Samsung had announced its 256 Gb 3-bit multi-level cell K9AFGY8S0M 3D V-NAND as early as August 2015, stating that it would be used in a variety of solid state drives (SSD), and would be on the market in early 2016. True to their word, we managed to find them in their 2 TB capacity, mSATA, T3 portable SSD shown in Figure 1.
Tearing open the drive, we find a double-sided circuit board containing four 0.5 TB capacity K9DUB8S7M packages that are shown in Figure 2. Each of these packages contain 16 of the 48L V-NAND dies that we were looking for.
Figure 3 is a package cross section showing the 16 dies stacked one on top of the other and connected using conventional wire bonding technology. The dies are an outstandingly 40 µm thin, perhaps the thinnest dies that we have seen in a package. By comparison, the dies in Samsung’s 32L V-NAND that we examined in 2014 were about 110 µm thick and stacked 4 dies high in their package.
Other thin memory dies that we have seen include Hynix’s HBM1 memories used in AMD’s R9 Fury X graphics cards that are about 50 µm thick, and some 55 µm thick DRAM dies in Samsung’s DDR4 with 4 stacked dies with TSV interconnections.
So 40 µm is really thin and might be close to the thinnest that can be achieved with 300 mm diameter wafers without a carrier wafer. We are impressed!
One of the 256 Gb dies is shown in Figure 4 and comprises two 5.9 mm x 5.9 mm large banks of NAND Flash memory. We can calculate a gross measure of the memory density by dividing the entire die area into the memory size to get about 2,600 Mb/mm2. By comparison, Samsung’s 16 nm node planar NAND flash measures about 740 Mb/mm2. So while the V-NAND is fabricated at a larger process node (~21 nm vs. 16 nm), its memory density is almost 3.5 times better than the 16 nm planar NAND flash (see Table 1).