High Current Capability Research Articles

(Invited) The Application of Advanced Sige Complementary Bipolar Technologies to High Speed and High-Precision Applications

SiGe has rapidly grown to a mature process technology addressing a broad array of applications. Most of the literature discussing these applications focuses on RF circuits and very high-speed data links; both take advantage of the high switching speed, low noise, and current handling capabilities afforded by SiGe transistors. The addition of germanium into a silicon bipolar junction transistor (BJT) technology allows the component engineer to optimize different parameters. These applications usually force the focus on Ft or Fmax. While these are also important in the design of precision circuits and or high linearity amplifiers, current gain (Hfe) and Early voltage (Va) are often design limitations that force use of more complex circuits. Additionally, usually only NPN transistors are available which can significantly complicate the design of critical analog building blocks. SiGe in fact provides significant performance boost to PNP transistors and in the last couple of decades complementary SiGe BJT processes are offered by several major semiconductor manufacturers. Although generally the focus has been on relatively low voltage devices with Bvceos of significantly less than 5V, SiGe can also be applied to the design of much higher voltage transistors with a significant boost in performance. Many integrated circuits are built in such complementary SiGe Bipolar technologies and offer significant advantages over equivalent devices built in more conventional processes. To address low voltage applications, we will discuss how complementary SiGe can be applied to the design of a high-speed 16bit analog to digital convertor (ADC) and the design of a special buffer amplifier developed to condition the signal fed to such ADCs. Higher voltage (+/-15V supplies) precision amplifiers are still a significant market and have warranted the development of specialized complementary SiGe technologies. We will work through the design of a typical amplifier and show how the improved transistors lead to better end-product performance. Feedback amplifiers are generally easier to stabilize if there are fewer gain stages. Compensation techniques are available to stabilize complex amplifier designs which generally sacrifice performance. The increased gain offered by SiGe BJTs compared to alternatives can reduce the number of gain stages needed to meet a specific specification. The availability of a complementary PNP transistor can also significantly simplify circuit design. The combination of the gain of the SiGe BJT (due to high Va and Hfe) together with the simplicity and symmetry offered by complementary bipolar circuit design enables the design of very high performance operational amplifiers. We will detail an ampliier designed for very high performance portable audio applications. The combination of high Early Voltage and high Beta allows for a simple, single gain stage implementation, which results in low quiescent power, high capacitive load drive and high PSRR. The high beta and Ft of the SiGe transistors make this performance possible at low quiescent power.

Metacapacitors: Printed Thin Film, Flexible Capacitors for Power Conversion Applications

The Metacapacitors project aims to improve efficiency, functionality and form factor of offline power converters suitable for LED solid-state lighting, with a view to developing an attractive technology platform for load management and power conversion across a broad range of applications. Based on integrated switched-capacitor (SC) topologies, the project adopts an integrated approach from materials to devices to circuits. We designed capacitors based on high- $\kappa$ dielectric nanocrystals, that can be prepared using high-throughput microfabrication/nanotechnology techniques, ink deposition and multilayering. The capacitor dielectric, a nanocomposite composed of (Ba, Sr)TiO $_{3}$ nanocrystals in polyfurfuryl alcohol (BST/PFA, $\kappa$ $ > 20$ , $100 \text{Hz}$ – $1 \text{MHz}$ , loss $ , $20 \text{kHz}$ ), targets a high volumetric capacitance density and ripple current capability. The Dielectric is demonstrated to function in a finished capacitor $ > \! 1000 \text{h}$ at $125 ^\circ \text{C}$ . The capacitors were board integrated with a custom hybrid-switched-capacitor-resonant dc–dc converter IC. The converter integrates a balanced SC front-end with a series resonant tank, enabling nearly lossless current regulation and tranformerless galvanic isolation. The converter IC can be stacked in the voltage domain to interface a range of inputs. The tested driver delivers about $ 15\;\text{W}$ at $ 470\;\text{mA}$ to a string of $ 12$ LEDs with $ 90\%$ peak efficiency.

