Static Induction Thyristor Research Articles

Solid-State Contactor With Si Thyristor and SiC FET Hybrid Module for High-Efficiency Motor Control

Solid-State Contactor With Si Thyristor and SiC FET Hybrid Module for High-Efficiency Motor Control

Nanosecond-scale impulse generator for biomedical applications of atmospheric-pressure plasma technology.

This study proposes an improved high-voltage fast impulse generator based on an inductive energy storage system with a 4kV static induction thyristor. Nanosecond-scale impulses with pulse widths below 100ns and a peak voltage of up to 15kV can be generated by modifying the high-voltage transformer in the circuit and tuning the circuit capacitor. The resulting device is highly stable and can perform continuously if the discharge parameters are chosen within the recommended range. A plasma jet was operated using the generator at low temperature (below 37 °C). Together with its high stability and potential for continuous operation, the proposed generator offers promise for use in biomedical and agricultural applications. Furthermore, the nanosecond-scale high-voltage impulses produced by the generator enable it to achieve an electron density in the plasma one order of magnitude higher than the commercially available radio frequency plasma jet analog. We also show how to reduce the total cost of the generator.

Effect of Nitrogen Gas Plasma Generated by a Fast-Pulsed Power Supply Using a Static Induction Thyristor on Scrapie Prion.

Previous studies show that nitrogen gas plasma generated by a fast-pulsed power supply using a static induction thyristor has both virucidal and bactericidal effects. In this study, nitrogen gas plasma was further evaluated for its potential effects on prions, which are well known to be the most resistant pathogen to both chemical and physical inactivation. Aliquots (10 μL) of mouse brain homogenate infected with Chandler scrapie prion were spotted onto cover glasses and subjected to nitrogen gas plasma. Treated samples were recovered and subjected to further analyses. Control prion samples were prepared in exactly the same way but without plasma treatment. Protein misfolding cyclic amplification (PMCA) showed that nitrogen gas plasma treatment at 1.5 kilo pulse per second for 15 or 30 min caused a reduction in the in vitro propagation level of PrPres (proteinase K-resistant prion protein), which was used as an index of abnormal prion protein (PrPSc). Moreover, mice injected with prion treated with plasma for 30 min showed longer survival than mice injected with control prion, indicating that nitrogen gas plasma treatment decreased prion infectivity. Altogether, these results suggest that nitrogen gas plasma treatment can inactivate scrapie prions by decreasing the propagation activity and infectivity of PrPSc.

High current pulse forming network switched by static induction thyristor

A high-current pulse forming network (PFN) has been developed for applications to artificial solar-wind generation. It is switched by static-induction thyristor (SIThy) and is capable of generating pulsed current of ∼9.7 kA for a time duration of ∼1 ms. The SIThy switch module is made that it can be controlled by an optical signal and it can be operated at elevated electrical potential. The experiments reported in this paper used two switch modules connected in series for maximum operating voltage of 3.5 kV. The experimental results have demonstrated a pulsed high-current generator switched by semiconductor devices, as well as the control and operation of SIThy for pulsed power application.

Degradation and inactivation of Shiga toxins by nitrogen gas plasma

Shiga toxin (Stx)-producing Escherichia coli (STEC) leads to food poisoning by causing hemorrhagic colitis and hemolytic uremic syndrome. Some STEC produce Shiga toxin 1 (Stx1) and/or Shiga toxin 2 (Stx2), a relatively stable protein toxin, necessitating the development of an efficient inactivation method. Here we applied a nitrogen gas plasma apparatus to the inactivation of Stx. Samples of Stx1 and Stx2 were treated with a nitrogen gas plasma generated by a plasma device using a short high-voltage pulse applied by a static induction thyristor power supply at 1.5 kpps (kilo pulse per second). The recovered Stx samples were then analyzed for immunological and biological activities. Immunochromatography demonstrated that Stx1 and Stx2 were degraded by the gas plasma. Quantification by enzyme-linked immunosorbent assay (ELISA) showed that both toxins were efficiently degraded to less than 1/10th of their original concentration within 5 min of treatment. Western blotting further showed the gas plasma treatment degraded the A subunit, which mediates the toxicity of Stx. Moreover, an assay using HEp-2 cells as an index of cytotoxicity showed that gas plasma treatment reduced the toxic activity of Stx. Therefore, nitrogen gas plasma might be an efficient method for the inactivation of Stx.

