SEMINAR REPORTON

MEMRISTOR

Submitted for the partial fulfillment of awardof

Degree of Bachelors of Technology(Electronics and Communication Engineering)

BY: - ANKUR VERMA(ROLL NO: - 1113231046)

Department of Electronics and Communication

G.N.I.O.T. GREATER NOIDASession 2013-2014

CERTIFICATE

This is to certify that ANKUR VERMA (1113231046) of E.C. Third

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.

Mr. MANISH GUPTA Head of the department

(SEMINAR GUIDE) Brig. M.K.DEWAN

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.

Lastly, my sincere thanks to all our friends for their coordination in completion of this seminar report.

AKASH GARG

Roll No. : - 1113231016

(E.C. 3RD Year)

ABSTRACT

Typically electronics has been define three fundamental circuit components- resistors, inductors and capacitors are used to define 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. This lead to the idea and development of memristors.

In 1971, Leon Chua reasoned on the grounds of symmetry that there should be a fourth Fundamental circuit element which gives the relationship between flux and charge. He named this circuit element the memristor, which is short for memory resistor. In May 2008, Researchers at HP Labs published a paper announcing a model for the physical realization of the memristor.

Memristor is a concatenation of “memory resistors”. The most notable property of a memristor is that it can save its electronic state even when the current is turned off, making it a great candidate to replace today's flash memory. An outstanding feature is its ability to remember a range of electrical states rather than the simplistic "on" and "off" states that today's digital processors recognize. Memristor-based computers could be capable of far more complex tasks.

It is proposed that memory storage devices that has very high data density and computers that require no time for boot up can be developed using memristor based hardware. A new physical quantity which is also introduced associated with memristor. It also solves some unexplained voltage current characteristics observed in certain materials at atomic levels.

HP has already started produced an oxygen depleted titanium memristor.

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TABLE OF CONTENT

CHAPTER NO. TITLE PAGE

1.

2.

3.

4.

5.

6.

7.

8.

9.

10.

11.

12.

13.

14.

LIST OF FIGURE

INTRODUCTION…………………

HISTORY………………………….

ADVENT OF HP LABS…………..

MEMRISTOR THEORY…………

MEMRISTOR AND RESISTOR…

MEMRISTOR VS TRANSISTOR..

APPEARANCE OF MEMRISTOR

MEMRISTOR OPERATION……..

PIPE AND CURRENT ANALOGY

APPLICATION…………………….

BENEFITS OF MEMRISTOR……

FUTURE…………………………….

CONCLUSION……………………..

BIBLIOGRAPHY…………………..

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1

3

5

7

12

13

15

16

18

20

23

24

25

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LIST OF FIGURE

FIGURE NO.

FIGURE NAME PAGE

1.

2.

3.

4.

5.

6.

7.

8.

9.

10.

11.

ABOUT FOUR BASIC CIRCUIT ELEMENTS

ABOUT THE THREE FUNDAMENTAL CIRCUIT

ELEMENTS

SYMBOL OF THE MEMRISTOR

ABOUT V-I CHARACTERISTICS OF A

MEMRISTOR HYSTERESIS MODEL OF RESISTANCE

VS. VOLTAGE

CURRENT VOLTAGE CHARACTERISTIC OF RESISTOR

AND MEMRISTOR

CROSSBAR ARRAY STRUCTURE

MOVEMENT OF OXYGEN DEFICIENCY

DIAGRAM OF PIPE AND CURRENT EXAMPLE

NEURAL NETWORKS

FLEXIBLE MEMORY

3

7

8

11

11

12

15

16

18

21

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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.

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 (they 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.

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1 INTRODUCTION

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.

1

2

The story of the memristor is truly one for the history books. When Leon Chua, now an IEEE Fellow, wrote his seminal paper predicting the memristor, he was a newly minted and rapidly rising professor at UC Berkeley. Chua had been fighting for years against what he considered the arbitrary restriction of electronic circuit theory to linear systems. He was convinced that nonlinear electronics had much more potential than the linear circuits that dominate electronics technology to this day.

