U.S. patent application number 11/468829 was filed with the patent office on 2008-03-27 for data storage medium and method for high density data storage.
Invention is credited to Urs T. Duerig, Jane Elizabeth Frommer, Bernd Walter Gotsmann, Erik Christopher Hagberg, James Lupton Hedrick, Armin W. Knoll, Teddie Peregrino Magbitang, Robert Dennis Miller, Russell Clayton Pratt, Charles Gordon Wade.
Application Number | 20080076903 11/468829 |
Document ID | / |
Family ID | 39225878 |
Filed Date | 2008-03-27 |
United States Patent
Application |
20080076903 |
Kind Code |
A1 |
Duerig; Urs T. ; et
al. |
March 27, 2008 |
DATA STORAGE MEDIUM AND METHOD FOR HIGH DENSITY DATA STORAGE
Abstract
A composition of matter for a recording medium in atomic force
data storage devices. The composition includes polyimide oligomers
having covalently bonded monomers forming a backbone, the oligomer
thermally stable to at least 400.degree. C.; one or more covalent
bonding cross-linking moieties incorporated into the polyimide
oligomer; and one or more hydrogen bonding cross-linking moieties
incorporated into the polyimide oligomer. The covalent and hydrogen
bonding cross-linking of the polyimide oligomers may be tuned to
match thermal and force parameters required in read-write-erase
cycles.
Inventors: |
Duerig; Urs T.;
(Rueschlikon, CH) ; Frommer; Jane Elizabeth; (San
Jose, CA) ; Gotsmann; Bernd Walter; (Horgen, CH)
; Hagberg; Erik Christopher; (Evansville, IN) ;
Hedrick; James Lupton; (Pleasanton, CA) ; Knoll;
Armin W.; (Adliswil, CH) ; Magbitang; Teddie
Peregrino; (San Jose, CA) ; Miller; Robert
Dennis; (San Jose, CA) ; Pratt; Russell Clayton;
(Los Gatos, CA) ; Wade; Charles Gordon; (Los
Gatos, CA) |
Correspondence
Address: |
SCHMEISER, OLSEN & WATTS
22 CENTURY HILL DRIVE, SUITE 302
LATHAM
NY
12110
US
|
Family ID: |
39225878 |
Appl. No.: |
11/468829 |
Filed: |
August 31, 2006 |
Current U.S.
Class: |
528/310 |
Current CPC
Class: |
C08G 73/101 20130101;
C08G 73/1064 20130101; C08G 73/1085 20130101 |
Class at
Publication: |
528/310 |
International
Class: |
C08G 69/08 20060101
C08G069/08 |
Claims
1. A composition of matter, comprising: polyimide oligomers
comprising covalently bonded monomers, said monomers forming a
backbone, said polyimide oligomers thermally stable to at least
400.degree. C.; one or more covalent bonding cross-linking moieties
incorporated into said polyimide oligomers; and one or more
hydrogen bonding cross-linking moieties incorporated into said
polyimide oligomers.
2. The composition of claim 1, wherein said one or more hydrogen
bonding cross-linking moieties are located along said backbone.
3. The composition of claim 2, wherein said one or more hydrogen
bonding cross-linking moieties are selected from the group
consisting of ##STR00037## and moieties derived from imidazolyl,
pyrazolyl, pyrazinyl, pyrimidinyl, pyridazinyl indazoyl, purinyl,
phthalazinyl, naphthyridinyl, quinoxalinyl, quinazolinyl,
1,2,3-triazolyl, 1,2,4-triazolyl thiazolyl, isothiazolyl
1,3,5-triazinyl, 1,2,4-triazinyl, 1,2,3-triazinyl,
pyrido[3,4-b]-pyridinyl, pyrido[3,2-b]-pyridinyl,
pyrido[4,3-b]pyridinyl, purinyl, cinnolinyl, pteridinyl,
beta-carbolinyl, phenazinyl, 1,7-phenanthrolinyl,
1,10-phenanthrolinyl, 4,7-phenanthrolinyl, phenarsazinyl,
isothiazolyl, thienyl, and thianthrenyl imide.
4. The composition of claim 1, whereon said one or more hydrogen
bonding cross-linking moieties are located at terminal ends of said
backbone.
5. The composition of claim 5, wherein said one or more hydrogen
bonding cross-linking moieties are selected from the group
consisting of ##STR00038## moieties derived from
3,5-diamino-1,2,4-triazole, 2,6-diaminopurine,
2,6-diamino-8-purinol, 2,3-diaminopyridine, unsaturated
heterocyclic diamines derived by reduction of
2-amino-6-nitrobenzothiazole,
2-amino-5-(4-nitrophenylsulfonyl)thiazole,
2-amino-5-nitropyrimidine, 2-amino-5-nitrothiazole, or
3-amino-4-pyrazole carbonitrile, and moieties derived from ammonia
amination of 2-amino-5-bromopyrimidine, 2-amino-5-bromothiazole,
2-amino-4-chlorobenzothiazole, 2-amino-6-chlorobenzothiazole,
2-amino-4-(4-chlorophenyl)thiazole, 2-amino-6-chloropurine, or
2-amino-6-fluorobenzothiazole.
6. The composition of claim 1, wherein said covalent bonding
cross-linking moieties are located along said backbone.
7. The composition of claim 6 wherein said covalent bonding
cross-linking moieties have the structure: ##STR00039##
8. The composition of claim 1, wherein said covalent bonding
cross-linking moieties are located at terminal ends of said
backbone.
9. The composition of claim 8, wherein said covalent bonding
cross-linking moieties have the structure: ##STR00040##
10. The composition of claim 1, further including a reactive
diluent, said reactive diluent consisting of ##STR00041## where
R.sub.1, R.sub.2 and R.sub.3 are each independently selected from
the group consisting of hydrogen, alkyl groups, aryl groups,
cycloalkyl groups, alkoxy groups, aryloxy groups, alkylamino
groups, arylamino groups, alkylarylamino groups, arylthio,
alkylthio groups and ##STR00042##
11. A method, comprising: pushing a probe, heated to at least
100.degree. C., into a cross-linked resin layer formed by curing a
layer of the composition of claim 1; and removing said probe from
said resin layer, resulting in formation of a deformed region in
said resin layer.
12. The method of claim 11, said composition further including
covalent bonding cross-linking moieties located along said backbone
and wherein after said curing, said resin layer is cross-linked by
said covalent bonding cross-linking moieties.
