High Current Conduction Research Articles

Modelling SiC MOSFET module threshold voltage (VTH) and impact of parallel device ΔVTH on short circuit robustness

In SiC modules, where several power MOSFETs are connected in parallel for high current conduction capability, the issue of threshold voltage (VTH) variation between individual devices can become problematic. In instances where the standard deviation of device VTH is minimized by appropriate VTH pre-screening, non-uniform VTH shift under bias-temperature-instability can lead to increased VTH dispersion and potentially poor current sharing. Although non-destructive for normal operation, VTH dispersion in surge events like short circuits can cause premature module failure. In this paper, experimental investigations backed by theoretical models have been developed to explain the relationship between device VTH dispersion and module VTH shift. This is done for Si and SiC MOSFETs. Five Si/SiC MOSFETs are paralleled in a custom printed-circuit-board allowing individual VTH and module VTH measurements. It is shown that the module VTH is typically between the smallest VTH and the mean VTH, depending on the VTH standard deviation. Using empirical models for MOSFETs in weak inversion derived from the measured subthreshold gate transfer characteristics, the model can estimate module VTH from a dispersion of individual MOSFET VTH. It can also predict the impact of non-uniform VTH shift between constituent devices on the overall module VTH. Finally, the impact of VTH mismatch on current sharing during short circuits in parallel connected SiC MOSFETs is presented. The results show that VTH mismatch in parallel connected SiC MOSFETs reduces the short circuit withstand time from 5 μs to 4.5 μs compared to VTH matched SiC MOSFETs.

FEM-based analysis of avalanche ruggedness of high voltage SiC Merged-PiN-Schottky and Junction-Barrier-Schottky diodes

Through comprehensive experimental measurements and TCAD simulation, it is shown that the avalanche ruggedness of SiC MPS & JBS diodes outperforms that of closely rated Silicon PiN diodes taking advantage of the wide-bandgap properties of SiC which leads to a high ionization and activation energy given the strong covalent bonds. Although the MPS diode structure favours a high reverse blocking voltage with small leakage current and a high current conduction, the localise current crowding caused by the multiple P+ implanted region leads to the avalanche breakdown at lower load currents than the SiC JBS diode. The results of Silvaco TCAD Finite Element modellings have a good agreement with the experimental measurements, indicating that SiC JBS diode can withstand the high junction temperature induced by avalanche in line with the calculated avalanche energy.

Studies on tuning surface electronic properties of hydrogenated diamond by oxygen functionalization

Ultra-wide bandgap and the absence of shallow dopants are the major challenges in realizing diamond based electronics. However, the surface functionalization offers an excellent alternative to tune electronic structure of diamonds. Herein, we report on tuning the surface electronic properties of hydrogenated polycrystalline diamond films through oxygen functionalization. The hydrogenated diamond (HD) surface transforms from hydrophobic to hydrophilic nature and the sheet resistance increases from ~8 kΩ/sq. to over 10 GΩ/sq. with progressive ozonation. The conductive atomic force microscopic (c-AFM) studies reveal preferential higher current conduction on selective grain interiors (GIs) than that of grain boundaries confirming the surface charge transfer doping on these HDs. In addition, the local current conduction is also found to be much higher on (111) planes as compared to (100) planes on pristine and marginally O-terminated HD. However, there is no current flow on the fully O-terminated diamond (OD) surface. Further, X-ray photoelectron spectroscopic (XPS) studies reveal a redshift in binding energy (BE) of C1s on pristine and marginally O-terminated HD surfaces indicating surface band bending whilst the BE shifts to higher energy for OD. Moreover, XPS analysis also corroborate c-AFM study for the possible charge transfer doping mechanism on the diamond films which results in high current conduction on GIs of pristine and partially O-terminated HDs.

