The rapid development of the information technology industry has led to the ever-increasing demand for mass data storage that has driven research towards high-capacity memory devices. Multi-level memory (MLM) enables high-density data storage per unit area without reducing the size of memory cells, hence overcoming downscaling limitations of lithography technology as well as reducing manufacturing costs. Owing to their multi-bit storage capability, non-destructive read-out, low cost, and good compatibility with flexible substrates, non-volatile organic field-effect transistor (OFET) memory has been regarded as a highly-promising candidate for applications in next-generation, large-area printed electronics. To date, considerable efforts have been devoted to improving the charge-trapping capacity of OFET memory devices by developing functional gate dielectrics. In fact, the ability to tune the charge-trapping property within the organic semiconductor layer could also enable OFETs with memory functionality but currently has received far less attention from the research community.
In this work, non-volatile OFET memory devices based on pentacene/N,N′-ditridecylperylene-3,4,9,10-tetracarboxylic diimide (P13)/pentacene trilayer organic heterostructures are demonstrated. The judiciously-controlled discontinuous n-type P13 film embedded into p-type pentacene layers can not only provide electrons in the semiconductor layer that facilitates electron trapping; it also works as charge trapping sites, which is attributed to the quantum well-like pentacene/P13/pentacene organic heterostructures. The synergistic effects of charge trapping in the discontinuous P13 film together with the gate-dielectric-modification charge-trapping layer, composed of poly(4-vinylphenol), can drastically improve the memory performance. The devices exhibit excellent non-volatile memory characteristics with stable data endurance characteristics of 3,000 programming/erasing cycles and long data retention time (extrapolated to >10 years). MLM characteristics with four stable data storage states are achieved due to the high charge capacity as well as the large memory window. Moreover, the trilayer organic heterostructures are also successfully applied to flexible non-volatile memory devices that remain excellent memory performance even after 10,000 bending cycles (bending radius = 10 mm), demonstrating their extraordinary mechanical properties. This study introduces novel organic heterostructures for the fabrication of high-capacity OFET memory devices for applications in next-generation printed electronics. More importantly, the concept of the quantum well-like organic heterostructures provides general guidelines to construct high-performance multi-bit OFET memory from the large library of organic materials to form similar energetically-favourable hetero-systems.
 Y.-H. Chou, et al., Polym. Chem., 2015, 6, 341-352.
 W. Li, et al., Adv. Sci., 2017, 4, 1700007.