13. The method of claim 11, said composition further including
covalent bonding cross-linking moieties located at terminal ends of
said backbone and wherein after said curing, said resin layer is
cross-linked by said covalent bonding cross-linking moieties.
14. The method of claim 11, said composition, further including a
reactive diluent, wherein said polyimide oligomers are covalently
cross-linked by reactive diluent groups derived from said reactive
diluent during said curing.
15. A method, comprising: bringing a thermal-mechanical probe into
proximity with a cross-linked resin layer multiple times to induce
deformed regions at points in said resin layer, said resin layer
formed by curing a layer of the composition of claim 1, said
thermal mechanical probe heating said points in said resin layer
above about 100.degree. C. to write information in said resin
layer.
16. The method of claim 15, further including: bringing said
thermal-mechanical probe into proximity with said points in said
resin layer to read said information.
17. The method of claim 16, further including: bringing said
thermal-mechanical probe into proximity with one or more of said
deformed regions in said resin layer, said thermal mechanical probe
heating said one or more of said deformed regions to above about
100.degree. C. to deform said one or more of said deformed regions
in such a way as to eliminate said one or more deformed regions to
erase said information.
18. The method of claim 17, further including: repeatedly writing,
reading and erasing information at said points in said resin
layer.
19. A data storage device, comprising: a recording medium for
storing data, said recording medium comprising a resin layer
overlying a substrate, said data represented by topographical
states of said resin layer, said resin layer comprising a thermally
cured layer of the composition of claim 1; a read-write head for
reading and writing data to said recording medium, said read-write
head having one or more thermo-mechanical probes, each of said
thermo-mechanical probes including an electrical resistive heating
region; and means for scanning said read-write head across a
surface of said recording medium.
20. The data storage device of claim 19, wherein: said one or more
thermal-mechanical probes are arranged in a two dimensional array;
and said data storage device further including: means for
independently applying electrical current to respective resistive
heating regions of each of said thermo-mechanical probes; means for
independently applying an electrostatic force on each of said
thermo-mechanical probes; means for independently writing data bits
to said recording medium with each of said one or more
thermo-mechanical probes; and means for independently reading data
bits from said recording medium with each of said one or more
thermo-mechanical probes.
21. The data storage device of claim 20, further including: means
for contacting said recording medium with respective tips of said
one or more thermo-mechanical probes.
22. A composition of matter comprising: a backbone structured as
E.sub.1 A.sub.1-A.sub.2-A.sub.3- . . . -A.sub.N E.sub.2, wherein N
is between about 10 and about 45, wherein A.sub.1-A.sub.2-A.sub.3-
. . . -A.sub.N is a linearly connected sequence of N covalently
bonded monomeric backbone units, wherein each of A.sub.1, A.sub.2,
A.sub.3 . . . A.sub.N is independently either a hydrogen bonding
cross-linking moiety, a covalently bonding cross-linking moiety or
a non-cross-linking moiety and E1 and E2 are terminal cross-linking
moieties.
23. The composition of matter of claim 22, wherein E.sub.1 and
E.sub.2 are both covalently bonding cross-linking moieties.
24. The composition of matter of claim 22, wherein E.sub.1 and
E.sub.2 are both hydrogen-bonding cross-linking moieties.
25. A method, comprising: bringing a thermal-mechanical probe into
proximity with a cross-linked resin layer multiple times to induce
deformed regions at points in said resin layer, said resin layer
formed by curing a layer of the composition of claim 22, said
thermal mechanical probe heating said points in said resin layer
above about 100.degree. C. to write information in said resin
layer.
26. The method of claim 25, further including: bringing said
thermal-mechanical probe into proximity with said points in said
resin layer to read said information.
27. The method of claim 26, further including: bringing said
thermal-mechanical probe into proximity with one or more of said
deformed regions in said resin layer, said thermal mechanical probe
heating said one or more of said deformed regions to above about
100.degree. C. to deform said one or more of said deformed regions
in such a way as to eliminate said one or more deformed regions to
erase said information.
28. A data storage device, comprising: a recording medium for
storing data, said recording medium comprising a resin layer
overlying a substrate, said data represented by topographical
states of said resin layer, said resin layer comprising a thermally
cured layer of the composition of claim 22; a read-write head for
reading and writing data to said recording medium, said read-write
head having one or more thermo-mechanical probes, each of said
thermo-mechanical probes including an electrical resistive heating
region; and means for scanning said read-write head across a
surface of said recording medium.
29. The data storage device of claim 28, wherein: said one or more
thermal-mechanical probes are arranged in a two dimensional array;
and said data storage device further including: means for
independently applying electrical current to respective resistive
heating regions of each of said thermo-mechanical probes; means for
independently applying an electrostatic force on each of said
thermo-mechanical probes; means for independently writing data bits
to said recording medium with each of said one or more
thermo-mechanical probes; and means for independently reading data
bits from said recording medium with each of said one or more
thermo-mechanical probes.
30. The data storage device of claim 29, further including: means
for contacting said recording medium with respective tips of said
one or more thermo-mechanical probes.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to the field of high-density
data storage and more specifically to compositions for a data
storage medium, a data storage method and a data storage system
using the data storage compositions.
BACKGROUND OF THE INVENTION
[0002] Current data storage methodologies operate in the micron
regime. In an effort to store ever more information in ever-smaller
spaces, data storage density has been increasing. As data storage
size increases and density increases and integrated circuit
densities increase, there is a developing need for data storage and
imaging methodologies that operate in the nanometer regime.
SUMMARY OF THE INVENTION
[0003] A first aspect of the present invention is a composition of
matter, comprising: polyimide oligomers comprising covalently
bonded monomers, the monomers forming a backbone, the polyimide
oligomers thermally stable to at least 400.degree. C.; one or more
covalent bonding cross-linking moieties incorporated into the
polyimide oligomers; and
[0004] one or more hydrogen bonding cross-linking moieties
incorporated into the polyimide oligomers.
[0005] A second aspect of the present invention is a method,
comprising: pushing a probe, heated to at least 100.degree. C.,
into a cross-linked resin layer formed by curing a layer of the
composition of the first aspect; and removing the probe from the
resin layer, resulting in formation of a deformed region in the
resin layer.
[0006] A third aspect of the present invention is a method,
comprising: bringing a thermal-mechanical probe into proximity with
a cross-linked resin layer multiple times to induce deformed
regions at points in the resin layer, the resin layer formed by
curing a layer of the composition of the first aspect, the thermal
mechanical probe heating the points in the resin layer above about
100.degree. C. to write information in the resin layer.