Quality assessment of needle coke used in the production of graphite electrodes for metallurgical furnaces

Needle coke is a special kind of carbon material that has a developed anisotropic fibrous structure, high current conductivity in the fiber direction and low coefficient of linear thermal expansion. This material has found a wide application in steel industry where it is used for the production of graphite electrodes of the SHP (50–75 kA) and UHP (up to 100 kA) grades designed for high-power electric arc furnaces. This paper describes the results of assessing the quality of the needle coke that is commercially used at El 6 for the production of carbon and graphite products. The quality of the material was analyzed based on two groups of techniques: spectral analysis (SEM and optical microscopy, XRD, Raman spectroscopy) and analysis of physical and chemical properties (CTE, real density, sulfur, ash, moisture, electrical resistivity). A study and a comparative analysis were carried out using seven samples of calcined petroleum and pitch needle cokes. Six of them are used commercially (imported) and one was produced in laboratory conditions from Russian raw materials. The study confirmed that a better needle coke structure tends to form from petroleum coke versus pitch coke. Using the results of spectral analysis, the studied samples of needle cokes were classified into three groups based on their morphology and structure, which correlates with the results of the analysis that looked at their physical and chemical properties. The combination of research and data processing techniques presented in the paper ensures a comprehensive analysis of the studied needle coke and suggests that the material in view can be used in the production of graphite electrodes.The authors would like to thank Evgeny S. Gorlanov, deputy director of the Research Center for the Problems of Processing Mineral and Man-Made Resources at Saint Petersburg Mining University, and Andrey L. Kvanin, who oversees research and engineering projects at El 6, for their valuable advice and assistance in preparing this paper.This research was carried out as part of the State Assignment 0792-2020-0010 by the Ministry of Education and Science of the Russian Federation: Elaborating the innovative technologies of processing heavy hydrocarbons into environmentally friendly motor fuels and new carbon materials with controllable macro- and microstructures of the mesophase”.

Ceria Boosting on In Situ Nitrogen-Doped Graphene Oxide for Efficient Bifunctional ORR/OER Activity.

In the present work, a highly efficient and excellent electrocatalyst material for bifunctional oxygen reduction/evolution reaction (ORR/OER) was synthesized using the microwave-assisted hydrothermal method. In brief, ultrafine hexagonal cerium oxide (CeO2) nanoparticles were tailored on the layered surface of in situ nitrogen-doped graphene oxide (NGO) sheets. The nanocomposites exhibited a high anodic onset potential of 0.925 V vs. RHE for ORR activity and 1.2 V for OER activity with a very high current density in 0.5 M KOH. The influence of oxygen cluster on Ce3+/Ce4+ ion decoration on outward/inward in situ nitrogen-coupled GO enhanced the physicochemical properties of composites and in turn increased electron transferability. The microwave-assisted hydrothermal coupling technique provides a higher density, active sites on CeO2@NGO composites, and oxygen deficiency structures in ultrafine Ce-O particles and boosts higher charge transferability in the composites. It is believed that the physical states of Ce-N- C, Ce-C=O, and a higher amount of oxygen participation with ceria increase the density of composites that in turn increases the efficiency. N-doped graphene oxide promotes high current conduction and rapid electron transferability while reducing the external transport resistance in oxygen electrocatalysis by sufficient mass transfer through in-built channels. This study may provide insights into the knowledge of Ce-enabled bifunctional activity to guide the design of a robust catalyst for electrochemical performance.

High electrical conductivity and breakdown current density of individual monolayer Ti3C2Tx MXene flakes

High electrical conductivity and breakdown current density of individual monolayer Ti3C2Tx MXene flakes

Engineering of a highly stable metal-organic Co-film for efficient electrocatalytic water oxidation in acidic media

Water oxidation is traditionally performed over IrO2 and RuO2 owing to their high stability at low pH compared to molecular O2 evolution catalysts. The low stability of molecular complexes in acids limits their industrial exploitation as anodes in water-splitting devices, where high current densities and proton conductivity are required. Herein, an existing Co(1,10-phenanthroline)2 complex film is engineered to improve its pH-stability via extra OH substituents on the ligand, i.e. 1,10-phenanthroline-4,7-diol. This novel Co(1,10-phenanthroline-4,7-diol)2 complex film is active for water oxidation at low overpotentials and stable at low pH. Since the calculated water oxidation overpotentials of both complexes are similar, the difference in water oxidation activity is attributed to a smaller charge transfer resistance, which originates from a different anchoring style to the electrode via the OH groups of the ligand. This result is supported by electrochemical impedance measurements. The high pH-stability of the Co(1,10-phenanthroline-4,7-diol)2 film is computationally rationalized by a high crystal formation energy observed in DFT calculations. In summary, an acid-stable and active cobalt-based metal-organic film is reported that competes well with most reported earth-abundant catalysts for water oxidation under similar conditions.

