RU2430432C2 - Magneto-optical disc for recording, storing and reproduction of information and method of making said disc - Google Patents

Abstract

FIELD: information technology.

SUBSTANCE: disc has a magneto-optical layer and top and bottom dielectric layers. The magneto-optical layer is a polycrystalline ferrite-garnet film with the composition Y_3-xBi_xFe_5-yOa_yO₁₂ (where x=1.5-2.5; y=0-1.5). The magneto-optical layer, top and bottom dielectric layers are in electretic state.

EFFECT: high percentage yield of discs during manufacturing, high stability of their operational parameters when used in the most diverse conditions, high probability of storing information during recording, high storage stability of the recorded information.

2 cl, 1 dwg

Description

The invention relates to the field of applied magneto-optics and can be used for recording, storage and playback of video information in digital and analog modes.

Currently, magneto-optical disks (MO disks) are known, which are a four-layer structure deposited on a glass substrate:

- a rare-earth metal film - a transition metal (RZ-PM), - a working medium (magneto-optical layer, working layer) of a MO disk (applied directly to the substrate);

- SiO layer (the so-called lower dielectric layer of thickness h = λ / 4, where λ is the wavelength of light; the layer simultaneously plays the role of an antireflection coating, is applied over the working layer);

- Cu layer (the so-called reflective layer);

- SiO layer (the so-called upper dielectric layer, which plays the protective role of a copper layer against oxidation) (see: 1. Frolov GI, Seredkin VA, Yakovchuk V.Yu. Thermomagnetic recording on film alloys of transition and rare-earth metals Preprint IF SAS AN USSR. No. 386 F. Krasnoyarsk, 1986. - 48 p. (P. 93-95).

2. Frolov G.I., Zhigalov B.C. Physical properties and application of magnetofilm nanocomposites. Novosibirsk Publishing House SB RAS, 2006.

3. Frolov G.I. Amorphous ferrimagnetic films for optical information processing devices. In: Magnetic Properties of Crystalline and Amorphous Media. Novosibirsk, Science, Siberian Branch, 1989 .-- 252 p. (p. 218-234).

These drives have the following disadvantages:

1) low yield for manufacturing;

2) the deterioration of the stability of the operational parameters of the disk when working in conditions of high humidity, high humidity and high temperature;

3) a strong dependence of the coercive force and uniaxial anisotropy of the working layer (RZ-PM film) on the technological parameters of the disk;

4) have limitations for recording at the compensation point, since RE-PM films are characterized by a strong temperature dependence of the coercive force near the compensation temperature, and in some cases there is a loss of information during recording; 5) have high values of the reflection coefficient from each layer and the resulting insufficiently high signal-to-noise ratio.

The closest (prototype) to the proposed magneto-optical disk is the Xerox MO disk, which is the following four-layer structure deposited on a glass substrate:

- layer A1 (reflective layer) deposited on a substrate;

- SiO ₂ layer (lower dielectric layer of thickness h = λ / 4, where λ is the wavelength of light; applied to the reflective layer);

- film (RZ-PM), - the working medium of the MO disk (applied on top of the lower dielectric layer);

- SiO ₂ layer (upper dielectric layer of thickness h = λ / 2, where λ is the wavelength of light, which plays the protective role of the working layer from oxidation; is applied over the RE-PM film). (see: 1. Connel GAN, Alien R., Mansuripur M. Interference enhanced Kerr spectroscopy for very thing absorbing films application to amorphous terbium iron. J. Mag. and Magn. Mater. 1983. vol. 35, N1-3. P.337-339.

2. Mansuripur M., Connel G. A.N., Treves D. Optimum disk structures and energetics of domain formation in magneto-optical recording. IEEE Trans. Magn. 1982. Vol. MAG-18, N6. P.1241-1243.

3. Mansuripur M., Connel G. A.N., Goodman J.W. Signal and noise in magneto-optical readout. J. Appl. Phys. 1982. Vol. 53, N6. P.4485-4494).

Due to the fact that the thicknesses of the lower and upper dielectric layers are equal to λ / 4 and λ / 2, respectively, the light reflected from layer A1 returns in phase with the component reflected directly from the working layer, and in this case there is an addition of outgoing rays, which is essential reduces reflection loss.

