[Show abstract][Hide abstract] ABSTRACT: Multilevel high-resistance states are achieved in TiN/HfOx/Pt resistive switching random access memory device by controlling the reset stop voltage. Impedance spectroscopy is used to study the multilevel high-resistance states. It is shown that the high-resistance states can be described with an equivalent circuit consisting of the major components , , and corresponding to the series resistance of the TiON interfacial layer, the equivalent parallel resistance, and capacitance of the leakage gap between the TiON layer and the residual conductive filament, respectively. These components show a strong dependence on the stop voltage, which can be explained in the framework of oxygen vacancy model and conductive filament concept. On the other hand, is observed to decrease with dc bias, which can be attributed to the barrier lowering effect of the Coulombic trap well in the Poole–Frenkel emission model.
IEEE Transactions on Electron Devices 08/2015; 62(8):2684-2688. DOI:10.1109/TED.2015.2445339 · 2.47 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Although synaptic behaviours of memristors have been widely demonstrated, implementation of an even simple artificial neural network is still a great challenge. In this work, we demonstrate the associative memory on the basis of a memristive Hopfield network. Different patterns can be stored into the memristive Hopfield network by tuning the resistance of the memristors, and the pre-stored patterns can be successfully retrieved directly or through some associative intermediate states, being analogous to the associative memory behaviour. Both single-associative memory and multi-associative memories can be realized with the memristive Hopfield network.
[Show abstract][Hide abstract] ABSTRACT: Localized surface plasmon resonance (LSPR) and electron confinement effects on the interband transitions and free-electron absorption in ultrathin Au films with the film thicknesses of about 1-12 nm are investigated. A significant evolution of the LSPR, interband transition energies, plasma energy, and conductivity with the film thickness is observed. The evolution is attributed to the changes in the size, shape, and spacing of the self-assembled gold nanoparticles (Au NPs) with the sizes from several nanometers to 110 nm as well as the aggregation of the Au NPs in the Au films.
Journal of Nanoparticle Research 02/2015; 17(2). DOI:10.1007/s11051-015-2880-1 · 2.18 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Dielectric function of amorphous indium gallium zinc oxide (a-IGZO) thin films is found to shift significantly with the film thickness, which is attributed to the changes in both the bandgap and electron concentration of the IGZO thin films with the film thickness. The ultrathin films (film thickness < ∼20 nm) exhibit a bandgap expansion with reducing film thickness due to the quantum confinement effect; while the thicker films (thickness > ∼35 nm) demonstrate the free-electron effect, i.e. the Burstein-Moss shift and increase of free-electrons absorption with increasing electron concentration
[Show abstract][Hide abstract] ABSTRACT: Synaptic Long-Term Potentiation (LTP), which is a long-lasting enhancement in signal transmission between neurons, is widely considered as the major cellular mechanism during learning and memorization. In this work, a NiOx-based memristor is found to be able to emulate the synaptic LTP. Electrical conductance of the memristor is increased by electrical pulse stimulation and then spontaneously decays towards its initial state, which resembles the synaptic LTP. The lasting time of the LTP in the memristor can be estimated with the relaxation equation, which well describes the conductance decay behavior. The LTP effect of the memristor has a dependence on the stimulation parameters, including pulse height, width, interval, and number of pulses. An artificial network consisting of three neurons and two synapses is constructed to demonstrate the associative learning and LTP behavior in extinction of association in Pavlov's dog experiment.
[Show abstract][Hide abstract] ABSTRACT: Tunable light resonance transportation along a single long Au hemisphere nanoparticles (NPs) chain was studied. The realistic experimentally determined gold dielectric function was used for the simulation of Au localized surface plasmon polariton (LSPPs) effect. The resonance light energy with minimized attenuation and its bandwidth were quantitatively analyzed by inducing the effective mass which was observed to increase only with the length of Au NPs between the source and the test point. The geometric ratio g/r of NP size and gap were investigated at 5 mu m far of NPs with different gaps from 0 to 70 nm. Strongest resonance can be achieved with g/r = 1.2 by the factor of 1.5 than the connected NPs. This resonance mode falls in the wavelength lambda = 555 nm (green light), which is exactly the maximum sensitivity of a light-adapted eye of human beings.
Journal of Nanoparticle Research 10/2014; 16(10). DOI:10.1007/s11051-014-2630-9 · 2.18 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Evolution of dielectric function of Al-doped ZnO (AZO) thin films with annealing temperature is observed. It is shown that the evolution is due to the changes in both the band gap and the free-electron absorption as a result of the change of free-electron concentration of the AZO thin films. The change of the electron concentration could be attributed to the activation of Al dopant and the creation/annihilation of the donor-like defects like oxygen vacancy in the thin films caused by annealing. (C) 2014 Optical Society of America
[Show abstract][Hide abstract] ABSTRACT: Reactive sputtering has been used to synthesize Al-rich Al2O3 thin films. After post-deposition thermal annealing, the excess Al content forms Al nanocrystals (nc-Al) which are dispersed in the Al2O3 matrix. In the Al/Al-rich Al2O3/p-Si
structure, the current conduction which follows a Schottky emission process can be greatly enhanced by a charging process with negative voltage pulses and then maintained for considerable duration, realizing write-once-read-many-times (WORM) memory behaviors. The current conduction enhancement
is attributed to the reduction of effective Schottky barrier caused by charging-induced hole trapping in the nc-Al related defects near the oxide/p-Si interface. It is found that the sample with lower concentration of nc-Al has a larger memory window due to the lower initial current.
