Magnetic RAM: The Universal Memory
Overview
• Introduction
• Historical perspective
• Technical Description
• Challenges
• Principals
• Market impacts
• Summary
Overview
Introduction
Historical Perspective
Technical Description
Challenges / Constraints
Principals
Market
Summary
Introduction
• Non-volatile– Information is saved even when there is
no power• Immediate boot up
– No need to wait for your computer to boot up
• MRAM, SRAM and DRAM– MRAM is potentially capable of replacing
both DRAM, SRAM and many advantages over technology currently used in electronic devices
Overview
Introduction
Historical Perspective
Technical Description
Challenges / Constraints
Principals
Market
Summary
Introduction • DRAM
– Advantages: cheap– Disadvantages: Comparatively slow
and loses data when power is off• SRAM
– Advantages: fast – Disadvantages: cost up to 4 times as
much as DRAM loses data when power is off
• Flash memory– Advantages: save data when power is
off– Disadvantages: saving data is slow and
use lot of power
Overview
Introduction
Historical Perspective
Technical Description
Challenges / Constraints
Principals
Market
Summary
Historical Overview• Why MRAM Became an Important Research Topic
– Universal Memory (Computing & Electronics)
– “Instant-On” Computing
– Read & Write to Memory Faster
– Reduced Power Consumption
– Save Data in Case of a Power Failure
• Modern MRAM Technology Emerged from Several Technologies :– Magnetic Core Memory
– Magnetoresistive RAM
– Giant Magnetoresistance
Overview
Introduction
Historical Perspective
Technical Description
Challenges / Constraints
Principals
Market
Summary
Magnetic Core Memory• In 1953 a team at MIT called Whirlwind
introduced the magnetic core memory
• Magnetic core memory utilized arrays of thousands of small ring magnets threaded with wires
• Data bits were stored and manipulated by sending electric current pulses through the magnets
• Magnetic cores were the most reliable and inexpensive memories for almost twenty years
Photo Courtesy: Magnetism Group, Trinity College, Dublin
Overview
Introduction
Historical Perspective
Technical Description
Challenges / Constraints
Principals
Market
Summary
Giant Magnetoresistance Materials
Overview
Introduction
Historical Perspective
Technical Description
Challenges / Constraints
Principals
Market
Summary
• Giant Magnetoresistance Materials (GMR) were discovered in 1989
• By 1991 GMR technology provided a magnetoresistance ratio of 6% (3 times that provided by previous technologies)
• Read access time of 50 ns (9 times improvement)
• Still not as fast as semiconductor memory
• Large size because lines of 1micron were required
Technical Overview
Overview
Introduction
Historical Perspective
Technical Description
Challenges / Constraints
Principals
Market
Summary
• 3 MRAM Technologies are Currently Being Developed– Hybrid Ferromagnet Semiconductor Structures
– Magnetic Tunnel Junctions
– All-Metal Spin Transistors & Spin Valves
• Writing Data to a Cell is Similar for all 3 Technologies
• Reading a Cell’s Data Reads the Direction of Magnetization of a Ferromagnetic Element, but the Method Varies for Each Technology
Basic Principles
Overview
Introduction
Historical Perspective
Technical Description
Challenges / Constraints
Principals
Market
Summary
• The 2 Possible Magnetization States of a Ferromagnetic Element can be Described by a Hysteresis Loop
• Magnetization of Film vs. Magnetic Field
Diagram Courtesy: IEEE Spectrum
• A magnetic field, with magnitude greater than the switching field, sets magnetization in direction of applied field
Writing a Bit
Overview
Introduction
Historical Perspective
Technical Description
Challenges / Constraints
Principals
Market
Summary
• MRAM Utilizes a Wire Directly Over & Magnetically Coupled to the Magnetic Element
• A Current Pulse Traveling Down the Wire Creates a Magnetic Field Parallel to the Wire
• Each Cell is Inductively Coupled with a Write Wire From a Row & a Column
Diagram Courtesy: IBM
Hybrid Ferromagnet Semiconductor Structures
Overview
Introduction
Historical Perspective
Technical Description
Challenges / Constraints
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Market
Summary
• A Ferromagnetic Element is Placed Directly Over a Semiconducting Channel
• The Fringe Field has a Large Component Perpendicular to the Plane of the Channel
Diagram Courtesy: IEEE Spectrum
Magnetic Tunnel Junctions
Overview
Introduction
Historical Perspective
Technical Description
Challenges / Constraints
Principals
Market
Summary
• 2 Ferromagnetic Films Separated by a Dielectric Tunnel Barrier
• Resistance Between Films Depends on their Magnetic States
• Parallel Fields: Low Resistance
• Antiparallel Fields: High Resistance
Diagram Courtesy: IEEE Spectrum
Comparison
Overview
Introduction
Historical Perspective
Technical Description
Challenges / Constraints
Principals
Market
Summary
• Hybrid Ferromagnet Semiconductor:– Problems with Cross-Talk Between Cells
– Compatable with Standard CMOS Processing
• Magnetic Tunnel Junction– Fabrication Requirements Cause Problems with
Operating Margins and Yields
– Not Compatable with Standard CMOS Processing
• All-Metal Spin Valve– Low Impedance, Low Readout Voltage
– Not Compatable with Standard CMOS Processing
Current Challenges
