Memory Storage in Near Space Environment

Collin Jones University of Montana

Department of Physics and Astronomy

UM BOREALIS

• We suspended an experimental payload containing UV detection, particle capture, and the cosmic radiation test (MRAM).

ExperimentalPayload

Significance of Memory Storage

• Not always an option to have real time datatherefore criteria for memory storage:• Efficiency

– Energy– Temperature

• Radiation EffectsOptions:• 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

Toggle MRAM structure

www.ece.nus.edu

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 resistivitywhen a magnetic field is present. Two of the mostuseful 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 ValveA spin valve structure is one with a ferromagnetic-nonmagnetic-ferromagnetic layering scheme such as the one below.

• 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.

60%Co-40%Fe 80%Ni-20%Fe

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

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.

• A sample of collected Geiger Data is displayed above

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