MEMRISTOR:(a future memory device)
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| FIG:memristor symbol |
What is a memristor? Memristors are basically a fourth class of
electrical circuit, joining the resistor, the capacitor, and the
inductor, that exhibit their unique properties primarily at the
nanoscale. Theoretically, Memristors, a concatenation of “memory
resistors”, are a type of passive circuit elements that maintain a
relationship between the time integrals of current and voltage across a
two terminal element. Thus, a memristors resistance varies according to
a devices memristance function, allowing, via tiny read charges, access
to a “history” of applied voltage. The material implementation of
memristive effects can be determined in part by the presence of
hysteresis (an accelerating rate of change as an object moves from one
state to another) which, like many other non-linear “anomalies” in
contemporary circuit theory, turns out to be less an anomaly than a
fundamental property of passive circuitry.
Until recently, when HP Labs under Stanley Williams developed the
first stable prototype, memristance as a property of a known material
was nearly nonexistant. The memristance effect at non-nanoscale
distances is dwarfed by other electronic and field effects, until scales
and materials that are nanometers in size are utilized. At the
nanoscale, such properties have even been observed in action prior to
the HP Lab prototypes.
But beyond the physics of electrical engineering, they are a
reconceptualizing of passive electronic circuit theory first proposed in
1971 by the nonlinear circuit theorist Leon Chua. What Leon Chua, a UC
Berkeley Professor, contended in his 1971 paper Transactions on Circuit
Theory, is that the fundamental relationship in passive circuitry was
not between voltage and charge as assumed, but between
changes-in-voltage, or flux, and charge. Chua has stated: “The situation
is analogous to what is called “Aristotle’s Law of Motion, which was
wrong, because he said that force must be proportional to velocity. That
misled people for 2000 years until Newton came along and pointed out
that Aristotle was using the wrong variables. Newton said that force is
proportional to acceleration–the change in velocity. This is exactly the
situation with electronic circuit theory today. All electronic
textbooks have been teaching using the wrong variables–voltage and
charge–explaining away inaccuracies as anomalies. What they should have
been teaching is the relationship between changes in voltage, or flux,
and charge.”
As memristors develop, its going to come down to, in part, who can
come up with the best material implementation. Currently IBM, Hewlett
Packard, HRL, Samsung and many other research labs seem to be hovering
around the titanium dioxide memristor, but there are quite a few other types of memristors with vectors of inquiry.
