DOI: 10.1021/la901896z 11713 Langmuir 2009, 25(19), 11713–11719 Published on Web 09/10/2009 pubs.acs.org/Langmuir © 2009 American Chemical Society Programmable Permanent Data Storage Characteristics of Nanoscale Thin Films of a Thermally Stable Aromatic Polyimide Dong Min Kim, † Samdae Park, † Taek Joon Lee, Suk Gyu Hahm, Kyungtae Kim, Jin Chul Kim, Wonsang Kwon, and Moonhor Ree* Department of Chemistry, National Research Laboratory for Polymer Synthesis and Physics, Center for Electro-Photo Behaviors in Advanced Molecular Systems, Division of Advanced Materials Science, Polymer Research Institute, and BK School of Molecular Science, Pohang University of Science & Technology, Pohang 790-784, Republic of Korea. † These authors contributed equally to this study. Received January 31, 2009. Revised Manuscript Received August 7, 2009 We have synthesized a new thermally and dimensionally stable polyimide, poly(4,4 0 -amino(4-hydroxyphenyl)- diphenylene hexafluoroisopropylidenediphthalimide) (6F-HTPA PI). 6F-HTPA PI is soluble in organic solvents and is thus easily processed with conventional solution coating techniques to produce good quality nanoscale thin films. Devices fabricated with nanoscale thin PI films with thicknesses less than 77 nm exhibit excellent unipolar write-once- read-many-times (WORM) memory behavior with a high ON/OFF current ratio of up to 10 6 , a long retention time and low power consumption, less than (3.0 V. Furthermore, these WORM characteristics were found to persist even at high temperatures up to 150 °C. The WORM memory behavior was found to be governed by trap-limited space-charge limited conduction and local filament formation. The conduction processes are dominated by hole injection. Thus the hydroxytriphenylamine moieties of the PI polymer might play a key role as hole trapping sites in the observed WORM memory behavior. The properties of 6F-HTPA PI make it a promising material for high-density and very stable programmable permanent data storage devices with low power consumption. Introduction In recent decades, there has been much interest in the use of organic molecules and polymeric materials in electronic devices with various functions, such as light-emitting diodes, 1 transis- tors, 2 and solar cells. 3 More recently, much attention has been paid to the use of electrically bistable resistive switching organic molecules and polymeric materials in the fabrication of nonvola- tile memory devices because they have significant advantages over inorganic silicon- and metal-oxide-based memory materials in that their dimensions can easily be miniaturized, and their properties can easily be tailored through chemical synthesis. 4-16 In general, the organic molecules used in memory devices are insoluble and thus require elaborate and expensive fabrication processes such as vacuum evaporation and deposition. 4-7 In contrast, polymeric materials only require solution processes such as spin-coating, dip-coating, spray-coating, and inkjet printing, which can be carried out at low cost; with their use, the multistack layer structures required for high density memory devices can easily be fabricated. Further, polymeric materials exhibit easy processa- bility, flexibility, high mechanical strength, and good scalability. As a result, significant research effort is currently being invested in the development of polymer switching materials with properties and processability that meet the requirements of nonvolatile memory devices. Some polymeric materials with memory effects and appli- cations have been reported. 8-20 However, most of these polymers have aliphatic hydrocarbon backbones with low dimensional stability. 8-18 Furthermore, they exhibit high ON- and OFF-switch- ing voltages 8,9,11,17,18 as well as high OFF currents. 9,17 Only a few polyimide materials have recently been reported as thermally and dimensionally stable polymers for use in memory devices: poly- (4,4 0 -aminotriphenylene hexafluoroisopropylidenediphthalimide) (6F-TPA PI), 19 poly(N-(N 0 ,N 0 -diphenyl-N 0 -1,4-phenyl)-N,N-4,4 0 - diphenylene hexafluoroisopropylidene-diphthalimide) (6F-2TPA PI), 20 poly(3,3 0 -bis(N-ethylenyloxycarbazole)-4,4 0 -biphenylene hexafluoroisopropylidenediphthal-imide) (6F-HAB-CBZ PI), 21 *To whom correspondence should be addressed. E-mail: ree@postech.edu. Tel: þ82-54-279-2120. Fax: þ82-54-279-3399. (1) Friend, R. H.; Gymer, R. W.; Holmes, A. B.; Burroughes, J. H.; Marks, R. N.; Taliani, C.; Bradley, D. D. 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