Modification of interface between PEDOT:PSS and perovskite film inserting an ultrathin LiF layer for enhancing efficiency of perovskite light-emitting diodes

Abstract PEDOT:PSS has been widely used in perovskite light-emitting diodes (PeLEDs) due to its high hole current conductivity and work function. However, the unbalanced charge injection and severe exciton quenching in PEDOT:PSS restrict the EL performance of PeLEDs. In this work, a facile interface modification method is introduced in which an ultrathin LiF layer is inserted at the interface between PEDOT:PSS and MAPBBr3 perovskite film. Our results indicate that the inserted ultrathin LiF layer contributes to an efficient interface passivation effect between the PEDOT:PSS layer and the perovskite film, which significantly suppresses both the exciton quenching by the conductive PEDOT chains and the perovskite film defect density at the interface. Moreover, balanced charge injection is realized by adjusting the thickness of the LiF layer, which also serves as an electron blocking layer, in order to preferentially hinder electron current over hole current. Consequently, the optimal PeLED with a 2 nm LiF layer exhibits a significantly decreased turn-on voltage of 2.8 V compared to 4.9 V of the pristine device without a LiF layer, combined with an over 100-fold enhancement in the maximum luminance (10415 cd/m2), current efficiency (12.1 cd/A), and external quantum efficiency (3.5%).

Design of the controller module of mobile carrier radioactive source

A control module for mobile carrier radioactive source has been designed. Mobile carrier radioactive source is a tool used to carry out testing for radiation characteristics both statically and dynamically and to conduct calibration on the Radiation Portal Monitor according to the requirements of SNI IEC 62244-2016. The control module is designed to meet the that requirements, it can set a carrier speed of at least 8 km/h, it can adjust the height of the radioactive source between 1 m and 2.5 m, it has automatic forward and backward direction mode. Furthermore, the mobile carrier can be controlled remotely for personnel tester safety. The control module can stop the mobile carrier suddenly when an emergency occurs. The mobile carrier uses a portable power supply so that it can move freely and easily shifted. To meet these requirements, the driving power of the carrier a motor of 24-volt dc with 250 watts. The radioactive source uses a driving power of 12-volt dc motor with a minimum lift power of 5 kg. The control module designed uses a microcontroller with an android application-based interface that is connected by wireless. In the android application there are virtual numbers and input buttons to give commands to the control module. The application can also receive carrier speed information and the height of the radioactive source. To break the power of driving motor of carrier and the driving power of the lifter of the radioactive source, the mobile carrier uses two-level relays, namely low current conductivity relays and relays with high current conductivity. Next in order to move forward and backward automatically, at each end of the carrier is equipped with a limit switch. The button and top position barriers on the radioactive source lifter use a limit switch.

Bipolar Analog Memristive Switching of In2O3 Using Al Nanoparticles

Aluminum nanoparticles (AlNPs) were embedded into a sol-gel synthesized In₂O₃ thin film by using a combination of thermal evaporation and glancing Angle Deposition technique. Presence of different sizes of aluminum nanoparticles was confirmed from field emission gun scanning electron microscopy. The high-resolution X-ray diffraction confirms the formation of Al₂O₃ NPs by surface oxidation of aluminum nanoparticles. Embedded Metal-Oxide-Semiconductor like device Al/In₂O₃/AlNPs/In₂O₃/p-Si was fabricated, and its memristor behavior was analyzed. The Al/In₂O₃/AlNPs/In₂O₃/p-Si device possessed high current conduction and analog resistive switching as compared to Al/In₂O₃/p-Si device. Significant and consistent memory window up to 150 current (I)-voltage (V) loop was obtained for Al/In₂O₃/AlNPs/In₂O₃/p-Si device between ±6 V applied bias. The Al/In₂O₃/AlNPs/In₂O₃/p-Si device measured high free carrier concentration, i.e., (Nd)~1.93 × 1020 cm-3 calculated from capacitance (C)-Voltage (V) measurement. The memory was retained in accumulation and depletion regions as obtained from the C-V looping curves.

