Ferroelectric RAM FRAM Seminar Report

Seminar Report ’03 FRAM

INTRODUCTION:

A ferroelectric memory cell consists of a ferroelectric

capacitor and a MOS transistor. Its construction is similar to

the storage cell of a DRAM. The difference is in the

dielectric properties of the material between the capacitor's

electrodes. This material has a high dielectric constant and

can be polarized by an electric field. The polarisation

remains until it gets reversed by an opposite electrical field.

This makes the memory non-volatile. Note that ferroelectric

material, despite its name, does not necessarily contain

iron. The most well-known ferroelectric substance is

BaTiO3.

A Ferroelectric memory cell consists of a ferroelectric

capacitor and a MOS transistor. Its construction is similar to

the storage cell of a DRAM. The difference is in the

dielectric properties of the material between the capacitor's

electrodes. This material has a high dielectric constant and

can be polarized by an electric field. The polarisation

Dept. of CSE MESCE, Kuttippuram1


remains until it gets reversed by an opposite electrical field.

This makes the memory non-volatile.

Data is read by applying an electric field to the

capacitor. If this switches the cell into the opposite state

(flipping over the electrical dipoles in the ferroelectric

material) then more charge is moved than if the cell was

not flipped. This can be detected and amplified by sense

amplifiers. Reading destroys the contents of a cell which

must therefore be written back after a read. This is similar

to the precharge operation in DRAM, though it only needs

to be done after a read rather than periodically as with

DRAM refresh.

FRAM is found mainly in consumer devices and

because of its low power requirements, could also be used

in devices that only need to activate for brief periods. FRAM

allows systems to retain information even when power is

lost, without resorting to batteries, EEPROM, or flash.

Access times are the same as for standard SRAM, so there's

no delay-at-write access as there is for EEPROM or flash. In



addition, the number of write cycles supported by the FRAM

components is nearly unlimited—up to 10 billion

read/writes. FRAM combines the advantages of SRAM -

writing is roughly as fast as reading, and EPROM - non-

volatility and in-circuit programmability



FRAM Technology

When an electric field is applied to a ferroelectric

crystal, the central atom moves in the direction of the field.

As the atom moves within the crystal, it passes through an

energy barrier, causing a charge spike. Internal circuits

sense the charge spike and set the memory. If the electric

field is removed from the crystal, the central atom stays in

position, preserving the state of the memory. Therefore, the

FRAM memory needs no periodic refresh and when power

fails FRAM memory retains its data. It's fast, and doesn't

wear out!

To increase the memory capacity, the cell size must

always be reduced, and the design, process, and materials

have been improved aggressively for this purpose.

ferroelectric RAM products (FRAMs) are the most advanced

of the flash challengers. The pioneer, Ramtron International

Corp. (Colorado Springs, Colo.), has been selling FRAM

chips since 1992. Their memory capacities are low,

however, the largest being 256Kb—still a small fraction of

the multimegabit chips offered by the major flash memory

makers. In current commercial FRAMs, the interconnects



that link individual transistors into circuits are 0.5 µm wide

and operate at 3 V. Narrower interconnects are desirable so

that memory cells may be made smaller and be packed in

greater numbers onto an IC. Ramtron's FRAMs are made by

Fujitsu Ltd., Tokyo, which also sells its own FRAM products,

mostly as embedded memory in microcontrollers and smart

cards.

The biggest hurdle for FRAM developers is to advance

the manufacturing technology to smaller geometries and

lower voltages. R&D at Ramtron is aiming at 0.35-µm

interconnect widths and 1.8-V operation. And last

November, Texas Instruments Inc. (Dallas) announced that

it had built a 64Mb FRAM in a standard 0.13-µm CMOS

process, using technology licensed from Ramtron.

At the core of an FRAM cell is a capacitor filled with a

ferroelectric crystalline material, usually a lead-zirconium-

titanate (PZT) compound .Each unit cell (a crystal's basic

building block) of a ferroelectric material has a permanent

electric field around it. That's because the geometric center



of all the electrons in the unit cell is at a different spot from

the geometric center of all the protons. It's as though two

small particles with equal and opposite charges are

separated from each other by a short distance—in short, it

is an electric dipole.

Many materials form electric dipoles. But what sets

ferroelectric materials apart from other dipolar materials is

that millions of dipoles, in a region called a domain, line up

to point in the same direction. When an electric field is

applied in the opposite direction, the dipoles flip over so

that they again point in the direction of the electric field.

