Other Things We’ve Wondered About…
Floating Gate vs CTF
One of the things we recently learned from Micron was that charge trap flash technology (which most NAND manufacturers are moving to for 3D NAND) has endurance limitations due to charge spreading. Micron indicated that Floating Gate technology isn’t as susceptible to rapid charge loss, and that CTF increases in complexity during 3D NAND scaling. We wanted to hear this directly from Intel.
Crooke said that floating gate technology has been the foundation of NAND for 20 years, and IMFT understands the physics very well due to its extensive familiarity with floating gate technology.
3D NAND allowed IMFT to take a step back to a larger process, and instead increase the density via vertical stacking. This allows for bigger floating gates. 3D floating gates are difficult to engineer, but they still offer more robust endurance characteristics.
On the other hand, charge trap technology suffers from leakage at higher densities. The cells aren’t as discretely isolated as they are with floating gate, so CTF is susceptible to charge dispersal and interference across cells. Crooke made an analogy to a strip of cloth that is a continuous sheet of nitride, and putting oil dots on it. The dot is contained in one spot at first, but over time, the oil disperses.
Intel is all about solving the hard challenges, Crooke bragged, so it is sticking with floating gate. He said that the company’s first 3D NAND product would be the world’s first 256Gb 3D MLC NAND, and its TLC product will extend density to an unheard-of 384Gb.
QLC (Four-Bit MLC)
Quad-level cell is the next natural progression to increase the density of NAND, and this technology would prove to be very efficient when utilized in tandem with 3D XPoint caching in a hybrid implementation. 3D XPoint would be a natural type of super-fast cache front end for a massive low-endurance (and low-cost) QLC SSD data store.
When I asked Crooke about whether Intel was developing this type of implementation, he gave a knee-jerk, enthusiastic “Yes!" before throttling back down and indicating that everyone in the industry is merely thinking about it and researching it. First it would have to work.
TLC 3D NAND
Samsung has been busy with data center SSDs featuring its 3D TLC V-NAND. In fact, every one of its new enterprise SSDs (which it announced at the Flash Memory Summit 2015) utilize 3D TLC NAND. During a question and answer session at FMS, Ryan Smith, the Director of NAND Marketing at Samsung Semiconductor, indicated that TLC is the “killer” application for 3D NAND, and Samsung foresees it taking over every single vertical.
Crooke would not pre-announce anything, of course, but he did say Intel has some exciting 3D NAND products coming. We recently reported our discovery of Intel’s (apparently) pending DC P3520 Series. The DC P3520 appears to be an Intel NVMe controller paired with 32-layer IMTF 3D NAND.