Nonlinear Current-voltage Behavior Research Articles

Development of MWCNTs@PDMS nanocomposites with enhanced hydrophobicity and thermo-oxidative stability

This paper presents the fabrication of hydrophobic polymer nanomaterials with improved thermal characteristics based on MWCNTs and poly(dimethylsiloxane). The samples were synthesized by physical adsorption of poly(dimethylsiloxane) onto P-MWCNTs surfaces in the amount from 5 to 20 wt%. The effect of different content of adsorbed polymer on the structure and properties of the prepared nanocomposites was studied in detail using ATR-FTIR, SEM, TEM, XRD and RS techniques. XPS results showed that with the increase of adsorbed PDMS onto the MWCNTs surfaces, the Si 2p atomic percentage increased from 1.5 to 5.0 at.%. The investigation of thermal properties using TGA/DSC techniques in air atmosphere revealed that polymer adsorption on the MWCNTs surfaces enhances the thermo-oxidative stability of the nanocomposites to a great extent. The WCA of MWCNTs@PDMS-1000(20) nanocomposite reached 138.9° while this value was 81.8° in the case of the P-MWCNTs. The electrical characterization of the examined samples demonstrated a non-linear current–voltage behaviour and the invariance of the electrical current value with the increasing polymer content in the nanocomposites. The results suggest that the obtained nanocomposites have multi-functional surfaces and are promising for integration into a silicon-based polymer matrix for the development of new materials for electronic devices.

Origins of midgap states in Te-based Ovonic threshold switch materials

The non-linear threshold-type current-voltage behavior that characterizes selector devices for three-dimensional (3D) crossbar-type nonvolatile memory devices relies upon a phenomenon known as Ovonic threshold switching (OTS). Because current practical OTS materials are based on toxic elements, such as Se and As, Te-based OTS materials are expected to offer a more environmentally friendly option. However, the electronic structure that determines the OTS behavior of Te-based OTS materials is not well understood. In this paper, the electronic structure of amorphous Si0.29Te0.71, has been explored using hard X-ray photoelectron spectroscopy (HAXPES) in conjunction with density functional theory (DFT) calculations. The HAXPES results show that the Si0.29Te0.71 amorphous network of the simulated amorphous structure is based upon Te-Te, Te-Si, and Si-Si bonding. DFT calculations revealed that Si3p and Te5p states contribute to bonding, whereas occupied non-bonding Te5p states form the top of the valence state. A projected local density of states analysis shows that the Si site forms conduction-tail states, whereas the Te site forms both conduction- and valence-tail states. Furthermore, Te-Te dimers contribute significantly to the midgap states that characterize the OTS behavior. Finally, the valence-tail state extension within the mobility gap of Si0.29Te0.71 was experimentally demonstrated.

Influence of location junction on ion transfer behavior in conical nanopores with bipolar polyelectrolyte brushes

A bipolar ion diode consists of two positively and negatively charged surfaces that show the distribution of specific ions under different applied voltages. One of the most important electrokinetic phenomena occurring in bipolar nanopores is ionic current rectification (ICR). ICR in nanopores occur when, by applying a voltage to both ends of a nanochannel, the system exhibits non-linear current-voltage behavior or diode-like behavior, in other words, ionic current occurs in a specific direction. In modeling bipolar soft nanochannels, it is usually assumed that the properties of the soft layer and the electrolyte are the same, which is not true for soft layers with high charge densities. In the present work, the effect of sharp and wide aperture radius of nanochannels on ionic current rectification in bipolar nanochannels by coating polyelectrolytic layer with conical geometry in different values of soft layer lengths was studied. For this purpose, by adopting a numerical calculation approach Finite element, Poisson-Nernst-Planck and Navier-Stokes equations were solved for steady-state by considering different permeability values, diffusion coefficient, and dynamic viscosity for polyelectrolyte and electrolyte In general, it can be concluded that the bipolar conical nanopore has a higher ICR than the cylinder geometry with the same average radius If the junction is at the tip of the nanopore. For example, when the mole concentration was equal to c0=50mM, the ICR for the bipolar conical nanopore with a soft layer with an optimal junction at the tip of the nanopore reached 45, while in the bipolar cylindrical nanopore at best (the optimal junction in the middle of the nanopore) reached 25.

