Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Making named article
Reexamination Certificate
2003-04-30
2004-07-06
McPherson, John A. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Making named article
C430S296000, C430S945000, C360S017000
Reexamination Certificate
active
06759183
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a master medium which bears information, and is used in a process of magnetically transferring the information from the master medium to a slave medium.
2. Description of the Related Art
Recently, the amount of information which is required to be handled and stored is increasing. Therefore, there are demands for an inexpensive magnetic recording medium which can store a large amount of information, and be preferably accessed at high speed so that an arbitrary portion of information can be read out quickly. The high-density flexible disk is known as an example of such a magnetic recording medium.
The so-called tracking servo technique plays an important role in realizing a high-density flexible disk having great capacity. Due to the tracking servo technique, a magnetic head can move precisely within a narrow track width, and a signal can be regenerated with a high S/N ratio. A so-called preformat including tracking servo signals, address information signals, regeneration clock signals, and the like is recorded on the track of the disk in such a manner that the signals constituting the preformat appear at predetermined intervals during each rotation of the disk. The magnetic head is arranged so that the magnetic head can move precisely on the track by reading the signals in the preformat and correcting its own position.
Conventionally, the preformat is produced by recording the signals on each disk on a track-by-track basis by using a dedicated servo recording apparatus. However, it takes a long time to record the preformat by using the servo recording apparatus. Therefore, the cost of the preformat recording forms a considerable proportion of the total manufacturing cost, and thus reduction of the preformat recording cost is required.
On the other hand, Japanese Unexamined Patent Publications Nos. 63 (1988)-183623, 10 (1998)-40544, and 10 (1998)-269566 disclose techniques of recording a preformat by magnetic transfer, instead of recording signals constituting the preformat on the track-by-track basis. However, the above patent publications do not substantially disclose concrete procedures. In particular, conditions of the magnetic fields which are applied during magnetic transfer and constructions of apparatuses for generating the magnetic fields are not disclosed.
For example, JUPP63 (1988)-183623 and JUPP10 (1998)-40544 disclose methods of recording magnetization patterns corresponding to information signals on a magnetic recording medium (as a slave medium) In the disclosed methods, a master medium is prepared for magnetic transfer. The master medium is produced by forming relieved portions having shapes corresponding to the information signals on a surface of a substrate, and further forming a thin magnetic film at least on the relieved portions of the substrate. The slave medium has the form of a sheet or disk, and includes a thin ferromagnetic film or a magnetic-powder layer. The magnetic transfer is achieved by placing the slave medium in close contact with the magnetic film of the master medium, and applying an AC or DC bias magnetic field to the master medium so as to excite the magnetic material (thin film) formed on the relieved portions of the master medium. Thus, the magnetization patterns corresponding to the relieved portions of the master medium are recorded on the slave medium.
Since, according to the above methods of recording magnetization patterns by magnetic transfer, the relieved portions of the master medium are placed in close contact with the slave medium which is to be preformatted, and the magnetic material on the relieved portions are concurrently excited so as to record the predetermined patterns on the slave medium, the patterns can be statically recorded on the slave medium without changing the relative positions of the master medium and the slave medium. Thus, the preformat can be precisely recorded, and the time needed for the preformatting is very short.
However, when the above methods of recording magnetization patterns by magnetic transfer are used for recording servo signals on a magnetic recording medium (as a slave medium), it is necessary to precisely form servo patterns at respectively appropriate positions on the entire area of a magnetic recording medium, where the servo patterns each have a size of the order of one micrometer or less. For example, the 3.5-inch and 2.5-inch magnetic recording mediums have diameters of 3.5 and 2.5 inches, respectively. Since the servo patterns respectively indicate addresses of information items, the respective servo patterns must be different.
Micropatterns as mentioned above can be recorded by the lithography techniques which are conventionally used in manufacturing semiconductor devices or magnetic heads. However, in the lithography techniques, an original image is reduced in order to increase accuracy. Therefore, the area which can be exposed by each exposure shot is limited to about 2 cm square. When a large-size pattern is recorded by repeating the exposure of the 2 cm square, the large-size pattern includes an array of identical patterns. That is, it is difficult to form the servo patterns on a magnetic recording medium by using the above lithography techniques since the servo patterns are respectively different.
In addition, in the methods of recording magnetization patterns by magnetic transfer, the master medium is placed in close contact with the slave medium during the magnetic transfer operation. Therefore, when the magnetic transfer operation is performed a number of times, the relieved patterns representing information wear down, and therefore the accuracy of the magnetic transfer decreases. Further, when dust exists between the master medium and the slave medium, the dust may scratch the surfaces of the relieved portions of the master medium. In these cases, the master medium must be replaced. Therefore, it is desirable that the master medium is easy to produce, and inexpensive. However, the production of the master medium by repetition of the micropattern exposure requires complicated quality control operations, and is disadvantageous in qualitative stability and production cost.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a master medium for use in magnetic transfer, which is inexpensive and easy to produce.
(1) According to the first aspect of the present invention, there is provided a master medium for use in magnetic transfer of information. The master medium comprises a metal disk which has a first relief or recess pattern representing the information. The metal disk is produced by exposing a photoresist film formed on a base disk with a laser or electron beam modulated with the information while rotating the base disk, developing the photoresist film so as to form an original disk having a second relief or recess pattern, depositing metal on the original disk so as to mold the metal disk on the original disk, and removing the metal disk from the original disk.
The master medium according to the first aspect of the present invention may also have one or any possible combination of the following additional features (i) to (x).
(i) The original disk may be formed by etching the base disk after the photoresist film is developed.
(ii) The base disk may be made of glass or quartz.
(iii) The original disk may be made of a material containing Ni as a main component.
(iv) Preferably, the first relief or recess pattern has a height or depth of 80 to 800 nm. More preferably, the height or depth of the first relief or recess pattern is 150 to 600 nm.
(v) The master medium may further comprise a soft magnetic layer formed on the first relief or recess pattern.
(vi) The master medium having the feature (v) may further comprise a nonmagnetic layer formed between the soft magnetic layer and the first relief or recess pattern.
(vii) In the master medium having the feature (v), preferably, the soft magnetic layer has a thickness of 50 to 500 nm. More preferably, the thickness of the
Nagao Makoto
Nishikawa Masakazu
Watanabe Seiichi
Fuji Photo Film Co. , Ltd.
McPherson John A.
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