Strained material cleans up memory

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.