I was at the Solid State Storage Symposium a couple of weeks ago where Robin Harris (StorageMojo) gave the keynote presentation. In his talk, Robin mentioned a new technology on the horizon which holds the promise of replacing DRAM, SRAM and NAND called resistive random access memory (ReRAM or RRAM).
Problems with NAND
There are a few problems with NAND today but the main problem that affects future NAND technologies is as devices shrink they lose endurance. For instance, today’s SLC NAND technology has an endurance of ~100K P/E (program/erase) cycles, MLC NAND can endure around 5000 P/E cycles and eMLC somewhere in between. Newly emerging TLC (three bits/cell) has less even endurance than MLC.
But that’s all at 30nm or larger. The belief is that as NAND feature size shrinks below 20nm its endurance will get much worse, perhaps orders of magnitude worse.
While MLC may be ok for enterprise storage today, much less than 5000 P/E cycles could become a problem and would require ever more sophistication in order to work around these limitation. Which is why most enterprise class, MLC NAND based storage uses specialized algorithms and NAND controller functionality to support storage reliability and durability.
ReRAM solves NAND, DRAM and NvRAM problems.
Enter ReRAM, it has the potential to be faster than PCM-RAM, has smaller features than MRAM which means more bits per square inch and uses lower voltage than racetrack memory and NAND. The other nice thing about ReRAM is that it seems readily scaleable to below 30nm feature geometries. Also as it’s a static memory it doesn’t have to be refreshed like DRAM and thus uses less power.
In addition, it appears that ReRAM is much more flexible than NAND or DRAM which can be designed and/or tailored to support different memory requirements. Thus, one ReRAM design can be focused on standard DRAM applications while another ReRAM design can be targeted at mass storage or solid state drives (SSD).
On the negative side there are still some problems with ReRAM, namely the large “sneak parasitic current” [whatever that is] that impacts adjacent bit cells and drains power. There are a few solutions to this problem but none yet completely satisfactory.
But it’s a ways out, isn’t it?
No it’s not. BBC and Tech-On reported that Panasonic will start sampling devices soon and plan to reach volume manufacturing next year. Elpida-Sharp and HP-Hynix are also at work on ReRAM (or memristor) devices and expect to ship sometime in 2013. But for the moment it appears that Panasonic is ahead of the pack.
At first, these devices will likely emerge in low power applications but as vendors ramp up development and mass production it’s unclear where it will ultimately end up.
The allure of ReRAM technology is significant in that it holds out the promise of replacing both RAM and NAND used in consumer devices as well as IT equipment with the same single technology. If you consider that the combined current market for DRAM and NAND is over $50B, people start to notice.
Whether ReRAM will meet all of its objectives is yet TBD. But we seldom see any one technology which has this high a potential. The one remaining question is why everybody else isn’t going after ReRAM as well, like Samsung, Toshiba and Intel-Micron.
I have to thank StorageMojo and the Solid State Storage Symposium team for bringing ReRAM to my attention.
[Update] @storagezilla (Mark Twomey) said that “… Micron’s aquisition of Elpida gives them a play there.”
Wasn’t aware of that but yes they are definitely in the hunt now.
Image: Memristor by Luke Kilpatrick