Crucial roles of reactive chemical species in modification of respiratory syncytial virus by nitrogen gas plasma

The exact mechanisms by which nanoparticles, especially those composed of soft materials, are modified by gas plasma remain unclear. Here, we used respiratory syncytial virus (RSV), which has a diameter of 80–350nm, as a model system to identify important factors for gas plasma modification of nanoparticles composed of soft materials. Nitrogen gas plasma, generated by applying a short high-voltage pulse using a static induction (SI) thyristor power supply produced reactive chemical species (RCS) and caused virus inactivation. The plasma treatment altered the viral genomic RNA, while treatment with a relatively low concentration of hydrogen peroxide, which is a neutral chemical species among RCS, effectively inactivated the virus. Furthermore, a zero dimensional kinetic global model of the reaction scheme during gas plasma generation identified the production of various RCS, including neutral chemical species. Our findings suggest the nitrogen gas plasma generates RCS, including neutral species that damage the viral genomic RNA, leading to virus inactivation. Thus, RCS generated by gas plasma appears to be crucial for virus inactivation, suggesting this may constitute an important factor in terms of the efficient modification of nanoparticles composed of soft materials.

Nitrogen gas plasma treatment of bacterial spores induces oxidative stress that damages the genomic DNA.

Gas plasma, produced by a short high‑voltage pulse generated from a static induction thyristor power supply [1.5 kilo pulse/sec (kpps)], was demonstrated to inactivate Geobacillus stearothermophilus spores (decimal reduction time at 15min, 2.48min). Quantitative polymerase chain reaction and enzyme‑linked immunosorbent assays further indicated that nitrogen gas plasma treatment for 15min decreased the level of intact genomic DNA and increased the level of 8-hydroxy-2'-deoxyguanosine, a major product of DNA oxidation. Three potential inactivation factors were generated during operation of the gas plasma instrument: Heat, longwave ultraviolet-A and oxidative stress (production of hydrogen peroxide, nitrite and nitrate). Treatment of the spores with hydrogen peroxide (3x2‑4%) effectively inactivated the bacteria, whereas heat treatment (100˚C), exposure to UV-A (75‑142 mJ/cm2) and 4.92mM peroxynitrite (•ONOO‑), which is decomposed into nitrite and nitrate, did not. The results of the present study suggest the gas plasma treatment inactivates bacterial spores primarily by generating hydrogen peroxide, which contributes to the oxidation of the host genomic DNA.

Degradation and detoxification of aflatoxin B1 using nitrogen gas plasma generated by a static induction thyristor as a pulsed power supply

Toxic fungal metabolite aflatoxin B1 (AFB1) is a stable carcinogen that is sometimes found in foods, such as peanuts and peppers. In this study, AFB1 was applied to a coverglass and subjected to treatment with nitrogen gas plasma generated by a plasma apparatus using a short high voltage pulse from a static induction thyristor power supply at 1.5 kpps (kilo pulse per second). Enzyme-linked immunosorbent assay showed that a 20 μL aliquot of a 200 ppb solution of AFB1 was efficiently degraded to less than one tenth of the original level within 15 min. High-performance liquid chromatography confirmed the loss of AFB1 after plasma treatment and the generation of small fragments, possibly originating from the degradation process. Moreover, a cell-based assay using HepG2 as an index to measure the cell-growth promoting properties of AFB1 showed that the gas plasma treatment reduced the biological activity of the mycotoxin. Although the amount of heat and ultraviolet light is insufficient to inactivate the toxin, the reactive chemical products appear to contribute to the degradation of AFB1. Controlling and optimizing the conditions for producing these reactive chemical species during plasma generation would lead to efficient inactivation of AFB1.

Nitrogen Gas Plasma Generated by a Static Induction Thyristor as a Pulsed Power Supply Inactivates Adenovirus.

