Programmable digital memory devices based on nanoscale thin films of a thermally dimensionally stable polyimide.
We have fabricated electrically programmable memory devices with thermally and dimensionally stable poly(N-(N',N'-diphenyl-N'-1,4-phenyl)-N,N-4,4'-diphenylene hexafluoroisopropylidene-diphthalimide) (6F-2TPA PI) films and investigated their switching characteristics and reliability. 6F-2TPA PI films were found to reveal a conductivity of 1.0 x 10(-13)-1.0 x 10(-14) S cm(-1). The 6F-2TPA PI films exhibit versatile memory characteristics that depend on the film thickness. 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 to 10(10). Therefore, these WORM memory devices can provide an efficient, low-cost means of permanent data storage. On the other hand, the 100 nm thick PI films exhibit excellent dynamic random access memory (DRAM) characteristics with polarity. The ON/OFF current ratio of the DRAM devices is as high as 10(11). The observed electrical switching behaviors were found to be governed by trap-limited space-charge-limited conduction and local filament formation and further dependent on the differences between the highest occupied molecular orbital and the lowest unoccupied molecular orbital energy levels of the PI film and the work functions of the top and bottom electrodes as well as the PI film thickness. In summary, the excellent memory properties of 6F-2TPA PI make it a promising candidate material for the low-cost mass production of high density and very stable digital nonvolatile WORM and volatile DRAM memory devices.
Depart. of Chemistry, National Research Lab for Polymer Synthesis and Physics, Center for Integrated Molecular Systems, Polymer Research Institute, and BK School of Molecular Science, Pohang University of Science and Technology, Pohang , Republic of Korea.
Taek Joon
TJ
Lee
Cha-Wen
CW
Chang
Suk Gyu
SG
Hahm
Kyungtae
K
Kim
Samdae
S
Park
Dong Min
DM
Kim
Jinchul
J
Kim
Won-Sang
WS
Kwon
Guey-Sheng
GS
Liou
Moonhor
M
Ree