Freescale MRAM – an in-depth examination
Once promised as the replacement to conventional non-volatile memory, the prospects around MRAM are no longer as clear. Only two vendors have succeeded in bringing MRAM parts to the mass market – Cypress and Freescale. That said, Cypress discontinued their offering shortly after release and Freescale, which announced MRAM back when they were still known as Motorola, just realized commercial production of a 4M magenetoresistive memory. It’s interesting to see the Motorola symbol used on the final production device. Maybe this chip has been sitting in a warehouse for the last two years. The Freescale 4M MR2A16A MRAM was allegedly sampling since early in 2004 after all. MRAM densities and yields remain low and it’s questionable whether this technology can make up for lost ground.
Catching up is the difficulty faced by every new generation of “flash replacement.” It seems like I have heard the end of flash technology decried throughout my career in semiconductors. Progress in our industry depends a lot on consensus as seen in predications like the International Technology Roadmap for Semiconductors maintained by the SIA. Their position is that none of the currently known NVM technologies have any longer life in terms of scalability than flash. SI’s in depth analyses of the Freescale MRAM device provides insight into the prospects for MRAM and future evolution of the memory market.
When all the world was buzzing with the promise of the new universal memory in 2004, a few predicitions proved to be accurate. Mark LaPedus at EETimes forecast MRAM as a non-event for 2005. This is a great success story for technology analysts everywhere. I wonder whether anyone predicted MRAM as a non-event for this year. I think not considering MRAM’s media shine had tarnished by late last year. Colleagues of mine at Semiconductor Insights have been studying the technology very closely for more than five years. The status of MRAM in 2001 was exhaustively examined in SI’s report An Examination of Current Developments and Future Directions of MRAM Technology. At that time, Motorola was working on magnetic tunnel junctions or MTJ. Our analysis in 2001 showed that MTJ would face significant challenges to integration with CMOS devices. Freescale thought the same thing since they switched to a magnetoresistive cell for production devices.
Let’s sum up where MRAM is today:
- MRAM will not replace DRAM because it is slower, therefore
- The “instant-on” computer is not around the corner, but
- MRAM can boot operating systems or other code faster than present-day NOR flash.
But MRAM is not going to displace Spansion or Intel flash from cell phones any time soon either. Even low-end phones have a minimum of 16M, so four of Freescale’s 4M die need to be bundled together to meet that spec. How they can catch up is anybody’s guess if you compare die efficiencies between current NOR and this Freescale MRAM. Even the single bit cell NOR flash from Intel in 90nm is over two orders of magnitude better at around 4Mbits/mm2. MRAM is that much further behind multi-bit technology which leads the industry at over 11 Mbits/mm2.
MRAM may be only middle of the pack in read time as well. The Freescale device is specified to 35ns read, while the Intel W18 series claims 11ns burst and 20ns page read times. Keep in mind that the write speed is the same, so that’s where this device shines compared to NOR. Maybe the hardest sell is in power consumption which has long been a knock on MRAM technology. The Freescale MR2A16A datasheet gives 18mA for stand-by current! Read mode current is listed at 55mA and write mode at 105mA.
But it is the high cost-per-bit that makes MRAM a non-event in the big application markets, and not necessarily the average performance or low density. In defense of Freescale’s accomplishment, it is not fair to compare a first-generation MRAM to a mature product like Flash (invented in 1984; commercially introduced in 1988). Besides, MRAM has advantages beyond speed and density such as virtually unlimited R/W cycles that makes it interesting for mission-critical applications where battery-backed-up SRAM or NV-SRAM is currently used. But that is a niche market.
The bottom line may be evolution — not revolution as Freescale’s new MRAM device seems most suited to critical military and space applications where MRAM has already been deployed at lower resolutions. MRAM is very likely to start to replace NV-SRAM since it must be cheaper to produce a more or less standard die in a standard package than to start adding batteries to the mix. DARPA at least should be happy with its early investments in Motorola and Honeywell research even if this technology doesn’t give us better cell phones or MP3 players. To really understand the how’s and why’s of Freescale’s MRAM launch, I suggest investigating one of our detailed studies of the technology.
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