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8/2/2019 Memristor Seminar Report[1]
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2. HISTORY
The transistor was invented in 1925 but lay dormant until finding a corporate
champion in BellLabs during the 1950s. Now another groundbreaking electronic circuitmay be poised for the same kind of success after laying dormant as an academic curiosity
for more than three decades.
Hewlett-Packard Labs is trying to bring the memristor, the fourth passive circuit
element after the resistor, and the capacitor the inductor into the electronics mainstream.
Postulated in 1971, the memory resistor represents a potential revolution in electronic
circuit theory similar to the invention of transistor.
The history of the memristor can be traced back to nearly four decades ago
when in 1971, Leon Chua, a University of California, Berkeley, engineer predicted that
there should be a fourth passive circuit element in addition to the other three known passive
elements namely the resistor, the capacitor and the inductor. He called this fourth element a
memory resistor or a memristor.
Examining the relationship between charge, current, voltage and flux in
resistors, capacitors, and inductors in a 1971 paper, Chua postulated the existence of
memristor. Such a device, he figured, would provide a similar relationship between
magnetic flux and charge that a resistor gives between voltage and current. In practice, thatwould mean it acted like a resistor whose value could vary according to the current passing
through it and which would remember that value even after the current disappeared.
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3. NEED FOR MEMRISTOR
A memristor is one of four basic electrical circuit components, joining theresistor, 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.
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 to relate charge to magnetic flux. That is where the needfor the fourth fundamental element comes in. This element has been named as 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
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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.
Figure 3.1 Fundamental circuit Elements and Variables.
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4. TYPES OF MEMRISTOR
Titanium dioxide memristor Polymeric memristor
Spin memristive systems
4.1 Titanium Doxide memristor:-
Interest in the memristor revived in 2008 when an experimental solid state version
was reported by R. Stanley Williams of Hewlett Packard. A solid-state device could not beconstructed until the unusual behavior of nanoscale materials was better understood. The
device neither uses magnetic flux as the theoretical memristor suggested, nor stores charge
as a capacitor does, but instead achieves a resistance dependent on the history of current
using a chemical mechanism.
The HP device is composed of a thin (5 nm) titanium dioxide film between two
electrodes. Initially, there are two layers to the film, one of which has a slight depletion of
oxygen atoms. The oxygen vacancies act as charge carriers, meaning that the depleted layer
has a much lower resistance than the non-depleted layer.
When an electric field is applied, the oxygen vacancies drift (see Fast ion
conductor), changing the boundary between the high-resistance and low-resistance layers.
Thus the resistance of the film as a whole is dependent on how much charge has been
passed through it in aparticulardirection, which is reversible by changing the direction of
current. Since the HP device displays fast ion conduction at nanoscale, it is considered a
nanoionic device.
Memristance is displayed only when both the doped layer and depleted layer contribute toresistance. When enough charge has passed through the memristor that the ions can no
longer move, the device enters hysteresis. It ceases to integrate q=Idt but rather keeps q at
an upper bound and M fixed, thus acting as a resistor until current is reversed.
Memory applications of thin-film oxides had been an area of active investigation
for some time. IBM published an article in 2000 regarding structures similar to that
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described by Williams.Samsung has a pending U.S. patent application for several oxide-
layer based switches similar to that described by Williams. Williams also has a pending
U.S. patent application related to the memristor construction.
Although the HP memristor is a major discovery for electrical engineering theory, it
has yet to be demonstrated in operation at practical speeds and densities. Graphs in
Williams' original report show switching operation at only ~1 Hz. Although the small
dimensions of the device seem to imply fast operation, the charge carriers move very
slowly. In comparison, the highest known drift ionic mobilities occur in advanced
superionic conductors, such as rubidium silver iodide with about 2104 cm/(Vs)
conducting silver ions at room temperature. Electrons and holes in silicon have a mobility
~1000 cm/(Vs), a figure which is essential to the performance of transistors. However, a
relatively low bias of 1 volt was used, and the plots appear to be generated by amathematical model rather than a laboratory experiment.
4.2 Polymeric memristor:-
In July 2008, Victor Erokhin and Marco P. Fontana, in Electrochemically
controlled polymeric device: a memristor (and more) found two years ago,claim to have
developed a polymeric memristor before the titanium dioxide memristor more recently
announced.
4.3 Spin memristive systems:-
A fundamentally different mechanism for memristive behavior has been proposed
by Yuriy V. Pershin and Massimiliano Di Ventra in their paper "Spin memristive systems".
