Memristor - The Missing Element

A SEMINAR REPORT
ON
MEMRISTOR
MAHARANA PRATAP ENGINEERING COLLEGE
KOTHI MANDHANA, KANPUR
Session : 2009-2010
Staff Counselor: Submitted by:
DEPARTMENT OF MANGAL DAS
ELECTRONICS AND COMMUNICATION HIMANSHU RAMCHANDANI
ENGINEERING E.C- IV yr.
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CERTIFICATE
This is to certify that Mr. Mangal Das and Mr. Himanshu Ramchandani of E.C. Final Year have
submitted their seminar report on Memristor under the guidance of Electronics Engineering
Department. This seminar report is partial fulfillment of their B.Tech course from Uttar Pradesh
Technical University, Lucknow.
Er. PRIYANKA BAWA Er. SUDHA PANDEY
(SEMINAR GUIDE) (SEMINAR GUIDE)
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ABSTRACT
Typically electronics has been defined in terms of three fundamental elements such
as resistors, capacitors and inductors. These three elements are used to define the four fundamental
circuit variables which are electric current, voltage, charge and magnetic flux. Resistors are used to
relate current to voltage, capacitors to relate voltage to charge, and inductors to relate current to
magnetic flux, but there was no element which could relate charge to magnetic flux.
To overcome this missing link, scientists came up with a new element called
Memristor. These Memristor has the properties of both a memory element and a resistor (hence
wisely named as Memristor). Memristor is being called as the fourth fundamental component,
hence increasing the importance of its innovation.
Its innovators say “memrisrors are so significant that it would be mandatory to re-
write the existing electronics engineering textbooks.”
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CONTENTS
1. Acknowledgement 5
2. Introduction. 6
3. Fundamental Elements of Electronics. 7
4. The Missing Element: Memristor 14
5. Memristor Theory and Properties 16
6. Delay in Discovery of Memristor. 21
7. Working of Memristor 23
8. Analogous System 25
9. Potential Applications 26
10. New Horizons 28
11. Conclusion 29
12. Bibliography 30
ACKNOWLEDGEMENT
We would like to express our immense gratitude to all those who have directly or indirectly helped
us in completing our seminar on Memristor. I would like to thank them for their effective guidance
& kind cooperation without which we would not have been able to introduce a good presentation and
complete this seminar report.
We would like to thank the faculty members of Department of Electronics & Communication
Engineering for their permission grant, constant reminders and much needed motivation, which
helped us to extract maximum knowledge from the available sources.
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Lastly, my sincere thanks to all our friends for their coordination in completion of this seminar
report.
Mangal Das
Himanshu Ramchandnai
(E.C. 4th
Year )
INTRODUCTION
Generally when most people think about electronics, they may initially think of products such
as cell phones, radios, laptop computers, etc. others, having some engineering background, may think
of resistors, capacitors, etc. which are the basic components necessary for electronics to function.
Such basic components are fairly limited in number and each having their own characteristic
function.
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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.
The reason that the Memristor is radically different from the other fundamental circuit
elements is that, unlike them, it carries a memory of its past. When you turn off the voltage to the
circuit, the Memristor still remembers how much was applied before and for how long. That's an
effect that can't be duplicated by any circuit combination of resistors, capacitors, and inductors,
which is why the Memristor qualifies as a fundamental circuit element.
The arrangement of these few fundamental circuit components form the basis of almost all of
the electronic devices we use in our everyday life. Thus the discovery of a brand new fundamental
circuit element is something not to be taken lightly and has the potential to open the door to a brand
new type of electronics. HP already has plans to implement Memristors in a new type of non-volatile
memory which could eventually replace flash and other memory systems.
FUNDAMENTAL ELEMENTS OF ELECTRONICS
1 .RESISTOR
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A resistor is a two-terminal electronic component that produces a voltage across its terminals that is
proportional to the electric current through it in accordance with Ohm's law which states
“Voltage (V) across a resistor is proportional to the current (I) through it where the constant of
proportionality is the resistance (R)”.