Each unit cell of PZT is shaped like an elongated cube.

At each of the cube's eight corners is an atom of lead; in

the center of each cube face is an oxygen atom; and in the

interior of the cube is an atom of either zirconium or

titanium. This last has two stable positions, explains Mike

Alwais, Ramtron's vice president of FRAM products: "One is

near the cube's top face and the other is near the bottom."

Apply an electric field and the atoms in the interiors of

all the unit cells in the ferroelectric material move in the



field's direction. Remove the field and the atoms stay put.

The positions of the atoms in the cubes store the bit of

data, a binary 1 or 0.

To read a bit, an electric field is applied. If the atoms

are near the cube "floors" and the electric field pushes

them to the top, the cell gives off a current pulse. This

pulse, representing a stored 1 or 0, is detected by a sense

amplifier. Contributing to pulse amplitude are the

movements of the interior atoms in the crystals of the

ferroelectric material and the capacitor itself. If the atoms

are already near their cubes' "ceilings," they don't budge

when the field is applied and the cell gives off a smaller

pulse, due only to the electric charges stored on the cell

capacitor.

Reading an FRAM cell destroys the data stored in its

capacitor. So after the bit is read, the sense amplifier writes

the data back into the cell, just as in a DRAM.

The FRAM in fact is like the DRAM in every way but

one: the DRAM cell's capacitor is of a nonferroelectric



material, usually silicon dioxide. When data is stored as

charge on the DRAM cell's capacitor, the charge leaks away

into the silicon substrate almost immediately—unless it is

rewritten several times a second. That requirement drives

up power consumption, and of course when the power is

turned off, the charge stored in the capacitors quickly

disappears.

Because the basic operation and structure of the FRAM

and the DRAM are so similar, Alwais expects that FRAMs will

eventually run as fast as DRAMs with the

same memory capacity and cell size. Texas

Instruments is interested in FRAMs for

embedded applications—for example, for on-

chip storage of the operating instructions for

digital signal processors and microcontrollers.

Memory Basic

FRAM offers a unique set of features relative to other

memory technologies. Traditional mainstream



semiconductor memories can be divided into two primary

categories -- volatile and nonvolatile. Volatile memories

include SRAM (static random access memory) and DRAM

(dynamic random access memory). They share the property

that they lose their contents after power is removed from

the electronic system. RAM type devices are very easy to

use, and are high performing, but they share the annoying

quirk of losing their mind when the lights go out.

Nonvolatile memories do not lose their contents when

power is removed. However all of the mainstream

nonvolatile memories share a common ancestry that

derives from ROM (read only memory) technology. The

disadvantage is that read only memory is not easy to write

it's impossible. All of its descendants make it very difficult

to write new information into them. They include

technologies called EPROM (almost obsolete now), EEPROM,

and Flash. ROM based technologies are very slow to

write.Another disadvantage is that ROM based memories

wear out after being written a small number of times, and

use a large amounts of power to write.



FRAM offers features consistent with a RAM

technology, but is nonvolatile like a ROM technology. FRAM

bridges the gap between the two categories and creates

something completely new -- a nonvolatile RAM.

FRAM SPECIFATION :

4MB FRAM Nonvolatile Memory Module

Features:

Organization:4 banks >< 32k >< 32 bits

Highest density: Ferroelectric Memory over 22.4kb/mm

10 year data retension at 85o C

Unlimited read /write cycles.

Advanced high reliability ferroelectric process

SRAM & DRAM Compatible

70ns Access time



130ns Cycle time.

Equal access & cycle time for Read and Writes.

LOW POWER OPERATION:

2.7V to 3.6V operation .

15mA Active Current.

15microA stand by Current.

The latest 32-Mbit ferroelectric RAM highest density

RAM reported has been developed by Toshiba Corp. This

FRAM uses a new chain cell structure that links together

eight memory cells .Each cell has a ferroelectric capacitor

and field effect transistor in parallel and not in series.The

32Mbit FRAM is made on0.2micron processing ,which

provides 1.875square micron cell size on a 96 square

millimetre die.



APPLICATIONS:

FRAM is faster than flash memory,because it is fast

memory with a very low power requirement, it is expected

to have many applications in small consumer devices such

as personal digital assistants (PDAs), handheld phones,

power meters, and smart card, and in security systems.

