| PATENT NUMBER | This data is not available for free |
| PATENT GRANT DATE | 31.12.02 |
| PATENT TITLE |
Polycarbonate-containing liquid chemical formulation and methods for making and using polycarbonate film |
| PATENT ABSTRACT | A liquid chemical formulation suitable for making a thin solid polycarbonate film contains polycarbonate material and a liquid typically capable of dissolving the polycarbonate material to a concentration of at least 1%. The polycarbonate material may consist of homopolycarbonate or/and copolycarbonate. Examples of the liquid include pyridine, a ring-substituted pyridine derivative, pyrrole, a ring-substituted pyrrole derivative, pyrrolidine, a pyrrolidine derativive, chlorobenzene, and cyclohexanone. A liquid film (36A) of the formulation is formed over a substructure (30) and processed to remove the liquid. The resultant solid polycarbonate film can later serve as a track layer through which charged particles (70) are passed to form charged-particle tracks (72). Apertures (74) are created through the track layer by a process that entails etching along the tracks. The aperture-containing polycarbonate track layer is typically used in fabricating a gated electron-emitting device |
| PATENT INVENTORS | This data is not available for free |
| PATENT ASSIGNEE | This data is not available for free |
| PATENT FILE DATE | October 29, 1999 |
| PATENT REFERENCES CITED |
Apai et al., "Surface Analysis of Polycarbonate Thin Films by High-Resolution Electron Energy Loss Spectroscopy: Negative Ion Resonances and Surface Vibrations," Langmuir, vol. 7, 1991, pp. 2266-2272. Archer, Industrial Solvents Handbook (Marcel Dekker, Inc.), 1996, pp. 1-4, 35-56, and 297-309 and diskette pp. 1-19. Bagen, "Extrusion Coating of Polymer films for Low-Cost Flat Panel Display Manufacturing," Dig. Tech. Paps., 1996 Display Mfg. Tech. Conf., vol. 3, 1996, pp. 35-36. Barton, CRC Handbook of Polymer-Liquid Interaction Parameters and Solubility Parameters (CRC Press), 1990, pp. 443-444. Blunt et al., "Production of thin metallised plastic films," Nucl. Instr. and Meth. in Phys. Res. A, vol. 334, 1993, pp. 251-253. Bosch, "A charge and energy study of the track response of Lexan," Nucl. Instr. and Meth. in Phys. Res. B, vol. 84, 1994, pp. 357-360. Bosch et al., "A study of the dependence of the bulk etch rate and the reduced etch rate on the concentration of etched products of Lexan," Nucl. Instr. and Meth. in Phys. Res. B, vol. 93, 1994, pp. 57-62. Budavari et al., The Merck Index (12th ed., Merck & Co.), 1996, p. 215. Busta, "Vacuum Microelectronics--1992," J. Micromech. Microeng. vol. 2, 1992, pp. 43-74. Cowie, Polymers: Chemistry & Physics of Modern Materials, (2d ed., Blackie Academic & Professional), 1991, pp. 1-25, 157-213, and 247-273. Cowie, Polymers: Chemistry & Physics of Modern Materials, (2d ed., Blackie Academic & Professional), 1991, pp. 104, 105, 115-120, and 350-355. Domininghaus, Plastics for Engineers: Materials, Properties, Applications (Carl Hanser Verlag), 1993, pp. 423-441, translated and revised by Haim et al. from Die Kunstoffe und ihre Eigenschaften (3d ed., VDI-Verlag GmbH), 1988. Fischer et al., "Production and use of nuclear tracks: imprinting structure on solids," Reviews of Modern Physics, vol. 55, No. 4, Oct. 1983, pp. 907-948. Frechet et al., "New Condensation Polymers as Resist Materials Capable of Chemical Amplification" Procs. 192nd ACS Symp. Polymeric Materials Sci. & Engrg., 1986, pp. 299-303. Frechet et al., "Thermally Depolymerizable Polycarbonates V. Acid Catalyzed Thermolysis of Allylic and Benzylic Polycarbonates: A New Route to Resist Imaging," Polymer J., vol. 19, No. 1, 1987, pp. 31-49. Hoffman, "Inorganic membrane filter for analytical separations," American Laboratory, Aug. 1989, pp. 70-73. Hosokawa et al., "Bright blue electroluminescence from hole transporting polycarbonate," Appl. Phys. Huizenga, et al., "Submicron entrance window for an ultrasoft x-ray camera," Rev. Sci. Instrum., vol. 52, No. 5, May 1981, pp. 673-677. Kambour et al., "Bisphenol-A Polycarbonate Immersed in Organic Media Swelling and Response to Stress," Macromolecules, vol. 7, No. 2, Mar.-Apr. 1974, pp. 248-253. Kent, "EUV Band Pass Filters for the ROSAT Wide Field Camera," Proceedings, SPIE, vol. 1344, 1990, pp. 255-266. Nakamura et al., "Photocurrent of Solution-Grown Thin Polycarbonate Films Containing Soluble Nickel-Phthalcyanine," Japanese Journal of Applied Physics, vol. 28, No. 6, Jun. 1989, pp. 991-995. Shriver et al., The Manipulation of Air-Sensitive Compounds (2d ed., John Wiley & Sons) 1986, pp. 84-96. Skinner, "A Study of the Thermal Stability of Cardo-Polymers and Their Electronic Susceptibility to the Capto Dative Effect," Ph.D. dissertation, Polytechnic Univ., Jun. 7, 1993, cover p. and pp. 21-36 and 55-58. Spohr, Ion Tracks and Microtechnology, Principles and Applications (Viewig), edited by K. Bethge, 1990, pp. 246-255. Stevens, Polymer Chemistry, An Introduction (2d ed., Oxford University Press), 1990, pp. 28, 344, 345, 394, 395, and 400-403. Stoner, "Casting thin films of cellulose nitrate, polycarbonate, and polypropylene," Nucl. Instr. and Meth. in Phys. Res. A, vol. 362, 1995, pp. 167-174. Streitwieser et al., Introduction to Organic Chemistry (3d ed., Macmillan Publishing Co.), 1985, pp. 10-15. Su, "Comparison of Chemical Etching with the Alkali-Alcohol Mixture and the Ultrasonic Etchings of Fission Fragment and Alpha Particle Tracks in Lexan Polycarbonates," Radiation Effects and Defects in Solids, vol. 114, 1990, pp. 157-166. CRC Handbook of Chemistry and Physics (65th ed., CRC Press), 1984, pp. C-137, C-541, C-572, and C-573. "Handling air-sensitive reagents," Tech. Bull. AL-134, Aldrich Chemical Co., Dec. 1994, 8 pages. "Instruments for Research, Industry, and Education," catalog, Cole-Parmer Instrument Co., 1991-1992, pp. 663-665, 772, and 773. 1990 Nuclepore Laboratory Products Catalog, 1990, cover page and pp. 3, 8, and 9. |
