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NANOCOMPUTING BY FIELD-COUPLED NANOMAGNETS

- AUTHORS:

Gyorgy Csaba

Alexandra Imre

Gary H. Bernstein

Wolfang Porod (fellow IEEE)

Vitali Metlushko

- REFERENCE :

IEEE TRANSACTION ON NANOTECHNOLOGY, VOL 1, NO. 4, DECEMBER 2002

Andrea Anzalone

Marco Scagno

- CIRCLE :

course of:

NANOELETTRONICA 1

professor:

E. DIZITTI

SUMMARY

- INTRODUCTION
- SPICE MODEL FOR SIMULATION
- NANOMAGNETIC WIRE
- MAGNETIC MAJORITY GATE
- FINAL REMARKS

INTRODUCTION

Achievements:

from

thin magnetic film technologies

to

patterned magnetic media on the deep

submicron and nanoscale

TARGET DEVICES :

STORAGE :

Hard Disk Drives (HDDs)

Magnetic Random Access Memories (MRAM)

NANOMAGNETIC WIRES

MAGNETIC MAJORITY GATES

( “programmable” elementary logic devices )

FIG 1 - (a) Individual access of nanomagnets in an MRAM device (b) Field-coupled structure

Presence of dipolar interaction between neighbouring magnetic particles:

THIS EFFECT IS :

a disadvantage for HDDs and MRAM

( limit to packing density of dots)

an advantage for nanomagnetic wires and magnetic majority gates

1) General mathematical approach :

use of the well-established theory of micromagnetics

- PROBLEM : this theory is:
- TOO COMPLEX
- COMPUTATIONALLY INTENSIVE

2) Use of SPICE macromodels :

based on single-domain approximation ( SDA )

THIS IS A NEW, INNOVATIVE

SOLUTION

useful to design large dots arrays

ADVANTAGES:

- more efficient simulations

- very powerful possibility to design nanomagnetic structures integrated in microelectronic circuits

FIG 3 - Schematic diagram of the dot-circuit. It have six inputs and three-outputs

FIG 4 - Operating scheme of the nanowire. (a) Initial configuration (b) High-field state before and (c) after the application of the input. (d) Final ordered state.

Digital information is represented by the vertical component of the magnetization (mz)

- mz = 1 if BIT = ‘1’
- mz = -1 if BIT = ‘0’

An external magnetic field is applied to drive the dots from an arbitrary initial state to the ordered final state

STANDARD STEPS FOR A NANOWIRE :

- 2) an initial strong external field erase the “memory” of the initial state:
- mz = 0 for each dot

STANDARD STEPS FOR A NANOWIRE :

- 3) an input current influence the magnetization of the input dot

STANDARD STEPS FOR A NANOWIRE :

- 4) the external field is adiabatically lowered and the input signal can propagate through the structure

FIG 5 - SPICE simulation of the nanowire. The driver current and the mz components are shown . The phases (a), (b), (c), (d), corresponds to schematics of FIG 4 . The dashed line is the pump field

IT IS THE BASIC LOGIC BUILDING BLOCK OF NANOMAGNETIC CIRCUITS

FIG 6 - Physical layout of the majority gate. The input dots (dot 2, 3, 4) are driven by electric wires and the result of the computation is represented by dot 6

IT HAS:

- 3 inputs
- 1 output

- The device is clocked by an external pumping field in a similar way to the nanowires

THE INPUTS HAVE NO PREDEFINED FUCTIONS:

if we force one of them to ‘1’ the device realizes a logic NOR function between the other two inputs and the output

if one input is ‘0’ the gate computes the NANDfunction

FIG 7 - SPICE simulation of the magnetic majority gate. The currents correspond to the perpendicular magnetization of the dots. The dashed line is the pump field.

Need of input wires and output sensors only at the interface of the device:

WHITIN IT EACH SINGLE BASIC MODULE CAN BE CONNECTED USING NANOWIRES

- High integration density:
- above TERABIT / inch²

If only quasi-static behaviour is of interest the dinamic circuit model can be replaced by its non-linear static model:

IT DEPENDS ON GEOMETRIC PARAMETERS :

High pliability for the models

- USE OF NANOMAGNETICS ARRAYS TO SIMULATE BEHAVIOUR OF GENERAL NON LINEAR CIRCUITS

We have seen that a magnetic majority gates can perform basic logic functions ( NAND & NOR ):

we can suppose to use more gates (connected with nanowires) to realize any kind of boolean function and more in general to manage signal-processing tasks

PROMISING APPLICATIONS FOR THE FUTURE:

- Intelligent magnetic field sensors
- Processing-in-memory type architectures
- Complex signal-processing units

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