[0007] A fourth aspect of the present invention is a data storage
device, comprising: a recording medium for storing data, the
recording medium comprising a resin layer overlying a substrate,
the data represented by topographical states of the resin layer,
the resin layer comprising a thermally cured layer of the
composition of the first aspect; a read-write head for reading and
writing data to the recording medium, the read-write head having
one or more thermo-mechanical probes, each of the thermo-mechanical
probes including an electrical resistive heating region; and means
for scanning the read-write head across a surface of the recording
medium.
[0008] A fifth aspect of the present invention is a composition of
matter comprising: a backbone structured as E.sub.1+
A.sub.1-A.sub.2-A.sub.3- . . . -A.sub.N E.sub.2, wherein N is
between about 10 and about 45, wherein A.sub.1-A.sub.2-A.sub.3- . .
. -A.sub.N is a linearly connected sequence of N covalently bonded
monomeric backbone units, wherein each of A.sub.1, A.sub.2, A.sub.3
. . . A.sub.N is independently either a hydrogen bonding
cross-linking moiety, a covalently bonding cross-linking moiety or
a non-cross-linking moiety and E1 and E2 are terminal cross-linking
moieties.
[0009] A sixth aspect of the present invention is a method,
comprising: bringing a thermal-mechanical probe into proximity with
a cross-linked resin layer multiple times to induce deformed
regions at points in the resin layer, the resin layer formed by
curing a layer of the composition of the fifth aspect, the thermal
mechanical probe heating the points in the resin layer above about
100.degree. C. to write information in the resin layer.
[0010] A seventh aspect of the present invention is a data storage
device, comprising: a recording medium for storing data, the
recording medium comprising a resin layer overlying a substrate,
the data represented by topographical states of the resin layer,
the resin layer comprising a thermally cured layer of the
composition of the fifth aspect; a read-write head for reading and
writing data to the recording medium, the read-write head having
one or more thermo-mechanical probes, each of the thermo-mechanical
probes including an electrical resistive heating region; and means
for scanning the read-write head across a surface of the recording
medium.
BRIEF DESCRIPTION OF DRAWINGS
[0011] The features of the invention are set forth in the appended
claims. The invention itself, however, will be best understood by
reference to the following detailed description of an illustrative
embodiment when read in conjunction with the accompanying drawings,
wherein:
[0012] FIGS. 1A through 1C illustrate the structure and operation
of a tip assembly for a data storage device including the data
storage medium according to the embodiments of the present
invention;
[0013] FIG. 2 is an isometric view of a local probe storage array
including the data storage medium according to the embodiments of
the present invention;
[0014] FIG. 3 is a scanning force microscopy (SFM) image recorded
using thermo-mechanical sensing of a layer of polyimide resin
formulated according to an embodiment of the present invention
after a writing operation; and
[0015] FIG. 4 is an SFM image recorded using thermo-mechanical
sensing of the layer of polyimide resin of FIG. 3 after an erasing
operation.
DETAILED DESCRIPTION OF THE INVENTION
[0016] FIGS. 1A through 1C illustrate the structure and operation
of a tip assembly 100 for a data storage device including the data
storage medium according to the embodiments of the present
invention. In FIG. 1A, probe tip assembly 100 includes a U-shaped
cantilever 105 having flexible members 105A and 105B connected to a
support structure 110. Flexing of members 105A and 105B provides
for substantial pivotal motion of cantilever 105 about a pivot axis
115. Cantilever 105 includes a tip 120 fixed to a heater 125
connected between flexing members 105A and 105B. Flexing members
105A and 105B and heater 125 are electrically conductive and
connected to wires (not shown) in support structure 110. In one
example, flexing members 105A and 105B and tip 120 comprise
highly-doped silicon and have a low electrical resistance, and
heater 125 is formed of lightly doped silicon having a high
electrical resistance sufficient to heat tip 120, in one example,
between about 100.degree. C. and about 400.degree. C. when current
is passed through heater 125. The electrical resistance of heater
125 is a function of temperature.
[0017] Also illustrated in FIG. 1A is a storage medium (or a
recording medium) 130 comprising a substrate 130A, and a cured
polyimide resin layer 130B. In one example, substrate 130A
comprises silicon. Cured polyimide resin layer 130B may be formed
by solution coating, spin coating, dip coating or meniscus coating
uncured polyimide resin formulations and performing a curing
operation on the resultant coating. In one example, cured polyimide
resin layer 130B has a thickness between about 10 nm and about 500
nm and a surface roughness of less than about 1.0 nm evaluated in a
1 micron by 1 micron field and a variation in thickness of less
than about 10% across the cured polyimide resin layer. Cured
polyimide resin layer 130B includes thermally reversible hydrogen
bonding cross-linking moieties as well as thermally irreversible
(to at least 400.degree. C.) covalent bonding cross-linking
moieties. The composition of the uncured polyimide resin and cured
polyimide resin layer 130B is described in detail infra. An
optional penetration stop layer 130C is shown between cured
polyimide resin layer 130B and substrate 130A. Penetration stop
layer 130C limits the depth of penetration of tip 120 into cured
polyimide resin layer 130B.
[0018] Turning to the operation of tip assembly 100, in FIG. 1A, an
indentation 135 is formed in cured polyimide resin layer 130B by
heating tip 120 to a writing temperature T.sub.W by passing a
current through cantilever 105 and pressing tip 120 into cured
polyimide resin layer 130B. Heating tip 120 and applying a load
force, e.g. by electrostatic means as described in Patent
Application EP 05405018.2, 13 Jan. 2005, allows the tip to
penetrate the cured polyimide resin layer 130B forming indentation
135, which remains after the tip is removed. In one example, the
cured polyimide resin layer 130B is heated to about 150.degree. C.
or higher (depending upon the composition of cured polyimide layer
130B) by heated tip 120, and a load force of less than 500 nN is
applied (the exact value depending upon the composition of cured
polyimide layer 130B, the temperature of the heated tip and the
desired indentation size) to form indentation 135. As indentations
135 are formed, a ring 135A of cured polyimide oligomer is formed
around the indentation. Indentation 135 represents a data bit value
of "1", a data bit value of "0" being represented by an absence of
an indentation.
[0019] FIGS. 1B and 1C illustrate reading the bit value. In FIGS.