| PATENT PARENT CASE TEXT | This data is not available for free |
| PATENT CLAIMS |
We claim: 1. A liquid chemical formulation comprising: polycarbonate material comprising copolycarbonate in which at least one carbonate repeat unit has free radical stabilization; and a liquid capable of dissolving the polycarbonate material to a concentration of at least 1% by mass of the liquid formulation at 20.degree. C. and 1 atmosphere, the polycarbonate material being dissolved in the liquid. 2. A liquid formulation as in claim 1 wherein the polycarbonate material is present in the liquid at a higher mass fraction than any other constituent present in the liquid. 3. A liquid formulation as in claim 1 wherein the copolycarbonate constitutes at least 5% by mass of the polycarbonate material. 4. A liquid formulation as in claim 1 wherein the copolycarbonate constitutes at least 10% by mass of the polycarbonate material. 5. A liquid formulation as in claim 1 wherein the copolycarbonate constitutes more than 50% by mass of the polycarbonate material. 6. A liquid formulation as in claim 1 wherein the copolycarbonate comprises copolycarbonate molecules, each comprising: a primary carbonate component formed with repetitions of a primary carbonate repeat unit; and a further carbonate component formed with repetitions of at least one further carbonate repeat unit different from the primary repeat unit, each further repeat unit having a lower minimum homolytic bond cleavage energy than the primary repeat unit such that each further repeat unit undergoes decarboxylation more readily than the primary repeat unit. 7. A liquid formulation as in claim 6 wherein the primary carbonate components together constitute more than 50% by mass of the copolycarbonate. 8. A liquid formulation as in claim 7 wherein the primary carbonate components together constitute at least 80% by mass of the copolycarbonate. 9. A liquid formulation as in claim 7 wherein the primary repeat unit of each copolycarbonate molecule constitutes bisphenol A carbonate repeat unit. 10. A liquid formulation as in claim 9 wherein each further repeat unit of each copolycarbonate molecule constitutes a selected one of allylic cyclohexene, benzylic, and tertiary carbonate repeat units. 11. A liquid formulation as in claim 1 wherein the liquid is capable of dissolving the polycarbonate material to a concentration of at least 5% by mass of the liquid formulation at 20.degree. C. and 1 atmosphere. 12. A liquid formulation as in claim 1 wherein the liquid has a boiling point of at least 80.degree. C. at 1 atmosphere. 13. A liquid formulation as in claim 1 having no more than 1% water by mass of the liquid formulation. 14. A liquid formulation as in claim 1 wherein the copolycarbonate has a copolycarbonate core representable as: (--A.sub.1 --. . . --A.sub.p --).sub.n where: p is a plural integer; each A.sub.i is a different bivalent carbonate repeat unit for i being an integer varying from 1 to p; and n is a multiplicity indicator indicating that each carbonate repeat unit A.sub.i occurs multiple times in the copolycarbonate core. 15. A liquid chemical formulation comprising: polycarbonate material; a liquid capable of dissolving the polycarbonate material to a concentration of at least 1% by mass of the liquid formulation at 20.degree. C. and 1 atmosphere, the polycarbonate material being dissolved in the liquid; and a water scavenger. 16. A liquid formulation as in claim 15 wherein the polycarbonate material is present in the liquid at a higher mass fraction than any other constituent present in the liquid. 17. A liquid formulation as in claim 15 wherein the liquid has a boiling point of at least 80.degree. C. at 1 atmosphere. 18. A liquid formulation as in claim 15 having no more than 1% water by mass of the liquid formulation. 19. A liquid formulation as in claim 15 wherein the polycarbonate material comprises copolycarbonate. 20. A liquid formulation as in claim 15 wherein at least one carbonate repeat unit in the polycarbonate material has free radical stabilization. 21. A liquid chemical formulation comprising: polycarbonate material comprising copolycarbonate; and a liquid comprising a principal solvent which consists of at least one of pyridine, a ring-substituted pyridine derivative, pyrrole, a ring-substituted pyrrole derivative, pyrrolidine, a pyrrolidine derivative, and cyclohexanone, the polycarbonate material being dissolved in the liquid. 22. A liquid formulation as in claim 21 wherein the polycarbonate material is present in the liquid at a higher mass fraction than any other constituent present in the liquid. 23. A liquid formulation as in claim 21 wherein the copolycarbonate constitutes at least 5% by mass of the polycarbonate material. 24. A liquid formulation as in claim 23 wherein the copolycarbonate constitutes at least 10% by mass of the polycarbonate material. 25. A liquid formulation as in claim 21 wherein the copolycarbonate constitutes more than 50% by mass of the polycarbonate material. 26. A liquid formulation as in claim 21 wherein at least one carbonate repeat unit in the copolycarbonate has free radical stabilization. 27. A liquid formulation as in claim 21 wherein the copolycarbonate comprises copolycarbonate molecules, each comprising: a primary carbonate component formed with repetitions of a primary carbonate repeat unit; and a further carbonate component formed with repetitions of at least one further carbonate repeat unit different from the primary repeat unit, each further repeat unit having a lower minimum homolytic bond cleavage energy than the primary repeat unit such that each further repeat unit undergoes decarboxylation more readily than the primary repeat unit. 28. A liquid formulation as in claim 27 wherein the primary carbonate components together constitute more than 50% by mass of the copolycarbonate. 