Western Digital and SK hynix both talked about 128-layer 3D NAND at the Flash Memory Summit in Santa Clara this week, with SK hynix outlining a roadmap to 800+ layers in 2030.

The increase in 3D NAND layers is leading to huge capacity increases at the die level and consequent developments of zoning technology. Zoning will help manage SSDs made with such flash to extend its life. Specifically it can reduce the setting aside of spare cells to replace worn-out ones; over-provisioning.

SK hynix

The Korean NAND fabber has already announced work on 128-layer (128L) flash. It calls this technology version 6 of its 4D NAND but all other manufacturers refer to this as 3D NAND.

NAND product using SK hynix’ 1Tbit 128-layer die.

At FMS 2019 SK hynix revealed its layer count roadmap:

V4 – 72 layers – mass production now

V5 – 96 layers – mass production now and taking over from V4

V6 – 128 layers – mass production starts in Q4 2019

V7 – 176 layers in 2020

V? – 500 layers in 2025 and 30 per cent increase in TB/wafer

V? – 800+ layers in 2030 and 50 per cent increase in TB/wafer to 150-200TB

The 128L die is 1Tbit in size. Adding more layers on their own could mean:

176 layers – 1.38 Tbit die

500 layers – 3.9 Tbit die

800 layers – 6.25 Tbit die

These are huge numbers. A 15TB SSD made using SK hynix’s 128L 1Tbit die could become a 93.75TB drive using 800L technology.

In common with Western Digital, SK hynix is keen on zoning SSDs – partitioning them into different zones for different purposes.. The company thinks zoning will enable 67 per cent reduction in write-amplification, 25 per cent improvement in read latency, and 86 per cent reduction in NAND over-provisioning in SSDs.

Western Digital

Western Digital is shipping 64-layer flash product today, using the so-called BiCS3 process, and bringing on 96-layer (BiCS4.) Production of 96-layer NAND is expected to surpass 64-layer volumes this quarter.

BiCS5 will introduce 128 layers, referred to as 1XXL. This is slated for debut in 2020.

According to Western Digital, the transition from 64L to 96L entails a 60 per cent increase in manufacturing capital costs. The 96L to 1XXL transition could need additional 15 per cent more capital expense.

In its FMS presentation Western Digital illustrated the manufacturing difficulties involved in transitions to more layers.

The table above show the 128-layer die is denser on all counts. There are two ways of making a 128-layer die. One is to add 32 more layers to the existing 96-layer die. The other, known as string-stacking, is to stack two 64-layer dies one above the other and interconnect them. WD did not talk about string-stacking in its presentation.

Putting more bits on a wafer lowers the cost per bit but the wafer can then be more expensive to make.

the manufacturer’s overall cost/bit goes down as long as the manufacturing cost increase is less than the cost decrease from adding more layers. That can facilitate a price drop.

An SSD using 128-layer 3D NAND nominally has one-third more capacity than a 96-layer SSD, as each die could hold a third more bits. A 3TB SSD, made with 96L 3D NAND could become a 4TB SSD with 128 layers.

But the manufacturer could, instead of increasing capacity, offer SSDs with 128 layers at the same capacity as 96L product, and price it at a lower cost/bit.

Comment

Blocks & Files believes all the NAND manufacturers have roadmaps out to 200+ layers and beyond. But they are not publicising them – except for SK Hynix. SK hynix wants to be taken more seriously as a client and enterprise SSD manufacturer.

Wells Fargo senior analyst Aaron Rakers notes the company held a three per cent and 10 per cent share of enterprise and client SSD capacity shipped over the year to March 2019, rising from the <1 per cent and seven per cent in the previous year. Publishing a long-term technology road map could help convince OEMs and enterprises that SK hynix is a serious, long-term player.



Acknowledgement

Aaron Rakers mailed clients about these presentations at FMS 2019 and we have extracted the layer count and zoning information from his newsletter.