JP2566111B2 - Magneto-optical memory device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magneto-optical memory device which performs at least one operation of recording, reproducing and erasing information by light such as laser light.

[0002]

2. Description of the Related Art In recent years, an optical memory device that records, reproduces, and erases information by light has attracted attention in various fields as a high-density and large-capacity memory. In particular, an optical disk memory having a disk-shaped recording element is characterized in that it can be accessed at a higher speed than a tape-shaped element, and many studies have been conducted.

The recording unit of this optical memory device is 1 μm.
Since the size is about mφ, it is an important technique to bring the light beam to a predetermined position at the time of recording / reproducing or erasing. That is, since it is difficult to perform positioning with only mechanical accuracy, various servo technologies are used.

For example, in an optical disk memory, a focus servo is used to deal with the surface deviation of a disk, and a tracking servo is used to the center deviation. The latter can be performed by referring to the bits already recorded in the read-only memory (usually the concave and convex holes provided in the substrate such as PMMA or polycarbonate), but additionally recordable memory (so-called write-once). In a memory) or an erasable and rewritable memory, it is common to previously form a groove serving as a guide and a pit-shaped address signal portion indicating the position of the groove on a substrate.

The structure of a conventional guide groove used in, for example, an additionally recordable memory will be described with reference to FIG.

FIG. 10 is a partially enlarged view of a cross section of a disk along a concentric or spiral guide groove provided in a conventional optical memory disk.

In FIG. 10, reference numeral 1 is a substrate made of PMMA, glass or the like and having a thickness of about 1 to 1.5 mm, and 2
Is a photosensitive resin layer (so-called 2P layer having a thickness of about 10 μm to 100 μm) for providing the guide groove. Further, 3 is a guide groove for recording information, and 4 is a pit portion for an address signal indicating the number of the guide groove 3. The depth of this pit portion 4 is set to λ / 4n (where λ is the wavelength of the reproduction laser beam and n is the refractive index of the 2P layer) so that the normal address signal is reproduced optimally, and the portion of the guide groove 3 is It is made to have a depth of λ / 8n in order to obtain many tracking signals.

[0008]

The guide groove 3 and the address signal pit 4 are formed by molding the 2P method or the resin such as PMMA or polycarbonate as described above, and the recording plate and the guide groove 3.
Generally, the pit portion 4 is integrally formed. However, in both cases, since the recording medium is laminated on the resin surface, water contained in the resin layer causes deterioration of the recording medium.

In order to solve the above-mentioned problems, the applicant of the present invention has previously proposed a method of directly forming concave and convex grooves on a glass substrate in Japanese Patent Application No. 58-84613 ("Method for manufacturing optical memory element").
Is proposed as.

This method is a method in which a resist film is coated on a substrate, guide grooves and address signals are recorded on the resist film with a laser beam, and after development, the pattern is directly formed on a glass substrate by reactive ion etching. is there.
According to this method, the depth of the guide groove 3 and the address signal portion 4 is
Since the glass substrate is determined by the time of exposure to plasma during reactive ion etching, it is difficult to make the depths of the guide groove portion 3 and the address signal portion 4 different. Therefore, it is necessary to determine the shapes of the guide groove and the address signal portion in consideration of the address signal output, the tracking output, or the read signal output.

Therefore, the present invention has been made in view of the above points, and has a guide groove portion and an address signal pit portion having a shape capable of sufficiently obtaining a tracking signal, an address signal, and a reproduction signal of recorded information. An object of the present invention is to provide a magneto-optical memory device including the.

[0012]

In order to achieve the above object, the present invention provides a guide groove for recording a magneto-optical signal and a pit portion provided on the extension line thereof and having a pit width narrower than the guide groove. And a width of the guide groove is narrower than a width of a light beam for recording a magneto-optical signal so that a track servo signal can be obtained.

[0013]

According to the above configuration, the tracking servo signal,
It is possible to obtain a high quality magneto-optical memory element for all of the address signal and the information reproduction signal.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to the drawings with reference to the accompanying drawings.

FIG. 1 is an enlarged view of an address signal pit portion showing an address of a guide groove portion of the optical memory element of the present invention, and FIG. 2 is a partial enlarged view of a cross section of the optical memory element disc along the guide groove portion. .

