Chun Hung Lai

Influence of embedding Cu nano-particles into a Cu/SiO2/Pt structure on its resistive switching

Cu nano-particles (Cu-NPs) were embedded into the SiO2 layer of a Cu/SiO2/Pt structure to examine their influence on resistive switching characteristics. The device showed a reversible resistive switching behavior, which was due to the formation and rupture of a Cu-conducting filament with an electrochemical reaction. The Cu-NPs enhanced the local electric field within the SiO2 layer, which caused a decrease in the forming voltage. During successive switching processes, the Cu-NP was partially dissolved, which changed its shape. Therefore, the switching voltages were not reduced. Moreover, the Cu-NPs caused a non-uniform Cu concentration within the SiO2 layer; thus, the Cu-conducting filament should be formed in a high Cu concentration region, which improves switching dispersion. The Cu-NPs within the SiO2 layer stabilize the resistive switching, resulting in a larger switching window and better endurance characteristics.

Improved Resistive Switching Dispersion of NiOx Thin Film by Cu-Doping Method

Thermally grown NiOx and Cu-doped NiOx (Cu:NiOx) thin films were fabricated as resistive layers for Cu/NiOx/Pt and Cu/Cu:NiOx/Pt devices and their resistive switching properties were investigated. The two devices had reversible resistive switching properties, nondestructive readout, and long retention. However, the Cu/NiOx/Pt device had large voltage dispersions in the resistive switching operation. This work improved the voltage dispersions of the resistive switching operation by Cu-doping in the NiOx thin film. The operating voltages of the Cu/Cu:NiOx/Pt device were also smaller than those of the Cu/NiOx/Pt device. This study suggests the conducting filament model to explain resistive switching behavior and improved resistive switching dispersions. The Cu-doping method produced more defects within the NiOx thin film, which improved voltage dispersion and decreased operation voltages.

The effects of Nd2O3 additives and Al2O3SiO2TiO2 sintering aids on the electrical resistivity of (Ba,Sr)TiO3 PTCR ceramics

Abstract The influences of Nd donors and Al 2 O 3 SiO 2 TiO 2 (AST) sintering aids on the electrical properties of (Ba,Sr)TiO 3 materials have been investigated. The room-temperature resistivity and the temperature coefficient of the anomalous resistivity rise were used to characterize the performance of the samples. From derivations based on the Heywang-Jonker barrier model, both characterizing parameters are expected to increase as a result of higher acceptor-state density at the grain boundary. The surface acceptor density, whose value was extracted from the slope in the Arrhenius plot of resistivity versus 1/( Tϵ m ), where ϵ m is the measured permittivity and T the absolute temperature, was found to decrease with the Nd content and increase with the AST dopant. A satisfactory interpretation of the observed variations in resistivity-temperature curves caused by additions of various dopants was thus obtained in the light of the resultant acceptor state density.

Conduction Behavior of V-SrZrO3 Thin Film Showing Resistive Switching

This paper examines the electrical properties of V-doped SrZrO3 sputtered films showing bistable on/off resistive switching. The temperature dependence of dc sweep I-V data in the range of 25–100°C implies the prominent role played by the off-state conduction in determining the R-switch ratio. The defects in off-state are investigated via Frenkel-Poole relation and the associated trap energy extraction. It is found that the oxygen vacancies are the possible major defects in off-state and are verified by the treatment of N2 and O2 annealing ambience hereafter. The nearly unchanged currents suggest the relatively more stable nature in on-state, which is consistent with the following findings: 1) the frequently observed I-V jiggle during on to off switching, 2) successful forming only found for sweep direction to on-state, 3) the better thermal disturbance immunity by longer retention for on-state, 4) the shorter pulse width needed to on-state switching for electric pulse induced resistance (EPIR) effect.

