chauhan (2)
-
Upload
saahiel-bharadwaj -
Category
Documents
-
view
231 -
download
0
Transcript of chauhan (2)
-
8/7/2019 chauhan (2)
1/25
A SEMINAR
ON
MEMRISTOR
(ELECTRICAL & ELECTRONICS DEPARTMENT)
SUBMITTED TO:-
SUBMITTED BY:-
MR. ABHINAV
ANKUSH KUMAR
(LECTURER)
0812821008
-
8/7/2019 chauhan (2)
2/25
3RD YEAR
ACKNOWLEDGEMENT
I would like to thank Mr. ARVIN RAJA (HOD E.N. DEPTT.) for
providing me exposure to the whole TOPIC. I would also like to
thank Mr. ABHINAV GOEL (LECTURER E.N. DEPTT.) for their
enduring support and guidance throughout the seminar. I am very
grateful to the whole control and Instrumentation Department for
their support and guidance.
Lastly, I would like to thank the almighty and my
parents for their moral support and my friends with whom I
shared day-to-day experience and received lots of suggestions
that improved my quality of work.
-
8/7/2019 chauhan (2)
3/25
-
8/7/2019 chauhan (2)
4/25
A memristor (pronounced / mmrstr/; a portmanteau
of "memory resistor") is a passive two-terminal circuit element in
which the resistance is a function of the history of the current andvoltage through the device. Memristor theory was formulated and
named by Leon Chua in a 1971 paper. On April 30, 2008 a team
at HP Labs announced the development of a switching memristor
based on a thin film of titanium dioxide. It has a regime of
operation with an approximately linear charge-resistance
relationship as long as the time-integral of the current stays
within certain bounds. These devices are being developed for
application in nanoelectronic memories, computer logic, and
neuromorphic computer architectures.
-
8/7/2019 chauhan (2)
5/25
Memristor
An array of 17 purpose-built oxygen-depleted titanium dioxide memristors built at
HP Labs, imaged by an atomic force microscope. The wires are about 50 nm, or150 atoms, wide. Electric current through the memristors shifts the oxygen
vacancies, causing a gradual and persistent change in electrical resistance.
A memristor (pronounced a portmanteau of "memory resistor") is a passive
two-terminal circuit element in which the resistance is a function of the history of
the current and voltage through the device. Memristor theory was formulated and
named by Leon Chua in a 1971 paper.
On April 30, 2008 a team at HP Labs announced the development of a switching
memristor based on a thin film of titanium dioxide. It has a regime of operationwith an approximately linear charge-resistance relationship as long as the time-
integral of the current stays within certain bounds. These devices are being
developed for application in nanoelectronic memories, computer logic, and
neuromorphic computer architectures.
Background
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.
More generally, a memristor is a two-terminal component in which the resistancedepends 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
-
8/7/2019 chauhan (2)
6/25
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 circuitvariables of current and voltageand their time-integrals, just like the resistor,
capacitor, and inductor. Unlike those three elements however, which are allowed in
linear time-invariant or LTI system theory, memristors of interest have a nonlinear
function and may be described by any of a variety of functions of net charge. There
is no such thing as a standard memristor. Instead, each device implements a
particular function, wherein the integral of voltage determines the integral of
current, and vice versa. A linear time-invariant memristor is simply a conventional
resistor.
In his 1971 paper, memristor theory was formulated and named by Leon Chua,
extrapolating the conceptual symmetry between the resistor, inductor, and
capacitor, and inferring that the memristor is a similarly fundamental device.
(However, as mentioned above, if it has no non-linearity then it is the same as a
standard resistor. It is more meaningful to compare it with a varistor, which has a
non-linear relationship between current and voltage.) Other scientists had already
proposed fixed nonlinear flux-charge relationships, but Chua's theory introduced
generality. Like other two-terminal components (e.g., resistor, capacitor,
inductor), real-world devices are never purely memristors ("ideal memristor"), butwill also exhibit some amount of capacitance, resistance, and inductance. Note
however that a "memristor" with constant M and a resistor with constant R (i.e. not
a varistor) are the same thing.
