Semiconductor device manufacturing: process – Making device or circuit emissive of nonelectrical signal – Including integrally formed optical element
Reexamination Certificate
2002-10-17
2004-01-20
Picardat, Kevin M. (Department: 2822)
Semiconductor device manufacturing: process
Making device or circuit emissive of nonelectrical signal
Including integrally formed optical element
C438S099000, C257S040000, C205S078000
Reexamination Certificate
active
06680215
ABSTRACT:
BACKGROUND OF THE INVENTION
Since the discovery of conducting polymers in 1977, Shirakawa, H.; Lewis, E. J.; MacDiarmid, A. G.; Chiang, C. K.; Heeger, A. J. 1977, 578, extensive research has focused on developing these materials for organic electronic devices. Organic semiconductors such as poly(phenylene vinylene), poly(thiophene), poly(acetylene) and poly(pyrrole) have found application in devices ranging from organic light-emitting diodes (OLEDs) to field effect transistors (FETs). Katz, H. E.; Bao, Z.
Journal of Physical Chemistry B
2000, 104, 671-678; Greiner, A.
Polymers For Advanced Technologies
1998, 9, 371-389; Gurunathan, K.; Vadivel Murugan, A.; Marimuthu, R.; Mulik, U. P.; Amalanerkar, D. P.
Journal of Materials Chemistry and Physics
1999, 61, 173-191. Organic electronics do not match the performance of inorganic, silicon-based devices, due to fundamental limitations on charge carrier mobility in conducting polymers. Katz, H. E.; Bao, Z.
Journal of Physical Chemistry B
2000, 104, 671-678. The oft stated advantages of organic electronics, i.e., low cost, mechanical flexibility and ease of processing, could open entire new areas of technical development such as large area displays and disposable electronics—areas not currently accessible with silicon based devices. However, the most promising organic electronics to date are fabricated using vapor sublimated single crystal films of organic molecules patterned using conventional, silicon-based technology. Katz, H. E.; Bao, Z.
Journal of Physical Chemistry B
2000, 104, 671-678; Cui, J.; Huang, Q. L.; Wang, Q. W.; Marks, T. J.
Langmuir
2000, 17, 2051-2054. Achieving the goals of low cost and ease of processing requires the development of room temperature, aqueous, solution-based processes for fabricating thin films of conducting polymers.
Both chemical and electrochemical approaches to form thin films of conducting polymers have been developed. Bradley, D. D. C.; Grell, M.; Grice, A.; Tajbakhsh, A. R.; O'Brien, D. F.; Bleyer, A.
Optical Materials
1998, 9, 1-11. Sato, M. A.; Sakamoto, M. A.; Miwa, M.; Hiroi, M.
Polymer
2000, 41, 5681-5687. Pei, Q. B.; Zuccarello, G.; Ahlskog, M.; Inganas, O.
Polymer
1994, 35, 1347-1351. Dietrich, M.; Heinze, J.; Heywang, G.; Jonas, F.
Journal of Electroanalytical Chemistry
1994, 369, 87-92. A variety of monomers can be electropolymerized in polar organic solvents, and these films have been used to make both OLEDs and organic FETs. Tasch, S.; Gao, J.; Wenzl, F. P.; Holzer, L.; Leising, G.; Heeger, A. J.; Scherf, U.; Mullen, K.
Electrochemical and Solid State Letters
1999, 2, 303-305; Johansson, T.; Mammo, W.; Andersson, M. R.; Inganas, O.
Chemistry of Materials
1999, 11, 3133-3139; Pei, J.; Yu, W. L.; Huang, W.; Heeger, A. J.
Macromolecules
2000, 33, 2462-2471; Sainova, D.; Miteva, T.; Nothofer, H. G.; Scherf, U.; Glowacki, I.; Ulanski, J.; Fujikawa, H.; Neher, D.
Applied Physics Letters
2000, 76, 1810-1812; Osaka, T.; Komaba, S.; Fujihana, K.; Okamoto, N.; Momma, T.; Kaneko, N.
Journal of the Electrochemical Society
1997, 144, 742-748. The main limitation is that polymeric films are typically amorphous and contain a large number of defects. One way to reduce defects is through use of substituted monomers such as 3,4-ethyldioxythiophene (EDOT) or by polymerizing short oligomers such as bithiophene. Kabasakaloglu, M.; Kiyak, T.; Toprak, H.; Aksu, M. L.
Applied Surface Science
1999, 152, 115-125.
