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MEMRISTORS A Technical Seminar Report Submitted to JAWAHARLAL NEHRU TECHNOLOGYICAL UNIVERSITY, ANANTAPUR In partial fulfillment of the requirement for the award of the degree of BACHELOR OF TECHNOLOGY In ELECTRONICS AND COMMUNICATION ENGINEERING By B.VENKATA SAI SRAVAN KUMAR 08691A04B7 Department of Electronics and Communication Engineering MADANAPALLE INSTITUTE OF TECHNOLOGY AND SCIENCE (Approved by AICTE, New Delhi, Affiliated to JNTU, Anantapur) P.B.No.14,Angallu,Madanapalle 517325,Andhra Pradesh MADANAPALLE INSTITUTE OF TECHNOLOGY & SCIENCE (Approved by AICTE, New Delhi, Affiliated to JNTU, Anantapur) DEPARTMENT OF ELECTRONICS AND COMMUNICATION ENGINEERING BONAFIDE CERTIFICATE This is to certify that this seminar report “MEMRISTORS” submitted in partial fulfillment of the requirement for the award of the degree of Bachelor of Technology in Electronics and communication Engineering is a result of the bonafide work carried out by B.Venkata Sai Sravan Kumar (08691A04B7). He/She/They is /are bonafide student /students of this college studying IV year B.Tech during the academic year 2011-2012. Prof.A.R.REDDY,M.Tech.,Ph.D Head of the department Dept of ECE Page | 2 acknoeledment Page | 3 INDEX (I) Abstract 5 Chapter 1. INTRODUCTION 6 Chapter 2. BACKGROUND 8 2.1 Physical restrictions Chapter 3. MEMRISTIVE SYSTEMS 10 11 3.1 Operation as a Switch 3.2 Physical restrictions 3.3 Types of Memristors 11 12 14 Chapter 4. APPLICATIONS OF MEMRISTORS 15 4.1 Potential Applications 18 Chapter 5. CONCLUSION 21 Chapter 6. REFERNCES 22 Page | 4 (1)ABSTRACT The Mysterious Memristor-The future memory device Imagine a computer system that can think like the human brain & take the decisions on its own. Researches at HP (Hewlett Packard) labs have solved a decades-old mystery by proving the existence of a fourth element in integrated circuits that could make it possible to develop computers with some of the pattern-matching abilities of the human brain. A memristor is a passive twoterminal circuit element in which the resistance is a function of the history of the current through and voltage across the device. Memristor theory was formulated and named by Leon Chua in 1971.Considering the relationships between charge and flux in resistors, capacitors, and inductors Chua postulated the existence of a fourth element called the memory resistor. Such a device, he figured, would provide a similar relationship between magnetic flux and charge that a resistor gives between voltage and current. In practice, that would mean it acted like a resistor whose value could vary according to the current passing through it and which would remember that value even after the current disappeared.Here we are going to present about the resent trends in electronics about the memristor as a future fastest memory device. Page | 5 MEMRISTORS CHAPTER 1 INTRODUCTION What Are Memristors? Fig 1.1 Classification of devices What is a MEMRISTOR? Memristors are basically a fourth class of electrical circuit, joining the resistor, the capacitor, and the inductor, that exhibit their unique properties primarily at the nanoscale. Theoretically, Memristors, a concatenation of “memory resistors”, are a type of passive circuit elements that Page | 6 maintain a relationship between the time integrals of current and voltage across a two terminal element. Thus, a memristors resistance varies according to a devices memristance function, allowing, via tiny read charges, access to a “history” of applied voltage. The material implementation of memristive effects can Fig 1.2 Memristor be determined in part by the presence of hysteresis (an accelerating rate of change as an object moves from one state to another) which, like many other non-linear “anomalies” in contemporary circuit theory, turns out to be less an anomaly than a fundamental property of passive circuitry. Researchers were able to formulate a physics-based model of a memristor and build nanoscale devises in their lab that demonstrates all of the necessary operating characteristics to prove that the memristor was real. 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 stores charge as a capacitor does, but instead achieves a resistance dependent on the history of current. Page | 7 CHAPTER 2 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. Here in this figure we can see the relation between the flux & voltage(Φ & v) and the relation between voltage & charge(v & q) and the relation between charge & current(q & i) but the missing relation is in between the charge & flux(q & Φ). So, this is given by the memristive relation. This made the scientists think of the fourth fundamental element the MEMRISTOR. More generally, a memristor is a twoterminal component in which the resistance depends on the integral of the input applied to the terminals (rather than on the instantaneous value of the input as in a resistor). Since the element "remembers" the amount of current that has passed through it in the past, it was tagged by with the name "memristor." Fig 2.1 Relationship with devices Page | 8 Another way of describing a memristor is that it is any passive two-terminal circuit elements that maintains a functional relationship 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 only on the fundamental circuit variables of current and voltage and 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. Memristor theory was formulated and named by Leon Chua, extrapolating the conceptual symmetry between the resistor, inductor, and capacitor, and inferring the memristor was a similarly fundamental device. 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), realworld devices are never purely memristors ("ideal memristor"), but will also exhibit some amount of capacitance, resistance, and inductance. Note however that a "memristor" with constant M and a resistor with constant R are the same thing. Page | 9 Newton said that force is proportional to acceleration–the change in velocity. This is exactly the situation with electronic circuit theory today. All electronic textbooks have been teaching using the wrong variables–voltage and charge– explaining away inaccuracies as anomalies. What they should have been teaching is the relationship between changes in voltage, or flux, and charge.” 