Low Residual Voltage Research Articles

High-voltage fast diode with “soft” recovery

High-voltage fast silicon p+Nn+ diodes used in almost all modern electrical energy converters must have a low residual voltage in the conducting state, but can simultaneously be rapidly switched to the off state with low commutation losses without producing a surge overvoltage. Such a combination of parameters is usually ensured by producing the profile concentration distribution for recombination centers in the N base with a peak of the p+N junctions. Such a distribution is produced by irradiating the p+Nn+ diode in vacuum by protons or α particles on the side of the p+N junctions. We report on the results of testing of diodes in which profile distribution for the centers is obtained using a simpler and more productive method by electron bombardment in a certain energy range in air. It is shown using the specially designed devices with a blocked voltage up to 5 kV that all dynamic characteristics of the diodes correspond to the world standard, and the residual voltage in the conducting state for the working current density is approximately 30% lower.

Nickel oxide doping effects on electrical characteristics and microstructural phases of ZnO varistors with low residual voltage ratio

The effects of nickel oxide (Ni2O3) additives on electrical characteristics and microstructural phases of ZnO varistors with low residual voltage ratio are studied. The breakdown electrical fields increase remarkably with the amount of the doped nickel oxide increased. The minimum of the residual voltage ratios of the samples reaches 1.39. While the amount of the doped nickel oxide is more than 2 mol %, a new phase of chrombismite Bi16CrO27 is observed from X-ray diffraction (XRD) and scanning electron microscopy (SEM). The δ-Bi2O3 phase decreases and the BiO2−x phase increases correspondingly. In addition, the capacitance versus voltage (C–V) characteristics of the samples are measured and analyzed.

Photoalignment of nematic liquid crystal on polyamic‐acid‐based soluble polyimide with no side fragments

Abstract— The photoalignment of nematic LC on a layer of newly synthesized UV‐sensitive polyimide without side fragments is reported. The photoaligning polymer advantageously differs from other photoaligning materials because of its extremely low sticking effect and residual DC voltage. These parameters, as well as the UV and thermal stability of the alignment, are not worse than those of rubbed polyimides. At the same time, the new material possesses all the advantages of photoaligning polymers.

Cascode turn-off of field-controlled integrated thyristors

The residual voltage drop in the on state of an insulated-gate bipolar transistor, the basic device of today’s power electronics, is considerably higher than that of conventional thyristor-type devices, which is a serious disadvantage of the former. Field-controlled integrated thyristors offering a low residual voltage, as with conventional thyristors, and, at the same time, low turn-on and turn-off power losses in the control circuit, as is the case with insulated-gate bipolar transistors, seem to be promising for high-voltage high-power applications. Turn-off of these devices in the cascode mode with a series-connected low-voltage powerful FET is studied.

Novel Closing Switches Based on Propagation of Fast Ionization Fronts in Semiconductors

Power kilovolt electric pulses with subnanosecond rise time can be formed by means of semiconductor switches based on the propagation of ionization fronts in Si structures. We describe a new generation of such devices-which are deep-level dynistors (DLDs). The triggering of the ionization front in the DLDs occurs due to the field-enhanced ionization of deep-level electron traps. The DLDs are able to form high-current pulses with subnanosecond rise time and low residual voltage just after switching. We describe two power generators based on the DLDs as examples. In addition, we discuss the possibility of picosecond switching based on tunneling-assisted impact-ionization fronts.

The effect of aluminium oxide on the residual voltage of ZnO varistors

Abstract The role of aluminium oxide is investigated in an attempt to obtain low residual voltage ZnO varistors fabricated in the traditional way. The samples were sintered at three different temperatures: 1150, 1200, and 1250 °C for three different times: 1, 2, and 3 h. The effect of aluminium additions, in the range of 500–10,000 ppm, on the characteristics of electric field–current density was investigated. Addition of Al2O3 shifts the upturn region to higher current density due to the increase of the conductivity of the ZnO grains up to an optimal value. After 1000 ppm, the beneficial effect on the onset of upturn voltage is no more efficient. This work highlighted the ambivalent role of aluminium (donor or acceptor) and the need for tuning both an optimal concentration and sintering time to obtain the greatest conductivity. Our results suggest that Al3+ substitutes first to Zn2+ sites in the ZnO wurtzite structure and then, when thermodynamic saturation is reached, interstitial sites.

