Current Field Characteristics Research Articles

Effects of Varying Annealing Ambient towards Performance of Ternary GaxCeyOz Passivation Layers for Metal-Oxide-Semiconductor Capacitor

In this work, different annealing ambient (nitrogen-oxygen-nitrogen (N2-O2-N2), forming gas-oxygen-forming gas (FG-O2-FG), and argon-oxygen-argon (Ar-O2-Ar)) were explored to investigate the feasibility of employing the annealed ternary GaxCeyOz passivation layer (PL) for development of Si-based metal-oxide-semiconductor (MOS) capacitors. The impact of nitrogen and/or hydrogen in hindering the growth of silicon dioxide (SiO2) interfacial layer (IL) was quantitatively evaluated. The combination of effects brought by nitrogen attached to oxygen vacancies, nitrogen-silicon bonding, and nitrogen accumulation at the GaxCeyOz/Si interface effectively minimized the formation of SiO2 IL. Consequently, among all the samples, the GaxCeyOz PL annealed in N2-O2-N2 ambient exhibited superior MOS characteristics in terms of low effective oxide charge, slow trap density, interface trap density, and interface state density, which have translated into good leakage current density-electric field characteristics.

Growth of gallium cerium oxide passivation layer on 4H-Silicon carbide substrate and its metal-oxide-semiconductor characteristics

Gallium cerium oxide (GaxCeyOz) passivation layer was successfully grown on 4H-silicon carbide (SiC) through postdeposition annealing at 800 °C in nitrogen-oxygen-nitrogen (N2–O2–N2) ambient. The gracing incident X-ray diffraction and ultraviolet–visible spectrophotometer measurements have confirmed the successful incorporation of Ga3+ cation into the CeO2 lattice to form the ternary GaxCeyOz passivation layer. In addition, the thicknesses of GaxCeyOz passivation layer and silicon dioxide (SiO2) interfacial layer (IL) were determined using field-emission scanning electron microscopy and X-ray reflectivity characterizations. A high dielectric constant (k) value of 24.11 was attained for the investigated Al/GaxCeyOz/4H–SiC/Al metal-oxide-semiconductor (MOS) structure attributable to the nitrogen ions accumulating at the interface that have retarded the growth of SiO2 IL. Besides, the effective oxide charge, slow trap density, interface trap density, interface state density, as well as leakage current density-electric field characteristic of the investigated GaxCeyOz passivation layer on 4H–SiC substrate was presented in this work.

Electrical Conduction and Space Charge in Gamma-Irradiated XLPE

It is well known that ionizing radiation impact dielectric and mechanical properties of polymers, as a result of chain scission, crosslinking, and oxidation steps. The electrical conductivity is generally substantially increased after irradiation. We analyze such effects in XLPE after gamma-irradiation. Current measurements reveal a substantial increase in conductivity after irradiation at doses up to 200 kGy. Current-field characteristics change after irradiation and appear indicative of an ionic-type conduction. Space charge measurements confirm the mechanism with obvious heterocharge build-up after irradiation.

A review of the modeling approaches of the lightning M-component with special attention to their current and electric field characteristics

A review of the modeling approaches of the lightning M-component with special attention to their current and electric field characteristics

Electrical and microstructural evaluation of ZnO varistor ceramics with different CaSiO3 contents

In the present study, the impact of CaSiO3 addition on microstructure and electrical characteristics of a ZnO-based varistor system was investigated. The ceramic materials were prepared by solid-state reaction route by varying the CaSiO3 concentrations (0, 3, 6, 9, 12, and 15 wt%) and sintered at 1300 °C. Characterization of the pelletized samples was carried out by density measurement, scanning electron microscopy, energy dispersive X-ray, X-ray diffraction, and current density-electric field characteristics measurement. The growth of ZnO grain was restrained with the introduction of CaSiO3; the average grain size decreases from 18.09 to 10.85 μm, whereas their relative density increases up to 99.79%. Structural results indicated the existence of the CaSiO3-rich phase without any other secondary phase formation. It is also revealed that different CaSiO3 contents significantly affect the electrical properties, prominently in the sample with 12 wt% CaSiO3 addition. The maximal value of the nonlinear coefficient, breakdown voltage, and barrier height acquired in this work were 4.41, 0.80 V/mm, and 0.691 eV, respectively, along with a sharp decline in leakage current density to 373.93 μA/cm2. Further increase in CaSiO3 content (15 wt%) eventually caused a deterioration in varistor behavior.

