TechInsights takes a first look at the SanDisk/Toshiba 48L 3D NAND's cell structure, as found in the iPhone 7, compared with Samsung 48L 3D TLC V-NAND.
Finally, SanDisk and Toshiba have revealed their first mass-produced devices with a 48L 3D NAND cell structure. TechInsights, merged with Chipworks since last June, tore down the newly released Apple iPhone 7 and analyzed the SanDisk/Toshiba 3D NAND devices with THGBX6T1T82LFXF package markings (Figure 1) found inside.
The die markings show ‘SANDISK/TOSHIBA FPL9 256G 1.8/3.3V’ as in Figure 2. Toshiba, with SanDisk, has been developing a new 3D NAND structure for more than a decade, and last year they shipped customer samples (CS) with 48L 3D NAND (48 NAND cell gates vertically arranged in a NAND string). However, we always wondered whether their 3D NAND cell structure for high volume products would be BiCS (Bit Cost Scalable) or P-BiCS (Pipe-shaped BiCS). These are different from Samsung’s 3D V-NAND which are based on a modified TCAT (Terabit Cell Array Transistor) structure. In this article, we perform a quick overview their die floor plan and 3D NAND cell structure comparing the Toshiba/SanDisk 2D planar NAND and Samsung’s 48L V-NAND devices.
Figure 1. SanDisk/Toshiba 3D NAND package with 48L tore down from iPhone 7 (Source: TechInsights)
Figure 2. Die markings of SanDisk/Toshiba 3D NAND device (Source: TechInsights)
The first 3D NAND device torn down from the iPhone 7 has a 256 GB TLC 3D NAND die with two planes the same as their current 2D planar NAND devices such as the 15 nm Z-version (Figure 3). Die area is measured to be 105.4 mm2 which is a 5.4 % increase from their 15 nm planar NAND die. Memory density per die is 2.43 Gb/mm2 which is almost two times that of the 15 nm TLC NAND. Memory density in a plane is increased as well, about 80%, although the plane area is a little larger, 11%, than 15 nm NAND die. SanDisk and Toshiba use the same die floor plan with their 2D NAND device. The placements of the wordline decoder/switch, page buffer, charge pump, auto routing area and bonding pads are the same as well. The area of wordline decoder/switch region is slightly increased, though.
Figure 3. Die photograph of SanDisk/Toshiba 3D NAND device (Source: TechInsights)
Comparing with Samsung’s 256 GB 48L 3D TLC V-NAND die, the SanDisk/Toshiba 3D NAND die has the same memory amount, 256 GB, as Samsung’s. However, the die area is 5% larger than Samsung’s and is longer in bitline direction. Memory density in a die is 2.43 Gb/mm2 slightly lower, 5.3%, than Samsung’s. Plane size (SanDisk/Toshiba 37.1 mm2, Samsung 36.0 mm2) and memory density in a plane (SanDisk/Toshiba 3.45 Gb/mm2, Samsung 3.55 Gb/mm2) are almost same in each device, with less than 3% difference. Table 1 shows a comparison of die floor plan for three different TLC NAND devices, SanDisk/Toshiba 15 nm 2D, 48L 3D and Samsung 48L V-NAND.
Table 1. A comparison of die floor plan for SanDisk/Toshiba 15 nm 2D, 48L 3D and Samsung 48L V-NAND (Source: TechInsights)