Influence of morphology and chemical surface composition on electrical conductivity of SiC microspheres

The present work provides a comparative study on the electrical properties (i.e. current-voltage characteristics) of spherically shaped SiC micro-sized particles that have been prepared by a thermal sintering process. As a typical field grading material, SiC exhibits a non-linear current-voltage behavior, which is exploited to reduce electrical stresses within composite materials. This is of particular interest in high-voltage applications to avoid material breakdown and to enhance the electrical components’ lifetime. As the current-voltage characteristics are affected by transport mechanisms at the grain contact, the electrical performance can be controlled by changing the chemical surface composition and morphology of the SiC particles. Advancing from irregular SiC flakes, the current work focuses on the electrical properties of SiC microspheres that have been tailored by applying selected thermal annealing steps and by chemical surface functionalization with organosilanes. The chemical surface composition of the microspheres prior to and after the modification step was studied by XPS and EDX, whilst SEM was employed to visualize the morphology of the particles’ surface and cross-section. In addition, the current-voltage characteristics were determined as a function of the particles’ morphology and chemical surface composition. The results clearly show that sintering aids, annealing temperature, morphology of particles and surface modification strongly govern the non-linear current-voltage behavior of SiC microspheres.

Correlation hard gap in antidot graphene

We have measured low-temperature variation of resistance and nonlinear current-voltage behavior in antidot graphene in the vicinity of the charge neutrality point. The data are found to be consistent with the manifestations of a variable-range hopping electronic density of states (DOS) with a small hard gap of $\ensuremath{\sim}1$ meV around the Fermi level, in conjunction with a parallel tunneling conduction channel that exists at the center of the gap. The hard gap is confirmed by the appearance of a low-conductive plateau at low-bias electric field, whereas the parallel tunneling conduction channel, with temperature-independent conductance, is manifest through the nonlinear electric field variation. Unified good agreement between the temperature and electric field dependencies of conductance, for both channels, is obtained with the predictions of a proposed DOS model. An increase in the gap size with applied magnetic field is observed.

Varistor performance of a SnO2-based system doped with low content of SrTiO3

The search and design of new SnO2-ceramics with non-linear current-voltage behavior is quite an important task due to the possibility of their practical application as varistors, devices for the protection of electrical circuits against voltage surges. This work reports the doping impact of the low content of SrTiO3 (0, 0.05, 0.1, 0.2, and 0.4 mol%) on the microstructure and non-ohmic properties of the SnO2-Co3O4-Cr2O3-Nb2O5 system which is frequently used in varistor design. It is found that the SrTiO3-addition results in the increase of activation energy of electrical conduction and the decrease of the leakage current in obtained materials compared with undoped ceramics. The reported materials with SrTiO3-addition possess a smaller average grain size, higher porosity, and their density is lower than that of unmodified SnO2-Co3O4-Cr2O3-Nb2O5 ceramics. The highest non-linear coefficient (α = 17.24) is observed for material with 0.05 mol% SrTiO3 while for undoped ceramics it reaches only 2.68. Energy dispersive spectroscopy (EDS) revealed agglomeration of SrTiO3 which was observed in materials with 0.1–0.4 mol% of SrTiO3. The obtained results are discussed in terms of the known barrier model for varistors based on the information from dc and ac electrical measurements, scanning electron microscopy, X-ray diffraction patterns, and EDS-data.

