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

15

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

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

21

•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 .

22

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.

23

Ferroelectric Capacitor

Access Transistor

WRITE “1” OPERATION

24

Timing Diagram

State Sequence For the FE Capacitor

WRITE “0” OPERATION

25

Timing Diagram

State Sequence For the FE Capacitor

READ OPERATION

(Destructive Read)

26

•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

27

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

28

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)

29

QUESTIONS?

30