Researchers from the University of Wisconsin
at Madison, Pennsylvania State University, Research Center Jülich and
the Institute for Crystal Growth in Germany and the University of Michigan
have found a way to make a version of promising type of flash computer
memory that does not contain environmentally toxic lead.
The electrical properties of ferroelectric materials like lead
can be switched between two stable states that can represent the 1s and
0s of computer information. Because the states that represent information
are stable, ferroelectric memory is nonvolatile, meaning it does not use
data when powered down. Ferroelectric random access memory is also faster
and uses less power than today's flash memory chips, but is traditionally
made from bismuth and lead.
The researchers made this type of memory without lead by improving
the temperature range and duration of the ferroelectric properties of
barium titanate using strain engineering, which changes material properties
by stacking ultrathin layers of materials whose atoms do not exactly match
up. The engineered material's ferroelectric properties nearly match lead,
according to the researchers.
The first practical application will be ferroelectric random access
memory for computer devices; the material could also be used in optoelectronic
devices, according to the researchers. Optoelectronic devices convert
light signals to electrical signals.
The researchers' next step is to integrate the new material into
the silicon used in today's computer chips. Barium titanate is widely
used in dynamic random access memory (DRAM) chips.
The method could be used practically within two to five years,
according to the researchers. The work appeared in the November 4, 2004
issue of Science.
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