Programmable digital memory devices based on nanoscale thin films of a thermallydimensionally stable polyimide

Abstract

We have fabricated electrically programmable memory devices with thermally and dimensionally stablepoly(N-(N′,N′-diphenyl-N′-1,4-phenyl)-N,N-4,4′-diphenylene hexafluoroisopropylidene-diphthalimide) (6F-2TPA PI) films and investigated theirswitching characteristics and reliability. 6F-2TPA PI films were found to reveal a conductivity of1.0 × 10−13–1.0 × 10−14 S cm−1. The 6F-2TPA PI films exhibit versatile memory characteristics that depend on the filmthickness. All the PI films are initially present in the OFF state. The PI films with a thickness of>15 to<100 nm exhibit excellent write-once-read-many-times (WORM) (i.e. fuse-type)memory characteristics with and without polarity depending on the thickness.The WORM memory devices are electrically stable, even in air ambient,for a very long time. The devices’ ON/OFF current ratio is high, up to1010. Therefore, these WORM memory devices can provide an efficient, low-costmeans of permanent data storage. On the other hand, the 100 nm thick PI filmsexhibit excellent dynamic random access memory (DRAM) characteristicswith polarity. The ON/OFF current ratio of the DRAM devices is as high as1011. The observed electrical switching behaviors were found to be governed by trap-limitedspace-charge-limited conduction and local filament formation and further dependent on thedifferences between the highest occupied molecular orbital and the lowest unoccupiedmolecular orbital energy levels of the PI film and the work functions of the top and bottomelectrodes as well as the PI film thickness. In summary, the excellent memory properties of6F-2TPA PI make it a promising candidate material for the low-cost mass production ofhigh density and very stable digital nonvolatile WORM and volatile DRAM memorydevices.