The problem is that as transistors shrink and bits increase, the electrons that represent the data stored in them leak from one cell to another and create data errors. That means more sophisticated error correction code (ECC) has been needed to keep memory reliable. That, too, has grown increasingly difficult.
The result: Instead of continuing to make memory smaller and denser, manufacturers have begun making vertical NAND like tiny skyscapers -- stacking layers of microscopic NAND atop one another using charge trap technology.
Don't get too nostalgic for planar NAND flash.
Consider Toshiba's and SanDisk's latest 3D NAND chips, which doubled capacity from 128Gbit in a chip announced earlier this year, to 256Gbit in the chip announced this week.
Today, SanDisk offers a 200GB microSD card that's about the size of a thumbnail. Its new 256Gbit chips have to potential to double that capacity to 400GB next year, according to Siva Sivaram, executive vice president of SanDisk's Memory Technology.
"3D NAND effectively gives you back predictability of scaling for quite some time into the future," Sivaram said, referring to the consistent scaling that planar NAND afforded the industry for decades. Planar NAND doubled in capacity every year or so.
SanDisk and Toshiba this week introduced their 48-layer 3D NAND. But 3D NAND technology is expected to reach 100 levels of stacked cells by 2017, according to industry experts. That will allow 1Tbit-per-chip density.
A 1Tbit chip, extrapolated into an SD card's capacity, would mean a product capable of storing 800GB to 1TB of capacity in an object half the size of a postage stamp.
Toshiba and SanDisk are so certain about the future of their 3D NAND that they demolished their Fabrication number 2 plant in Mie prefecture, Japan, and are building a larger wafer fabrication facility on the same site to exclusively produce 3D NAND flash chips. The plant will be completed next year, and products will begin mass production by the second quarter, according to Sivaram.
"Our focus right now is on 3D NAND," Sivaram said. "We're not making another 2D product."
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