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FUTURE
NON-VOLATILE
MEMORY
TECHNOLOGIES
ANKIT SHAH VINEETH VIJAYAKUMARAN
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Outline
Current Memory Technologies
Future Memory Technologies
What is MRAM ?
Working of MRAM
Advantages & Disadvantages - MRAM
What is Ferroelectric RAM (FeRAM or FRAM) ?
FeRAM -Superior Features
Compare FeRAM with EEPROM & FLASH
FeRAM –Memory cell , Write , Read , Application
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Current Memory Technologies
DRAMs
Volatile
Require standby power
Flash Memories
Limited write endurance
Low write speed
SRAMs
Volatile
Large cell size
Combined revenues of these 3 memory technologies were ~26B$ in 2002
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Future Memory Technologies
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Magnetoresistive RAM
(MRAM)
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What is MRAM ??
It is non-volatile memory.
Made up of millions of pairs of tiny ferromagnetic plates called as memory cells (Magnetic plates with very thin insulating material sandwiched between the plates).
Data is not stored as electric charge but by magnetic storage elements.
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Magnetoresistive Effect Magnetic layer has a polarity – north pole and the
south pole.
Their magnetic moments can have a parallel orientation or anti-parallel orientation.
Memory cell has low resistance when magnetic moments have parallel orientation and high resistance when magnetic moments have anti-parallel orientation.
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Continued The magnetic moments and hence the resistance of
the memory cell can be changed by application of magnetic field.
This effect is called as Magnetoresistive Effect.
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Working of MRAM
MRAM uses Magnetoresistive Effect.
Working of MRAM consists of mainly 2 parts
i. Reading data from the memory cell.
ii. Writing data to the memory cell.
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Read Operation MRAM reads information
by measuring the electric resistance of the specific cell.
Resistance is measured by passing a current through the memory cell.
It reads a ‘1’ if resistance is low and ‘0’ if resistance is high
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Write Operation Current pulses are
passed through the digit line and the bit line.
Currents generates a magnetic field that changes the orientation of the magnetic moments of particular memory cell.
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CONT‟D Write takes place only on the bit in the array which is
at cross point of the 2 lines.
The value stored depends on the resultant of the applied magnetic fields.
The “1” or “0” is stored by putting the free layer magnetic moment into the anti-parallel or parallel state.
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Advantages of MRAM Non-volatile memory.
High speed read writes.
Unlimited Endurance.
Low power as compared to DRAM.
Magnetic polarization does not leak away with time like charge does.
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Disadvantages of MRAM Cost ( $25 for 0.5 MB).
Limitation to reduction in cell size. Sense lines cannot get narrower than 1 micron.
Power required to write data is 3 to 8 times higher than power required to read data.
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Applications of MRAM Current Application
i. Cache buffers
ii. Configurable Storage memories.
Potential Applications
i. Cell phones, PDA’s, Notebooks.
ii. Computing and Networking.
iii. RFID
iv. Military
v. Cell phones and Mobile computing
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July 10th 2006 Freescale moved MRAM in volume production (4 MB product).
FeRAM / FRAM
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Ferroelectric RAM (FeRAM or
FRAM) • Random access memory similar in construction to DRAM
• Uses a ferroelectric layer instead of a dielectric layer to
achieve non-volatility
• 320 patents granted by the U.S. patent office in last 3
years. More than 120 ,during the past year alone.
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Superior Features
Short programming time
Lower power usage
Faster write performance
FeRAM – A possible alternative for Flash
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Compare FeRAM with
EEPROM & FLASH
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FeRAM- FerroElectric Materials
Unique Characteristics
Upon the application of an electric field, there exists a Spontaneous electric polarization inherent to the crystal structure of the material
Furthermore, the polarization does not disappear even when the electric field is removed
Exhibits Hysteresis
Example - Perovskites - PZT (PbO,ZrO2, TiO2) Lead-Zirconate-Titanate
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Electric Field on Ferroelectric
Material
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•Applied External Electric Field moves the
Center Atom in the direction of the field
•Remain in that state even after the field is
removed.
•The position of the „central‟ atom affects the
voltage which is used to determine whether it
represents a 0 or a 1
Stable States Central Atom
Electric Field
FeRAM - Ferroelectric capacitor
Ferroelectric capacitor?
A regular capacitor substituted with a ferroelectric
material instead of a dielectric
Hence provides non-volatility .
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Ferroelectric Material
FeRAM – 1T-1C (one transistor, one
capacitor) Memory cell
When the Access Transistor is ON, the Ferroelectric
Capacitor(FE) is connected to the bitline(BL) and can be written to or read by the plateline (PL).
“CBL ” represents the total parasitic capacitance of the bitline.
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Ferroelectric Capacitor
Access Transistor
WRITE “1” OPERATION
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Timing Diagram
State Sequence For the FE Capacitor
WRITE “0” OPERATION
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Timing Diagram
State Sequence For the FE Capacitor
READ OPERATION
(Destructive Read)
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•Precharge BL to 0 V •Activating WL establishes a capacitor divider between the PL and the ground is established •Depending on the data stored, FE capacitor can be approximated by C0 or C1 and thus voltage could be V0 or V1
•PL raised to VDD
•At this point, the sense amplifier is activated to drive the BL If BL is V1 then full VDD
If BL is V0 then full 0V •The WL is kept activated until the sensed voltage on the BL restores the original data back into the memory cell
Application - FeRAM
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Salient Features –
Low Write Access time Low power consumption Digital Camera –Fast frequent writes in order to store and restore images into the memory in less than 0.1 s. Contactless smart cards –Only use electromagnetic coupling to power up the electronic chips on the card. NOTE: FeRAM may play a major role in future 3G phones and personal digital systems .
Conclusion
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References MRAM
“The future of things” website (http://thefutureofthings.com/articles/36/mram-the-birth-
of-the-super-memory.html)
MRAM from wikipedia
(http://en.wikipedia.org/wiki/Magnetoresistive_random_access_memory)
FeRAM
A Survey of Circuit Innovations in Ferroelectric Random-Access Memories, Ali
Sheikholeslami, MEMBER, IEEE, AND P. Glenn Gulak, SENIOR MEMBER,
IEEE (http://www.eecg.utoronto.ca/~ali/papers/survey_proc.pdf)
FeRAM from wikipedia (http://en.wikipedia.org/wiki/Ferroelectric_RAM)
Presentation from Stefan Lai Co-Director, California Technology and
Manufacturing February
2003(http://www.ece.umd.edu/courses/enee759h.S2003/references/Stefan_Korea_0
22703.pd)
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QUESTIONS?
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