A smart card is a plastic card about the size of a credit

card, with an embedded microchip that can be loaded with



data, used for telephone calling, electronic cash payments,

and other applications, and then periodically refreshed for

additional use. . A Smart Card is an IC card that contains a

microcomputer, storage circuit, and RF circuit. The

ferroelectric RAM (FRAM) has been developed as a

nonvolatile memory that satisfies the above requirements.

An FRAM embedded in an LSI must operate as a low-voltage

peripheral logic IC. We have developed a new FRAM sensing

scheme that can read bit-line potentials close to the GND

potential.

Currently or soon, you may be able to use a smart card to:

Dial a connection on a mobile telephone and be charged on

a per-call basis

Establish your identity when logging on to an Internet

access provider or to an online bank

Pay for parking at parking meters or to get on subways,

trains, or buses

Give hospitals or doctors personal data without filling out a

form

Make small purchases at electronic stores on the Web (a

kind of cybercash)



Buy gasoline at a gasoline station

Fujitsu has developed Smart Cards and other high-

security devices that use secure ferroelectric RAM (FRAM)

memory. This type of memory has an anti-tampering

function and is used to keep the keys and parameters

needed for encryption/decryption algorithms, modify the

keys and parameters for application services, store a high-

speed calculation table for encryption/decryption systems,

and support a firewall between applications.

Contactless Smart Cards in particular have rapidly

come into wide use because they are easy to use, can

perform high-speed processing, and can be used in a wide

variety of applications. In keeping with this trend, Fujitsu

has produced various FRAM-embedded (ferroelectric-RAM-

embedded) LSIs for Contactless Smart Cards.

Current applications for FRAM memory products can be

divided into the following four categories:

Data collection and logging

configuration storage



nonvolatile buffer

SRAM replacement & Expansion

Data Collection & Logging

FRAM allows system designers to write data to

nonvolatile memory faster and more often -- a luxury not

afforded to users of EEPROMs.

Data collection consists of the acquisition and storage

of data, which must be retained in the absence of power

(not temporary or scratchpad in nature). These are

systems, or subsystems that have the primary function of

collecting data that varies over time. In most cases, a

history of the changes is important.

End system applications: metering (electric, gas, water,

flow), RF/ID, instrumentation, and certain automotive

application such as airbag controllers.

Configuration Storage

FRAM helps system designers overcome the woes of



sudden power loss by providing the flexibility to store

configuration information in real time -- not just on power

down.

Configuration storage deals with the tracking of a

system as it changes over time. The goal is either to restore

its state on power up, or to identify the cause of an error. In

general, data collection is often the function of a system or

subsystem, where as configuration storage is a low level

engineering function regardless of the system type.

End system applications: laser printers and copiers,

industrial process control, networking, cable modems and

set top boxes, and white goods

Nonvolatile Buffer

FRAM can store operating data quickly, before transmitting

or storing in other nonvolatile media.

In this case, information is being sent from one

subsystem to another, this information is critical and should

not be lost if power fails. In some cases, the target system

is a larger storage device. FRAM, with its fast write and high



endurance allows the user to store data before it is sent on

to another system.

End system applications: industrial systems and in banking

systems such as ATM machines, future applications will

include hard disk drives with nonvolatile caching.

SRAM Replacement & Expansion

FRAM's fast write and nonvolatile features allow

system designers to combine SRAM and EEPROM into one

device, or simply expand SRAM.

In many cases, a system uses multiple memory types.

FRAM offers the ability to perform ROM, RAM, and EEPROM

functions with one device, saving space, power and

sometimes cost. The most common example is an

embedded microcontroller with external serial EEPROM.

FRAM can replace the EEPROM, and offer additional SRAM

functionality to the micro as well.

End system applications: all-in-one memories tend to occur

in portable applications, and in any system using low-end

(resource poor) microcontrollers.



FUTURE APPLICATIONS:

APPLICATIONS OF FRAM ON AUTOMOTIVE

APPLICATIONS:-

Today's passenger automobiles and trucks offer

increased electronic content and this trend is expected to

accelerate. With some 55 million passenger vehicles sold

worldwide in 2002 and numerous applications that can

benefit from FRAM technology, the automotive market is

certainly very attractive for FRAM. The average low end

auto has five to ten electronic control units while a luxury

car may have fifty to sixty. Recent introductions include

improved ABS systems with traction control, continuously

variable transmissions, electronic shift, dynamic stability



control, and digital radio platforms. In the coming years,

new electronic applications will include adaptive cruise

control with collision avoidance, DVD players with car

navigation, and control by wire (x-by-wire), and crash

recording (black-box) technology. Additional sophisticated

network technologies will continue to improve behind the

scenes automation and performance.

