Electrically programmable multilevel nonvolatile memories based on solution-processed organic floating-gate transistors

The development of nonvolatile organic field-effect transistor (OFET) memories with a satisfactory solution processability is highly desirable to fabricate the data storage media for flexible and printed electronic devices. In this study, we fabricate top-gate/bottom-contact OFET memories having an organic floating-gate structure by a spin-coating process and investigate their memory characteristics. An ambipolar polymer semiconductor of poly(N-alkyldiketopyrrolo-pyrrole-dithienylthieno[3,2-b]thiophene) (DPP-DTT) was used to fabricate an organic semiconductor layer, on which an organic composite of polystyrene and 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-pentacene) was deposited to form an organic floating-gate structure through vertical phase separation. The existence of a deep lowest unoccupied molecular orbital (LUMO) level and the excellent electron transport property of the DPP-DTT enables the injection of electrons from the Au source-drain electrodes to the DPP-DTT semiconductor layer and the storage of electrons in the LUMO level of the TIPS-pentacene floating gates by programming under dark conditions. A high work function metal oxide layer of MoO3 was inserted at the Al gate electrode/CYTOP gate insulator interface to tune the energy level difference between the Au source-drain and Al gate electrodes. The DPP-DTT FET memories with MoO3/Al gate electrodes exhibit satisfactory retention characteristics and, because of the ambipolar trapping characteristics, allow the storing of holes in the highest occupied molecular orbital level of the TIPS-pentacene floating gates in the erasing process. Furthermore, the molecular floating-gate OFET memories exhibit a high storage capacity for multi-level data, and four state levels can be recorded with stable retention characteristics.