V = IR
Electronic symbol
(Europe) (US)
Resistors are elements of electrical networks and electronic circuits and are ubiquitous in most
electronic equipment. Practical resistors can be made of various compounds and films, as well as
resistance wire (wire made of a high-resistivity alloy, such as nickel/chrome).
The primary characteristics of a resistor are the resistance, the tolerance, maximum working
voltage and the power rating. Other characteristics include temperature coefficient, noise, and
inductance. Less well-known is critical resistance, the value below which power dissipation
limits the maximum permitted current flow, and above which the limit is applied voltage.
Critical resistance depends upon the materials constituting the resistor as well as its physical
dimensions; it's determined by design.
Resistors can be integrated into hybrid and printed circuits, as well as integrated circuits. Size,
and position of leads (or terminals) are relevant to equipment designers; resistors must be
physically large enough not to overheat when dissipating their power.
COLOUR CODING OF RESISTOR
Four-band identification is the most commonly used color-coding scheme on resistors. It
consists of four colored bands that are painted around the body of the resistor. The first two
bands encode the first two significant digits of the resistance value, the third is a power-of-ten
multiplier or number-of-zeroes, and the fourth is the tolerance accuracy, or acceptable error, of
the value.
Each color corresponds to a certain digit, progressing from darker to lighter
colors, as shown in the chart below
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For example, green-blue-yellow-red is 56×104
Ω = 560 kΩ ± 2%. An easier description can be
as followed: the first band, green, has a value of 5 and the second band, blue, has a value of
6, and is counted as 56. The third band, yellow, has a value of 104
, which adds four 0's to
the end,creating 560,000Ω at ±2% tolerance accuracy. 560,000Ω changes to 560 kΩ ±2%
(as a kilos 103
).
2. CAPACITOR
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A capacitor or condenser is a passive electronic component consisting of a pair of conductors
separated by a dielectric. When a voltage potential difference exists between the conductors, an
electric field is present in the dielectric. This field stores energy and produces a mechanical force
between the plates. The effect is greatest between wide, flat, parallel, narrowly separated conductors.
An ideal capacitor is characterized by a single constant value, capacitance, which is measured in
farads. This is the ratio of the electric charge on each conductor to the potential difference between
them. In practice, the dielectric between the plates passes a small amount of leakage current. The
conductors and leads introduce an equivalent series resistance and the dielectric has an electric field
strength limit resulting in a breakdown voltage.
Capacitors are widely used in electronic circuits to block the flow of direct current while allowing
alternating current to pass, to filter out interference, to smooth the output of power supplies, and for
many other purposes. They are used in resonant circuits in radio frequency equipment to select
particular frequencies from a signal with many frequencies.
ELECTRONIC SYMBOL
CURRENT-VOLTAGE RELATION
The current i (t ) through a component in an electric circuit is defined as the rate of change of the
charge q (t ) that has passed through it. Physical charges cannot pass through the dielectric layer of
a capacitor, but rather build up in equal and opposite quantities on the electrodes: as each electron
accumulates on the negative plate, one leaves the positive plate. Thus the accumulated charge on the
electrodes is equal to the integral of the current, as well as being proportional to the voltage (as
discussed above). As with any antiderivative, a constant of integration is added to represent the initial
voltage v (t0).
This is the integral form of the capacitor equation,
.
Taking the derivative of this, and multiplying by C, yields the derivative form,
.
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The dual of the capacitor is the inductor, which stores energy in the magnetic field rather than the
electric field. Its current-voltage relation is obtained by exchanging current and voltage in the
capacitor equations and replacing C with the inductance L.
