MOLECULAR COMPUTING: INTEGRATION OF MOLECULES FOR NANOCOMPUTING - Bio-Inspired and Nanoscale Integrated Computing - page 295

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MOLECULAR COMPUTING:
INTEGRATION OF MOLECULES
FOR NANOCOMPUTING
James M. Tour and Lin Zhong
Molecular computing seeks to implement nanoscale computation systems using
molecules or molecular bundles. Enormous progress has been made in construct-
ing nanoscale switching devices from molecules. Devices based on individual
molecules and molecular bundles have been demonstrated for logic gates and
memory units. However, the construction of a practical molecular computer will
require the molecular switches and their related interconnect technologies to
behave as large-scale heterogeneous logic, with input/output wires scaled to
molecular dimensions so that we can take advantage of the ultrasmall size of
the molecules. While numerous innovations have been made in fabrication and
design methodologies, no implementations have yet been reported to be at any
scale comparable to what can be achieved by the conventional silicon MOSFET
technology. In this chapter, we will describe the switching and memory effects of
molecular bundles and address practical circuit and architecture solutions for
large-scale integration of molecular switches for computing.
We further show that molecules can be employed to enhance silicon-based
computing. The drain current I D and threshold voltage V T in pseudo-MOSFETs
can be controllably modulated by grafting a monolayer of molecules atop oxide-
free H-passivated silicon surfaces, and this effect should be extenuated in
nanoscale devices where the surface-to-volume ration increases. The technology
provides a new mechanism to control process variations and leakage power
consumption in conventional MOSFET circuits. Moreover, intrinsic silicon
nanowires with different surface states exhibited a p-type doping behavior with
clear differences in resistivity and hole mobility. By controlling the surface state
density, acceptable electrical operation can be achieved directly on intrinsic Si
nanowires without bulk doping. The technology provides a potential alternative to
bulk impurity doping for nanoscale silicon structures.