Microwave-Assisted Synthesis of Silver Vanadium Phosphorus Oxide, Ag2VO2PO4: Crystallite Size Control and Impact on Electrochemistry

Silver vanadium phosphorus oxide, Ag2VO2PO4, is a promising cathode material for Li batteries due in part to its large capacity and high current capability. Herein, a new synthesis of Ag2VO2PO4 based on microwave heating is presented, where the reaction time is reduced by approximately 100× relative to other reported methods, and the crystallite size is controlled via synthesis temperature, showing a linear correlation of crystallite size with temperature. Notably, under galvanostatic reduction, the Ag2VO2PO4 sample with the smallest crystallite size delivers the highest capacity and shows the highest loaded voltage. Further, pulse discharge tests show a significant resistance decrease during the initial discharge coincident with the formation of Ag metal. Thus, the magnitude of the resistance decrease observed during pulse tests depends on the Ag2VO2PO4 crystallite size, with the largest resistance decrease observed for the smallest crystallite size. Additional electrochemical measurements indicate a qua...

Three-Phase Bidirectional DC/DC Converter With Six Inverter Legs in Parallel for EV Applications

The success of electric vehicles (EVs) greatly depends on battery size, cost, lifetime, and capacity. The battery capacity of EVs has to contain enough energy to allow EV users to drive, at least, the minimum distance that internal combustion engine vehicles take. However, even with very efficient EVs and combining all the available highly efficient EV technologies, the battery capacity still needs to be large. Thus, one alternative to reduce the battery size is to improve the charging infrastructure by implementing sufficient public/private fast-charging locations, which will significantly increase the EV driving range with relatively low battery capacities. However, this kind of infrastructure requires charging with higher current capability, due to the high power levels involved in the fast-charging process. In this paper, a bidirectional dc/dc converter with six inverter legs connected to a three-phase output is proposed. The converter is similar to a three-phase dual-active-bridge (DAB) converter with more inverter legs in parallel. These additional inverter legs increase the converter current capability, without affecting the DAB main characteristics, preserving similar modulation techniques and DAB advantages. An accurate study about the proposed topology is carried out in this paper, and simulations and experimental results are shown for a 20-kW prototype, validating the theoretical analysis.

Reverse blocking IGCT optimised for 1 kV DC bi‐directional solid state circuit breaker

This study presents the simulation and experimental results of the newly developed 2.5 kV reverse blocking-integrated gate commutated thyristor (RB-IGCT) which has been designed and optimised to have very low conduction losses and high turn-off current capability for DC solid state circuit breaker (SSCB) applications. The device has been optimised through anode engineering, thickness and resistivity to achieve the required blocking capability of 2.5 kV and to have very low conduction losses below 1 kW at 1 kA, that is, the on-state voltage drop is as low as 0.9 V at 1 kA. This study also presents the simulation and experimental results at the system level including the influence of the surge arrester (SA) which is connected in parallel to the RB-IGCT to clamp the overvoltage and to absorb the energy stored in the system inductance at the current interruption. The influence of different voltage rating SAs and parallel combination of SAs on the switching behaviour of the RB-IGCT has been investigated. A bi-directional SSCB for 1 MW application based on 2.5 kV RB-IGCT has been built successfully. The device simulations show that the results are in good agreement with the measurement results both at the device and system levels.

Parallel Connected 12 Pulse Rectifier using Inter Phase Transformer

This paper presents simulation and analysis of twelve pulse rectifier transformer unit configured in series and also in parallel to have higher current capability and reduced harmonics, which creates the current imbalance and hence circulating current can be observed with parallel connection. Balanced current can be achieved with the introduction of Inter Phase Transformer (IPT) while paralleling two six pulse rectifier in rectifier transformer unit. PSCAD is used for performing all the simulations.

Electrode Erosion Characteristics of Repetitive Long-Life Gas Spark Switch Under Airtight Conditions

With the rapid developments in pulse power technology, the gas spark switch has broadened its application in both industrial fields and research fields, such as the extraction of unconventional gas resources and underwater electrical wire explosion. Thus, the repetitive switch needs high current capability, small breakdown voltage variance, and long lifetime in an airtight cavity. The performances of the switch directly influence the output characteristics of the system, but electrode erosion is inevitable, which may decrease the self-breakdown voltage and the lifetime. The purpose of this paper was to investigate the electrode erosion characteristics under adverse conditions. The cathode showed a worse erosion surface. Compared with the central zone of the electrodes, the outer zone showed a worse surface roughness for both the cathode and the anode.