2.1 Physical restrictions on M(q) M(q) is physically restricted to be positive for all values of q (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 Φm. It is not realistic for the function M(q) to contain an infinite amount of information over this infinite range. Three alternatives avoid this physical impossibility: M(q) approaches zero, such that Φm = ∫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. M(q) is periodic, so that M(q) = M(q − Δq) for all q and some Δq, 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. Page | 10 Chapter 3 MEMRISTIVE SYSTEMS The memristor was generalized to memristive systems in 1976 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. Chua applied this model to empirically observed phenomena, including the Hodgkin-Huxley model of the axon and a thermistor at constant ambient 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. 3.1 Operation as a switch Page | 11 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. This power characteristic differs fundamentally from that of a metal 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. Another kind of switch would have a cyclic M(q) so that each off-on event would be followed by an on-off event under constant bias. Such a device would act as a memristor under all conditions, but would be less practical. 3.2 Replacement for D-RAM The research team made it possible for engineers to develop integrated circuit designs that take advantage of its ability to retain information. This opens up a whole new door in thinking about how chips could be designed and operated. Engineers could develop a new kind of computer memory that would supplement and eventually replace today’s commonly used dynamic random access memory (D-RAM). 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 computers , Page | 12 a slow ,energy –consuming “Boot up “ process is necessary to retrieve data stored on a magnetic disc required to run the system. fig 3.2 Computer Memristor Memristor- based computers would not require that process, using less power and possibly increasing system resiliency and reliability. The memristor could have applications for computing, cell phones, video games-anything that requires a lot of memory without a lot of battery power drain. 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 D-RAM, replacing both components. 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).The memristor is currently about one – tenth the speed of D-RAM. The device’s resistance would be read with alternating current so that the stored value would not be affected. Page | 13 The applications of memristors are innumerable from programmable logic, signal processing, neural networks, and control systems and many other devices will use these in future. 3.3 TYPES OF MEMRISTORS Many types of memristors are under development such as: Titanium dioxide memristors Polymeric (ionic) memristors Manganite memristive systems Resonant-tunneling diode memristors Spin based and magnetic memristive systems Spintronic memristors 3-terminal memristors Hybrid memristor-transistor Meminductor and memcapacitor fig 3.3 Types of Memristor Page | 14 CHAPTER 4 APPLICATION OF MEMRISTOR What Memristive applications are on the horizon, and how close are they to reality? We look at a survey of memristor applications and technology, starting from what the first devices will look like, and where they might go. This reference page will be updated as advances in each of the areas are made. Non-volatile memory applications: fig 4.1 NVRAM Memristors can retain memory states, and data, in power-off modes. Nonvolatile random access memory, or NVRAM, is pretty much the first to-market memristor application we’ll be seeing. There are already 3nm Memristors in fabrication now. Crossbar latch memory (see below) developed by Hewlett Packard is reportedly currently about one-tenth the speed of DRAM. Page | 15 Low-power and remote sensing applications: Coupled with memcapacitors and meminductors, the complementary circuits to the memristor which allow for the storage of charge, memristors can possibly allow for nano-scale low power memory and distributed state storage, as a further extension of NVRAM capabilities. These are currently all hypothetical in terms of time to market. Crossbar Latches as Transistor Replacements or Augmenters: The hungry power consumption of transistors has been a barrier to both miniaturization and microprocessor controller development. Solid-state memristors can be combined into devices called crossbar latches, which could replace transistors in future computers, taking up a much smaller area. There are difficulties in this area though, although the benefits these could bring are focusing a lot of money in their development. Unless a competition war amongst industry giants becomes one of those patent showdowns, where companies buy out technological advances to bury them. Remember 3G? Well, someone bought out 4G back in 2004, before 3G even came to market, and has been sitting on it ever since. And have profited greatly. Analog computation and circuit Applications: Analog computations embodied a whole area of research which, unfortunately, were not as scalable, reproducible, or dependable (or politically expedient in some cases) as digital solutions. However, there still exist some very important areas of engineering and modeling problems which require extremely complex and difficult workarounds to synthesize digitally: in part, because they map economically onto analog models. The early work of Norbert Wiener has already started to be revisited, after the analog/digital split between him and Page | 16 John von Neumann. Analog was great, but required management for scalability beyond what even the extremely complex initial digital vacuum tube computers could provide. Programmable Logic and Signal Processing, and a variety of Control System memristor patents are out there, waiting for the microchips