-
8/7/2019 chauhan (2)
7/25
BEFORE INVENTION OF MEMRISTOR
-
8/7/2019 chauhan (2)
8/25
-
8/7/2019 chauhan (2)
9/25
ACTIVE ELEMENTS
WHEN ELEMENT IS CAPABLE OF DELIVERING THE ENERGY TO THE
CIRCUIT THEN THE ELEMENT IS CALLED AS ACTIVE ELEMENT.
EXAMPLE- VOLTAGE SOURCE AND CURRENT SOURCE ARE THE
INDEPENDENT ACTIVE ELEMENTS WHEREAS OP-AMP AND
TRANSISTOR ARE DEPENDENT ACTIVE ELEMENTS
PASIVE ELEMENTS
WHEN ELEMENT IS NOT CAPABLE OF DELIVERING THE ENERGY TOTHE CIRCUIT THEN THE ELEMENT IS CALLED AS PASSIVE ELEMENT
EXAMPLE- RESISTOR, INDUCTOR, CAPACITOR ARE THE PASSIVEELEMENTS BECAUSE THESE ENTIRE DEVICE ARE NOT CAPABLE TODELIVER THE ENERGY.
RESISTOR:
INDUCTOR:
CAPACITOR:
MEMRISTOR:
-
8/7/2019 chauhan (2)
10/25
MEMRISTIVE SYSTEMS
Ideal memristor V=M(q(t))i
Current-controlledMemristive system
),,( tiwfdt
dw=
itiwMV ),,(=
VtVwGi ),,(=
),,( tVwfdt
dw=
-
8/7/2019 chauhan (2)
11/25
PROPERTIES
Passivity criterion:
No energy discharge property:
Frequency behavior: - as a non-linear resistor atlowfrequencies;
- as a linear resistor at highfrequencies.
Doubled-valued Lissajous figure property.
Pinched Hysteresis LoopMemristor Fingerprint
0),,( tiwM
0)()()( = titVtp
-
8/7/2019 chauhan (2)
12/25
OPERATION AS A SWITCH
For some memristors, applied current or voltage will cause agreat change in resistance. Such devices may be characterized asswitches by investigating the time and energy that must be spentin order to achieve a desired change in resistance. Here we willassume that the applied voltage remains constant and solve forthe energy dissipation during a single switching event. For amemristor to switch from Ron to Roff in time Ton to Toff, thecharge must change by Q = QonQoff. To arrive at the finalexpression, substitute V=I(q)M(q), and then dq/V = Q/V forconstant V. This powercharacteristic differs fundamentally from
that of a metal oxide semiconductor transistor, which is acapacitor-based device. Unlike the transistor, the final state of thememristor in terms of charge does not depend on bias voltage.The type of memristor described by Williams ceases to be idealafter switching over its entire resistance range and entershysteresis, also called the "hard-switching regime." Another kindof switch would have a cyclic M(q) so that each off-on eventwould be followed by an on-off event under constant bias. Such adevice would act as a memristor under all conditions, but would
be less practical.
3-TERMINAL MEMRISTOR
Although the memristor is defined in terms of a 2-terminalcircuit element, there was an implementation of a 3-terminal
device called a memistor developed by Bernard Widrow in 1960.Memistors formed basic components of a neural networkarchitecture called ADALINE developed by Widrow and Ted Hoff(who later invented the microprocessor at Intel). In one of thetechnical reports[38] the memistor was described as follows: Likethe transistor, the memistor is a 3-terminal element.
-
8/7/2019 chauhan (2)
13/25
The conductance between two of the terminals is controlled bythe time integral of the current in the third, rather than itsinstantaneous value as in the transistor.
Reproducible elements have been made which are continuouslyvariable (thousands of possible analog storage levels), and whichtypically vary in resistance from 100 ohms to 1 ohm, and coverthis range in about 10 seconds with several milliamperes ofplating current. Adaptation is accomplished by direct currentwhile sensing the neuron logical structure is accomplishednondestructively by passing alternating currents through thearrays of memistor cells.