1B and 1C, tip assembly 100 is scanned across a portion of cured
polyimide resin layer 130B. When tip 120 is over a region of cured
polyimide resin layer 130B not containing an indentation, heater
125 is a distance D1 from the surface of the cured polyimide resin
layer (see FIG. 1B). When tip 120 is over a region of cured
polyimide resin layer 130B containing an indentation, heater 125 is
a distance D2 from the surface of the cured polyimide resin layer
(see FIG. 1C) because the tip "falls" into the indentation. D1 is
greater than D2. If heater 125 is at a temperature T.sub.R (read
temperature), which is lower than T.sub.W (write temperature),
there is more heat loss to substrate 130A when tip 120 is in an
indentation than when the tip is not. This can be measured as a
change in resistance of the heater, thus "reading" the data bit
value. It is advantageous to use a separate heater for reading,
which is mechanically coupled to the tip but thermally isolated
from the tip. A typical embodiment is disclosed in Patent
Application EP 05405018.2, 13 Jan. 2005.
[0020] "Erasing" (not shown) is accomplished by positioning tip 120
in close proximity to indentation 135, heating the tip to a
temperature T.sub.E (erase temperature), and applying a loading
force F.sub.E, which causes the previously written indent to relax
to a flat state whereas a new indent is written slightly displaced
with respect to the erased indent. The cycle is repeated as needed
for erasing a stream of bits whereby an indent always remains at
the end of the erase track. The erase temperature T.sub.E and the
erase force F.sub.E may be chosen differently from the write
temperature T.sub.W and the write force F.sub.W. Typically, T.sub.E
is greater than T.sub.W, and/or F.sub.E is smaller than F.sub.W.
The erase pitch is typically on the order of the rim radius. In one
example, the cured polyimide resin layer 130B is heated to about
150.degree. C. or higher by heated tip 120, and the erase pitch is
10 nm to eliminate indentation 135.
[0021] FIG. 2 is an isometric view of a local probe storage array
140 including the data storage medium according to the embodiments
of the present invention. In FIG. 2, local probe storage array 140
includes substrate 145 having a cured polyimide resin layer 150 the
same as cured polyimide resin layer 130B of FIGS. 1A, 1B and 1C,
which acts as the data-recording layer. An optional tip penetration
stop layer may be formed between cured polyimide resin layer 150
and substrate 145. In one example, substrate 145 comprises silicon.
Cured polyimide resin layer 150 may be formed by solution coating,
spin coating, dip coating or meniscus coating uncured polyimide
resin formulations and performing a curing operation on the
resultant coating. In one example, cured polyimide resin layer 150
has a thickness between about 10 nm and about 500 nm and a
variation in thickness across a writeable region of cured polyimide
resin layer 150 of less than about 1.0 inn across the cured
polyimide resin layer. The composition of cured polyimide resin
layer 150 is the same as cured polyimide resin layer 130B of FIG.
1C. Positioned over cured polyimide resin layer 150 is a probe
assembly 155 including an array of probe tip assemblies 100
(described supra). Probe assembly 155 may be moved in the X, Y and
Z directions relative to substrate 145 and cured polyimide resin
layer 150 by any number of devices as is known in the art.
Switching arrays 160A and 160B are connected to respective rows
(X-direction) and columns (Y-direction) of probe tip assemblies 100
in order to allow addressing of individual probe tip assemblies.
Switching arrays 160A and 160B are connected to a controller 165
which includes a write control circuit for independently writing
data bits with each probe tip assembly 100, a read control circuit
for independently reading data bits with each probe tip assembly
100, an erase control circuit for independently erasing data bits
with each probe tip assembly 100, a heat control circuit for
independently controlling each heater of each of the probe tip
assembles 100, and X, Y and Z control circuits for controlling the
X, Y and Z movement of probe assembly 155. The Z control circuit
controls a contact mechanism (not shown) for contacting the cured
polyimide resin layer 150 with the tips of the array of probe tip
assemblies 100.
[0022] During a write operation, probe assembly 155 is brought into
proximity to cured polyimide resin layer 150 and probe tip
assemblies 100 are scanned relative to the cured polyimide resin
layer. Local indentations 135 are formed as described supra. Each
of the probe tip assemblies 100 writes only in a corresponding
region 170 of cured polyimide resin layer 150. This reduces the
amount of travel and thus time required for writing data.
[0023] During a read operation, probe assembly 155 is brought into
proximity to cured polyimide resin layer 150 and probe tip
assemblies 100 are scanned relative to the cured polyimide resin
layer. Local indentations 135 are detected as described supra. Each
of the probe tip assemblies 100 reads only in a corresponding
region 170 of cured polyimide resin layer 150. This reduces the
amount of travel and thus the time required for reading data.
[0024] During an erase operation, probe assembly 155 is brought
into proximity to cured polyimide resin layer 150, and probe tip
assemblies 100 are scanned relative to the cured polyimide resin
layer. Local indentations 135 are erased as described supra. Each
of the probe tip assemblies 100 reads only in a corresponding
region 170 of cured polyimide resin layer 150. This reduces the
amount of travel and thus time required for erasing data.
[0025] Additional details relating to data storage devices
described supra may be found in the articles "The Millipede--More
than one thousand tips for future AFM data storage," P. Vettiger et
al., IBM Journal of Research and Development. Vol. 44 No. 3, May
2000 and "The Millipede--Nanotechnology Entering Data Storage," P.
Vettiger et al., IEEE Transaction on Nanotechnology, Vol. 1, No, 1,
March 2002. See also United States Patent Publication 2005/0047307,
Published Mar. 3, 2005 to Frommer et al. and United States Patent
Publication 2005/0050258, Published Mar. 3, 2005 to Frommer et al.,
both of which are hereby included by reference in there
entireties.
[0026] Turning to the composition of cured polyimide resin layer
130B of FIGS. 1A through 1C and cured polyimide resin layer 150 of
FIG. 2, there are multiple uncured resin formulations of polyimide
oligomers (dianhydride/diamine condensation oligomers) and
cross-linking agents that, when reacted (cured) together,
cross-link to formed cured polyimide resin layers. It should be
understood that for the purposes of the present invention curing an
oligomer implies cross-linking the oligomer to form a resin.
Oligomers themselves are short chain oligomers. The polyimide
oligomers of the embodiments of the present invention
advantageously have molecular weights between about 4000 Daltons
and about 12000 Daltons.
[0027] The polyimide medium or imaging layer of the embodiments of
the present invention advantageously meets certain criteria. These
criteria include high thermal stability to withstand millions of
write and erase events, low wear properties (low pickup of material
by tips), low abrasion (tips do not easily wear out), low viscosity
for writing, glassy character with little or no secondary
relaxations for long data bit lifetime, and shape memory for
erasability.
