Synthesis and nonvolatile memory characteristics of thermally, dimensionally and chemically stable polyimides

A series of soluble poly(amic acid) precursors were prepared from a new carbzole-containing monomer, 3,3'-bis[9-carbazole(ethyloxy)biphenyl]-4,4'-diamine (HAB-CBZ) by polycondensation with four different aromatic dianhydrides: pyromellitic dianhydride (PMDA), 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), 3,3',4,4'-diphenylethertetracarboxylic dianhydride (ODPA), and 3,3',4,4'-diphenylsulfonyltetracarboxylic dianhydride (DSDA). From the precursors, nanoscale thin films of polyimides (PIs) were prepared by spin-coating and subsequent thermal imidization. All the PIs exhibited excellent thermal and dimensional stability. In particular, the PIs based on the PMDA and BPDA units revealed excellent chemical resistance to organic solvents, in addition to the high thermal and dimensional stability, which are required for the fabrication of high performance memory devices in three-dimensionally multi-stack structure. Devices fabricated with nanoscale thin PI films exhibited excellent unipolar write-once-read-many-times (WORM) memory behavior with a high ON/OFF current ratio of up to 10(10). The active PI films were found to operate at 2.2-3.3 V, depending on the chemical structures. This study found that the imide rings as local charge trap sites are necessary to enhance the memory performance in addition to carbazole moiety. All the results collectively indicate that the thermally, dimensionally and chemically stable PIs of this study are a promising material for the mass production at low cost of high performance, programmable nonvolatile WORM memory devices that can be operated with low power consumption in unipolar switching mode. (C) 2011 Elsevier Ltd. All rights reserved.