Abstract:
A composition of matter for the recording medium of nanometer scale thermo-mechanical information storage devices and a nanometer scale thermo-mechanical information storage device. The composition includes: one or more polyaryletherketone copolymers, each of the one or more polyaryletherketone copolymers comprising (a) a first monomer including an aryl ether ketone and (b) a second monomer including an aryl ether ketone and a first phenylethynyl moiety, each of the one or more polyaryletherketone copolymers having two terminal ends, each terminal end having a phenylethynyl moiety the same as or different from the first phenylethynyl moiety. The one or more polyaryletherketone copolymers are thermally cured and the resulting cross-linked polyaryletherketone resin used as the recording layer in an atomic force data storage device.

Description:
This application is a continuation of copending U.S. patent application Ser. No. 11/618,940 filed on Jan. 2, 2007. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to the field of high-density data storage and read-back and more specifically to a data storage and read-back medium, a data storage and read-back system, and a data storage and read-back method. 
     BACKGROUND OF THE INVENTION 
     Current data storage and imaging methodologies operate in the micron regime. In an effort to store ever more information in ever-smaller spaces, data storage density has been increasing. In an effort to reduce power consumption and increase the speed of operation of integrated circuits, the lithography used to fabricate integrated circuits is pressed toward smaller dimensions and denser imaging. As data storage size increases and density increases and integrated circuit densities increase, there is a developing need for compositions of matter for the storage media that operate in the nanometer regime. 
     SUMMARY OF THE INVENTION 
     A first aspect of the present invention is a composition of matter, comprising: one or more polyaryletherketone copolymers, each of the one or more polyaryletherketone copolymers comprising (a) a first monomer including an aryl ether ketone and (b) a second monomer including an aryl ether ketone and a first phenylethynyl moiety, each of the one or more polyaryletherketone copolymers having two terminal ends, each terminal end having a phenylethynyl moiety the same as or different from the first phenylethynyl moiety. 
     A second aspect of the present invention is a method, forming a layer of polyaryletherketone resin by applying a layer of one or more polyaryletherketone copolymers and thermally curing the layer of one or more polyaryletherketone copolymers, each of the one or more polyaryletherketone copolymers comprising (a) a first monomer including an aryl ether ketone and (b) a second monomer including an aryl ether ketone and a first phenylethynyl moiety, each of the one or more polyaryletherketone copolymers having two terminal ends, each terminal end having a phenylethynyl moiety the same as or different from the first phenylethynyl moiety, and bringing a thermal-mechanical probe heated to a temperature of greater than about 100° C. into proximity with the layer of a polyaryletherketone resin multiple times to induce deformed regions at points in the layer of the polyaryletherketone resin, the polyaryletherketone resin the thermal mechanical probe heating the points in the layer of the resin and thereby writing information in the layer of the resin. 
     A third aspect of the present invention is a data storage device, comprising: a recording medium comprising a layer of polyaryletherketone resin overlying a substrate, in which topographical states of the layer of the polyaryletherketone resin represent data, the polyaryletherketone resin comprising thermally cured one or more polyaryletherketone copolymers, each of the one or more polyaryletherketone copolymers comprising (a) a first monomer including an aryl ether ketone and (b) a second monomer including an aryl ether ketone and a first phenylethynyl moiety, each of the one or more polyaryletherketone copolymers having two terminal ends, each terminal end having a phenylethynyl moiety the same as or different from the first phenylethynyl moiety; a read-write head having one or more thermo-mechanical probes, each of the one or more thermo-mechanical probes including a resistive region for locally heating a tip of the thermo-mechanical probe in response to electrical current being applied to the one or more thermo-mechanical probes; and a scanning system for scanning the read-write head across a surface of the recording medium. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       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: 
         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; and 
         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; and 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       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  105 A and  105 B connected to a support structure  110 . Flexing of members  105 A and  105 B provides for substantial pivotal motion of cantilever  105  about a pivot axis  115 . Cantilever  105  includes an indenter tip  120  fixed to a heater  125  connected between flexing members  105 A and  105 B. Flexing members  105 A and  105 B and heater  125  are electrically conductive and connected to wires (not shown) in support structure  110 . In one example, flexing members  105 A and  105 B and indenter tip  120  are formed of 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 indenter tip  120 , in one example, to between about 100° C. and about 500° C. when current is passed through heater  125 . The electrical resistance of heater  125  is a function of temperature. 