The challenge of handling and storing data is a

pervasive theme in the proliferation of automotive

electronics. One implication is that increased data handling

results in an increase in the frequency of data updates.

Existing memory choices are often inadequate in managing

the frequent updates. FRAM, with fast write and effectively

unlimited endurance offers unique benefits for data

handling and storage intensive applications. Consequently

it is expected to be widely adopted in automotive

applications in the coming years.

The real opportunities for FRAM:



Below are some of the applications for which

automotive development engineers are evaluating or

designing with FRAM products today.

Airbag

A principle feature of airbag and restraint systems in

the near future will be crash recorders, commonly know as

black-boxes. The automotive black box will be integrated

into the airbag or restraint system, it is unlikely to be a

separate assembly such as the aircraft black box. This

architecture is attractive because the sensor data that is

critical for a crash recorder is largely available to the

controller or can be accessed via busses already in place

such as CAN.

A crash recorder is a data logger. It may be called on

to collect data frequently over a long period of time in a

circular buffer, or to respond very quickly based on sensor

readings. Ideally the crash recorder would offer both

capabilities. In this rugged environment the data must be

stored in a true nonvolatile memory as any form of battery



backup will present crash survivability challenges.

Technologies such as Flash face performance problems as

they provide write endurance which is limited when it

comes to long term data collection and they are far too

slow to store data in the moment of impact. Crash statistics

show high percentages of serious crashes result in a power

outage during the crash, therefore data must be stored

instantly and in a non-volatile state, before power leaves

the vehicle and data is lost. Ramtron is a member of the

IEEE P1616 committee to define a standard for Motor

Vehicle Event Data Recorders (MEVDR). As a result we have

gained valuable insight into data recorder requirements.

Today crash recorders are being designed with FRAM

products from 16Kb to 64Kb, typically with a SPI interface

such as the FM25640.

Telematics/navigation

Telematic functions are increasingly part of a high end

vehicle electronics package. These systems provide

dynamic maps that allow routing to be adjusted based on

traffic patterns or other criteria. FRAM memories are used


http://www.ramtron.com/products/Bulletins/FM25640Bulletin.htm


today in such system to store navigation waypoints,

bookmarks etc. 16Kb memories are commonly used in this

application. Last year Matsushita selected Ramtron's FRAM

for its in-car navigation system. The 16K FM25C160’s fast

read/write and high-endurance features provide Matsushita

mobile automotive devices with a distinctive resume play

function. The FM25C160 stores scene changes and unique

user data upon power down, enabling the user to continue

where they left off when the unit is powered back up.

Entertainment

Digital car radios are gaining in popularity. Such radios

can download station information and store it in nonvolatile

memory. The uncertainty of changes in this data makes it

risky to use a limited endurance memory such as EEPROM.

A common work-around is to maintain such download data

in RAM and write it when power is turned off. This requires

the use of a large capacitor which can maintain power on

the EEPROM while it is written. While inexpensive, these

capacitors are physically bulky and undesirable in ever


http://www.ramtron.com/products/Bulletins/FM25C160Bulletin.htm



shrinking electronic radios. Matsushita designed a 16K

FRAM into their in-car entertainment systems. The

FM25C160 saves system board space by eliminating

components and allowing a reduced capacitor size, which

would not be possible with alternative memory solutions.

Instrument Cluster

Instrument clusters provide varying capabilities. The

presence of a low density nonvolatile memory is common,

and tracking elapsed miles often leads to frequent writes.

The problem of intermittent data errors is frequently

experienced by users in this application, possibly

associated with electrical noise interfering with slower

writing nonvolatile memories. A 4Kb FRAM such as the

FM24C04 has been used in such instrumentation with great

success and provides robust operating and data integrity in

a noisy environment.