Memristance was first predicted by Professor Leon Chua in his paper Memristor. The missing circuit element published in the IEEE Transactions on Circuits Theory (1971). In that paper, Prof. Chua proved a number of theorems to show that there was a 'missing' two terminal circuit element from the family of "fundamental" passive devices: resistors (which provide static resistance to the flow of electrical charge), capacitors (which store charges), and inductors (which resist changes to the flow of charge)—, or elements that do not add energy to a circuit. He showed that no combination of resistors, capacitors, and inductors could duplicate the properties of a memristor. This inability to duplicate the properties of a memristor with the other passive circuit elements is what makes the memristor fundamental. However, this original paper requires a considerable effort for a non-expert to follow. In a later paper, Prof. Chua introduced his 'periodic table' of circuit elements.

Fig 1: Diagram describing the relation between charge, current, voltage and magnetic flux to one another

2 HISTORY

3

The pair wise mathematical equations that relate the four circuit quantities-charge, current, voltage, and magnetic flux to one another. These can be related in six ways. Two are connected through the basic physical laws of electricity and magnetism, and three are related by the known circuit elements: resistors connect voltage and current, inductors connect flux and current, and capacitors connect voltage and charge. But one equation is missing from this group: the relationship between charge moving through a circuit and the magnetic flux surrounded by that circuit. That is what memristor, connecting charge and flux.

Even before Chua had his eureka moment, however, many researchers were reporting what they called anomalous current-voltage behavior in the micrometer-scale devices they had built out of unconventional materials, like polymers and metal oxides. But the idiosyncrasies were usually ascribed to some mystery electrochemical reaction, electrical breakdown, or other spurious phenomenon attributed to the high voltages that researchers were applying to their devices.

Leon’s discovery is similar to that of the Russian chemist Dmitri Mendeleev who created and used a periodic table in 1869 to find many unknown properties and missing elements.

4

Even though Memristance was first predicted by Professor Leon Chua, Unfortunately, neither he nor the rest of the engineering community could come up with a physical manifestation that matched his mathematical expression.

Thirty-seven years later, a group of scientists from HP Labs has finally built real working memristors, thus adding a fourth basic circuit element to electrical circuit theory, one that will join the three better-known ones: the capacitor, resistor and the inductor.

Interest in the memristor revived in 2008 when an experimental solid state version was reported by R. Stanley Williams of Hewlett Packard. HP researchers built their memristor when they were trying to develop molecule-sized switches in Teramac (tera-operation-persecond multiarchitecture computer). Teramac architecture was the crossbar, which has since become the de facto standard for nanoscale circuits because of its simplicity, adaptability, and redundancy.

A solid-state device could not be constructed until the unusual behavior of nanoscale materials was better understood. 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 using a chemical mechanism.

The HP team’s memristor design consisted of two sets of 21 parallel 40-nm-wide wires crossing over each other to form a crossbar array, fabricated using nano imprint lithography. A 20-nm-thick layer of the semiconductor titanium dioxide (TiO2) was sandwiched between the horizontal and vertical nanowires, forming a memristor at the intersection of each wire pair. An array of field effect transistors surrounded the memristor crossbar array, and the memristors and transistors were connected to each other through metal traces.

The crossbar is an array of perpendicular wires. Anywhere two wires cross, they are connected by a switch. To connect a horizontal wire to a vertical wire at any point on the grid, you must close the switch between them. Note that a crossbar array is basically a storage system, with an open switch representing a zero and a closed switch representing a one. You read the data by probing the switch with a small voltage. Because of their simplicity, crossbar arrays have a

3 ADVENT OF HP LABS

5

much higher density of switches than a comparable integrated circuit based on transistors.

Stanley Williams found an ideal memristor in titanium dioxide the stuff of white paint and sunscreen. In TiO2, the dopants don't stay stationary in a high electric field; they tend to drift in the direction of the current. Titanium dioxide oxygen atoms are negatively charged ions and its electrical field is huge. This lets oxygen ions move and change the material’s conductivity, a necessity for memristors.

