October 5, 2022

SK hynix announces 238-layer NAND

As the 2022 flash memory summit continues, SK hynix is ​​the latest vendor to announce its next generation of NAND flash memory at the show. Showcasing the company’s upcoming 238-layer NAND TLC for the first time, which promises both improved density/capacity and improved bandwidth. At 238 layers, SK hynix has, at least for now, earned bragging rights for the most layers in a TLC NAND die – although mass production isn’t expected to begin until 2023, so it will take some time. before the company’s newest NAND appears in retail products.

Hot on the heels of Micron’s 232L TLC NAND announcement last week, SK hynix is ​​upping the ante ever so slightly with a 238-layer design. While the difference in layer count is largely inconsequential when you’re talking about NAND arrays with over 200 layers to begin with, in the highly competitive flash memory industry, it gives SK hynix bragging rights in the number of layers, breaking the previous deadlock between them, Samsung, and Micron at 176L.

From a technical standpoint, SK hynix’s 238L NAND builds more on the basic design of their 176L NAND. So we’re once again looking at a string-stacked design, with SH hynix using a 119-layer bridge pair, up from 88 layers in the previous generation. This makes SK hynix the third flash memory vendor to master building bridges over 100 layers high, and is what allows them to produce a 238L NAND design that maintains the two-bridge line.

SK hynix’s NAND boards continue to be built with their charge trap CMOS under die (CuA) architecture, which sees most of the NAND logic placed below the NAND memory cells. According to the company, their initial 512 Gbit TLC coin has a die size of 35.58 mm2which corresponds to a density of approximately 14.39 Gbit/mm2. This is a 35% improvement in density over their previous generation NAND 176L TLC chip at equivalent capabilities. Notably, this means that SK hynix will lag slightly behind Micron’s 232L NAND despite their overall layer count advantage, as Micron claims to have achieved a density of 14.6 Gbit/mm.2 on their 1Tbit dies.

SK hynix 3D TLC NAND Flash Memory
238L 176L
Layers 238 176
Bridges 2 (x119) 2 (x88)
Matrix capacity 512 GB 512 GB
Die size (mm2) 35.58mm2 ~47.4mm2
Density (Gbit/mm2) ~14.39 10.8
I/O speed 2.4MT/s
(ONFi 5.0)
(ONFI 4.2)
CuA/PuC Yes Yes

Speaking of 1Tbit, unlike Micron, SK hynix doesn’t use density enhancements to build higher capacity dies – at least not yet. While the company has announced that it will build 1 Tbit dies next year using its 238L process, for now it holds 512 Gbit, the same capacity as its previous generation. So, all other factors being equal, we shouldn’t expect the first drives built using 238L NAND to have a higher capacity than the current generation. But, if nothing else, at least SK hynix’s initial 238L dies are pretty small – although that translates to smaller packages remains to be seen.

Along with the density improvements, SK hynix has also improved the performance and power consumption of their NAND. Like other NAND vendors, SK hynix uses this next generation NAND to introduce ONFi 5.0 support. ONFi 5.0 is notable not only for increasing the maximum transfer rate to 2400MT/second – a 50% improvement over ONFi 4.2 – but it also introduces a new NV-LPDDR4 signaling method. Because it is based on LPDDR signaling (unlike the DDR3-derived mode in ONFi 4.x), NV-LPDDR4 offers tangible reductions in the amount of power consumed by NAND signaling. SK hynix doesn’t detail their power consumption figures at this level of detail, but for overall power consumption, they tout a 21% reduction in power consumed for read operations. Presumably it’s per bit, so it will be outweighed by the 50% improvement in bandwidth.

This week’s announcement comes as SK hynix has begun shipping samples of the 238L NAND to its customers. As mentioned earlier, the company does not plan to launch mass production until the first half of 2023, so it will be some time before we see the new NAND appear in retail products. According to SK hynix, their plan is to ship NANDs for consumer SSDs first, followed by smartphones and high-capacity server SSDs. This, in turn, will be followed with the introduction of 1Tbit 238L NAND later in 2023.