     Also illustrated in  FIG. 1A  is a storage medium (or a recording medium)  130  comprising a substrate  130 A, and a cured polyaryletherketone resin layer  130 B. In one example, substrate  130 A comprises silicon. Cured polyaryletherketone resin layer  130 B may be formed by solution coating, spin coating, dip coating or meniscus coating polyaryletherketone copolymer and reactive diluent formulations and performing a curing operation on the resultant coating. In one example, cured polyaryletherketone resin layer  130 B has a thickness between about 10 nm and about 500 nm. The composition of cured polyaryletherketone resin layer  130 B is described infra. An optional penetration stop layer  130 C is shown between cured polyaryletherketone resin layer  130 B and substrate  130 A. Penetration stop layer  130 C limits the depth of penetration of indenter tip  120  into cured polyaryletherketone resin layer  130 B. 
     Turning to the operation of tip assembly  100 , in  FIG. 1A , an indentation  135  is formed in cured polyaryletherketone resin layer  130 B by heating indenter tip  120  to a writing temperature T W  by passing a current through cantilever  105  and pressing indenter tip  120  into cured polyaryletherketone resin layer  130 B. Heating indenter tip  120  allows the tip to penetrate the cured polyaryletherketone resin layer  130 B forming indentation  135 , which remains after the tip is removed. In a first example, the cured polyaryletherketone resin layer  130 B is heated by heated indenter tip  120 , the temperature of the indenter tip being not greater than about 500° C., to form indentation  135 . In a second example, the cured polyaryletherketone resin layer  130 B is heated by heated indenter tip  120 , the temperature of the indenter tip being not greater than about 400° C., to form indentation  135 . In a third example, the cured polyaryletherketone resin layer  130 B is heated by heated indenter tip  120 , the temperature of the indenter tip being between about 200° C. and about 500° C., to form indentation  135 . In a fourth example, the cured polyaryletherketone resin layer  130 B is heated by heated indenter tip  120 , the temperature of the indenter tip being between about 100° C. and about 400° C., to form indentation  135 . As indentations  135  are formed, a ring  135 A of cured polyaryletherketone resin 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. Indentations  135  are nano-scale indentations (several to several hundred nanometers in width). 
       FIGS. 1B and 1C  illustrate reading the bit value. In  FIGS. 1B and 1C , tip assembly  100  is scanned across a portion of cured polyaryletherketone resin layer  130 B. When indenter tip  120  is over a region of cured polyaryletherketone resin layer  130 B not containing an indentation, heater  125  is a distance D 1  from the surface of the cured polyaryletherketone resin layer (see  FIG. 1B ). When indenter tip  120  is over a region of cured polyaryletherketone resin layer  130 B containing an indentation, heater  125  is a distance D 2  from the surface of the cured polyaryletherketone resin layer (see  FIG. 1C ) because the tip “falls” into the indentation. D 1  is greater than D 2 . If heater  125  is at a temperature T R  (read temperature), which is lower than T W  (write temperature), there is more heat loss to substrate  130 A when indenter tip  120  is in an indentation than when the tip is not. This can be measured as a change in resistance of the heater at constant current, 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. 
     “Erasing” (not shown) is accomplished by positioning indenter tip  120  in close proximity to indentation  135 , heating the tip to a temperature T E  (erase temperature), and applying a loading force similar to writing, 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. T E  is typically greater than T W . The erase pitch is typically on the order of the rim radius. In a first example, the cured polyaryletherketone resin layer  130 B is heated by heated indenter tip  120 , the temperature of the indenter tip is not greater than about 500° C., and the erase pitch is 10 nm to eliminate indentation  135 . In a second example, the cured polyaryletherketone resin layer  130 B is heated by heated indenter tip  120 , the temperature of the indenter tip is not greater than about 400° C., and the erase pitch is 10 nm to eliminate indentation  135 . In a third example, the cured polyaryletherketone resin layer  130 B is heated by heated indenter tip  120 , the temperature of the indenter tip is between about 200° C. and about 400° C., and the erase pitch is 10 nm to eliminate indentation  135 . In a fourth example, the cured polyaryletherketone resin layer  130 B is heated by heated indenter tip  120 , the temperature of the indenter tip is between about 200° C. and about 500° C., and the erase pitch is 10 nm to eliminate indentation  135 . 
