NMRC: Research Highlights - Nanotechnology

Recent advances in our understanding of fundamental physical and chemical processes and in our ability to manipulate structures at the sub-micron and nanometer scale have given birth to a new field of scientific and engineering research - nanoscale science and technology.

This emerging field of research is aimed at increasing control over material structures of nanoscale size (1 to 100 nanometres) in at least one dimension. Nanotechnology, therefore, comprises a cluster of emerging techniques combined from physics, chemistry, biology, engineering and microelectronics that are capable of manipulating matter at the minutest levels of detail - the nanoscale. This discipline will, over the coming decades, result in the development of new scientific knowledge and new technologies in areas ranging from ICT to medicine and biotechnology.

Highlights of the nanotechnology activities at NMRC during 1999 are as follows:-

NMRC Funded as Irish Nanotechnology Hub

Figure 25:- NMRC is the driver of a cross-disciplinary inter-departmental Nanoscale Science and Technology Research Initiative at University College Cork and Cork Institute of Technology (CIT).

In July 1999, NMRC received significant capital funding, under the Irish Government funded HEA Programme for Research in Third Level Institutions 1999- 2001 to establish a National Nanofabrication Facility. The facility mission is to achieve international pre-eminence in the microelectronics technologies that underpin design, fabrication and application of nanosystems and to enable Irish researchers to conduct world-class nanotechnology research. In addition, NMRC will drive a university-wide Nanoscale Science and Technology Initiative at UCC. The objective will be to establish a new fourth level of world-class research activity within state-of-the-art research facilities and to ultimately position UCC at the forefront of nanoscale science and technology research in Ireland and worldwide (see Figure 25).

Molecular Electronics

Advanced methods for nanoscale electronic device fabrication are under development at NMRC. An interdisciplinary approach exploiting strategies borrowed from chemistry, molecular biology and biotechnology is being taken. Biomolecule-based self- assembly is being used to fabricate nanoscale electronic devices such as single electron transistors by localising single molecular electronic components at pre- defined junctions within nanoscale circuits. Fabrication and characterisation of these devices is being undertaken within a newly established nanotechnology biomaterials laboratory and electrical measurement facility (see Figures 26 and 27).

Figure 26:- DNA synthesis facilities in the Nanotechnology Biomaterials Laboratory.

Figure 27:- Nanoscale electronic device characterisation facility.

Silicon Nanoelectronics

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Fabrication of quantum devices based on epitaxially grown, Si/SiGe heterostructures has resulted in the development of new types of enhancement-mode heterostructure field effect transistors (HFETs), n-type and p-type modulation-doped field effect transistors (MODFETs) and strained-silicon MOSFETs. A key advance within the CMOS-based fabrication process has been the replacement of deposited gate oxides with oxides grown by wet thermal oxidation. Development of Si/SiGe-based, resonant tunnelling diodes (RTDs) is also underway, (see Figure 28). These devices, showing negative differential resistance, have potential applications in high-frequency circuits and in fast, low-power logic and memory circuits. Device modelling activity in collaboration with faculty members at UCC has been undertaken to aid with design of layer structures (see Figure 29). This is used as a design aid for specifying material growth parameters and to optimise device characteristics. Finally, in collaborative research with the University of Cambridge, NMRC is attempting to understand metal-insulator transitions in inversion layers of silicon MOS devices at very low temperatures. High quality devices showing mobilities up to 17,000 cm2/Vs at 2 K have been fabricated at NMRC for these studies.

Expand Figure 28:- Schematic depiction of Si/SiGe resonant tunnel diode wafer structure.

Expand Figure 29:- Potential energy profile of a Si/SiGe modulation-doped field-effect transistor structure, calculated using a simultaneous Poisson/Schroedinger solver to account for quantum-mechanical effects.

Advanced Lithography

Figure 30:- Manual removal of a cured PDMS micromould from the surface of a glass microscope slide.

Non-photolithographic methods for patterning micron and sub-micron scale structures such as micromoulding in capillaries (MIMIC) are under development at NMRC. Micromoulds are formed by casting a pre-polymer, polydimethylsiloxane (PDMS), against a master fabricated using conventional patterning techniques. The PDMS polymer is cured and then easily removed by peeling away from the master (see Figure 30). Capillaries are formed when a PDMS micromould is subsequently brought into conformal contact with a substrate. These capillaries may be filled with a precursor solution of choice by drawing it through the capillary network by capillary action. Curing of such solutions in-situ within the micromould thereby produces patterned 3-D microstructures in a single step process with a re-usable tool. MIMIC technology is currently being employed within NMRC to pattern photonic microstructures such as integrated waveguides.

DNA based Self-assembly of Optoelectronic Integrated Systems

Figure 31:- Electronically addressable test chips used for electric field direct ed self-assembly of optoelectronic integrated systems and for development of genomic array technologies.

Self-assembly is a fabrication paradigm not necessarily restricted to the construction of nanometre scale devices. Self-assembly of micron scale objects is being undertaken at NMRC with the objective of fabricating optoelectronic-integrated systems (OEIS). Electronically addressable test chips, comprising n x n matrices of microelectrodes each bearing photolithographically-defined oligonucleotides of programmed base sequence, have been developed as experimental platforms for the self-assembly and interconnection of oligonucleotide-modified optoelectronic components, e.g., LEDs and photodetectors (see figure above).

DNA-modified optoelectronic components are transported to the surface of a microelectrode using electrophoresis whereupon sequence-specific, oligonucleotide interactions direct component localisation and binding (figure shows electric field induced transport of a 20 micron diameter GaAs dummy component towards the electrically active microelectrode pad on an addressable test chip surface). This biomimetic method of component transport and localisation is an entirely new approach to circuit fabrication.

Nanobiotechnology

Within the area of nanobiotechnology research, the hybrid microelectronics-molecular biology technologies developed above for the DNA-based self-assembly of OEIS are also being employed as tools for genomic research. At NMRC methodologies for the fabrication of high-density oligonucleotide arrays using photolithographic methods commonly employed within the microelectronics industry are being developed for detection of mutations and polymorphisms in DNA (see Figure 33).

Figure 33:- Schematic depiction of the complex "interfacial engineering" required to link hybridisation active oligonucleotide strands onto a silicon surface.

Also, electronically- addressable, microelectrode arrays, similar to those already mentioned, are being developed to facilitate complete on-chip detection and analysis of genetic information by hybridisation.

Future Nanotechnology Research

During the coming year, the Nanotechnology initiative at NMRC will continue its innovative and focused approach to nanoscale science and technology research and will further develop its understanding of nanoscale phenomena in order to construct new nanoscale structures, devices and systems. These nanoscale systems will subsequently be used as a tool-kit in the investigation of key physical and biological research problems such as, for example, understanding the nature of electron transport in nanoscale electronic devices and identifying gene function and relevance to the life cycle of cells and organisms in their changing environments.