There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Wide bandgap semiconductors show superior material properties enabling potential power device operation at higher temperatures, voltages, and switching speeds than current Si technology. As a result, a new generation of power devices is being developed for power converter applications in which traditional Si power devices show limited operation. The use of these new power semiconductor devices will allow both an important improvement in the performance of existing power converters and the development of new power converters, accounting for an increase in the efficiency of the electric energy transformations and a more rational use of the electric energy. At present, SiC and GaN are the more promising semiconductor materials for these new power devices as a consequence of their outstanding properties, commercial availability of starting material, and maturity of their technological processes. This paper presents a review of recent progresses in the development of SiC- and GaN-based power semiconductor devices together with an overall view of the state of the art of this new device generation.

A Survey of Wide Bandgap Power Semiconductor Devices

High-frequency-link (HFL) power conversion systems (PCSs) are attracting more and more attentions in academia and industry for high power density, reduced weight, and low noise without compromising efficiency, cost, and reliability. In HFL PCSs, dual-active-bridge (DAB) isolated bidirectional dc-dc converter (IBDC) serves as the core circuit. This paper gives an overview of DAB-IBDC for HFL PCSs. First, the research necessity and development history are introduced. Second, the research subjects about basic characterization, control strategy, soft-switching solution and variant, as well as hardware design and optimization are reviewed and analyzed. On this basis, several typical application schemes of DAB-IBDC for HPL PCSs are presented in a worldwide scope. Finally, design recommendations and future trends are presented. As the core circuit of HFL PCSs, DAB-IBDC has wide prospects. The large-scale practical application of DAB-IBDC for HFL PCSs is expected with the recent advances in solid-state semiconductors, magnetic and capacitive materials, and microelectronic technologies.

Overview of Dual-Active-Bridge Isolated Bidirectional DC–DC Converter for High-Frequency-Link Power-Conversion System

This paper proposes a novel dual-phase-shift (DPS) control strategy for a dual-active-bridge isolated bidirectional DC-DC converter. The proposed DPS control consists of a phase shift between the primary and secondary voltages of the isolation transformer, and a phase shift between the gate signals of the diagonal switches of each H-bridge. Simulation on a 600-V/5-kW prototype shows that the DPS control has excellent dynamic and static performance compared to the traditional phase-shift control (single phase shift). In this paper, the concept of ldquoreactive powerrdquo is defined, and the corresponding equations are derived for isolated bidirectional DC-DC converters. It is shown that the reactive power in traditional phase-shift control is inherent, and is the main factor contributing to large peak current and large system loss. The DPS control can eliminate reactive power in isolated bidirectional DC-DC converters. In addition, the DPS control can decrease the peak inrush current and steady-state current, improve system efficiency, increase system power capability (by 33%), and minimize the output capacitance as compared to the traditional phase-shift control. The soft-switching range and the influence of short-time-scale factors, such as deadband and system-level safe operation area, are also discussed in detail. Under certain operation conditions, deadband compensation can be implemented easily in the DPS control without a current sensor.

/pdf/eliminate-reactive-power-and-increase-system-efficiency-of-3j7gowjzlm.pdf

Eliminate Reactive Power and Increase System Efficiency of Isolated Bidirectional Dual-Active-Bridge DC–DC Converters Using Novel Dual-Phase-Shift Control

This article reviews recent advances and developments in the field of wearable sensors with emphasis on a subclass of these devices that are able to perform highly-sensitive electrochemical analysis Recent insights into novel fabrication methodologies and electrochemical techniques have resulted in the demonstration of chemical sensors able to augment conventional physical measurements (ie heart rate, EEG, ECG, etc), thereby providing added dimensions of rich, analytical information to the wearer in a timely manner Wearable electrochemical sensors have been integrated onto both textile materials and directly on the epidermis for various monitoring applications owing to their unique ability to process chemical analytes in a non-invasive and non-obtrusive fashion In this manner, multi-analyte detection can easily be performed, in real time, in order to ascertain the overall physiological health of the wearer or to identify potential offenders in their environment Of profound importance is the development of an understanding of the impact of mechanical strain on textile- and epidermal (tattoo)-based sensors and their failure mechanisms as well as the compatibility of the substrate employed in the fabrication process We conclude this review with a retrospective outlook of the field and identify potential implications of this new sensing paradigm in the healthcare, fitness, security, and environmental monitoring domains With continued innovation and detailed attention to core challenges, it is expected that wearable electrochemical sensors will play a pivotal role in the emergent body sensor networks arena

Wearable Electrochemical Sensors and Biosensors: A Review

With efforts to reduce the cost, size, and thermal management systems for the power electronics drivetrain in hybrid electric vehicles (HEVs) and plug-in hybrid electric vehicles (PHEVs), wide band gap semiconductors including silicon carbide (SiC) have been identified as possibly being a partial solution. Research on SiC power electronics has shown their higher efficiency compared to Si power electronics due to significantly lower conduction and switching losses. This paper focuses on the development of a high power module based on SiC JFETs and Schottky diodes. Characterization of a single device, a module developed using the same device, and finally an inverter built using the modules is presented. When tested at moderate load levels compared to the inverter rating, an efficiency of 98.2% was achieved by the initial prototype.

