Bistable Organic Memory Device with Gold Nanoparticles Embedded in a Conducting Poly(N-vinylcarbazole) Colloids Hybrid

Abstract

ABSTRACT:We report on the nonvolatile memory characteristics of a bistable organic memory (BOM) device with Au nanoparticles (NPs) embedded in a conducting poly-(N-vinylcarbazole) (PVK) colloids hybrid layer deposited on flexible poly(ethyleneterephthalate) (PET) substrates. Transmission electron microscopy (TEM) images show the Au nanoparticles distributed isotropically around the surface of a PVK colloid. The average induced charge on Au nanoparticles, estimated using the C-V hysteresis curve, was large, as much as 5 holes/NP at a sweeping voltage of (3 V. The maximum ON/OFF ratio of the current bistability in the BOM devices was as large as 1 Â 10 5 . The cycling endurance tests of the ON/OFF switching exhibited a high endurance of above 1.5 Â 10 5 cycles, and a high ON/OFF ratio of ∼10 5 could be achieved consistently even after quite a long retention time of more than 1 Â 10 6 s. To clarify the memory mechanism of the hole-mediated bistable organic memory device, the interactions between Au nanoparticles and poly(Nvinylcarbazole) colloids was studied by estimating the density of states and projected density of state calculations using density functional theory. Au atom interactions with a PVK unit decreased the band gap by 2.96 eV with the new induced gap states at 5.11 eV (HOMO, E 0 ) and LUMO 4.30 eV and relaxed the HOMO level by 0.5 eV (E 1 ). E 1 at ∼6.2 eV is very close to the pristine HOMO, and thus the trapped hole in E 1 could move to the HOMO of pristine PVK. From the experimental data and theoretical calculation, it was revealed that a low-conductivity state resulted from a hole trapping at E o and E 1 states and subsequent hole transportation through Fowler-Nordheim tunneling from E 1 state to Au NPs and/or interface trap states leads to a high conductivity state.

Resistive switching of in situ polymerized polystyrene matrix copolymerized with alkanedienyl passivated Si nanoparticles

“…Second, the Si NPs' preparation process by top-down method is relatively simple in this study [10,11]. In addition, the surface of Si NPs can be more easily grafted or passivated with organic moieties by surface alkylation reaction than other metallic, ZnO, and iron oxide NPs [5][6][7][8]. The organic moiety attached to Si NPs can be used for further functionalities such as chemical incorporation of the Si NPs into polymer matrix like PS [2,3].…”

“…Memory devices having polymeric layers including nanoparticles (NPs) for charge trapping have been introduced for decades in resistive switching memory device formats, which have showed reversible control of electronic resistivity [1][2][3][4][5][6][7]. The polymeric memories have implemented two stable resistance states governed by external electrical field for the data storage applications.…”

“…For many cases, methodologies of construction for the memory device have been based on mixture of NPs and host polymeric materials. The NPs could be gold (Au), zinc oxide (ZnO), and C60, which have been frequently referred to metallic or semiconductor host that could be used as electron or hole transport layer to confine NPs embedded in insulating polymeric materials [1,3,4,6]. In the other hand, for the matrix materials, inert or dielectric polymer, such as polystyrene (PS), polyvinyl alcohol (PVA), and poly methylmethacrylate (PMMA) have been utilized so far.…”

“…In the other hand, for the matrix materials, inert or dielectric polymer, such as polystyrene (PS), polyvinyl alcohol (PVA), and poly methylmethacrylate (PMMA) have been utilized so far. The PS has been most frequently used matrix for resistive switching devices [1][2][3]6].…”

“…Typically, overall conduction mechanism for organic resistive switching have been dominated by many aspects of Ohmic conduction, Schottky emission, thermionic emission, space charge-limited current (SCLC), tunneling current, ionic conduction, hopping conduction, and impurity conduction [5,6]. Especially for the NPs based devices, the conduction mechanisms could determine digital switching or analog switching, i.e., gradual changing resistance or phenomena that could mimic adaptive synaptic mechanism of neuromorphic system [8,9].…”