The authors show that certain types of semiconductor spintronic structures belong to a
broad class of memristive systems as defined by Chua and Kang. The mechanism ofmemristive behavior in such structures is based entirely on the electron spin degree of
freedom which allows for a more convenient control than the ionic transport in
nanostructures. When an external control parameter (such as voltage) is changed, the
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adjustment of electron spin polarization is delayed because of the diffusion and relaxation
processes causing a hysteresis-type behavior.
This result was anticipated in the study of spin extraction at semiconductor/ferromagnet
interfaces,but was not described in terms of memristive behavior. On a short time scale,
these structures behave almost as an ideal memristor this result broadens the possible range
of applications of semiconductor spintronics and makes a step forward in future practical
application of the concept of memristive systems.
.
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5. MEMRISTOR THEORY AND ITS PROPERTIES
5.1 Definition of Memristor:-
The memristor is formally defined as a two-terminal element in which the
magnetic flux m between the terminals is a function of the amount of electric charge q that
has passed through the device.
Figure 5.1. 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
5.2 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.
5.3 Theory:-
Each memristor is characterized by its memristance function describing the charge-
dependent rate of change of flux with charge.
.5.3.1
Noting 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 form
...............................5.3.2
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It can be inferred from this that memristance is simply charge-dependent resistance.
. i.e.
V(t) = M (q(t))*I(t)............5.3.3
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.
The power consumption characteristic recalls that of a resistor, I2R.
..5.3.4
As long as M (q(t)) varies little, such as under alternating current, the memristor
will appear as a resistor. If M (q(t)) increases rapidly, however, current and power
consumption will quickly stop.
5.5 Current vs. Voltage characteristics:-
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.
In ordinary resistors there is a linear relationship between current and voltage sothat a graph comparing current and voltage results in a straight line. However, for
memristors a similar graph is a little more complicated as shown in Fig. 3 illustrates the
current vs. voltage behavior of memristance.
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
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materials. It is notable from Fig. 3 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.
Figure-5.2. Current vs. Voltage curve demonstrating hysteretic effects of memristance.
Fig. 6 illustrates an idealized resistance behavior demonstrated in accordance
with Fig.7 wherein the linear regions correspond to a relatively high resistance (RH) and
lowresistance (RL) and the transition regions are represented by straight lines.
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Figure 5.3 Idealized hysteresis model of resistance vs. voltage for memristance switch.
Thus for voltages within a threshold region (-VL2
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6. WORKING OF MEMRISTOR
Figure 6.1 Al/TiO2 or TiOX /Al Sandwich
The memristor is composed of a thin (5 nm) titanium dioxide film between two
electrodes as shown in figure 5(a) above. Initially, there are two layers to the film, one of
which has a slight depletion of oxygen atoms. The oxygen vacancies act as charge carriers,
meaning that the depleted layer has a much lower resistance than the non-depleted layer.
When an electric field is applied, the oxygen vacancies drift changing the boundary
between the high-resistance and low-resistance layers.
Analogy of Memristor:-
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.
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7. POTENTIAL APPLICATIONS
Figure7.1.showing 17 memristors in a row
Thus the resistance of the film as a whole is dependent on how much charge has
been passed through it in a particular direction, which is reversible by changing the
direction of current. Since the memristor displays fast ion conduction at nanoscale, it is
considered a nanoionic device .Figure 5(b) shows the final memristor component
Williams' solid-state memristors can be combined into devices called crossbarlatches, which could replace transistors in future computers, taking up a much smaller area.
They can also be fashioned into non-volatile solid-state memory, which would allow
greater data density than hard drives with access times potentially similar to DRAM,
replacing both components. HP prototyped a crossbar latch memory using the devices that
can fit 100 gigabits in a square centimeter. HP has reported that its version of the
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memristor is about one-tenth the speed of DRAM. The devices' resistance would be read
with alternating current so that they do not affect the stored value. Some patents related to
memristors appear to include applications in programmable logic, signal processing, neural
networks, and control systems. Recently, a simple electronic circuit consisting of an LC
contour and a memristor was used to model experiments on adaptive behavior of
unicellular organisms. It was shown that the electronic circuit subjected to a train of
periodic pulses learns and anticipates the next pulse to come, similarly to the behavior of
slime molds Physarum polycephalum subjected to periodic changes of environment. Such a
learning circuit may find applications, e.g., in pattern recognition.