In addition, the retention is also better since the release of trapped charges is more difficult with less nc-Al related leakage paths present in the oxide film. The concentration of excess Al content in the Al-rich Al2O3 thin film can be optimized to achieve large memory
windows as well as good retention characteristics in the associated WORM memory devices.
[Show abstract][Hide abstract] ABSTRACT: Resistive switching memristor, predicted as the fourth fundamental passive circuit element (in addition to resistor, capacitor, and inductor) in the world by Leon Chua in 1971 and demonstrated by Hewlett Packard laboratory in 2008, has attracted extensive research attention for its
high scalability and versatility. In this paper, we reviewed the working mechanisms and mathematical models of nanostructured resistive switching memristors, and examined various emerging applications of the memristors, including memory, analog, logic and neuromorphic applications.
[Show abstract][Hide abstract] ABSTRACT: Resistive switching can occur in Al-rich AlO
thin films depending on the Al content, i.e., the films with a small Al content exhibit resistive switching, but no resistive switch is observed in the films with a large Al content. The forming voltage,
set/reset voltages, currents at the low- and high-resistance states, and conduction behavior of the low-resistance state are found to be dependent of the Al content. The phenomena can be explained by the changes in the complete filaments that consist of the metallic filaments formed by Al
nanophases and the non-metallic filaments formed by oxygen vacancies.
[Show abstract][Hide abstract] ABSTRACT: Lateral charge transfer in a Si nanocrystal (nc-Si) layer embedded in a SiO2 thin film synthesized by Si ion implantation is investigated. When the nc-Si in one metal-oxide-semiconductor device is charged, the charging effect on both the charged device itself and the neighboring
devices is monitored. With the existence of a continuous nc-Si layer in the spacing regions between the charged device and the neighboring devices, the charging operation induces a large flat-band voltage shift in the neighboring devices, and at the same time the charged device itself is also
strongly affected in return. The phenomenon depends on both the nc-Si separation and the device spacing. It is attributed to the lateral charge transfer in the nc-Si layer. The result has an important indication for non-volatile memory applications of the nc-Si synthesized by the ion implantation
[Show abstract][Hide abstract] ABSTRACT: Dielectric function, band gap, and exciton binding energies of ultrathin ZnO films as a function of film thickness have been obtained with spectroscopic ellipsometry. As the film thickness decreases, both real (ε1) and imaginary (ε2) parts of the dielectric function decrease significantly, and ε2 shows a blue shift. The film thickness dependence of the dielectric function is shown related to the changes in the interband absorption, discrete-exciton absorption, and continuum-exciton absorption, which can be attributed to the quantum confinement effect on both the band gap and exciton binding energies.
[Show abstract][Hide abstract] ABSTRACT: The contributions of localized surface plasmon resonance (LSPR) and Drude (free electrons) absorption to the complex dielectric function of ultrathin Au films were investigated with spectroscopic ellipsometry. When the Au film thickness is thinner than ~10 nm, Au nanoparticles (NPs) are formed as a result of the discontinuity in the films, leading to the emergence of LSPR of Au NPs; and the LSPR exhibits a splitting when the films thinner than ~8 nm, which could be attributed to the near-field coupling of the Au NPs and/or the inhomogeneous polarizations of the Au NPs. On the other hand, the delocalization of electrons in Au NPs due to the aggregation of Au NPs in a thicker film leads to an increase in the free-electron absorption and a suppression of the LSPR.
[Show abstract][Hide abstract] ABSTRACT: A write-once-read-many-times (WORM) memory devices based on O2 plasma-treated indium gallium zinc oxide (IGZO) thin films has been demonstrated. The device has a simple Al/IGZO/Al structure. The device has a normally OFF state with a very high resistance (e.g., the resistance at 2 V is ∼109 Ω for a device with the radius of 50 μm) as a result of the O2 plasma treatment on the IGZO thin films. The device could be switched to an ON state with a low resistance (e.g., the resistance at 2 V is ∼103 Ω for the radius of 50 μm) by applying a voltage pulse (e.g., 10 V/1 μs). The WORM device has good data-retention and reading-endurance capabilities.
[Show abstract][Hide abstract] ABSTRACT: The effect of short-duration ultraviolet (UV) exposure on the threshold voltage (Vth) of amorphous indium gallium zinc oxide thin film transistors (TFTs) and its recovery characteristics were investigated. The Vth exhibited a significant negative shift after UV exposure. The Vth instability caused by UV illumination is attributed to the positive charge trapping in the dielectric layer and/or at the channel/dielectric interface. The illuminated devices showed a slow recovery in threshold voltage without external bias. However, an instant recovery can be achieved by the application of positive gate pulses, which is due to the elimination of the positive trapped charges as a result of the presence of a large amount of field-induced electrons in the interface region.