A cost-effective technology to improve power performance of nanoribbons GaN HEMTs

A cost-effective fabrication process is developed to improve the power performance of AlGaN/GaN High Electron Mobility Transistors (HEMTs). This process uses nitrogen ion (N+) implantation to form multiple parallel nanoribbons on AlGaN/GaN heterostructures, with a thin buffer layer (AlGaN/GaN NR-HEMTs). The stopping and range of ions in matter simulations of the N+ implantation combined with measured current-field characteristics reveal a good electrical isolation beneath the two-dimensional electron gas, resulting in substantial increase in the breakdown field of the NR-HEMTs, when compared to conventional AlGaN/GaN HEMTs. The fabricated AlGaN/GaN NR-HEMTs performed (i) an ON/OFF current ratio more than two orders of magnitude larger and (ii) a buffer leakage current more than one order of magnitude weaker than that of the conventional AlGaN/GaN HEMTs. The on-resistance, RON, and series resistance, RS, of AlGaN/GaN NR-HEMTs are both reduced by one order of magnitude when compared to those of the conventional AlGaN/GaN HEMTs. These have boosted the drive current density by up to 435%. Furthermore, we have found that the architecture of the AlGaN/GaN NR-HEMTs reduces the destructive impact of electron traps in the device. An optimized AlGaN/GaN NR-HEMT exhibited a better electrostatic integrity, a subthreshold slope of ∼210 mV/dec instead of 730 mV/dec for a conventional GaN HEMT. A higher linearity in the transconductance, gm, of NR-HEMTs is observed, twice of that of a conventional GaN HEMT. These results demonstrate the great interest of developed process technology of NR-HEMTs for high-power switching applications.

Dynamical ordering in a two-dimensional electron crystal confined in a narrow channel geometry

We present both time-averaged and time-resolved transport measurements of a two-dimensional electron (Wigner) crystal on the surface of superfluid helium confined in a narrow microchannel. We find that the field-current characteristics of the driven crystal obtained by the time-averaged measurements exhibit oscillations and negative differential conductivity. This unusual transport behavior was observed previously by Glasson et al. [Phys. Rev. Lett. 87, 176802 (2001)] and was attributed to a nonequilibrium transition of the electron system to a novel dynamically ordered phase of current filaments aligned along the channels. Contrarily to this explanation, our time-resolved transport measurements reveal that oscillating field-current characteristics appear due to dynamical decoupling (slipping) and recoupling (sticking) of the uniform electron crystal to the liquid helium substrate. Our result demonstrates that this unusual non-linear transport effect is intrinsic, does not depend on the device geometry, and is associated with the dynamical interaction of Wigner crystal with the surface excitations of the liquid substrate.

Electrical properties of Na0.5Bi0.5TiO3 thin films deposited on sitall substrates

We report some special features of Na0.5Bi0.5TiO3 (NBT) thin films growth process, as well as structural and electrical properties of these films. The films were grown on Pt/sitall substrates by high-frequency (13.56 MHz) magnetron deposition method. To crystallize the films the NBT/Pt/sitall structure was annealed at a temperature around 500 °C ÷ 700 °C in air. Results of X-ray diffraction showed that annealing at 700 °C led to the crystallization of the NBT films in the perovskite phase with minor inclusions of the pyrochlore phase. Temperature dependences of dielectric hysteresis loops (P-E) and current density-electrical field (J-E) characteristics were investigated. A tendency of narrowing of the hysteresis loops with an increase of the temperature to 180 °C was detected, which can be probably associated with the features of the diffuse rhombohedral/tetragonal phase transition. The remanent polarization (Pr) and the coercive field (Ec) values measured at room temperature were 9 μC/cm2 and 40 kV/cm, respectively. It was found that with an increase of the temperature the leakage currents increased in the entire investigated range of applied electrical fields. Charge transfer mechanisms responsible for the leakage currents in NBT thin films are discussed.

Preparation features and electrical properties of Na0.5Bi0.5TiO3 thin films

Some special features of Na0.5Bi0.5TiO3 (NBT) thin films preparation process and electrical properties of the films are presented. The NBT films were grown on both Pt/sitall and Pt/TiO2/SiO2/Si substrates by ex-situ method with high-frequency (13.56 MHz) magnetron deposition. Thermal treatment of the films was carried out in the temperature range 550°С – 700°С in air. Obtained X-ray diffraction data show that annealing at 700°C promotes crystallization of NBT films in ferroelectric perovskite phase with minor inclusions of pyrochlore phase. Dielectric hysteresis (P-E) loops in electric field of 90 kV/cm (50 Hz) and the current density-electric field (J-E) characteristics of the films are investigated. It is found that densities of leakage currents in weak fields depend on the film substrate and are significantly lower for the films deposited on the Pt/sitall structure (~6.9 10-10 A/cm2) in comparison with the films deposited on the Pt/TiO2/SiO2/Si structure (~10-6 A/cm2). The main mechanisms of leakage currents in thin NBT ferroelectric films and the role of structural defects in charge transfer process are discussed.

