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Micron 3D NAND wafer

When Micron announced that it would bring QLC (quad-level cell) NAND to market earlier this year, we were genuinely surprised to hear it. While stuffing more than bits of information into each NAND cell is one of the nearly central means to amend NAND storage capacity, the manufacture went through significant teething issues on TLC (triple level jail cell) and didn't start shipping TLC drives in high volume until the shift abroad from planar NAND built on 20nm nodes to 3D NAND built on older 40nm nodes. QLC NAND had seemed out-of-reach under such conditions — and perchance still are.

Co-ordinate to a report from DigiTimes, multiple manufacturers are struggling to yield QLC. The publication as well makes some interesting references to low TLC yields from earlier this year that may have caused supply concatenation struggles. This could be related to efforts to calibration up the number of manufacturing layers in 3D NAND products.

3d-nand-flash

3D-NAND (general diagram)

As the number of layers in 3D NAND increases, so does the manufacturing difficulty. While DigiTimes doesn't explicitly link any TLC issues to 3D NAND density increases, it'south the virtually likely reason, especially given the way density has been improving year-on-yr — and the report heavily implies that the TLC NAND coming out of the industry in 2022 hasn't been very good. This isn't the get-go fourth dimension we've heard reports of low yield on QLC, however — a story from Tweaktown at the end of August claimed that QLC NAND yields at Micron were below 50 percent equally well.

Low yields would explain why Micron launched enterprise QLC drives before its consumer counterparts. Because in that location's a trade-off between how many bits of data you store per jail cell of NAND flash and the durability of the bulldoze, TLC NAND debuted in consumer systems first, before making its manner towards college-cease markets. When we spoke to Intel at the launch, the company stated that it was able to put QLC into enterprise products because better NAND flash profiling and the sheer chapters of college-terminate products made it possible to deal with the reduced number of P/E (program/erase) cycles without compromising enterprise-grade reliability. Both of these statements are likely truthful, but poor yields could nevertheless have made an enterprise launch more financially attractive.

One of import point is that we don't know exactly what "low yield" means in this context. NAND flash tin be reconfigured on-the-fly to store varying amounts of information per jail cell — that's how TLC and QLC drives are able to dynamically allocate an SLC enshroud to better performance today. Equally the amount of free infinite available on the drive shrinks, the amount of space dedicated to SLC caching decreases as well and overall performance drops. Low yield could mean that manufacturers aren't getting usable NAND at all — or it could mean that they're getting NAND that works beautifully in MLC or TLC configurations but can't store plenty voltage levels to retain QLC data. But regardless of short-term teething bug, all of the major manufacturers are planning to introduce QLC 3D NAND drives for both consumer and enterprise applications over the side by side 12 months.

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