graphene based memory device mason overby. outline memory device intro – motivation behind...
TRANSCRIPT
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