Adenovirus is one of the most important causative agents of iatrogenic infections derived from contaminated medical devices or finger contact. In this study, we investigated whether nitrogen gas plasma, generated by applying a short high-voltage pulse to nitrogen using a static induction thyristor power supply (1.5 kilo pulse per second), exhibited a virucidal effect against adenoviruses. Viral titer was reduced by one log within 0.94 min. Results from detection of viral capsid proteins, hexon and penton, by Western blotting and immunochromatography were unaffected by the plasma treatment. In contrast, analysis using the polymerase chain reaction suggested that plasma treatment damages the viral genomic DNA. Reactive chemical products (hydrogen peroxide, nitrate, and nitrite), ultraviolet light (UV-A) and slight temperature elevations were observed during the operation of the gas plasma device. Viral titer versus intensity of each potential virucidal factor were used to identify the primary mechanism of disinfection of adenovirus. Although exposure to equivalent levels of UV-A or heat treatment did not inactivate adenovirus, treatment with a relatively low concentration of hydrogen peroxide efficiently inactivated the virus. Our results suggest the nitrogen gas plasma generates reactive chemical products that inactivate adenovirus by damaging the viral genomic DNA.

Failure Modes of 15 kV SiC SGTO Thyristors during Repetitive Extreme Pulsed Overcurrent Conditions

SiC SGTO thyristors are an advanced solution for increasing the power density of medium voltage power electronics. However, for these devices to replace Si thyristor technology in industrial applications their characteristics and failure modes must be understood. This letter presents the failure modes of two 15-kV SiC SGTO thyristors during repetitive overcurrent conditions. The devices were evaluated with 2-kA (3.85 kA/cm2) square pulses of 100 ${\boldsymbol \mu}$ s duration using a pulse forming network. Throughout testing, each devices’ static characteristics were analyzed for signs of degradation; upon degradation, testing was ceased and the physical failure mode was determined through imaging with a scanning electron microscope (SEM) in conjunction with a focused ion beam. The electrical results demonstrate the failure modes of both SiC SGTO thyristors during pulsed overcurrents electrically manifested themselves as a conductive path through the gate-anode junction and an increased device on-state voltage. SEM imaging revealed one SiC thyristor formed an approximately ${10\hbox{-}\mu{\rm m}}$ wide cylindrical void, and the second SiC thyristor formed an approximately ${200\hbox{-}\mu{\rm m}}$ long crack. However, the experimental results demonstrate these 15-kV SiC SGTO thyristors’ robust ability to repetitively switch at extreme high current density for tens of thousands of cycles.

Comparative analysis of static characteristics of insulated gate bipolar transistors and thyristors with static induction

Two-dimensional numerical simulation of equivalent silicon insulated gate bipolar transistors (IGBT) and static induction thyristors (SITh) with a trench structure in the conductive and blocking states has been performed. Thickness d of the high-resistance n base was changed within 120–456 μm at donor concentrations N d = 7.0−1.75 × 1013 cm−3 and diffusion length of nonequilibrium charge carriers L = 0.25−1.0d. Comparative analysis of the results has shown that the blocking characteristics of the SITh and IGBT are almost the same but breakdown voltage U b varies in the range of 1.4–4.6 kV depending on d, N b , and L. The voltage drop in the conductive states in the IGBT without a stop layer is much larger than in the SITh. The superiority of the SITh increases with growth U b and with decreasing L. The reason for this is the relatively low injection efficiency of the cathode emitter of the IGBT, leading to a strong decrease in nonequilibrium charge carrier concentration near the cathode and a corresponding increase of the field strength. Introduction of an additional thin n-type stop layer between the base and the collector of the IGBT leads to significant weakening of the leakage of the holes. This improves the efficiency of injection and results in a significant increase of electron and hole concentrations and reduces the field strength in the half of the base of the IGBT that is nearest to the cathode. As a result, the voltage drops on the IGBT and SITh converge, especially with decreasing L and current density and with increasing U b . However, even in such a modified IGBT, concentration n is lower and the field strength is greater than in an SITh. Therefore, at current density J > 10 A/cm2, the SITh has a lower on-state resistance than the equivalent modified IGBT.