Dielectric response of ZrO2–CeO2 nanocrystalline solid solution above room temperature

Here we report the dielectric response of partially stabilized zirconia above room temperature. The conductivity increases with rise in temperature and frequency, obeying a power law type nature. The frequency exponent study shows that the Correlated Barrier Hopping model governs the conductivity process. The value of dielectric permittivity increases with increase in milling hour. It is observed that both free charge and space charge conductivities increase as the temperature increases. The complex dielectric permittivity is found to be increased with increase in temperature and decrease with frequency. Complex impedance study shows the grain boundary resistance is higher than the grain resistance. The current density-electric field characteristics show that the Poole Frenkel Emission model is the best suited model for the prepared samples and the trap height varies non-linearly with temperature.

Microstructure and Electrical Properties of Low-Voltage Barium Titanate Doped Zinc Oxide Varistor Ceramics

In the present, varistor ceramics through the combination of zinc oxide (ZnO) with a perovskite material have become widespread because of their unique properties for a wide range of applications in electronic protection devices. Low-voltage zinc oxide (ZnO) varistors with fast response and highly nonlinear electrical properties for overvoltage protection in an integrated circuit are increasingly significant in the application of low-voltage electronics. The present study highlights the interaction between barium titanate (BaTiO3) and ZnO varistors through the employment of solid-state reaction method in the production of low-voltage varistors. The effects of BaTiO3 on the microstructure of ZnO varistors were analyzed through scanning electron microscopy (SEM), energy dispersive X-ray analysis spectroscopy (EDS) and X-ray diffraction (XRD). The EDS analysis and XRD measurements suggest the presence of ZnO and BaTiO3 phases. The electrical properties of BaTiO3-doped ZnO varistors were examined based on the current density-electric field (J-E) characteristics measurement. The varistor properties showed the nonlinear coefficient (α) from 1.8 to 4.8 with the barrier height (φB) ranged from 0.70 to 0.88 eV. The used of BaTiO3 additive in ZnO varistors produced varistor voltages of 4.7 to 14.1 V/mm with the voltage per grain boundary (Vgb) was measured in the ranges 0.03 to 0.05 V. The lowest leakage current density was 348 μA/cm2, obtained at the samples containing 12 wt.% BaTiO3 with high barrier height. The reduction in barrier height with increasing BaTiO3 content was associated with the excessive amount of BaTiO3 phase, hence cause the deterioration of active grain boundary due to the variation of oxygen (O) vacancies in the grain boundary.

Significantly improved giant dielectric response in giant dielectric response in CaCu2.95Ni0.05Ti4-xGexO12 (x = 0.05, 0.10) ceramics

The dielectric properties and electrical responses of an undoped CaCu3Ti4O12 ceramic and isovalent codoped CaCu2.95Ni0.05Ti4-xGexO12 (x = 0.05 and 0.10) ceramics were investigated. Significant increases in the grain size can be observed in all the CaCu2.95Ni0.05Ti4-xGexO12 ceramics. The CaCu2.95Ni0.05Ti4-xGexO12 ceramics were shown to exhibit giant dielectric properties, high dielectric permittivities ∼4.83–4.96 × 104, and very low tanδ values ∼0.029–0.030. Additionally, the ceramics all demonstrated nonlinear current density-electric field (J-E) characteristics. The significantly improved dielectric properties of the (Ni2+, Ge4+)-codoped CaCu3Ti4O12 ceramics are closely associated with the enhanced grain boundary response. Clearly, the giant dielectric properties of the CaCu3Ti4O12 and CaCu2.95Ni0.05Ti4-xGexO12 ceramics could be well described by an internal barrier layer capacitor (IBLC) mechanism, which was confirmed by the results of the impedance spectroscopy and applied DC bias analysis. The important roles of the Ni2+ and Ge4+ isovalent dopants are discussed.

Nonlinear electrical properties and dielectric properties of ZnO ceramics doped with K2CO3

ZnO ceramics with different amounts of K2CO3 from 0.0 to 1.0 mol% are prepared by traditional solid-state sintering technique. The K2CO3-doping effects on the microstructure, nonlinear electrical properties and dielectric properties of ZnO ceramics are investigated. The grain size of ZnO ceramics increases from 0.9 to 1.5 μm with increasing K2CO3 content. The leakage current density versus electric field characteristics indicate that ZnO ceramic samples exhibit similar nonlinear electrical properties. The switching field and nonlinear coefficient decrease in the range of 246.2 to 1.3 V/mm and 5.3 to 2.4 with the increase of K2CO3 content. The varistor voltage decreases from 344.9 to 2.0 V/mm, while the leakage current increases from 323.0 to 646.1 μA. Meanwhile, as K2CO3 content increases, the dielectric constant and dielectric loss of ZnO ceramics are improved in the frequency range from 102 to 106 Hz at room temperature.