These drives have the following disadvantage:

1) low yield for manufacturing;

2) the deterioration of the stability of the operational parameters of the disk when working in conditions of high humidity, high humidity and high temperature;

3) a strong dependence of the coercive force and uniaxial anisotropy of the working layer (RZ-PM film) on the technological parameters of the disk;

4) have limitations for recording at the compensation point, since RE-PM films are characterized by a strong temperature dependence of the coercive force near the compensation temperature, and in some cases there is a loss of information during the recording process.

The aim of the present invention is:

1) increase the percentage of yield of disks during production;

2) increasing the stability of the operational parameters of the disks when working in a variety of operating conditions;

1) an increase in the likelihood of saving information during the recording process;

2) improving the reliability of storage of recorded information.

This goal is achieved in that the working medium (magneto-optical layer) of the disk is a polycrystalline ferrite-garnet film of the composition Y _3-x Bi _x Fe _5-y Ga _y O ₁₂ (where x = 1.5-2.5; y = 0 -1.5), in addition, the working medium, the upper and lower dielectric layers are in an electret state.

The invention consists in the following.

The electret state of the magneto-optical layer leads to the induction of a highly coercive state in it (see: 1. Kostishin V.G., Letiuk L.M. Effect of corona treatment on the shape of the hysteresis loop of epitaxial films of garnet-garnets. Journal of Technical Physics, 1995, t .65, B.7. C.179-183.

2. Kostishyn V.G., Letyuk L.M., Shipko M.N., Kirpenko A.G. Influence of corona discharge on the hysteresis loop of magnetic garnet films. J. ofMagn. and Magn. Mater., 1996, V.169. P.363-364.

3. Kostishyn V.G., Letyuk L.M. Use of corona electret state in Bi-containing ferrite-garnet heterocompositions for thermomagnetic data recording. J. of Magn. and Magn. Mater., 2003, V.254-255. P.556-558),

which is one of the basic requirements for materials for thermomagnetooptical information recording. The upper and lower dielectric layers, being in an electret state, in addition to their main functions, also play the role of stabilizers of the electret state of the working layer. Due to the high content of Bi ³⁺ ions in the structure of the garnet film, the working layer has a high Faraday rotation, which is sufficient for high-contrast magneto-optical recording and reading of information.

The existence of a high coercive force in the working layer induced by the electret state completely eliminates the strong temperature dependence of the coercive force characteristic of RE-PM films for the selected type of working layer and, thus, completely eliminates the loss of information during recording.

It should also be noted that the highly coercive state induced in the working layer by processing in the corona significantly increases the reliability of storage of recorded information.

Thus, the hallmarks of the proposed magneto-optical disk in comparison with the prototype are the following.

1. The working medium (magneto-optical layer) of the disk is a polycrystalline ferrite-garnet film of the composition Y _3-x Bi _x Fe _5-y Ga _y O ₁₂ (where x = 1.5-2.5; y = 0-1.5 )

2. The working medium, the upper and lower dielectric layers are in an electret state.

The use of the above features to achieve the goal set in this application is unknown to the authors.

The most suitable for the proposed in this application is a method of producing magneto-optical disks for recording and storing information, which consists in spraying on a substrate of optically transparent material with formed spiral grooves of the mirror layer, the lower dielectric layer of thickness h = λ / 4 (where λ is the wavelength of light ), magneto-optical layer, upper dielectric layer of thickness h = λ / 2 (where λ is the wavelength of light), (see: 1. Connel GAN, Allen R., Mansuripur M. Interference enhanced Kerr spectroscopy for very thing absorbing films application to amorphous terbium iron. J. Mag. and Magn. Mater. 1983. vol. 35, N1-3. P.337-339.

2. Mansuripur M., Connel G. A.N., Treves D. Optimum disk structures and energetics of domain formation in magneto-optical recording. IEEE Trans. Magn. 1982. Vol. MAG-18, N6. P.1241-1243.

3. Mansuripur M., Connel G. A.N., Goodman J.W. Signal and noise in magneto-optical readout. J. Appl. Phys. 1982. Vol. 53, N6. P.4485-4494).