Ruggedness of 1200 V SiC MPS diodes

SiC merged-pin-Schottky (MPS) diodes possess fast switching ability combined with low losses. Compared to conventional Schottky diodes they also provide a high surge current capability making them rugged against surge current pulses of more than seventeen times the rated current for a 10ms half-sine pulse. In this paper further aspects of device ruggedness are presented such as the surge current capability of two diodes in parallel and the turn-off behavior at application condition and at overcurrent. It was found that the turn-off characteristics are almost independent from the applied voltage. Further, the diode could withstand turn-off from fifteen times the rated current.

Mixed Metal Phosphorous Oxides: Prospects for Secondary Lithium Based Batteries

Cathode materials containing phosphate have met with success in lithium based batteries, with a notable example being lithium iron phosphate, LiFePO4. A recent focus for our research has been the investigation of bimetallic phosphates (MM’PxOy, where Mn+ = Ag, Cu), motivated by the desire to obtain the stability observed in phosphate based cathode materials and the opportunity for multiple electron transfers per formula unit due to the bimetallic composition of the materials. Our initial electrochemical studies focused on Ag2VO2PO4 where the material provided a discharge capacity of 272 mAh/g and high current pulse capability. In-situ formation of silver nanoparticles upon initiation of reduction was accompanied by a 15,000 fold increase in cathode conductivity. Our paradigm of current enhancement via reduction displacement was in evidence. An alternate composition Ag0.48VOPO4 material with lower silver content per formula unit shows a high operating voltage and characteristic multi-plateau voltage profile. Counter to Ag2VO2PO4, the reduction of Ag+ to Ag0 occurs later in the discharge process for Ag0.48VOPO4. Based on the delayed reduction of silver, we hypothesized that the MVOPO4 material class may demonstrate improved reversibility relative to the AgVO2PO4 system. The MVOPO4 material is explored for secondary lithium based battery applications. The electrochemistry of the analogous silver and copper containing MVOPO4 materials will be compared and contrasted in this presentation. The inclusion of copper instead of silver in the structure is motivated by lower cost of copper versus silver and the accessibility of divalent Cu2+ which can provide 2 electron equivalents per metal center. However, the silver containing material offers the advantage of higher operating voltage. The electrochemistry will be summarized in the context of prior work other members of the MM’PxOy and MM’O material families.

Preliminary failure-mode characterization of emerging direct-lead-bonding power module. Comparison with standard wire-bonding interconnection

Direct-lead-bonding (DLB) and wire-bonding, in epoxy-moulded package, are compared in terms of functional characteristics, failure-mode and post-fault high-current capability of a dual-chip power module (PM), with respect to I2T and critical energy. Wire-bonding power modules have shown poor thermal behaviour, a high and unstable RCE (the chip fault residual resistance), and sometimes a fuse-effect when used in gel-filled power modules. However, DLB power modules demonstrated a very good thermal and electrical behaviour, a very low and stable RCE under high energy failure. After non-destructive defect localization thanks to Lock-In Thermography coupled to RX tomography, the authors were able to confirm the formation of a metallic bridge under wire-bondings and through the chips and solder in DLB, which explains low RCE values for this technology. The DLB interconnection appears to be a promising technology for power module. Nevertheless, the absence of wire-fuse-effect in case of extreme failure, compared to classical wire-bonding, leads the authors to rethink fail-safe and fault-tolerant strategies for critical converter.

4H-SiC VJFETs with Self-Aligned Contacts

Trenched-implanted-gate 4H–SiC vertical-channel JFET (TI-VJFET) have been fabricated with self-aligned nickel silicide source and gate contacts using a process sequence that greatly reduces process complexity as it includes only four lithography steps. The effect of the channel geometry on the electrical characteristics has been studied by varying its length (0.3 and 1.2μm) and its width (1.5-5μm). The transistors exhibited high current handling capabilities (Direct Current density 330A/cm2). The output current reduces with the increase of the measurements temperature due to the decrease of the electron mobility value. The voltage breakdown exhibits a triode shape, which is typical for a static-induction transistor operation.