       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 polyaryletherketone resin layer  150  (similar to cured polyaryletherketone resin layer  130 B of  FIGS. 1A ,  1 B and  1 C), which acts as the data-recording layer. An optional tip penetration stop layer may be formed between cured polyaryletherketone resin layer  150  and substrate  145 . In one example, substrate  145  comprises silicon. Cured polyaryletherketone resin layer  150  may be formed by solution coating, spin coating, dip coating or meniscus coating uncured polyaryletherketone resin formulations and performing a curing operation on the resultant coating. In one example, cured polyaryletherketone resin layer  150  has a thickness between about 10 nm and about 500 nm and a root mean square surface roughness across a writeable region of cured polyaryletherketone resin layer  150  of less than about 1.0 nm across the cured polyaryletherketone resin layer. The composition of cured polyaryletherketone resin layer  150  is described infra. Positioned over cured polyaryletherketone 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 polyaryletherketone resin layer  150  by any number of devices as is known in the art. Switching arrays  160 A and  160 B 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  160 A and  160 B 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 polyaryletherketone resin layer  150  with the tips of the array of probe tip assemblies  100 . 
     During a write operation, probe assembly  155  is brought into proximity to cured polyaryletherketone resin layer  150  and probe tip assemblies  100  are scanned relative to the cured polyaryletherketone 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 polyaryletherketone resin layer  150 . This reduces the amount of travel and thus time required for writing data. 
     During a read operation, probe assembly  155  is brought into proximity to cured polyaryletherketone resin layer  150  and probe tip assemblies  100  are scanned relative to the cured polyaryletherketone 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 polyaryletherketone resin layer  150 . This reduces the amount of travel and thus the time required for reading data. 
     During an erase operation, probe assembly  155  is brought into proximity to cured polyaryletherketone resin layer  150 , and probe tip assemblies  100  are scanned relative to the cured polyaryletherketone 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 polyaryletherketone resin layer  150 . This reduces the amount of travel and thus time required for erasing data. 
     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 their entireties. 
     Turning to the composition of cured polyaryletherketone resin layer  130 B of  FIGS. 1A through 1C . It should be understood that for the purposes of the present invention curing a polymer implies cross-linking the polymer to form a cross-linked polymer or resin. 
     The polyaryletherketone resin 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 (little or no pickup of material by tips), low abrasion (tips do not easily wear out), low viscosity for writing, glassy character with no secondary relaxations for long data bit lifetime, and shape memory for erasability. 
     Cured polyaryletherketone resins according to embodiments of the present invention have high temperature stability while maintaining a low glass transition temperature (Tg). In a first example, cured polyaryletherketone resins according to embodiments of the present invention have a Tg of less than about 180° C. In a second example, cured polyaryletherketone resins according to embodiments of the present invention have a Tg of between about 100° C. and about 180° C. 
     The glass transition temperature should be 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 g  leads to high write currents and damage to the probe tip assemblies described supra. 
     A formulation of polyaryletherketone copolymer according to embodiments of the present invention comprises one or more polyaryletherketone copolymers, each polyaryletherketone copolymer of the one or more polyaryletherketone copolymers having the structure: 
     (i) m repeat units represented by the structure —R 1 —O—R 2 —O— (e.g., randomly) interspersed with n repeat units represented by the structure —R 1 —O—R 3 —O—, and terminated by a first terminal group represented by the structure R 4 —O— and a second terminal group represented by the structure —R 1 —O—R 4 , or 
     (ii) m repeat units represented by the structure —R 1 —O—R 2 —O— (e.g., randomly) interspersed with n repeat units represented by the structure —R 1 —O—R 5 —O—, and terminated by a first terminal group represented by the structure R 4 —O— and a second terminal group represented by the structure —R 1 —O—R 4 , or 
     (iii) m repeat units represented by the structure —R 1 —O—R 2 —O— (e.g., randomly) interspersed with n repeat units represented by the structure —R 1 —O—R 3 —O—, terminated by a first terminal group represented by the structure R 6 —O— and a second terminal group represented by the structure —R 1 —O—R 6 , or 
     (iv) m repeat units represented by the structure —R 1 —O—R 2 —O— (e.g., randomly) interspersed with n repeat units represented by the structure —R 1 —O—R 5 —O—, a first terminal group represented by the structure R 6 —O— and a second terminal group represented by the structure —R 1 —O—R 6 ; 
     wherein O=oxygen, and occurs as a link between all R groups; 
     wherein R 1  is selected from the group consisting of: 
     
