NAND flash write endurance seems to decrease as manufacturing processes get smaller. The time between process shrinks seems to grow with every node, even at big research spenders like Intel. With these two limitations in mind, one way to increase the capacity and performance of NAND flash chips is to stack more layers on each die. This is the approach SK Hynix has taken with its latest 256 Gb (or 32 GB) 72-layer 3D NAND chips.
SK Hynix says that it has rapidly increased the number of layers in its 3D NAND chips, moving from 128 Gb 36-layer chips in April of last year to 256 Gb 48-layer dies last November, all the way up to 256 Gb 72-layer chips today. The company says the 72-layer design stacks 50% more cells into the same area compared to its previous offerings, all the while using existing mass production facilities. That large increase in cell count at the same capacity suggests the increase in layers may have been spurred at least in part by a need to increase chip yields. According to the manufacturer, the new chips read and write 20% faster than the previous-generation units of the same capacity, too.
We reported about SK Hynix's ₩3.15 trillion ($2.6 billion) investment into additional manufacturing facilities last December. At that time, we mentioned the chipmaker's expectation that chip output per area of floor space would decrease, and the escalating number of layers in 3D NAND chips is likely one element of this trend. The company says it will begin manufacturing the 72-layer chips in the second half of this year.