Galvanomagnetic Effects in Semiconductors at High Electric Fields

Electrical characterization and carrier transportation in Hf-silicate dielectrics using ALD gate stacks for 90 nm node MOSFETs

Understanding nonlinear dielectric behavior in polar polymers is crucial to their potential application as next generation high energy density and low loss dielectrics. In this work, we studied nonlinear dielectric properties of a biaxially oriented poly(vinylidene fluoride) (BOPVDF) film under both low and high electric fields. For fundamental nonlinear dielectric constants at low fields (<30 MV/m), Novocontrol high-voltage broadband dielectric spectroscopy (HVBDS) was accurate enough to measure up to the third harmonics. It was observed that the low-field dielectric nonlinearity for the BOPVDF disappeared above 10 Hz at room temperature, suggesting that the low-field dielectric nonlinearity originated from ionic migration of impurity ions rather than dipolar relaxation of the amorphous segments. Above the coercive field (EC ≈ 70 MV/m), bipolar electric displacement-electric field (D-E) loop tests were used to extract the nonlinear behavior for pure PVDF crystals, which had a clear origin of ferroelectric switching of polar crystalline dipoles and domains and nonpolar-to-polar (α → δ → β) phase transformations. By using HVBDS, it was observed that the ferroelectric switching of polar crystalline dipoles and domains in BOPVDF above the EC always took place between 20 and 500 Hz regardless of a broad range of temperature from -30 to 100 °C. This behavior was drastically different from that of the amorphous PVDF dipoles, which had a strong dependence on frequency over orders of magnitude.

The development of high-voltage DC cables is mainly limited by the properties of insulating materials. Adding an appropriate amount of nanoparticles can improve the dielectric properties of materials. To study the effect of high temperature and nano-filler concentration on the conductivity characteristics of the dielectric, LDPE/Sio <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> nanocomposites with the particle size of 7 nm and mass fraction of 0.5wt%, lwt%, and 3wt% were prepared by filling LDPE with nano- Sio <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> particles. The DC conductance at 90°C and 100°C was measured at the electric field strength of1-100 kV/mm, and the temperature sensitivity of the samples were analyzed. The results show that in the condition of high temperature and low electric field, the nanocomposite can effectively reduce the conductivity current density and improve the conductivity performance, and the first threshold electric field increases with the increase of nano-filling concentration. Under the high electric field at high temperatures, temperature becomes one of the main factors that affect the carrier transport process. Among all samples, the LDPE/Sio <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> nanocomposite with a mass fraction of 3wt% has the best conductivity and the lowest temperature sensitivity.

The electrical activation energy in CdO-P 2O 5 glasses under high and low electric fields

Smart wound management with sustainable pH sensing and dynamic electrotherapy.

Electric-field-induced polarization fatigue of [001]-oriented [formula omitted] single crystals

High-field electron transport properties in a two-dimensional nanolayer are studied by an application of the anisotropic nonequilibrium distribution function, a natural extension of the Fermi-Dirac distribution by inclusion of energy gained/absorbed in a mean free path (mfp). The drift velocity for conical band structure of graphene is shown to rise linearly with the electric field in a low electric field that is below the critical electric field. The critical electric field, equal to thermal voltage divided by the mfp, marks the transition from ohmic linear transport to saturated behavior in a high electric field. As field rises beyond its critical value, the drift velocity is sublinear resulting in ultimate saturation; the ultimate saturation velocity is comparable to the Fermi velocity in graphene. The quantum emission is found not to affect the mobility, but is efficient in lowering the saturation velocity. Excellent agreement is obtained with the experimental data for graphene on silicon dioxide substrate.

A phenomenological thermodynamic theory is applied to investigate the effect of misfit strain and electric field on the electrocaloric effect of P(VDF-TrFE)/SrTiO3 bilayer thin films. Theoretical results indicate that the low electric field results in the decrease of the average polarization with the increase of the relative thickness of SrTiO3 layer, and the high electric field has an opposite effect on it. Moreover, the electrocaloric effect strongly depends on the electric field. The low electric field and the small field change can lead to a maximum of the electrocaloric effect, meanwhile the high electric field or the large field change results in the opposite trend.

The electric conductivity of stationary and homogeneous electrolytes up to concentrations c ≈ 1 mol/l and high electric fields

The current-voltage character and Hall coefficient of n-type InSb with different electron density were measured in a pulsive high electric field, at 77°K. In a high electric field, impact ionization from full band to conduction band occurred and the resistivity and Hall coefficient of n-type InSb decreased rapidly with increasing electric field. In the same region of electric field, Hall mobility decreased and drift velocity reached a maximum value and then decreased. In the curve of the electron density versus µ E 2 , the rate of energy gain from electric field, there existed a critical value of µ E 2 where the electron density increased infinitely. This critical value of µ E 4 increased with decreasing electron mobility at low field, and, in one sample, also increased with decreasing strength of the transverse magnetic field.

We report the current-voltage characteristics of an oxygen implant-isolated region of a GaAs/AlGaAs heterostructure between 25 and 295 K. Current conduction was dominated by bulk rather than metal contact limited effects. Bulk conduction in the implant-isolated region is due to several different mechanisms; at low electric fields a resistive current; at low temperatures and high electric fields, field ionization current proportional to V2 exp(−V0/V); and at high temperatures and high electric fields, Poole–Frenkel conduction proportional to V exp(aV1/2/rkT−qφb/rkT). The resistive current can further be separated into two components, one of which dominates at low temperatures and is proportional to V exp(−B/T1/4), and the other which dominates at high temperatures and is proportional to V exp(−Ea/kT). These results are applicable to any GaAs-based structure rendered semi-insulating by an isolation implant, and describe the current conduction characteristics from zero bias to breakdown. Such a description is critical to understanding leakage currents in GaAs/AlGaAs devices such as high-performance heterojunction bipolar transistors, field-effect transistors, and laser diodes that commonly employ implant isolation as a part of the fabrication process.

