Micro/Nanoelectronics

Over the last 40 years, the silicon semiconductor industry has been driven by “ Moore’s Law” which states that the number of transistors on a silicon chip will double roughly every two years. This has been enabled by high volume manufacturing of reduced geometry structures which has resulted in digital circuits with critical dimensions in the nanometre size range, and with enormously-increased performances and functionalities relative to those obtained even a few years ago.

This ongoing development of integrated micro/nanoelectronic solutions requires significant advances in materials and processes to overcome the dimensional limitations imposed by current technologies thereby enabling the definition and control of structures and devices at the nanoscale.

The key areas in micro/nanoelectronics research being pursued at Tyndall include:

The fabrication and characterisation of novel nanoscale device structures on silicon. This work is designed to help industry to continue along the trajectory defined by Moore’s Law.
The heterogeneous integration of nanoscale materials into practical working devices of interest to the electronics industry.

The integration of novel functional materials onto active silicon devices, designed to permit the delivery of added functionality for systems-on-chip (SoC) applications including on-chip power, sensing and actuation.

Looking forward, the long-term aim of this research is to deliver a fully integrated post-processing capability for novel materials onto silicon CMOS platforms that will be compatible with current and future wafer processing technologies.

High-k Materials on Silicon

The development of transistors for future integrated circuits will require radical changes to the materials that make up the device. The combination of high permittivity (high-k) gate oxides and semiconductor substrates with higher carrier mobility are seen as essential to continue transistor scaling well into the next decade. S

FI investigator Paul Hurley, working in collaboration with researchers at Tyndall, Dublin City University, Trinity College Dublin and Intel Ireland, has recently demonstrated a new approach for the formation of high-k materials on silicon and on high mobility substrates, which will be a key element in the production of future integrated circuits with reduced power dissipation and increased speed.

Functional Organic Nanowires

Semiconducting polymers are attractive materials for opto-electronic applications because their optical and electronic properties can be manipulated by altering their chemical composition. The Nanotechnology Group, led by Gareth Redmond, has focused on developing routes for formation of organic nanowires and nanotubes. The group has recently used single polymer nanowires as ultra-miniature photodetectors based on generation of an electrical current by incident light photons.

Photoconductivity measurements on a single polymer nanowire device yielded external quantum efficiencies of approximately 0.1% (electrons out per incident photon), comparable with inorganic nanowire devices. The group are currently focusing on extending this approach to the demonstration of other key opto-electronic functionalities, including electrically-driven light emission.

Magnetic Nanocables

Further miniaturisation of electronic circuits will necessitate the construction of multi-layered, nanostructure devices with dimensions below 100 nm. Researchers in the Materials and Supercritical Fluids Research Group, led by Justin Holmes, have successfully produced high-density arrays of coaxial nanocables.

These nanocables consist of cobalt (Co) nanowires surrounded by magnetite (Fe3O4) nanotube sheaths. The combination of separate hard (Co) and soft (Fe3O4) magnetic materials in such a radial structure is potentially a very powerful tool for the future fabrication of new multifunctional devices, such as spin valves and high-density magnetic storage devices.

Heterostructure Photonic Crystals

Photonic crystals are periodic optical nanostructures designed to control and manipulate the propagation of light. The Advanced Materials & Surfaces Group, led by Martyn Pemble, recently fabricated composite (heterostructure) photonic crystals prepared from silica particles of two different sizes.

Careful tuning of the relative sizes of the particles results in an “optical diode" effect, where the intensity of the reflected light depends on whether the structure is illuminated from the front or the back. This could find application in a wide range of devices including light filters, waveguides or even in light confinement devices for improved solar cells.