[0028] Thermal and oxidative stability was imparted to cured
polyimide resins by incorporating a large aromatic content in the
polyimide oligomers and by ladder type linkages such as imide
moieties. The polyimide oligomers incorporate irreversible covalent
bonding cross-linking moieties in the backbone of the polyimide
oligomer (backbone covalent bonding linkers) or irreversible
covalent bonding cross-linking moieties at the terminal ends of the
polyimide oligomer (terminal covalent bonding linkers), or both
backbone and terminal covalent bonding linkers. Cured polyimide
resins according to embodiments of the present invention have high
temperature stability while maintaining a low glass transition
temperature (T.sub.g), which is contrary to current teaching that
high temperature stability results in a high T.sub.g and vice
versa. In one example, cured polyimide resins according to
embodiments of the present invention are thermally and oxidatively
stable to at least 400.degree. C.
[0029] Wear and erasability (and writeability) of the media were
improved by incorporation of thermally reversible hydrogen bonding
cross-linking moieties into the backbone of the polyimide oligomer
(backbone hydrogen bonding linkers) or incorporation of thermally
reversible hydrogen bonding cross-linking moieties at the terminal
ends of the polyimide oligomer (terminal hydrogen binding linkers)
or by incorporation of both backbone and terminal hydrogen bonding
linkers into the polyimide oligomer. Because the cross-linking
bonds between polyimide oligomers formed by the hydrogen bonding
linkers are thermally reversible, less energy is required to
thermally deform the polyimide resin as breaking the hydrogen bonds
effectively and momentarily lowers the T.sub.g of the polyimide
resin which then returns to its higher value when the heat source
is removed and the hydrogen bonds reestablish themselves.
[0030] Further control over the cross-link density was achieved by
adding controlled amounts of reactant diluents described infra that
enhance covalent cross-linking. These reactive diluents form a high
density of cross-links that enhance the wear properties of the
polyimide medium without greatly increasing the T.sub.g or breadth
of the glass transition.
[0031] The glass transition temperature was adjusted for good write
performance. To optimize the efficiency of the write process there
should be a sharp transition from the glassy state to the rubbery
state. A sharp transition allows the cured resin to flow easily
when a hot tip is brought into contact and quickly return to the
glassy state once the hot tip is removed. However, too high a
T.sub.g leads to high write power and damage to the probe tip
assemblies. Examples of cured polyimide resins of the embodiments
of the present invention have T.sub.gs between about 150.degree. C.
and about 280.degree. C.
[0032] Good flow and low viscosities necessary for writing were
obtained by the incorporation of hetero-atoms such as oxygen and
sulfur in the polyimide resin backbone and varying the catenation
of aromatic rings from para to meta linkages. General formulations
of uncured polyimide resins according to embodiments of the present
invention are illustrated in Table I. An "X" under one of uncured
formulations A, B1, B2, C, D1, D2, E, F1, F2, G1, G2, H1, H2, I1
and I2 indicates the polyimide oligomer includes the moiety and
functionality indicated. (See Note 1 for an important proviso.) It
should be noted that the primary monomer diamine does not have
hydrogen-bonding capability, but can be replaced in some
formulations (i.e. B2, D2, F2, G2, H2 and I2) with a diamine that
does have hydrogen-bonding capability.
TABLE-US-00001 TABLE I FORMULATION MOIETIES A B1 B2 C D1 D2 E F1 F2
G1 G2 H1 H2 I1 I2 Primary Monomer X X X X X X X X X X X X X X X
(Dianhydride) Primary Monomer X X X X X X X X X (Diamine) No
H-Bonding Terminal End X.sup.1 X X X X X X.sup.1 X.sup.1 X.sup.1
X.sup.1 Covalent Bonding Cross Linker Backbone X X X X X X X X X X
Covalent Bonding Cross Linker Terminal End X.sup.1 X X X.sup.1
X.sup.1 X.sup.1 X.sup.1 X X Hydrogen Bonding Cross Linker Backbone
X X X X X X X X X X X X Hydrogen Bonding Cross Linker Notes
.sup.1The same polyimide oligomer cannot have both a terminal end
covalent bonding cross linker and a terminal end hydrogen bonding
cross linker. Note 2 - all polyimide oligomers according the
various embodiments of the present invention advantageously have a
molecular weight of from about 5,000 Daltons to about 15,000
Daltons.
[0033] It is a feature of the embodiments of the present invention
that the polyimide oligomers include both a covalent bonding
cross-linking moiety and a hydrogen bonding cross-linking moiety.
Inclusion of a reactive diluent in the uncured formulation is
optional for all uncured formulations. All uncured formulations
advantageously include a casting solvent to allow solution coating,
spin coating, dip coating or meniscus coating of the uncured
formulations to form a layer of uncured resin on a substrate. The
solvent is then driven off during thermal curing. In one example,
curing is performed at about 350.degree. C. to about 400.degree. C.
Examples of casting solvents include, but are not limited to, polar
organic solvents such as tetrahydrofuran (THF), dichloromethane
(CH.sub.2Cl.sub.2), N-methylpyrrolidone (NMP), and cyclohexanone
and mixtures of THE and acids such as hydrochloric acid, acetic
acid and trifluoroacetic acid. The acids act as solubilizing
agents, breaking the cross-linking hydrogen bonds between oligomer
chains.
[0034] A general example of uncured formulation B1/B2
(incorporating backbone hydrogen bonding moieties) comprises
polyimide oligomers having the structure:
##STR00001##
[0035] wherein R' is selected from a first group consisting of
##STR00002##
[0036] wherein each R'' group is independently selected from a
second group, a third group or from both the second and third
groups, the second group consisting of
##STR00003##
[0037] said third group consisting of
##STR00004##
imidazolyl, pyrazolyl, pyrazinyl, pyrimidinyl, pyridazinyl
indazoyl, purinyl, phthalazinyl, naphthyridinyl, quinoxalinyl,
quinazolinyl, 1,2,3-triazolyl, 1,2,4-triazolyl thiazolyl,
isothiazolyl 1,3,5-triazinyl, 1,2,4-triazinyl, 1,2,3-triazinyl,
pyrido[3,4-b]-pyridinyl, pyrido[3,2-b]-pyridinyl,
pyrido[4,3-b]pyridinyl, purinyl, cinnolinyl, pteridinyl,
beta-carbolinyl, phenazinyl, 1,7-phenanthrolinyl,
1,10-phenanthrolinyl, 4,7-phenanthrolinyl, phenarsazinyl,
isothiazolyl, thienyl, and thianthrenyl imide, and
[0038] wherein n is an integer from about 5 to about 50.
