Substantial effort has been placed on developing semiconducting carbon nanotubes and nanowires as building blocks for electronic devices--such as field-effect transistors--that could replace conventional silicon transistors in hybrid electronics or lead to stand-alone nanosystems. Attaching electric contacts to individual devices is a first step towards integration, and this step has been addressed using lithographically defined metal electrodes. Yet, these metal contacts define a size scale that is much larger than the nanometre-scale building blocks, thus limiting many potential advantages. Here we report an integrated contact and interconnection solution that overcomes this size constraint through selective transformation of silicon nanowires into metallic nickel silicide (NiSi) nanowires. Electrical measurements show that the single crystal nickel silicide nanowires have ideal resistivities of about 10 microOmega cm and remarkably high failure-current densities, >10(8) A cm(-2). In addition, we demonstrate the fabrication of nickel silicide/silicon (NiSi/Si) nanowire heterostructures with atomically sharp metal-semiconductor interfaces. We produce field-effect transistors based on those heterostructures in which the source-drain contacts are defined by the metallic NiSi nanowire regions. Our approach is fully compatible with conventional planar silicon electronics and extendable to the 10-nm scale using a crossed-nanowire architecture.

Single-crystal metallic nanowires and metal/semiconductor nanowire heterostructures

The development of manipulation tools that are not too ‘fat’ or too ‘sticky’ for atomic scale assembly is an important challenge facing nanotechnology1. Impressive nanofabrication capabilities have been demonstrated with scanning probe manipulation of atoms2,3,4,5 and molecules4,6 on clean surfaces. However, as fabrication tools, both scanning tunnelling and atomic force microscopes suffer from a loading deficiency: although they can manipulate atoms already present, they cannot efficiently deliver atoms to the work area. Carbon nanotubes, with their hollow cores and large aspect ratios, have been suggested7,8 as possible conduits for nanoscale amounts of material. Already much effort has been devoted to the filling of nanotubes8,9,10,11 and the application of such techniques12,13. Furthermore, carbon nanotubes have been used as probes in scanning probe microscopy14,15,16. If the atomic placement and manipulation capability already demonstrated by scanning probe microscopy could be combined with a nanotube delivery system, a formidable nanoassembly tool would result. Here we report the achievement of controllable, reversible atomic scale mass transport along carbon nanotubes, using indium metal as the prototype transport species. This transport process has similarities to conventional electromigration, a phenomenon of critical importance to the semiconductor industry17,18.

Carbon nanotubes as nanoscale mass conveyors

Exotic features of a metal/oxide/metal sandwich, which will be the basis for a drastically innovative nonvolatile memory device, is brought to light from a physical point of view. Here the insulator is one of the ubiquitous and classic binary-transition-metal oxides (TMO), such as ${\mathrm{Fe}}_{2}{\mathrm{O}}_{3}$, $\mathrm{NiO}$, and $\mathrm{CoO}$. The sandwich exhibits a resistance that reversibly switches between two states: one is a highly resistive off state and the other is a conductive on state. Several distinct features were universally observed in these binary TMO sandwiches: namely, nonpolar switching, nonvolatile threshold switching, and current-voltage duality. From the systematic sample-size dependence of the resistance in on and off states, we conclude that the resistance switching is due to the formation of ``electric faucet'' at the interface, which shows up as a homogeneous to inhomogeneous transition of the current distribution.

Nonpolar resistance switching of metal/binary-transition-metal oxides/metal sandwiches: Homogeneous/inhomogeneous transition of current distribution

The effect of the application of a dc current on the annealing of point defects in Ni3Ti was investigated by positron annihilation spectroscopy. An increased defect annealing rate was observed under the influence of the current and was attributed to a 24% decrease in the activation energy of mobility. The results are interpreted in terms of the electron wind effect and the complex nature of diffusion in ordered intermetallic phases. They provide direct evidence for an increase in defect mobility in ordered intermetallics under the influence of a current.

/pdf/electric-current-enhanced-defect-mobility-in-ni3ti-3xescrps99.pdf

Electric current enhanced defect mobility in Ni3Ti intermetallics

We propose a fault-tolerant approach to reliable microprocessor design. Our approach, based on the use of an online checker component in the processor pipeline, provides significant resistance to core processor design errors and operational faults such as supply voltage noise and energetic particle strikes. We show through cycle-accurate simulation and timing analysis of a physical checker design that our approach preserves system performance while keeping area overheads and power demands low. Furthermore, analyses suggest that the checker is a fairly simple state machine that can be formally verified, scaled in performance, and reused. Further simulation analyses show virtually no performance impacts when our simple checker design is coupled with a high-performance microprocessor model. Timing analyses indicate that a fully synthesized unpipelined 4-wide checker component in 0.25 /spl mu/m technology is capable of checking Alpha instructions at 288 MHz. Physical analyses also confirm that costs are quite modest; our prototype checker requires less than 6% the area and 1.5% the power of an Alpha 21264 processor in the same technology. Additional improvements to the checker component are described which allow for improved detection of design, fabrication and operational faults.

/pdf/a-fault-tolerant-approach-to-microprocessor-design-206tcn0jiw.pdf

P.G. Brusius

Papers

Electromigration: A review