NAND flash memory typically employs a planar structure with a single cell layer. For years, we’ve heard whispers about three-dimensional memory with multiple cell layers. Now, Samsung has started mass-producing it. The flash giant has started manufacturing what it’s calling the "industry’s first three-dimensional (3D) Vertical NAND." Dubbed V-NAND, these initial chips weigh in at 128Gb (16GB) each—the same density as the flash employed by Samsung’s latest 840 EVO solid-state drive.
Instead of using a floating gate to store the electrical charge associated with data, Samsung’s V-NAND traps electrons in a non-conductive silicon nitride layer. This charge trap architecture is supposed to cut down on the cell-to-cell interference that makes it difficult to scale gate-based flash memory down to finer lithography. V-NAND’s cell layers are connected with a "proprietary vertical interconnect" that can stack up to 24 layers.
Unfortunately, there’s no word on how many layers are used in the first V-NAND chips. We’ve asked Samsung to elaborate—and also to shed light on the memory’s die area and fabrication process, neither of which are mentioned in the press release. The 128Gb planar NAND in the 840 EVO is fabbed on a 19-nm process, and the 64Gb chips in the 840 Series and 840 Pro are made using 21-nm tech. V-NAND is probably in the same ballpark.
Thanks to its unique cell structure, V-NAND promises 2X-10X "higher reliability" than Samsung’s 19-nm NAND. The 3D flash also boasts twice the write performance of its planar peer. Faster, higher-density chips are in the works, as well; Samsung claims its V-NAND tech is capable of cramming a terabit (128GB) onto a single chip.
Samsung doesn’t say how long it will take for V-NAND to make its way into consumer products, but we probably won’t be waiting for too long. Less than five months passed between the introduction of Samsung’s 128Gb TLC NAND and the 840 EVO SSD based on those chips. If Samsung can manage a similar turnaround with V-NAND, we could see the three-dimensional flash pop up in solid-state drives early next year.
Update: Samsung has confirmed that its first V-NAND chips use 24 layers to reach 128Gb. The company wouldn’t tell us the chip’s die size or its exact process geometry. However, according to Senior PR Manager John Lucas, the fabrication process is "roughly the equivalent of a planar process technology in the mid-teens."
