emerging memory technologies sudhanva gurumurthi gurumurthi
TRANSCRIPT
Emerging Memory Technologies
Sudhanva Gurumurthi
http://www.cs.virginia.edu/~gurumurthi
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Hard Disk Drive (HDD)Solid State Drive (SSD)
The Transistor
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If the voltage applied at the gate > a threshold voltage, a conducting channel forms between the source and drain
Flash Memory
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• Floating Gate Transistor (FGT)– Has a “floating
gate” between the gate and the channel that is surrounded by SiO2
• Removing the voltage on the gate leaves the induced charges on the floating gate– Non-Volatility
Tunneling
6Image Source: http://www.bun.kyoto-u.ac.jp/~suchii/Bohr/tunnel.html
Quantum mechanics provides for wave-particle duality
Flash Cell Wearout• Writing and erasing flash cells is bad!
7Floating-Gate
Transistor
Write
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Erase
State After Write
State After Erase
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Impact on Retention Time
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Memory cell state at time ‘t’
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Memory cell state after retention period
- - Time to LeakTime to Leak
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Charge trapping increases Stress Induced Leakage Current (SILC)
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Boosting Flash EnduranceComputed for a Flash Cell Using Our Model
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Magnetic Tunnel Junctions
• If tunnel barrier is thin enough, electrons can tunnel from one ferromagnet to the other
• Electrical resistance of the MTJ depends on the orientation of the fields on the two plates
12Image Source: Wikipedia
Data Representation in an MTJ
13Image Source: http://www.mdm.imm.cnr.it/SPAM3/background.html
Used in Magnetic RAM (MRAM) and Spin Transfer-Torque RAM (STT-RAM)