-
8/7/2019 chauhan (2)
14/25
-
8/7/2019 chauhan (2)
15/25
Theory
The memristor is essentially a two-terminal variable resistor, with resistance
dependent upon the amount of charge q that has passed between the terminals.
To relate the memristor to the resistor, capacitor, and inductor, it is helpful to
isolate the term M(q), which characterizes the device, and write it as a differential
equation.
Device Characteristic property (units) Differentialequation
Resistor Resistance (V per A, or ohm, ) R = dV / dI
Capacitor Capacitance (C per V, or farad) C = dQ / dV
Inductor Inductance (Wb per A, or henry) L = dm / dI
Memristor Memristance (Wb per C, or ohm) M = dm / dQ
where Q is defined by I = dQ/dt, and m is defined by V = dm/dt.
Note that the above table covers all meaningful ratios of I, Q, m, and V. No
device can relate I to Q, or m to V, because I is the derivative ofQ and m is
the integral ofV.
The variable m ("magnetic flux linkage") is generalized from the circuit
characteristic of an inductor. It does notrepresent a magnetic field here, and itsphysical meaning is discussed below. The symbol m may simply beregarded as
the integral of voltage over time.
Thus, the memristor is formally defined as a two-terminal element in which the
flux linkage (or integral of voltage) m between the terminals is a function of the
amount of electric charge Q that has passed through the device. Each memristor is
characterized by its memristance function describing the charge-dependent rate of
change of flux with charge.
Substituting that the flux is simply the time integral of the voltage, and charge is
the time integral of current, we may write the more convenient form.
It can be inferred from this that memristance is simply charge-dependent
resistance. IfM(q(t)) is a constant, then we obtain Ohm's Law R(t) = V(t)/I(t). If
M(q(t)) is nontrivial, however, the equation is not equivalent because q(t) and
M(q(t)) will vary with time. Solving for voltage as a function of time we obtain
This equation reveals that memristance defines a linear relationship between
-
8/7/2019 chauhan (2)
16/25
current and voltage, as long as M does not vary with charge. Of course, nonzero
current implies time varying charge. Alternating current, however, may reveal the
linear dependence in circuit operation by inducing a measurable voltage without
net charge movementas long as the maximum change in q does not cause much
change in M. Furthermore, the memristor is static if no current is applied. If I(t) =0, we find V(t) = 0 and M(t) is constant. This is the essence of the memory effect.
The power consumption characteristic recalls that of a resistor, I2R.
As long as M(q(t)) varies little, such as under alternating current, the memristor
will appear as a constant resistor. IfM(q(t)) increases rapidly, however, current
and power consumption will quickly stop.
Derivation of "flux linkage" in a passivedevice
In an inductor, magnetic flux m relates to Faraday's law of induction, which
states that the energy to push charges around a loop (electromotive force, in units
of Volts) equals the negative derivative of the flux through the loop:
This notion may be extended by analogy to a single device. Working against an
accelerating force (which may be EMF, or any applied voltage), a resistor produces
a decelerating force, and an associated "flux linkage" varying with opposite sign.
For example, a high-valued resistor will quickly produce flux linkage.
The term "flux linkage" is generalized from the equation for inductors, where it
represents a physical magnetic flux: If 1 Volt is applied across
an inductor for 1 second, then there is 1 Vs of flux linkage in the inductor, which
represents energy stored in a magnetic field that may later be obtained from it. The
same voltage over the same time across a resistor results in the same flux linkage
(as defined here, in units of V-s), but the energy is dissipated, rather than stored ina magnetic field there is no physical magnetic field involved as a link to
anything. Voltage for passive devices is evaluated in terms of energy lost by a
unit of charge, so generalizing the above equation simply requires reversing the
sense of EMF.
-
8/7/2019 chauhan (2)
17/25
Observing that m is simply equal to the integral over time of the potential drop
between two points, we find that it may readily be calculated, for example by an
operational amplifier configured as an integrator.
