Mechanism Investigation Of Electrical Bistable Memory Devices Based On Nano-materials/Organic Polymer Composite

The electrical bistable memory devices(EBMDs)based on hybrid nano-materials/organic polymer have attracted considerable attention for its fast response,non-destructive program/erase operations,high data storage density and simple,feasible preparation approach.Many researches have suggested that the surface defects of nano-materials and electronic energy level structures related to the quantum size have the important influence on the electron transport process and device storage mechanism.In this paper,the EBMDs are prepared utilizing two nano-materials of Zn-Cu-In-S nanocrystals(ZCIS NCs)and Carbon quantum dot(CDs)as active laye.Furthermore,the electron transport process and memory mechanism are accordingly described based on surface functional groups,the internal defects and the device energy level structure.1.A write-only-read-many-times(WORM)electrical bistable device is fabricated utilizing hybrid quaternary ZCIS NCs and PMMA as active layer.The electron transport process and memory mechanism are described based on the fitted current-voltage curves and the energy band diagrams.The conduction models are described as thermionic emission(TE),space-charge-limited current(SCLC)and Fowler-Nordheim(FN)tunneling in the transition from the high resistance state(HRS)to low resistance state(LRS),respectively.And the Ohmic conduction is dominant after the device transits to the LRS.The captured electrons by high-density defects in quaternary ZCIS NCs and the high barrier between ZCIS NCs and PMMA are considered to contribute to the WORM characteristic.The maximum ON/OFF current ratio of 4×103 and the retention time of 1×104 s can be obtained.For device performance optimization,an additional PMMA layer is pre-deposited on the ITO substrate surface.The enhancement in ON/OFF ratio with 50 times larger is reasonably related to the decrease in surface contact resistance between electrode ITO and active layer.The better retention capacity is considered to derive from thickened tunnel barrier preventing the release of the captured electrons by the PMMA inserted layer.2.CDs synthesized by high-temperature pyrolysis method are sandwiched in between two layers of polymer PVP.The capacitance-voltage curves of as fabricated device show a hysteresis behavior of metal-insulator-semiconductor(MIS).The device Al/ZnO/PVP/CDs/PVP/ITO/Glass and the device Au/PVP/CDs/PVP/ZnO/Al/Glass are assembled in consideration of the electrons conduction of ZnO.The ZnO layer improves the electron injection efficiency and neutralizes the captured holes by CD in the device of Al/ZnO/PVP/CDs/PVP/ITO/Glass.For device Au/PVP/CDs/PVP/ZnO/Al/Glass,the better wettability between ZnO and Al film improve the optimal ON/OFF ratio and memory window.3.The hysteretic current-voltage characteristic is observed in the multilayer films of PMMA/CDs/PEDOT:PSS using the ITO and Al metals as the electrodes through spinning-coating method,where the device has obviously larger hysteresis window in compared to the non-CDs additional layer.The phenomenon that short circuit current(Isc)and open circuit voltage(Voc)increase with scanning voltage range increase is observed until the threshold voltage is ±15 V.The specific current-voltage hysteresisis ascribed to the reverse polarized field induced by electric dipoles between the PMMA and the PEDOT:PSS layer.