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Graphene Based Memory Device Mason Overby
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Outline Memory device intro – Motivation behind spintronic devices How to use graphene? GaMnAs-based device Can we incorporate all-in-one?
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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
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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
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Graphene device T. Shen, A. Chernyshov 2 m Ni
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compressively strained magnetization easy axes [100] and [010] Properties of GaMnAs M I H φMφM φHφH
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Large resistance anisotropy transverse anisotropic magnetoresistance (TrAMR) M I H φMφM φHφH
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Determining Magnetization Direction M I H φMφM φHφH
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Use graphene as spin injector Minimize spin scattering GaMnAs polarizes current (1) Polarized current change state (2) GaMnAs Graphene um (1) (2)
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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
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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
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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
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