[0039] Structure (XI) is triazole.
[0040] The endgroup, having the structure:
##STR00005##
provides terminal covalent cross-linking of the polyimide
oligomers. In structure (I) there are (n+1)R'' groups. In a first
example, some of the (n+1)R'' groups are selected from the second
group and some of the (n+1)R'' groups are selected from the third
group. In a second example, all the (n+1)R'' groups are selected
from the third group. The ratio of the number of R'' groups
incorporated into the backbone of a B1/B2 type oligomer from the
second group to the number of R'' groups incorporated from the
third group may be controlled by adjustment of the relative amounts
of primary monomer diamine (with no hydrogen bonding capability)
and backbone hydrogen bonding cross linker reagents used in the
polyimide oligomer preparation reaction, examples of which are
provided infra.
[0041] A general example of uncured formulation F1/F2
(incorporating backbone hydrogen bonding moieties and backbone
covalent bonding moieties) comprises linear polyimide oligomers
having the structure:
E.sub.1 A.sub.1-A.sub.2-A.sub.3- . . . -A.sub.N E.sub.2
(XIII-A)
wherein E.sub.1 is structured as
##STR00006##
wherein each of A.sub.1, A.sub.2, A.sub.3 . . . A.sub.N is
independently either
##STR00007##
wherein E.sub.1 is structured as
##STR00008##
wherein N is an integer from about 10 to about 45 and wherein from
about 8 to about 35 of A.sub.1, A.sub.2, A.sub.3 . . . A.sub.N
are
##STR00009##
and from about 2 to about 10 of A.sub.1, A.sub.2, A.sub.3 . . .
A.sub.N are
##STR00010##
wherein R' is selected from the first group consisting of
##STR00011##
[0042] wherein each R'' group is independently selected from a
second group, a third group or from both the second and third
groups, the second group consisting of
##STR00012##
[0043] the third group consisting of
##STR00013##
imidazolyl, pyrazolyl, pyrazinyl, pyrimidinyl, pyridazinyl
indazoyl, purinyl, phthalazinyl, naphthyridinyl, quinoxalinyl,
quinazolinyl, 1,2,3-triazolyl, 1,2,4-triazolyl thiazolyl,
isothiazolyl 1,3,5-triazinyl, 1,2,4-triazinyl, 1,2,3-triazinyl,
pyrido[3,4-b]-pyridinyl, pyrido[3,2-b]-pyridinyl,
pyrido[4,3-b]pyridinyl, purinyl, cinnolinyl, pteridinyl,
beta-carbolinyl, phenazinyl, 1,7-phenanthrolinyl,
1,10-phenanthrolinyl, 4,7-phenanthrolinyl, phenarsazinyl,
isothiazolyl, thienyl, and thianthrenyl imide, and
[0044] wherein at least one R'' group is selected from the third
group.
[0045] Structure (XI) is triazole. In one example structure
(XIII-A) has a molecular eight of from about 5,000 Daltons to about
15,000 Daltons, with a molecular weight of bout 7,000 Daltons to
about 9000 Daltons preferred.
[0046] The endgroup, having the structure:
##STR00014##
provides terminal covalent cross-linking of the polyimide
oligomers.
[0047] The backbone group, having the structure:
##STR00015##
provides backbone covalent cross-linking of the polyimide
oligomers.
[0048] In a first example, some R'' groups included in structure
(XIII-A) are selected from the second group and some R'' groups are
selected from the third group. In a second example, all R'' groups
included in structure (XIII-A) are selected from the third group.
The ratio of the number of R'' groups incorporated into the
backbone of a F1/F2 type oligomer from the second group to the
number of R'' groups incorporated from the third group may be
controlled by adjustment of the relative amounts of primary monomer
diamine (with no hydrogen bonding capability) and backbone hydrogen
bonding cross linker reagents used in the polyimide oligomer
preparation reaction, examples of which are provided infra.
[0049] A general example of uncured formulation C (incorporating
terminal hydrogen bonding moieties) comprises polyimide oligomers
having the structure:
##STR00016##
[0050] wherein R' is selected from the group consisting of
##STR00017##
[0051] wherein each R'' group is selected from the group consisting
of
##STR00018##
[0052] wherein said Z is selected from the group consisting of
##STR00019##
3,5-diamino-1,2,4-triazole, 2,6-diaminopurine, and
2,6-diamino-8-purinol, 2,3-diaminopyridine; and
[0053] wherein n is an integer from about 5 to about 50.
[0054] Z may also be selected from unsaturated heterocyclic diamine
moities produced by reduction of 2-amino-6-nitrobenzothiazole,
2-amino-5-(4-nitrophenylsulfonyl)thiazole,
2-amino-5-nitropyrimidine, 2-amino-5-nitrothiazole, or
3-amino-4-pyrazole carbonitrile.
[0055] Z may also be selected from moieties produced by from
ammonia Amination of 2-amino-5-bromopyrimidine,
2-amino-5-bromothiazole, 2-amino-4-chlorobenzothiazole,
amino-6-chlorobenzothiazole, 2-amino-4-(4-chlorophenyl)thiazole,
2-amino-6-chloropurine, or 2-amino-6-fluorobenzothiazole.
[0056] Examples of reactive diluents include structure (XXIII):
##STR00020##
where R.sub.1, R.sub.2 and R.sub.3 are each independently selected
from the group consisting of hydrogen, alkyl groups, aryl groups,
cycloalkyl groups, alkoxy groups, aryloxy groups, alkylamino
groups, arylamino groups, alkylarylamino groups, arylthio,
alkylthio groups and
##STR00021##
[0057] It should be noted that reactive diluents (XXIII) and (XXIV)
contain three substituted phenylethynyl groups. The phenylethynyl
groups of the polyimide oligomers and the phenylethynyl group's
reactive diluents provide the cross-linking of the polyimide
oligomers into a polyimide resin.
[0058] An exemplary hydrogen-bonding cross-linking of polyimide
oligomers according to embodiments of the present invention is
illustrated in structure (XXV). The thermally reversible hydrogen
bonds (indicated by the dashed lines) are capable of evanescence
and reversion. Generally speaking evanescence and reversion of a
thermally reversible bond is an equilibrium process. Above a
threshold temperature, evanescence of the bond is favored. Below
the threshold temperature, reversion of the bond is favored.