Two unintuitive concepts are at play:
Magnetic flux is defined here as generated by a resistance in opposition to anapplied field or electromotive force.
In the absence of resistance, flux due to constant EMF, and the magnetic field
within the circuit, would increase indefinitely. The opposing flux induced in a
resistor must also increase indefinitely so the sum with applied EMF remains
finite.
Any appropriate response to applied voltage may be called "magnetic flux," as
the term is used here. The upshot is that a passive element may relate some
variable to flux without storing a magnetic field. Indeed, a memristor always
appears instantaneously as a resistor. As shown above, assuming non-negative
resistance, at any instant it is dissipating power from an applied EMF and thus has
no outlet to dissipate a stored field into the circuit.
This contrasts with an inductor, for which a magnetic field stores all energy
originating in the potential across its terminals, later releasing it as an
electromotive force within the circuit.
Physical restrictions on M(q)
M(q) is physically restricted to be positive for all values ofq (assuming the device
is passive and does not become superconductive at some q). A negative value
would mean that it would perpetually supply energy when operated with
alternating current.
An applied constant voltage potential results in uniformly increasing m.
It is not realistic for the function M(q) to contain an infinite amount ofinformation over this infinite range. Three alternatives avoid this physical
impossibility:
M(q) approaches zero, such that m = M(q)dq = M(q(t))I(t) dt remains
bounded but continues changing at an ever-decreasing rate. Eventually, this would
encounter some kind of quantization and non-ideal behavior.
-
8/7/2019 chauhan (2)
18/25
M(q) is periodic, so that M(q) = M(q q) for all q and some q, e.g.
sin2(q/Q).
The device enters hysteresis once a certain amount of charge has passed through,
or otherwise ceases to act as a memristor.
Memristive systems
The memristor was generalized to memristive systems in a 1976 paper by Leon
Chua. Whereas a memristor has mathematically scalar state, a system has vector
state. The number of state variables is independent of, and usually greater than, the
number of terminals.
In this paper, Chua applied this model to empirically observed phenomena,
including the Hodgkin-Huxley model of the axon and a thermistor at constantambient temperature. He also described memristive systems in terms of energy
storage and easily observed electrical characteristics. These characteristics match
resistive random-access memory and phase-change memory, relating the theory to
active areas of research.
In the more general concept of an n-th order memristive system the defining
equations are where the vector w represents a set ofn state variables describing
the device. The pure memristor is a particular case of these equations, namely
when M depends only on charge (w=q) and since the charge is related to the
current via the time derivative dq/dt=I. For pure memristors fis not an explicitfunction ofI.
Operation as a switch
For some memristors, applied current or voltage will cause a great change in
resistance. Such devices may be characterized as switches by investigating the time
and energy that must be spent in order to achieve a desired change in resistance.Here we will assume that the applied voltage remains constant and solve for the
energy dissipation during a single switching event. For a memristor to switch from
Ron to Roff in time Ton to Toff, the charge must change by Q = Qon Qoff.
To arrive at the final expression, substitute V=I(q)M(q), and then dq/V= Q/V
for constant V. This power characteristic differs fundamentally from that of a metal
-
8/7/2019 chauhan (2)
19/25
oxide semiconductor transistor, which is a capacitor-based device. Unlike the
transistor, the final state of the memristor in terms of charge does not depend on
bias voltage.
The type of memristor described by Williams ceases to be ideal after switchingover its entire resistance range and enters hysteresis, also called the "hard-
switching regime." Another kind of switch would have a cyclic M(q) so that each
off-on event would be followed by an on-offevent under constant bias. Such a
device would act as a memristor under all conditions, but would be less practical.
ImplementationsTitanium dioxide memristor
Interest in the memristor revived in 2008 when an experimental solid state version
was reported by R. Stanley Williams of Hewlett Packard. The article was the first
to demonstrate that a solid-state device could have the characteristics of a
memristor based on the behavior of nanoscale thin films. The device neither uses
magnetic flux as the theoretical memristor suggested, nor do stores charge as a
capacitor does, but instead achieves a resistance dependent on the history of
current. Although not cited in HP's initial reports on their TiO2 memristor, the
resistance switching characteristics of titanium dioxide was originally described in
the 1960s.
