Stock material or miscellaneous articles – Circular sheet or circular blank
Reexamination Certificate
2001-06-05
2003-06-10
Mulvaney, Elizabeth (Department: 1774)
Stock material or miscellaneous articles
Circular sheet or circular blank
C428S064500, C428S064600, C430S270130
Reexamination Certificate
active
06576318
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to data storage media and methods of manufacturing data storage media.
2. Description of the Related Art
FIG. 1
illustrates an ultra-high-density data storage device
10
according to the related art. The data storage device
10
is made up of a storage medium
20
and a tip wafer
30
positioned proximate to one surface of the storage medium
20
. The storage medium
20
contains nanometer-scaled data bits
40
that are written to and read from the storage medium
20
by emitters
50
located on the surface of the tip wafer
30
closest to the storage medium
20
. The writing and reading operations will be discussed below.
The emitters
50
bombard the data bits
40
with electron beams that are focused to nanometer-scaled spots. If the beams are of sufficiently high energy, the bombarded data bits
40
experience a phase change (e.g., between a crystalline and amorphous state). Effecting such a phase change constitutes writing to the storage medium
20
.
In the data storage device
10
illustrated in
FIG. 1
, a number of nanometer-scaled data bits
40
are contained within the storage medium
20
. If these data bits
40
have been written to by any of the emitters
50
as discussed above, they can be considered as data bits
40
that represent the number “1”. On the other hand, the data bits
40
that have not been written to can be considered to be data bits
40
that represent the number “0”.
Whether a data bit
40
represents a “1” or a “0” can be determined by bombarding the data bit
40
in question with a lower energy beam than is used in the writing operation and monitoring the interactions of the beam with the data bits
40
. Performing such steps is known as “reading” from the storage medium
20
.
An example of a reading operation includes bombarding the data bits
40
of the storage medium
20
with a low-energy electron beam that would not effectuate a phase change of the data bits
40
being bombarded. This exemplary reading operation also includes monitoring how the low-energy bombarding electrons interact with the data bit
40
. When a crystalline data bit
40
gets bombarded, a different number of electron-hole pairs are generated than when the low-energy electron beam bombards an amorphous data bit
40
. Hence, by monitoring the number of generated electron-hole pairs, it becomes possible to determine whether a data bit
40
represents a “1” or a “0”.
FIG. 2
illustrates a close-up view of the related art storage medium
20
used in the data storage device
10
illustrated in FIG.
1
. According to
FIG. 2
, the storage medium
20
is made up of a substrate
60
and of a crystalline phase-change layer
70
formed on one surface of the substrate
60
. Although not illustrated, the data bits
40
discussed above are written to and read from the crystalline, phase-change layer
70
.
FIG. 2
shows that the surface of the crystalline phase-change layer
70
furthest from the substrate
60
contains a high degree of surface roughness. Typically, the surface roughness exceeds 4.0 nanometer root-mean-square (RMS). Among other drawbacks, a surface roughness of this magnitude makes it difficult to form data bits
40
that are of a consistent size and therefore limits the resolution of the data storage device
10
.
According to the related art method of forming the crystalline phase-change layer
70
illustrated in
FIG. 2
, high-temperature deposition methods are used. However, under high-temperature conditions (e.g., about 300 degrees Celsius), the crystalline phase-change layer
70
formed on the substrate
60
develops the relatively rough surface illustrated in FIG.
2
and can have a granular surface morphology that is disfavored for ultra-high-density storage devices
10
.
Surface roughness is disfavored at least because it causes the data bits
40
to vary in geometry and can lead to added signal noise when reading from the storage medium
20
. Further, the high-temperature deposition of the crystalline phase-change layer
70
according to the related art can lead to the loss of volatile group VI elements such as selenium and tolerium (Se, Te) that are typically used in the storage medium
20
.
BRIEF SUMMARY OF THE INVENTION
According to one embodiment, a method of fabricating a data storage medium that includes forming a phase-change layer over a substrate, forming a thick capping layer over the phase-change layer, changing the phase-change layer from a first phase to a second phase, removing the thick capping layer, and forming a thin capping layer over the phase-change layer.
According to another embodiment, a data storage medium that includes a substrate, a phase-change layer positioned over the substrate, and a thin capping layer positioned over the phase-change layer, wherein a first surface of the phase-change layer is positioned closest to the thin capping layer and wherein the first surface of the phase-change layer has a root mean square (rms) surface roughness of less than 2 nanometers.
REFERENCES:
patent: 5557596 (1996-09-01), Gibson et al.
patent: 2001/0040860 (2001-11-01), Kondo
Bicknell-Tassius Robert
Lee Heon
Hewlett--Packard Development Company, L.P.
Mulvaney Elizabeth
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