Download MRAM (MagnetoResistive Random Access Memory)

MRAM
(MagnetoResistive Random Access Memory)
By : Dhruv Dani 200601163
Shitij Kumar 200601084
Team - N
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
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‘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 Magnetoresistence
memory 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
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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/mrammemory-technology.php
 http://www.avrfreaks.net/index.php?name=PNphpBB2&file=printview&t=6
3351&start=0
Thank You!!!
Queries???