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Professor Park Cheolmin

"Professors Park Cheolmin and Lee Hyungsuk’s International Research Team develops Foldable and bendable Memory devices"

"Development of Non-volatile Field Effect Transistor Memory with Extreme Mechanical Flexibility"

Professors Park Cheolmin (Materials Science and Engineering) and Lee Hyungsuk (Mechanical Engineering) and Prof. Jean-Charles Riberre of Kyushu University in Japan has successfullydeveloped high performance, non-volatile organic memory devices that can operate under various mechanical deformations such as bending and folding. On April 8, 2014, the article “non-volatile organic memory with sub-millimetre bending radius” was published in nature Communications. To realize the electronic devices that can operate at extreme mechanical deformations, various organic materials were developed as semiconductors and insulators. In particular, organic memories with severe bending have rarely been demonstrated and bending radii lower than 1 mm remain exceptional, preventing rational and low-cost strategies from developing. Furthermore, no memory device has been properly operated with extreme mechanical deformation, i.e. folding which results in permanent, plastic deformation of a device. Prof. Park’s team reported on the realization of high-performance non-volatile organic memory with ultimate mechanical flexibility. The solution-processed ferroelectric field effect transistor memory with ferroelectric poly (vinylidene fluoride-trifluoroethylene) (PVDF-TrFE) and semiconducting dicyanomethylenesubstituted quinoidal quaterthiophene derivative [QQT(Cn)4] exhibited p-type and n-type current hysteresis, and in both switching modes, the memory device showed outstanding mechanical flexibility. They were highly reliable with excellent data retention and endurance of more than 6000 s and 100 cycles, respectively even after both multiple bending cycles at extreme bending radii as low as 500 μm and sharp folding involving inelastic deformation of the device. Through the stress analysis of composite films during bending in combination with nanoindentation and nano-scratch experiments, Prof. Park’s team then suggest that both the plasticity of QQT(Cn)4 and its firm interface with PVDF-TrFE are responsible for resisting inelastic mechanical deformation such as folding. This work represents a major step in the development of ultra-flexible organic memories.

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