29. A liquid formulation as in claim 28 wherein the primary carbonate components together constitute at least 80% by mass of the polycarbonate. 30. A liquid formulation as in claim 28 wherein the primary repeat unit of each copolycarbonate molecule constitutes bisphenol A carbonate repeat unit. 31. A liquid formulation as in claim 28 wherein each further repeat unit of each copolycarbonate molecule constitutes a selected one of allylic cyclohexene, benzylic, and tertiary carbonate repeat units. 32. A liquid formulation as in claim 21 wherein the liquid has a boiling point of at least 80.degree. C. at 1 atmosphere. 33. A liquid formulation as in claim 21 wherein the copolycarbonate has a copolycarbonate core representable as: (--A.sub.1 --. . . --A.sub.p --).sub.n where: p is a plural integer; each A.sub.i is a different bivalent carbonate repeat unit for i being an integer varying from 1 to p; and n is a multiplicity indicator indicating that each carbonate repeat unit A.sub.i occurs multiple times in the copolycarbonate core. 34. A liquid formulation as in claim 21 wherein both pyridine and the pyridine derivative are representable as: ##STR20## where: N is nitrogen; C is carbon; and each R.sub.j is a monovalent covalent substituent, j being an integer varying from 1 to 5. 35. A liquid formulation as in claim 34 wherein at least two adjacent ones of R.sub.1 -R.sub.5 form a fused ring or a derivative of a fused ring. 36. A liquid formulation as in claim 34 wherein each R.sub.j is a hydrogen atom, a deuterium atom, a hydrocarbon group, a substituted hydrocarbon group, an acetyl group, a carboxaldehyde group, a halogen, or a pseudo-halogen substituent. 37. A liquid formulation as in claim 21 wherein both pyrrole and the pyrrole derivative are representable as: ##STR21## where: N is a nitrogen atom; C is a carbon atom; and each R.sub.j is a monovalent covalent substituent, j being an integer varying from 1 to 5. 38. A liquid formulation as in claim 37 wherein at least two adjacent ones of R.sub.1 -R.sub.5 form a fused ring or a derivative of a fused ring. 39. A liquid formulation as in claim 37 wherein each R.sub.j is a hydrogen atom, a deuterium atom, a hydrocarbon group, a substituted hydrocarbon group, an acetyl group, a carboxaldehyde group, a halogen, or a pseudo-halogen substituent. 40. A liquid formulation as in claim 21 wherein both pyrrolidine and the pyrrolidine derivative are generally representable as: ##STR22## where: N is a nitrogen atom; C is a carbon atom; each R.sub.j is a monovalent covalent substituent, j being an integer varying from 1 to 9, subject to any pair of R.sub.2 -R.sub.9 on any of the carbon atoms being replaced with a single bivalent substituent double covalently bonded to that carbon atom, or/and up to one pair of R.sub.2 -R.sub.9 on an adjacent pair of carbon atoms being replaced with a covalent bond between that pair of carbon atoms to create a double covalent bond therebetween, or/and R.sub.1 and R.sub.2 being replaced with a covalent bond between the nitrogen atom and the carbon atom bonded to R.sub.2 to create a double covalent bond therebetween. 41. A liquid formulation as in claim 40 wherein each R.sub.j is a hydrogen atom, a deuterium atom, a hydrocarbon group, a substituted hydrocarbon group, an acetyl group, a carboxaldehyde group, a halogen, or a pseudo-halogen substituent. 42. A liquid formulation as in claim 21 wherein the liquid consists principally of 1-methylpyrrolidinone. 43. A liquid formulation as in claim 21 further including a non-chlorobenzene cosolvent, different from the principal solvent, for modifying at least one property of the liquid formulation. 44. A liquid formulation as in claim 43 wherein the cosolvent produces change in at least one of (a) boiling point of the liquid, (b) viscosity of the liquid formulation, (c) tact time of a liquid film created from the liquid formulation, (d) leveling of the liquid film, and (e) flammability characteristics of a solid film created from the liquid film. 45. A liquid chemical formulation comprising: polycarbonate material; and a liquid comprising (a) a principal solvent consisting of at least one of pyridine, a ring-substituted pyridine derivative, pyrrole, a ring-substituted pyrrole derivative, pyrrolidine, a pyrrolidine derivative, and cyclohexanone and (b) a non-chlorobenzene cosolvent, different from the principal solvent, for modifying at least one property of the liquid formulation, the polycarbonate material being dissolved in the liquid. 46. A liquid formulation as in claim 45 wherein the polycarbonate material is present in the liquid at a higher mass fraction than any other constituent present in the liquid. 47. A liquid formulation as in claim 45 wherein the cosolvent produces change in at least one of (a) boiling point of the liquid, (b) viscosity of the liquid formulation, (c) tact time of a liquid film created from the liquid formulation, (d) leveling of the liquid film, and (e) flammability characteristics of a solid film created from the liquid film. 48. A liquid formulation as in claim 45 wherein the cosolvent is present in the liquid at a lower mass fraction than the principal solvent. 49. A liquid formulation as in claim 45 wherein the cosolvent comprises at least one of methoxybenzene, ethyl lactate, cyclopentanone, mesitylene, and hexyl acetate. 50. A liquid formulation as in claim 45 wherein at least one carbonate repeat unit in the polycarbonate material has free radical stabilization. 51. A liquid chemical formulation comprising: polycarbonate material; a liquid comprising at least one of pyridine, a ring-substituted pyridine derivative, pyrrole, a ring-substituted pyrrole derivative, pyrrolidine, a pyrrolidine derivative, chlorobenzene, and cyclohexanone, the polycarbonate material being dissolved in the liquid; and a water scavenger. 