The researchers then sandwiched two thin titanium dioxide layers between two 5 nm thick electrodes. Applying a small electrical current causes the atoms to move around and quickly switch the material from conductive to resistive, which enables memristor functionality.

When an electric field is applied, the oxygen vacancies drift 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 In the process, the device uses little energy and generates only small amounts of heat. Also, when the device shuts down, the oxygen atoms stay put, retaining their state and the data they represent.

On April 30, 2008, the Hewlett-Packard research team proudly announced their realization of a memristor prototype.

6

Origin of the Memristor :-

There are four fundamental circuit variables in circuit theory. They are current, voltage, charge and flux. There are six possible combinations of the four fundamental circuit variables. We have a good understanding of five of the possible six combinations. The three basic two-terminal devices of circuit theory namely, the resistor, the capacitor and the inductor are defined in terms of the relation between two of the four fundamental circuit variables. A resistor is defined by the relationship between voltage and current, the capacitor is defined by the relationship between charge and voltage and the inductor is defined by the relationship between flux and current. In addition, the current is defined as the time derivative of the charge and according to Faraday’s law the voltage is defined as the time derivative of the flux. These relations are shown in Fig. 2

Fig.2: The three circuit elements defined as a relation between four circuit variables

4 MEMRISTOR THEORY

7

Definition of a Memristor :-

Memristor, the contraction of memory resistor, is a passive device that provides a functional relation between charge and flux. It is defined as a two-terminal circuit element in which the flux between the two terminals is a function of the amount of electric charge that has passed through the device. Memristor is not an energy storage element. Fig. 3 shows the symbol for a memristor.

Fig.3: Symbol of the memristor

A memristor is said to be charge-controlled if the relation between flux and charge is expressed as a function of electric charge and it is said to be flux-controlled if the relation between flux and charge is expressed as a function of the flux linkage.

What is Memristance?

Memristance is a property of the memristor. When charge flows in a direction through a circuit, the resistance of the memristor increases. When it flows in the opposite direction, the resistance of the memristor decreases. If the applied voltage is turned off, thus stopping the flow of charge, the memristor remembers the last resistance that it had. When the flow of charge is started again, the resistance of the circuit will be what it was when it was last active.

8

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:

Where Q is defined by I=

dQdt and ϕ is defined by V=d∅

dt

The variable Φ ("magnetic flux linkage") is generalized from the circuit characteristic of an inductor. The symbol Φ may simply be regarded 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) Φ 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. If M(q(t)) is a constant, then we obtain Ohm's lawR(t) = V(t)/ I(t).However, the equation is not equivalent because q(t) and M(q(t)) will vary with time.

9

Solving for voltage as a function of time we obtain

This equation reveals that memristance defines a linear relationship between current and voltage, as long as M does not vary with charge.

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.

Properties of a Memristor

Current–Voltage Curve of a Memristor

An important fingerprint of a memristor is the pinched hysteresis loop current voltage characteristic. For a memristor excited by a periodic signal, when the voltage v(t) is zero, the current i(t) is also zero and vice versa. Thus, both voltage v(t) and current i(t) have identical zero-crossing. Another signature of the memristor is that the ―pinched hysteresis loop‖ shrinks with the increase in the excitation frequency. Figure 4 shows the pinched hysteresis loop‖ and an example of the loop shrinking with the increase in frequency. In fact, when the excitation frequency increases towards infinity, the memristor behaves as a normal resistor.

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Fig. 4: The pinched hysteresis loop and the loop shrinking with the increase in frequency

HYSTERESIS MODEL

Hysteresis model illustrates an idealized resistance behavior demonstrated in accordance with above current-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. 

Fig 5: Idealized hysteresis model of resistance vs. voltage for memristance switch.

Thus for voltages within a threshold region (-VL2<V<VL1 in Fig. 5) 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. 

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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 so that a graph comparing current and voltage results in a straight line. However, for memristors a similar graph is a little more complicated.

