PLEDM Memory Offers Storage Potential
-- Semiconductor International, 12/1/1999
A group at the Hitachi Cambridge Laboratory
(Cambridge, U.K.) under Professor Haroon Ahmed is developing a Phase-state Low
Electron number Drive Memory (PLEDM) that should enable a full-length film of
images and sound to be stored on a single chip. The memory cell uses two
transistors to form a gain cell that needs less silicon area than a conventional
DRAM cell. It is stacked on the silicon dioxide gate of a normal MOSFET device
using a standard 200 nm silicon process. This type of cell requires the same
silicon area as a single transistor: about 400 x 200 nm. Thermal nitridation of
silicon is used to make the extremely thin 2 nm insulating layers in the
critical barriers.
The read/write times are less than 10 nsec, but further work may lead to a
fast, non-volatile PLEDM cell. The use of transistors, instead of the
conventional capacitors, enables large signals to be obtained even at very low
supply voltages. 
