Traditional “planar” NAND flash won’t be able to keep up the capacity increases that are required for SSDs to continue to thrive as a storage technology. This is because they must increase areal density to increase capacity, which means shrinking the lithography of the NAND flash cell. But as the traces in silicon are squeezed closer together (19nm and less), bit errors increase, eventually hitting a point of diminishing returns. Given these constraints on areal density, Micron is expanding “up” with 3D NAND technology.
Back in February, at their analyst event in San Jose, Micron made clear that instead of relying on TLC (triple-level cell) planar NAND flash, they were committed to 3D NAND, which was the subject of an announcement this week, in conjunction with Micron’s chip partner Intel. This is a technology that essentially adds more writable layers to the flash chip, somewhat analogous to adding more platters to a conventional disk drive. StorageSwiss Founder, George Crump, wrote a piece on 3D NAND earlier this year as well.
By stacking these layers, flash capacity can increase while the areal density of each layer is reduced and the lithography essentially stepped back from the sub-20nm edge that planar NAND technologies have reached. In fact, the areal density with current generation 3D NAND is actually comparable to 50nm planar technology. And according to Micron, this isn’t just a workaround.
This density ‘headroom’, combined with the ability to add more layers to 3D NAND (current generation products have 32), will give Micron a decade or two of room to grow this technology and support the cost reductions that flash must show in order to remain viable, and indeed to thrive. According to Micron’s roadmaps all SSD product groups are projected to be 100% 3D NAND flash by 2016.
Micron and Intel are in initial production now, actively sampling OEM customers and expect to be in high-volume product by the second half of 2015. From a capacity perspective, this first generation 3D NAND will yield 256Gbit per die with MLC and 384Gbits per die in TLC NAND devices. This translates into a 3x capacity increase over current planar technologies and should enable 10TB and greater flash device capacities.
Planar NAND flash technologies seem to have ‘hit the wall’ in terms of storage growth, since they’re dependent on increasing areal density to get each generation’s improvement in capacity. Adding more layers to the flash cells is a logical solution to the density problem – as it was in disk drives – making 3D NAND is the probable successor to planar technologies.
To be clear, 3D NAND is not unique to Micron. All of the major manufacturers have or will have 3D NAND products available, with new generations coming on line that increase the number of layers to 48. But Micron’s projection to be all 3D NAND by the end of next year is unique and demonstrates their confidence that this is the technology for today, not just the future.