3. INDUCTOR
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An inductor or a reactor is a passive electrical component that can store energy in a magnetic
field created by the electric current passing through it. An inductor's ability to store magnetic energy
is measured by its inductance, in units of henries. Typically an inductor is a conducting wire shaped
as a coil, the loops helping to create a strong magnetic field inside the coil due to Faraday's law of
induction. Inductors are one of the basic electronic components used in electronics where current
and voltage change with time, due to the ability of inductors to delay and reshape alternating currents
Inductance (L) (measured in henries) is an effect resulting from the magnetic field that forms around
a current-carrying conductor that tends to resist changes in the current. Electric current through the
conductor creates a magnetic flux proportional to the current. A change in this current creates a
change in magnetic flux that, in turn, by Faraday's law generates an electromotive force (EMF) that
acts to oppose this change in current. Inductance is a measure of the amount of EMF generated for a
unit change in current. For example, an inductor with an inductance of 1 henry produces an EMF of
1 volt when the current through the inductor changes at the rate of 1 ampere per second. The number
of loops, the size of each loop, and the material it is wrapped around all affect the inductance.
An inductor opposes changes in current. An ideal inductor would offer no resistance to a
constant direct current; however, only superconducting inductors have truly zero electrical resistance.
In general, the relationship between the time-varying voltage v(t) across an inductor with
inductance L and the time-varying current i(t) passing through it is described by the differential
equation:
.
Inductors are used extensively in analog circuits and signal processing. Inductors in conjunction
with capacitors and other components form tuned circuits which can emphasize or filter out specific
signal frequencies. Applications range from the use of large inductors in power supplies, which in
conjunction with filter capacitors remove residual hums known as the Mains hum or other
fluctuations from the direct current output, to the small inductance of the ferrite bead or torus
installed around a cable to prevent radio frequency interference from being transmitted down the
wire. Smaller inductor/capacitor combinations provide tuned circuits used in radio reception and
broadcasting.
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Two (or more) inductors which have coupled magnetic flux form a transformer, which is a
fundamental component of every electric utility power grid. The efficiency of a transformer may
decrease as the frequency increases due to eddy currents in the core material and skin effect on the
windings. Size of the core can be decreased at higher frequencies and, for this reason, aircraft use
400 hertz alternating current rather than the usual 50 or 60 hertz, allowing a great saving in weight
from the use of smaller transformers.
An inductor is used as the energy storage device in some switched-mode power supplies. The
inductor is energized for a specific fraction of the regulator's switching frequency, and de-energized
for the remainder of the cycle. This energy transfer ratio determines the input-voltage to output-
voltage ratio. This XL is used in complement with an active semiconductor device to maintain very
accurate voltage control.
Inductors are also employed in electrical transmission systems, where they are used to depress
voltages from lightning strikes and to limit switching currents and fault current. In this field, they are
more commonly referred to as reactors.
Larger value inductors may be simulated by use of gyrator circuits.
Fig: An inductor with two 47mH windings, as may be found in a power supply
THE MISSING LINK :
There are six different mathematical relations connecting pairs of four fundamental circuit
variables viz. current I, voltage v, charge q, and magnetic flux Φ.
One of these relation (the charge is time integral of current) is determined from the definition
of two of the variables and another (the flux is the timeintegral of the electromotive force or
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Φ=Li
voltage) is determined from faraday’s law of induction. Thus there should be four basic
circuit elements described by the remaining relation between the variables .
The relation between these fundamental elements can be shown as :
The relation between the charge and the flux was unknown, and so the device which
describes it. This led to the discovery of the fourth fundamental element which describes the
above missing relation between Charge And Flux.
THE 4TH
NEW FUNDAMENTAL ELEMENT : MEMRISTOR
Memristor is one of four basic electrical circuit components, joining the resistor, capacitor, and
inductor. The Memristor, short for “memory resistor” was first theorized by student Leon Chua in
the early 1970s. He developed mathematical equations to represent the Memristor, which Chua
believed would balance the functions of the other three types of circuit elements.
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(q=Cv)
(v=dΦ/dt) (i=dq/dt)
Voltage
(v)
Current
(i)
Charge
(q)
Flux
(Φ)
RESISTORS
INDUCTORSCAPACITORS
?
?
