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Nanotechnology Computer Aided Design

Objective

The development of novel devices at the nanometer scale with potential for large-scale integration and room temperature operation is a challenging task. The quest for nanotechnology information devices will greatly benefit from a more intensive use of tools for detailed modelling of molecular and nanoelectronic devices. Nanotcad is an integrated theoretical and experimental project aimed at
1) developing and validating a software package for the simulation and the design of a wide spectrum of nanoscale devices, based both on semiconductors and on transport through single molecules. The NANOTCAD package will be made freely available to the Nanotechnology Information Device community.
2) The fabrication and optimisation of semiconductor and molecular nanodevices on the basis of the modelling tools developed.
The development of novel devices at the nanometer scale with potential for large-scale integration and room temperature operation is a challenging task. The quest for nanotechnology information devices will greatly benefit from a more intensive use of tools for detailed modelling of molecular and nanoelectronic devices. Nanotcad is an integrated theoretical and experimental project aimed at
1) developing and validating a software package for the simulation and the design of a wide spectrum of nanoscale devices, based both on semiconductors and on transport through single molecules. The NANOTCAD package will be made freely available to the Nanotechnology Information Device community.
2) The fabrication and optimisation of semiconductor and molecular nanodevices on the basis of the modelling tools developed.

OBJECTIVES
The NANOTCAD project has four main objectives:
1. The development and the validation of a software package for the simulation and the design of a wide spectrum of devices, based both on semiconductors and on transport through single molecules.
2. The demonstration of a procedure for the realisation of prototype nanoscale devices based on detailed modeling.
3. The design, fabrication, characterization and optimisation of single and double quantum-dot HFETs for use as single /few electron memories.
4. The design, fabrication, characterization and optimisation of molecular field effect transistors based on Mott transition.

DESCRIPTION OF WORK
The pursuit of the objectives of the NANOTCAD project requires a very close collaboration between the theoretical and the experimental activities.
The experimental activity encompasses two nanofabrication approaches that include a significant degree of self-assembly, and are promising for ultra large scale of integration: "Molecular Nanofabrication" (WP6) is focused on the fabrication of two and three terminal devices at the molecular level. "Semiconductors Nanofabrication" (WP4) is focused on the fabrication of devices based on self-assembled InGaAs heterostructures. The theoretical activity covers a broad range of approaches to electron transport in nanoscale devices.
A continuous exchange of information between the groups involved in modelling will define a common framework for the different approaches and will allow integration of various modelling codes.
The theoretical activity is structured into five workpackages (WP):L%"Molecular Modeling" (WP5) aims at the detailed modelling of transport through single molecules connected to metal electrodes, also in the presence of an external electric field due to a control gate.
"Semiconductor Modelling-quasi equilibrium" (WP1) addresses transport in nanoscale devices in the linear response and in the tunnelling regimes, with a complete quantum-mechanical model.
"Semiconductor Modelling -coupling with Drift-Diffusion codes" (WP2) aims at coupling the simulation of single electron with standard simulators of semiconductor devices.
"Quantum Monte Carlo modelling" (WP3) aims at the solution of quantum transport in far from equilibrium conditions with Monte Carlo algorithms.
Finally, "Integration" (WP7) aims at the definition of a common interface for all codes, that allows to exchange material parameters, devices structures, potential profiles and charge densities, and to integrate algorithms from different workpackages.
Project objectives have been largely met. A set of software tools have been developed and freely distributed to the European nanotechnology community through the Phantoms Simulation Hub (www.phantomshub.com) and comprehensive manuals have been prepared for non-expert users. Such tools include codes for the self-consistent solution of Poisson-Schrodinger equation in semiconductor nanostructures with regions subjected to strong quantum confinement based on density functional theory (NANOTCAD1D, NANOTCAD2D, NANOTCAD3D), a quantum Monte Carlo code for the physically detailed simulation of one-dimensional devices operating in far from equilibrium conditions and in presence of strong dissipative phenomena (VMC), a code for the simulation of transport through single molecules contacted with metal electrodes immersed in a generic scalar potential (VICI), and a code for the three-dimensional simulation of semiconductor nanostructures (SIMNAD) coupled to a commercial drift-diffusion simulator (DESSIS_ISE).

As far as semiconductor nanofabrication is concerned, very interesting results have been obtained: memories consisting of an AlGaAs-GaAs HFET with a single layer and a double layer of InGaAs quantum dots have been demonstrated, with very fast write and erase times, and promising retention retention times. In addition, nanoscale FETs have been fabricated and characterized in which a unique signature of ballistic transport has been identified in the transconductance behaviour as a function of gate bias. A series of nanoscale devices have been fabricated that have helped in validating and testing the software tools developed within the project. The molecular nanofabrication activity has successfully led to the demonstration of two techniques to fabricate a molecular device in which a small molecule bridges two metal electrodes separated by a gap of 1 nm. The first technique allowed to contact benzenedithiol molecules between two wires in crossed geometry. The second technique allowed to place benzenedithiol molecules in nanogaps induced by controlled electromigration. In both cases it was possible to measure current-voltage characteristics exhibiting non-linear features close to those observed by other groups. Notwithstanding the instrinsicly poor reproducibility of molecular structures, results achieved within NANOTCAD are at the state of the art in the field.

Funding Scheme

CSC - Cost-sharing contracts

Coordinator

UNIVERSITA DI PISA
Address
Lungarno Pacinotti 43/44
56100 Pisa
Italy

Participants (5)

BAYERISCHE JULIUS-MAXIMILIANS UNIVERSITAET WUERZBURG
Germany
Address
Sanderring 2
97070 Wuerzburg
EIDGENOESSISCHE TECHNISCHE HOCHSCHULE ZUERICH
Switzerland
Address
Raemistrasse 101
8092 Zuerich
MAX-PLANCK GESELLSCHAFT ZUR FOERDERUNG DER WISSENSCHAFTEN E.V.
Germany
Address
Hofgartenstrasse 8
80539 Muenchen
TECHNISCHE UNIVERSITAET WIEN - INSTITUT FUER MIKROELEKTRONIK
Austria
Address
Gusshausstrasse 27-29
1040 Wien
UNIVERSITY COLLEGE CORK - NATIONAL UNIVERSITY OF IRELAND, CORK
Ireland
Address
Western Road
Cork