52. A liquid formulation as in claim 51 wherein the polycarbonate material is present in the liquid at a higher mass fraction than any other constituent present in the liquid. 53. A liquid formulation as in claim 51 having no more than 1% water by mass of the liquid formulation. 54. A liquid formulation as in claim 51 having no more than 0.1% water by mass of the liquid formulation. 55. A method comprising the steps of: providing a liquid chemical formulation in which polycarbonate material comprising copolycarbonate is dissolved in a liquid capable of dissolving the polycarbonate material to a concentration of at least 1% by mass of the liquid formulation at 20.degree. C. and 1 atmosphere, at least one carbonate repeat unit in the copolycarbonate having free radical stabilization; forming a liquid film of the liquid formulation over a substructure; and processing the liquid film to largely remove the liquid and convert the liquid film into a solid, largely polycarbonate film. 56. A method as in claim 55 wherein the polycarbonate material is present in the liquid at a higher mass fraction than any other constituent present in the liquid. 57. A method as in claim 55 wherein the copolycarbonate constitutes at least 5% by mass of the polycarbonate material. 58. A method as in claim 55 wherein the copolycarbonate constitutes at least 50% by mass of the polycarbonate material. 59. A method as in claim 55 wherein the liquid has a boiling point of at least 80.degree. C. at 1 atmosphere. 60. A method as in claim 55 wherein the providing step comprises combining the liquid and the polycarbonate material in a substantially water-free environment. 61. A method as in claim 55 wherein the providing step includes introducing a water scavenger into the liquid. 62. A method as in claim 55 wherein the providing step includes drying the polycarbonate material and/or the liquid to remove water. 63. A method as in claim 55 wherein the forming step comprising extrusion coating at least part of the liquid formulation over the substructure. 64. A method as in claim 55 wherein the processing step includes annealing the solid film to relieve stress in the solid film. 65. A method as in claim 55 further including the steps of: causing charged particles to pass into the solid film to form a multiplicity of charged-particle tracks at least partway therethrough; and creating corresponding apertures at least partway through the solid film by a procedure that entails etching the solid film along the charged-particle tracks. 66. A method as in claim 65 wherein the copolycarbonate comprises copolycarbonate molecules, each comprising: a primary carbonate component formed with repetitions of a primary carbonate repeat unit; and a further carbonate component formed with repetitions of at least one further carbonate repeat unit different from the primary repeat unit, each further repeat unit having a lower minimum homolytic bond cleavage energy than the primary repeat unit such that each further repeat unit undergoes decarboxylation more readily than the primary repeat unit. 67. A method as in claim 66 wherein the primary carbonate components constitute more than 50% by mass of the copolycarbonate. 68. A method as in claim 67 wherein the primary repeat unit of each copolycarbonate molecule constitutes bisphenol A carbonate repeat unit. 69. A method comprising the steps of: providing a liquid chemical formulation in which polycarbonate material is dissolved in a liquid furnished with a water scavenger and capable of dissolving the polycarbonate material to a concentration of at least 1% by mass of the liquid formulation at 20.degree. C. and 1 atmosphere; forming a liquid film of the liquid formulation over a substructure; and processing the liquid film to largely remove the liquid and convert the liquid film into a solid, largely polycarbonate film. 70. A method as in claim 69 wherein the polycarbonate material is present in the liquid at a higher mass fraction than any other constituent present in the liquid. 71. A method as in claim 69 wherein the providing step comprises: introducing the water scavenger into the liquid; and subsequently dissolving the polycarbonate material in the liquid. 72. A method as in claim 69 further including the steps of: causing charged particles to pass into the solid film to form a multiplicity of charged-particle tracks at least partway therethrough; and creating corresponding apertures at least partway through the solid film by a procedure that entails etching the solid film along the charged-particle tracks. 73. A method comprising the steps of: providing a liquid chemical formulation in which polycarbonate material comprising copolycarbonate is dissolved in a liquid comprising a principal solvent which consists of at least one of pyridine, a ring-substituted pyridine derivative, pyrrole, a ring-substituted pyrrole derivative, pyrrolidine, a pyrrolidine derivative, and cyclohexanone; forming a liquid film of the liquid formulation over a substructure; and processing the liquid film to largely remove the liquid and convert the liquid film into a solid, largely polycarbonate film. 74. A method as in claim 73 wherein the polycarbonate material is present in the liquid at a higher mass fraction than any other constituent present in the liquid. 75. A method as in claim 73 wherein the copolycarbonate constitutes at least 5% by mass of the polycarbonate material. 76. A method as in claim 73 wherein the copolycarbonate constitutes at least 50% by mass of the polycarbonate material. 77. A method as in claim 73 wherein the liquid has a boiling point of at least 80.degree. C. at 1 atmosphere. 78. A method as in claim 73 wherein the providing step comprises combining the liquid and the polycarbonate material in a substantially water-free environment. 