The Resistive Switching Characteristics in ZrO2 and Its Filamentary Conduction Behavior

This study investigated the conduction properties of sputtered ZrO2 exhibiting reversible and stable resistance change. Similar current distributions in on/off conduction and set/reset switching were observed in top electrodes with a diameter of 150, 250, and 350 µm. The size independence of current magnitude implied the presence of an uneven filamentary path over the electrode area. Increased current compliance was imposed on the turn-on process, and the observed increase in on-state current and turn-off threshold was attributed to incremental filament diameter. Variations in current conduction and resistance switching were analyzed by monitoring sweeping bias limits in both positive and negative polarities. These experimental observations were interpreted based on the aspect ratio of channels comprising conductive and oxidized filament portions, thereby elucidating the characteristics of filamentary resistive switching.

Direct current voltage sweep and alternating current impedance analysis of SrZrO3 memory device in ON and OFF states

The resistive switching (RS) effect of sputtered SrZrO3 memory cell is investigated by current-voltage (I-V) and impedance spectroscopy (IS) measurements for ON and OFF states. While the ON-state conduction in I-V exhibits ohmic relation of slightly temperature dependence, the OFF-state transport follows Frenkel-Poole mechanism and Arrhenius plot detects a single trap at 0.37 eV. An equivalent circuit model derived from the combined impedance-modulus spectra is proposed to characterize the real IS response. The extracted film capacitance and contact resistance keep constant at 25–100 °C and, by contrast, the film resistance reveals activation energy of 0.08 eV. Both I-V and IS analyses indicate the domination of the OFF-state film conduction on the observed RS behavior and thermal effect. For doped perovskites, the OFF-state electrical property is associated with the presence of film-interior oxygen vacancies.

Planar Octagon Monopole Antenna for UWB Applications

A planar octagon monopole antenna for ultrawideband(UWB) application is proposed and experimentally studied. The proposed antenna has wide impedance bandwidth from 2.8 GHz to more than 10.7 GHz with better than -10 dB return loss. The design is demonstrated assuming FR4 substrate with a relative dielectric constant of 4.4 and thickness of 1.6 mm. The size of the antenna is 40 mm×50 mm. Details of the proposed antenna design and simulation results for UWB operations are presented and discussed.

Effect of Annealing Temperature on Electrical Properties of ZnTe Layers Grown by Thermal Evaporation

The electrical properties of evaporated ZnTe films were investigated with emphasis on the effects of an annealing temperature from 600oC to 800oC by RTA technique. Crystallinity, carrier concentration, sheet resistance, and mobility are shown to be dependent on the annealing temperature. The highest carrier concentration and lowest sheet resistance are 7.9×1015 cm-3 and 9300 Ω/□ at an annealing temperature of 700oC, respectively. The mobility was found to vary from 20 to 50 cm2V-1S-1. The ZnTe thin films using thermal evaporation can find applications in solar cell or light emitting diodes

Fabrication of Ti-Doped ZnO Thin Films by Chemical Bath Deposition

Effect of thermal treatments on the structural and electrical properties of the chemical bath deposition derived Ti-doped ZnO thin films are studied. XRD results show that the annealed Ti-doped ZnO films with wurtzite structure are randomly oriented. Crystallite structure, carrier concentration, resistivity and mobility are found to be dependent on the treatment temperature. At a treatment temperature of 100°C, the Ti-doped ZnO film possesses a carrier concentration of 2.5×1020 cm-3, a resistivity of 2.8×10-3 Ω-cm, and a mobility of 12 cm2/Vs.

Preparation and Properties of Perovskite Thin Films for Resistive Nonvolatile Memory Applications

Various perovskite structure electroceramic thin films have been studied for semiconductor memory applications. The high permittivity and ferroelectric remanent polarization properties of these materials give the promise of a new generation of advanced dynamic and/or nonvolatile memory devices. The recent study indicates that perovskite oxide showing bistable resistance switching behavior is a highly promising candidate for nonvolatile semiconductor device, the so-called resistance random access memory (RRAM). RRAMs exhibit sufficiently fast switching capability and low operation voltages as compared with flash memory, and bring about the current upsurge in research. This paper summarizes the fabrication and characterization of these potential materials, and provides a broad view of the current status and future trends for perovskite oxides-based RRAMs. The associated conduction mechanisms are also discussed with specific examples from recent literature.