New photopatternable polyimide and programmable nonvolatile memory performances

We report the first photopatternable, nonvolatile memory consisting of high-temperature polyimide (PI), poly(hexafluoroisopropylidenediphthalimide-4-cinnamoyloxytri-phenylamine) (6F-HTPA-CI), and we demonstrate the successful fabrication and programmable operation of ‘write-read-erase’ memory devices based on nanoscale thin films of 6F-HTPA-CI. The PI thin film enables scalable fine patternability, providing lines and spaces with excellent pattern fidelity. Isolated individual memory devices were successfully fabricated on a bottom electrode via a sequential process of coating, photopatterning, top electrode deposition, developing, rinsing and drying. The 6F-HTPA-CI cells exhibited excellent nonvolatile memory performances in three different modes (unipolar permanent, unipolar flash and bipolar flash memories), regardless of photo-exposure doses. The switching-ON (writing) voltage was in the range of ±1.5 to ±2.0 V, and the switching-OFF (erasing) voltage was in the range of ±0.3 to ±0.8 V; these voltages are quite low, indicating that power consumption by the devices during operation is low. The ON/OFF current ratio of the devices was in the range of 104–109. Overall, the photopatternable PI 6F-HTPA-CI opens up the possibility of low-cost mass production of high-performance, high-speed, energy-efficient, permanent or rewritable high-density nonvolatile polymer memory devices suitable for future advanced electronics in highly integrated systems. Electroactive polymer that naturally becomes insoluble and toughens up when exposed to ultraviolet light is a good candidate for future high-density flash memory. Plastic knock-offs of silicon memory chips offer cost savings and innovative, flexible designs, but many polymers have trouble in handling the wet chemicals used during multilayered device fabrication. Moonhor Ree and colleagues from POSTECH in Korea have developed nanoscale polyimide films that can survive through sequentially coating, patterning and electrode deposition steps. The new aromatic polymer's multifunctionality proved key to its durability: it imparted mechanical and thermal strength and contained functional groups that interlinked the plastic together during the ultraviolet patterning step. This approach produced isolated memory cells in a dense layout that underwent successful ‘read–write–erase’ actions at minimal voltages. Low crosstalk between patterned cells yielded excellent data-retention characteristics. Novel digital memory devices were fabricated with a new photo-patternable polyimide (PI), poly(hexafluoroisopropylidenediphthalimide-4-cinnamoyloxytriphenylamine (6F-HTPA-CI). The finely patterned PI device cells demonstrated excellent programmable nonvolatile memory characteristics in three different modes (unipolar permanent memory, and unipolar and bipolar flash memories). Overall, this photopatternable polymer is very suitable for future energy-efficient, faster speed and high density nonvolatile memory devices in highly integrated systems.