The HP device is composed of a thin (50 nm) titanium dioxide film between two 5
nm thick electrodes, one Ti, the other Pt. Initially, there are two layers to the
titanium dioxide 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 a particular direction, 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.
-
8/7/2019 chauhan (2)
20/25
Memristance is displayed only when both the doped layer and depleted layer
contribute to resistance. When enough charge has passed through the memristor
that the ions can no longer move, the device enters hysteresis. It ceases to
integrate q=Idtbut rather keeps q at an upper bound and M fixed, thus acting as
a constant 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
described by Williams. Samsung has a U.S. patent for oxide-vacancy 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 ~1Hz. Although the
small dimensions of the device seem to imply fast operation, the charge carriers
move very slowly, with an ion mobility of 1010 cm2/(V*s).
In comparison, the highest known drift ionic mobilities occur in advanced
superionic conductors, such as rubidium silver iodide with about 2.104 cm2/
(V*s) conducting silver ions at room temperature. Electrons and holes in silicon
have a mobility ~1000 cm2/ (V*s), a figure which is essential to the performanceof transistors. However, a relatively low bias of 1 volt was used, and the plots
appear to be generated by a mathematical model rather than a laboratory
experiment.
In April 2010, HP labs announced that they had practical memristors working at
1ns switching times and 3 nm by 3 nm sizes, with electron/hole mobility of 1 m/s,
which bodes well for the future of the technology. At these densities it could easily
rival the current sub-25 nm flash memory technology.
Polymeric memristor
-
8/7/2019 chauhan (2)
21/25
In July 2008, Victor Erokhin and Marco P. Fontana, in Electrochemically
controlled polymeric device: a memristor (and more) found twoyears ago, claim to have developed a polymeric memristor before the titanium
dioxidememristor more recently announced.
In 2004, Juri H. Krieger and Stuart M. Spitzer published a paper "Non-traditional,Non-volatile Memory Based on Switching and Retention Phenomena in Polymeric
Thin Films" at the IEEE Non-Volatile Memory Technology Symposium,
describing the process of dynamic doping of polymer and inorganic dielectric-like
materials in order to improve the switching characteristics and retention required to
create functioning nonvolatile memory cells.
Described is the use of a special passive layer between electrode and active thin
films, which enhances the extraction of ions from the electrode. It is possible to use
fast ion conductor as this passive layer, which allows to significantly decrease the
ionic extraction field.
Spin memristive systems SpintronicMemristor
Yiran Chen and Xiaobin Wang, researchers at disk-drive manufacturer Seagate
Technology, in Bloomington, Minnesota, described three examples of possible
magnetic memristors in March, 2009 in IEEE Electron Device Letters. In one of
the three, resistance is caused by the spin of electrons in one section of the device
pointing different direction than those in another section, creating a "domain wall,"
a boundary between the two states.
Electrons flowing into the device have a certain spin, which alters the
magnetization state of the device. Changing the magnetization, in turn, moves the
domain wall and changes the device's resistance.
This work attracted significant attention from the electronics press, including an
interview by IEEE Spectrum.
Spin Torque Transfer Magnetoresistance
Spin Torque Transfer MRAM is a well-known device that exhibits memristive
behavior. The resistance is dependent on the relative spin orientation between two
-
8/7/2019 chauhan (2)
22/25
sides of a magnetic tunnel junction. This in turn can be controlled by the spin
torque induced by the current flowing through the junction. However, the length of
time the current flows through the junction determines the amount of current
needed, i.e., the charge flowing through is the key variable.
Additionally, as reported by Krzysteczko et al.,[30] MgO based magnetic tunneljunctions show memristive behavior based on the drift of oxygen vacancies within
the insulating MgO layer (resistive switching). Therefore, the combination of spin
transfer torque and resistive switching leads naturally to a second-order memristive
system with w=(w1,w2) where w1 describes the magnetic state of the magnetic
tunnel junction and w2 denotes the resistive state of the MgO barrier. Note that in
this case the change of w1 is current-controlled (spin torque is due to a high
current density) whereas the change of w2 is voltage-controlled (the drift of
oxygen vacancies is due to high electric fields).