7.1 MEMRISTOR-THE FOURTH BASIC CIRCUIT ELEMENT:-
From the circuit-theoretic point of view, the three basic two-terminal circuit
elements are defined in terms of a relationship between two of the four fundamental circuit
variables, namely; the current i, the voltage v, the charge q, and the flux-linkage cp. Out of
the six possible combinations of these four variables, five have led to well-known
relationships . Two of these relationships are already given by 9 Q(t) =
I (t) dt and O (t) = v(t) dt.
. Three other relationships are given, respectively, by theaxiomatic definition of the three classical circuit elements, namely, the resistor (defined by
a relationship between v and i), the inductor (defined by a relationship between cp and i),
and the capacitor defined by a relationship between q and v). Only one relationship remains
undefined, the relationship between o and q. From the logical as well as axiomatic points of
view, it is necessary for the sake of completeness to postulate the existence of a fourth
basic two-terminal circuit element which is characterized by a o-q curve.
This element will henceforth be called the memristor because, as will be
shown later, it behaves somewhat like a nonlinear resistor with memory. The proposed
symbol of a memristor and a hypothetical o-q curve are shown in Fig. l(a). Using a
,mutated , a memristor with any prescribed o-q curve can be realized by connecting an
appropriate nonlinear resistor, inductor, or capacitor across port 2 of an M-R mutated, an
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M-L mutated, and an M-C mutated, as shown in Fig. l(b), (c), and (d), respectively. These
mutators, of which there are two types of each, are defined and characterized in Table I.3
Hence, a type-l M-R mutated would transform the VR -IR< curve of the nonlinear resistor
f(VR, IR)=O into the corresponding o-q curve f(o,q)=O of a memristor. In contrast to this,
a type-2 M-R mutated would transform the IR,VR curve of the nonlinear resistor
f(IR,VR)=O into the corresponding o-q curve f(o,q) = 0 of a memristor. An analogous
transformation is realized with an M-L mutated (M-C mutated) with respect to the ((oL,iL)
or (iL, oL) [(vC, qC) or (qC, vC)] curve of a nonlinear inductor (capacitor).10 t
(a) Memristor and its o-q curve.
(b). Memristor basic realization 1: M-R mutated terminated by nonlinear Resistor R.
(c) Memristor basic realization 2: M-L mutated terminated by nonlinear inductor L
(d) Memristor basic realization M-C mutatedterminated by nonlinear capacitor C
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8. FEATURES
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 thevoltage 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.
8.1 New Memristor Could Make Computers Work like HumanBrains:-
After the resistor, capacitor, and inductor comes the memristor. Researchers at HP
Labs have discovered a fourth fundamental circuit element that can't be replicated by a11
combination of the other three. The memristor (short for "memory resistor") is unique
because of its ability to, in HP's words, "[retain] a history of the information it has
acquired." HP says the discovery of the memristor paves the way for anything from instant
on computers to systems that can "remember and associate series of events in a manner
similar to the way a human brain recognizes patterns." Such brain-like systems would
allow for vastly improved facial or biometric recognition, and they could be used to make
appliances that "learn from experience."
In PCs, HP foresees memristors being used to make new types of system memory
that can store information even after they lose power, unlike today's DRAM. With
memristor-based system RAM, PCs would no longer need to go through a boot process to
load data from the hard drive into the memory, which would save time and power
especially since users could simply switch off systems instead of leaving them in a "sleep"
mode
8.2 Memristors Make Chips Cheaper:-
The first hybrid memristor-transistor chip could be cheaper and more energy
efficient. Entire industries and research fields are devoted to ensuring that, every
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year,computers continue getting faster. But this trend could begin to slow down as the
components used in electronic circuits are shrunk to the size of just a few
atoms.Researchers at HP Labs in Palo Alto, CA, are betting that a new fundamental
electronic component--the memristor--will keep computer power increasing at this rate for
years to come.
They are nanoscale devices with unique properties: a variable resistance and the
ability to remember the resistance even when the power is off.Increasing performance has
usually meant shrinking components so that more can be packed onto a circuit. But instead,
Williams's team removes some transistors and replaces them with a smaller number of
memristors. "We're not trying to crowd more transistors onto a chip or into a particular
circuit," Williams says. "Hybrid memristor-transistor chips really have the promise for
delivering a lot more performance."12 A memristor acts a lot like a resistor but with onebig difference: it can change resistance depending on the amount and direction of the
voltage applied and can remember its resistance even when the voltage is turned off. These
unusual properties make them interesting from both a scientific and an engineering point of
view. A single memristor can perform the same logic functions as multiple transistors,
making them a promising way to increase computer power. Memristors could also prove to
be a faster, smaller, more energy-efficient alternative to flash storage.