Properties of the transient of avalanche transistor switching at extreme current densities

Avalanche transistor switching at extreme currents is studied under conditions in which the charge of the excess carriers drastically rebuilds the collector field domain, causing fast switching and a low residual voltage across the switched-on device. The dynamic numerical model includes carrier diffusion and considers different dependencies of the velocities and ionization rates for the electrons and holes in the electric field. These dependences determine the principal difference in the switching process between n/sup +/-p-n/sub 0/-n/sup +/ and p/sup +/-n-p/sub 0/-p/sup +/ structures. Reasonably good agreement is found between the simulated and measured temporal dependences of the collector current and voltage drop across the device for a particular type of avalanche transistor. Certain differences in the switching delay can partly be attributed to limitations in the one-dimensional (1-D) approach. It is now certain that collector domain reconstruction defines the transient in a n/sup +/-p-n/sub 0/-n/sup +/ transistor at high currents, but is not very pronounced in a p/sup +/-n-p/sub 0/-p/sup +/ transistor. Some nontrivial features of the device operation are found, depending on the semiconductor structure. In particular, it is shown that the thickness of the low-doped collector region affects mainly the switching delay, and does not significantly effect the current rise time.

"Paradoxes" of carrier lifetime measurements in high-voltage SiC diodes

For Silicon Carbide (SiC) high-voltage rectifier diodes, contradictions appear when the most important parameter of the diodes, the minority carrier lifetime, is measured by different techniques. A qualitative analysis and a computer simulation have been carried out to clarify the origin of these contradictions. For 4H-SiC p/sup +/n diodes with 6 kV blocking capability, data on residual voltage drop at high current densities, switch-on time, reverse current recovery, and post-injection voltage decay are analyzed. It is shown that the whole set of experimental data can be explained by the existence of a thin (l/spl sim/0.1 /spl mu/m) layer near the metallurgical boundary of the p/sup +/n junction with very small carrier lifetime /spl tau//sub l/ that is essentially smaller than the carrier lifetime /spl tau/ across the remaining part of the 50-/spl mu/m n-base. It is emphasized that the existence of such a layer allows, under certain conditions, the combination of a relatively low residual forward voltage drop and very fast reverse recovery. Approaches to minority carrier lifetime measurements are discussed.

Process control during diamond coating of tools: F.Deuerler et al. (Fachhochschule Gelsenkirchen, Bocholt, Germany.) Int. J. Refractory Metals Hard Mater., vol 16, no 3, 1998, 191–199

The present study focuses on the effect of indium doping on the microstructure and electrical properties of Y-doped ZnO varistor ceramics. At a given concentration of the rare-earth element yttrium, the leakage currents of sintered varistors first decreased markedly with increased indium doping, before increasing at higher doping levels. The nonlinear coefficient showed the opposite trend. A fraction of the doped In3+ ions dissolved into the grains and caused the grain resistance to decrease, leading to a low level residual voltage. The In3+ ions present at the grain boundaries increased the barrier height, and further inhibited increases in the leakage current. When doped with 0.025 mol% indium and 0.9 mol% yttrium, the sintered varistors showed optimal electrical properties with a leakage current of 4.15 μA/cm2, nonlinear coefficient of 51.84, residual voltage ratio of 1.61, and voltage gradient of 615.59 V/mm.

P‐68: Influence of Polyamide Structures on Electrical Properties of Active‐Matrix Liquid‐Crystal Cells

AbstractThe electrical properties of liquid crystal cells were estimated using various kinds of polyimide(PI) films. It is clarified that the PI structures and its layer structures affects electrical properties of LC cells. Based on the result, we developed a new alignment layers that exhibit a high voltage holding ratio and a low residual DC voltage at the same time.

GaAs Hall devices produced by local ion implantation

GaAs Hall devices were produced by complete planar technology using two selective silicon ion implantation steps. The fundamental characteristics of these devices with respect to reproducible implantation dose and geometry of cross-shaped elements are obtained both by experiment and calculation. The prominent properties of the GaAs Hall elements presented are high sensitivity and linearity, small temperature dependence of sensitivity and resistance, and low residual voltage.