Graphene Based Memory Device

Mason Overby

Outline

Memory device intro– Motivation behind spintronic devices

How to use graphene? GaMnAs-based device Can we incorporate all-in-one?

non-volatile memory devices

http://en.wikipedia.org/wiki/File:MagneticMedia.png

http://www.research.ibm.com/research/gmr.html

• “Permanent” memory state• Large writing currents required• Density of “grains”, read/write limiting factor

GMR info on IBM site

Spintronics the solution?

Carrier spin used as two state device ( )

Able to integrate computing and memory into one device utilizing charge/spin.

GMR spin-valves

http://en.wikipedia.org/wiki/File:Spin-valve_GMR.svg

Graphene device

-0.2 -0.1 0.0 0.1 0.2

1.910

1.915

1.920

1.925T = 4K

R (

k)

B (T)

field field

T. Shen, A. Chernyshov

2 m

Ni

compressively strained magnetization easy axes

[100] and [010]

Properties of GaMnAs

100

010

110

101

M

I

H

φM

φH

Properties of GaMnAs

100

010

110

101

|| || where for || , for I M I M

Large resistance anisotropy

|| m( )sin cosxy mR

m IM

transverse anisotropic magnetoresistance(TrAMR)

M

I

H

φM

φH

Determining Magnetization Direction

010

001

M

I

H

φM

φH

001010100

010

Use graphene as spin injector

Minimize spin scattering

GaMnAs polarizes current (1)

Polarized current change state (2)

GaMnAsGraphene

um(1)

(2)

Limitations/difficulties

Need accurate “stamping” of graphene as conductive pads (Kim K., Nature, 475, 706 (2009)) – Lithography and plasma etch “work around”

GaMnAs Tc ~200K and below

Room Temp Integrated Device

Short-term Ni contact pad structure Stamp grid of memory cells and evaporate Ni

contacts Potential to integrate computation and

memory devices

Conclusion

Several methods to incorporate Graphene into memory device design

Relies on “stamping method” or etching step For Ni-contact device, need external

magnetic field Potential for GaMnAs device if Tc ~ RT