1 TB, 6 die levels with 50% more I/O bandwidth

Ahead of next week’s flash memory summit, Micron is announcing this morning that the new generation of Layer 232 NAND has started shipping. Micron’s sixth generation of 3D NAND technology, the 232L is set to offer both improved bandwidth and larger die sizes — most notably, introducing Micron’s first 1Tbit TLC NAND templates, which are at this point the most dense in the industry. According to the company, the new NAND is already being shipped to customers and in Crucial SSD products in limited quantities, with volumes increasing later in the year.

Micron first announced its 232L NAND back in May during its Investor Day event, revealing that NAND will be available this year, and that the company intends to ramp up production by the end of the year. And while that high yield continues, Micron’s Singapore fab is already able to produce enough new NAND that Micron is comfortable announcing that it’s shipping, albeit obviously in limited quantities.

From a technical perspective, Micron’s 232L NAND builds on core design elements honed in that generation. So we’re looking again at a string-stacked design, using Micron’s 116-layer pair, up from 88 layers in the previous generation. The 116-layer layer, in turn, is noteworthy because this is the first time Micron has been able to produce a single surface in excess of 100 layers, a feat previously limited to Samsung. This, in turn, has allowed Micron to produce only high-end NAND with two floors, something that may not be possible for much longer as companies push towards designs with more than 300 layers total.

Micron’s NAND surfaces continue to be built using the charging trap, CMOS under the Array (CuA) architecture, which sees the bulk of the NAND logic placed under NAND memory cells. Micron has long cited this as giving it a continuous advantage in NAND density, and this is again shown on the 232L NAND model. According to the company, they have achieved a density of 14.6 Gbit/mm2, which is about 43% denser than the 176 liter NAND. And according to Micron, it’s anywhere between 35% to 100% denser than competing TLC products.

Micron 3D TLC NAND Flash Memory
232 liters
176 liters
Layers 232 176
floors 2 (x116) 2 (x 88)
die capacity 1 TB 512 GB
Mold Size (mm2) ~ 70.1 mm 2 ~49.8 mm 2
Density (Gb/mm2) 14.6 10.3
Input/output speed 2.4 million tons/sec
(ONFi 5.0)
1.6 million tons/sec
(ONFI 4.2)
Program Productivity ? ?
Planes 6 4
CuA/PuC yes yes

The improved density allowed Micron to produce its first 1TB TLC die, which from a production standpoint means Micron can now also produce 2TB chip packages by stacking 16 of its 232L die dies. This is good news for SSD capacities, which are often limited to the number of packages that can fit. Although this does mean that there is a potential loss of performance at lower capacities due to decreased parallelism from executing fewer packages.

At the same time, Micron is also working on the size of the foil packages, as a result, the larger capacity means that the die size has increased on the basis of generations (we estimate ~70.1 mm).2 Given Micron’s density numbers), they’re still reducing their chip packaging by 28%. As a result, the single-chip package has decreased from 12mm x 18mm (216mm2) to 11.5 mm x 13.5 mm (~155 mm2). So for Micron’s downstream customers, the combination of the larger capacity and virtually smaller packets of Micron’s NAND means device manufacturers can reduce the amount of space they devote to NAND packets, or go the other way and try to cram more packets into the same amount of space.

Besides density improvements, Micron’s latest generation of NAND also allows the company to upgrade its hardware to take advantage of newer I/O technologies, as well as implement its own improvements to increase transfer speeds. The big news here is that Micron has increased the number of planes inside the NAND dies from 4 to 6, further improving the parallelism available within each die. Quadrupole (four) aircraft designs have become popular in the previous generation of NAND, and as the NAND density grows, the number of aircraft also increases in order to keep up with transmission rates with this greater density. Micron has confirmed that the planes in the 232L NAND provide independent readouts, although it’s not entirely clear on what kind of word line dependencies are left to write.

This increase in parallelism, combined with improved internal transfer rates, has allowed Micron to dramatically improve read and write speeds for each die. According to the company, read speeds have improved by more than 75% compared to the 176-liter NAND generation, at the same time write speeds have almost doubled.

Besides, Micron has also implemented the latest generation of ONFi on its peripheral logic. Completed in 2021 and now being rolled out in first NAND products, ONFi increases NAND-controller transfer rates by 50%, bringing it to 2,400 Mt/s. ONFi 5.0 also introduced a new NV-LPDDR4 signaling method, which is available at the same rate of 2400MT/s, but because it is based on LPDDR technology, it consumes less power. According to Micron, they see a power transmission savings per bit of over 30%, which results in a significant reduction in power consumption. Although, as always with these types of comparisons, it should be noted that bandwidth gains exceed power savings (50% vs. 30%), so we expect total power consumption to rise for high-performance products operating at the fastest speeds supported by 232L NAND from Micron.

For throughput, Micron offers 232L NAND as a full stack alternative to 176L NAND – which means Micron considers it suitable for everything from mobile devices and the Internet of Things to customer and data center products. To that end, the company is already making initial shipments to its customers, including its subsidiary Crucial. As with previous Micron NAND generations, getting started early with Crucial allows the company to gain some hands-on experience developing full-featured products with their new NAND prior to incorporating it into their enterprise equipment. Interestingly, however, Micron is not announcing any new Crucial products at this time, which means Crucial will begin implementing new NAND into existing products. If so, important customers will want to pay attention to what’s going on and review the drive they’re buying, as a larger 1TB die can have performance implications for products originally designed around 512G.

To wrap things up, today’s announcement should be the tip of the iceberg for Micron’s 232L shipments. With volume expected to continue increasing through the end of this calendar year, Micron’s plans call for the company to significantly increase the amount of next-generation NAND it ships, beyond these initial volumes. Ultimately, this means that products equipped with 232 liters of NAND will be relatively few for this year, and will rise in 2023 after the volume rises. So while Micron’s 232L NAND is already shipping, from a consumer standpoint, we’re probably still several (or more) months away from seeing it become a staple in SSDs and other products.

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