Organic materials offer new electronic functionality not available in inorganic devices. Promising examples of novel characteristics in organic devices range from the memory effects observed in monolayers and polymer films to negative differential resistance devices. However, the integration of organic compounds within nanoscale electronic circuitry poses considerable challenges for materials physics and chemistry, and a detailed understanding of the conduction mechanisms, switching and memory is still lacking. With increasing research into very different material systems such as oxides, solid-state electrolytes, phase-change memory materials, it is becoming clear that electronic switching on the smallest length scale cannot be purely electronic phenomena. Rather, a motion of heavier constituents has to be involved that will in turn change the electronic properties. New work conducted at Bell Labs demonstrates the success of such a line of thought in molecular systems. The Bell scientists demonstrated a novel approach to creating and chemically modifying conducting electronic states in nanoscale molecular devices.
In the future, wearable electronics will go far beyond just very small electronic devices. Not only will such devices be embedded on textile substrates, but an electronics device or system could become the fabric itself. Electronics textiles will allow the design and production of a new generation of garments with distributed sensors and electronic functions. Such e-textiles will have the revolutionary ability to sense, act, store, emit, and move (think biomedical monitoring functions or new man-machine interfaces) while leveraging an existing low-cost textile manufacturing infrastructure. Reporting a novel approach through the construction of all-organic wire electrochemical transistor devices (WECT) , researchers in Sweden show that textile monofilaments can be coated with continuous thin films of a conducting polymer and used to create microscale WECTs on single fibers. They also demonstrate inverters and multiplexers for digital logic. This opens an avenue for three-dimensional polymer micro-electronics, where large-scale circuits can be designed and integrated directly into the three-dimensional structure of woven fibers.
A few years ago it was discovered that the process of thermal inkjet printing can be applied to fabricate hard tissue scaffolds (such as bones) and, just recently, soft tissue with liquid biomaterials. Research is also underway to use inkjet printing for the fabrication of organic semiconductors, which, because of their low stability, will be targeted at one-time-only applications such as water purity testers. Compared to the research done with respect to organic materials, inkjet printing of inorganic materials for the formation of active devices is relatively rare. To date, only a handful of inorganic materials have been inkjet printed, primarily because of the difficulty in preparing inkjet-printable precursors. Current methods for the production of functional inorganic electronic devices are quite expensive because they require the sequential deposition, patterning, and etching of selected semiconducting, conducting, and insulating materials, involving multiple photolithography and vacuum-deposition processes. Now though, researchers have come up with a process for printable inorganic semiconductors, opening a route to the fabrication of high-performance and ultra low-cost electronics such as transparent electronics and thin film solar cells.
Nanoelectronics devices often are made by integrating dissimilar classes of semiconductors and various other disparate materials into one heterogeneous single system. The two primary modes of combining these materials - mechanical bonding and epitaxial growth processes - place stringent requirements on the ultimate scale or constituent materials of circuits. With mechanical bonding, there is a limited ability to scale to large areas (i.e., larger than the wafers) or to more than a few stacking layers; incompatibility with unusual materials (such as nanostructured materials) and/or low-temperature materials and substrates; challenging fabrication and alignment for the through-wafer electrical interconnects; demanding requirements for planar bonding surfaces; and bowing and cracking that can occur from mechanical strains generated by differential thermal expansion and contraction of disparate materials. Epitaxy avoids some of these problems but places severe restrictions on the quality and type of materials that can be grown. Using a process akin to the printing press, researchers have managed to bypass the need for epitaxial growth or wafer bonding to integrate wide ranging classes of dissimilar semiconducting nanomaterials onto substrates for the purpose of constructing heterogeneous, three dimensional electronics.
Gears, bearings, and liquid lubricants can reduce friction in the macroscopic world, but the origins of friction for small devices such as micro- or nanoelectromechanical systems (NEMS) require other solutions. Despite the unprecedented accuracy by which these devices are nowadays designed and fabricated, their enormous surface-volume ratio leads to severe friction and wear issues, which dramatically reduce their applicability and lifetime. Traditional liquid lubricants become too viscous when confined in layers of molecular thickness. This situation has led to a number of proposals for ways to reduce friction on the nanoscale, such as superlubricity and thermolubricity. Researchers in Switzerland now describe a resonance-induced superlubricity, which also occurs in many natural phenomena from biological systems to the motion of tectonic plates. This new method provides an efficient way to switch friction on and off at the atomic scale and, as a simple way of preventing mechanical damage without chemical contamination, could be of enormous importance for the development of NEMS.
There is much discussion of molecules as components for future electronic devices and in recent years it has been possible to position single molecules in electrical junctions. Molecular and nanoscale structures have been shown to be capable of basic electronic functions such as rectification, negative differential resistance and single-electron transistor behavior. These observations show that molecular-electronic functions can be controlled through chemical manipulation. However, the contacts, the local environment and the temperature can all affect molecules' electrical properties. This sensitivity, particularly at the single-molecule level, may limit the use of molecules as active electrical components, and therefore it is important to design and evaluate molecular junctions with a robust and stable electrical response over a wide range of junction configurations and temperatures. A step in this direction, researchers in the UK now report an approach to monitor the electrical properties of single-molecule junctions, which involves precise control of the contact spacing and tilt angle of the molecule.
If current research is an indicator, wearable electronics will go far beyond just very small electronic devices. Not only will such devices be embedded on textile substrates, but an electronics device or system could become the fabric itself. Electronics textiles will allow the design and production of a new generation of garments with distributed sensors and electronic functions. Such e-textiles will have the revolutionary ability to sense, act, store, emit, and move (think biomedical monitoring functions or new man-machine interfaces) while leveraging an existing low-cost textile manufacturing infrastructure. Today, only a few steps towards new architectural possibilities of realizing circuit topologies that can be implemented with textile technique have been made: one an example of nonplanar devices and one of textile based devices. Researchers in Italy have now developed an organic field effect transistor (OFET) fully compatible with textile processing techniques.
'Carrier mobility' is a major factor in determining the speed of electronic devices. Aggressive scaling of the complementary metal-oxide-semiconductor (CMOS) transistor technology requires a high drive current, which depends on the charge carrier mobility. As the dimensions of nanoelectronic circuits continue to shrink, it is important that the carrier mobility does not deteriorate and, if possible, improves. The search for nanostructures where the carrier mobility values can be preserved or even improved continues owing to the extremely high technological pay-off if successful. Nanowires represent a convenient system to understand the effects of low dimensionality on the carrier drift mobility. One can also look at nanowires as an ultimately scaled transistor channel. New research at the University of California - Riverside demonstrates a method for the significant enhancement of the carrier mobility in silicon nanowires. Such mobility enhancement would allow to make smaller and faster transistors and improve heat removal.