High current carrying and thermal conductive copper-carbon conductors

The surging demand for miniaturized compact devices has generated the need for new metal conductors with high current carrying ampacity, electric and thermal conductivity. Herein, we report carbon-metal conductors that exhibit a high breakdown current density (39% higher than copper) and electrical conductivity (e.g. 63% higher than that of copper at 363 K) in a broad temperature range. The mechanistic studies of thermal conductivity through first-principle modeling show that the multilayer graphene percolation networks efficiently decrease the electron-phonon coupling in the copper-graphene composites, even if phonon modes are activated at a high temperature. These results imply that the copper-based composites have the potential to be the next generation metal conductor with high electrical and thermal conductivity, as well as excellent current-carrying ampacity. More importantly, the developed composite can be deployed in the ink form, making it possible to be utilized by the microelectronic fabrication process.

Sodium distribution at the surface of silicon nitride film after potential-induced degradation test and recovery test of photovoltaic modules

Migration routes of Na ions towards the surface and into SiNx films of Si cells during the potential-induced degradation (PID) test were analyzed by microscale measurements such as X-ray photoelectron spectroscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy, and conductive atomic force microscopy. These measurements showed the appearance of high Na concentrations near the finger electrodes and at the top of texture structures of the SiNx film surface. However, a high current conductivity of SiNx films was observed at halfway between two finger electrodes and at the top of texture structures. These results suggest that focusing of electric fields originating from finger electrodes and the shape of texture structures affected the Na distributions and migration into the SiNx films. The influence of the PID recovery test on the Na ion migration and SiNx films is also discussed in the paper.

Electrical conduction mechanisms and dielectric relaxation in Al2O3 thin films deposited by thermal atomic layer deposition

In the present work, aluminum oxide (Al2O3) thin films were deposited on p-type silicon substrates by thermal atomic layer deposition technique. The structural properties of as-deposited Al2O3 thin films were characterized by grazing-incidence x-ray diffraction and it was determined that the films had an amorphous structure. Electrical transport mechanisms and dielectrical properties of the amorphous Al2O3 thin films were then investigated by fabricating and characterizing Al/Al2O3/p-Si metal–oxide-semiconductor (MOS) capacitors by performing the dc current-voltage and frequency-dependent dielectric measurements. As a function of the applied gate electric fields, the current conduction in low electric fields consists of Schottky emission, but in relatively high electric fields current conduction is dominated by space-charge limited conduction. From the frequency-dependent dielectric measurements, the dielectric loss showed two peaks at the frequencies of 10 kHz and 0.7 MHz which evidence of the dielectric relaxation. The low and high frequency dielectric relaxation behaviors were attributed to space charge polarization and orientation-polarization of dipoles, respectively. It was concluded that defects related localized states in the Al2O3 films may contribute to dielectric properties at high frequency.

Evaluation of SiC Schottky Diodes Using Pressure Contacts

The thermomechanical reliability of SiC power devices and modules is increasingly becoming of interest especially for high-power applications, where power cycling performance is critical. Press-pack assemblies are a trusted and reliable packaging solution that has traditionally been used for high-power thyristor-based applications in FACTS/HVDC, although press-pack IGBTs have become commercially available more recently. These press-pack IGBTs require antiparallel PiN diodes for enabling reverse conduction capability. In these high-power applications, paralleling chips for high current conduction capability is a requirement, hence, electrothermal stability during current sharing is critical. SiC Schottky diodes not only exhibit the advantages of wide bandgap technology compared to silicon PiN diodes, but they have significantly lower zero temperature coefficient (ZTC), meaning they are more electrothermally stable. The lower ZTC is due to the unipolar nature of SiC Schottky diodes as opposed to the bipolar nature of PiN diodes. This paper investigates the implementation and reliability of SiC Schottky diodes in press-pack assemblies. The impact of pressure loss on the electrothermal stability of parallel devices is investigated.

Microstructural Transformation during Dissimilar Friction Stir Welding (FSW) of Aluminum-Cooper Alloys

This paper presents some results obtained in Friction Stir Welding (FSW) of aluminum and cooper alloys, as a result of joint researches carried out in University Politehnica Timisoara and National R&D Institute for Welding and Material Testing – ISIM Timisoara. Microstructural investigations revealed a nugget zone well defined, in which the two materials are well mixed and adjacent zones (thermos-mechanically affected zones) in which thin vanes from one material is mixed into the other material. SEM and EDX analysis revealed the blending of the two materials which provides good continuity of the welded joint. The tool and welding technology developed during the researches provides a good quality FSW welded joint. which will give the possibility to engineer components with high electric current conductivity and in the same time low weight, needed by the automotive industry in developing the new generation of electric vehicles.

