Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Radiation sensitive composition or product or process of making
Reexamination Certificate
2000-08-30
2003-02-25
Angebranndt, Martin (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Radiation sensitive composition or product or process of making
C430S945000, C428S064200
Reexamination Certificate
active
06524766
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an optical disk medium which records and reproduces information using light, and in particular to a super-resolution optical disk medium which reads out recording marks at equal to or less than an optical resolution determined by a diffraction limit light spot diameter.
2. Description of the Related Art
Due to recent advances in information technology, information communications and multimedia technology, there is an increasing demand for higher densities and higher capacities of optical disk media. The upper limit of recording density of an optical disk medium is mainly limited by the beam diameter of a light spot which records or reads out information. It is known that, if the wavelength of a light source is &lgr; and the numerical aperture of an object lens required to form the light spot is NA, the light spot diameter is effectively given by &lgr;/NA. If the light spot diameter used is reduced, the recording density can be increased, but the wavelength &lgr; of the light source is thought to be limited due to absorption by an optical element or the sensitivity characteristics of a detector, while increase of NA is effectively limited by the permitted amount of tilt of the medium. In other words, there is a limit to increase of recording density achievable by reduction of the light spot diameter.
As a means of overcoming this limitation, super-resolution media exist in the art which reduce the effective light spot diameter using the optical characteristics of the recording medium. Typical examples of this super-resolution medium technology are as follows:
(1) Magnetic super-resolution (Jpn. J. Appl. Phys 31 (1992), pp. 529-533)
(2) Super-resolution using inorganic oxide films (Joint MORIS/ISOM '97 Post-Deadline Papers Technical Digest, pp.21-22)
(3) Super-resolution reading by mask layer using organic pigments (Preprint of the Soc. of Jpn. Appl. Phys. (1994-Fall), p.1000(19p-K-6))
(4) Super-resolution by photo-chromic mask layer (Optical Review 4 (1997), pp.655-659)
(5) Super-resolution reading using melting of phase change material (Jpn. J. Appl. Phys. 32 (1993), p.5210).
These techniques create an effect which masks recording marks so as to make the effective spot contributing to recording/read-out smaller by using the variation of temperature distribution or transmittance, and thereby increase the recording/read-out density.
FIG. 1
schematically shows this medium super-resolution effect. Alight spot
11
scans the surface of a super-resolution medium in a direction shown by
13
, and thereby performs recording/read-out. During normal read-out, all recording marks
12
inside the light spot
11
contribute to the read-out signal, but in the case of super-resolution media, regions apart from a center region
14
in the light spot which has a strong light intensity are masked, and only a recording mark
15
inside the region
14
is read out. This is equivalent to reducing the effective light spot diameter contributing to read-out. Conversely to the example of
FIG. 1
, it is also possible to mask the region
14
, and detect recording marks outside the region
14
with the light spot
11
.
Method (1) can be applied only to magneto-optical disks, and cannot be applied to read only disks such as CD-ROM and DVD-ROM which are presently widely available. Methods (3) and (4) use organic materials as mask layers which are easily damaged by heat, consequently, the total number of possible reads is of the order of 10,000 or less, and as the reliability of reading out information is low, they have not been commercialized. Further as they are destroyed by heat, they cannot be applied to rewritable disks. Method (5) employs fusion of a phase change material in the super-resolution mask layer, so film flow occurs due to repeat reads, the number of possible reads is limited to about 10,000 or less, and as the reliability of information read-out is low, it also has not been commercialized. Moreover, as read-out is performed at a temperature above the melting point of the phase change material, with a rewritable disk, recording marks disappear at high temperatures during read-out, so this method can be used only for read-only disks. However, in Jpn. J. Appl. Phys. 38 (1999), p.1656, it is reported that by using a disk having an inorganic oxide super-resolution film, the disk can be read 100,000 or more times, and that a phase change medium applying this super-resolution film can be rewritten. This shows that, as method (2) employs inorganic materials, the disk,is not readily destroyed by heat as compared to a disk with organic materials. Due to this fact, inorganic oxide super-resolution films are expected to be applied as super-resolution materials suitable for both read-only disks and rewritable disks.
An inorganic super-resolution film has a property whereby its complex refractive index changes when it is irradiated by a laser beam of intensity exceeding a certain threshold. When this inorganic super-resolution film is applied to an optical disk, it will have a multi-layer structure such as shown in FIG.
2
. When this optical disk is read out, the complex refractive index changes in the center part of the light spot where the temperature is high, and the reflectance also changes in the region where the complex refractive index changed due to multi-interference in the laminated film. As a result, the signal corresponding to part of the light spot is emphasized when the disk is read, and the effective spot diameter contributing to read-out is reduced.
A super-resolution film
23
, substrate protecting film
22
and thermal buffer film
24
are designed with regard to the following three-stage mechanism.
(1) Light absorption occurs in the super-resolution film
23
.
(2) The heat produced by-this light absorption is not dissipated by the reflecting film
25
, but causes a temperature rise in the super-resolution film.
(3) The complex refractive index of the super-resolution film
23
changes, and the reflectance changes due to multi-interference in the laminated film.
The substrate protecting film
22
also has the role of preventing deformation of the substrate
21
due to the heat produced in the super-resolution film
23
.
A prototype disk was designed and manufactured using an oxide film (referred to hereafter as a Co—Si—Na—Ca—O film) comprising Co, Si, Na, Ca for the super-resolution film
23
, a ZnS—SiO
2
film for the substrate protecting film
22
and thermal buffer film
24
, and an Al—Ti film for the reflecting film
25
. The reflectance R (before change) and R (after change) was calculated relative to the film thickness of the substrate protective film
22
and thermal buffer film
24
taking account of multi-interference in the multi-layer film, assuming that the change of complex refractive index of the Co—Si—Na—Ca—O film was from n (refractive index)=2.48 and k (extinction coefficient)=0.48, to n=2.41, k=0.57 when the incident light became intense.
FIG. 3
is a plot of the calculated results for the reflectance variation rate (R (after change)—R (before change))/R (before change) assuming the film thickness of the Co—Si—Na—Ca—O film was 50 nm and the film thickness of the reflecting film
25
was 100 nm. From these results, it is seen that the reflectance changes most when the substrate protective film
22
has a thickness in the range from 120 nm to 150 nm, and the thermal buffer film
24
has a thickness in the range from 30 nm to 50 nm. A disk prototype was therefore manufactured comprising a laminate of the substrate protecting film
22
(ZnS—SiO
2
film) of thickness 120 nm, the super-resolution film
23
(Co—Si—Na—Ca—O film) of thickness 50 nm, the thermal buffer film
24
(ZnS—SiO
2
film) of thickness 30 nm, and the reflecting film
25
(Al—Ti film) of thickness 100 nm. The results of measuring reflected light intensity relative to incident light intensity on this prototype disk are shown in FIG.
4
. In the case of result
41
where there is no super-re
Ariyoshi Tetsuo
Shimano Takeshi
Shintani Toshimichi
Terao Motoyasu
Angebranndt Martin
Hitachi , Ltd.
Mattingly Stanger & Malur, P.C.
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