Hydrogen bonding may also be described as a donation and withdrawal
of electrons to a thermally reversible bond.
##STR00022##
[0059] By contrast, covalent bonds are not capable of evanescence
and reversion as described supra, but remain relatively stable over
a range of temperatures, until such temperatures at which the bond
irreversibly/permanently degrades
EXPERIMENTAL
[0060] In the following preparation examples, Table II lists the
polyimide oligomer reagents used and the moiety/functionality
provided by each reagent as well as the shorthand notation
used.
TABLE-US-00002 TABLE II Chemical Name Notation Moiety/Functionality
1,3,bis(4'-aminophenoxy)benzene APB Diamine (backbone) Non
H-Bonding 4,4'(4,4'-isopropyidene- BisADA Dianhydride (backbone
diphenoxy)bisphthalic anhydride 3,5-diamino-4'-phenylethynyl DABPP
Backbone covalent benzophenone bonding linker
4-phenylethynylpthalic anhydride DABPPE Terminal covalent bonding
linker 3,5-diamino-1,2,4-triazole DAT Backbone hydrogen- bonding
linker 3-amino-1,2,4-triazole AT Terminal hydrogen bonding
linker
[0061] All materials were purchased from Aldrich and used without
further purification. The monomers 1,3-bis(4'-aminophenoxy)benzene
and 4,4'(4,4'-isopropyidene-diphenoxy)bisphthalic anhydride) were
purchased from ChrisKev. The dianhydride was recrystallized from
toluene and acetic anhydride.
[0062] In general polyimide synthesis comprised dissolving the
monomers, a diamine and a dianhydride (and other reagents from
which the cross-linking moieties are derived) in dry NMP under a
dry atmosphere. The reactants were stirred for between 14 and 20
hours after which 3 mole equivalents of triethylamine and acetic
anhydride were added to effect imidization. The reaction was then
allowed to stir for about 48 hours at room temperature followed by
two hours at 60.degree. C. The oligomer was precipitated by pouring
the reaction mixture into stirring methanol. The oligomer was
collected by vacuum filtration and was washed on the frit with
water, saturated sodium bicarbonate solution, and methanol. Finally
the oligomer was precipitated twice from NMP and dried overnight in
a 60.degree. C. vacuum oven.
EXAMPLE 1a
Terminal Covalent Cross-Linking with Backbone Hydrogen-Bonding
Cross-Linking (Example of Formulation B1 of Table I)
[0063] To a round bottom flask equipped with a stirrer 1.047 grams
(0.00358 mol) of APB, 0.152 gram (0.153 mol) of DAT, 2.181 grams
(0.0042 mol) of bis ADA and 0.457 gram (0.00184 mol) of DABPPE were
charged and rinsed down with 40 ml of NMP and allowed to stir
overnight (between 14 and 20 hours) to generate the
poly(amic-acid). Triethylamine (1.52 grams) and acetic anhydride
(1.0 gram) were added to effect imidization and the reaction was
then allowed to stir for 48 hours at room temperature followed by
two hours at 60.degree. C. The oligomer was precipitated by pouring
the reaction mixture into stirring methanol. The oligomer was
collected by vacuum filtration and was washed on the frit with
water, saturated sodium bicarbonate solution, and methanol. Finally
the oligomer was precipitated twice from NMP and dried overnight in
a 60.degree. C. vacuum oven.
##STR00023##
[0064] The polyimide oligomer of example 1a should not be thought
of as requiring the monomers within the ( )n being in a linear
subsequence followed by all monomers within the ( )m being in a
second linear subsequence; they are shown that way to indicate
there n and m numbers of the two monomers. Rather, the two monomers
may be arranged in a linear sequence with (a) all n type monomers
in one subsequence and all m type monomers in another subsequence,
(b) in an alternating sequence, (c) in other regular repeating
sequences or (d) in random sequence.
EXAMPLE 1b
Terminal Covalent Cross-Linking with Backbone Hydrogen-Bonding
Cross-Linking (Example of Formulation B2 of Table I Where the
Primary Monomer Diamine and the Backbone Hydrogen-Bonding
Cross-Linker are the Same Reagent)
[0065] To a round bottom flask equipped with a stirrer 0.506 grams
(0.55 mol) of DAT, 2.181 grams (0.0042 mol) of bis ADA and 0.457
gram (0.00184 mol) of DABPPE were charged and rinsed down with 40
ml of NMP and allowed to stir overnight (between 14 and 20 hours)
to generate the poly(amic-acid). Triethylamine (1.52 grams) and
acetic anhydride (1.0 gram) were added to effect imidization and
the reaction was then allowed to stir for 48 hours at room
temperature followed by 2 hours at 60.degree. C. The oligomer was
precipitated by pouring the reaction mixture into stirring
methanol. The oligomer was collected by vacuum filtration and was
washed on the frit with water, saturated sodium bicarbonate
solution, and methanol. Finally the oligomer was precipitated twice
from NMP and dried overnight in a 60.degree. C. vacuum oven.
##STR00024##
EXAMPLE 2
Terminal Hydrogen-Bonding Cross-Linking with Backbone Covalent
Cross-Linking (Example of Formulation C of Table I)
[0066] To a round bottom flask equipped with a stirrer 1.087 gram
(0.0037 mol) of APB, 2.659 grams (0.0051 mol) of bis ADA and 0.290
gram (0.00093 mol) of DABPPE and 0.77 gram (0.00092 mol) of AT were
charged and rinsed down with 40 ml of NMP and allowed to stir
overnight (between 14 and 20 hours) to generate the
poly(amic-acid). Triethylamine (1.52 grams) and acetic anhydride
(1.0 gram) were added to effect imidization and the reaction was
then allowed to stir for 48 hours at room temperature followed by 2
hours at 60.degree. C. The oligomer was precipitated by pouring the
reaction mixture into stirring methanol. The oligomer was collected
by vacuum filtration and was washed on the frit with water,
saturated sodium bicarbonate solution, and methanol. Finally the
oligomer was precipitated twice from NMP and dried overnight in a
60.degree. C. vacuum oven.
##STR00025##
[0067] The polyimide oligomer of example 2 should not be thought
requiring the monomers within the ( )n being in a linear
subsequence followed by all monomers within the ( )m being in a
second linear subsequence; they are shown that way to indicate
there a n and m numbers of the two monomers. Rather, the two
monomers may be arranged in a linear sequence with (a) all n type
monomers in one subsequence and all m type monomers in another
subsequence, (b) in an alternating sequence, (c) in other regular
repeating sequences or (d) in random sequence.