       
                 
         
             
             
         
      
     
     wherein R 2  is selected from the group consisting of: 
     
       
                 
         
             
             
         
      
     
     wherein R 3  is selected from the group consisting of mono(arylacetylenes), mono(phenylethynyls), 
     
       
                 
         
             
             
         
      
     
     wherein R 4  is selected from the group consisting of mono(arylacetylenes), mono(phenylethynyls), 
     
       
                 
         
             
             
         
      
     
     wherein R 5  is selected from the group consisting of mono(arylacetylenes), mono(phenylethynyls), 
     
       
                 
         
             
             
         
      
     
     wherein R 6  is selected from the group consisting of mono(arylacetylenes), mono(phenylethynyls), 
     
       
                 
         
             
             
         
      
     
     wherein m is an integer of 2 or more, n is an integer of 1 or more, m is greater than n and m+n is from about 5 to about 50. 
     The molar ratio of a first repeat unit (containing R 1  and R 2  groups) to a second repeat unit (containing either R 1  and R 5  groups or R 3  and R 2  groups) in structures (i), (ii), (iii) and (iv) is kept greater than 1, therefore the ratio m/n is greater than 1. The acetylene moieties in the R 3 , R 4 , R 5 , and R 6  groups, whichever are present, react during thermal curing with each other to cross-link the polyaryletherketone copolymers into a polyaryletherketone resin by cyclo-addition. 
     In a first example, polyaryletherketone copolymers according to embodiments of the present invention advantageously have a molecular weight between about 3,000 Daltons and about 10,000 Daltons. In a second example, polyaryletherketone copolymers according to embodiments of the present invention advantageously have a molecular weight between about 4,000 Daltons and about 5,000 Daltons. 
     SYNTHESIS EXAMPLES 
     All materials were purchased from Aldrich and used without further purification unless otherwise noted. 
     Synthesis of the Reactive Endgroup 3-(phenylethynyl)phenol (Structure XV) 
     
       
                 
         
             
             
         
      
     
     3-Iodophenol (5.00 gram, 22.7 mmol), bis(triphenylphospine)palladium(II) dichloride (PdCl 2 (PPh 3 ) 2 ) (160 mg), triphenylphospine (PPh 3 ) (420 mg), and CuI (220 mg) were suspended in triethylamine (NEt 3 ) (150 mL) under an N 2  atmosphere. Phenylacetylene (3.1 mL, 2.9 gram, 28.4 mmol, 1.25 eq) was added by syringe. The reaction mixture was then stirred and heated to 70° C. using an oil bath for 38 hours. Excess NEt 3  was removed under reduced pressure. The remaining solids were extracted with 3×50 mL diethyl ether, which was then filtered and evaporated. The crude product was purified by column chromatography (silica, 3:1 hexanes-ethyl acetate) to give 4.1 gram of an orange solid. Further purification was accomplished by sublimation (100° C., 28 mTorr) to give 3-(phenylethynyl)phenol as a white solid (3.3 g, 75% yield). 
     Synthesis of the Reactive Cross-Linking Group 3,3′-dihydroxydiphenylacetylene (Structure XVII) 
     
       
                 
         
             
             
         
      
     
     To a suspension of 3-iodophenol (3.73 gram, 17 mmol), PdCl 2 (PPh 3 ) 2  (120 mg), CuI (161 mg), and PPh 3  (333 mg) in NEt 3  (100 mL) under N 2  was added a solution of 3-hydroxyphenylacetylene (2.00 gram, 17 mmol) in NEt 3  (10 mL). The mixture was stirred and heated to 70° C. using an oil bath for 18 h. Excess NEt 3  was removed under reduced pressure, and the remaining solids were extracted with 4×50 mL diethyl ether which was then filtered and evaporated. The crude product was purified by suspending in 80 mL CH 2 Cl 2 , stirring for 1 hour, and filtering to give the final product as a yellow powder (2.96 g, 83% yield). 
     Synthesis of a Polyaryletherketone Copolymer (Structure XXI) 
     
       
                 
         
             
             
         
      
     
     In a multi-necked flask equipped with a mechanical stirring apparatus and a Dean-Stark trap, 4,4′-difluorobenzophenone (1.4187 gram, 6.502 mmol), resorcinol (0.5326 g, 4.838 mmol), 3,3′-dihydroxydiphenylacetylene (0.2540 g, 1.209 mmol), 3-hydroxydiphenylacetylene (0.1753 g, 0.9037 mmol), and potassium carbonate (3 g, 22 mmol) were suspended in a mixture of dimethylformamide (DMF) (10 mL) and toluene (20 mL). The reaction mixture was vigorously stirred and heated to 130° C. for 16 hours under a slow flow of dry nitrogen, and toluene was removed periodically via the Dean-Stark trap. At the end of the 16 h period, the temperature was increased to 150° C. for another 8 hours. The reaction was then cooled and the polymer was isolated by multiple precipitations using THF and methanol. Molecular weights were adjusted by using different proportions of (R 1 +R 2 ) to (R 3 ) and several different molecular weight polymers were prepared. 
     Thus, the embodiments of the present invention provide for compositions of matter for the storage media that operate in the nanometer regime. 
     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.