Fig 6: Current voltage characteristic of resistor and memristor

5 MEMRISTOR AND RESISTOR

12

The first transistor was a couple of inches across which was developed about 60 years ago. Today, a typical laptop computer uses a processor chip that contains over a billion transistors, each one with electrodes separated by less than 50 nm of silicon. This is more than a 1000 times smaller than the diameter of a human hair. These billions of transistors are made by top down methods that involve depositing thin layers of materials, patterning nano-scale stencils and effectively carving away the unwanted bits. This approach has become overly successful. The end result is billions of individual components on a single chip, essentially all working perfectly and continuously for years on end. No other manufactured technology comes close in reliability or cost.

Still, miniaturization cannot go on forever, because of the basic properties of matter. We are already beginning to run into the problem that the silicon semiconductor, copper wiring and oxide insulating layers in these devices are all made out of atoms. Each atom is about 0.3 nm across.

The entire body of the transistor is being doped less consistently throughout as its sizes are reduced below the nanometers which make the transistor more unpredictable in nature. It will be more difficult and costly to press forward additional research and equipment involving these unpredictable behaviors as they occur. Therefore the electronic designs will have to replace their transistors to the memristors which are not steadily infinitesimal, but increasingly capable.

The memristor is very likely to follow the similar steps of how the transistor was implemented in our electronic systems. They may argue that the transistor took approximately sixty years to reach the extent of today’s research and capabilities. Therefore, the memristors may take approximately just as long to actually create some of its promising potentials such as artificial intelligence. This new advancement means more jobs for research and development and more potential for inventions and designs. Also, the dependency on getting the transistors to work efficiently in atom sized is lessened.

6 MEMRISTOR VS TRANSISTOR

13

Transistor Memristor

3-terminal switching device with an input electrode (e.g. source), an output electrode (e.g. drain), and a control electrode (e.g. gate).

Requires a power source to retain a data state.

Stores data by electron charge. Scalable by reducing the lateral

length and width dimensions between the input and output electrodes.

Capable of performing analog or digital electronic functions depending on applied bias voltages.

Fabrication requires optical lithography.

2-terminal device with one of the electrodes acting either as a control electrode or a source electrode depending on the voltage magnitude.

Does not require a power source to retain a data state.

Stores data by resistance state. Scalable by reducing the

thickness of the memristor materials.

Capable of performing analog or digital electronic functions depending on particular material used for memristor.

Fabrication by optical lithography but alternative (potentially cheaper) mass production techniques such as nano imprint lithography and self assembly have also been implemented

Another reason for incorporating memristors is the materials used to make each element. Transistors are usually made of silicon, a non-metal. While this has proven to be a very reliable source, it returns to the problem of transistors needing to become smaller. Because they are made of a non-metal it is much harder to make them much smaller. Memristors, on the other hand, are made of titanium oxide. Titanium is a metal which is much easier to make into smaller size. Since memristors have twelve times the power of transistors, however, products can be made smaller and more powerful without reducing the size of the product that powers them.

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HP Labs' memristor has Crossbar type memristive circuits contain a lattice of 40-50nm wide by 2-3nm thick platinum wires that are laid on top of one another perpendicular top to bottom and parallel of one another side to side. The top and bottom layer are separated by a switching element approximately 3-30nm in thickness. The switching element consists of two equal parts of titanium dioxide (TiO2). The layer connected to the bottom platinum wire is initially perfect TiO2 and the other half is an oxygen deficient layer of TiO2 represented by TiO2-x where x represents the amount of oxygen deficiencies or vacancies. The entire circuit and mechanism cannot be seen by the naked eye and must be viewed under a scanning tunneling microscope, as seen in Figure 6, in order to visualize the physical set up of the crossbar design of the memristive circuit described in this section.

Fig 7: figure showing crossbar architecture and magnified memristive switch having platinum electrodes and 2 layers of TiO2

7 APPEARANCE OF MEMRISTOR

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The memristor’s operation as a switch can be explained in three steps. These first of these steps is the application of power or more importantly current to the memristor. The second step consists of the amount of time that the current flows across the crossbar gap and how the titanium cube converts from a semi-conductor to a conductor. The final step is the actual memory of the cube that can be read as data.