(v=Ri)

Since, there is no proof of any practical device which shows memristance, according to Chua’s paper
In the beginning of 2006, the group of researchers headed by R.Stanley Williams at HP labs,
developed a simple model of binary switch based on the coupled movement of both charge dopants
and electrons in the semiconductor and saw that the defining equations for this switch were identical
to Chua’s mathematical definitions of memristor and they were able to write down a defining
equation for memristance of this device interms of its physical and geometric properties
MEMRISTOR
FIG: A CROSSBAR ARRAY OF MEMRISTOR
NEED OF MEMRISTOR
The known three fundamental circuit elements as resistor, capacitor and inductor relates four
fundamental circuit variables as electric current, voltage, charge and magnetic flux. In that we were
missing one element to relate charge to magnetic flux. That is where the need for the fourth
fundamental element comes in. This element has been named as MEMRISTOR.
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FIG: RELATION BETWEEN ALL FOUR FUNDAMENTAL ELEMENTS OF
ELECTRONICS
MEMRISTOR: THEORY AND PROPERTIES
 Definition of Memristor
o “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.”
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 Electronic Symbol
 Chua defined the element as a resistor whose resistance level was based on the amount of
charge that had passed through the Memristor
 MEMRISTANCE
o 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.
 Chua’s. Theory
o Each Memristor is characterized by its memristance function describing the charge-
dependent rate of change of flux with charge.
o
 As we know from, Faraday's law of induction that magnetic flux is simply the time integral of
voltage, and charge is the time integral of current, we may write the more convenient
o It can be inferred from this that memristance is simply charge-dependent resistance. .
i.e. ,
 V(t) = M(q(t))*I(t)
 This equation reveals that memristance defines a linear relationship
between current and voltage, as long as charge does not vary. Of course,
nonzero current implies instantaneously varying charge. Alternating current,
however, may reveal the linear dependence in circuit operation by inducing a
measurable voltage without net charge movement—as long as the maximum
change in q does not cause much change in M.
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o
 As we know from, Faraday's law of induction that magnetic flux is simply the time integral of
voltage, and charge is the time integral of current, we may write the more convenient
o It can be inferred from this that memristance is simply charge-dependent resistance. .
i.e. ,
 V(t) = M(q(t))*I(t)
 This equation reveals that memristance defines a linear relationship
between current and voltage, as long as charge does not vary. Of course,
nonzero current implies instantaneously varying charge. Alternating current,
however, may reveal the linear dependence in circuit operation by inducing a
measurable voltage without net charge movement—as long as the maximum
change in q does not cause much change in M.
 CURRENT VS. VOLTAGE CHARACTERISTICS
o This new circuit element shares many of the properties of resistors and shares the
same unit of measurement (ohms). However, in contrast to ordinary resistors, in
which the resistance is permanently fixed, memristance may be programmed or
switched to different resistance states based on the history of the voltage applied to the
memristance material. This phenomena can be understood graphically in terms of the
relationship between the current flowing through a Memristor and the voltage
applied across the Memristor.
o In ordinary resistors there is a linear relationship between current and voltage so that a
graph comparing current and voltage results in a straight line. However, for
Memristors a similar graph is a little more complicated. It illustrates the current vs.
voltage behavior of memristance.
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Current vs. Voltage curve demonstrating hysteretic effects of memristance.
o In contrast to the straight line expected from most resistors the behavior of a
Memristor appear closer to that found in hysteresis curves associated with magnetic
materials. As observed above that two straight line segments are formed within the
curve. These two straight line curves may be interpreted as two distinct resistance
states with the remainder of the curve as transition regions between these two states.
HYSTERESIS MODEL
Hysteresis model illustrates an idealized resistance behavior demonstrated in accordance with above curretnt-
voltage characteristic wherein the linear regions correspond to a relatively high resistance (RH) and low
resistance (RL) and the transition regions are represented by straight lines.
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Fig: Idealized hysteresis model of resistance vs. voltage for memristance switch.
Thus for voltages within a threshold region (-VL2<V<VL1 in Fig. 4) either a high or low resistance exists for
the Memristor. For a voltage above threshold VL1 the resistance switches from a high to a low level and for a
voltage of opposite polarity above threshold VL2 the resistance switches back to a high resistance.
