FRAM
       Ferroelectric Random Access Memory (RAM, IC)
       

Ferroelectric Random Access Memory
Ferroelectric RAM
FRAM

    (FRAM) 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.  Current (Feb
   1997) disadvantages are high cost and low density, but that
   may change in the future.  Density is currently at most 32KB
   on a chip, compared with 512KB for SRAM, 1MB for EPROM and 8MB
   for DRAM.

   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, which does not contain iron.

   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.
   In fact it is most like the operation of ferrite core
   memory.

   FRAM has similar applications to EEPROM, but can be written
   much faster.  The simplicity of the memory cell promises high
   density devices which can compete with DRAM.

   RAMTRON is the company behind FRAM.

   (1997-02-17)