Memory Storage in Near Space
Environment
Collin Jones
University of Montana
Department of Physics and
Astronomy
UM BOREALIS
Experimental
Payload
• We suspended an experimental payload containing
UV detection, particle capture, and the cosmic
radiation test (MRAM).
Significance of Memory
Storage
• Not always an option to have real time data
therefore criteria for memory storage:
• Efficiency
– Energy
– Temperature
• Radiation Effects
Options:
• Flash memory – commercially available
• What Else?
Future Option
• What is MRAM?
• Does it meet our criteria?
• Physical Phenomena
– Ferromagnetism
– Magnetoresistance
• How does MRAM work?
• Our Experimental Findings
What is MRAM?
Magnetoresistive Random Access Memory
stores information as an orientation of
magnetic polarity, not as an electric charge
www.ece.nus.edu
Toggle MRAM structure
Does MRAM meet out
criteria?
• Nonvolatile
– If the device is switched off, memory is preserved
• Instant-ON technology
– Energy Savings
• Potential in aerospace applications
– Radiation Hard (Our experiment)
• Endurance as a memory storage
device (~1015 write cycles)
Physical Phenomena
Governing MRAM
Ferromagnetism
• Matter contains positive and negative charges
which in general are in equal numbers.
• In addition to charge electrons also have an
inherent property called spin,
either up or down.
• In general most matter has
equal numbers of spin up
and spin down electrons
which cancel any effect.
• Ferromagnets are materials where there is a net
spin. This tendency of electron spins to align with
one another is due to the quantum mechanical
exchange interaction.
Magnetoresistance
This is the observable change in electrical resistivity
when a magnetic field is present. Two of the most
useful types of magnetoresistance are;
• Giant Magnetoresistance
• Tunneling Magnetoresistance
Giant Magnetoresistance (GMR)
GMR can occur between two adjacent
ferromagnetic layers separated by a spacer.
• Electrons with their spins aligned with the
ferromagnetic moment are less likely to
scatter which leads to lower resistance.
– High resistivity = antiparallel alignment
– Low resistivity = parallel alignment
GMR – Spin Valve
A spin valve structure is one with a ferromagnetic-nonmagnetic-
ferromagnetic layering scheme such as the one below.
60%Co-40%Fe 80%Ni-20%Fe
• We can control the layers orientation by using external
magnetic fields.
• We can detect which orientation the layers are in by measuring
the resistance.
•The 2007 Nobel Prize in Physics was awarded to Albert Fert and
Peter Grunberg for their discovery of the GMR effect.
Tunnel Magnetoresistance
(TMR)
• TMR is analogous to GMR
• Parallel small resistivity large tunneling probability
• Anti-parrallel large resistivity small tunneling probability
Courtesy of: physicsworld.com
How MRAM Works
Writing and Reading
Courtesy of: www.ece.nus.edu.sg/isml
* The bottom layer is fixed.
Writing and Reading (Cont’d)
• To write to a given bit, current passes through the
word line an then the bit lines
• Reading is determined by the resistivity of the
individual MTJs
Our Experimental Findings
• A sample of
collected Geiger Data
is displayed above
Our experiment indicates that the radiation
dose during our three hour flight was insufficient to
corrupt the data in either of the chips, MRAM or
flash memory.
Wrap-up
• MRAM remained unaffected by
radiation dosage from cosmic rays.
• Pros
– Nonvolatile
– Endurance
– Radiation Hard
• Cons
– Scaling Issues for large storage (16 Mb)
– Cost of Production
Conclusion
• We have found both MRAM and Flash
are viable technologies for short term
high altitude flight applications.
• MRAM is potentially advantageous in
applications:
– With a larger radiation dose
– Where immediate memory retrieval is
necessary
– Where energy efficiency is critical
e.g. short term high altitude balloon
flights.
Literature and Sources
• Physics of Ferromagnetism by Soshin
Chikazumi
• Journal of Research and Development,
Jan. 2006, IBM
Special Thanks to Dr. Schneider and
Jen Fowler