Polymer memory devices using poly(N-vinylcarbazole) (PVK) as the active layer, incorporated with various weight ratios (0, 0.083, and 0.2) of dodecanethiol capped gold nanoparticles (Au NPs), are investigated. Electrical bistability is demonstrated for all three PVK-based devices, regardless of Au-NP ratios. However, current fluctuation is observed during stress test for both zero (PVK-only) and Au NPs:PVK=0.2:1 devices, while good current stability is obtained for the Au NPs:PVK=0.083:1 device. Capacitance-frequency (C-f) curves present the comparable negative capacitance feature for all three devices in both high-conductivity (“on”) state and low-conductivity (“off”) state, indicating that the carrier transport is dominated by the PVK matrix. However, minor differences in the C-f curves are dependent on the weight ratios of Au NPs, and the connection is discussed.

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A distinct unipolar but single-polarity resistive switching behavior is observed in a TiO(x)/Pt/TiO(x) trilayer structure, formed by thermal oxidation of a Ti/Pt/Ti stack. As a comparison, a memory device with a single TiO(x) active layer (without addition of Pt midlayer) is also fabricated but it cannot perform resistive switching. Energy band diagrams are illustrated to realize the modulation of Schottky barrier junctions and current conduction in TiO(x)-based devices under various biasing polarities. Introduction of the Pt midlayer creates two additional Schottky barriers, which mediate the band bending potential at each metal-oxide interface and attains a rectifying current conduction at the high-resistance state. The rectifying conduction behavior is also observed with an AFM-tip as the top electrode, which implies the rectifying property is still valid when miniaturizing the device to nanometer scale. The current rectification consequently leads to a single-polarity, unipolar resistive switching and electrically rewritable performance for the TiO(x)/Pt/TiO(x) device.

Electrical bistability is demonstrated in a polymer memory device using polystyrene containing an organic conjugated compound (8-hydroxyquinoline) and gold nanoparticles (Au NPs) capped with different alkanethiols of carbon chain lengths as the active layer between two metal electrodes. Au NPs capped with three different alkanethiols [1-octanethiol (C8), 1-dodecanethiol (C12), and 1-octadecanethiol (C18)] are investigated for the correlation with the memory performance. Above a threshold voltage, the as-fabricated device can transit from low conductivity state to high conductivity state. By applying a certain positive voltage, the high conductivity state can return to the low conductivity state. The switch-on voltages of thiol-derivatized Au NPs based organic memory devices are almost the same. Current fluctuations appeared in the static current–voltage characteristic of Au NPs capped with a 1-octadecanethiol (C18) based memory device. This feature is related to quantized charging and discharging of Au NPs because of the Coulomb repulsion between electrons confined in nanocrystals.