FUTURE NON-VOLATILE MEMORY TECHNOLOGIES

FUTURE
NON-VOLATILE
MEMORY
TECHNOLOGIES
ANKIT SHAH
VINEETH VIJAYAKUMARAN
1

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
2

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
3

Future Memory Technologies
4

Magnetoresistive RAM
(MRAM)
5

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.
6

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.
7

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.
8

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.
9

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
10

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.
11

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.
12

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.
13

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.
14

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
July 10 th 2006
Freescale moved
MRAM in volume
production (4 MB
product).
15

FeRAM / FRAM
16

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.
17

Superior Features
• Short programming time
• Lower power usage
• Faster write performance
FeRAM – A possible alternative for Flash
18

Compare FeRAM with
EEPROM & FLASH
19

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
20

Electric Field on Ferroelectric
Material
•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
Electric Field
Central Atom
Stable States
21

FeRAM - Ferroelectric capacitor
• Ferroelectric capacitor?
A regular capacitor substituted with a ferroelectric
material instead of a dielectric
• Hence provides non-volatility .
Ferroelectric
Material
22

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.
Access
Transistor
Ferroelectric
Capacitor
23

WRITE “1” OPERATION
Timing Diagram
State Sequence For the FE Capacitor
24

WRITE “0” OPERATION
Timing Diagram
State Sequence For the FE Capacitor
25

READ OPERATION
(Destructive Read)
•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
26

Salient Features –
‣Low Write Access time
‣Low power consumption
Application - FeRAM
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 .
27

Conclusion
28

References
‣ MRAM
“The future of things” website (http://thefutureofthings.com/articles/36/mram-the-birthof-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)
29

QUESTIONS?
30