Dynamic information storage or retrieval – Storage medium structure – Specified material
Reexamination Certificate
2001-03-07
2004-03-30
Huber, Paul W. (Department: 2653)
Dynamic information storage or retrieval
Storage medium structure
Specified material
C369S283000
Reexamination Certificate
active
06714510
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to an information recording medium such as an optical disc, for recording video signals, voice signals, etc., therein. More particularly, the invention relates to a layer structure of an information recording medium in which information is recorded into a plurality of recording layers, which are laminated with intermediate layers being interlayered therebetween. Further, the invention relates to a reproducing device capable of reproducing the recorded information from the information recording medium.
2. Description of the Related Art
In recent years, in the field of the optical disc, how to increase a recording density for each side of the optical disc is under investigation. A double layer DVD having two recording layers is a typical example of such. A layer structure of the double layer DVD is shown in FIG.
9
.
The DVD shown in
FIG. 9
is formed with a first substrate
1
having a recording layer
2
, a first reflecting layer
3
, an intermediate layer
4
having a recording layer
5
, a second reflecting layer
6
, and a protecting layer
7
. In
FIG. 9
, the first substrate
1
is made of a material permitting light to pass therethrough, such as PC (polycarbonate). The recording layer
2
having a first pit train for information recording is layered on the first substrate
1
. The first reflecting layer
3
as an intermediate reflecting layer, which is made of gold (Au) or silicon carbide (SiC), is formed on the recording layer
2
. The intermediate layer
4
is layered on the first reflecting layer
3
. The intermediate layer
4
is made of photo-setting resin, such as ultraviolet curing acrylic resin, and has the recording layer
5
on the surface thereof, which is opposite to its surface being in contact with the first reflecting layer
3
. The recording layer
5
has a second pit train for information recording.
The second reflecting layer
6
is formed on the recording layer
5
of the intermediate layer
4
by deposition process or the like. The second reflecting layer is formed with a reflecting layer made of aluminum (Al), which is higher in reflectivity than the intermediate reflecting layer. The protecting layer
7
of about 600 &mgr;m thick and made of resin or the like is layered on the second reflecting layer
6
. The protecting layer
7
is formed, for example, in a manner that the surface of the second reflecting layer
6
is coated with resin coating or the like. Pits each having a size corresponding to a wavelength of 650 nm carrying information are spirally or concentrically formed on each recording layer according to a given modulation method.
To reproduce information from the recording layer
2
, the first reflecting layer
3
must permit some quantity of a laser beam to transmit therethrough. For this reason, the first reflecting layer
3
is made of a material having some degree of reflectivity and some degree of transmissivity, and is generally formed with a gold (Au) film of about 15 nm thick, or the like.
Information recorded in the double layer disc maybe played back or reproduced by a disc play-back or reproducing device. To play back the information, a laser beam converged by an objective lens, which is contained in a pickup optical system, is irradiated from the first substrate
1
of the rotating DVD toward the upper or lower recording layer. A reflecting light which is reflected by the reflecting layer (or intermediate reflecting film) formed on the recording layer) formed on the recording layer and is optically modulated by pits, grooves or the like, is received again through the objective lens, and converted into an electrical signal, and in this way a readout signal is formed. By using the readout signal, the information born by the recording layers is reproduced. Accordingly, when the DVD whose recording layer consists of double layers is compared with the DVD whose recording layer consists of a single layer, the former may have an increased recording capacity per one disc.
As described above, in the optical disc, its recording capacity per disc may be increased as the number of the recording layers increases. However, with increase of the number of the recording layers, the number of the intermediate layers also increases. To read information from a multi-layer disc having a number of recording layers, a laser beam passes through the intermediate layers. By the intermediate layers, a spherical aberration tends to occur. A reflecting light coming from the recording layer located far from the first substrate
1
contains a great spherical aberration component. This results in incorrect reproduction of information.
To lessen the adverse effect on the reflecting lights from the respective intermediate layers by the spherical aberration, each intermediate layer must be formed so as to have a thickness as thin as possible.
One of possible solutions to the above problem is to manufacture the multi-layer disc whose intermediate layer interlayered between the adjacent recording layers is extremely thin, e.g., about 3 &mgr;m. Such a disc allows information to exactly be read out of each recording layer without giving rise to an interlayer cross talk when the method disclosed in JP-A-11-242824 is used.
In actually manufacturing the multi-layer disc, a transparent sheet of a fixed thickness is sandwiched between the recording layers, and those layers are bonded together, whereby an intermediate layer is formed between the recording layers. And a space between the adjacent recording layers (interlayer distance) is determined by a thickness of the intermediate layer. Only the sum of the thickness of the transparent sheet and the bonding layer for bonding the recording layers reaches the target interlayer distance (e.g., 3 &mgr;m). Accordingly, it is difficult to manufacture a multi-layer disc having a small and stable space between the recording layers.
SUMMARY OF THE INVENTION
From the above background reasons, the present invention is to provide a multi-layer information recording medium in which a layer, e.g., an intermediate layer, formed between a multiple of recording layers is stably formed having a uniform predetermined height over the entire area of the layer, and a reproducing device which is capable of faithfully reproducing information from the recording layers.
To achieve the above object, there is provided a first information recording medium which comprises a substrate, and one or a plurality of layers formed on the substrate, wherein at least one of the layers is formed by mixing a base material and a hard material which has a predetermined thickness and determines a predetermined thickness of the layer.
In the first recording medium, the hard material of at least one of the layers is sandwiched between it and the adjacent substrate and a reflecting layer of another layer, so that the layer is stably formed while having a thickness equal to the height of the hard material over the entire layer.
In a second information recording medium, which depends from the first recording medium, the hard material contains spherical particles each of which has a predetermined outside diameter.
In the second recording medium, the hard material of the layer consisting of the hard material and the base material is sandwiched between it and the adjacent substrate and a reflecting layer of another layer, so that the layer is stably formed while having a thickness equal to the outside diameter of each particle contained in the hard material over the entire layer.
In a third information recording medium, which depends from the first recording medium, the hard material contains particles each configured like a column to have an outside diameter of a predetermined height.
In the third recording medium, the side face of a column-like material of the hard material of the layer consisting of the hard material and the base material is sandwiched between it and the adjacent layer or the reflecting layer of another layer, so that the layer is stably formed while having
Iwasaki Masayuki
Maeda Takanori
LandOfFree
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