to fall where they may. The memristive applications in these areas will remain relatively the same, because it will only be a change in the underlying physical architecture, allowing their capabilities to expand, however, to the point where their applications will most likely be unrecognizable as related. Memristor on a chip, by substituting some transistors with memristors, more physical space can be created for more components to be added, increasing the computing power in the process-and reducing energy consumption. Brain-like systems, Memristors are virtually immune from radiation that can disrupt transistor–based technology; they are an attractive way to allow eversmaller but ever-more-powerful devises. Because they do not “forgot”. Memristors can allow computers that turn on and off like a light switch. Since our brains are made of memristors, the flood gate is now open for commercialization of computers that would compute like human brains, which is totally different from the von Neumann architecture underpinning all digital computers. A new architecture within which multiple layer of memristor memory can be stacked on top of each other in a single chip. These chips could be used to create handles devices that offer ten times greater embedded memory than exists today or to power supercomputers that allow work like movie rendering and genomic research to be done dramatically faster. Page | 17 Fifaamfsk Hybrid memristor-transistor, Instead of increasing the number of transistors on a circuit, a hybrid circuit with fewer transistors could be built with the addition of memristors leading to more functionality. Fig 4.2 Hybrid Memristor Memristor technologies could enable more energy-efficient high- density circuits. A hybrid chip using conventional CMOS technology and nanoscale switching devices was developed. “Recently, logic circuits also have been demonstrated that use two or three elements of a one-dimensional memristor array, although such passive devices without gain are difficult to cascade. These circuits fall short of the requirements for a scalable, multifunctional nanoprocessor, owing to challenges in materials, assembly and architecture on the nanoscale. 4.1 POTENTIAL APPLICATIONS Solid-state memristors can be combined into devices called crossbar latches, which could replace transistors in future computers, taking up a much smaller area. They can also be fashioned into non-volatile solid-state memory, which would allow greater data density than hard drives with access times potentially similar to DRAM, replacing both components. HP prototyped a crossbar latch memory using the devices that can fit 100 gigabits in a square centimeter, 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 Page | 18 about one-tenth the speed of DRAM. The devices' resistance would 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 was shown that the electronic circuit subjected to a train of periodic pulses learns and Fig 4.3 Potential Application anticipates the next pulse to come, similarly to the behavior of slime molds Physarum polycephalum subjected to periodic changes of environment. Such a learning circuit may find applications, e.g., in pattern recognition. The DARPA’s SYNAPSE project has funded HP Labs, in collaboration with the Boston University Neuromorphics Lab, to develop neuromorphic architectures which may be based on memristive systems. In 2010, Massimiliano Versace and Ben Chandler co-wrote an article describing the MoNETA (Modular Neural Exploring Traveling Agent) model. MoNETA is the first large-scale neural network model to implement whole-brain circuits to power a virtual and robotic agent compatibly with memristive hardware computations. Page | 19 CHAPTER 5 CONCLUSION The semiconductor industry’s obsession with the shrinking of transistors and their commensurate steady doubling on a chip about every two years has been the source of a 50 years technical and economic revolution. Whether this scaling model last for five more years or 15, it will eventually come to an end. The emphasis in electronics design will have to shift to devices that are not just increasingly infinitesimal but increasingly capable. Memristor is the perfect example for such a device. Emulating the behavior of a single memristor, it was demonstrated that a circuit with at least 15 transistors and systems could be replaced by a single memristor. These memristors can be turned into “integrated other passive elements. The implications are extordinary circuits that remember information, consume far less power just imagine how many kinds of circuits could be than existing devices, and may someday learn from past supercharged by replacing a handful of transistors with one behavior. An analog computer is a computational device in single memristor. It turns out that memristance is becoming stronger as the feature sizes in circuits are getting smaller. At some point as we scale into the realm of nanoelectronics, it will be necessary to explicitly take account of memristance in the circuit models in order to simulate and design electronic circuits properly. Combined with transistors in a hybrid chip, memristors could radically improve the performance of digital circuits without shrinking transistors. In the end, Page | 20 memristors might even become the cornerstone of new analog circuits that compute using architecture much like that of the brain. The future of memristors is very bright and many applications from virtual reality, robotics, medical that will have far reaching benefits to the industry as well as the users. Page | 21 CHAPTER 6 REFERNCES [1] Memristor -the Missing Circuit Element . (1971 ) , Leon Chua [2] Missing link of electronics (2008-04-30), Marks. P [3] HP nano device implements memristor ((2 May 2008)), Bush.S [4] HP makes memory from a once-theoretical circuit (30 April 2008), Kanellos.M [5] Reproducible switching effect in thin oxide films for memory applications, Beck.A [6] Memristor Pattern Recognition Circuit Architecture for Robotics, Mouttet Blaise L [7]Study of Test Structures of a Molecular Memory Element (1993), Krieger Page | 22