Information recording medium and information...

Details Information recording medium and information... Information recording medium and information...

1999-10-25

2001-11-06

Evans, Elizabeth (Department: 1774)

Stock material or miscellaneous articles

Circular sheet or circular blank

C428S064400, C428S064500, C428S064600, C428S913000, C430S270130, C430S495100, C430S945000, C369S283000, C369S288000

Reexamination Certificate

active

06312779

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to an information recording medium for optical disks and to a recording apparatus to make records thereon.
There are many known principles of recording information on a thin film (recording film) by irradiating it with a laser beam. One of them utilizes the phase transition (or phase change) of film material or the photo darkening, which are due to the change in atomic arrangement induced by irradiation with a laser beam. It offers the advantage of causing almost no deformation to the thin film and hence gives an information recording medium of double-sided disk structure which is formed by bonding together two disks.
Such an information recording medium is usually made up of a substrate, a protective layer, a recording film of GeSbTe or the like, a protective film of ZnS—SiO
2
, and a reflective layer. The recording film is higher in reflectivity when it is in the crystalline state than when it is in the amorphous state. Therefore, the recording film has a greater absorptance when it is in the amorphous state. If over-write is carried out in this state, the amorphous region increases in temperature faster than the crystalline region due to recording and hence the newly formed record marks become large enough to distort reproduced signals.
Attempts have been made to eliminate this drawback by making the recording film to increase in absorptance more when it is in the crystalline state than when it is in the amorphous state. For example, literature (1) mentions the reversion of absorptance by providing a very thin (10 nm) reflective layer of Au. (Yamada and other three, Shingaku Gihou. MR92-71, CPM92-148 (1992-12) p. 37) Further, literature (2) mentions the reversion of absorptance by using a 65-nm thick silicon film as the reflective layer. (Okada and other six, Shingaku Gihou. MR93-53, CPM93-105 (1993-12) p. 1)
It is known from accelerated tests that the protective layer of this kind poses a problem with deterioration of record marks when high-density recording is carried out or when the recording medium is stored at room temperature or apparatus temperature for 10 years or more.
In this specification, the term “phase change” implies not only the phase change between the crystalline state and the amorphous state but also the phase change that takes place at the time of melting (change into liquid phase) and recrystallization and the phase change between the crystalline state and the crystalline state. The flow of the recording film occurs as the recording film flows due to irradiation with a laser beam at the time of recording and also as the recording film is gradually pushed by the deformation (thermal expansion) of the protective layer and intermediate layer. The term “mark edge recording” means the recording system which makes the edge of the record mark to correspond to the signal “1” and the space between marks and the mark inside to correspond to the signal “0”.
Conventional information recording media suffer the disadvantage that jitter increases when rewriting is repeated frequently, record marks deteriorate during storage, and reflectivity level fluctuates in the case where they are used as high-density, rewritable information recording media of phase transition type that employ the mark edge recording system.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a new information recording medium which has good recording sensitivity, permits easy film forming, retains good recording and reproducing characteristics even after repeated rewriting, has a long archival life, and fluctuates less in reflectivity level than conventional ones.
The present invention is summarized below.
(1) An information recording medium which comprises a film of recording layer on a substrate to record information by means of the change in atomic arrangement induced by irradiation with light, said recording layer having at least one interface layer laminated at its interface.
(2) An information recording medium as defined in (1), wherein the interface layer contains nitrogen whose amount accounts for more than 10 atom % of the total atoms therein.
(3) An information recording medium as defined in (1) or (2), wherein it has at least another interface layer at the opposite side of said substrate.
(4) An information recording medium as defined in any of (1) to (3), which further comprises one protective layer between the substrate and said recording layer.
(5) An information recording medium as defined in any of (1) to (4), wherein it has a laminated absorptance control layer at the opposite side of the substrate to form said recording film thereon.
(6) An information recording medium as defined in any of (1) to (5), which has a track pitch D
tp
which is related with the wavelength &lgr; of laser for recording and the numerical aperture NA of the objective as follows.
0.5&lgr;/NA≦D
tp
≦0.6&lgr;/NA
(7) An information recording medium as defined in any of (1) to (6), wherein said interface layer has a composition represented by N
s
Z
t
, where 0.10≦s≦0.66 and s+t=1, and Z denotes one or more members selected from H, Li, Na, K, Rb, Cs, Be, Mg, Ca, Sr, Ba, Sc, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Re, Fe, Ru, Os, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, Zn, Cd, Hg, B, Al, Ga, In, Tl, C, Si, Ge, Sn, Pb, P, As, Sb, Bi, O, S, Se, Te, F, Cl, and Br, and said recording film has a composition represented by
Ge
x-w
Sb
y
Te
z
M
w
where 0.15≦x≦0.46, 0.10≦y≦0.29, 0.50≦z≦0.60, w≦0.10 and x+y+z=1, and M is one member selected from Na, Mg, Al, P, S, Cl, Li, Ca, Sc, Zn, Ga, As, Se, Br, Rb, Sr, Y, Zr, Nb, Ru, Rh, Cd, In, Sn, I, Cs, Ba, La, Hf, Ta, Re, Os, Ir, Hg, Tl, Pb, Th, U, Ag, Cr, W, Mo, Pt, Co, Ni, Pd, Si, Au, Cu, V, Mn, Fe, Ti, and Bi, x+w−23≦s5≦x+w−19, 22≦x+w≦36, and 10≦s.
(8) An information recording medium as defined in any of (5) to (7), wherein the absorptance control layer has a thickness in the range of 10 nm to 50 nm.
(9) An information recording medium as defined in any of (5) to (8), wherein the absorptance control layer is made of a material having a refractive index (n) of 1.2 to 6 and an attenuation factor (k) of 0.3 to 3.0.
(10) An information recording medium as defined in any of (5) to (9), wherein the reflectivity of crystalline state is lower than of amorphous state, and it needs a minimum power to be able to record a minimum mark in its amorphous state which is equal to or smaller than a minimum power to be able to record a minimum mark in its crystalline state under the same conditions.
(11) An information recording medium as defined in any of (5) to (10), wherein the interface layer contains a component identical with that of the absorptance control layer, said component being composed of more than 50% of the total number of atoms.
(12) An information recording medium as defined in any of (5) to (11), wherein it comprises at least one reflective layer made of Cu alloy, Al alloy, or Au alloy on the absorptance control layer.
(13) An information recording medium as defined in any of (5) to (12), which has at least one intermediate layer between the recording film and the absorptance control layer.
(14) An information recording apparatus having a laser emitter and an objective lens to make a record on the information recording medium defined in (5), which is characterized by that the information recording medium has a track pitch D
tp
which is related with the wavelength &lgr; of laser for recording and the numerical aperture NA of the objective lens as follows.
0.5&lgr;/NA≦D
tp
≦0.6&lgr;/NA
(15) Said interface layer has a composition represented by (ZnS)
30
(TaN)
70
.
TaN in (ZnS)
30
(TaN)
70
may be replaced by any of Cr—N, Hf—N, and Nb—N without any change in the result. It may also be replaced by any of Mo—N, Ti—N, V—N, W—N, Y—N, Zr—N, Al—N, Ge—N, Si—N, and Zn—N without appreciable change in the result. The first six members have a high melting point and cause reflectivity to fluctuate only lit

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