In FIGS. 1 and 2, 11 is a substrate such as glass, 12 is a guide groove formed in the substrate 11, 13 is a pit portion for an address signal indicating the number of the guide groove 12 formed in the substrate 11. Therefore, as shown in FIG. 1, the pit width t ₁ of the pit portion 13 is formed narrower than the groove width t ₂ of the guide groove 12.

FIG. 3 is a conceptual diagram showing the structure of an optical system for a magneto-optical disk in which recorded information can be rewritten.
1 is a glass substrate, 15 is a magneto-optical recording medium, 16 is an objective lens, 17 is a reflective lens, 18 is a beam splitter, 1
9 is a beam shaping prism, 20 is a collimator lens, 21 is a semiconductor laser, 22 is a beam splitter, 2
3 is a lens, 24 is a cylindrical lens, 25 is a 4-division PIN photodiode, 26 is a λ / 2 filter plate, 2
7 is a lens, 28 is a polarization beam splitter, 29 and 3
Reference numeral 0 is an avalanche photodiode.

In FIG. 3, the tracking signal is constructed so as to be obtained from the 4-division PIN photodiode 25 using the push-pull method, and the address signal is the sum of the outputs of the two avalanche photodiodes 29 and 30. The information signal is obtained by the so-called differential detection method by taking the difference between the photodiodes 29 and 30. In addition, the N.V. A. Is 0.6 and the beam is focused to about 1.1 μm at 1 / e ² .

FIG. 4 is a partially enlarged view of a cross section of the magneto-optical disk reproduced by the optical system of FIG. 3 in a direction orthogonal to the guide groove 12, showing the AlN film 3 on the glass substrate 11 with the uneven guide groove.
1, GdTbFe32, AlN film 33 and AlNi film 3
4 are stacked.

FIG. 5 is a plot of C / N as a function of track width t ₂ when a 1 MHz signal is recorded / reproduced on a magneto-optical disk having the guide groove (track) depth of 700 Å in FIG.

FIG. 6A is a diagram showing a reproduced waveform of an address signal in the track width of 0.75 μm of the magneto-optical disk used in the measurement of FIG. 5, and FIG. 6B is an address signal in the track width of 0.48 μm. The reproduced waveform of is shown.

As is clear from FIG. 5, the wider the track width is, the better the C / N of the information signal. This is shown in Figure 7 (a).
As shown in FIG. 7, it depends on the relationship between the beam diameter 36 and the width t ₃ of the signal bit 35, and ideally the beam diameter 3 is as shown in FIG.
It will be easily explained from the two points that the width of the bit 35 is larger than 6 and that the bit width is limited to the width t ₂ of the guide groove 12 in the disk with the guide groove.

Further, from FIG. 6, it is understood that the narrower the address signal pit width t ₁ is, the better. This is the pit width t ₁
If the signal bit 35 is considered to be an address signal pit in FIG.
If you come to the center of the pit, the beam 36 is completely
It becomes equal when there is virtually no pit inside, and the amount of light returning to the detector increases. Therefore, as shown in FIG. 6A, the signal has a high central portion.

As described above, in the magneto-optical recording, when the guide groove 12 and the address signal pit 13 having the depth of about λ / 8n (that is, about 650 to 700Å) are provided, the guide groove 12 as shown in FIG. It is understood that the wider the width t ₂ of the address signal and the narrower the width t _{1 of} the address signal pit portion 13, the better.

In addition, the above configuration, that is, FIG.
When the optical head having the structure shown in FIG. 3 is used for the disc as shown in FIGS. 2 and 4, if the track width t ₂ is within 1 μm, a sufficient tracking signal can be obtained.

As described above, one of the features of the structure of the magneto-optical memory device of the present invention is that when the depth of the guide groove and the address signal pit is the same as shown in FIG. 1, the width of the address signal pit is the same. Is narrowed and the width of the guide groove is widened.

Next, a method of manufacturing a glass disk embodying the present invention will be described in the order of steps.

Step (1) ... A resist film 37 is applied on the glass substrate 11 which is highly reliable against the passage of oxygen, moisture and the like (impermeable to oxygen and moisture).

