Memristors By, Saransh Singh

Contents Introduction Basic Memristor Model V-I Characteristics Formula for Memristance Types for Memristors Working of Memristors Merits and Demerits Possible Applications Conclusion

Introduction Currently known fundamental passive elements – Resistors, Capacitors & Inductors. Leon O. Chua formulated Memristor theory in his paper “Memristor-The Missing Circuit Element” in 1971. Later Memristor was named the 4th Fundamental element It is a 2 terminal passive device, relates charge to flux

Behaves like a nonlinear resistor with memory. The memristor is currently under development by a team at Hewlett Packard (HP).

Combination of the 4 Variables Integral of current is charge dq/dt = I (amperes) Integral of voltage is flux dΦ/dt = V (volts) Resistor dv = R di , dv/di = R(ohms) Capacitor dq = C dv , dq/dv = C(farad) Inductor dΦ = L di , dΦ/di = L (henry) dΦ/dq = ?

What is Memristance ? Memristance is a property of an electronic component. When charge flows in one direction, its resistance increases, and if direction is reversed, resistance decreases. When v=0, charge flow stops & component will ‘remember’ the last resistance it had. When the flow of charge regains, the resistance of the circuit will be the value when it was last active.

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

Basic Memristor Model Doped: region of low resistance Undoped: region of high resistance R off : Resistance when w/d=0 R on: Resistance when w/d=1

V-I Characteristics In ordinary resistors there is a linear relationship between current and voltage However, for memristors a similar graph is a little more complicated 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. 

Formula for Memristance The Basic Fromula is The 2nd term in the parentheses which contribute more to memristance becomes larger when D is in the nanometer range Thus memristance is important characteristics of a device when critical dimension shrink to nanometer scale

Types of Memristors Spintronic Memristor Spin Torque Transfer Magneto resistance Titanium dioxide memristor Polymeric memristor Spin memristive systems Magnetite memristive systems Resonant tunneling diode memristor

Working of Memristors Spintronic Memristor Spin of electrons Magnetism Magneto resistance principal Electrons flow alters the magnetization state

Titanium Memristors Two thin layer sandwich, 1st layer is oxygen deficient The oxygen vacancies act as charge carriers and this implies that the depleted layer has a much lower resistance than the non-depleted layer When an electric field is applied, the oxygen vacancies drift, changing the boundary between the high-resistance and low- resistance layers

Titanium Memristor

Memristors as a Storage element Nonvolatile Energy required during switching Memristor as switches in crossbar architecture Crossbar Architecture Connected mesh of perpendicular wires Crossing wires connected by switch Switch closed applying positive voltage Switch opened by reversed voltage

Merits and Demerits Merits: Eliminates delay Speed inversely proportional to size Large density 1terabit/cm2 Analog data storage possible Demerits: Dissipates heat No design standards Needs defect engineering

Possible Applications Cheaper Memristor made chips: They are nanoscale devices with unique properties: a variable resistance and the ability to remember the resistance even when the power is off A single memristor can perform the same logic functions as multiple transistors, making them a promising way to increase computer power Memristors could also prove to be a faster, smaller, more energy-efficient alternative to flash storage

Memristor as Digital and Analog: A memristive device can function in both digital and analog forms In digital mode, it could substitute conventional solid-state memories (Flash) with high-speed and less steeply priced nonvolatile random access memory (NVRAM)

No Rebooting: The memristor's memory has consequences The reason computers have to be rebooted every time they are turned on is that their logic circuits are incapable of holding their bits after the power is shut off But because a memristor can remember voltages, a memristor- driven computer would arguably never need a reboot

Conclusion Latest technology, High speed memory devices, Low power requirements 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

Memristors made to replace flash memory will likely appear first; HP's goal is to offer them by 2012 Beyond that, memristors will likely replace both DRAM and hard disks in the 2014-to-2016 time frame As for memristor-based analog computers, that step may take 20-plus years