1-D and 2-D Nanocontacts for Reliable and Efficient Terahertz Photomixers

New types of continuous-wave (CW) terahertz (THz) photomixers were fabricated using 1-D and 2-D nanocontacts on low-temperature-grown (LTG) GaAs as well as nitrogen-ion-implanted $({\rm N}^{+}{\rm i})$ GaAs. The 1-D and 2-D nanocontacts were formed by silver nanowires and graphene sheets, respectively. A silver nanowire (Ag-NW) with a physical diameter of $\varnothing \hbox{60 nm}$ and $\varnothing \hbox{120 nm}$ can handle currents of $>\! \hbox{10}$ and $>\! \hbox{30 mA}$ , respectively, without electromigration, thus enabling reliable high photocurrents. The small diameter of such a nanowire electrode in 1-D photomixers reduces the device capacitance by a factor of more than ten compared with photomixers with conventional interdigital fingers. Thus, these nanowire properties can be used for the fabrication of photomixers with cut-off frequencies $>\hbox{2 THz}$ and with extremely reliable operation. A multilayer graphene (MLG) of 6–8 layers shows unique properties with high short-circuit current capabilities of $>\hbox{9 mA/(10}~\mu \hbox{m width})$ and reliable high photocurrents. Furthermore, the MLG absorbs only 2.3% of white light and is ideal as a transparent nanocontact. The use of these graphene electrodes in 2-D photomixers allows an efficient optical power illumination for high photocurrent generation and shows the potential for reliable CW THz emission. Initial THz measurements confirmed the high possibilities of these new nanocontact photomixers.

열전지 양극용 FeS2분말의 성형성에 미치는 Li2O 첨가 및 열처리의 효과

<TEX>$FeS_2$</TEX> has been widely used for cathode materials in thermal battery because of its high stability and current capability at high operation temperature. Salts such as a LiCl-KCl were added as a binder for improving electrical performance and formability of <TEX>$FeS_2$</TEX> cathode powder. In this study, the effects of the addition of <TEX>$Li_2O$</TEX> in LiCl-KCl binder on the formability of <TEX>$FeS_2$</TEX> powder compact were investigated. With the increasing amount of <TEX>$Li_2O$</TEX> addition to LiCl-KCl binder salts, the strength of the pressed compacts increased considerably when the powder mixture were pre-heat-treated above <TEX>$350^{\circ}C$</TEX>. The heat-treatment resulted in promoting the coating coverage of <TEX>$FeS_2$</TEX> particles by the salts as <TEX>$Li_2O$</TEX> was added. The observed coating as <TEX>$Li_2O$</TEX> addition might be attributed to the enhanced wettability of the salt rather than its reduced melting temperature. The high strength of compacts by the <TEX>$Li_2O$</TEX> addition and pre-heat-treatment could improve the formability of <TEX>$FeS_2$</TEX> raw materials.

400-A (Pulsed) Vertical GaN p-n Diode With Breakdown Voltage of 700 V

There is a great interest in monolithic GaN semiconductor devices with high current capability for power electronics. In this letter, large area vertical GaN p-n diodes fabricated on bulk GaN substrates are discussed. Diodes with areas as large as 16 ${\rm mm}^{2}$ with breakdown voltages exceeding 700 V and pulsed (100 $\mu{\rm s}$ ) currents approaching 400 A are reported. This is made possible for the first time in part due to the recent availability of improved quality bulk GaN substrates.

Fabrication of Carbon Nanotubes and Investigating the Characteristics

nanotubes (CNT) are the fantastic nano-material which exhibits a very low thermal expansion and high current capability. It has a wide variety of methods for synthesis. One of the most reliable and best suited is Arc Discharge method. Multi walled CNT (MWCNT) are synthesized in an experimental setup. Soot deposited is in mixture form of nanoparticles and hence it is purified and MWCNT are separated and collected. XRD analysis and TEM images are taken for CNT. MWCNT are coated on the silica substrate through DIP coating. Dispersion of CNT is handled and the resistivity and morphology of cnt dip coated are studied. The change in resistivity is determined by the graph plotted through Four Point Probe method. Investigation concludes that the MWCNT developed is suitable for contacts in transistors and miniature sensors for fabrication due to its low resistivity.

In‐situ Stabilization of Tin Nanoparticles in Porous Carbon Matrix derived from Metal Organic Framework: High Capacity and High Rate Capability Anodes for Lithium‐ion Batteries

AbstractIt is a formidable challenge to arrange tin nanoparticles in a porous matrix for the achievement of high specific capacity and current rate capability anode for lithium‐ion batteries. This article discusses a simple and novel synthesis of arranging tin nanoparticles with carbon in a porous configuration for application as anode in lithium‐ion batteries. Direct carbonization of synthesized three‐dimensional Sn‐based MOF: [K2Sn2(1,4‐bdc)3](H2O) (1) (bdc = benzenedicarboxylate) resulted in stabilization of tin nanoparticles in a porous carbon matrix (abbreviated as Sn@C). Sn@C exhibited remarkably high electrochemical lithium stability (tested over 100 charge and discharge cycles) and high specific capacities over a wide range of operating currents (0.2–5 Ag–1). The novel synthesis strategy to obtain Sn@C from a single precursor as discussed herein provides an optimal combination of particle size and dispersion for buffering severe volume changes due to Li‐Sn alloying reaction and provides fast pathways for lithium and electron transport.