In order to obtain a high-quality magneto-optical disk based on a polycrystalline ferrite-garnet film (YBi) ₃ (FeGa) ₅ O ₁₂ , we specified this method by the following operation.

1. The magneto-optical disk of the proposed design is treated for 5-15 hours in a negative corona discharge at a temperature of 100-300 ° C and a corona current I _k = 50-350 μA.

The essence of the proposed method is as follows. Since the proposed MO disk is a combination of three dielectric layers, during prolonged treatment in a negative corona discharge an electret state will form in each layer (see: A. Gubkin, Electrets. M .: Nauka, 1978. - 192 p. .). The formation of the electret state at elevated temperature (100-300 ° C) will allow this state to persist at room temperature for virtually infinite time. Due to the use of a small thickness (thickness 0.05-0.1 μm) as a working layer of the MO disk of a ferrite-garnet film (YBi) ₃ (FeGa) ₅ O ₁₂ , the electret state induces a coercive force Н _c of 20 in the working layer -25 times higher than H _from the same film without an electret state, and also very significantly (40-50%) increases the uniaxial anisotropy of this film.

The use of a negative corona discharge for processing is advisable from the considerations that with this type of corona during processing on the surface of the processed material it is possible to obtain large values of the surface density of the polarization charge and thus achieve a higher surface density of polarization charges. The experiments showed that treatment in the corona for less than five hours does not give the required results for the value of the growth of the coercive force H _{c of the} working layer. Processing for a time exceeding 15 hours is impractical because it does not lead to further growth of H _c . The limits of variation of the corona current are selected from the following considerations. When using a corona current of less than 50 μA, the processing time is greatly increased to achieve the required value of the coercive force of the MO disk. The use of a corona current of more than 350 μA for processing MO disks is impractical, since a further increase in the current value does not lead to a significant increase in the achieved effects.

In order to uniformly process the MO disk in the corona discharge, the disk rotates at a constant speed during processing.

Thus, the proposed method of manufacturing a magneto-optical disk for recording, storage and playback of information has, in comparison with the prototype, the following distinctive features.

1. The MO disk is processed in negative corona discharge.

2. The processing of the MO disk in the corona discharge is carried out at a temperature of 100-300 ° C.

3. The processing of the MO disk in a negative corona discharge is carried out at a value of the corona current I _k = 50-350 μA.

4. The processing time of the MO disk in the corona is 5-15 hours.

The use of these signs to achieve the goal set in the application is unknown to the authors.

It should also be noted that the highly coercive state induced in the working layer by processing in the corona significantly increases the reliability of storage of recorded information.

MO disks made in accordance with the proposed design and the proposed technology allow efficient recording and playback of both digital and analog information using the Faraday effect and the Kerr effect.

It should be noted that the MO disk of the proposed design and the method of its production in comparison with the prototype increase:

- 40% - yield;

- 25% - the stability of the operational parameters of the disks during operation in harsh operating conditions (at high humidity and temperature);

- 10% chance of saving information during the recording process.

The drawing shows a setup diagram for processing a MO disk in a negative corona discharge. The processing device includes: 1 - a high voltage rectifier; 2 - corona electrode; 3 - rotating plate-electrode; 4 - a tripod; 5 - magneto-optical disk; 6 - high-voltage connecting wires; 7 - microammeter; 8 - kilovoltmeter; 9 - box for monitoring processing conditions.

Example 1. Two prototypes of the MO disk of the proposed design were manufactured by the developed method on a glass substrate with a diameter of 120 mm. The thickness of the magneto-optical layer (polycrystalline film Y _0.6 Bi _2.4 Fe _3.5 Ga _1.5 O ₁₂ ) was 0.12 μm. Upon receipt of all the required layers, the disks were treated for 8 hours in a negative corona discharge at a temperature of 200 ° C, a pressure of 760 mm Hg and a humidity of 0%. A corona electrode of the "multi-needle electrode" type was used. The voltage at the corona electrode was U _k = 20 kV. The corona current during processing was within I _k = 180-200 μA. Table 1 presents the main parameters of the working layer of the manufactured MO disk before and after corona treatment. The results of a study of the stability of the results obtained by processing in the corona for 40 months are also presented.