79. A method as in claim 73 wherein the providing step includes introducing a water scavenger into the liquid. 80. A method as in claim 73 wherein the providing step includes drying the polycarbonate material and/or the liquid to remove water. 81. A method as in claim 73 wherein the forming step comprising extrusion coating at least part of the liquid formulation over the substructure. 82. A method as in claim 73 wherein the processing step includes annealing the solid film to relieve stress in the solid film. 83. A method as in claim 73 wherein the liquid further includes a non-chlorobenzene cosolvent, different from the principal solvent, for modifying at least one property of the liquid formulation. 84. A method as in claim 83 wherein the providing step comprises: dissolving the polycarbonate material in the principal solvent; and subsequently combining the cosolvent with the principal solvent including the dissolved polycarbonate material. 85. A method comprising the steps of: providing a liquid chemical formulation in which polycarbonate material comprising copolycarbonate is dissolved in a liquid comprising at least one of pyridine, a ring-substituted pyridine derivative, pyrrole, a ring-substituted pyrrole derivative, pyrrolidine, a pyrrolidine derivative, chlorobenzene, and cyclohexanone; forming a liquid film of the liquid formulation over a substructure; processing the liquid film to largely remove the liquid and convert the liquid film into a solid, largely polycarbonate film; causing charged particles to pass into the solid film to form a multiplicity of charged-particle tracks at least partway therethrough; and creating corresponding apertures at least partway through the solid film by a procedure that entails etching the solid film along the charged-particle tracks. 86. A method as in claim 85 wherein the copolycarbonate comprises copolycarbonate molecules, each comprising: a primary carbonate component formed with repetitions of a primary carbonate repeat unit; and a further carbonate component formed with repetitions of at least one further carbonate repeat unit different from the primary repeat unit, each further repeat unit having a lower minimum homolytic bond cleavage energy than the primary repeat unit such that each further repeat unit undergoes decarboxylation more readily than the primary repeat unit. 87. A method as in claim 86 wherein the primary carbonate components constitute more than 50% by mass of the copolycarbonate. 88. A method as in claim 86 wherein the primary repeat unit of each copolycarbonate molecule constitutes bisphenol A carbonate repeat unit. 89. A method as in claim 85 further including the step of etching an electrically non-insulating layer of the substructure through the apertures to form corresponding openings in the non-insulating layer. 90. A method as in claim 89 further including the step of defining electron-emissive elements respectively centered approximately on the openings in the non-insulating layer. 91. A method as in claim 90 wherein (a) the non-insulating layer comprises a gate layer, (b) an electrically insulating layer is provided below the gate layer, and (c) a lower electrically non-insulating emitter region is provided below the insulating layer, the defining step comprising: etching the insulating layer through the openings in the gate layer to form corresponding dielectric open spaces through the insulating layer down to the emitter region; and forming electron-emissive elements in the dielectric open spaces so as to contact the emitter region. 92. A method comprising the steps of: providing a liquid chemical formulation in which polycarbonate material is dissolved in a liquid comprising (a) a principal solvent which consists of at least one of pyridine, a ring-substituted pyridine derivative, pyrrole, a ring-substituted pyrrole derivative, pyrrolidine, a pyrrolidine derivative, and cyclohexanone and (b) a non-chlorobenzene cosolvent, different from the principal solvent, for modifying at least one property of the liquid formulation; forming a liquid film of the liquid formulation over a substructure; and processing the liquid film to largely remove the liquid and convert the liquid film into a solid, largely polycarbonate film. 93. A method as in claim 92 wherein the polycarbonate material is present in the liquid at a higher mass fraction than any other constituent present in the liquid. 94. A method as in claim 92 wherein the cosolvent produces change in at least one of (a) boiling point of the liquid, (b) viscosity of the liquid formulation, (c) tact time of a liquid film created from the liquid formulation, (d) leveling of the liquid film, and (e) flammability characteristics of a solid film created from the liquid film. 95. A method as in claim 92 wherein the providing step comprises: dissolving the polycarbonate material in the principal solvent; and subsequently combining the cosolvent with the principal solvent including the dissolved polycarbonate material. 96. A method comprising the steps of: providing a liquid chemical formulation in which polycarbonate material is dissolved in a liquid comprising (a) a principal solvent which consists of at least one of pyridine, a ring-substituted pyridine derivative, pyrrole, a ring-substituted pyrrole derivative, pyrrolidine, a pyrrolidine derivative, chlorobenzene, and cyclohexanone and (b) a cosolvent, different from the principal solvent, for modifying at least one property of the liquid formulation; forming a liquid film of the liquid formulation over a substructure; processing the liquid film to largely remove the liquid and convert the liquid film into a solid, largely polycarbonate film; causing charged particles to pass into the solid film to form a multiplicity of charged-particle tracks at least partway therethrough; and creating corresponding apertures at least partway through the solid film by a procedure that entails etching the solid film along the charged-particle tracks. 