Tailoring Mixed Ionic/Electronic Conductivity with Grain Boundaries: (La,Sr)(Ga,Mg)O3-X Case Study

Modified point defect chemistry at grain boundaries can be leveraged to turn a predominantly ionic conductor or a predominantly electronic conductor into a mixed conductor, by changing the grain boundary density [1,2]. There are reports indicating that introducing some electronic conductivity into the ionically conducting electrolyte of a solid oxide electrolysis cell could help to alleviate the problem of delamination at or near the electrolyte-oxygen electrode interface [3]. For this reason, we revisited the possible role of grain boundaries in tailoring mixed conduction in the fast oxide-ion conductor La0.9Sr0.1Ga0.9Mg0.1O3-x (LSGM). LSGM is a candidate electrolyte as it exhibits good thermo-chemo-mechanical compatibility with adjacent perovskite-structured electrodes. Previous work has indicated enhanced p-type electronic transference numbers at the grain boundaries of LSGM compared to the bulk, attributed to space charge effects on the basis of the observed non-linear current-voltage behavior of the grain boundaries at sufficiently high voltages [4]. However, the interplay of processing route, grain size, and dopant concentration in tailoring the extent of this effect had not been investigated. In this work [5] we fabricated dense LSGM pellets with non-dilute doping levels typical of electrolytes, with a range of average grain sizes from ~100 nm to ~6 μm, using field- and pressure- assisted sintering with various post-annealing steps as well as conventional sintering. The electrical transport behavior of grain cores and grain boundaries (GBs) was subsequently studied by impedance spectroscopy as a function of temperature, oxygen partial pressure, and dc bias. The brick layer model and the nano-grain composite model were applied to determine specific GB conductivities and electrical widths from the impedance data. Structure and composition were evaluated by X-ray diffraction, thermogravimetric analysis, transmission electron microscopy, scanning transmission microscopy, and energy dispersive X-ray spectroscopy. With increasing sintering temperature (and grain size), the following trends were observed: increasing pO2-dependence of the GB conductivity indicating higher local electronic transference numbers, higher apparent GB potentials, lower specific GB conductivity, lower pre-exponential factor for specific GB conductivity, increasing electrical GB widths, and greater dc bias dependence of GB conductivity. On the other hand, as expected, grain core electrical behavior was independent of processing route, grain size, and pO2. The results are suggestive of an increasing grain boundary space charge effect with increasing sintering temperature (and grain size), as has been observed for other ionic conductors where grain size and sintering temperature/time were coupled. Additionally, in all cases, the GB electronic transference numbers in these highly doped samples appeared to be smaller than those reported for lightly doped LSGM. Microscopy and EDS revealed that while grain boundaries appeared to be well-crystalline and “clean” in all samples, there was increasing microstructural and compositional homogeneity in samples that were sintered at progressively higher temperatures. The significance of the nanoscale compositional and microstructural fluctuations in the small-grained samples is not yet clear, as the apparent phase purity and density of all the samples was very similar macroscopically. Nonetheless, it seems possible that such inhomogeneity (pores and Sr- rich and Mg-rich areas not limited to GB regions) might limit the space charge contribution at GBs, and that some of the pores could have arisen from residual volatile impurities trapped during the pressure-assisted sintering. Overall, the results confirm that 1) grain boundaries can be sites of mixed conduction in an otherwise predominantly ionically conducting electrolyte and 2) processing route (thermal, pressure, and electrical history) is an important variable for tailoring the magnitude of the local ionic and electronic conductivities and transference numbers. [1] Y.M. Chiang et al., Applied Physics Letters, 69(2), 185-187 (1996).[2] A.M. Saranya et al., Advanced Energy Materials, 5(11), 1500377 (2015). [3] A.V. Virkar et al., International Journal of Hydrogen Energy, 40, 5561-5577 (2015). [4] C.T. Chen et al., Physical chemistry chemical physics, 14, 9047-9049 (2012). [5] T. Chen et al., “Modifying grain boundary ionic/electronic transport in nano-Sr- and Mg- doped LaGaO3-δ by sintering variations,” (under review)

Three dimensional phase diagram of superfluidity controlled voltage nonlinearity in superconductors