STEP 1:-

As explained above, each gap that connects two platinum wires contains a mixture of two titanium oxide layers. The initial state of the mixture is halfway between conductance and semi-conductance. Two wires are selected to apply power to in either a positive or negative direction. A positive direction will attempt to close the switch and a negative direction will attempt to open the switch. The application of this power will be able to completely open the circuit between the wires but it will not be able to completely close the circuit since the material is still a semi-conductor by nature. Power can be selectively placed on certain wires to open and close the switches in the memristor.

Fig 8: TiO2-x layer having oxygen deficiencies over insulating TiO2 layer. (b) Positive voltage applied to top layer repels oxygen deficiencies in to the insulating TiO2 layer

below. (c) Negative voltage on the switch attracts the positively charged oxygen bubbles pulling them out of the TiO2.

8 MEMRISTOR OPERATION

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STEP 2:-

The second step involves a process that takes place at the atom level and is not visible by any means. It involves the atomic process that the gap material, made from titanium dioxide, goes through that opens and closes the switch. The initial state of the gap is neutral meaning that it consists of one half of pure titanium dioxide TiO2 and one half of oxygen starved titanium dioxide TiO2-x where x in the initial state is 0.05. As positive current is applied, the positively charged oxygen vacancies push their way into the pure TiO2 causing the resistance in the gap material to drop, becoming more conductive, and the current to rise. Inversely, as a negative current is applied the oxygen vacancies withdraw from the pure TiO2 and condense in the TiO2-x half of the gap material causing the pure and more resistive TiO2 to have a greater ratio slowing the current in the circuit. When the current is raised the switch is considered open (HI) and for data purposes a binary 1. As current is reversed and the current is dropped the switch is considered closed (LOW) or a binary 0 for data purposes.

STEP 3:-

Step three explains the final step of memristance and is the actual step that makes the circuit memristive in nature. As explained previously, the concept of memristance is a resistor that can remember what current passed through it. When power is no longer applied to the circuit switches, the oxygen vacancies remain in the position that they were last before the power was shut down. This means that the value of the resistance of the material gap will remain until indefinitely until power is applied again. This is the true meaning of memristance. With an insignificant test voltage, one that won’t affect the movement of molecules in the material gap will allow the state of the switches to be read as data. This means that the memristor circuits are in fact storing data physically.

If we want a positive voltage to turn the memristor off, then we want the titanium oxide layer with vacancies on the top layer. But if you want a positive voltage to turn the memristor on, then you need the layers reversed. In its initial state, a crossbar memory has only open switches, and no information is stored. But once you start closing switches, you can store vast amounts of information compactly and efficiently.

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A common analogy to describe a memristor is similar to that of a resistor. Think of a resistor as a pipe through which water flows. The water is electric charge. The resistor’s obstruction of the flow of charge is comparable to the diameter of the pipe: the narrower the pipe, the greater the resistance. For the history of circuit design, resistors have had a fixed pipe diameter. But a memristor is a pipe that changes diameter with the amount and direction of water that flows through it. If water flows through this pipe in one direction, it expands (becoming less resistive). But send the water in the opposite direction and the pipe shrinks (becoming more resistive). Further, the memristor remembers its diameter when water last went through. Turn off the flow and the diameter of the pipe freezes until the water is turned back on. , 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.

Fig 9 .Schematic diagram of pipe and current example

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

9 PIPE AND CURRENT ANALOGY

18

circuit combination of resistors, capacitors, and inductors, which is why the memristor qualifies as a fundamental circuit element. Technically such a mechanism can be replicated using transistors and capacitors, but, it takes a lot of transistors and capacitors to do the job of a single memristor.

Memristance is measured by the electrical component memristor. The way a resistor measures resistance, a conductor measures conduction, and an inductor measures inductance, a memristor measures memristance. An ideal memristor is a passive two-terminal electronic device that expresses only memristance. However it is difficult to build a pure memristor, since every real device contains a small amount of another property.