/pdf/high-power-sic-modules-for-hevs-and-phevs-1vw17raggb.pdf

High power SiC modules for HEVs and PHEVs

The purpose of this research is to assess the reliability of Ag-In joints in thermal cycling (TC) environment. Si chips and Cu substrates were bonded using silver (Ag) and indium (In) multilayer structure without applying any flux. After bonding, the samples were annealed in air at 250 °C for 190 h to convert the joint into an alloy of small intermetallic grains and solid solution (Ag). The resulting joint has a melting temperature higher than 800 °C. Si-Cu pair was chosen because of the large coefficient of thermal expansion mismatch, i.e., 2.7 × 10-6/°C of Si versus 17 × 10-6/°C of Cu. Two TC tests were performed. All 10 samples passed 100 cycles of initial TC test between -40 °C and 85 °C. They were then subjected to 5000 cycles of TC test between -40 °C and 200 °C. Seven of ten samples survived beyond 5000 cycles. Three samples broke at 850, 2600, and 3000 cycles, respectively. The early failure was probably caused by imperfections and defects in the joints. Based upon these results, it seems that our Ag-In joints compare favorably with sintered silver joints. The Ag-In joints not only have high-melting temperature but also survive harsh TC environment.

http://ieeexplore.ieee.org/iel7/5503870/6889140/06868954.pdf

Thermal Cycling Reliability Study of Ag–In Joints Between Si Chips and Cu Substrates Made by Fluxless Processes

Wafer warpage is one of the most important challenges in the fabrication of modern electronic devices. Other challenges include handling, tool faults, and misalignments and even wafer breakage. The wafer warpage translates into die warpage that has a remarkable impact on die pick, stack and attach. This paper describes the work performed to simulate the silicon wafer warpage as a function of the wafer thickness and the film stresses using the commercial finite element code ABAQUS. The model accounts for the silicon anisotropy to better simulate the deformation. The computed values of the warpage were compared with experimental data and showed good correlation. The numerical model developed can be used to better understand the relation between the film stress and the wafer warpage. Furthermore it can be used to predict the warpage based on the wafer thickness and the film stress, which can help mitigate the warpage by depositing films to reduce the overall wafer warpage.

Numerical simulation of silicon wafer warpage due to thin film residual stresses

The circuit boards of many mixed-signal and digital systems are now dominated by individually placed discrete passive (DP) components. This article looks at thin-film integrated passives (IPs) as an alternative to DPs in the effort to save board space and improve electrical performance and system reliability. Integrated passive components have been utilized successfully with ceramic substrate technology for over 50 years in the form of thick-film resistive and dielectric firable pastes. However, this considerable infrastructure cannot be transferred to FR4 and flex substrates due to the high firing temperatures required, and these board materials make up the vast majority of interconnect substrates, in consumer and commercial systems. Mmat has been lacking is thin-film IP materials and fabrication processes that are compatible with organic boards.

Getting aggressive with passive devices

Spray cooling is a high flux heat removal technique considered for systems dissipating high power within small areas such as advanced lasers. Recently Selvam and Ponnappan (2004 & 2005) identified the importance of modeling heat transfer in a thin liquid film on a hot surface at the micro level and illustrated how this micro level modeling could help to improve the macro level spray cooling. The goal of this research is to advance the theoretical understanding of spray cooling to enable efficient system level hardware designs. Two-phase flow modeling is done using the level set method to identify the interface of vapor and liquid. The modifications made to the incompressible Navier-Stokes equations to consider surface tension and phase change are presented. The equations are solved using the finite difference method. The effect of liquid droplet impact on a 40 μm thick liquid film containing vapor bubble and the consequent heat removal is explained with a sequence of temperature vs. time contours. From that, the importance of fast transient conduction in the liquid film leading to high heat flux in a short time is illustrated. The optimum positioning of the droplet with respect to the vapor bubble for effective heat removal is also systematically investigated. This information is expected to help in proper positioning of the droplet in three-dimensional modeling.Copyright © 2005 by ASME

Fred Barlow

Papers

High power SiC modules for HEVs and PHEVs

Thermal Cycling Reliability Study of Ag–In Joints Between Si Chips and Cu Substrates Made by Fluxless Processes

Numerical simulation of silicon wafer warpage due to thin film residual stresses

Getting aggressive with passive devices

Computer Modeling of Liquid Droplet Impact on Heat Transfer During Spray Cooling