High Current Density and Low Thermal Conductivity of Atomically Thin Semimetallic WTe2.

Two-dimensional (2D) semimetals beyond graphene have been relatively unexplored in the atomically thin limit. Here, we introduce a facile growth mechanism for semimetallic WTe2 crystals and then fabricate few-layer test structures while carefully avoiding degradation from exposure to air. Low-field electrical measurements of 80 nm to 2 μm long devices allow us to separate intrinsic and contact resistance, revealing metallic response in the thinnest encapsulated and stable WTe2 devices studied to date (3-20 layers thick). High-field electrical measurements and electrothermal modeling demonstrate that ultrathin WTe2 can carry remarkably high current density (approaching 50 MA/cm(2), higher than most common interconnect metals) despite a very low thermal conductivity (of the order ∼3 Wm(-1) K(-1)). These results suggest several pathways for air-stable technological viability of this layered semimetal.

Reduced Graphene Oxide Films with Ultrahigh Conductivity as Li-Ion Battery Current Collectors.

Solution processed, highly conductive films are extremely attractive for a range of electronic devices, especially for printed macroelectronics. For example, replacing heavy, metal-based current collectors with thin, light, flexible, and highly conductive films will further improve the energy density of such devices. Films with two-dimensional building blocks, such as graphene or reduced graphene oxide (RGO) nanosheets, are particularly promising due to their low percolation threshold with a high aspect ratio, excellent flexibility, and low cost. However, the electrical conductivity of these films is low, typically less than 1000 S/cm. In this work, we for the first time report a RGO film with an electrical conductivity of up to 3112 S/cm. We achieve high conductivity in RGO films through an electrical current-induced annealing process at high temperature of up to 2750 K in less than 1 min of anneal time. We studied in detail the unique Joule heating process at ultrahigh temperature. Through a combination of experimental and computational studies, we investigated the fundamental mechanism behind the formation of a highly conductive three-dimensional structure composed of well-connected RGO layers. The highly conductive RGO film with high direct current conductivity, low thickness (∼4 μm) and low sheet resistance (0.8 Ω/sq.) was used as a lightweight current collector in Li-ion batteries.

Structure oriented compact model for advanced trench IGBTs without fitting parameters for extreme condition: Part II

Compact model for expressing turn-off waveform for advanced trench gate IGBTs is proposed even under high current density condition. The model is analytically formulated only with device structure parameters so that no fitting parameters are required. The validity of the model is confirmed with TCAD simulation for 1.2–6.5kV class IGBTs. The proposed turn-off model is sufficiently accurate to calculate trade-off curve between turn-off loss and saturation collector voltage under extremely high current conduction, so that the model can be used for system design with the advanced trench gate IGBTs.

Current–voltage characteristics and fast imaging of HPPMS plasmas: transition from self-organized to homogeneous plasma regimes

Current–voltage characteristics within the temporal pulse were recorded in high-power pulsed magnetron sputtering discharges for different target materials. These curves allowed identifying at a first glance the existence of separated plasma regimes clearly differentiated by the plasma conductivity and by the spatial arrangement of the plasma emission. We could establish that regimes of high plasma conductivity are univocally associated to the self-organization of the plasma in well-defined ionization zones. As the applied power is gradually increased, the high conductivity regime is abruptly replaced by a regime of high current and low plasma conductivity, associated to homogeneous plasma emission.

Fabrication of a SiC Double Gate Vertical Channel JFET and It's Application in Power Electronics

The fabrication process of an innovative epitaxial trench JFET with vertical channel and double gate control is reviewed. Due to the excellent doping and thickness control of the epitaxial re-growth techniques, the sub-micron channel can be tailored for normally-on and -off operation. Due to the vertical channel design the epitaxial trench JFETs have narrow cell pitch for high-density power integration and high saturation current capabilities. The excellent performance of these fabricated and packaged JFET devices is demonstrated with on-wafer measurements and power switching tests. High current conduction tests are performed at room temperature and elevated temperatures of 125{degree sign}C with switching frequencies of 30 kHz and 200 kHz.