Monday, July 10, 2006

A Better Memory Chip

Continued from page 1

By Kate Greene

Flash memory is also seen as a potential alternative to RAM because, like MRAM, it might eliminate boot-up time on a computer (see "Starting Your PC in a Flash"). The problem with Flash memory is that one can't use it forever. It is nonvolatile because the memory cells that store the charge have high barriers that keep the charge from leaking out. In order to overcome these barriers to read and write data, a large electric field is needed, explains Bill Gallagher, research staff member at the IBM Thomas J. Watson Research Center. However, this design creates a problem because over time, large electric fields wear out the material used to store charge in the cells, limiting the number of read-write cycles to around 100,000. In addition, Flash is relatively slow, taking hundreds of nanoseconds to write information. For these reasons, Flash "is not well suited for the sort of writes you do in a computer system," says Burger.

The properties of MRAM combine the best of Flash memory and RAM. Like RAM, it doesn't wear out, so it's better suited than Flash for instant-on computers and other electronics. Additionally, by not needing constant power, it could be used in small devices where battery power is at a premium, from cell phones to millimeter-sized sensors.

It may take a few years, however, for MRAM to completely replace Flash or RAM. Today, Freescale's MRAM chip can store only four megabits of information, a measly amount compared to Flash memory, which can hold several gigabits.

Increasing the space on an MRAM chip could pose problems. At this point, it's unknown whether the current MRAM materials and design will be well suited for future MRAM chips with smaller feature sizes. The magnetic fields used to store data in MRAM chips have distinctive shapes, Burger explains, and it's not clear what adjustments will need to be made to these fields to maintain product quality as the features shrink.

IBM's Gallagher said that with today's materials, he thinks it's possible to increase the storage density by 100-fold. And as research progresses, he says, "we could have [an MRAM] device with the storage capacity of a hard disk drive."