THE UNIQUE FEATURE: SELF PROGRAMMING
Stanley found an interesting feature of memristor that it can Re-program itself according to its
previous state for a given output.
This feature is revolution in the programming field of modern era. To verify their statement, they
have done a experiment which was related to programming of memristors.
The specifications of their experiment, which proved the fact about re-programming, is described by
an example.
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Fig: Programmed memristor map and transistor interconnections.
In this figure, “A” shows equivalent circuit schematic of the hybrid programmable logic array. The
dashed lines define the nanocrossbar boundary, the black dots are the programmed memristors, VA
through VD are the 4 digital voltage inputs and VOUT is the output voltage. V1 and V2 are the transistor
power supply voltage inputs. A single nanowire has a resistance of ≈33 kΩ, and 4 connected in series
provides a ≈130-kΩ on-chip load resistor for a transistor.
Figure “B” illustrates the map of the conductance of the memristors in the crossbar. The straight
lines represent the continuous nanowires, and their colors correspond to those of the circuit in A. The
broken nanowires are the missing black lines in the array. The squares display the logarithm of the
current througheach memristor at a 0.5-V bias.
The above figure is the equivalent circuit for testing the compound logic operation . This circuit
computes AB+CD from 4 digital voltage inputs, VA to VD, representing the 4 input values A to D,
respectively. The operations AB and CD are performed on 2 different rows in the crossbar, and the
results are output to inverting transistors, which then restore the signal amplitudes and send voltages
corresponding to NOT(AB) and NOT(CD), or equivalently A NAND B and C NAND D and denoted
using Boolean algebra as AB and CD, respectively, back onto the same column of the crossbar.
There, the operation AB X CD is performed and the result is sent to another inverting transistor,
which outputs the result AB X CD = AB + CD = AB + CD, following from De Morgan’s Law, as an
output voltage level on VOUT. The signal path is emphasized by the thick coloured lines red–blue–
green from the inputs to the output. In red, 2 programmed-ON memristors are linked to a transistor
gate to perform as a NAND logic gate with the inputs VA and VB in one operation or VC and VD in the
other. In blue, the outputs from the first 2 logic gates are then connected to the second
stage NAND gate formed from 2 other programmed-ON memristors and 1 transistor. The green line
shows the output voltage.This experiment began with the configuration of the array.The conductivity
of all of the crossbar nanowires was measured by making external connections with a probe station to
the contact pads at the ends of the fanout wires connected to each nanowire, and those that were not
broken or otherwise defective are shown as straight black or coloured lines.
Each required programmed-ON memristor was configured by externally applying a voltage pulse of
+4.5 V across its contacting nanowires, whereas all other memristors in the row and column of the
target junction were held at 4.5/2 = 2.25 V, a voltage well below the effective threshold such that
those junctions were not accidentally programmed ON.
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DELAY IN DISCOVERY OF MEMRISTOR
Memristor, was not been seen before because the effect depends on atomic-scale movements, it
only poped up on the nanoscale of William’s devices. Information can be written into the material as
the resistance state of the memristor in a few nanoseconds using few picojoules of energy-“ as good
as anything needs to be”.
THE COUPLED VARIABLE-RESISTOR MODEL FOR A MEMRISTOR
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 The Diagram with a simplified equivalent circuit. V, voltmeter; A, ammeter.
 Applied voltage and resulting current as a function of time t for a typical
memristor
The equation given below describes the memristance of any device as a function of charge :
where
M(q) = Memristance of a device as a function of charge
Roff = High resistance state
Ron = Low resistance state
µv = Mobility of charge
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q(t) = Charge flowing thorgh device at any time t
D = Thickness of semiconductor film sandwiched between two metal conatcts
For any material, this term is 1,000,000 times larger in absolute values at nanometer scale then is at
micrometer scale because of factor 1/D2
and memristance is correspondingly more significant. So it
was not possible to get the feel of memristance at millimeter scale, that is why it took 30 years to
discover this nanoscale component.