Step (2) ... The resist film 37 applied on the glass substrate 11 is irradiated with light 38 such as Ar laser through the optical modulators 39 and 40, the mirror 41 and the condenser lens 42 to produce a magneto-optical image. A line having the same width as the width t _{2 of the} guide groove (see 12 in FIG. 1) for the memory element and an interrupted line having a width t ₁ for recording the address signal pit portion 13 are written (FIG. 8). In the step of recording the guide groove 12 and the address signal portion 13 with the laser beam 38 on the resist film 37, the laser power for recording the guide groove 12 is made larger than the laser power for recording the address signal portion 13 to obtain the above-mentioned invention. It is possible to obtain each width of the guide groove 12 and the address signal portion 13 having the above characteristics.

Specifically, as shown in FIG. 8, optical modulators 39 and 40 are provided in the optical path of the laser (eg, Ar) light 38.
, And one is used for modulating the address signal, and the other is operated so that the power is slightly lowered only when the address signal is recorded. In this case, a modulator whose degree of modulation linearly changes by input is used without necessarily using two modulators, and the input power height of the recording of the address signal portion shown by the reference numeral 43 in FIG. It suffices to make the recording with the power height lower than that input at the time of recording in the guide groove portion shown in.

Step (3) ... The resist film 37 on which the lines and the intermittent lines are written is passed through a developing process to form concave and convex grooves in the resist film 37.

[0032] Step (4) ... groove in clothing state of the resist film 37 having grooves of the asperities, the glass substrate 11 subjected to sputtering (reactive ion etch N'grayed) in CF _4, CHF etching gas, such as ₃ 12 and the pit portion 13 are formed.

Step (5) ... The resist film 37 is removed by sputtering in a solvent such as acetone or O ₂ . As a result, the guide groove 12 having the groove width t ₂ is formed on the glass substrate 11.
And an address signal pit portion 13 having a pit width t ₁ is formed.

As described above, the guide groove 12 and the address signal pit portion 13 having the shape shown in FIG.
Formed on top.

Although the above embodiments have been described based on the combination of the glass disk and the magneto-optical disk, the present invention is not necessarily limited to the above embodiments, and is within the scope of the gist of the present invention. It goes without saying that various modifications and applications of are possible.

[0036]

As described above, according to the present invention, it is possible to obtain a magneto-optical memory device of good quality over all of the tracking servo signal, the address signal, and the information reproducing signal.

[Brief description of drawings]

FIG. 1 is an enlarged view of a guide groove portion of a magneto-optical memory device of the present invention and an address signal pit portion representing an address of the guide groove portion.

FIG. 2 is a partially enlarged cross-sectional view of a magneto-optical memory element disk along a guide groove.

FIG. 3 is a conceptual diagram showing a configuration of a magneto-optical disk pickup.

FIG. 4 is a partially enlarged view showing a cross section of a magneto-optical disk.

FIG. 5 is a diagram showing a relationship between C / N and track width.

FIG. 6 is a diagram showing a difference in address signal depending on a track width.

FIG. 7 is a diagram showing a relationship between a recording signal or address signal pit portion and a beam diameter.

FIG. 8 is a diagram showing one means for manufacturing the magneto-optical memory element of the present invention.

FIG. 9 is a diagram showing an example of an electric input signal for manufacturing the optical memory device of the present invention.

FIG. 10 is a partially enlarged view showing a sectional structure of a conventional optical disc substrate.

[Explanation of symbols]

11 glass substrate 12 guide groove 13 address signal pit t ₁ pit width of pit t ₂ groove width of guide groove

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshihisa Exit 22-22 Nagaike-cho, Abeno-ku, Osaka-shi, Osaka Within Sharp Corporation (72) Inventor Shigeki Maeda 22-22 Nagaike-cho, Abeno-ku, Osaka, Osaka Sharp Corporation (56) References JP-A-60-121550 (JP, A) JP-A-59-101043 (JP, A)

Claims (2)

(57) [Claims] 1. A guide groove for recording a magneto-optical signal and a pit portion provided on an extension of the guide groove and having a pit width narrower than the guide groove, wherein the width of the guide groove is for recording a magneto-optical signal. A magneto-optical memory device characterized in that a track servo signal can be obtained by making the width of the light beam narrower than that of the light beam. 2. The magneto-optical memory element according to claim 1, wherein the guide groove and the pit portion have the same depth.