FERROELECTRIC RAM [FRAM]

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FERROELECTRIC RAMFRAM

• Presented by
• Javad.P
• N030

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• FEATURES OF FRAM
• 1.FRAM allows systems to retain information even
  when power is lost i.e. non-volatile.
• 2.The number of write cycles supported by the
  FRAM components is
• nearly unlimitedup to 10 billion read/writes.
• 3.Low power requirements.
• 4.When an electric field is applied to a
  ferroelectric crystal,
• the central atom moves in the direction of the
  field.
• 5.As the atom moves within the crystal, it passes
  through an energy barrier, causing a charge
  spike.
• 6.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. This
• makes FRAM non-volatile, without any periodic
  refresh.
• 7.Once a cell is accessed for a read operation,
  its data are presented in the form of an
  analSignal to sense amplifier, where they are
  compared against a reference voltage to findthe
  logic level.

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BASIC MEMORY CELL STRUCTURE

Bitline(BL)
word line (WL)

Plateline(PL)
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• A ferroelectric memory cell, known as IT- IC (one
  transistor, one capacitor) structure which is
  similar to that of DRAM.
• The difference is that ferroelectric film is
  used as its storage capacitor rather than
  paraelectric material as in DRAM.
• Figure above shows memory cell structure,
  consists of a single ferroelectric capacitor that
  is connected to a Plateline(PL) at one end and,
  via an access transistor, to a Bitline(BL) at the
  other end. Raising the wordline (WL) and hence
  turning ON the access transistor accesses the
  cell.

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FERRO ELECTRIC CRYSTAL
Ferroelectric CrystaI The center atom moves to
store ones and zeros

• Consist of 8 atom of lead at corners
• 6 atom of oxygen at face centers
• 1 atom of titanium at cube centers

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FRAM TECHONOLOGY

• 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.
• This makes FRAM non-volatile, without any
  periodic refresh

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• 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. 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.
• 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.

FRAM READ OPERATION
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FRAM WRITE OPERATION

• To write a "1" into the memory
  cell,
• the BL is raised to Vdd-
• Then the WL is raised to Vdd Vt.
• This allows a full Vdd to appear across the
  ferroelectric capacitor
• At this time the state of ferroelectric is
  independent of its initial state.
• Next, the PL is pulsed, WL stays activated until
  
• the PL is pulled down completely and the BL is
  driven back to zero.
• The final state of the capacitor is a negative
  charge state S1.

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To write a "0" into the cell

• the BL is driven to 0V prior to activating the
  WL.
• The rest of the operation is similar to that of
  writing a "1
• The written data is held in the cell even though
  the selection of the wordline is changed to non
  selected state (i.e. transistor is OFF), so it is
  nonvolatile.

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FRAM AS RAM AND ROM

FRAM memory fills the RAM and ROM performance gap

• The key advantage to FRAM over DRAM is what
  happens between the read and write cycles. In
  DRAM, every cell must be periodically read and
  then re-written, a process known as refresh..
• In contrast, FRAM only requires power when
  actually reading or writing a cell. The vast
  majority of power used in DRAM is used for
  refresh power usage about 99 lower than DRAM.

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RAMTRON-FRAM
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COMPARISON
FRAM EEPROM Flash Memory DRAM SRAM
Memory Type Non-volatile Non-volatile Non-volatile Volatile Volatile
Read Cycle 100ns 200ns 120ns 70ns 85 ns .
Write Cycle 100ns 10ns 100ns 70ns 85ns
Power Consumption 1nJ lnJ 2nJ 4nJ 3nJ.
Current to retain Data Unnecessary Unnecessary Unnecessary' Necessary Necessary
Internal Write Voltage 2V-5V 14V 9V 3.3V 3.3V
Cell Structure 1T-1C 2T IT 1T-1C 6T,4TR
Area/Cell 4 3 1 2 4 -

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• ADVANTAGES
• 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.
• Low power consumption, low voltage operation and
  high write endurance make it superior than
  other non-volatile memories like EEPROM FLASH.
• It is less expensive than magnetic memories.

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• DISADVANTAGES
• Present high cost.
• Low density compared to DRAM SRAM.
• FUTURE OF FRAM
• Increased memory capacity
• High density, to operate under very high
  temperatures.
• Combine FRAM with other logic technologies to
  offer more enhanced devices.

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• APPLICATIONS
• Personal digital assistants (PDAs), handheld
  phones, power meters, and smart card, and in
  security systems
• SMART CARDS USING FRAM
• 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

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CONCLUSION

• Ferroelectric memories are superior to EPROMs
  Flash memories
• in terms of write access time overall power
  consumption.Two eg of
• such applications are contactless smart cards
  digital cameras.
• Future personal wireless connectivity
  applications that are battery
• driven will demand large amounts of non volatile
  storage to retain
• accessed internet webpages, contain compressed
  video, voice and
• data. The density and energy efficiency of
  writing data to memory
• would seem to indicate that ferroelectric
  memory will play a major role
• in these types of consumer products.

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THANK YOU