NAND flash memory is a key enabler in today’s systems, but it’s a difficult business. NAND suppliers require deep pockets and strong technology to survive in the competitive landscape. And going forward, vendors face new challenges on several fronts.

On one front, for example, the overall NAND market is currently in the doldrums, amid soft product prices and a mild capacity glut. Demand is expected to rebound in the second half of 2016, although there is still uncertainty in the market.

Then, on the technology front, today’s planar NAND is reaching its physical scaling limit. And so NAND suppliers are pinning their future hopes on the successor to planar NAND—3D NAND.

3D NAND is shipping, but the technology is taking longer than expected to enter the mainstream. It is more difficult to make than previously thought. 3D NAND resembles a vertical skyscraper, in which horizontal levels or layers are stacked and then connected using tiny vertical channels.

“The early movers, such as Samsung and Micron, are ramping up 3D NAND quickly, while SK Hynix and SanDisk/Toshiba are lagging,” said Greg Wong, an analyst with Forward Insights. “The technology and yield learning is taking longer.”

And it isn’t getting any easier. Today’s leading-edge 3D NAND chips are 32- and 48-layer devices, but the technology will likely hit the ceiling at 128 layers in the 2018 timeframe or so. So to extend 3D NAND beyond 128 layers, vendors are quietly developing a technology called string stacking. Still in R&D, string stacking involves a process of stacking individual 3D NAND devices on top of each other.

For example, a vendor might stack three separate 48-layer 3D NAND devices, creating a 144-layer chip. Even with string stacking, though, 3D NAND could hit the wall at 300 layers. It will take vast resources and capital to extend current and futuristic 3D NAND devices to 128 layers and beyond. “Scaling the number of layers is not just a technical challenge, but an economic one as well,” Wong said.

In any case, OEMs will need to keep close tabs on the technology. To help OEMs, Semiconductor Engineering has taken a look at the status of the following technologies—planar NAND; 3D NAND; and futuristic 3D NAND with string stacking.

By: DocMemory
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