Bistable organic memory device with gold nanoparticles embedded in a conducting poly(N -vinylcarbazole) colloids hybrid

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 × 10⁵. The cycling endurance tests of the ON/OFF switching exhibited a high endurance of above 1.5 × 10⁵ 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 × 10⁶ s. To clarify the memory mechanism of the hole-mediated bistable organic memory device, the interactions between Au nanoparticles and poly(N-vinylcarbazole) 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, E₀) and LUMO 4.30 eV and relaxed the HOMO level by 0.5 eV (E₁). E₁ at ∼6.2 eV is very close to the pristine HOMO, and thus the trapped hole in E₁ 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 E₁ 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.