Influence of impact-ionization-induced base current reversal onbipolar transistor parameters

In this paper we describe a set of measurements representing a complete characterization of impact-ionization effects in bipolar transistors. We demonstrate that impact-ionization significantly influences the dependence of base resistance on current and voltages applied to the device. A dc method for the simultaneous extraction of all parasitic resistances in bipolar transistors is presented. The method can separate the influence of current-crowding on the base resistance from that of base width and conductivity modulation; the collector parasitic resistance is measured in the active region. Starting from the parameters extracted by means of these techniques, a complete and accurate circuit-model of impact-ionization effects can be defined     

Achieving high energy storage performance and breakdown strength in modified strontium titanate ceramics

Journal of Materials Science: Materials in Electronics - Lead-free ceramic capacitors with attractive properties such as their environmental friendliness, superior energy density, fast charge and...     

La3+-induced (micro)structural changes and origin of the relaxor-like phase transition in ferroelectric lead barium niobate electroceramics

Lead barium niobate (Pb_1?x Ba _x Nb₂O₆, PBN) ferroelectric materials have been and are the subject of numerous studies in literature due to their potential for wide-ranging applications in the electronic industry. In this work, La³⁺-doped Pb_0.56Ba_0.44Nb₂O₆ (PBN44) electroceramics were prepared and investigated in terms of X-ray diffraction, scanning electron microscopy, thermal spectra of dielectric permittivity, Curie–Weiss law, and hysteresis loop characteristics. It was noted that La³⁺ doping favors the formation of orthorhombic mm2 phase in PBN44, which originally shows only the tetragonal 4mm symmetry-related phase. In particular, the PBN44 material with 1 wt% La₂O₃ displays (micro)structural characteristics and dielectric properties similar to those from PBN compositions lying within their morphotropic phase boundary region. Our results also show that La³⁺ is able to promote a change of the ferroelectric to paraelectric phase transition appearance of PBN44 from pseudo-normal to really diffuse. However, conversion to a diffuse plus relaxor transition behavior reveals directly linked to incommensurate superstructures present and dielectrically-active in PBN materials toward low temperatures, with an intrinsically frequency-dispersive dielectric response. This statement is also supported by observation of hysteresis loops showing a transformation trend to pseudo-slim-like, even in the normal-like ferroelectrics, when moving into the temperature region of incommensuration manifestation.     

High and tunable piezoelectric coefficients in 0.675Pb(Mg⅓Nb⅔)O3–0.325PbTiO3 ceramics

In this study, ceramic samples with composition 0.675Pb(Mg_?Nb_?)O₃–0.325PbTiO₃ were tested and assessed in terms of piezoelectric applications. This material showed relaxor ferroelectric behavior at temperatures around the ferro-paraelectric phase transition. In this temperature region, the material also had a high real dielectric permittivity, which fell slightly with the application of an electric field between 0 and 1 kV/mm. Consequently, high effective piezoelectric coefficients were observed for this material, which were found to be almost linearly tunable with electric fields between 1 and 3 kV/mm. Hence, the material studied here appears to be a promising candidate for the manufacture of certain piezoelectric devices.     

Effect of the CoFe2O4 initial particle size when sintered by microwave on the microstructural,dielectric, and magnetic properties

The particle size of CoFe₂O₄ powders (average particle size of 350 nm) was reduced to 50 nm by high-energy milling. In this paper, special attention was given for analyzing the densification and grain growth of both particle sizes (350 and 50 nm) subject to ultrafast sintering assays using microwave sintering and their effect on the magnetic and electric properties. The results indicated that the grain growth was 10 times higher for the nanoparticle system, reaching similar sizes of ~1 μm in both cases after sintering. The relative density values were higher (95%) in the nanoparticle system due to the wide distribution of particle sizes generated in the grinding process. Qualitatively inferred microscopy analysis showed high sinterability of fine particles with a narrow distribution of grain size when subjected to ultrafast firing processes. Magnetization measurements at room temperature clearly show the reduction of Hc with increasing grain size. Electric resistivity, dielectric constant (ε′), and dielectric loss tangent (tan δ) were measured as a function of frequency at room temperature. The low values of dielectric constant (ε′) and dielectric loss (tan δ) in the low frequency range, shown for all samples sintered by microwave, prove the excellent uniformity in the microstructure.