Samsung produces first 3D NAND, aims to boost densities, drive lower cost per GB

Samsung produces first 3D NAND, aims to boost densities, drive lower cost per GB

Samsung has announced the mass production of the first 3D NAND chips — and with them, the beginning of a manufacturing initiative that will push solid-state cost-per-GB ever closer to magnetic storage territory. It’s been over a year since we first previewed the advances from capital equipment manufacturers like Applied Materials. Samsung’s new V-NAND (vertical NAND) flips a conventional 2D cell structure up on edge. A skyscraper analogy is actually in order — imagine that a conventional NAND chip is a single-story rectangular building. Stand it on edge, and you’ve got the same amount of storage taking up much less ground space.

The trick to building vertical NAND is that you’ve got to build each section of every floor perfectly, from the top down. The density and performance increases are fabulous if you can do it, but the difficulty is much higher. We first previewed the technology a little over a year ago, so Samsung’s ability to roll out a product in 2013 is actually right on schedule. Samsung’s secret is an extension of the CTF (charge flash trap) technology first commercially developed by AMD and Fujitsu and deployed in 2002. CTF designs trap an electrical charge in between two insulating layers, whereas floating gate NAND stores a charge in a conductive floating gate. Samsung has prototyped CTF NAND in the past and discussed deploying the tech in vertical NAND before, so today’s announcement means the Korean chaebol has worked out the kinks of the new arrangement.

Driving density

These shifts should improve NAND endurance and help offset some of the scaling problems associated with smaller process geometries. The problem conventional NAND faces today is that as geometries get smaller, the gap between cells shrinks. Writing to NAND flash requires a high input voltage and damages the cell every time a write occurs. Over time, this damage results in a cell that can no longer hold data for any length of time. Similarly, making the cell geometries smaller increases leakage. Current NAND flash drives claim that they’ll hold data for up to 12 months, while a conventional hard drive can hold data indefinitely. Below 19nm, both the data retention and program/erase cycle issue (P/E) become worse.

Moving to vertical NAND, in other words, helps density. Moving to CTF technology instead of floating gate should improve data retention time and endurance. Samsung is claiming a reliability increase of between 2 and 10x — the size of this range likely reflects the density of the NAND (SLC, MLC, or TLC). Currently, Samsung is offering a 128-gigabit V-NAND chip (16GB), which is on par with conventional planar NAND. Over time, the density gap between conventional planar and vertical NAND will increase.

The shift to V-NAND could help enterprise adoption of flash in another way. To date, the adoption of SLC NAND has been stymied by density issues. While it offers by far the best performance and endurance of any NAND, SLC only stores one bit per cell compared to two and three bits for MLC and TLC. Tilting the NAND on edge allows for more NAND in a given area, period, and could therefore help reduce SLC costs substantially. (See: Researchers use ultrasound to improve SSD storage density.)

Over the next few years, vertical NAND will be the first in a series of density-boosting enhancements that help push solid state storage prices down towards HDD levels. The gap between the two isn’t expected to close entirely, but the advent of TLC and vertical NAND together should allow for drives that push down to 40-50 cents per GB.