Tire Pressure





Automobiles are adopting tire pressure sensing

technology in order to mitigate the risks associated with

driving with under-inflated tires. Today this technology is

implemented by sensing rotational differences between

tires and inferring tire pressure. Future systems will likely

involve direct sensor technology that can measure tire

pressure. A natural extension of this data generation is

logging. A historical record of tire pressures could present

compelling documentation in determining liability should

tire pressure contribute to an accident. Tire pressure logs

might be implemented in the car and also in the tire, and

FRAM is an ideal solution for this application given its

unlimited ability to write in low power environments, such

as that of a tire-based historical logger.

ABS - Stability Control

ABS has evolved from its basic form to include traction

control and more recently to include stability control.

Traction control uses the wheel slip information already



produced by ABS sensors to regulate power to prevent

spinning tires due to slippery conditions. Stability control is

a more sophisticated variety where power is regulated to

each wheel depending on driving conditions. Based on

speed, turn radius and road conditions the rotation of

individual wheels is managed. Such systems are very

sophisticated and involve learning algorithms. To use a

FRAM for example in this application would be more

suitable for users since FRAM allows for unrestricted

updates of system data. Currently temperatures for FRAM

are specified to 85C and ABS system electronics must

normally operate at 125C, however the road map for FRAM

products includes meeting these temperature

requirements.

Power Train

Like stability control, power train management

systems are ever more adaptive and can benefit from a

nonvolatile memory that can be updated quickly and often.

Also like ABS, these systems operate at 125C and will



depend on a future generation of FRAM products, most

likely 256Kb parts rated at 125C or higher.



ADVANTAGES:

1. FRAM allows systems to retain information even when

power is lost, without resorting to batteries, EEPROM, or

flash.

2. Access times are the same as for standard SRAM, so

there's no delay-at-write access as there is for EEPROM

or flash.

3. Low power consumption , low voltage operation and

high write endurance make it superior than other non-

volatile memories like EEPROM & FLASH

4. It is less expensive than magnetic memories which

require 4 extra mask

DISADVANTAGE:

1. Present high cost .

2. Low density compared to DRAM & SRAM.



FUTURE OF FRAM:

Development of FRAM in full range of densities

and operating temperatures to support automotive data

handling and storage applications will find a wide variety of

applications as said above.

In addition, the FRAM technology can easily be

combined with logic and mixed signal technologies to offer

more cost effective integrated solutions in the future.



CONCLUSION

The biggest obstacle to large memories is their large

power consumption, particularly for wireless applications.

But FRAM’s advantage is the low power consumption

compared to other new memory technologies , and hence

economic. The wide range of applications it has in case of

SMART cards and data storage applications, together with

the future automotive applications make it one of the best

memories among the new memory technologies among

ferromagnetic and ovonic memories.



REFERENCES

Information Technology Magazine

http://www.ieee.org

http://www.eetuk.com

http://www.savemyfiles.com


http://www.eetuk.com/

http://www.ieee.org/


ABSTRACT

FRAM is a type of non-volatile read/write random

access semiconductor memory. FRAM combines the

advantages of SRAM writing is roughly as fast as reading,

and EPROM non-volatility and in-circuit programmability.

FRAM (ferroelectric RAM) is a random access memory that

combines the fast read and write access of dynamic RAM

(DRAM) - the most common kind of personal computer

memory - with the ability to retain data when power is

turned off (as do other non-volatile memory devices such as

ROM and flash memory). Because FRAM is not as dense

(can not store as much ata in the same space) as DRAM

and SRAM, it is not likely replace these technologies. It is

fast memory with a very low power requirement, it is

expected to have many applications in small consumer

devices such as personal digital assistants (PDA), handheld

phones, power meters, and smart card, and in security

systems. FRAM is faster than flash memory. It is also

expected to replace EEPROM and SRAM for some



applications and to become a key component in future

wireless products.



CONTENTS

INTRODUCTION

FRAM TECHNOLOGY

MEMORY BASICS

ADVANTAGES & DISADVANTAGES.

APPLICATIONS OF FRAM.

(a)CURRRENT APPLICATIONS

(b)FUTURE APPLICATIONS

CONCLUSION



ACKNOWLEDGMENT

I express my sincere thanks to Prof. M.N

Agnisarman Namboothiri (Head of the Department,

Computer Science and Engineering, MESCE), Mr. Sminesh

(Staff incharge) for their kind

co-operation for presenting the seminar.

I also extend my sincere thanks to all other members

of the faculty of Computer Science and Engineering

Department and my friends for their co-operation and

encouragement.

ANUSHA.R.C


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Ferroelectric RAM FRAM Seminar Report

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