Carbon-based electronics

The semiconductor industry has been able to improve the performance of electronic systems for more than four decades by making ever-smaller devices. However, this approach will soon encounter both scientific and technical limits, which is why the industry is exploring a number of alternative device technologies. Here we review the progress that has been made with carbon nanotubes and, more recently, graphene layers and nanoribbons. Field-effect transistors based on semiconductor nanotubes and graphene nanoribbons have already been demonstrated, and metallic nanotubes could be used as high-performance interconnects. Moreover, owing to the excellent optical properties of nanotubes it could be possible to make both electronic and optoelectronic devices from the same material.     

Paper electronics

Paper is ubiquitous in everyday life and a truly low-cost substrate. The use of paper substrates could be extended even further, if electronic applications would be applied next to or below the printed graphics. However, applying electronics on paper is challenging. The paper surface is not only very rough compared to plastics, but is also porous. While this is detrimental for most electronic devices manufactured directly onto paper substrates, there are also approaches that are compatible with the rough and absorptive paper surface. In this review, recent advances and possibilities of these approaches are evaluated and the limitations of paper electronics are discussed.     

Nanotechnology-based flexible electronics

Research on flexible electronics has grown exponentially over the last decade. Researchers around the globe are developing a wide range of flexible systems, including displays [1, 2], sensors [3-5], RFID tags [6, 7] and other similar devices [8]. Innovations in materials have been key to the increased research success in this field of research in recent years [9]. Transistors, interconnects, memory cells, passive components and other assorted devices all have challenging material demands for flexible electronics to become a reality. Nanomaterials of various kinds have been found to represent a tremendously powerful tool, with nanoparticles [10], nanotubes, nanowires [3, 11] and engineered organic molecules [12, 13] contributing to the realization of high-performance semiconductors, dielectrics and conductors for flexible electronics applications. Nanomaterials offer tunability in terms of performance, solution processability and processing temperature requirements, which makes them very attractive as building blocks for flexible electronic systems. Indeed, such systems represent some of the largest families of commercially produced nanomaterials today, and numerous commercial products based on nanoparticle formulations are widely available. This special issue focuses on the rapidly blossoming field of flexible electronics, with a particular focus on the use of nanotechnology to facilitate flexible electronic materials, processes, devices and systems. Contributions to the issue describe the development of nanomaterials-including nanoparticles, nanotubes, nanowires and carbon-based thin films-for use in conductors, transparent electrodes, semiconductors and dielectrics. The articles feature innovations in nanomanufacturing and novel materials, as well as the application of these technologies to advanced flexible devices and systems. As flexible electronics systems move rapidly towards successful commercial deployment, it is extremely likely that they will exploit nanomaterials as building blocks. Developments in the field will help to leverage the power of these materials to realize novel functionalities in flexible form factors. This special issue provides a view of the state of the art in these technologies, and gives a vision of the coming innovations that will make flexible electronics a reality. References [1] Gelinck G H et al 2004 Flexible active-matrix displays and shift registers based on solution-processed organic transistors Nature Mater. 3 106-10 [2] Zhou L, Wanga A, Wu S C, Sun J, Park S and Jackson T N 2006 All-organic active matrix flexible display Appl. Phys. Lett. 88 083502 [3] Fan Z, Ho J C, Jacobson Z A, Razavi H and Javey A 2008 Large-scale, heterogeneous integration of nanowire arrays for image sensor circuitry Proc. Natl Acad. Sci. 105 11066 [4] Sekitani T et al 2009 Organic nonvolatile memory transistors for flexible sensor arrays Science 326 1516-9 [5] Mannsfeld S C B et al 2010 Highly sensitive flexible pressure sensors with microstructured rubber dielectric layers Nature Mater. 9 859-64 [6]Subramanian V, Frechet J M J, Chang P C, Huang D C, Lee J B, Molesa S E, Murphy A R, Redinger D R and Volkman S K 2005 Progress toward development of all-printed RFID tags: materials, processes, and devices Proc. IEEE 93 1330-8 [7] Jung M et al 2010 All-printed and roll-to-roll-printable 13.56 MHz-operated 1 bit RF tag on plastic foils IEEE Trans. Electron. Devices 57 571-80 [8] Kim D-H et al 2011 Epidermal electronics Science 333 838-43 [9] Wagner S and Bauer S 2012 Materials for stretchable electronics MRS Bull. 37 207 [10] Grouchko M, Kamyshny A and Magdassi S 2009 Formation of air-stable copper-silver core-shell nanoparticles for inkjet printing J. Mater. Chem. 19 3057-62 [11] Takei K et al 2010 Nanowire active-matrix circuitry for low-voltage macroscale artificial skin Nature Mater. 9 821-6 [12] Sekitani T, Zschieschang U, Klauk H and Someya T 2010 Flexible organic transistors and circuits with extreme bending stability Nature Mater. 9 1015-22 [13] Park S, Wang G, Cho B, Kim Y, Song S, Ji Y, Yoon M and Lee T 2012 Flexible molecular-scale electronic devices Nature Nanotechnol. 7 438-42.     

Superconducting electronics testing

An I/O assembly has been designed and constructed to support the operation of superconducting circuitry. The system, previously described⁹ for chip testing, has been adapted for use with a Josephson technology system level experiment. The cryoinsert assembly, constructed of non-magnetic parts, provides 80 high frequency I/O lines between room temperature and 4.2 K.     