We have studied current-voltage (IV) characteristics of (i) underdoped and (ii) electron doped high temperature superconductors (HTS) around the superconducting phase transition. Over a wide range of temperature below the critical temperature a nonlinear current-voltage behavior has been observed both in the undoped and electron doped sample. Following the dependence of the pinning potential on the current sweeping rates (CSR) several moderate values of CSR have been used for the measurement of IV at a constant temperature T. An exponent related to the superfluid density varies with CSR mostly at the range of the lower temperature. Variation of the nonlinear voltage with respect to the sweeping rate is found to be a function of both the applied current and temperature. On the basis of the variation we propose that the three dimensional phase diagram identifies the potential regions of nonlinearity. A collinear arrangement of maxima loops by the driving current is possible in a narrrow range of T.

The influence of yttrium-ions on the optical and electrical behavior of PVA polymeric films

The polyvinyl alcohol (PVA) films doped with various wt% of yttrium nitrate salt were synthesized by standard solution casting technique in order to examine the functional electrical and optical properties. The degree of the crystalline structure that evaluated in the films were investigated by x-ray diffraction and Fourier transform infrared spectroscopy measurements. In addition, the surface images have been obtained via scanning electron microscopy (SEM). The optical parameters have been calculated from UV–visible-NIR transmittance spectroscopy. Also, the dielectric constant measurement and the DC resistance that are arisen in the PVA films with different wt% of Y3+-ions have been done. All the samples show semi-crystalline phases. The average size, of the cluster Y3+-ions in the SEM images, increase to 1.63 μm for PVA/37 wt% Y3+-sample. Therefore, the optical absorption of this sample is higher than the others. The value of the energy gap decrease from 5.11 eV to 4.47 eV for PVA/0.037 wt% Y3+ and PVA/37 wt% Y3+-samples, respectively. The nonlinear current—voltage behavior, at high applied voltage, of the polymeric films, is observed with different values of slope, which is a characteristic of the varistor materials. So, these films could be used in different applications like optoelectronic and varistor devices.

Effect of the AlN interlayer on electroluminescent performance of n-SnO2/p-GaN heterojunction light-emitting diodes

Light emitting diodes (LEDs) based on n-SnO2/p-GaN heterojunction were fabricated by pulsed laser deposition (PLD). The effects of post-annealing treatment and interfacial layers on electroluminescence (EL) of n-SnO2/p-GaN were investigated. After annealing in vacuum, all the LED devices with different interfacial layers exhibit a nonlinear current-voltage behavior. The SnO2/p-GaN light emitting diodes exhibit two emission peaks, a violet peak (410 nm) and the broad yellow-orange emission band (600–700 nm), whereas only the yellow-orange EL spectra could be found in the SnO2/AlN/p-GaN. Using the band diagram, the carrier blocking process by different interfacial layer and the electroluminescence mechanisms of heterojunction LEDs were discussed in detail.

Tuning the nonlinear current-voltage behavior of CaCu3Ti4O12 ceramics by spark plasma sintering

CaCu3Ti4O12 ceramics have been prepared by the spark plasma sintering method. Our results indicate that facile fabrication process control can lead to an obvious microstructure change, and thus modulate the nonlinear current-voltage properties such as the breakdown electric field Eb (0.33–9.28 kV/cm) and nonlinear coefficient α (2.4–21.5). The SPS ceramics sintered at 900 °C for 5 min possess the largest Eb and α values, which are much higher than those of previous pure CaCu3Ti4O12 ceramics without dopants. It is suggested that the synergistic effects of enhanced barrier height, large activation energy at grain boundaries, and the evolution of microstructure lead to the superior J-E performance in present samples. These results reveal that the CaCu3Ti4O12 material has a promising prospect in the application as a varistor.

