Memristor
P.Balamurali Krishna & Rajesh.R
Department of Electronics and Communication Engineering
M.G. College of Engineering
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Abstract
A memristor is a passive two-terminal circuit element in which the resistance is a function of the history
of the current through and voltage across the device. Memristor theory was formulated and named
by Leon Chua in a 1971 paper. Chua strongly believed that a fourth device existed to provide conceptual
symmetry with the resistor, inductor, and capacitor. This symmetry follows from the description of basic
passive circuit elements as defined by a relation between two of the four fundamental circuit variables. A
device linking charge and flux (themselves defined as time integrals of current and voltage), which would
be the memristor, was still hypothetical at the time. However, it would not be until thirty-seven years
later, on April 30, 2008, that a team at HP Labs led by the scientist R. Stanley Williams would announce
the discovery of a switching memristor. Based on a thin film of titanium dioxide, it has been presented as
an approximately ideal device.
Introduction
A memristor is a passive two-terminal electronic
component for which the resistance (dV/dI) depends
in some way on the amount of charge that has flowed
through the circuit. When current flows in one
direction through the device, the resistance increases;
and when current flows in the opposite direction, the
resistance decreases, although it must remain
positive. When the current is stopped, the component
retains the last resistance that it had, and when the
flow of charge starts again, the resistance of the
circuit will be what it was when it was last active.
[8]
More generally, a memristor is a two-terminal
component in which the resistance depends on the
integral of the input applied to the terminals (rather
than on the instantaneous value of the input as in
a varistor). Since the element "remembers" the
amount of current that has passed through it in the
past, it was tagged by Chua with the name
"memristor." Another way of describing a memristor
is that it is any passive two-terminal circuit elements
that maintains a functional relationship between
the time integral of current (called charge) and the
time integral of voltage (often called flux, as it is
related to magnetic flux). The slope of this function is
called the memristance M and is similar to variable
resistance. Batteries can be considered to have
memristance, but they are not passive devices. The
definition of the memristor is based solely on the
fundamental circuit variables of current and voltage
and their time-integrals, just like
the resistor, capacitor, and inductor
Need For Memristor
Memristance (Memory + Resistance) is a property
of an Electrical Component that describes the
variation in Resistance of a component with the flow
of charge. Any two terminal electrical component
that exhibits Memristance is known as a Memristor.
Memristance is becoming more relevant and
necessary as we approach smaller circuits, and at
some point when we scale into nano electronics, we
would have to take memristance into account in our
circuit models to simulate and design electronic
circuits properly. An ideal memristor is a passive
two-terminal electronic device that is built to express
only the property of memristance (just as a resistor
expresses resistance and an inductor expresses
inductance). However, in practice it may be difficult
to build a 'pure memristor,' since a real device may
also have a small amount of some other property,
such as capacitance (just as any real inductor also has
resistance).A common analogy for a resistor is a pipe
that carries water. The water itself is analogous to
electrical charge, the pressure at the input of the pipe
is similar to voltage, and the rate of flow of the water
through the pipe is like electrical current. Just as with
an electrical resistor, the flow of water through the
pipe is faster if the pipe is shorter and/or it has a
larger diameter. An analogy for a memristor is an
interesting kind of pipe that expands or shrinks when
water flows through it. If water flows through the
pipe in one direction, the diameter of the pipe
increases, thus enabling the water to flow faster. If
water flows through the pipe in the opposite
direction, the diameter of the pipe decreases, thus
slowing down the flow of water. If the water pressure
is turned off, the pipe will retain it most recent
diameter until the water is turned back on. Thus, the
pipe does not store water like a bucket (or a
capacitor) – it remembers how much water flowed
through it.
Possible applications of a Memristor include
Nonvolatile Random Access
Memory (NVRAM), a device that can retain memory
information even after being switched off, unlike
conventional DRAM which erases itself when it is
switched off. Another interesting application is analog computation where a memristor will be able
to deal with analog values of data and not just binary
1s and 0s.
Memristor Theory And Its Properties:
Definition of Memristor
“The memristor is formally defined as a
two-terminal element in which the magnetic flux Φm
between the terminals is a function of the amount of
electric charge q that has passed through the device.”
Figure 5. Symbol of
Memristor.
Chua defined the element as a resistor whose
resistance level was based on the amount of charge
that had passed through the memristor
Memristance
Memristance is a property of an electronic
component to retain its resistance level even after
power had been shut down or lets it remember (or
recall) the last resistance it had before being shut off.
Conclusion
By redesigning certain types of circuits to include
memristors, it is possible to obtain the same function
with fewer components, making the circuit itself less
expensive and significantly decreasing its power
consumption. In fact, it can be hoped to combine
memristors with traditional circuit-design elements to
produce a device that does computation. The
Hewlett-Packard (HP) group is looking at developing
a memristor-based nonvolatile memory that could be
1000 times faster than magnetic disks and use much
less power.