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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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  • 2. 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) 2
  • 3. 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.” 3
  • 4. 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. 4
  • 5. 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. 5
  • 6. 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 6
  • 7. 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. 7
  • 8. 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 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). 8
  • 9. 2. CAPACITOR 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 9
  • 10. 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, . 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. 10
  • 11. 3. INDUCTOR 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. 11
  • 12. 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. 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. 12
  • 13. 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 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 : RESISTORS (v=Ri) Voltage Current (v) (i) (v=dΦ/dt) (i=dq/dt) INDUCTORS CAPACITORS (q=Cv) Φ=Li ? Charge Flux (q) (Φ) ? 13
  • 14. 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. 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 14
  • 15. 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. 15
  • 16. 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.”  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. 16
  • 17. 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. 17
  • 18. 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. 18
  • 19. 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. 19
  • 20. 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. 20
  • 21. 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 21
  • 22.  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 q(t) = Charge flowing thorgh device at any time t 22
  • 23. 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 oxygen vacancy is created(V0+) is created , which act as a donor of electrons. These positively 23
  • 24. 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 . 24
  • 25. 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. 25
  • 26. 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. 26
  • 27. 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
  • 28. 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 28
  • 29. 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 29
  • 30. 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