Nonlinear current–voltage behavior in PZT thin films

In this paper, Pb(Zr0.52Ti0.48)O3 (PZT) thin films were prepared by sol–gel synthesis and characterized by X-ray diffraction, field emission scanning electron microscopy and current–voltage measurements. Here, we demonstrate that in addition to the outstanding ferroelectric and dielectric properties, the PZT films also have remarkably nonlinear current–voltage characteristics. Considering the contact of semi-conductive grains in the PZT films, a double Schottky barrier (DSB) model may be responsible for such phenomena. The test results show that with the decrease of annealing temperature and the increase of the film thickness, the threshold voltages (V th) increase obviously. The maximum V th value of 60.95 V and the minimum value of 6.9 V in our experiments were obtained from the five-layered samples annealed at 600 °C and the two-layered samples annealed at 700 °C, respectively. As a result, PZT thin film may lead to efficient switching and sensing devices.

Nonlinear electrical properties and giant dielectric response in Na1/3Ca1/3Y1/3Cu3Ti4O12 ceramic

A new isostructural CaCu3Ti4O12–type perovskite, Na1/3Ca1/3Y1/3Cu3Ti4O12, was successfully synthesized using a solid state reaction method. In this material, Ca–sites in the CaCu3Ti4O12 structure were occupied by Na+, Ca2+, and Y3+ ions, each at a level of ∼33.3 at.%. The dielectric and non –Ohmic properties were investigated. The mean grain sizes of the Na1/3Ca1/3Y1/3Cu3Ti4O12 ceramics sintered at 1100–1110°C for 10–15h were of about ≈15μm. All of the sintered ceramics exhibited high dielectric permittivities (ε′) and low loss tangents (tanδ). By optimizing sintering conditions, a high ε′≈1.2×104 and low tanδ≈0.04 were achieved. Na1/3Ca1/3Y1/3Cu3Ti4O12 ceramics can exhibit nonlinear current-voltage behavior. The existence of Cu+, Cu3+, and Ti3+ ions was confirmed using an X–ray Absorption Near Edge Structure (XANES) and X–ray photoelectron spectroscopic analyses. The n–type semiconductivity inside the grains was primarily caused by the presence of Ti3+ ions, while the existence of Cu+ and Cu3+ may also have an effect on conduction inside the grains. Using impedance and admittance spectroscopy analyses under different conditions (i.e., varying frequency, temperature and DC bias), the giant dielectric response and nonlinear electrical properties could be well explained based on the internal barrier layer capacitor model.

Resistive switching characteristics of Al/Si3N4/p-Si MIS-based resistive switching memory devices

In this study, we proposed and demonstrated a self-rectifying property of silicon nitride (Si3N4)-based resistive random access memory device by employing p-type silicon (p-Si) as bottom electrode. The RRAM devices consisted of Al/Si3N4/p-Si are fabricated by a low presure chemical vapor deposition and exhibited an intrinsic diode property with non-linear current-voltage (I-V) behavior. In addition, compared to conventional metal/insulator/metal (MIM) structure of Al/Si3N4/Ti RRAM cells, operating current in whole bias regions for proposed metal/insulator/semiconductor (MIS) cells has been dramatically lowered because introduced p-Si bottom electrode efficiently suppresses the current in both low and high resistive states. As a result, the results mean that by employing p-Si as bottom electrode the Si3N4-based RRAM cells can be applied to selector-free RRAM cells.

Influence of thermal treatment on the nonlinear current–voltage behavior and restoration hysteresis effect of CaCu3Ti4O12 thin films

CaCu3Ti4O12 (CCTO) thin films were prepared through sol–gel method. The influences of sintering temperature and rapid thermal process (RTP) in oxygen-rich atmospheres on its nonlinear current–voltage (I–V) behavior and restoration hysteresis effect were investigated. The phase identification of the films was characterized by using X-ray diffractometer, the results show that in the as-sintered films which were treated through RTP in oxygen atmospheres, a weak CuO and TiO2 diffraction peaks could be detected. Field emission scanning electron microscope was performed to observe the microstructure of the films. A semiconductor parameter analyzer was used to determine the I–V behaviors. The results show that with sintering temperature increase, the threshold voltages of CCTO thin films decreased significantly. After the films were treated through RTP in oxygen-rich atmosphere, the height of Schottky barriers would increase obviously, resulting in the increase of threshold voltages of CCTO films, and the longer the time of RTP, the higher the Schottky barrier. The influence of RTP on restoration hysteresis effect of CCTO films was reported for the first time, and RTP could decrease the initial current and increase the resistivity. The double Schottky barrier model and the tunnel junction model were used to explain these phenomena, and the conduction mechanism in CCTO film was discussed to describe the restoration hysteresis effect.

