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 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

Graphene device T. Shen, A. Chernyshov 2 m Ni

compressively strained magnetization easy axes [100] and [010] Properties of GaMnAs M I H φMφM φHφH

Large resistance anisotropy transverse anisotropic magnetoresistance (TrAMR) M I H φMφM φHφH

Determining Magnetization Direction M I H φMφM φHφH

Use graphene as spin injector Minimize spin scattering GaMnAs polarizes current (1) Polarized current change state (2) GaMnAs Graphene 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 T c ~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 T c ~ RT