EXAMPLE 3
Terminal Covalent Cross-Linking with Backbone Hydrogen-Bonding
Cross-Linking (Example of Formulation I1 of Table I)
[0068] To a round bottom flask equipped with a stirrer 0.3687 gram
(0.0037 mol) of DAT, 2.659 grams (0.00093 mol) of bis ADA and 0.290
gram (0.00093 mol) of DABPPE and 0.077 gram (0.00092 mol) of AT
were charged and rinsed down with 40 ml of NMP and allowed to stir
overnight (between 14 and 20 hours) to generate the
poly(amic-acid). Triethylamine (1.52 grams) and acetic anhydride
(1.0 gram) were added to effect imidization and the reaction was
then allowed to stir for 48 hours at room temperature followed by 2
hours at 60.degree. C. The oligomer was precipitated by pouring the
reaction mixture into stirring methanol. The oligomer was collected
by vacuum filtration and was washed on the frit with water,
saturated sodium bicarbonate solution, and methanol. Finally the
oligomer was precipitated twice from NMP and dried overnight in a
60.degree. C. vacuum oven.
##STR00026##
[0069] The polyimide oligomer of example 3 should not be thought of
as requiring the monomers within the ( )n being in a linear
subsequence followed by all monomers within the ( )m being in a
second linear subsequence followed by the monomers within the ( )p
being in a third linear subsequence; they are shown that way to
indicate there n, m and p numbers of the three monomers. Rather,
the three monomers may be arranged in a linear sequence with (a)
all n type monomers in one subsequence, all m type monomers in a
second subsequence and all the p type monomers in a third
subsequence, (b) in an alternating sequence, (c) in other regular
repeating sequences or (d) in random sequence,
[0070] Samples having the structure:
##STR00027##
where R' was:
##STR00028##
and where some R'' groups were (A):
##STR00029##
and some R'' groups were (B):
##STR00030##
and n was consistent with the listed molecular weights in TABLE III
were prepared and the properties indicated in Table III were
measured.
TABLE-US-00003 TABLE III Poly-Dispersity Mol. Wt Index T.sub.g
(.degree. C.) T.sub.g (.degree. C.) T.sub.g (.degree. C.) SAMPLE
R'' = % A R'' = % B Daltons) (PDI) uncured cured TRIS-2 #1 10 90
7700 1.4 168 198 216 #2 30 70 6000 1.3 178 223 246
[0071] Table III indicates that that varying the amount of
hydrogen-bonding linker moieties incorporated into the backbone of
the polyimide oligomer allows tuning of such physical properties as
the glass transition temperature Tg. Similarly, melt viscosity,
modulus and shape memory of the cured polyimide resins can be
tuned. The last column gives the T.sub.g after curing uncured
samples #1 and #2 with 30% by weight of the reactive diluent
TRIS-2, structure (XXIV).
[0072] Samples having the structure:
##STR00031##
where R' was:
##STR00032##
where Z was:
##STR00033##
where some R'' groups were (A):
##STR00034##
and some R'' groups were (B):
##STR00035##
or (C):
##STR00036##
and n was consistent with the listed molecular weights in TABLE IV
were prepared and the properties indicated in Table IV were
measured.
TABLE-US-00004 TABLE IV Mol. Wt SAMPLE R'' = % A R'' = % B R'' = %
C Daltons PDI #3 80 0 20 8000 1.7 #4 0 80 20 7900 1.8
[0073] Table IV indicates that incorporation of hydrogen-bonding
linker moieties at the terminal ends of the polyimide oligomer
allows the cured polyimide resin to act as a high molecular weight
oligomer. However, upon heating the effective molecular weight of
the resin is reduced.
[0074] TGA studies of polyimide resins of the embodiments of the
present invention confirmed that the incorporation of
2,4-diaminotriazole (a backbone hydrogen bonding cross linker) did
not reduce the thermal stability of the oligomer compared to the
standard polyimide resins incorporating only backbone covalent
bonding linkers.
[0075] The hydrogen bonding of polyimide resins of the embodiments
of the present invention was studied by variable temperature FT-IR.
IR transparent silicon wafers were coated with 500 nm of a
polyimide oligomer with 30% of the repeat units containing the
hydrogen bonding triazole moiety and the films were cross-linked at
300.degree. C. to about 350.degree. C. IR spectra were taken over
the temperature range of 50 to 200.degree. C. At temperatures below
80.degree. C., a broad signal at 3481 wave numbers was observed due
to the N--H of the triazole moiety. As the temperature increased,
this signal shifted to 3496 wave numbers at 90.degree. C.
indicating dissociation of the hydrogen bond.
[0076] The nature of the hydrogen bonding of polyimide resins of
the embodiments of the present invention was also studied by
dynamic mechanical analysis. In addition to a large change in
modulus observed at the glass transition of the oligomer, a low
intensity relaxation was observed at about 105.degree. C. to about
110.degree. C. for samples containing 25% of the hydrogen-bonding
moiety. A local maximum in the tan delta (ratio of the loss modulus
to the storage modulus of the oligomer) was observed, which is
believed to result form the dissociation of the hydrogen bonds in
the sample. This feature becomes more pronounced with increasing
hydrogen bonding moiety content.
[0077] Write and erase studies were performed using sample #2
described supra to which end FIG. 3 is an SFM image recorded using
thermo-mechanical sensing of a layer of polyimide resin formulated
according to an embodiment of the present invention after a writing
operation and FIG. 4 is an SFM image recorded using
thermo-mechanical sensing of the layer of polyimide resin of FIG. 3
after an erasing operation.
[0078] In FIG. 3, data were written with a signal-to-distortion
(SDR) ratio of about 10 dB at densities of about 600 Gb/inch.sup.2.
In FIG. 4, the temperature of the erasing tip varies from about
200.degree. C. to about 550.degree. C. from the bottom to the top
of the micrograph.
[0079] Thus, the embodiments of the present invention provide data
storage and imaging methodologies that operate in the nanometer
regime.
[0080] The description of the embodiments of the present invention
is given above for the understanding of the present invention. It
will be understood that the invention is not limited to the
particular embodiments described herein, but is capable of various
modifications, rearrangements and substitutions as will now become
apparent to those skilled in the art without departing from the
scope of the invention. Therefore, it is intended that the
following claims cover all such modifications and changes as fall
within the true spirit and scope of the invention.
* * * * *