Mechanism of stress induced leakage current in Si3N4

In this paper, the experimental current density versus electric field characteristics of Si3N4 before and after the electrical field-induced stress were measured. It is shown that, the Frenkel model of Coulomb trap ionization, Hill-Adachi model of overlapping Coulomb traps, Makram-Ebeid and Lannoo multiphonon isolated trap ionization model do not describe the charge transport of Si3N4 before and after the electrical field-induced stress. The Nasyrov-Gritsenko model of phonon assisted tunneling between traps quantitatively describes the hole transport mechanism in Si3N4 before and after the induced stress at traps energies Wt = 1.6 eV and Wopt = 3.2 eV. The current leakage at different induced stresses in Si3N4 is explained by the increase of trap concentration via the creation of Si-Si bonds, which are traps in Si3N4.

Field emission from laser-processed niobium (110) single crystals

Niobium is a technologically important material, which is typically used for superconducting radio-frequency applications. Superconductive cavities made of niobium require contamination-free and smooth surfaces to ensure the best performance of a particle accelerator. Interior surfaces of niobium cavities are usually obtained by centrifugal barrel polishing, buffered chemical polishing, and electropolishing or a combination of these methods. However, a standard inspection of the inner cavity surface after the treatment still shows the presence of sharp features limiting cavity performance. Laser polishing is a potential alternative or can be used as an additional final step for a more efficient surface treatment toward higher electric field gradients. In the present study, a chemically polished (110)-oriented single crystal niobium surface was processed with a focused pulsed laser with a pulse duration of 3.5 ns and a repetition rate of 10 Hz. The laser fluence and the number of pulses were varied in the range from 0.68 up to $4.27\text{ }\text{ }\mathrm{J}/{\mathrm{cm}}^{2}$ and from 20 up to 200, respectively. The magnitude of laser-induced surface structures and boiling traces was systematically studied by means of scanning electron microscopy, atomic force microscopy, and optical profilometry. Finally, the local field emission behavior was investigated and correlated with the observed surface modifications. Typical current-field characteristics and a field enhancement statistic of laser-processed areas are presented in the study. The surface processing with a rather low laser fluence of $0.68\text{ }\text{ }\mathrm{J}/{\mathrm{cm}}^{2}$ yielded high onset electric fields of $650--940\text{ }\text{ }\mathrm{MV}/\mathrm{m}$ with field enhancement factors below 10. The processing with a higher laser fluence and/or a higher number of pulses resulted in boiledlike structures emitting at $70--190\text{ }\text{ }\mathrm{MV}/\mathrm{m}$.

Effect of niobium doping on the dielectric and nonlinear current–voltage characteristics of [formula omitted] ceramics

The effect of Nb5+ on the crystallographic structure, electrical properties and the dielectric behaviour of Na0.5La0.5Cu3Ti(4−x)NbxO12 ceramics prepared via the solid-state reaction method were investigated. Rietveld refinement of the powder diffraction data confirmed a cubic, single phase structure with space group Im3. A low frequency Debye-type relaxation is observed for the Nb-doped samples in addition to the usually observed high frequency relaxation. The grain boundary resistance decreased significantly with increasing Nb5+ dopant. The reduced grain boundary resistivity was found to be responsible for the decrease in the potential barrier at the grain boundary as observed from the overall variation of current density-electric field (J–E) characteristics. The dielectric constant at low Frequency is increased with increasing Nb content. The dielectric behaviour of the compound is explained on the basis of the Internal Barrier Layer Capacitance (IBLC) model.

Death and Resurrection of a Current by Disorder, Interaction or Periodic Driving

Because of disorder the current-field characteristic may show a first order phase transition as function of the field, at which the current jumps to zero when the driving exceeds a threshold. The discontinuity is caused by adding a finite correlation length in the disorder. At the same time the current may resurrect when the field is modulated in time, also discontinuously: a little shaking enables the current to jump up. Finally, in trapping models exclusion between particles postpones or even avoids the current from dying, while attraction may enhance it. We present simple models that illustrate those dynamical phase transitions in detail, and that allow full mathematical control.

