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

There is currently an urgent need for electronic devices with superior performance, robustness, smaller size, lower cost, user friendliness, and that do not increase the environmental burden. [ 1 , 2 ] Many materials scientists and engineers have been searching for novel fl exible semiconductive materials as integrated circuits (ICs) to achieve the properties of both fl exibility and stretchability. [ 3– 8 ] Meanwhile, other researchers focus on the substrate materials that cater to the “chip-on-fl ex technologies”, which are in a position of more imperative need in the current industry and consumer market. [ 1 , 9– 11 ] Recently, Siegel et al. demonstrated the feasibility of fabricating electrical circuits on paper for the purpose of foldable and disposable devices, which displays a promising future for the low-cost consumable electronic devices. [ 12 ] Compared to the conventional printed circuit board (PCB) technology, paper offers a few advantages. For example, paper is inexpensive and can decompose easily; it is much thinner than the ordinary PCBs and can be folded, unfolded, and creased easily; electronics based on paper can be stored in smaller spaces or made to form 3D self-standing structures. [ 12 , 13 ] Finally, with the porous and breathable nature, paper can potentially be applied in disposable components for adhesives and clinical diagnosis, such as being combined with portable analytical devices. [ 14 , 15 ] However, because ordinary

Silver Nanowires: From Scalable Synthesis to Recyclable Foldable Electronics

As an increasing attention towards sustainable development of energy and environment, the power electronics (PEs) are gaining more and more attraction on various energy systems. The insulated gate bipolar transistor (IGBT), as one of the PEs with numerous advantages and potentials for development of higher voltage and current ratings, has been used in a board range of applications. However, the continuing miniaturization and rapid increasing power ratings of IGBTs have remarkable high heat flux, which requires complex thermal management. In this paper, studies of the thermal management on IGBTs are generally reviewed including analyzing, comparing, and classifying the results originating from these researches. The thermal models to accurately calculate the dynamic heat dissipation are divided into analytical models, numerical models, and thermal network models, respectively. The thermal resistances of current IGBT modules are also studied. According to the current products on a number of IGBTs, we observe that the junction-to-case thermal resistance generally decreases inversely in terms of the total thermal power. In addition, the cooling solutions of IGBTs are reviewed and the performance of the various solutions are studied and compared. At last, we have proposed a quick and efficient evaluation judgment for the thermal management of the IGBTs depended on the requirements on the junction-to-case thermal resistance and equivalent heat transfer coefficient of the test samples.

Thermal Management on IGBT Power Electronic Devices and Modules

Power module packaging technologies have been experiencing extensive changes as the novel silicon carbide (SiC) power devices with superior performance become commercially available. This article presents an overview of power module packaging technologies in this transition, with an emphasis on the challenges that current standard packaging face, requirements that future power module packaging needs to fulfill, and recent advances on packaging technologies. The standard power module structure, which is a widely used current practice to package SiC devices, is reviewed, and the reasons why novel packaging technologies should be developed are described in this article. The packaging challenges associated with high-speed switching, thermal management, high-temperature operation, and high-voltage isolation are explained in detail. Recent advances on technologies, which try to address the limitations of standard packaging, both in packaging elements and package structure are summarized. The trend toward novel soft-switching power converters gave rise to problems regarding package designs of unconventional module configuration. Potential applications areas, such as aerospace applications, introduce low-temperature challenges to SiC packaging. Key issues in these emerging areas are highlighted.

A Review of SiC Power Module Packaging Technologies: Challenges, Advances, and Emerging Issues

This paper discusses the current state of SiC electronics research at Arkansas Power Electronics International, Inc. (APEI) with regard to high-temperature environments and applications. The University of Arkansas (UA) researchers' modeling and characterization of SiC power devices for these high-temperature environments are also discussed. Devices to be covered include SiC Schottky diodes, SiC power MOSFETs, and SiC static-induction-transistors (SITs). The paper reviews the current application of these devices to the specific harsh environments of deep Earth drilling and combat electric vehicles, as well as outline APEI's research work into developing operational SiC motor drives for these systems. It is proposed that this technology development be transferred to NASA space exploration applications. Two areas within the NASA program that would find this technology highly beneficial are (1) probes and landers that must operate in high-temperature environments and (2) ultra-lightweight power electronics for satellite and spacecraft power converter systems.

Silicon-carbide (SiC) semiconductor power electronics for extreme high-temperature environments

An overview to integrated power module design for high power electronics packaging

Low cost flex substrates for miniaturized electronic assemblies

Electronic power converters have been designed, produced, and disseminated in mass quantities using a number of fabrication techniques, from standard PCB technologies for low cost applications, to thick film on ceramic, to direct bond copper (DBC) for high power, higher cost applications. Each approach holds a share of the power packaging market, but they all restrict, for the most part, circuit and package designs to 2D boards. One potential pathway into the third dimension is by the use of multilayers, an approach which becomes increasingly difficult with each additional layer added beyond the first, and with the exception of high performance solutions is typically cost prohibitive for the majority of applications. This paper demonstrates the feasibility and viability of an alternative low cost power packaging option which uses familiar industry technologies in a unique manner: flexible polymer substrates. Flex technology uses industry standard PCB and/or thick film processes, offers the lower cost, higher performance solutions inherent with the majority of polymer plastics, and as a final bonus, frees the designer to more efficiently use all three dimensions. The researchers have shown the feasibility of this low cost alternative solution through the fabrication and testing of integrated power modules (IPMs) which use flex polymer substrates in conjunction with both surface mount and bare dice. These DC/DC power converters transform 120 V/240 V inputs to 9V, 7 W outputs, and illustrate the miniaturization advantages of fully utilizing the 3D space offered by flex circuitry.

Polymer thick film (PTF) and flex technologies for low cost power electronics packaging

The current trend in commercial and industrial drives, such as electric vehicles and electronic motor drives, is toward the elimination of traditional mechanical or electromechanical systems in favor of power electronics systems (1kW and larger). Market pressures are forcing the design and packaging of power electronics to be compact in size, more reliable, thermally superior, and integrated with intelligence and control systems. As a result, new strategies in the topology design and materials selection are needed in order to fulfill these highly demanding requirements. Toward that end, the researchers have developed a low cost Power Packaging Strategy which extends the concept of Multichip Modules to high power electronic assemblies. This paper will discuss a novel power packaging design which allows for two high conductivity metal layers for power routing and up to ten layers of signal routing in a single compact module. Low power control and interface circuits have been integrated into the power module in bare die and packaged form using chip and wire as well as surface mount attachment. Proper thermal management is achieved through the use of an integrated Metal Matrix Composite heat spreader and substrate. In addition, a 3kW inverter has been fabricated using both the conventional approach and the new packaging concept. A thermal analysis and electrical characterization, as well as a comparison of these power module designs have been performed in this work and will be discussed in the paper.

High Density Power Modules: A Packaging Strategy

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.

A. B. Lostetter

Papers

An overview to integrated power module design for high power electronics packaging

Low cost flex substrates for miniaturized electronic assemblies

Polymer thick film (PTF) and flex technologies for low cost power electronics packaging

High Density Power Modules: A Packaging Strategy

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