Tariq Hashmat Tauheed-- Under the Supervision of Prof. M. Hasan
--
Final Year B.Tech. Electronics Engg.
Zakir Husain College of Engineering & Technology
MRAM& ITS
APPLICATIONS
Why Are We Here To Talk
About MRAM?
• Moore’s Law Faces a Brick Wall.
• Steep rise in power dissipation per chip.
• Fundamentally unavoidable thermal noise to severely limit
miniaturisation.
• Heat generated from an average workstation may shoot up to
Mega Watts.
• Leakage currents – critical Issue in CMOS.
So, MRAM?
The Magneto resistive RAM is a promising candidate to challenge CMOS dominated memory world.
• NON-VOLATILITY
• HIGH SPEED PERFORMANCE
• INFINITE ENDURANCE
• LOW COST
MRAMs exert superiority over contemporary memory cells like SRAMs and DRAMs, in that they take the
best out of these.
Structure of MRAM
The MAGNETIC TUNNEL JUNCTION is the heart of MRAM
Minimum MTJ stack constitutes:• Two magnetic layers,• Thin dielectric barrier,• A mechanism to hold the polarization of one
of the magnetic layers in a fixed direction
Transistor(s) and various electrodes and current carrying lines.
Direction of polarization of the free magnetic layer is used for information storage.
The three-layer Synthetic
Anti Ferromagnet (SAF)
Pinned/Ru/Fixed structure
results in a magnetically
rigid system and helps
control magnetic
coupling to the free layer.
Operation of MRAM
• Resistance of the memory bit either low or high depending on the relative magnetization, [parallel or antiparallel] of the free layer with respect to the fixed layer.
• Information storage a function of the magnetic orientation of the ferromagnetic layers in the MTJ.
• Therefore, external agent to switch the magnetic orientation.
• Multiple ways in which the magnetic switching can be done.
The Read Process
• Transistor in the cell is kept on.
• ‘Sense Current’ Isense flown through the MTJ.
• Resistance encountered by Isense is measured.
• High resistance Antiparallel Magnetisation of MTJ Digital Value ‘0’.
• Low resistance Parallel Magnetisation of MTJ Digital Value ‘1’.
The Field Writing MRAMFW-MRAM
• Magnetic induction for storage of data bits.
• Combination of currents through the Bit Line (IB) and the Digit Line (ID).
• Magnetic orientation of the free layer in the MTJ is changed according to the induced magnetic field.
• Transistor kept off during the process.
Spin Torque Transferred MRAMSTT-MRAM
• Magnetic switching based on “Spin-Polarised Current”.
• ‘Torque' applied by the injected electron spins helps in magnetic switching of the free layer of the MTJ.
• The phenomenon of Spin Polarised Current induced Magnetic Switching was predicted by Slonczeski and
Berger, 1996.
Applications of MRAM
Embedded STT-MRAM for Mobile Applications
In embedded mobile systems, STT-MRAM finds its use as:
• NVM Cache• ROM• Tightly Coupled Memory (TCM).
Qualcomm Inc. presented some opportunities for embedded STT-MRAM in mobile applications.
• The Multi Chip Package (MCP) in conventional embedded systems can be replaced by a single chip, courtesy high density.
• Significant power savings due to the absence of EBI power for MCP.
• Simpler architecture cuts down the costs.
• STT-MRAM Cache memory in an embedded system is about THREE TIMES smaller than its SRAM contemporary,
Logic Computing using the Magnetoresistive Element of
MRAM• Input lines A and B are
operated with positive or negative currents I(A) and I(B) of equal magnitude.
• Third input C with current I(C) needed for rotation of both magnetic layers.
• Two step procedure: Presetting the MR, followed by the logical operation.
The AND Gate• Before the logic operation the system is set to the
“antiparallel” configuration by applying ZERO at both inputs A and B. This corresponds to output ZERO.
• A & B addressed independently with a ZERO or a ONE. Direction of magnetization remains unchanged if ZERO is applied at both inputs A and B. Same applicable for a ZERO and a ONE at the inputs.
• Magnetization of the upper layer can only be switched by applying a logical ONE at both inputs A & B.
Recent Industry Timeline• 2010: July - Researchers create a new STT-RAM structure,
reduces current by a factor of fifty. September - ENP announces a new single-board
computer with 512KB of MRAM. • 2011: February - BMW use new automotive-temperate
Everspin MRAM in the S-1000RR super bike. August - Toshiba to use MRAM as cache for HDD and
NAND.• 2012: November - Everspin announces the world's first
STT- MRAM chip, launch in early 2013 December - Toshiba developed the lowest power
consumption STT-MRAM, to accelerate R&D.• 2013: June - Samsung seeks STT-MRAM research partners,
offers funding and collaboration.August - Everspin announces sale of over 10 million
MRAM chips, raised $15 million
The Everspin STT-MRAM chip
References• Laszlo B. Kish, “End of Moore’s law: thermal (noise) death of
integration in micro and nano electronics”, Elselvier Physics Letters A 305 (2002) 144–149.
• J. M. Slaughter et al, “Fundamentals of MRAM Technology”, Journal of Superconductivity: Incorporating Novel Magnetism, Vol. 15, No. 1,
February 2002. • Dr G. Pan, “MRAM - present state-of-the-art and future challenges”,
DSNetUK Workshop, January 2006.
• Richard William Dorrance, “Modeling and Design of STT-MRAMs”, MS Dissertation, University of California, 2011.
• L. Prejbeanu et al, “Thermally assisted MRAM”, Journal of Physics: Condensed Matter, 2007.
• A. Ney et al,” Programmable computing with a single magnetoresistive element”, Letters to Nature, Vol 425, October 2003.
• Seung H. Kang (Qualcomm Inc.), “Embedded STT-MRAM for Mobile Applications: Enabling Advanced Chip Architectures”, Non-Volatile Memories Workshop, UCSD, April 2010.
• Website: http://www.mram-info.com, last accessed 22nd October 2013, 23:33hrs