Carbon nanotube electronics

Presents experimental results on single-wall carbon nanotube field-effect transistors (CNFETs) operating at gate and drain voltages below 1V. Taking into account the extremely small diameter of the semiconducting tubes used as active components, electrical characteristics are comparable with state-of-the-art metal oxide semiconductor field-effect transistors (MOSFETs). While output as well as subthreshold characteristics resemble those of conventional MOSFETs, we find that CNFET operation is actually controlled by Schottky barriers (SBs) in the source and drain region instead of by the nanotube itself. Due to the small size of the contact region between the electrode and the nanotube, these barriers can be extremely thin, enabling good performance of SB-CNFETs.     

Quantum-interference-controlled molecular electronics

Quantum interference in coherent transport through single molecular rings may provide a mechanism to control the current in molecular electronics. We investigate its applicability, using a single-particle Green function method combined with ab initio electronic structure calculations. We find that the quantum interference effect (QIE) is strongly dependent on the interaction between molecular pi-states and contact sigma-states. It is masked by sigma tunneling in small molecular rings with Au leads, such as benzene, due to strong pi-sigma hybridization, while it is preserved in large rings, such as [18]annulene, which then could be used to realize quantum interference effect (QIE) transistors.     

Semiconductor-superconductor hybrid electronics

This paper examines the feasibility and potential for applications of intimately combining semiconductor and superconductor devices at circuit and system levels. The focus is mainly on the temperature range 27–77 K. One of the main issues is the heat produced by the semiconductor devices, since the superconductor devices produce much less heat and are sensitive to temperature changes. It is shown that Josephson junctions made with high temperature superconductors can be placed very close to transistors on a properly heatsunk chip. A second important issue is interfacing the low voltages of superconducting devices to the much higher voltages needed for transistors; an existing technique is discussed in the context of high temperature superconductors. Only well developed semiconductor technologies have been considered; although there is some possibility of making low voltage transistors, this is not explored here. The paper concludes with an analysis of the various applications that can be realized, depending on the type of device available in high temperature superconductor technology: passive patterned films, nonhysteretic Josephson devices or Josephson tunnel juntions.     

Solders in electronics

The metallurgy and mechanical behaviour of the principal solder types based on lead-tin alloys are reviewed. Particular emphasis is placed upon their performance under simulated service conditions, fatigue, creep and ageing, and life prediction. Requirements for improved and more environmentally compatible solders are explored.     

Introducing molecular electronics

Molecular electronics and optoelectronics depend for their existence on the molecular organization of space. The fundamental mechanisms underlying the rich phenomena that have been discovered in these areas arise from mixing of electronic energies in the molecule with external, macroscopic structures. Mechanisms of charge injection and transport, and their manifestations in the physical properties of molecular electronic junctions, are discussed. Major questions that remain unresolved are placed in the contexts of fundamental understanding and device considerations.In the natural world, molecules are used for many purposes. Using molecule-based materials for electronics, sensing, and optoelectronics is a new endeavor, called molecular electronics, and the subject both of riveting new research and substantial popular press interest.     

Structural integrity in electronics

With continuing miniaturisation, increased performance demands and the requirement to remove lead from solder alloys, the challenges to structural integrity and reliability of electronic equipment are substantial and increasing. This paper outlines typical features in electronic equipment of which the structural integrity community may be generally unaware. Potential failure modes in service are described, and the problems of scale and material characteristics are considered. Progress in the application of fracture mechanics to the life prediction of interconnections is reviewed. The limited evidence available suggests that the crack growth resistance of silver‐containing lead‐free solders is superior to that of the traditional Sn‐37Pb under cycle‐controlled conditions but there is no difference when time‐dependent conditions prevail. In several respects, it is contended that the electronics sector is faced with challenges at least equivalent to those encountered in gas turbines and nuclear power generation.     

Mechanics of stretchable electronics

Recent advances in mechanics and materials provide routes to develop stretchable electronics that offer performance of conventional wafer-based devices but with the ability to be deformed to arbitrary shape. Many new applications become possible ranging from electronic eye cameras to wearable electronics, to bio-integrated therapeutic devices. This paper reviews mechanics of stretchable electronics in terms of two main forms of stretchable designs. One is wavy design, which can provide one-dimensional stretchability. The other is island-bridge design, which can be stretched in all directions. Mechanics models and their comparisons to experiments and finite element simulations are reviewed for these two designs. The results provide design guidelines for the development of stretchable electronics.     

Review of superconducting electronics

This review will sketch the present state of affairs in applications of Josephson junctions and SQUIDs to: magnetometry, DC and RF metrology, detection and amplification of electromagnetic signals, frequency metrology, noise thermometry and computers. It will also mention recent progress in super-stable oscillators using superconducting resonant circuits, pulse transmission lines, and thin-film deviees to detect radiation or charged particles. Many of these topics are maturing nicely.     

Organic electronics on banknotes

Organic transistors and circuits are fabricated directly on the surface of banknotes. The transistors operate with voltages of 3 V and have a field-effect mobility of about 0.2 cm2 V?1s?1. For an array of 100 transistors a yield of 92% is obtained.     

Single-walled carbon nanotube electronics

Single-walled carbon nanotubes (SWNTs) have emerged as a very promising new class of electronic materials. The fabrication and electronic properties of devices based on individual SWNTs are reviewed. Both metallic and semiconducting SWNTs are found to possess electrical characteristics that compare favorably to the best electronic materials available. Manufacturability issues, however, remain a major challenge