Electric field involved transport at elevated temperature in nanocrystalline silicon carbide nitride (nc-SiCN) thin films for harsh environment applications

The present study represents a systematic temperature dependent charge transport and dielectric properties of nanocrystalline silicon carbide nitride (nc-SiCN) thin films grown on Pt/Ti/SiO2/Si substrate. A large negative temperature coefficient of resistance (TCR) ranging from 6200 to 2300 ppmK-1 in the temperature range 300–773 K, suggests that the nc-SiCN thin films could be useful for futuristic thermal-based sensors. The current density vs. electric field (J-E) characteristics was measured at different temperatures (300–673 K). Detailed J-E analysis revealed an ohmic conduction at the low applied electric field (<65 kV/cm) within the entire temperature range. However, at high electric field (>65 kV/cm), space charge limited conduction (SCLC) mechanism was found to be dominating in low measurement temperature (300–473K), whereas, a transition from SCLC mechanism to Poole-Frenkel mechanism was observed with further increment in the temperature beyond 473 K. The temperature invariant dielectric tunability (nr ∼10%) and low zero electric field leakage current density (J ∼10−7A/cm2) at 673 K temperature, demonstrates the feasibility of nc-SiCN thin films for tunable device applications in the high-temperature and harsh environment.

Synergistic effect of ZnO microspherical varistors and carbon fibers on nonlinear conductivity and mechanical properties of the silicone rubber-based material

Polymeric materials filled with ZnO varistors microspheres can exhibit the intriguing nonlinear current-field characteristic that is promising for electrical field grading applications. However, the switching field of the composite material is hardly controllable by current approaches, and the nonlinear current-field characteristic of the composite material is attained at the expense of significantly compromised mechanical properties. In this study, we developed silicone rubber (SR)-based ternary composites containing ZnO microspherical varistors and carbon fibers (CF) for simultaneous control over the electrical and mechanical properties to satisfy the practical requirement in electrical field grading. The measured J-E characteristics showed that introducing CF into conventional ZnO microspherical varistors/SR binary composites could largely broaden the range of switching field and improve the nonlinear characteristic. The mechanical tensile tests of the ternary composite samples revealed remarkably enhanced mechanical properties compared with ZnO microspherical varistors/SR binary composites. This paper demonstrated the synergistic effect in tailoring the nonlinearity and mechanical performance of nonlinear polymeric composites for advanced field grading materials.

Self-assembly and electrical characteristics of 4-pentynoic acid functionalized Fe3O4-γ-Fe2O3 nanoparticles on SiO2/n-Si

A novel investigation on a relationship between temperature-influential self-assembly (70–300°C) of 4-pentynoic acid functionalized Fe3O4-γ-Fe2O3 nanoparticles (NPs) on SiO2/n-Si with electrical properties was reported with the interests for metal-oxide-semiconductor applications. X-ray diffractometer (XRD) analysis conveyed that 8±1nm of the NPs were assembled. Increasing heating temperature induced growth of native oxide (SiO2). Raman analysis confirmed the coexistence of Fe3O4-γ-Fe2O3. Attenuated Total Reflectance Infrared (ATR-IR) spectra showed that self-assembly occurred via SiOC linkages. While SiOC linkages were broken down at elevated temperatures, formations of Si-OH defects were amplified; a consequence of physisorbed surfactants disintegration. Atomic force microscopy (AFM) showed that sample with more physisorbed surfactants exhibited the highest root-mean-square (RMS) roughness (18.12±7.13nm) whereas sample with lesser physisorbed surfactants displayed otherwise (12.99±4.39nm RMS roughness). Field Emission Scanning Electron Microscope (FE-SEM) analysis showed non-uniform aggregation of the NPs, deposited as film (12.6μm thickness). The increased saturation magnetization (71.527Am2/kg) and coercivity (929.942A/m) acquired by vibrating sample magnetometer (VSM) of the sample heated at 300°C verified the surfactants’ disintegration. Leakage current density-electric field (J-E) characteristics showed that sample heated at 150°C with the most aggregated NPs as well as the most developed SiOC linkages demonstrated the highest breakdown field and barrier height at 2.58×10−3 MV/cm and 0.38eV respectively. Whereas sample heated at 300°C with the least SiOC linkages as well as lesser aggregated NPs showed the lowest breakdown field and barrier height at 1.08×10−3 MV/cm and 0.19eV respectively. This study opens up better understandings on how formation and breaking down of covalent linkages as well as accumulation of defects, particularly prior temperature influential self-assembly at the interfaces, affected electrical breakdown field and barrier height. Hence, possible future development of self-assembly silicon-based metal-oxide-semiconductor (MOS) structure particularly in the presence of SiO2 can be deliberated.