If molecular electronics is to become technologically
significant we must find ways to combine the " bottom-up"
self-assembly of simple nanoscale structures with the
arbitrarily complex "top-down" design and manufacturing of
the entire circuit that will allow a designer to create
exactly what she wants. Reconfigurable computer
architectures allow the downloading of logically complex
(high entropy) structures into highly symmetric (low
entropy) nanoscale assemblies. These architectures
additionally solve the problem of defect-tolerance - how to
efficiently map a perfect logical circuit onto an imperfect
self-assembled structure.
[A5.002] Molecular Materials and Devices
Cherie Kagan (IBM T. J. Watson Research Center)
Efforts to fabricate devices based on active molecular
components have been driven by both the fundamental interest
in using chemistry to build function at the molecular level
and the looming technological expectation of the end of
Moore’s law. In this talk, we describe the directed assembly
of organic and metal-metal bonded supramolecular systems
that are interesting materials for potential electronic and
memory device applications. Molecules are chosen with head
groups that bind to metal or oxide surfaces and tail groups
that bind to metal electrodes or that template the growth of
the particular molecular system. Optical spectroscopy,
scanning probe microscopy, electrochemistry, and electrical
measurements are used to characterize the chemistry and
physics of molecular assemblies and the behavior of devices.
We demonstrate the layer-by-layer assembly of metal-metal
bonded supramolecules and utilize this approach to fabricate
molecular devices.
[A5.003] Intrinsic Electron Conduction Mechanisms in Molecules
Mark Reed (Departments of Applied Physics and Electrical Engineering, Yale University)
Electron devices containing molecules as the active region have been an active area of research over the last few years. This talk presents measurements in a variety of molecular systems to elucidate the transport mechanisms, specifically in self-assembled monolayers (SAMs) using nanometer scale devices. Detailed kinetic studies are necessary to distinguish between different conduction mechanisms; for example, in alkanes temperature-independent electron transport is observed, proving tunneling as the dominant conduction mechanism when defects are eliminated from the device structure. This is distinct from Langmuir-Blodgett films, where only defect or filamentary conduction has been observed. A barrier height of 1.39 +/- 0.01 eV and a zero field decay coefficient of 0.79 /1 0.01 Å-1 are determined for alkanethiols.[1] The results are consistent with inelastic electron tunneling spectroscopy of the molecules in the junction. Deviation from this classic behavior for more complex molecule structures, and a comparison of the differences and pitfalls of various fabrication and characterization approaches, will be discussed.
[1] W. Wang et al., Phys. Rev. B 68, 035416 (2003)
[A5.004] Molecular and Nanowire Nanoelectronics
M. Meyyappan (NASA Ames Center for Nanotechnology)
Several alternatives have been proposed to go beyond CMOS
technology. At NASA Ames Center for Nanotechnology (NACNT),
we have focused on building vertically aligned semiconductor
single crystal nanowire (NW) and molecular wire (MW)
platforms for 3D integration of nanoelectronic devices and
systems. The platforms allow high performance device
architecture implementation, for example, vertical surround
gate transistors (VSGT) and VSGT based memory and logic and
multilevels or multibits information processing, which are
radically different from conventional planar CMOS
architectures. This approach allows ultrahigh density
fabrication and integration while compatible with typical
CMOS processing. In this talk, we will present recent
demonstrations of multilevel MW-NW memory devices and
vertical top and surround gate NW transistors. In addition
to intriguing chemistry and physics, the demonstrations also
reveal challenges in materials, interfaces, integration, and
heat dispassion. However, given the flexibility in materials
choice, nanoscale interface, 3D integration and
compatibility with CMOS fabrication and operation, these
challenges can be turned into opportunities to go beyond
CMOS limit. Contributions from Jie Han, H.T.Ng and Bin Yu
are acknowledged.
[A5.005] Signal Processing in Atomistic Systems
Jorge Seminario (University of South Carolina)
Scenarios for signal processing in molecular electronics (moletronics) whereby microelectronics can further be scale-down below its minimum feature size making use of the programmability feature of molecular devices will be presented. Since the minimum feature size also determines the smallest addressable distances in the fabrication of electronic circuits, any potential molecular device in the nanometer size would be discarded, except if this device could be programmed remotely to perform a specific function. Recent work showed with examples based on ab initio quantum calculations how molecules with high nonlinear behavior able to be assembled on an array by chemical (as opposed to lithographic) means can have multi-valued responses and thus are able to be programmed. Molecular programmability compensates for the inability to address feature sizes in the range of one nanometer, and therefore complements and expands the capabilities of present microelectronics to the nanometer domain. Thus, we analyzed and proposed the solution to the critical point for the development of molecular electronics, i.e., the programmability of the electronic devices to compensate for the inability to perfectly address chemically assembled molecules. A description of the methods and techniques that comprise the molecular electronics design automation tools will be presented followed by the presentation of several scenarios for the processing of signals, including the use of molecular electrostatic potentials, electron transfer, and molecular vibrations.