While consumers have seen the
price of data storage media of all kinds drop while storage capacity and
densities have risen, one thing remains constant for all bit-based mechanisms:
binary 0s and 1s represent data. They may be stored and interpreted by
different means, but binary is the system that all our personal electronics use
from data storage to volatile memory to processing itself.
One way to further increase density could be to add a third state, or a 2.
UPenn's nanowire storage medium does just that. The wire itself is a coaxial
system, like the cable that carries television into your cable box. The
nanowire's shell is composed of germanium telluride (GeTe), while the core is a
more complex germanium/antimony/tellurium compound Ge2Sb2Te5 .
Both of these materials are known as phase-change materials. Under the stimulus
of an electric field, the materials change from a crystalline, ordered
structure to an amorphous, unordered. To supplement this, the core and shell
can be separately modified from crystalline to amorphous.
To make this work as a data storage device, picture the crystalline state to be
a 0 and the amorphous to be a 1. When the compounds are in a crystalline state,
they have a very low resistance to electricity thanks to their crystalline
structure. When an electric pulse is applied, the compound heads and becomes
amorphous, greatly increasing its resistance to current flow. In this way,
measuring the resistance of the nanowire can result in either a 0 or 1.
Where the magic happens is when the shell and core are separately tuned, one
crystalline while the other is amorphous. This creates a third level of
resistance over the nanowire – the 2.
In addition to a third readable state, UPenn's nanowires
have other properties which make them ideal for volatile memory storage. Due to
the third state itself, densities become much greater. This could either enable
smaller memory devices for portable electronics, or much more storage in
current form factors.
Such tiny structures have been known to self-assemble. A bottom up assembly
would revolutionize memory production which typically relies on a top down
approach. Rather than etching circuits into various materials, the nanotubes
could be coaxed to assemble themselves into usable structures. Combined with a
crystal's tendency to lack defects, this could enable entirely new production
methods which involve less outside manipulation, cutting cost and loss simultaneously.