NANOCOMPUTING BY FIELD-COUPLED NANOMAGNETS

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

REPORT EDITED BY : 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

INTRODUCTION Basic structure: use of individual ferromagnetic dots ONE DOT ONE BIT OF INFORMATION

INTRODUCTION ADVANTAGES: • Lower energy dissipation • Higher speed • Larger storage density

INTRODUCTION 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

SPICE MODEL FOR SIMULATION 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

SPICE MODEL FOR SIMULATION We need models for: • each single micromagnetic dot • interaction dot to dot

SPICE MODEL FOR SIMULATION 1) General mathematical approach : use of the well-established theory of micromagnetics • PROBLEM : this theory is: • TOO COMPLEX • COMPUTATIONALLY INTENSIVE

SPICE MODEL FOR SIMULATION 2) Use of SPICE macromodels : based on single-domain approximation ( SDA ) THIS IS A NEW, INNOVATIVE SOLUTION useful to design large dots arrays

SPICE MODEL FOR SIMULATION ADVANTAGES: • more efficient simulations • very powerful possibility to design nanomagnetic structures integrated in microelectronic circuits

FIG 2 - Circuit blocks of two coupled nanomagnets i e j

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

NANOMAGNETIC WIRE WHAT IS IT ? • It is a line of coupled nanomagnets

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.

NANOMAGNETIC WIRE Digital information is represented by the vertical component of the magnetization (mz) • mz = 1 if BIT = ‘1’ • mz = -1 if BIT = ‘0’

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

NANOMAGNETIC WIRE STANDARD STEPS FOR A NANOWIRE : • 1) we considered a general initial configuration

NANOMAGNETIC WIRE STANDARD STEPS FOR A NANOWIRE : • 2) an initial strong external field erase the “memory” of the initial state: • mz = 0 for each dot

NANOMAGNETIC WIRE STANDARD STEPS FOR A NANOWIRE : • 3) an input current influence the magnetization of the input dot

NANOMAGNETIC WIRE 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

MAGNETIC MAJORITY GATE 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

MAGNETIC MAJORITY GATE IT HAS: • 3 inputs • 1 output • The device is clocked by an external pumping field in a similar way to the nanowires

MAGNETIC MAJORITY GATE 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.

FINAL REMARKS 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

FINAL REMARKS 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

FINAL REMARKS 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

FINAL REMARKS PROMISING APPLICATIONS FOR THE FUTURE: • Intelligent magnetic field sensors • Processing-in-memory type architectures • Complex signal-processing units

NANOCOMPUTING BY FIELD-COUPLED NANOMAGNETS