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FeRAM, MRAM, RRAM

Static RAM, SRAM. Stored data is unchanged as long as power is supplied.Fast, but expensive to produce (4-6 transistors/ cell).In PC:s mostly used for cache memory.. I. I. . . . . NAND. NAND. . . . . . . . . Input. . . Output. . . There are two stable configurations; current in the red or the

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FeRAM, MRAM, RRAM

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    1. FeRAM, MRAM, RRAM Possible successors of DRAM and SRAM

    2. Static RAM, SRAM Stored data is unchanged as long as power is supplied. Fast, but expensive to produce (4-6 transistors/ cell). In PC:s mostly used for cache memory.

    3. Dynamic RAM, DRAM Stored data needs to be refreshed. Hence ”dynamic”. DRAM is cheaper, but slower, than static RAM. (One transistor and capacitor/cell) At least in PC:s, DRAM constituates all RAM except CPU-caches.

    4. Development aims for RAM: More memory Faster readouts Neither SRAM nor DRAM can fulfill both aims properly. Would another technology make it possible?

    5. FeRAM - Theory Spontaneous polarization: above the Curie-temperature TC is the structure cubic, below a dipole moment occurs (displacement) A different charge ?Q can be observed whether the material is switching or non-switching:

    6. FeRAM – Failure mechanisms A decrease of the remanent polarization reduces the difference between switching- and non-switching charge Polarization fatigue (after repeated read-write cycles) Retention loss (with time) Imprint shift of the hysteresis loop leads to preference of one polarization state (write failure; only critical at low voltage) or loss of polarization (read failure) Increase of temperature leads to worse material properties (i.e. defect distribution)

    7. FeRAM - Requirements Small size High speed High lifetime Destructive reading (after every reading operation is a writing operation required) Low coercive field Low power memory devices Large hysteresis High remanent polarization

    8. FeRAM - Technological Aspects Different cell designs: Problem: reduced thickness increases coercive field and reduces remanent polarization High quality semiconductor/ferroelectric material Using proper electrode material to obtain high remanent polarization and low coercive field (i.e. Pt electrodes for PZT)

    9. FeRAM - 1T/1C-Cell Write WL: adressed DL: pulse +VCC (half length) BL: +VCC: “1”, ground:”0” Read WL: adressed DL: adressed with positive voltage +Vcc BL: capacitor divider between Cfe and Cbl, sense amplifier compares voltage with Vref V<Vref: Binary state 0 V>Vref: Binary state 1 But: reading operation is destructive, information needs to be restored

    10. M-RAM – physical principle Tunnel MagnetoResistance (TMR)

    11. M-RAM – simple scheme

    12. M-RAM – real design & operation /1

    13. M-RAM – real design & operation /2

    14. M-RAM – technological issues Accomplished: sub-micrometric lithography uniform deposition of thin films (<1nm for isolation and RKKY coupling barrier) integration of TMR material with CMOS Challenges in scaling M-RAM techonolgy: reducing the resistance-area product value (RA) mantaining the MR ratio generating the switching magnetic fields using shrinking metal lines accomodating the increased magnetostatic fields generated by the reduced dimensions

    20. Performance of FeRAM, MRAM, RRAM All three technologies: Already much faster than DRAM and uses less energy. Good possibilities to reach SRAM speeds. Non-volatile. Possibly replacing hard-drives and almost eliminating booting time. MRAM seems to be further ahead commercially than FeRAM. RRAM has size independent properties and performance is not degraded at higher temperatures. Failures and destructive reading proposes problems for FeRAM

    21. Conclusion MRAM is a good candidate to replace DRAM on a few years sight. RRAM is far from commercial production, but will probably prevail over the others in due time.

    22. References SRAM C.R. Nave, hyperphysics.phyastr.gsu.edu/hbase/electronic/ nandlatch.html, Georgia State University, 2005 DRAM A Cardon & LJL Fransen, Dynamic Semiconductor RAM Structures, Pergamon, 1984 Charles M. Kozierok, www.pcguide.com/ref/ram/, 2004 FeRAM Rainer Waser (Ed.), Nanoelectronics and Information Technology – Advanced Electronic Materials and Novel Devices, Wiley-VCH, 2003 Kenji Uchino, Ferroelectric Devices, Marcel Dekker, 2000

    23. Yuhuan Xu, Ferroelectric Materials and Their Applications, North-Holland, 1991 www.fujitsu.com (pictures) MRAM Rainer Waser (Ed.), Nanoelectronics and Information Technology – Advanced Electronic Materials and Novel Devices, Wiley-VCH, 2003 V. Korenivski, Text reference for Spintronics, 5A1379, KTH-Physics, Stockholm, 2005 J. Slonczewski and V. Korenivski, Elements of Spintronic Theory for Magnetic Memory, IBM and KTH, 2005 S. Parkin, Magnetic Tunneling Junctions and Transistors: Magnetic Memory and Field Sensors, IBM, 2002

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