Spin Memrisitive System
A fundamentally different mechanism for memristive behavior has been propose
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 of memristive 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 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 ofapplications of semiconductor spintronics and makes stepforward in future practical applications of the concept of memristive systems.
Manganite memristive systems
-
8/7/2019 chauhan (2)
23/25
Although not described using the word "memristor", a study was done of bilayer
oxide films based on manganite for non-volatile memory by researchers at the
University of Houston in 2001. Some of the graphs indicate a tunable resistance
based on the number of applied voltage pulses similar to the effects found in thetitanium dioxide memristor materials described in the Nature paper "The missing
memristor found".
Resonant tunneling diode memristor
In 1994, F. A. Buot and A. K. Rajagopal of the U.S. Naval Research Laboratory
demonstrated that a 'bow-tie' current-voltage (I-V) characteristics occurs in
AlAs/GaAs/AlAs quantum-well diodes containing special doping design of thespacer layers in the source and drain regions, in agreement with the published
experimental results.
This 'bow-tie' current-voltage (I-V) characteristic is characteristic of a memristor
although the term memristor was not explicitly used in their papers. No magnetic
interaction is involved in the analysis of the 'bow-tie' I-V characteristics.
3-terminal Memristor (Memistor)
Although the memristor is defined in terms of a 2-terminal circuit element, there
was an implementation of a 3-terminal device called a memistor developed by
Bernard Widrow in 1960.
Memistors formed basic components of a neural network architecture called
ADALINE developed by Widrow and Ted Hoff (who later invented the
microprocessor at Intel). In one of the technical reports the memistor was described
as follows:
Like the transistor, the memistor is a 3-terminal element. Theconductance betweentwo of the terminals is controlled by thetime integral of the current in the third, rather than itsinstantaneous value as in the transistor. Reproducible elementshave been made which are continuously variable (thousands ofpossible analog storage levels), and which typically vary in
-
8/7/2019 chauhan (2)
24/25
resistance from 100 ohms to 1 ohm, and cover this range inabout 10 seconds with severalmilliamperes of plating current. Adaptation is accomplished bydirect current while sensing the neuron logical structure is
accomplished nondestructively by passing alternating currentsthrough the arrays of memistor cells.Since the conductance was described as being controlled by the time integral of
current as in Chua's theory of the memristor, the memistor of Widrow may be
considered as a form of memristor having three instead of two terminals. However,
one of the main limitations of Widrow's memistors was that they were made from
an electroplating cell rather than as a solid-state circuit element. Solid-state circuit
elements were required to achieve the scalability of the integrated circuit which
was gaining popularity around the same time as the invention of Widrow's
memistor.A Google Knol article suggests that the Floating Gate MOSFET as well as other 3-
terminal "memory transistors"
may be modeled using memristive systems equations.
Potential applications
Williams' solid-state memristors can be combined into devices called crossbar
latches, which could replace transistors in future computers, taking up a muchsmaller 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, and has designed a highly scalable 3D design (consisting of
up to 1000 layers or 1 petabit per cm3). HP has reported that its version of the
memristor is currently about one-tenth the speed of DRAM. The devices' resistancewould be read with alternating current so that the stored value would not be
affected. 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 network and a memristor
was used to model experiments on adaptive behavior of unicellular organisms. It
-
8/7/2019 chauhan (2)
25/25
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
Physarumpolycephalum subjected to periodic changes of environment. Such
a learning circuit may find applications, e.g., in pattern recognition.
Memcapacitors and Meminductors
In 2009, Massimiliano Di Ventra, Yuriy Pershin and Leon Chua co-wrote an
article extending the notion of memristive systems to capacitive and inductive
elements in the form of memcapacitors and meminductors whose properties
depend on the state and history of the system.