By : Dhruv Dani 200601163

Shitij Kumar 200601084

Team - N

MRAM(MagnetoResistive Random Access Memory)

Flow of Presentation Current Memory Technologies

Riddles

Introduction

Principle, Structure and Working

Working Modes

Schematic Overview

MRAM v/s Other Memory Elements

Applications in Embedded Systems

Case Studies

Supported Microcontrollers and Companies

Constraints

References

Current Memory Technologies

Volatile

When the power is switched off the information is lost.

Restarting: programs and data need to be reloaded resulting in

increase of idle time.

Non -Volatile

Can retain stored information permanently

Stores information that does not require frequent changing.

Read/Write/Erase cycles consume a lot of time.

Commonly Known Memories

Volatile – Static RAM (SRAM), Dynamic RAM (DRAM)

Non –Volatile – Flash, EEPROM

Riddle - 1 A car component manufacturing company ‘X’ has to built Air Bag

systems for a range of cars.

The requisites of building such a system are that it has to interact

with the various sensors which detect and record passenger weight

and are employed in other safety devices on the vehicle which

perform various crucial tasks like detecting the impact of the

possible collision.

Such a real time system requires the memory to be susceptible to

continuous reads, writes and overwrites in each clocked interval.

As an embedded engineer for this company X which kind of

memory would you use to implement such a system?

Riddle - 2 The Defense Research and Development Organization of a nation

‘C’ has to build a system which can be employed by them for their military and aerospace applications.

These systems at present require constant power supply to maintain various kinds databases consisting of confidential information.

The battery generally acts as the power supply and is entrusted to keep the information accessible and safe at all times.

But it has been experienced day in and day out that systems which use battery back-up have an inherent reliability problem.

As an embedded engineer what modifications would you do to such a system?

What might be the solution???

MRAM Magneto-resistive RAM, or Magnetic RAM is a form of

non-volatile RAM memory technology that uses magnetic charges to store data instead of electric charges.

In the early 1990’s the company Honeywell conceived a new class of Magnetoresistencememory devices which offered promise for high density, random access and non–volatile memory.

Commercially, the first mass production of MRAMS was started by Freescale – Everspin.

Principle on which MRAM works!!

Principle

MRAM works on the principle Magnetoresistance.

The change in resistance with the magnetic state of the device is

an effect known as Magnetoresistance.

The resistance with which the magnetic state is associated is

measured on the basis of the magnetic moment of the inherent

layers of the MRAM.

Structure of the MRAM MRAM is constituted of various storage elements called

Magnetic Tunnel Junctions (MTJ) integrated with CMOS processing.

Each MTJ is composed of two layers (ferromagnetic plates), fixed and free separated by a thin dielectric material.

Fixed layer : Magnetic polarity is fixed

Free Layer : Magnetic polarity is subject to change in accordance with the magnetic field which is the resultant of the applied current.

Working of MRAM When a bias is applied to the MTJ, electrons that are spin polarized by

the magnetic layers traverse the dielectric barrier through a process

known as tunneling.

The MTJ device has a low resistance when the magnetic moment of the

free layer is parallel to the fixed layer and a high resistance when the free

layer moment is oriented anti-parallel to the fixed layer moment.

The data is stored as a magnetic state rather than a charge, and sensed by

measuring the resistance without disturbing the magnetic state.

The magnetic polarization does not leak away with time like charge

does, so the information is stored even when the power is turned off.

Switching the magnetic polarization between the two states does not

involve actual movement of electrons or atoms, and thus no known

wear-out mechanism exists.

Working Modes

Write Mode

During the write operation, current pulses are passed through a

digit line and a bit line, writing only the bit at the cross point

of those two lines.

Read Mode

During the read operation, the target bit’s isolation transistor is

turned on to bias the MTJ, and the resulting current is

compared to a reference to determine if the resistance state is

low or high using the sense line.

Schematic Overview (1/2)

Schematic Overview (2/2)

MRAM V/s Other Existing Memory Elements

(1/4)

Flash - Continuous writes can wear out some flash

memories in 10 days. Meanwhile, MRAM can endure infinite

write cycles because no charging or discharging is involved.

Rotation of magnetic polarities during , is a non-destructive

and non - degrading operation. MRAM uses current that

creates a magnetic field to program the free layer.

