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Encyclopedia > Ferroelectric RAM

Ferroelectric RAM (FRAM or FeRAM) is a type of non-volatile computer memory, similar to EEPROM but based on electric field orientation and with near-unlimited number (exceeding 1010 for 5V devices and even more for 3.3V ones) of write-erase cycles. The main vendor of FRAM chips is Ramtron International. Non-volatile memory, or non-volatile storage, is computer memory that can retain the stored information even when not powered. ... The terms storage (U.K.) or memory (U.S.) refer to the parts of a digital computer that retain physical state (data) for some interval of time, possibly even after electrical power to the computer is turned off. ... To meet Wikipedias quality standards, this article or section may require cleanup. ...


Constructionally, FRAM is an array of ferroelectric capacitors, a DRAM with the dielectric layer in the memory capacitors replaced with a thin ferroelectric film, typically made of lead zirconate titanate (PZT). The resulting cell is electrically similar to the capacitors used in a conventional DRAM cell, but the ferroelectric film will retain a electric field even after the charge in the capactor (quickly) drains. Depending on the direction of the current flow when the cell is charged, the film will be polarized into one of two directions. Ferroelectric capacitor is a capacitor used in digital electronics as a component of computer memory. ... Dynamic random access memory (DRAM) is a type of random access memory that stores each bit of data in a separate capacitor. ... A dielectric, or electrical insulator, is a substance that is highly resistant to the flow of electric current and has a relative permittivity greater than unity. ... In physics, the ferroelectric effect is an electrical phenomenon whereby certain ionic crystals may exhibit a spontaneous dipole moment. ... Lead zirconium titanate (PZT, also Lead zirconate titanate) is a ceramic perovskite material that shows a marked piezoelectric effect - that is, it develops a voltage difference across two of its faces when compressed, and ferroelectric effect. ... Dram can mean several things: for the imperial unit of volume see dram (volume) for the imperial unit of weight or mass see avoirdupois and apothecaries system of mass for the Armenian monetary unit see dram (currency) DRAM is a type of RAM and unlike dram is spelled in all... In physics, an electric field or E-field is an effect produced by an electric charge (or a time-varying magnetic field) that exerts a force on charged objects in the field. ...


The bit is read by applying an electric field across the capacitor. If the cell is currently in a "1" state the magnetic field will resist the voltage, and will not allow current to flow until it reaches a critical point at a somewhat higher voltage. Measuring this voltage allows the memory device to read the current state of the cell, revealing it to be "1". If the cell had been in the "0" state, the voltage would remain lower, revealing the "0". However reading the cell also flips the polarity of the magnetic field, meaning that all reads must be followed by a write to restore the contents, just as on DRAM. In physics, an electric field or E-field is an effect produced by an electric charge (or a time-varying magnetic field) that exerts a force on charged objects in the field. ... International danger high voltage symbol. ...


Generally the operation of FRAM is similar to ferrite core memory, one of the primary forms of computer memory in the 1960s. In comparison, FRAM requires far less power to flip the state of the film's polarity, and does so much faster. The requirement for a write cycle for each read cycle, together with the high but not infinite write cycle limit, poses a potential problem for some special applications. A 16×16 cm area core memory plane of 128×128 bits, i. ...


Physically FRAM is almost identical to current DRAMs, with the additional ferroelectic layer. Since the charge quickly drains from the capacitor, DRAMs must be continually "refreshed" with additional current. Unlike DRAM, the charge stored in the capactor does not form the memory in FRAM cells. Although the power needed to read or write an FRAM cell is thus slightly higher than in a DRAM, there is no need for power when idle, meaning that overall power use is dramatically reduced. Additionally FRAM will retain its contents with no power at all.


It is possible to make FRAM cells using two additional masking steps during normal semiconductor manufacture, leading to the possibility of full integration of FRAM into microcontrollers and other chips. Flash typically requires nine masks. This makes FRAM particularly attractive as an embedded non-volatile memory on microcontrollers, where the simpler process can reduce costs. However, the materials used to make FRAMs are not commonly used elsewhere in integrated circuit manufacturing. Both the PZT ferroelectric layer and the noble metals used for electrodes raise process compatibility and contamination issues. A microcontroller (MCU) is a computer-on-a-chip used to control electronic devices. ... A microcontroller (MCU) is a computer-on-a-chip used to control electronic devices. ...


FRAM does not yet offer the bit density of DRAM and SRAM, but is non-volatile, is faster than Flash/EEPROM memory (write times under 100 nanoseconds, roughly as fast as reading), and has very low power requirements, as unlike the EEPROMs they do not require a charge pump. It is expected to replace EEPROM chips in applications where very many write cycles are required. The very low current consumption makes them suitable for contactless chip cards. A six-transistor CMOS SRAM cell. ... It has been suggested that this article or section be merged with voltage multiplier. ... Radio frequency identification (RFID) is a method of remotely storing and retrieving data using devices called RFID tags. ... A chip card is a debit or credit card offered to customers of some banks. ...


In theory, however, FRAM can be scaled to much smaller cell sizes than currently being utilized. Bulk ferroelectric materials can be self-organized into small magnetic domains only a few nanometers across, known as quantum dots. If a manufacturing technique evolves that allows circuits to be able to interact with these dots, FRAM will have cell sizes on the order of 5 nm, in comparison with Flash which is currently having real difficulty scaling below 65 nm.


Even without this sort of miniaturization, FRAM uses less components per cell (bit) than Flash. Each Flash cell consists of several transistors and a single high-quality insulator. FRAM is much simpler, consisting of a single transistor and the capacitor/magnet. Using the same production lines as modern DRAM devices, even in its current form FRAM should be much less expensive and higher density than Flash. However, Flash production lines have been scaled up to meet massive demand, while DRAM lines are already at capacity. FRAM may not become common until the market demands higher density than Flash can provide.


See also


  Results from FactBites:
 
Ferroelectric effect - Wikipedia, the free encyclopedia (308 words)
The term ferroelectricity is used in analogy to ferromagnetism, in which a material exhibits a permanent magnetic moment.
The effect in barium titanate, a typical ferroelectric of the displacive type, is due to a polarization catastrophe, in which, if an ion is displaced from equilibrium slightly, the force from the local electric fields due to the ions in the crystal increase faster than the elastic restoring forces.
Ferroelectrics often have very large dielectric constants, and thus are often used as the dielectric material in capacitors.
Ferroelectric RAM - Wikipedia, the free encyclopedia (785 words)
Ferroelectric RAM (FRAM or FeRAM) is a type of non-volatile computer memory, similar to EEPROM but based on electric field orientation and with near-unlimited number (exceeding 10
Constructionally, FRAM is an array of ferroelectric capacitors, a DRAM with the dielectric layer in the memory capacitors replaced with a thin ferroelectric film, typically made of lead zirconate titanate (PZT).
The resulting cell is electrically similar to the capacitors used in a conventional DRAM cell, but the ferroelectric film will retain a electric field even after the charge in the capactor (quickly) drains.
  More results at FactBites »

 
 

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