Inactivation of Salmonella by nitrogen gas plasma generated by a static induction thyristor as a pulsed power supply

Salmonella is one of the most important causative agents of food borne infections in terms of food hygiene. In this study, we investigated whether N2 gas plasma, generated by applying a short high-voltage pulse to N2 using a static induction thyristor power supply (1.5 kilo pulse per second), exhibited a bactericidal/disinfecting effect against Salmonella. Viable cell number of Salmonella was efficiently decreased with a decimal reduction time (D value) of 0.178 min (initial slope) and 3.105 min (single-slope approximation). Plasma treatment altered the surface structure of Salmonella, as observed by scanning electron microscopy. In addition, this treatment induced a marked degradation in O antigen. Polymerase chain reaction (PCR) analysis also suggested that the Salmonella genomic DNA was damaged by the plasma treatment. Reactive chemical products (hydrogen peroxide-like chemicals), ultraviolet light (UV-A) and slight temperature elevations were observed during the operation of the gas plasma device. Viable cell number versus intensity of each potential bactericidal factor were used to identify the primary mechanism of disinfection of Salmonella. Although equivalent levels of UV-A or heat treatment did not inactivate Salmonella, treatment with a low concentration of hydrogen peroxide efficiently inactivated the bacteria. Our results suggest the N2 gas plasma generates reactive chemical species that alter components of Salmonella such as the cell surface as well as damaging the genomic DNA. The combined effect of these reactive species is to induce cell death.

Development of a high-power solid-state switch using static induction thyristors for a klystron modulator

We developed a solid-state switch with static induction thyristors for the klystron modulator of the L-band electron linear accelerator (linac) at the Institute of Scientific and Industrial Research, Osaka University. This switch is designed to have maximum specifications of a holding voltage of 25kV and a current of 6kA at the repetition frequency of 10Hz for forced air cooling. The turn-on time of the switch was measured with a matched resistor to be 270ns, which is sufficiently fast for the klystron modulator. The switch is retrofitted in the modulator to generate 1.3GHz RF pulses with durations of either 4 or 8μs using a 30MW klystron, and the linac is successfully operated under maximum conditions. This finding demonstrates that the switch can be used as a high-power switch for the modulator. Pulse-to-pulse variations of the klystron voltage are measured to be less than 0.015%, and those of RF power and phase are lower than 0.15% and 0.1°, respectively. These values are significantly smaller than those obtained with a thyratron; hence, the stability of the main RF system is improved. The solid-state switch has been used in normal operation of the linac for more than a year without any serious trouble. Thus, we confirmed the switch’s robustness and long-term reliability.

Physical effect of carrier distribution in the channel of static induction thyristor

The physical effects of the carrier distribution in the channel on the dynamical performance of a static induction thyristor (SITH) have been studied numerically and experimentally. The analytical expressions of the minority carrier distribution in the channel of the SITH were also derived and the space charge distribution controlling mechanism on the current of the SITH under high level injection have been analyzed deeply. The relationships among the minority carrier distribution, potential distribution, I–V characteristics and transient performances of the SITH are revealed.

Switching performances of static induction thyristor with buried-gate structure

The switching characteristics of SITh are not only determined by the conductance modulation in channel between the gate regions, but also affected by the external gate driving circuit. The physical mechanism and behavior of switching process are studied deeply based on the fabrication practice of SITh. The dependence of switching performances of SITh on material, geometric structure and technological parameters are analytically discussed by using two-dimensional dynamical model firstly proposed in this paper. A series of optimum matching technological approaches have been developed for improving the switching characteristics of SITh. A versatile testing circuit is designed to get more accurate switching parameters and more stable switching-off process with lower power consumptions. The switching times t on and t off are reduced from 0.2 μs and 1.2 μs to 0.08 μs and 1.0 μs, respectively, and the dynamic dv/dt value of more than 1000 V/μs at switching-off is obtained.