Furthermore, flash performs a write or erase operation on a

large block of the memory array. MRAM perform writes on

individual addresses.

MRAM V/s Other Existing Memory Elements

(2/4)

SRAM - It requires power to retain memory contents.

MRAM memory contents are held in the polarity of its free

magnetic layer. Since it is magnetic, this layer retains its state

even without power. The leakage effect comes into the

picture in the case of SRAMs technologies shrink. Given

MRAM's non-volatility, power down techniques can be used

in the system for zero current leakage.

Battery – Backed SRAM - This consists of an SRAM unit

and an accompanying battery in the same package to make it

non - volatile. Meanwhile, MRAM performs read/ write at a

speed faster than battery-backed SRAM. This improves

reliability and dismisses environmental issues linked with

battery disposal.

MRAM V/s Other Existing Memory Elements

(3/4)

EEPROM:This standalone memory has much slower

programming speeds compared with MRAM, and limited

write-cycling capability.

DRAM: Memory has to be frequently refreshed to retain

data because capacitors are used to store the data and there is

a continuous charge leakage. So more power is used.

FRAM: Ferroelectric RAM (FRAM) is non - volatile has

typical small array sizes ranging from 4Kbit to 1Mbit. The

array sizes are small because this technology has limited

scalability. Without such scalability limitations, MRAM can

offer larger memory arrays. Moreover, MRAM can be

programmed faster than FRAM.

MRAM V/s Other Existing Memory Elements

(4/4)

Applications in Embedded Systems

Some more Applications

Data Storage

Industrial Automation

Gaming

Energy Management

Communication

Transportation

Case Study 1

Automotive applications using sensors can benefit from

MRAM. Since sensors write data continuously, flash

memories have difficulty keeping up with such data flow.

New airbag systems also have sensors to detect and record

passenger weight, interactions with other safety devices on

the vehicle and the impact of collision.

Other automotive systems such as odometers, tire pressure

log and ABS require frequent writes to memory that easily

exceed the write-erase capabilities of flash and wear out its

memory. MRAM's unlimited write-cycling capability ensures

a more reliable system for mission-critical devices such as

airbags and ABS.

Case Study 2

The use of MRAM in the military is also gaining wide

acceptance. Many systems use battery-backed SRAM and

have inherent reliability issues with battery use.

We have already seen that MRAMS are faster than battery

backed SRAMs and are more environment friendly.

On similar grounds we feel that in future years MRAM can

be integrated with a GPS to replace its inherent battery –

backed memory.

Supported Microcontroller and

Companies

Rad – Hard MCS8051 instruction-compatible microcontrollers (MCUs)

that can directly interface with Honeywell's new HXNV-0100 64k x 16

radiation-hardened Magnetic RAM (mram).

Most readily available MRAM – Freescale’s MR2A16A.

3.3 V – Single Power Supply

35 ns – Access Time

8 bit – 16 bit – Flexible data bus.

IBM, Motorola, Infineon Technologies, Sony, HP, NVE Corporation are

some other manufacturers.

Renesas Technologies Plans to Launch MCU with Embedded MRAM in

2008, use MRAM to provide unified memory for MCUs

Constraints

Power Efficiency

Writing in to MRAM requires substantial current.

Changing data in magnetic fields requires a large power.

Size

Half select Problem: Induced field overlaps adjacent cells over a small area.

Manufacturing

As chips get smaller individual circuits hold less charge.

It has been found experimentally that the resistance of the

magnetic device varies exponentially with the thickness.

Cost

It is comparatively higher than the other memories

References www.everspin.com/technology.html - TSP – 12545_MRAM.pdf

http://www.industrial-embedded.com

http://www.nve-spintronics.com/mram-operation.php

http://www.mram-info.com/

http://www.eetasia.com

Freescale Semiconductor Datasheet – MR2A16A

http://www.scribd.com/doc/13178752/Magneto-Resistive-RAM-or-MRAM

http://www.freescale.com/files/memory/doc/fact_sheet/MRAMTECHFS.p

df

http://www.radio-electronics.com/info/data/semicond/memory/mram-

memory-technology.php

http://www.avrfreaks.net/index.php?name=PNphpBB2&file=printview&t=6

3351&start=0

Thank You!!!

Queries???