21-04-2012, 04:14 PM
Crystals and Snowflakes: Building Computation from Nanowire
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BOTTOM-UP APPROACH
A promising alternative to top-down lithography is
bottom-up material and device synthesis. Rather than
building a structure and carving out its shape, modern
chemical synthesis is demonstrating ways to build
structures of precise dimensions through bottom-up
self-assembly. Just as molecules and crystals have
precise, fixed dimensions, carbon nano tubes, atomic
layers, and silicon nano wires can be grown1 and
assembled to precise dimensions.2
Architecture for crystal-like structures
To exploit these bottom-up processes, our
architectures embrace the regularity and
randomness. We start with regular, orthogonal
layers of parallel nano wires, where the nano
wire dimensions and features are defined from
the bottom up. In building this “crossed-wire
crystal,” we assemble materials on the wires so
that the cross points can act as variableresistance,
wired-OR devices, and we control
the material’s composition in the nano wire so
that it has gate able regions integrated along its
length. This lets us build programmable
crossbars for memory, programmable logic array
(PLA), and crossbar interconnection. We use
coarse-grain, lithographic etching to divide the
chip into modest-size crossbar arrays, then
define the arrays as memory, logic, and
interconnect.
Nanowire composition
Nano wires can be composed of different
materials or do pants along their length, to nearatomic
precision by timed growth.3 significantly,
we can change the effective conduction
threshold along the length of the nano wire. This
lets us build nanostructures that act like wires,
always conducting along most of their length,
but including field-effect gate able regions at
selected points.