Fig: A MEMRISTOR AT NANOSCALE
WORKING OF MEMRISTOR
Semiconductors are doped to make them either p-type or n-type. For example, if silicon is doped
with arsenic, it become n-type. However, when we apply an electric field to piece of n-type silicon,
the ionized arsenics atoms sitting inside the silicon lattice will not move. We do not want them to
move, in any case. Pure titanium dioxide (TiO2), which is also a semiconductor, has high resistance,
just as in the case of intrinsic silicon, and it can also be doped to make it conducting. If an oxygen
atom, which is negatively charged, is removed from its substantial site in TiO2, a positively charged
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oxygen vacancy is created(V0
+
) is created , which act as a donor of electrons. These positively
charged oxygen vacancies (V0
+
) can be in the direction of current applying electric field. Taking
advantage of this ionic transport, a sandwich of thin conducting and non-conducting layers of TiO2
was used to release memristor
Fig : Conduction mechanism in a memristor
(a) Broader electronic barrier when a negative potential is applied to electrode A
(b) Thin electronic barrier when a positive potential is applied to electrode A
Consider, we have two thin layers of TiO2, one highly conducting layer with lots of oxygen
vacancies(V0
+
) and the other layer undoped, which is highly resistive. Suppose that good ohmic
contact are formed using platinum electrodes on either side of sandwich of TiO2 . the electronics barrier
between the undoped TiO2 and the metal looks broader. The situation remains the same, even when a
negative potential I applied to electrode A, because the positively charged oxygen vacancies(V0
+
) are attracted
towards electrode A and the length of undoped region increases. Under these conditions the electronics barrier
at the undoped TiO2 and the metal is still too wide and it will be difficult for the electrons to cross
over the barrier.
However, when a positive potential is applied at electrode A the positively charged oxygen vacancies
are repelled and moved into the undoped TiO2. This ionic movement towards electrode B reduces the
length of undoped region. When more positively charged oxygen vacancies(V0
+
) reach the TiO2 metal
interface, the potential barrier for the electrons become very narrow, as shown, making tunneling
through the barrier a real possibility. This leads to a large current flow, making the device turn ON.
In this case, the positively charged oxygen vacancies (V0
+
) are present across the length of device.
When the polarity of the applied voltage is reversed, the oxygen vacancies can be pushed back into
their original place on the doped side, restoring the broader electronic barrier at TiO2 metal interface.
This forces the device to turn OFF due to an increase in the resistance of the device and reduce
possibility for carrier tunneling .
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The speciality of Memristor is not just that it can be turned OFF or ON, but, that it can actually
remember the previous state. This is because when the applied bias is removed, the positively
charged Ti ions (which are actually the oxygen deficient sites) do not move anymore, making the
boundary between the doped and undoped layers TiO2 immobile. When we next apply a bias
(positive or neagtive ) to the device , it starts from where it was left. Unlike in the case of typical
semoconductors, such as silicon in which only mobile carrier moves, in the case of memristor bith
the ionic and the electron movement, into the undoped TiO2 and out of undoped TiO2 are responsible
for the hysterisis in its cuurent-coltage charactericstic
ANALOGOUS SYSTEM
In William switches, the upper resistor was made of pure semiconductor, and the lower of the
oxygen-deficient material metal. Applying a voltage to the device pushes charged bubbles up from
the metal, radically reducing the semiconductor’s resisitance and making it into a full-blown
conductor. A voltage applied in the other direction starts the merry-go-round revolving the other
way: the bubbles drain back into the lower layer, and the upper layer reverts to a high resistance,
semiconducting state.
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The crucial thing is that, every time when the voltage is switched off, the merry-go-round stops and
the resistance is frozen. When the voltage is switched on again, the system “remembers” where it
was, waking up in the same resistance state.
The analogous system of memory resistor or “memristor” is perfectly explained, assuming that
memristor behaves like a pipe whose diameter varies according to the amount and direction of
current passing through it.