97. A method comprising the steps of: providing a liquid chemical formulation in which polycarbonate material is dissolved in a liquid furnished with a water scavenger and comprising at least one of pyridine, a ring-substituted pyridine derivative, pyrrole, a ring-substituted pyrrole derivative, pyrrolidine, a pyrrolidine derivative, chlorobenzene, and cyclohexanone; forming a liquid film of the liquid formulation over a substructure; and processing the liquid film to largely remove the liquid and convert the liquid film into a solid, largely polycarbonate film. 98. A method as in claim 97 wherein the polycarbonate material is present in the liquid at a higher mass fraction than any other constituent present in the liquid. 99. A method as in claim 97 wherein the providing step comprises: introducing the water scavenger into the liquid; and subsequently dissolving the polycarbonate material in the liquid. 100. A method as in claim 97 wherein the water scavenger reacts with water in the liquid or/and the polycarbonate material to produce volatile species. 101. A liquid formulation as in claim 1 wherein the liquid has a protonated form whose acid dissociation constant is greater than 10.sup.-8 at 20.degree. C. and 1 atmosphere. 102. A liquid formulation as in claim 15 wherein the liquid has a protonated form whose acid dissociation constant is greater than 10.sup.-8 at 20.degree. C. and 1 atmosphere. 103. A liquid formulation as in claim 21 wherein the liquid has a protonated form whose acid dissociation constant is greater than 10.sup.-8 at 20.degree. C. and 1 atmosphere. 104. A liquid formulation as in claim 45 wherein the liquid has a protonated form whose acid dissociation constant is greater than 10.sup.-8 at 20.degree. C. and 1 atmosphere. 105. A liquid formulation as in claim 51 wherein the liquid has a protonated form whose acid dissociation constant is greater than 10.sup.-8 at 20.degree. C. and 1 atmosphere. 106. A method as in claim 55 wherein the liquid has a protonated form whose acid dissociation constant is greater than 10.sup.-8 at 20.degree. C. and 1 atmosphere. 107. A method as in claim 69 wherein the liquid has a protonated form whose acid dissociation constant is greater than 10.sup.-8 at 20.degree. C. and 1 atmosphere. 108. A method as in claim 73 wherein the liquid has a protonated form whose acid dissociation constant is greater than 10.sup.-8 at 20.degree. C. and 1 atmosphere. 109. A method as in claim 85 wherein the liquid has a protonated form whose acid dissociation constant is greater than 10.sup.-8 at 20.degree. C. and 1 atmosphere. 110. A method as in claim 92 wherein the liquid has a protonated form whose acid dissociation constant is greater than 10.sup.-8 at 20.degree. C. and 1 atmosphere. 111. A method as in claim 96 wherein the liquid has a protonated form whose acid dissociation constant is greater than 10.sup.-8 at 20.degree. C. and 1 atmosphere. 112. A method as in claim 97 wherein the liquid has a protonated form whose acid dissociation constant is greater than 10.sup.-8 at 20.degree. C. and 1 atmosphere |
| PATENT DESCRIPTION |
FIELD OF USE This invention relates to the formation of polycarbonate films, including the formation of apertures through polycarbonate films. BACKGROUND ART Polycarbonate is a colorless thermoplastic polymer, i.e., polycarbonate softens when heated and hardens when cooled. Polycarbonate is commonly used in applications which take advantage of its outstanding impact resistance and toughness, such as molded helmets, battery cases, bottles and packaging, and in applications which also demand optical transparency, such as bullet-proof and safety glass, eyewear, compact discs and automobile lenses. In thin-film form, polycarbonate is used for a variety of applications ranging from precision filters to electron-emitting devices. Polycarbonate membranes used as commercial filters are described in the 1990 Nucleopore.RTM. Laboratory Products Catalog, Costar Corp., 1990, pp. 3, 8 and 9. The membranes are created by subjecting stretched, crystalline polycarbonate film to irradiation, followed by etching to form pores. The Costar process is similar to that disclosed in Price et al., U.S. Pat. No. 3,303,085. The thickness of commercial membrane filters is typically 6 to 11 .mu.m. Bassiere et al., PCT Patent Publication WO 94/28569, disclose how thin polycarbonate layers are used in manufacturing electron-emitting devices. In one embodiment, Bassiere et al. provide a polycarbonate layer over a sandwich consisting of an upper conductor, an insulator and a patterned lower conductor. The multi-layer structure is irradiated with heavy ions to create radiation tracks through the polycarbonate layer. The tracks are etched to form pores through the polycarbonate layer down to the upper conductor. Using suitable etchants, the pore pattern in the polycarbonate layer is transferred to the upper conductor and then to the insulator, after which conical electron-emissive elements are formed in the resulting openings in the insulator. Bassiere et al. indicate that the thickness of their polycarbonate layer is approximately 2 .mu.m. This is significantly less than the thickness of the commercial polycarbonate membrane filters in the Costar product catalog. While Bassiere et al. specify that the polycarbonate layer in their structure can be created by spin coating, Bassiere et al. do not provide any further information on how to make the polycarbonate layer. Macaulay et al., PCT Patent Publication WO 95/07543, disclose a similar fabrication technique in which electron-emissive features in an electron-emitting device are defined by way of charged-particle tracks formed in a track layer. Polycarbonate is one of the materials that