Two properties of the memristor attracted much attention. Firstly, its memory characteristic, and, secondly, its nanometer dimensions. The memory property and latching capability enable us to think about new methods for nano-computing. With the nanometer scale device provides a very high density and is less power hungry. In addition, the fabrication process of nano-devices is simpler and cheaper than the conventional CMOS fabrication, at the cost of extra device defects.

At the architectural level, a crossbar-based architecture appears to be the most promising nanotechnology architecture. Inherent defect-tolerance capability, simplicity, flexibility, scalability, and providing maximum density are the major advantages of this architecture by using a memristor at each cross point.

Memristors are passive elements, meaning they cannot introduce energy into a circuit. In order to function, memristors need to be integrated into circuits that contain active elements, such as transistors, which can amplify or switch electronic signals. A circuit containing both memristors and transistors could have the advantage of providing enhanced functionality with fewer components, in turn minimizing chip area and power consumption.

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NON-VOLATILE MEMORY : -

Non-volatile memory is the dominant area being pursued for memristor technology. Of course most of the companies listed (with the exception of Hewlett Packard) do not refer to their memory in terms of the memristor and rather use a variety of acronyms (i.e. RRAM, CBRAM, PRAM, etc.) to distinguish their particular memory design. While these acronyms do represent real distinctions in terms of the materials used or the mechanism of resistance switching employed, the materials are still all memristors because they all share the same characteristic voltage-induced resistance switching behavior covered by the mathematical memristor model of Chua. Flash memory currently dominates the semiconductor memory market. However, each memory cell of flash requires at least one transistor meaning that flash design is highly susceptible to an end to Moore’s law. On the other hand, memristor memory design is often based on a crossbar architecture which does not require transistors in the memory cells. Although transistors are still necessary for the read/write circuitry, the total number of transistors for a million memory cells can be on the order of thousands instead of millions and the potential for addressing trillions of memory cells exists using only millions (instead of trillions) of transistors. Another fundamental limitation to conventional memory architectures is Von Neumann’s bottleneck which makes it more difficult to locate information as memory density increases. Memristors offer a way to overcome this hurdle since they can integrate memory and processing functions in a common circuit architecture providing a de-segregation between processing circuitry and data storage circuitry.

LOGIC/COMPUTATION : -

The uses of memristor technology for logic and computational electronics is less well developed than for memory architectures but the seeds of innovation in this area are currently being sown. Memristors appear particularly important to the areas of reconfigurable computing architectures such as FPGAs in which the arrangement between arrays of basic logic gates can be altered by reprogramming the wiring interconnections. Memristors may be ideal to improve the integration density and reconfigurability of such systems. In addition, since some

10 APPLICATIONS

20

memristor materials are capable of tunablity in their resistance state they can provide new types of analog computational systems which may find uses in modeling probabilistic systems (e.g. weather, stock market, bio systems) more efficiently than purely binary logic-based processors.

NEUROMORPHIC ELECTRONICS : -

Neuromorphics has been defined in terms of electronic analog circuits that mimic neurobiological architectures. Since the early papers of Leon Chua it was noted that the equations of the memristor were closely related to behavior of neural cells. Since memristors integrate aspects of both memory storage and signal processing in a similar manner to neural synapses they may be ideal to create a synthetic electronic system similar to the human brain capable of handling applications such as pattern recognition and adaptive control of robotics better than what is achievable with modern computer architectures.

Fig 10: neural networks

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MEMRISTOR MEMORY : -

Memristors can be used as non-volatile memory, allowing greater data density than hard drives. The memristor based crossbar latch memory prototyped by HP can fit 100 gigabits within a square centimeter. HP also claims that memristor memory can handle up to 1,000,000 read/write cycles before degradation, compared to flash at 100,000 cycles. In addition, memristors also consume less power.

In memristor memories, the reading operation is performed by applying a voltage lesser than the threshold value. The memristor will conduct even at this voltage if it is on. If it is off then it will not conduct. To write one of the logic levels (0 or 1) a voltage greater than the threshold value is applied. To write the other logic level, a voltage of opposite polarity whose magnitude is greater than the threshold voltage is applied. This turns the memristor off.