Nonlinear current–voltage behavior in La-doped CaCu3Ti4O12 thin films derived from sol–gel method

The effect of La3+ doping at Ca2+ sites in CaCu3Ti4O12 (CCTO) thin film was investigated. Samples with compositions of Ca(1−3x/2)LaxCu3Ti4O12 (x = 0, 0.05, 0.1, 0.15 and 0.2) were synthesized by sol–gel method. Remarkable non-Ohmic behaviors in all the samples were presented through a semiconductor parameter analyzer. Results showed that with the increase of dopant’s amount, the threshold voltage of CCTO thin films firstly increased and then decreased and the nonlinear coefficient decreases, good thermal and electric stability was found in all samples. XRD results confirmed the single phase formation of all the samples with similar cubic structure of CCTO and characterization with SEM showed a completely opposite trends between the grain size and the threshold voltage. The double Schottky barrier model is used to explain the nonlinearity of CCTO thin films and the relationship between grain size and threshold voltage in the thin films. The presence of Schottky barrier at the grain boundary is confirmed by a linear relationship between ln(J) and E1/2. A possible way is put forward to control the non-Ohmic properties of CCTO thin films based on this research.

(Invited) Tunnel-Barrier Rectifiers for Optical Nantennas

Thin film metal-insulator-metal (MIM) rectifying devices using double, triple or quadruple insulator layers are currently the focus of attention for the development of next-generation optical nantennas. The interest is driven by their nanoscale footprint, room temperature operation, zero bias voltage requirement, and ease of integration with Complementary Metal Oxide Semiconductor technology. Highly asymmetric and nonlinear current-voltage (IV) behaviour at low applied voltages is critical for these applications. The operation of a MIM device is based on quantum mechanical tunnelling through a thin insulating film positioned between two metal electrodes. Hence, the operation speed of MIM devices depends on the tunneling transmission time, typically in the range of femto seconds or less, and theoretically can reach to a few 100 THz or even into the range of the solar spectrum. Figures of merit for MIM devices include the asymmetry, nonlinearity, and turn-on voltage. Rectification performance in MIM devices is generally limited by the work function difference that can be achieved between the metal electrodes, the barrier heights at either interface, and the mechanism of charge transport through the insulator. The choice of insulator is crucial. Wide band gap insulators provide high turn-on voltage. Narrow band gap insulators, such as Ta2O5 or Nb2O5, are thus attractive since small metal/insulator barrier heights allow for low turn-on voltage. For stable, temperature insensitive, high-speed operation, conduction through the insulator should be dominated by tunneling. In this paper, we present comprehensive experimental and theoretical work on tunnel-barrier rectifiers comprising double (Nb2O5/Al2O3) and triple (Ta2O5/Nb2O5/Al2O3) insulator configurations engineered to enhance low voltage nonlinearity. There are two mechanisms that allow metal-insulator-insulator-metal rectifiers to have a high nonlinearity while keeping the resistance low: (i) resonant tunnelling, and (ii) so-called step tunnelling. Both will be discussed in the paper. A modified multi-layer Tsu-Esaki method has been used for IV calculations from the transmission coefficient by the transmission matrix method. The theoretical work indicates that the onset of resonant tunneling in MIIM and MIIIM rectifiers can be adjusted to close to zero volts by appropriate choice of work function difference of the metal contacts, the thickness of insulator layers, and the depth of quantum well. The double and triple insulator rectifiers were fabricated using atomic layer deposition and rf magnetron sputtering, while the metal contacts including Al and Ag were defined by photolithography or shadow mask and deposited by thermal evaporation. The thickness, band gap, roughness, band offsets, work functions and electron affinities have been extracted from variable angle spectroscopic ellipsometry, atomic force microscopy, x-ray and inverse photoelectron spectroscopy on fabricated devices to ascertain quality of the interfaces and measure barriers. The key rectifier properties, asymmetry, non-linearity and responsivity have been assessed from current voltage measurements performed in the range 293-370 K. A superior low voltage asymmetry (116 at 0.6 V) and responsivity (17 A/W at 0.7 V) for MIIIM rectifiers has been observed in advance of state-of-the-art experimental values. The results demonstrate enhanced rectification by atomically multilayering tunnel barriers in cascaded and non-cascaded MIIIM arrangements, for inclusion in optical nantennas. Acknowledgement. The work has been funded by EPSRC, UK, under project EP/K018930/1.