8.3 Memristor as Digital and Analog:-
A memristive device can function in both digital and analog forms, both having
very diverse applications. In digital mode, it could substitute conventional solid-state
memories (Flash) with high-speed and less steeply priced nonvolatile random access
memory (NVRAM). Eventually, it would create digital cameras with no delay between
photos or computers that save power by turning off when not needed and then turning
back on instantly when needed.
8.4 No Need of Rebooting:-
The memristor's memory has consequences: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
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memristor-driven computer would arguably never need a reboot. You could leave all your
Word files and spreadsheets open, turn off your computer, and go get a cup of coffee or go
on vacation for two weeks, says Williams. When you come back, you turn on your
computer and everything is instantly on the screen exactly the way you left it.that keeps
memory powered. HP says memristor-based RAM could one day replace DRAM
altogether.
8.5 MemristorsforNanoscaleelectronics:-
The main objective in the electronic chip design is to move computingbeyond the
physical and fiscal limits ofconventional silicon chips. For decades, increases in chip
performance have come about largely byputting more and more transistors on a circuit.
Higher densities, however, increase the problems of heat generation and defects and
affect thebasicphysics of the devices.
Instead of increasing the number of transistors on a circuit, we could create a
hybrid circuit with fewer transistorsbutwith the addition ofmemristorswhichcouldadd
functionality. Alternately, memristor technologies could enable more energy-efficient
high-density circuits.
9. FUTURE OF MEMRISTOR
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Although memristor research is still in its infancy, HP
Labs is working on a handful of practical memristor projects. And now Williams's team has
demonstrated a working memristor-transistor hybrid chip. "Because memristors are made
of the same materials used in normal integrated circuits," says Williams, "it turns out to be
very easy to integrate them with transistors." His team, which includes HP researcher
Qiangfei Xia, built a field-programmable gate array (FPGA) using a new design that
includes memristors made of the semiconductor titanium dioxide and far fewer transistors
than normal.Engineers commonly use FPGAs to test prototype chip designs because they
can be reconfigured to perform a wide variety of different tasks.
In order to be so flexible, however, FPGAs are
large and expensive. And once the design is done, engineers generally abandon FPGAs forleaner "application-specific integrated circuits." "When you decide what logic operation
you want to do, you actually flip a bunch of switches and configuration bits in the circuit,"
says Williams. In the new chip, these tasks are performed by memristors. "What we're
looking at is essentially pulling out all of the configuration bits and all of the transistor
switches," he says. According to Williams, using memristors in FPGAs could help
significantly lower costs. "If our ideas work out, this type of FPGA will completely change
the balance," he says. Ultimately, the next few years could be very important for memristor
research. Still, he predicts that memristors will arrive in commercial circuits within the next
three years.
Researchers say that no real barrier prevents implementing the memristor in
circuitry immediately. But it's up to the business side to push products through to
commercial reality. Memristors made to replace flash memory will likely appear first; HP's
goal is to offer them by 2012. Beyond that, memristors will likely replace both DRAM and
hard disks in the 2014-to-2016 time frame. As for memristor-based analog computers, that
step may take 20-plus years.
10. CONCLUSION
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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.
However, as experience shows, the most valuable applications of memristors will
most likely come from some young student who learns about these devices and has an
inspiration for something totally new recognition. You may think this is not an electrical
topic but the linear elements are also used in every electrical circuit and my intension is to
divert the minds of young future engineers to this memristor and to make there inventions
in this topic. I am glad that I am directing all the engineers in the right way.
11. BIBLIOGRAPHY
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1. www.google.com
2. www.wikipedia.com
3. http://www.memristor.org/
4. www.allaboutcircuits.com5. www.ieee.org
CONTENTS
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http://www.google.com/http://www.wikipedia.com/http://www.memristor.org/http://www.memristor.org/http://www.memristor.org/http://www.allaboutcircuits.com/http://www.google.com/http://www.wikipedia.com/http://www.memristor.org/http://www.allaboutcircuits.com/8/2/2019 Memristor Seminar Report[1]
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1. Introduction 1
2. History 23. Need for memristor 3
4. Types of memristor 5
5. Memristor theory 8
6. Working of memristor 12
7. Potential applications 13
8. Features 16
9. Future of memristor 19
10. Conclusion 20
11. Bibliography 21
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