Macaulay et al. consider for the track layer. The thickness of the track layer in Macaulay et al. is 0.1 to 2 .mu.m, typically 1 .mu.m. Consequently, the thickness of the track layer in Macaulay et al. is typically less than that of the polycarbonate layer in Bassiere et al. by a factor of up to twenty. Kanayama et al, European Patent Specification 500,128 B1, application published Aug. 26, 1992, describes a polycarbonate resin utilized in forming a solid polycarbonate film. The polycarbonate resin consists of copolycarbonate formed with repetitions of two different carbonate repeat units. The polycarbonate film is created by dissolving the copolycarbonate in a non-halogenated solvent such as toluene, xylene, or ethylbenzene, forming a liquid film of the resulting solution over a substrate, and drying the liquid film. The solid polycarbonate film of Kanayama et al may have enhanced mechanical strength. However, the film does not appear particularly suitable for receiving a fine pattern of small generally parallel apertures created by etching along the tracks of energetic charged particles that pass through the film. For example, the carbonate (CO.sub.3) groups in the repeat units do not appear to have significant free radical stabilization which would facilitate etching along the charged-particle tracks. As film thickness is reduced, it becomes progressively more difficult to make high-quality polycarbonate films. Controlling and maintaining the uniformity of film thickness and other properties, such as density, becomes harder. Structural and compositional defects also become more problematic in very thin polycarbonate films. It would be desirable to have a method for making a thin polycarbonate film whose thickness and other physical properties are highly uniform, especially a thin polycarbonate film in which a fine pattern, such as a group of small generally parallel apertures, is to be formed. It would also be desirable to have a method for providing small parallel apertures through the film, particularly for use in defining openings in the gate layer of a gated electron emitter. GENERAL DISCLOSURE OF THE INVENTION The present invention involves the preparation and usage of polycarbonate films. More particularly, the invention furnishes properties and compositions for a polycarbonate-containing liquid chemical formulation from which a thin polycarbonate film of highly uniform thickness can be made. The invention also furnishes processing techniques for making the polycarbonate film. Apertures are created through a so-prepared polycarbonate film by etching along substantially parallel charged-particle tracks. The aperture-containing polycarbonate film is typically employed in fabricating a gated electron-emitting device. The liquid chemical formulation of the invention is formed from polycarbonate material dissolved in a suitable liquid, preferably one capable of dissolving the polycarbonate material to a concentration of at least 1% by mass of the liquid formulation at 20.degree. C. and 1 atmosphere. The liquid preferably contains a principal solvent consisting of at least one of pyridine, a ring-substituted pyridine derivative, pyrrole, a ring-substituted pyrrole derivative, pyrrolidine, a pyrrolidine derivative, chlorobenzene, and cyclohexanone. The liquid may include a cosolvent, different from the principal solvent, for modifying one or more properties of the liquid formulation. Aside from the liquid and the polycarbonate material, the present liquid chemical formulation may be provided with one or more other constituents such as a water scavenger. To the extent that any other such constituent is present in the liquid formulation, each other such constituent is normally a minor component compared to the polycarbonate material. That is, the polycarbonate material is normally present in the liquid at a higher mass fraction than any other constituent present in the liquid. The polycarbonate material typically includes copolycarbonate whose molecules each contain two or more different monomeric carbonate repeat units. Each carbonate repeat unit is formed with a carbonate (CO.sub.3) group and another group, normally a hydrocarbon group. The copolycarbonate normally constitutes at least 5%, typically more than 50%, by mass of the polycarbonate material. Use of copolycarbonate leads to a polycarbonate film having properties that are highly advantageous when apertures are created in the polycarbonate film by etching along tracks formed by energetic charged particles. Each charged-particle track consists of a zone of damaged polycarbonate material in which the energy of one of the particles causes the polycarbonate molecules along the particle's path to cleave (undergo scission). A polycarbonate molecule typically cleaves along certain of its carbonate groups as decarboxylation occurs. Carbon dioxide is released from the molecule during decarboxylation. Apertures are created along the charged-particle tracks by removing the damaged polycarbonate material with etchant that attacks the remnants of the cleaved polycarbonate molecules much more strongly than the uncleaved polycarbonate molecules. Each polycarbonate molecule in the damaged polycarbonate material need not be cleaved into a large number of small parts for apertures to be created in the polycarbonate film by etching along the charged-particle tracks. Etchants are available which can selectively remove remnants of polycarbonate molecules cleaved at a relatively small number of locations, e.g., less than 10, typically 2-5, without significantly attacking uncleaved polycarbonate molecules. When apertures are to be created through a polycarbonate film by etching along charged-particle tracks, it is thus adequate for the polycarbonate molecules to have the property that each molecule cleaves most readily at only a relatively small