Memristors can remember even when the power is turned off. Thus, the computers developed using memristors will have no boot up time. The computer can be turned on, like turning on a light switch and it will instantly display all information that was there on it when it was turned off.

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Provides greater resiliency and reliability when power is interrupted in data centers.

Have great data density. Combines the jobs of working memory and hard drives into one tiny

device. Faster and less expensive than MRAM. Uses less energy and produces less heat. Would allow for a quicker boot up since information is not lost when

the device is turned off. Operating outside of 0s and 1s allows it to imitate brain functions. Does not lose information when turned off. Has the capacity to remember the charge that flows through it at a given

point in time. Conventional devices use only 0 and 1; Memristor can use anything

between 0 and 1(0.3, 0.8, 0.5, etc.) Faster than Flash memory. By changing the speed and strength of the current, it is possible to

change the behavior of the device. A fast and hard current causes it to act as a digital device. A soft and slow current causes it to act as an analog device. 100 GBs of memory made from memristors on same area of 16 GBs of

flash memory. High Defect Tolerance allows high defects to still produce high yields

as opposed to one bad transistor which can kill a CPU. Compatible with current CMOS interfaces. As non-volatile memory, memristors do not consume power when idle. 3 Memristors to make a NAND gate, 27 NAND gates to make a

Memristor!!! More magnetic than magnetic disks.

11 BENEFITS OF MEMRISTOR

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Memristor bridges the capability gaps that electronics will face in the near future according to Moore’s Law and will replace the transistor as the main component on integrated circuit (IC) chips.

The possibilities are endless since the memristor provides the gap to miniaturizing functional computer memory past the physical limit currently being approached upon by transistor technology.

When is it coming? 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 (at lower cost and lower power consumption) 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.

Fig 11: Flexible memory

12 FUTURE

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13 CONCLUSION

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. Memristor will change circuit design in the 21st century as radically as the transistor changed it in the 20th. Note that the transistor was lounging around as a mainly academic curiosity for a decade until 1956, when a revolutionary app the hearing aid brought it into the marketplace.

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.

Memristor open door to a wide area of research in the field of computer hardware and memory storage devices that has much higher data density. As rightly said by the originators of memristor, Leon Chua and R . Stanley Williams, “Memristors are so significant that it would be mandatory to re-write the existing electronic engineering textbooks.”

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14 BIBLIOGRAPHY

1. Memristor resistance modulation for analog applications Tsung Wen Lee and Janice H Nickel IEEE,electron device letters, vol 33,oct ,2012

2. Memristor applications for programmable analog ICs, Sangho Shin and Kyungmin Kim,IEEE Transactions on nanotechnology, vol 10,2011

3. Compact models for memristors based on charge flux constitutive relationships, IEEE,2010 IEEE Spectrum: The Mysterious Memristor By Sally Adee http://www.spectrum.ieee.org/may08/6207

4. Memristors Ready For Prime Time R. Colin Johnson URL:http://www.eetimes.com/showArticle.jhtml?articleID=208803176

5. Flexible memristor: Memory with a twist Vol. 453, May 1, 2008. PHYSorg.com

6. L. O. Chua, Memristor The missing circuit element, IEEE Trans. Circuit Theory, vol. CT-18, pp. 507–519, 1971.

7. Memristor - Wikipedia, the free encyclopedia8. http://www.hpl.hp.com/9. How We Found the Missing Memristor‖ By R. Stanley Williams,

December 2008 · IEEE Spectrum, www.spectrum.ieee.org10. http://avsonline.blogspot.com/11. http://memristor.pbworks.com/12. http://4engr.com/ 13. http://knol.google.com/14. http://newsvote.bbc.co.uk/mpapps/pagetools/email/news.bbc.co.uk/

2/hi/technology/7377 063.stm15. http://hubpages.com/topics/technology/533816. http://totallyexplained.com/

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