Table 1 Change in the main operational characteristics of the magneto-optical layer (polycrystalline film Y _0.6 Bi _2.4 Fe _3.5 Ga _1.5 O ₁₂ ) of the model of the developed MO disk during processing in a negative corona discharge (U _k = 25 kV; I _k = 180 -200 μA; T _arr = 200 ° C, P = 760 mm Hg, humidity = 60%) MO disk layout Coercive force N _c , E The field of uniaxial anisotropy - H _one , E before processing in the crown after treatment in the crown 8 hours 40 months after treatment in the crown before processing in the crown after treatment in the crown 8 hours 40 months after treatment in the crown one 36.0 790.00 790.00 2520.00 3650.00 3650.00 2 40,0 1,100.00 1,100.00 2650,00 3,780.00 3,780.00

As can be seen from the table, the properties of the magneto-optical layer of the obtained MO disks during the control period of 40 months completely retain the properties acquired by processing in a negative corona discharge at T _ar = 200 ° C.

Bitwise recording of information in fabricated MO disks was carried out by a semiconductor laser (λ = 0.8 μm). The laser power during recording was 15 mW, during playback - 8 mW. In the process of monitoring the stability of recorded information for 36 months, no deterioration in the quality of recorded information was found.

Example 2. Ten prototypes of MO disks were prepared using Xerox technologies (an amorphous Tb _0.225 Fe _0.775 film was used as a magneto-optical layer). The other ten prototypes of MO disks were made in accordance with the proposed technology and disk design (a polycrystalline film Y _0.7 Bi _2.3 Fe _4.5 Ga _0.5 O _{12 was} used as the magneto-optical layer). Of the ten layouts of disks made using Xerox technology, only six had satisfactory characteristics for thermomagnetooptic recording. At the same time, all ten disks made by the proposed technology had satisfactory characteristics for recording and reading information.

Example 3. Bit-wise recording of information was carried out in six mock-ups of MO disks made by Xerox technology, and six mock-ups of MO disks made by the proposed technology. High-quality recording was carried out by reproducing using the effects of Faraday and Kerr. Further information was erased. The process of recording and playback in all discs was carried out five times.

It was found that out of 30 recording cases, the information was completely stored for disks made using Xerox technology in 26 cases, and for disks made using the proposed technology in 29 cases. Thus, the proposed technology and design of the MO disk increase the likelihood of saving information during the recording process compared to the technology and design of the MO disk of Xerox by 10%.

Example 4. Stability tests were conducted for six prototypes of MO disks made using Xerox technology and six prototypes of MO disks made using the proposed technology. Test conditions: humidity - 85%, pressure - 760 mm Hg and temperature - 50 ° C. All twelve discs with recorded information were kept under test conditions for 10 days. After the specified period, the recorded information was checked. Then the disks were dried, the information was erased, the same information was recorded a second time, and the tests of all MO disks were repeated under the same conditions and during the same time.

The test results allowed us to detect errors in recording information in MO disks made using Xerox technology in four cases out of twelve, and in MO disks made using the proposed technology, in one case out of twelve.

Claims (2)

1. A magneto-optical disk for recording, storing and reproducing information containing a glass substrate in which spiral grooves are formed, a mirror layer, a lower SiO ₂ dielectric layer _of thickness h = λ / 4, where λ is the light wavelength, magneto-optical layer, upper dielectric SiO ₂ layer of thickness h = λ / 2, where λ is the wavelength of light, which simultaneously plays the role of an antireflection coating, characterized in that the magneto-optical layer is made in the form of a polycrystalline ferrite-garnet film of the composition Y _3-x Bi _x Fe _5-y Ga _y O ₁₂ (where x = 1,5-2,5; y = 0-1,5) , D & E ektricheskie layers and magneto-optical layer located in an electret state. 2. A method of manufacturing a magneto-optical disk for recording, storing and reproducing information, including spraying on a glass substrate with formed spiral grooves of the mirror layer, the lower dielectric layer of SiO ₂ with a thickness h = λ / 4, where λ is the wavelength of light, magneto-optical layer, upper dielectric a SiO ₂ layer with a thickness h = λ / 2, where λ is the wavelength of light, characterized in that the disk of this design is treated for 5-15 hours in a negative corona discharge at a temperature of 100-300 ° C and a corona current I _k = 50- 350 μA.