Excellent Performance of Few‐Layer Borocarbonitrides as Anode Materials in Lithium‐Ion Batteries

Borocarbonitrides (BxCyNz) with a graphene-like structure exhibit a remarkable high lithium cyclability and current rate capability. The electrochemical performance of the Bx Cy Nz materials, synthesized by using a simple solid-state synthesis route based on urea, was strongly dependent on the composition and surface area. Among the three compositions studied, the carbon-rich compound B0.15C0.73N0.12 with the highest surface area showed an exceptional stability (over 100 cycles) and rate capability over widely varying current density values (0.05-1 A g(-1)). B0.15C0.73N0.12 has a very high specific capacity of 710 mA h g(-1) at 0.05 A g(-1) . With the inclusion of a suitable additive in the electrolyte, the specific capacity improved drastically, recording an impressive value of nearly 900 mA h g(-1) at 0.05 A g(-1) . It is believed that the solid-electrolyte interphase (SEI) layer at the interface of BxCyNz and electrolyte also plays a crucial role in the performance of the BxCyNz .

Design and Evaluation of a High-Frequency LTCC Inductor Substrate for a Three-Dimensional Integrated DC/DC Converter

High operating frequency and integration technique are two main approaches to achieve high power density for the switching mode power supply. The emerging gallium nitride (GaN)-based power device enables a multimegahertz high-efficiency point-of-load (POL) converter with high current capability. The low-temperature cofire ceramic (LTCC)-based integration technique successfully extends the three-dimensional (3-D) integrated POL module from the low current level to the high current level (>10 A). This paper presents the low-profile LTCC inductor substrate design and evaluation for a multimegahertz 3-D integrated POL converter with large output current. The detailed study about the impact of frequency on the LTCC inductor shows that the high frequency not only shrinks the volume of the inductor, but also simplifies the inductor structure. The comparison between the LTCC inductor and the discrete inductor demonstrates that the LTCC inductor dramatically boosts the converter light-load efficiency due to its nonlinear inductance. Because of the low-profile design, the power density of the single-phase POL module with LTCC inductor achieves 1.1 kW/in3 at 5 MHz. The performance of the LTCC inductor can be further improved by the inverse coupling, which results in more than 40% core thickness and core loss reduction. Therefore, the power density of a two-phase integrated POL module is pushed to 1.5 kW/in3, which is around ten times of the power density of state-of-the-art industry products with the same current level.

Design of Digital Interface Circuit of Resolver Based on AD2S1200 in a Single Supply System

For applications of single supply, a digital interface circuit of resolver based on AD2S1200 is designed in a single 5V system. According to the given resolver, the amplification factor and driver capability of excitation signal is calculated and verified. In order to adjust the excitation signals amplitude and provide enough drive current to the resolvers primary winding, an operational amplifier with high current output capability AD8532 is chosen to set an excitation signal buffer circuit which works as a unity gain inverting proportional amplifier. Besides, the design greatly reduces the amount of components which is especially appropriate for the installation in a constriction space. To give a test for the interface circuit, the microcontroller ATmega16 is used to read the 12-bit parallel angle position data of resolver. The test result shows that the interface circuit can not only work well but also obtain an accuracy of angle position within 0.1°.

Some Considerations of the Pulse Power Switch Centered on Thyristor Device

For high energy short pulse discharge applications, like electromagnetic launchers or magnetic forming, mostly the thyristor technology is used. The presented thyristor switch assemblies using 125 mm wafer size are made to switch 62.4MJ stored energy into a load in very short time. The maximum transient peak current of 26 kilo-amperes peak for 20 ms with convection water and air cooling. For this presentation we concentrate on the Thyristor technology as this offer the highest current capability but are not in the position to switch-off any current. Some measures must be used to the pulse switch centered on Thyristor device, i.e., proper selection of the static and dynamic parameters of the thyristor, enough power for triggering the device, and efficient cooling of the device, which can make it possible to produce devices with high blocking voltage combined with very high current handling.