The DC Bias Voltage Effect and Non-Linear Dielectric Properties of Titanate Nanotubes.

This work reports the nonlinear current-voltage behavior and the effects of dc bias voltage on the dielectric and electrical properties of titanate nanotubes (TNTs) prepared by hydrothermal method at 130 degrees C for 24 h. The TNTs sample exhibited high dielectric constant of > 10(4) at 100 Hz at room temperature with slight dependence on frequency in the range of 10(2)-10(4) Hz. The external resistance forms at the interface between electrode and surface sample. It was found that the dielectric constant of the sample decreased with increasing dc bias voltage due to the decrease in the electrode capacitance. For the study of the non-linear dielectric properties, the breakdown electric field (E(b)) value of the prepared TNTs sample obtained with J = 1 mA cm(-1) was found to be 149 V cm(-1). The E(b) value of the sample was significantly decreased with increasing temperature. The non-ohmic behavior tends to become linear ohmic in characteristic as the temperature increased.

Giant dielectric, low loss tangent and non-ohmics properties of CaCu3Ti4.7O12 ceramics prepared by polymer pyrolysis method

In this work, CaCu3Ti4.7O12 (CCT4.7O) powder was prepared by polymer pyrolysis method. The influence of phase composition and microstructure were characterized using X ray diffraction (XRD) and scanning electron microscopy (SEM). The results show that the TiO2 secondary phase has a remarkable on the microstructure, dielectric loss tangent (tan and dielectric constant () of CCT4.7O ceramics, respectively. Interestingly, low loss tangent of ~0.03 and giant dielectric constant of 31,908 with temperature coefficients less than ±15% in the temperature range of −50–90 oC are observed in a ceramic sintered at 1060 oC for 10h (CCT4.7O-2). Both of ceramics sintered at 1060 oC for 6h (CCT4.7O-1) and 10 h (CCT4.7O-2) display a non linear current voltage with the non-linear coefficient () and breakdown field (Eb) values of 6.4, 5.6 and 1554, 1020, respectively. The dielectric constant, electrical response of grain boundaries, and related nonlinear currentvoltage behavior are found to be associated with the microstructure of CCT4.7O ceramics.

Multistate resistive switching in silver nanoparticle films

Resistive switching devices have garnered significant consideration for their potential use in nanoelectronics and non-volatile memory applications. Here we investigate the nonlinear current–voltage behavior and resistive switching properties of composite nanoparticle films comprising a large collective of metal–insulator–metal junctions. Silver nanoparticles prepared via the polyol process and coated with an insulating polymer layer of tetraethylene glycol were deposited onto silicon oxide substrates. Activation required a forming step achieved through application of a bias voltage. Once activated, the nanoparticle films exhibited controllable resistive switching between multiple discrete low resistance states that depended on operational parameters including the applied bias voltage, temperature and sweep frequency. The films’ resistance switching behavior is shown here to be the result of nanofilament formation due to formative electromigration effects. Because of their tunable and distinct resistance states, scalability and ease of fabrication, nanoparticle films have a potential place in memory technology as resistive random access memory cells.