FIG: A RESISTOR WITH MEMORY BEHAVES LIKE A PIPE
 The diameter of pipe remains same when the current is switched off, until it is switched on
again.
 The pipe, when the current is switched on again, remembers what current has flowed through
it.
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POTENTIAL APPLICATIONS
1. NANO-SCALE NATURE
The main objective in the electronic chip design is to move computing beyond the physical
and fiscal limits of conventional silicon chips. For decades, increases in chip performance have come
about largely by putting more and more transistors on a circuit. Higher densities, however, increase
the problems of heat generation and defects and affect the basic physics of the devices.
Instead of increasing the number of transistors on a circuit, we could create a hybrid circuit
with fewer transistors but with the addition of Memristors which could add functionality. Alternately,
Memristor technologies could enable more energy-efficient high-density circuits.
Memristor, was not been seen before because the effect depends on atomic-scale movements, it only
poped up on the nanoscale of William’s devices. Information can be written into the material as the
resistance state of the memristor in a few nanoseconds using few picojoules of energy-“ as good as
anything needs to be”. And once written memory stays written even when the power is shut.
2. REPLACEMENT OF FLASH MEMORY
The important potential use of memristor is as a powerful replacement for flash memory- the kind
used in applications thet require quick writing and rewriting capabilities, such as in cameras and USB
memory sticks. Like flash memory, memristiev memory can only be written 10,000 times or so
before the constant atomic movements within the device cause it to break down. It is possible to
improve the durability of memristors.
3. REPLACEMENT FOR DRAM
Computers using conventional D-RAM lack the ability to retain information once they are turned off.
When power is restored to a D-RAM-based computer, a slow, energy-consuming "boot-up" process
is necessary to retrieve data stored on a magnetic disk required to run the system. the reason
computers have to be rebooted every time they are turned on is that their logic circuits are incapable
of holding their bits after the power is shut off. But because a Memristor can remember voltages, a
Memristor-driven computer would arguably never need a reboot. “You could leave all your Word
27

files and spreadsheets open, turn off your computer, and go get a cup of coffee or go on vacation for
two weeks
4. BRAIN-LIKE SYSTEMS
As for the human brain-like characteristics, Memristor technology could one day lead to
computer systems that can remember and associate patterns in a way similar to how people do.
This could be used to substantially improve facial recognition technology or to provide more
complex biometric recognition systems that could more effectively restrict access to personal
information. These same pattern-matching capabilities could enable appliances that learn from
experience and computers that can make decisions.
It is observed that the complex electrical response of synapses to the ebb and flow of
potassium and sodium ions across the membrance of eeach cell which allows thw synapses to alter
their respose according to the frequency and strength of the signals. It looked maddeningly similar to
the response a memristor would produce.
FIG: NEURAL NETWORKS
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NEW HORIZONS :
After the discovery of memristor the authors have taken a new step towards the new devices with
properties like memristor.
There are two such elements which were next discovered :
1. MEMCAPACITOR
2. MEMINDUCTOR
The memcapacitor meminductor are the memdevices in which the capacitance and inductance respectively
depends on the state and history of the system.
They show pinched hysteresis loop in the constitutive variables that define them:-
Charge-voltage for Memcapaciatnce
Current –flux for Meminductance
The difference between the Memristor and both these devices is that they store energy whereas memristor
cannot.
MEMCAPACITOR MEMINDUCTOR
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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.
As rightly said by Leon Chua and R.Stanley Williams (originators of Memristor), “Memrisrors are
so significant that it would be mandatory to re-write the existing Electronics Engineering textbooks”.
30

BIBLIOGRAPHY
1. WWW.GOOGLE.COM
2. WWW.WIKIPEDIA.COM
3. WWW.HOWSTUFFWORKS.COM
4. LEON CHUA’S PAPER, 1971
5. HTTP://WWW.MEMRISTOR.ORG/
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Memristor - The Missing Element

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Memristor - The Missing Element