Ferroelectric RAM ==>
Ferroelectric Random Access Memory
<storage> (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
RAMTRON is the company behind FRAM.
Ferranti F100-L « ferrite core memory «
Ferroelectric RAM «
Ferroelectric Random Access Memory » Fetch »
fetch-execute cycle » FF