N 8322 gas plasma inactivates influenza virus mediated by oxidative stress

Here we show that N₂ gas plasma, produced by applying a short high-voltage pulse using a static induction (SI) thyristor power supply inactivates influenza virus. N₂ gas plasma treatment of influenza A and B viruses induced the degradation of viral proteins, including nucleoprotein, hemagglutinin, and neuraminidase. The injury of viral RNA genome and the inactivation of hemagglutination were also observed after N₂ gas plasma treatment. These changes were possibly due to changes in the viral envelope, because modification of the lipid content was also suggested by Fourier-transformed infrared spectroscopy. At least three major mechanisms of action (heat, UV-A, and oxidative stress (i.e. hydrogen peroxide-like molecules)) were found in this system. Among them, oxidative stress appeared to be the main factor in the inactivation of influenza virus. In addition, there was an increase in the nitrotyrosine content of viral proteins, suggesting that oxidative stress produced by N₂ gas plasma generation oxidized proteins. As a result, oxidation may be the most important factor in the inactivation, degradation, and modification of influenza virus by N₂ gas plasma.

Research on Switching Performance of Static Induction Thyristors

Physical mechanism for switching state of SITHs was discussed, the two-dimensional turn-off model was proposed, expressions of ton and toffwere mathematical derived. Measures to reduce the switching time of SITHs, such as reducing the gate width WG and n- region width Wn-, doping Boron atoms with higher density,etc.,were put forward and verified by experiments.

Sterilization mechanism of nitrogen gas plasma: induction of secondary structural change in protein

The mechanism of action on biomolecules of N₂ gas plasma, a novel sterilization technique, remains unclear. Here, the effect of N₂ gas plasma on protein structure was investigated. BSA, which was used as the model protein, was exposed to N₂ gas plasma generated by short-time high voltage pulses from a static induction thyristor power supply. N₂ gas plasma-treated BSA at 1.5 kilo pulses per second showed evidence of degradation and modification when assessed by Coomassie brilliant blue staining and ultraviolet spectroscopy at 280 nm. Fourier transform infrared spectroscopy analysis was used to determine the protein's secondary structure. When the amide I region was analyzed in the infrared spectra according to curve fitting and Fourier self-deconvolution, N₂ gas plasma-treated BSA showed increased α-helix and decreased β-turn content. Because heating decreased α-helix and increased β-sheet content, the structural changes induced by N₂ gas plasma-treatment of BSA were not caused by high temperatures. Thus, the present results suggest that conformational changes induced by N₂ gas plasma are mediated by mechanisms distinct from heat denaturation.

The Characteristics of ESD Protection Device Based on Static Induction Thyristors

A novel structure of ESD protection device based on the static induction thyristors (SITh) was in further investigation. Detailed analysis of the negative resistance characteristics of SITh was presented, especially its blocking and conducting states that satisfy the requirements in ESD events. The characteristics of SITh for ESD protection were obtained using the Time Domain Reflectometer (TDR) type of Transmission Line Pulse (TLP) testing system. The results illustrate that SITh for ESD protection has the following advantages: 1) It has a strong ESD stress handing capability (3.75 kV); 2) Its second breakdown current is large enough (2.5 A) to release great ESD current; 3) DC leakage current of SITh is very small (1 μA); 4) SITh can break through the limitations of transitional trigger voltages, whose trigger voltage is dynamically adjustable as well; 5) The ESD response time can be controlled through optimizing device structure of SITh.

N2Gas Plasma Inactivates Influenza Virus by Inducing Changes in Viral Surface Morphology, Protein, and Genomic RNA

We have recently treated with N2 gas plasma and achieved inactivation of bacteria. However, the effect of N2 gas plasma on viruses remains unclear. With the aim of developing this technique, we analyzed the virucidal effect of N2 gas plasma on influenza virus and its influence on the viral components. We treated influenza virus particles with inert N2 gas plasma (1.5 kpps; kilo pulses per second) produced by a short high-voltage pulse generated from a static induction thyristor power supply. A bioassay using chicken embryonated eggs demonstrated that N2 gas plasma inactivated influenza virus in allantoic fluid within 5 min. Immunochromatography, enzyme-linked immunosorbent assay, and Coomassie brilliant blue staining showed that N2 gas plasma treatment of influenza A and B viruses in nasal aspirates and allantoic fluids as well as purified influenza A and B viruses induced degradation of viral proteins including nucleoprotein. Analysis using the polymerase chain reaction suggested that N2 gas plasma treatment induced changes in the viral RNA genome. Scanning electron microscopy analysis showed that aggregation and fusion of influenza viruses were induced by N2 gas plasma treatment. We believe these biochemical changes may contribute to the inactivation of influenza viruses by N2 gas plasma.