other oxides possess the property o having a transmission coefficient which varies in accordance with the oxygen content, this content being capable of increase by heating~ as well as the property of having a refractive index likewise variable as a function of the oxygen content. By way of example, it is possible to quote chromium oxide, manganese oxide, tin oxide and zirconium oxide or mixtures of these oxides if capable of mixing. It is possible to add to these oxides an element which promotes the oxidation reaction.
It should be noted that at the time of recording, if the air in the neighbourhood of the layer contains insufficient oxygen, it is possible to carry out recording in an oxygen -enriched atmosphere.

Claims

WHAT I CLAIM IS :

1. A method of manufacturing a data carrier which can be optically read comprising a phase during which a material made up of at least one oxide, chosen from amongst the follo-wing : titanium oxide, iron oxide, chromium oxide, manganese oxide, tin oxide and zirconium oxide, is deposited by vapo-risation under vacuum upon one face of a substrate, said vaporisation being performed with a loss of oxygen atoms, the deposited layer thus being formed of a sub-oxide.

2. A method of manufacturing data carriers as claimed in claim 1, wherein said face of said substrate upon which the sub-oxide layer is deposited is a reflective face, said data carrier being designed for read-out by reflection.

3. A method of manufacturing a data carrier as claimed in claim 1, wherein said substrate is transparent, said data carrier being designed for read-out by transmission.

4. A method of manufacturing a data carrier as claimed in claim 1, comprising a second phase during which said sub-oxide layer is locally subjected to a recording radiation capable of raising said layer to a temperature sufficient to locally reoxidize it with neighbouring oxygen atoms, the thus reoxidized zones having a refractive index different from that the sub-oxide zones.

5. A method of manufacturing a data carrier as claimed in claim 4, wherein said sub-oxide zones and said reoxidized zones have different transmission coefficients.

6. A method of manufacturing data carriers as claimed in claim 1, wherein said material deposited by vapori-sation under vacuum is a mixture of titanium oxide and iron oxide.