Conventional silicon-based electronics have faced challenges in the realization of soft bioelectronics, such as wearable and implantable integrated devices, which necessitate electrically and mechanically interactive biotic–abiotic interfacing without disturbing the daily life of the user or posing biocompatibility issues. Recently, much effort has been directed at overcoming the mechanical limitations of conventional rigid electronics by replacement of bulky, thick, and rigid electronic materials with biocompatible, soft, and nanoscale electronic materials, which exhibit intrinsic mechanical deformability as well as superior electrical properties. Recent advances in the synthesis of unconventional nanomaterials, surface functionalization methods, and integrated device fabrication techniques have resulted in further improvements in the performance of nanomaterials-based soft bioelectronics. Numerous studies have focused on the biological, electrical, and mechanical analyses of heterogeneous nanomaterial–biosystem interfaces as well as the development of efficient integration processes of soft nanomaterials into devices. In this article, we summarize the latest advances and future prospects in nanomaterials synthesis, processing, and integration strategies for flexible and stretchable bioelectronics, and their application to wearable and implantable devices.

The BaNd2O4 compound and the BaO–Nd2O3 system are of interest for electroceramics. In this work, we synthesized BaNd2O4 by solid-state reaction, measured its heat capacity from 573 to 1273 K by differential scanning calorimetry, and determined its enthalpy of formation from component oxides at 298 K by high-temperature oxide melt solution calorimetry to be −43.75 ± 4.68 kJ/mol. Our newly determined values and available literature data were employed to assess the phase equilibria in the BaO–Nd2O3 system using CALPHAD methodology. A self-consistent thermodynamic database and the calculated phase diagram of the BaO–Nd2O3 system are provided. The optimized thermodynamic parameters are in good agreement with available experimental data. BaNd2O4 is calculated to melt incongruently at 2177 K. This thermodynamic analysis is essential for the optimization of synthesis conditions for materials and for the evaluation of their stability under appropriate technological operating conditions.

Lorentz reciprocity governs the symmetry with which electromagnetic signals travel in space and time. A reciprocal channel supports signal transport in two directions with the same transmission properties. Nonreciprocal devices do not obey this general symmetry, and therefore enable isolation and circulation, offering fundamental functionalities in modern GHz-to-THz photonic systems. While most nonreciprocal devices to date are based on magneto-optical phenomena, significant interest has been raised by approaches that avoid the use of magnetic materials, instead relying on artificial materials and circuits that mimic magnetically biased ferrites, enabling compact, light, integrated, and significantly cheaper nonreciprocal devices. Here, we review recent progress in and opportunities offered by artificial nonmagnetic materials that break reciprocity, revealing their potential for compact nonreciprocal devices and systems.

Research in functional materials is frequently driven by a desire to make informed choices in the quest for better, more effective materials. A great deal of recent attention has been focused on the modalities of how such informed choices can themselves be made in a better, more effective manner. The examples presented here examine some of these modalities, emphasizing the nexus between new synthesis, computational design and analysis, growth in high purity forms, and finally, end-use in terms of either application or of significant property measurement. The illustrations, many drawn from the recent literature, commence with the role that theory has played, both in property prediction and concomitant materials selection, in the areas of multiferroics and topological insulators. The importance of materials quality is emphasized, using examples from observation of the fractional Quantum Hall Effect, where new science has emerged as a result of improved materials. In the area of organic electronics, prospects for advancing the field are suggested, as are future directions in nanoscience. While the examples chosen here point to developments that require a highly collaborative “systems” approach to materials, the role that serendipity plays is not ignored.

The effect of calcination temperature during the formation of the solid solution Sn0.9Ti0.1O2 doped with 1.00 mol % CoO and 0.05 mol % Nb2O5 is presented. The structural characteristics of this system were studied using X-ray diffraction, and the changes in phase formation were analyzed using the Rietveld method. With an increase in calcination temperature, there is increasing miscibility of Ti into the (Ti,Sn)O2 phase and near 1000 °C, and the remaining TiO2 (anatase) was transformed into the rutile phase. The sintering process, monitored using dilatometry, suggests two mass transport mechanisms, one activated close to 900 °C associated with the presence of TiO2 (anatase) and the second mechanism, occurring between 1200 and 1300 °C, is attributed to a faster grain boundary diffusion caused by oxygen vacancies.