• Interference
• Manufacturing
• Uniformity
• Power efficiency
• Size
Overview
Introduction
Historical Perspective
Technical Description
Challenges / Constraints
Principals
Market
Summary
Interference
-Interference between adjacent cells
-Disturbance by digit line current to adjacent line current
-The effect of heat cause bit flip
Overview
Introduction
Historical Perspective
Technical Description
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Market
Summary
Manufacturing
• As chips get smaller the individual circuits hold less of the charge
• Risks of leaking current and other problems
• Hard to integrate with other silicon-based chips
• The resistance of the magnet device varies exponentially with it thickness
Overview
Introduction
Historical Perspective
Technical Description
Challenges / Constraints
Principals
Market
Summary
Uniformity
-Distribution of the electromagnetic field
Overview
Introduction
Historical Perspective
Technical Description
Challenges / Constraints
Principals
Market
Summary
Power efficiency
• High Current consumption– MRAM designs required a relatively
high current to write each single bit
• Power consumption is significantly greater than DRAM, only 99% of the total power is used in delivering electric current for writing data
• One transistor is required for each memory bit
Overview
Introduction
Historical Perspective
Technical Description
Challenges / Constraints
Principals
Market
Summary
The Players
Overview
Introduction
Historical Perspective
Technical Description
Challenges / Constraints
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Market
Summary
• Principal Players:
• Additional Players:– Bosch - Hewlett-Packard
– Intel - NVE Corporation
– Siemens - Sony
– Toshiba
Impacts on Broader Society
Overview
Introduction
Historical Perspective
Technical Description
Challenges / Constraints
Principals
Market
Summary
• Engineers / Scientists– Designing MRAM
– Designing Hardware/Software that Interacts with MRAM
– New Memory Standards
• Society– Added Convenience
• Longer Battery Life on Portable Electronics
• “Instant-On” Computing
– Higher Productivity• Data not Lost in Power Failure
• Faster Read & Write
Market impacts
• Huge demand of memory– MRAM is expected to be the standard
memory
• The market size was $21 billion in 1999 when DRAM came out
• $48 billion in 2001• $72 billion within 2007 with
MRAM
Overview
Introduction
Historical Perspective
Technical Description
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Market
Summary
Market analysis
• IBM being the leader in the development of MRAM is chase by:
• Motorola
• Intel
• Siemens
• Toshiba
Overview
Introduction
Historical Perspective
Technical Description
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Summary
Next 5 years
• IBM and Infineon are planning the mass production for 2004
• MRAM will become the standard memory for the next couple of year
• MRAM will be use in other devices
Overview
Introduction
Historical Perspective
Technical Description
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Market
Summary
I&O long term
• Digital camera• Cellular phones• PDA• Palm pilot• MP3• HDTV
Overview
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Historical Perspective
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Quality of life impacts
• MRAM will eliminate the boot up time• Electronic devices will be more power
efficient• It could enable wireless video in cell
phones• More accurate speech recognition• MP3, instead of hundred on songs,
MRAM will enable thousand of songs and movies
Overview
Introduction
Historical Perspective
Technical Description
Challenges / Constraints
Principals
Market
Summary
• Importance– Potentially Substantial Impact on Society
– Potentially Central to Computers and Electronics that Engineers are Designing
• The Future of MRAM– Expected to Replace SRAM, DRAM, & FLASH
– Predicted to be the Memory Standard in both Computers & Consumer Electronics
• Indicators of a Breakthrough– Price of MRAM is Equivalent to or Only Slightly
More than DRAM & FLASH
– MRAM is More Common in New PCs than DRAM & More Common in New Electronics than FLASH
Summary
Overview
Introduction
Historical Perspective
Technical Description
Challenges / Constraints
Principals
Market
Summary
• Bonsor, Kevin. How Magnetic RAM Will Work. 9 Feb 2003. <http://computer.howstuffworks.com/mram.htm>.
• Daughton, James. Magnetoresistive Random Access Memory (MRAM). 4 Feb 2000. 1-13. 13 Feb 2003. <http://www.math.uwaterloo.ca/~m2wang/cs690b/mram.pdf>.
• Goodwins, Rupert. Magnetic Memory Set to Charge the Market. ZDNet UK. 12 Feb 2003. 16 Feb 2003. <http://techupdate.zdnet.co.uk/story/0,,t481-s2130312,00.html>.
• Guth, M., Schmerber, G., Dinia, A. “Magnetic Tunnel Junctions for Magnetic Random Access Memory Applications.” Materials Science and Engineering. Online 2 Jan 2002: 19. Science Direct. 16 Feb 2003. <http://www.sciencedirect.com>.
• IBM Magnetic RAM Images. 16 Feb 2003. <http://www.research.ibm.com/resources/news/20001207_mramimages.shtml>.
• Johnson, Mark. “Magnetoelectronic memories last and last.” IEEE Spectrum 37 (2000 Feb): 33-40.
References
Overview
Introduction
Historical Perspective
Technical Description
Challenges / Constraints
Principals
Market
Summary