Magnetic Memory Chips

“Instant-on” magnetically





Magnetic memory chips are poised to give traditional DRAMs a run for their money

HAULING yourself up by the bootstraps has never been easy. But computers do this every time they are turned on—hence the verb “to boot”. Booting a computer takes valuable time, compounded by the rebooting that is inevitably necessary whenever a computer freezes.

The reason that this process takes so long is that a computer's operating system must be loaded from its hard disk into its random-access memory (RAM) every time the machine is turned on. Unlike magnetic tapes or hard disks, RAM is an electric form of memory. It is, in effect, an array of tiny capacitors which, when charged, represent a binary “1” and, when not charged, represent a binary “0”. This has allowed them to be much faster than magnetic memory, in which the binary digits (“bits”) are represented by magnetically polarised regions rather than electric charges. The big problem with electric memory, however, is that it is volatile—the capacitors have to be recharged frequently so that they can continue to remember a “1”. When a computer is turned off, they lose all the data stored in them.

The race has been on to build nonvolatile high-speed memories that will allow computers to be turned on and off like televisions. Whichever technology wins is almost certain to be used in all new computers, so the stakes are high. Motorola, IBM, and Hewlett-Packard are all developing magnetic RAM (MRAM) which seems poised to become the non-volatile technology of choice. Both Motorola and IBM have announced plans to bring the technology to market within 18 months, advancing their initial target date of 2004. Besides turning instantly on, computers equipped with such chips would consume less power, making the technology ideal for satellites and portable gizmos.

MRAM works by etching a grid of criss-crossing wires on a chip in two layers—with the horizontal wires being placed just below the vertical wires. At each intersection, a “magnetic tunnel junction” (MTJ) is created that serves as a switch—and thus as a repository for a single bit of memory. The MTJ is essentially a small magnet whose direction is easily flipped. Common materials for the MTJ include chromium dioxide and iron-cobalt alloys.

Earlier this year, Motorola unveiled a prototype MRAM chip that stores 256 kilobits and has a cycle time for reading and writing data of less than 50 nanoseconds (billionths of a second). That puts it in the same league as conventional dynamic-RAM (DRAM) chips. IBM, collaborating with Germany's Infineon Technologies, has developed a one-megabit (million bit) MRAM chip at its laboratories in East Fishkill, New York.

There is still a long way to go before MRAM is ready for prime time. Neither IBM nor Motorola, for instance, is expected to go into mass production until they prove that they can make 256 megabit chips—the standard memory module used today. But, as total sales of computer memory in 2000 were estimated by Semico Research Corporation to have been worth $48 billion, manufacturers have a considerable incentive to ensure that MRAM becomes a serious challenger for DRAM's crown.



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wow what a long read...but it was worth it. good find

 

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