The design, fabrication, and testing of a flexible, planar, anisotropic piezoelectric composite actuator utilizing machined PMN-32%PT single crystal fibers is presented. The device consists of a layer of rectangular single crystal piezoelectric fibers in an epoxy matrix, packaged between interdigitated electrode polyimide films. Quasistatic free-strain measurements of the single crystal device are compared with measurements from geometrically identical specimens incorporating polycrystalline PZT-5A and PZT-5H piezoceramic fibers. Free-strain actuation of the single crystal actuator at low bipolar electric fields (+/- 250 V/mm) is approximately 400% greater than that of the baseline PZT-5A piezoceramic device, and 200% greater than that of the PZT-5H device. Free-strain actuation under high unipolar electric fields (0-4kV/mm) is approximately 200% of the PZT-5A baseline device, and 150% of the PZT-5H alternate piezoceramic device. Performance increases at low field are qualitatively consistent with predicted increases based on scaling the low-field d(sub 33) piezoelectric constants of the respective piezoelectric materials. High-field increases are much less than scaled d(sub 33) estimates, but appear consistent with high-field freestrain measurements reported for similar bulk single-crystal and piezoceramic compositions. Measurements of single crystal actuator capacitance and coupling coefficient are also provided. These properties were poorly predicted using scaled bulk material dielectric and coupling coefficient data. Rules-of-mixtures calculations of the effective elastic properties of the single crystal device and estimated actuation work energy densities are also presented. Results indicate longitudinal stiffnesses significantly lower (50% less) than either piezoceramic device. This suggests that single-crystal piezocomposite actuators will be best suited to low induced-stress, high strain and deflection applications.

One of the major problems of polymeric insulation is their tendency to accumulate space charge at higher electric fields, especially in HVDC (High Voltage DC) applications. Nanodielectrics are an emerging area of research because of their potential as a novel insulating material in electrical apparatus and systems. Understanding space charge behavior in these new materials is crucial to their application in high field environment. In the present work, space charge behavior in epoxy alumina nanocomposites is investigated by using Pulse Electro Acoustics (PEA), Conduction Current (CC), and Electroluminescence techniques in conjunction. The PEA technique is used to measure accumulated charge density, and maps the space charge distribution in the volume of the dielectric. Polarization- Depolarization current measurements are carried out to extract conduction current density, dc conductivity, and permittivity. Electroluminescence measurements are related to injection and impact ionization of charge carriers. Space charge density, conduction current density, and electroluminescence counts, show a transition above a certain electric field. The electric field above which all three characteristics undergo a transition is associated with the threshold field for accumulation of space charge. Nano-dielectrics show lower space charge, and lower conductivity at higher fields than neat epoxy. The permittivity of the nanodielectrics is seen to be higher than neat epoxy at lower electric fields. At higher fields their permittivities are comparable. The complementary findings from all three techniques prove to be effective in characterizing the space charge in the nano dielectrics.

The influence of a high average electric field (∼1 V/nm) in the hydrophobic interior of a bilayer lipid membrane on short-wavelength in-plane phononic motions of lipid chains is considered. The average electric field is assumed to be nearly constant on a picosecond time scale and a nanometer length scale. This field may be induced, for instance, by externally applied subnanosecond electric pulses or the membrane dipole potential. Using a generalized hydrodynamic approach, we derive a corresponding electrohydrodynamic model generalized to high wave numbers. In the considered approximation, all electric field effects are reduced only to a constant contribution to the generalized isothermal compressibility modulus. The corresponding dynamic structure factor for a lipid bilayer is derived. We show that due to polarization effects, the high field can critically impact the dynamics of longitudinal acousticlike modes at wave numbers near the major peak of the static structure factor. We estimate quantitatively that for typical lipid bilayers, transverse high electric fields can cause strong phonon energy softening, enhancement of phonon population, and formation of a gap in the dispersion of excitation frequency. The results obtained agree with simulations of the initiation of lipid bilayer electropores, suggesting that the proposed model reproduces the essential features of the field's impact on atomic density fluctuations. The proposed mechanism may have significant implications for the understanding of electroporation, passive molecular transport, and spontaneous pore formation in lipid bilayers.

The influence of high electrical DC fields (>20 kV/mm) on aging, polarization and on the morphology of polyethylene (PE) is discussed. Infrared and positron annihilation spectroscopy measurements as well as capacitance measurements tend to suggest that the polymer morphology is modified by high fields. The author shows that the accelerated electrical aging characteristics of PE are linked directly to the morphology changes induced by the field. Below a so-called critical field, the activation volume of the aging process is dependent on the field-induced strain. Above the critical field, the amorphous phase is deformed significantly, and weak van der Waals bonds are broken, leading to another, faster, aging regime. There is an excellent agreement between the proposed model and experimental data obtained with various PE samples. The possible relation between the submicrocavity formation proposed in his aging model and various polarization measurements is discussed. It is his contention that strong charge injection occurs only after submicrocavity formation, i.e. after weak bond breakage. As is well known, the polarization currents obtained under high fields are controlled by space charges. It seems that the wave packets and the negative resistance observed at >100 kV/mm in PE are associated with a steady state in field-induced defect formation. This suggests that space charges are related to the formation of submicrocavities and, therefore, are a consequence, not a cause, of high field aging.