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.

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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

The researchers at Virginia Tech have developed a power packaging strategy which extends the concept of Multichip Modules (MCMs) to high power electronics assemblies dealing with power levels into the Kilowatt range This paper discusses an approach which allows for a high conductivity metal layer for power routing and up to ten layers for signal routing in a single compact module Low power control and interface circuits are integrated into the power module in bare die and packaged form using chip and wire, as well as surface mount attachment techniques Proper thermal management is achieved through the use of Metal Matrix Composite (MMC) heat spreaders and Aluminum Nitride (AlN) substrate materials Three kilowatt half-bridge power converters have been fabricated using both the conventional approach and this packaging concept in order to compare and illustrate the advantages of this concept The scope of this paper will cover the electronic packaging strategy as well as the MCM-L fabrication approach developed by the researchers in the Microelectronics Laboratories at Virginia Tech

Multilayer interconnects for a high power packaging strategy

Causality verification and enforcement is of great importance for performance evaluation of electrical interconnects. We present two techniques based on Kramers-Kronig dispersion relations, also called Hilbert transform relations, and construction of causal periodic continuations. The first method employes periodic polynomial continuations, while the second approach constructs Fourier continuations using a regularized singular value decomposition (SVD) method. Given a transfer function sampled on a bandlimited frequency interval, non-periodic in general, both approaches construct an accurate approximation on the given frequency interval by allowing the function to be periodic on an extended domain. This allows one to significantly reduce (for polynomial continuations) or even completely remove (for Fourier continuations) boundary artifacts that are due to the bandlimited nature of frequency responses. Using periodic continuations eliminates the necessity of approximating the transfer function behavior at ...

Causality Enforcement of High-Speed Interconnects via Periodic Continuations

The researchers in the Microelectronics Laboratory at Virginia Tech have developed a power packaging strategy which utilizes pa ckaging materials to apply a unique multilayer topology design, and extends the concept of Multichip Modules (MCM) to high power electr nics assemblies. This paper discusses the Integrated Power Module (IPM), which consists of a high conductivity metal layer for powe r routing and up to ten layers for signal routing in a single standard compact module. Low power control and interface circuits are inte grated into the power module in bare die form and packaged form using chip and wire, as well as surface mount attachment techniques. Proper th ermal management is achieved through the use of Metal Matrix Composite (MMC) heat spreader and high conductivity substrate materials, the topic of which has been thoroughly discussed by these authors in previous papers. This paper will address the current standard technology to realize power converter packaging design and miniaturization as well as the disadvantages involved with such an approach. Potential solutions to specific design and materials issues will be proposed, th e packaging strategy discussed, the fabrication processes explained, and the concept experimentally validated in the form of a 3kW DC-AC ha lf-bridge power converter.

Integrated power modules (IPMs), a novel MCM approach to high power electronics design and packaging

For embedded resistors in LTCC, the challenge is the high resistance tolerance, normally 20/spl sim/30%. This paper is aimed at modeling and reduction of the tolerance to meet the requirements for high frequency applications; less than 10% resistance tolerance. A mathematical equation for resistance tolerance was derived and experimentally validated. The predicted resistance tolerance agrees with the measured value. With the aid of this equation, resistance tolerance can be related to the tolerance of the print geometry, which is measurable and adjustable prior to firing. It is predicted that for the 10% resistance tolerance goal, print thickness tolerance must be no more than 8%. A comprehensive analysis and step-by-step strategy for tolerance reduction is presented in this work. Some experimental studies have been performed to determine the major factors affecting tolerance. Non-process related factors include resistor size (width and aspect ratio), number of resistor layers in the substrate, location of the resistors on a layer, and printer set-up. As for processing, if the printing is performed in a period of 7 to 17 minutes after paste is applied on the screen, consistent print geometry can be obtained. In addition, a 3-level and 5 factors design of experiments (DOE) shows that the printing parameters, except the low level of squeegee travel, have no significant effect on tolerance of print thickness and width. These results indicate that tolerance control must begin with the design, and include an optimized printer set-up for uniform print thickness across a large printed area. In addition, an appropriate printing process must be used to obtain high resolution rectangular resistors. Through these efforts, 6% to 10% thickness tolerance have been achieved for various print runs and process combinations. Further experiments are underway to evaluate tolerances from high volume production.

Fred Barlow

Papers

Multilayer interconnects for a high power packaging strategy

Causality Enforcement of High-Speed Interconnects via Periodic Continuations

Integrated power modules (IPMs), a novel MCM approach to high power electronics design and packaging

Modeling and control of resistance tolerance for embedded resistors in LTCC

Wideband electrical characterization of mcm materials