number of locations when struck by energetic charged particles. The homolytic bond cleavage energy in a carbonate repeat unit of a polycarbonate molecule normally reaches a minimum at a location along the repeat unit's carbonate group. There is invariably a difference in minimum homolytic bond cleavage energy among the different carbonate repeat units in a molecule of copolycarbonate. Consequently, copolycarbonate molecules can be configured to have the foregoing advantageous molecular cleavage property. More particularly, each copolycarbonate molecule contains a primary carbonate component and a further carbonate component. The primary carbonate component is formed with repetitions of a primary carbonate repeat unit. The further carbonate component is formed with repetitions of one or more further carbonate repeat units different from the primary carbonate repeat unit. Each further carbonate repeat unit has a lower minimum homolytic bond cleavage energy than the primary carbonate repeat unit. Accordingly, each further repeat unit undergoes decarboxylation, and accompanying molecular scission, more readily than the primary repeat unit. The number of carbonate groups along which a copolycarbonate molecule cleaves most readily when struck by an energetic charged particle is thus less than the total number of carbonate groups in the molecule. The primary carbonate components of the molecules of copolycarbonate in the polycarbonate material of the present liquid chemical formulation normally constitute more than 50%, preferably more than 80%, by mass of the copolycarbonate. Taking note of the fact that bisphenol is a readily available and relatively inexpensive hydrocarbon, the primary repeat unit of each copolycarbonate molecule preferably consists of bisphenol A carbonate. Because each further repeat unit in such an implementation of copolycarbonate cleaves more readily than the bisphenol A carbonate repeat unit, the copolycarbonate cleaves more readily at acceptable locations than polycarbonate material formed solely with bisphenol A carbonate repeat unit. By implementing the copolycarbonate in this way, the polycarbonate material in the present liquid chemical formulation yields a relatively inexpensive polycarbonate film having a fully adequate molecular cleavage property when apertures are to be created through the film by etching along charged-particle tracks. At least one carbonate repeat unit in the polycarbonate material, especially the copolycarbonate, preferably has free radical stabilization. When molecules of the polycarbonate material undergo scission due, for example, to being struck by energetic charged particles, the free radical stabilization inhibits the remnants of the cleaved polycarbonate molecules from combining with one another or with other material. The ability of the polycarbonate material to maintain the pattern generated by the charged particles or other cleavage-causing phenomenon is thereby enhanced. Manufacture of a polycarbonate film in accordance with the invention is accomplished by first providing a liquid chemical formulation variously having the properties described above. Water in the liquid formulation can cause undesired scission of the polycarbonate molecules. As a result, the liquid formulation is normally prepared in such a way as to strongly avoid the presence of water. For this purpose, a water scavenger is typically employed. The water scavenger is typically introduced into the liquid prior to dissolving the polycarbonate material in the liquid. A liquid film of the present liquid chemical formulation is formed over a substructure. Various techniques, such as extrusion coating, can be utilized to create the liquid film. The liquid film is further processed to remove volatile components. The material remaining after such processing is a solid, largely polycarbonate film. Depending on the constituency of the liquid chemical formulation, the polycarbonate film may include, as minor components, one or more other non-volatile constituents of the liquid formulation and/or their reaction products. Importantly, the polycarbonate film is of highly uniform thickness, especially when the average film thickness is in the range of 0.1 .mu.m to 2 .mu.m. As indicated above, apertures are created in the polycarbonate film by subjecting the film to charged particles and then etching along the charged-particle tracks. In a typical application, an electrically non-insulating layer of the substructure is etched through the apertures in the polycarbonate film to form corresponding openings in the non-insulating layer. As used here, "electrically non-insulating" generally means electrically conductive or/and electrically resistive. The openings in the non-insulating layer can then be used to define locations for electron-emissive elements of an electron emitter. For example, the non-insulating layer can be a gate layer that overlies an electrically insulating layer. The insulating layer is etched through the openings in the gate layer to form dielectric open spaces in the insulating layer. Electron-emissive elements are formed in the dielectric open spaces. When the polycarbonate film serves as a track layer in fabricating a gated electron emitter according to the foregoing process, providing the polycarbonate film with uniform thickness and uniform physical properties enables etching of the charged-particle tracks to be isotropic. As a consequence, the size of the gate openings created by using the aperture-containing polycarbonate track film varies little from opening to opening. The emission of electrons across the electron-emitting area of the electron emitter is quite uniform. A high quality electron-emitting device is thereby formed. In short, the invention provides a substantial technological advance |
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