Even without defects, the amorphous nature of electropolymerized films limits performance in organic devices. In an amorphous conducting polymer film, inter-chain charge hopping leads to non-radiative quenching of electron-hole pairs (excitons). Nanoscale control of the arrangement and orientation of organic molecules can improve the luminescence efficiency of OLEDs and increase the speed of organic FETs. Poly(thiophene) is a hole conductor (p-type) and is electroluminescent, meaning it can be used as either the hole transport or emissive layer of an OLED. Charge injection from an electrode into the hole-transporting layer is improved by orienting polymer chains normal to the electrode surface (parallel to the applied field), compared with a randomly oriented amorphous film. Markart, P.; Zojer, E.; Tasch, S.; Smith, R.; Gin, D.; Leising, G.
Synthetic Metals
1999, 102, 1155-1156. Isolating molecules reduces exciton quenching and improves the efficiency of OLEDs. Osterbacka, R.; An, C. P.; Jiang, X. M.; Vardeny, Z. V.
Science
2000, 287, 839-842. For organic FETs, aligning polymer chains is critical for improving device performance, enhancing both carrier mobility and conductivity. Bao, Z. N.; Rogers, J. A.; Katz, H. E.
Journal of Materials Chemistry
1999, 9, 1895-1904; Bjornholm, T.; Hassenkam, T.; Greve, D. R.; McCullough, R. D.; Jayaraman, M.; Savoy, S. M.; Jones, C. E.; McDevitt, J. T.
Advanced Materials
1999, 11, 1218-1221. This is one reason why single crystal films are often used. Chain alignment within a non-crystalline film enhances carrier mobility while remaining simpler to process.
Poor solubility of conducting polymers is the primary obstacle to using most conventional methods for aligning polymer chains. Thiophene, phenylene vinylene, and other precursors to conjugated polymers are soluble in many organic solvents, especially polar solvents like acetonitrile and tetrahydrofuran (THF). However, the conducting polymers they form are generally insoluble due to their tendency to &pgr;-&pgr; stack, causing long oligomers or polymers to aggregate in solution. Chemical or electrochemical polymerization of thiophene leads to an intractable, insoluble material that is difficult to characterize or process. Addition of long alkyl chains or other solubizing groups to the 3 or 4 position on the thiophene ring improves solubility. Sato, M. A.; Sakamoto, M. A.; Miwa, M.; Hiroi, M.
Polymer
2000, 41, 5681-5687; Kilbinger, A. F. M.; Feast, W. J.
Journal of Materials Chemistry
2000, 10, 1777-1784; Tour, J. M.; Wu, R. L.
Macromolecules
1992, 25, 1901-1907. Certain substituents even lead to water-soluble monomers and polymers. Stephan, O.; Schottland, P.; Le Gall, P. Y.; Chevrot, C.; Mariet, C.; Carrier, M.
Journal of Electroanalytical Chemistry
1998, 443, 217-226. However, large substituents sterically constrain the monomer, inhibiting electropolymerization and degrading electronic properties of the material. Without large solubilizing groups, orientation and alignment of organic semiconductors after polymerization is extremely difficult.
An alternate approach involves the use of a template to position the monomers and lock-in the orientation for alignment during polymerization. Liquid crystals (LCs) are an example of a self-organizing system. One type of lyotropic LC is formed by amphiphilic molecules containing hydrophobic and hydrophilic segments that segregate in a solvent. At low concentrations, amphiphilic molecules form spherical micelles in solution. At higher concentrations, several LC mesophases are possible, including hexagonal, cubic and lamellar structures. The particular mesophase formed depends on a balance between the attractive and repulsive forces on the hydrophilic head group and hydrophobic tail, and the relative volumes of these head/tail segments. Israelachvili, J.
Intermolecular
&
Surface Forces;
2 ed.; Academic Press: San Diego, Calif., 1992; Kunieda, H.; Umizu, G.; Yamaguchi, Y.
Journal of Colloid and Interface Science
1999, 218, 88-96.
OBJECTS OF THE INVENTION
In light of the foregoing, it is an object of the present invention to provide general methodologies relating to the use of liquid crystals to template the electropolymerization of precursors for conducting or light-emissive compositions. Various related objectives of this invention can be illustrated by comparison with the prior art.
For instance, P. Braun, et. al. used a liquid crystal to directly template hexagonal superlattices of cadmium sulfide. Braun, P. V.; Osenar, P.; Stupp, S. I.
Nature
1996, 380, 325-328; Braun, P. V.; Osenar, P.; Tohver, V.; Kennedy, S.
Hulvat James F.
Stupp Samuel I.
Northwestern University
Picardat Kevin M.
Reinhart Boerner Van Deuren s.c.
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