Self-assembly—the spontaneous generation of order in systems of components—is ubiquitous in chemistry; in biology, it generates much of the functionality of the living cell. Self-assembly is relatively unused in microfabrication, although it offers opportunities to simplify processes, lower costs, develop new processes, use components too small to be manipulated robotically, integrate components made using incompatible technologies, and generate structures in three dimensions and on curved surfaces. The major limitations to the self-assembly of micrometer- to millimeter-sized components (mesoscale self-assembly) do not seem to be intrinsic, but rather operational: selfassembly can, in fact, be reliable and insensitive to small process variations, but fabricating the small, complex, functional components that future applications may require will necessitate the development of new methodologies. Proof-of-concept experiments in mesoscale self-assembly demonstrate that this technique poses fascinating scientific and technical challenges and offers the potential to provide access to hard-to-fabricate structures.

After substantial investment in research and development over the last decade, silicon carbide materials and devices are coming of age. The concerted efforts that made this possible have resulted in breakthroughs in our understanding of materials issues such as compensation mechanisms in high-purity crystals, dislocation properties, and the formation of SiC/SiO2 interfaces, as well as device design and processing. The progress accomplished over the last eight years in SiC-based electronic materials is summarized in this issue of MRS Bulletin.

Advanced three-dimensional (3D) packaging techniques for electronic components are promising for the realization of “systems-in-packages.” Three-dimensional packages require the use of a variety of materials within a small physical size range. Materials selection is therefore critical from electrical, optical, mechanical, structural, thermal, and manufacturability viewpoints. The materials combination depends also on the intended application for the 3D packaged modules. This article reviews 3D packaging approaches, materials classes, and examples. Three-dimensional packaged systems using judiciously selected materials offer performance advantages that cannot be provided by planar implementation.

The drive toward higher density and higher performance in integrated circuits creates a need to keep interconnects short and eliminate layers of packaging. In this article, we propose a novel, ultrahigh-density (exceeding 104 leads per cm2), compliant, wafer-level, input/output interconnection technology called “sea of leads” as a key enabling technology for future high-performance microsystems. The mechanical compliance is addressed through slippery leads (leads released from the surface) and embedded air gaps. The ability to fabricate embedded air gaps has enabled the integration of optical interconnects with high index-of-refraction mismatches between the core and cladding.

The trend for microelectronic devices has historically been, and will continue to be, toward a smaller feature size, faster speeds, more complexity, higher power, and lower cost. The driving force behind these advances has traditionally been microprocessors. With the tremendous growth of wireless telecommunications, rf applications are beginning to drive many areas of microelectronics that traditionally were led by developments in microprocessors. An increasingly dominant factor in rf microelectronics is electronic packaging, and the materials needed to create the package, because the package materials strongly affect the performance of the electronics. Many challenges remain for the packaging of microprocessors as well. These challenges include increased speed, the number of input/output interconnects, decreased pitch, and decreased cost. This article highlights the key issues facing the packaging of high-performance digital and rf electronics.

The elimination of conventional peripheral LSI (large-scale integration) drivers is considered essential to the development of future low-cost, energy-efficient, lightweight, and thin displays. System-on-glass (SOG) displays are a type of display with various functional circuits integrated on a glass substrate. Low-temperature polycrystalline silicon (LTPS) thin-film transistors (TFTs) make the integration of circuits possible because they can be assembled into complex, high-current driver circuits. Furthermore, LTPS TFTs are attracting attention for driving organic light-emitting devices (OLEDs). This article introduces present and future LTPS TFT technologies for SOG displays.

An abrasive-free polishing (AFP) solution for chemical–mechanical planarization (CMP) of copper films on semiconductor wafers has been developed to overcome such disadvantages of conventional CMP as dishing, erosion, Cu and oxide loss, and microscratching. Electrochemical methods are an effective way of understanding the role of each chemical component in the AFP solution in order to optimize its performance. Analysis of the reaction layer of Cu elucidates the reasons for the excellent results that have been obtained. By applying the AFP solution for Cu CMP in combination with a slurry for CMP of the metal barrier layer, seven-level multilayer Cu interconnections can be successfully fabricated.

Combinatorial methods are high-efficiency methods to create large composition “libraries” of materials, for example, continuous composition variations, and test those compositions systematically in parallel for specific properties of interest, in contrast to the time-consuming one-composition-at-a-time approach. These methods have captured the attention of the materials industry with the promise of providing new discoveries “faster, better, and cheaper.” However, in the academic community, combinatorial methods often meet with less enthusiasm, perhaps due to the perception of combinatorial methodology as an Edisonian approach to science. The facts are quite to the contrary. In addition to impressive successes arising from the application of combinatorial methods to materials discovery, results coming out of systematic high-throughput investigations of complex materials phenomena (which would be too time-consuming or expensive to undertake) provide data leading to improvement in theories and models of materials chemistry and physics. Indeed, combinatorial methods provide a new paradigm for advancing a central scientific goal—the fundamental understanding of structure–property relationships of materials behavior.