Dr. David Mc Closkey

Electrical interconnects are essential elements of all integrated circuits (ICs), and constitute the wiring system that provides power and distributes clock signals to various functional blocks in a complementary metal oxide semiconductor (CMOS) IC. The international technology roadmap for semiconductors (ITRS) has identified metallic interconnect scaling as a key challenge limiting overall chip performance. Limited bandwidth of interconnects in processors has resulted in only 10% of transistors being active at any time, and has led to a stagnation in the rate of increase of computing power. As feature sizes continue to shrink in ICs, interconnect dimensions are becoming comparable to the electron mean free path. Electron scattering from grain boundaries, surfaces and defects now dominates the electrical transport resulting in greatly increased resistivity. Since electrons are the main carriers of heat in metallic systems the thermal conductivity is also greatly diminished. This means that heat cannot be easily removed from sources and the local temperature can spike leading to failure in devices. This problem is compounded by a reduction in material melting point at the nanoscale known as melting point depression. This project is designed to investigate electrical and thermal transport in chemically synthesised metallic nanowires in order to determine the ultimate scaling limit of metallic interconnects. A key differentiator in this project is that the local temperature will be determined using an optical technique, decoupling thermal and electrical measurements. Optical techniques allow non-invasive measurement of local temperature distributions with ~250 nm resolution, removing the need to rely on assumptions about the current induced heating in the nanowire. Understanding and controlling the thermal properties of nanomaterials will lead to disruptive breakthroughs in micro and nano-electronic devices with global technological and economic impact.

Spatial confinement and angular divergence of electromagnetic radiation are intimately related through diffraction, which imposes the so called diffraction limit on light confinement and imaging resolution using far-field optics. This limit can be surpassed close to particles or interfaces by incorporating evanescent fields. Recent studies show that light scattering from micron scale dielectric particles can produce optical near-fields extending relatively far from the particle, with features which break the free space diffraction limit. Specifically light can be focused to beams with a sub-wavelength waist and still retain a low divergence angle. In this thesis we explore fully light scattering in this size regime using an experimental model system of planar scatterers fabricated in silicon nitride using electron beam lithography. This system gives precise control over the shape, size and position of the scatterers. We show that these low divergence features are a general property observed in the near-field of arbitrarily shaped scatterers in this size regime. Controlling the direction and polarization of the incident light and the morphology of the particle allows direct control over the intensity distribution in the near-field.