MEMRISTORTHE BASIC MISSING CIRCUIT ELEMENT

ARUN PAL REETIKA CHATURVEDIECE ---3 Year 2 sem ECE--- 2 Year 2 semNarsimha Reddy Engg. College Narsimha Reddy Engg. College

ABSTRACT:

The objective of this paper is to make the students aware that there exits a fourth passive element other than resistor, inductor, and capacitor. And the name of the fourth passive element is MEMRISTOR. A memristor ("memory resistor") is any of various kinds of passive two-terminal circuit elements that maintain a functional relationship between the time integrals of current and voltage. A memristor possesses both data storage and signal processing capabilities. It replaces today’s commonly used dynamic random access memory (DRAM). A memristor circuit requires lower voltage, less power and less time to turn on than competitive memory like DRAM and flash. It does not require power to maintain its memory. It takes a lot of transistors and capacitors to do the job of a single memristor. No combination of R, L, C circuit could duplicate the memristance. So the memristor qualifies as a fundamental circuit element.

INTRODUCTION

Currently known fundamental passive elements –

Resistors,

Capacitors &

Inductors.

Does a 4th passive element exist

Leon O. Chua formulated Memristor theory in his paper “Memristor-The Missing Circuit Element” in 1971. Memristors are passive two terminal circuit elements. Behaves like a nonlinear resistor with memory. They maintains a functional relationship between time integrals of current and voltage. It takes a lot of transistors and capacitors to do the job of a single memoristor.

SYMBOL OF MEMRISTER

HISTORY OF MEMRISTOR:

Memristor, the missing basic circuit element, was first proposed in 1971 in a seminal paper published by Professor Leon O. Chua. The concept gained a broader scope in a paper co-published by Leon Chua and Sung Mo Kang in 1976. In 2008, Stan Williams at HP Labs unveiled a two-terminal titanium dioxide nanoscale device that exhibited memristor and memristive characteristics, thus igniting renewed interest in memristors. The first symposium on Memristor and Memristive Systems, held at UC Berkeley on November 21-22, 2008, inspired novel circuit applications and new efforts to develop memristors using various types of materials and nanoparticles, and also novel circuit applications and CAD models

SO 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

MEMRISTOR THEORY

Four fundamental circuit variables- Current I, voltage v, charge q, and flux linkage φ.

Six possible combinations of these four variables.

Five already defined as:

Resistor (dv=Rdi),

Capacitor (dq=Cdv),

Inductor(dφ=Ldi), q(t)=∫i(t)dt, φ(t)=∫v(t)dt.

The 6th relation defines memristance as dφ=Mdq

Two terminal devices in which magnetic flux Φm between its terminals is a function of amount of electric charge q passed through the device.

M (q) = dΦm/dq

M (q) = [dΦm/dt] / [dq/dt] = V/I

V (t) = M (q (t)) I(t)

RELATION BETWEEN FUNDAMENTAL CIRCUIT ELEMENTS AND VARIABLES

MICROSCOPIC IMAGE OF MEMRISTOR ROW

An atomic force microscope image of a simple circuit with 17 memristors lined up in a row.  Each memristor has a bottom wire that contacts one side of the device and a top wire that contacts the opposite side.  The devices act as 'memory resistors', with the resistance of each device depending on the amount of charge that has moved through each one. The wires in this image are 50 nm wide, or about 150 atoms in total width.

OPERATION AS A SWITCH

For some memristors, applied current or voltage will cause a great change in resistance. The semiconductor film has a region of high conc. of dopants having low resistance R ON & remaining portion having zero dopant conc. and much higher resistance R OFF. By application of external bias, we can move the boundary to adjust the device resistance from RON to ROFF.

v-i CHARACTERISTICS

The most common v-i trace is a ‘figure 8’ or a ‘pinched loop’. For this current i=0, when voltage v=0. On the application of electric field, oxygen vacancies drift, changing boundary between high & low resistance layers. Memristance is only displayed when the doped layer & depleted layer both contribute to resistance. The device enters hysteresis when enough charge has passed through memristor & ions can no longer move.

MEMRISTANCE FORMULA

For linear ionic drift in a uniform field with average ion mobility µv,

M(q) = Memristance of a device as a function of chargeRoff = High resistance state Ron = Low resistance state

µv = Mobility of charge

q(t) = Charge flowing through the device at time t D =Thickness of semicounductor film sandwiched Between two metal contacts.

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.

APPLICATIONS AND ADVANTAGES

1. Can now think about fabricating a non-volatile random access memory (RAM) – or memory chips that don't forget the data when a computer is shut off. Memristors carries a memory of its past.

2. Replace today’s commonly used dynamic random access memory (DRAM).

3. Denser cells allow memristor circuits to store more data than flash memory.

4. The Hewlett-Packard team has successfully created working circuits based on memristors that are as small as 15 nanometers. Ultimately, it will be possible to make memristors as small as about four nanometers.

5. A memristor circuit requires lower voltage, less power and less time to turn on than competitive memory like DRAM and flash.

6. It does not require power to maintain its memory.

7. The ability to store and retrieve a vast array of intermediate values also pave the way to a completely different class of computing capabilities like an analog computer in which you don't use 1s and 0s only

PRACTICAL LIMITATIONS:

The most significant limitation is that the memristors functions at about one-tenth the speed of today’s DRAM memory cells.

Its switching operation at only 1Hz

Although small dimension of device seems to imply fast operation, the charge move very slowly

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.

It takes a lot of transistors & capacitors to do the job of a single memristor

No combination of RLC circuit could duplicate the memristance

So memristor qualifies as a fundamental circuit element.