1 / 19

MRAM: Giant and Tunneling Magnetoresistance Phenomena

Outline. GMRTMRMRAM. Giant magnetoresistance (GMR). Magnetic metallic multilayers (Fe/Cr or Co/Cu)Ferromagnetic layersseparated by nonmagnetic metal layers of a few nm thick Magnetic fieldResistance changes. . Definition of GMR. GMR(%) = (RAP-RP)/RP with RAP: Resistance in the antiparallel configurationRP : Resistance in the parallel configuration.

arch
Download Presentation

MRAM: Giant and Tunneling Magnetoresistance Phenomena

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

    1. MRAM: Giant and Tunneling Magnetoresistance Phenomena

    2. Outline GMR TMR MRAM

    3. Giant magnetoresistance (GMR) Magnetic metallic multilayers (Fe/Cr or Co/Cu) Ferromagnetic layers separated by nonmagnetic metal layers of a few nm thick Magnetic field Resistance changes

    4. Definition of GMR GMR(%) = (RAP-RP)/RP with RAP: Resistance in the antiparallel configuration RP : Resistance in the parallel configuration

    5. Origin of GMR

    6. Different conductivities High conductivity of Cu In ferromagnetic 3d metals the d band is exchange-split High conductivity of majority-spin channel Low conductivity of the minority-spin channel Origin of GMR

    7. Interface Good band matching ? High transmission for the majority-spin electrons Large band mismatch ?Weak transmission of the minority-spin electrons Interface Co/Cu = spin-filter Origin of GMR

    8. Tunnel Magnetic Resistance Effect Spin dependant tunneling d band : Split exchange

    9. Tunnel Magnetic Resistance Effect Julliere’s Modell 2 Assumptions : Spin conservation during tunneling Current # Density of states

    10. Tunnel Magnetic Resistance Effect Magnetic Tunnel Jonction

    11. MRAM Bit Cell TMR effect ? 30 – 50% 2 resistance values ? 2 bit states Bit cell :

    12. MRAM Reading Process Measurement of the bit cell resistance by applying a current in the ‘bit line’ Comparison with a reference value mid-way between the bit high and low resistance values

    13. MRAM Writing Process Currents applied in both lines ? 2 magnetic fields Both fields are necessary to reverse the free layer magnetization When currents are removed : Same configuration ? Non-volatile memory, Low power consumption

    14. MRAM Device Bit cells arranged in array: Need of 2 magnetic fields for writing

    15. Improvements I Two pinned layers, separated by a thin coupling layer to allow for antiferromagnetic coupling Increases resistance against external fields Smaller size possible

    16. Writing Processes Toggle Writing Flips the direction of the free layer by a rotating current Only one current direction required Thermally Assisted Writing Heating the cell before writing to make it more susceptible to magnetic fields Spin Torque Transfer Writing by injecting spin-polarized current into the device Promises higher memory densities and faster write speeds Improvements II

    17. Comparison with other Tech Volatile DRAM High power consumption due to continuous refresh SRAM Very fast, but not as dense as DRAM Nonvolatile Flash Slow and limited write cycles

    18. History & Commercialization 1988 Discovery of GMR by Peter Grünberg and Albert Fert (Nobel Prize 2007)? 2000 IBM and Infineon establish joint research program 2003 First MRAM chips sold by Cypress, 128KBit July 2006 Freescale starts selling 4MBit chips August 2007 IBM and TDK to start researching spin-momentum-transfer for 65nm – MRAM - chips

    19. Future Depending on the material, the superparamagnetic effect does not allow single MRAM cells to become smaller than around 10nm Semiconductor processes will, at current development speed, reach 10nm at around 2015 MRAM will have to be developed into a working and economically producable and competetive product before then.

    20. References

More Related